Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

The thermal decomposition of 1-butene and 1-butene-4-d₃ Kebarle, Paul 1957-01-27

You don't seem to have a PDF reader installed, try download the pdf

Item Metadata

Download

Media
831-UBC_1957_A1 K3 T4.pdf [ 13.13MB ]
Metadata
JSON: 831-1.0062153.json
JSON-LD: 831-1.0062153-ld.json
RDF/XML (Pretty): 831-1.0062153-rdf.xml
RDF/JSON: 831-1.0062153-rdf.json
Turtle: 831-1.0062153-turtle.txt
N-Triples: 831-1.0062153-rdf-ntriples.txt
Original Record: 831-1.0062153-source.json
Full Text
831-1.0062153-fulltext.txt
Citation
831-1.0062153.ris

Full Text

T H E T H E R M A L D E C O M P O S I T I O N 0 P 1 - B U T E N E A N D l - B U T E N E - l i - d by PAUL KEBARLE D i p l . Ing. Chem., E. T. H. (Zurich), 1952 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY i n the Department of Chemistry We accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1957 - i i - A B S T R A C T The thermal decomposition of 1-butene and 1-butene-Ijv-d^ was studied i n the temperature range 14-90° to £60°C . i n a s t a t i c system. The majority of the re a c t i o n products were determined q u a l i t a t i v e l y and q u a n t i t a t i v e l y by gas chromatography and mass spectrometry. The reaction products consisted of a gas eous and a l i q u i d f r a c t i o n at S.T.P. The main products i n the gaseous f r a c t i o n were methane, propylene, ethylene and ethane.. The p r i n c i p a l l i q u i d products were cyclohexadiene, benzene, cyclopentene, cyclopentadiene, and toluene. The l i q u i d f r a c t  ion also contained a large number of other compounds i n trace amounts. The concentrations of the methane, propylene, ethy lene and ethane were found to increase almost l i n e a r l y with the time of reaction over the temperature range. The rates of formation of these products were found to follow a f i r s t order dependence on the i n i t i a l concentration of the butene. The o v e r a l l a c t i v a t i o n energy for the butene decomposition was found to be approximately 66 kcal/mole. The o v e r a l l a c t i v a t i o n en ergies f o r the formation of the i n d i v i d u a l gaseous hydrocarbons also were determined. The thermal decomposition of the 1-butene-l^-d^ was found to be nearly i d e n t i c a l with that of the 1-butene. The d i s t r i b  u t i o n of deuterium i n the p y r o l y s i s products was determined. The major components of the l i g h t hydrocarbons were: methanes, CHD^ ; propylenes, C ^ , C ^ D , C ^ D y , ethylenes, C ^ , C ^ i y ^ , C H D; ethanes, C0H_D . - i i i - The addition of 5$ by volume of mercury dimethyl to the i n i t i a l 1-butene or l-butene-l^-d^ was found to produce a large o acceleration of the decomposition at 1;90 C. The products of these s e n s i t i z e d reactions were determined q u a n t i t a t i v e l y and the deuterium d i s t r i b u t i o n i n the products from the l-butene-l|- d" experiment was obtained. 3 The r e s u l t s of this i n v e s t i g a t i o n provide strong evidence for the existence of complex free r a d i c a l reactions. A mech anism i s proposed which accounts at least q u a l i t a t i v e l y for the main features of the k i n e t i c s and predicts the observed d i s  t r i b u t i o n of deuterium isomers i n the pyrolysis of €he deuter- ated butene. A feature of the mechanism i s the extensive use of disproportionation reactions i n which disprbportionation i s assumed to occur by addition of a free r a d i c a l to the double bond of the butene, followed by rapid subsequent decomposition of the addition product, . . • • . o The mass spectrum of 1-butene-J^-d^ was measured i n a 90 Nier-type mass spectrometer using $0-volt electrons. High res olution nuclear magnetic resonance measurements showed that the methyl group was f u l l y deuterated and that there were no D atoms located elsewhere i n the molecule. A comparison of the mass spectrum with that of 1-butene shows that the t o t a l i n t e n s i t i e s of each group of CV, and fragments are the same for both compounds. This indicates equal p r o b a b i l i t i e s of C - C bond rupture i n the dissocation - i v - of the corresponding parent ions. The d i s t r i b u t i o n of fragments within the groups i n the deuterated compound shows, however, that extensive migration of the D atoms has occurred during i o n i z a t i o n . Migration i s also evident at much.lower energies (approximately 15 e.v.) In presenting t h i s thesis i n p a r t i a l f u l f i l m e n t of the requirements fo r an advanced degree at the University of B r i t i s h Columbia, I agree that the Library s h a l l make i t f r e e l y available f o r reference and study. I further agree that permission f o r extensive copying of t h i s thesis for s c h o l a r l y purposes may be granted by the Head of my Department or by h i s representative. It i s understood that copying or p u b l i c a t i o n of t h i s thesis f o r f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Chemistry The University of B r i t i s h Columbia, Vancouver 8, Canada. A p r i l 12 , 1957 -v- T A B L E O P C O N T E N T S Page INTRODUCTION 2 General 2 Survey of the Literature Ij. Investigations of the Decomposition of 1-Butene l\. Primary Step i n the Free Radical De composition of 1-Butene 9 Summary 12 EXPERIMENTAL l£ Method of Pyrolysis 15 Apparatus and Materials 15 Furnace and Temperature Control 1$ Description of a Typical Experiment 17 - Methods of Analysis 18 Direct Mass Spectrometric Analysis 18 Low Temperature Fractionation and Sub sequent Analysis of the Fractions with the Mass Spectrometer 19 Analysis by Gas Chromatography 23 Introduction 23 Apparatus and Procedure 25 General 25 Admission of Samples for Analysis into the Separating System 27 Separating Column* and Heater 28 Thermal Conductivity C e l l and Detection C i r c u i t 29 - v i - Page System for C o l l e c t i n g the Separated Components 33 Analysis with Gradual Increase of the Column Temperature 3k- Basis of the Quantitative Determinations 35 Results for the Pyrolysis of 1-Butene Obtained by Gas Chromatographic Analysis 39 Qualitative Determinations of the Light Hydrocarbons 39 Qualitative Determinations of the Polymers I4.O Quantitative Determinations of the Light Hydrocarbons I4.2 Quantitative Determinations of the Polymers I+.2 Total Analysis and Material Balances k\7 Conversion of the A n a l y t i c a l l y Determined Concentrations of the Reaction Mixtures to Concentrations i n the Reaction Vessel $1 K i n e t i c Results for the Pyrolysis of 1-Butene 54 Kinetic Order of the 1-Butene Decomposition 5 4 - Pressure Increase i n Reaction System and Act i v a t i o n Energy Prom Pressure Change 5° Rate and Overall A c t i v a t i o n Energy of Butene Decomposition 60 Rates of Formation and Overall A c t i v a t i o n Energies for the Light Hydrocarbons 68 Time and Temperature Dependence i n the Formation of the Polymer. Products 72 Thermal Decomposition of 1-Butene Sensitized with Mercury Dimethyl 77 Thermal Decomposition of 1 -Butene~l\.-d 79 Comparison of the Pyrolysas of 1-Butene and 1 -Butene-l^-d^ 79 A n a l y t i c a l Methods Used for the I d e n t i f i c a t i o n of the Deuterated Reaction Products 8l - v i i - Page Reaction Products from the Pyrolysis of l-Butene-Lj.-d^ 82 Deutero-Methanes 82 Deutero-Ethanes 89 Deutero-Ethylenes 91+ Deutero-Propylenes 98 Deutero-Butenes 102 Deuterium D i s t r i b u t i o n i n the Polymers 10J? DISCUSSION 110 Free Radical versus Molecular Mechanism 110 Primary Step of the Free Radical Decomposition of 1-Butene 112 Secondary Reactions i n the 1-Butene Decomposition 115 Hydrogen Abstraction by Methyl Radicals 115 Addition of Methyl Radicals 122 Reactions of the Free Radicals S t a b i l i z e d by Allyl-Type Resonance 132 Pyrolysis of 1,5-Hexadiene llj.0 Addition Reactions of Hydrogen Atoms II4.3 Mechanism of the Thermal Decomposition of 1-Butene and 1 -Butene-1^-d^ 11+8 Significance of some of the Findings and Suggestions for Further Experimental Work 15I4. Pyrolysis of 1-Butene i n the Presence of Deuterium 157 LITERATURE CITED 16$ APPENDIX I: QUALITATIVE INVESTIGATION OF THE POLYMER.PRODUCTS FORMED IN THE PYROLYSIS OF 1-BUTENE I69 Literature Cited 177 - v i i i - Page APPENDIX I I : DEUTERIUM MIGRATION DURING THE IONIZATION OP l-BUTENE-U,-d, BY ELECTRON IMPACT * 1 7 9 I n t r o d u c t i o n 1 7 9 E x p e r i m e n t a l l80 D i s c u s s i o n 183 L i t e r a t u r e C i t e d 190 - i x - TABLES Page I Thermal Decomposition of 1-Butene (Wheeler and Wood) ' 5 II Results from Low Temperature Fractionation and Subsequent Mass Spectrometric Analysis of the Fractions 22 III S e n s i t i v i t y of 1-Butene 38 IV V a r i a t i o n of S e n s i t i v i t i e s of Light Hydrocarbons Over a Month's Period 39 V A n a l y t i c a l Results for Light Hydrocarbons i |3 VI A n a l y t i c a l Results for Polymets ij.5 VII Total Composition of Reaction Mixtures i n Volume % 1+8 VIII Mass Balances l±9 IX Composition of Reaction Mixtures with Change i n I n i t i a l Pressure of 1-Butene 5E> X A c t i v a t i o n Energy from Pressure Increase 58 XI Analyses of Reaction Mixtures — Light Hydro carbons ( i n Mole %) 6 l XII Butene Decomposition, Variation of F i r s t Order Rate Constants with Reaction Time 6I4. XIII A c t i v a t i o n Energies f o r the Butene Decomposition 65 XIV Rate Constants f o r the Formation of the Light Hydrocarbons 67 XV A c t i v a t i o n Energies of the Light Hydrocarbons 68 XVI Thermal Decomposition of 1-Butene Sensitized with Mercury Dimethyl 76 XVII Increased Rate of Formation of Light Hydro carbons i n Sensitized Reaction 77 X V n i Light Hydrocarbons from the pyrolyses of 1-Butene and 1-Butene-i^-d^ 80 XIX Mass Spectra Used for Correction of the CH^D Spectrum 83 XX Deutero-Methanes•from the Pyrolysis of 1-Butene- l+-d3 . 86 -X- XXI XXII XXIII XXIV XXV XXVI XXVII XXVIII XXIX XXX XXXI XXXII XXXIII XXXIV XXXV XXXVI XXXVII Page Increased Rates of Formation of Deutero- Methanes i n Reaction Sensitized with Mercury Dimethyl 89 Deutero-Ethanes from the Pyrolysis of l-Butene-lj-d 91 Increased Rates of Formation of Deutero-Ethanes i n Reaction Sensitized with Mercury Dimethyl • 9I4- Deutero-Ethylenes from the Pyrolysis of 1 -Butene-i}.-d 96 Increased Rates for Formation ;of. Deutero- Ethylenes i n Reaction Sensitized with Mer cury Dimethyl 98 Deutero-Propylenes from the Pyrolysis of l-Butene-l4.-d^ 100 Increased Rates of Formation of Deutero- Propylenes i n Reaction Sensitized with Mercury Dimethyl 102 Mass Spectra of Deutero-Butenes 103 Comparison of Normal and Sensitized Decomposition of l-Butene-i^-d^ Deutero-Isomers of the Polymers from the Pyrolysis of 1 -Butene-i^-d^ Ratios of Total to Primary Decomposition of 1-Butene f o r 1 Minute Raaction Time Abstraction of Hydrogen Atoms by Methyl Radicals (Trotman-Dickenson and Steacie) Addition of Methyl Radicals to Unsaturated Hydrocarbons (Mandelcorn and Steacie) Decomposition Reactions of the C^H^. Radicals Ratios of Polymer Formation to Primary De composition of the l-^utene 101+ 106 115 117 125 128 136 Ratios of Hydrogen Gas Plus Chemically Bound Hydrogen i n Polymers to Chemically Bound Carbon i n Polymers 138 Hydrogen to Carbon Ratios i n Polymer Products Resulting from Various Reactions 139 - x i - Page XXXVTII Products from the P y r o l y s i s o f 1,5-Hex- adiene li+2 XXXIX R a t i o s of t o T o t a l M o l e c u l a r Hydrogen 11+7 APPENDIX I I Comparison of the Mass Spectrum of F r a c t i o n P 2 with t h a t of Cyclopentene 171 I I Mass S p e c t r a of F r a c t i o n P^, Trans - 2 - Pentene -4-yne, and Cyclopentadiene 173 I I I Mass Spectrum of F r a c t i o n H^ 174 IV Mass S p e c t r a of F r a c t i o n s H , H« and 1 ,3-Cyclohexadiene 175 V Mass S p e c t r a of F r a c t i o n X, and 0- Xylene 1 176 APPENDIX I I I V a r i a t i o n of Ion I n t e n s i t y w i t h E l e c t r o n A c c e l e r a t i n g P o t e n t i a l f o r CD 3CH 2CHCH 2 185 I I P y r o l y s i s Products f o r the Two Butenes a f t e r 5.0 Min. at 552 C l8«? I l l V a r i a t i o n o f R a t i o of the Sum of Masses 42, 43» and 44 to Mass I4I with E l e c t r o n Energy 187 - x i i - FIGURES Page l a . Pyrolysis Apparatus 16 l b . C i r c u i t Diagram of Furnace Heaters 16 l c . Furnace and Reaction Vessel with Thermocouples 16 2. Low Temperature Fractionation Apparatus 20 3. Gas Chromatographic Apparatus 26 lj.. Thermal Conductivity C e l l 30 5. Diagram of Thermal Conductivity Recording C i r c u i t 32 6. Gas Chromatographic Separation of the Light Hydrocarbons 3& 7. Gas chromatographic Separation of the Polymers i | l 8. Pressure Increase with Time 57 9. A c t i v a t i o n Energy from I n i t i a l Rate of Pressure Increase 59 10. Butene Decomposition as a Function of Time 63 11. Overall A c t i v a t i o n Energy of 1-Butene Decomposition 66 12. Time Dependence of Concentrations of Light Hydrocarbons 69 13. A c t i v a t i o n Energies f o r the Formation of the Light Hydrocarbons 71 li+. Time Dependence of Concentrations of Cyclo- hexadiene, Benzene and Toluene 73 15• Time Dependence of Concentrations of Cyclopentene and Cyclopentadiene 75 16. Comparison of Normal and Sensitized De composition of Butene-1 78 17. Composition of Deutero-Methanes as a Function of Temperature 88 - x i i i - Page 18. C o m p o s i t i o n o f Deutero-Ethanes as a F u n c t i o n o f Temperature 93 19. C o m p o s i t i o n o f D e u t e r o - E t h y l e n e s as a F u n c t i o n o f Temperature 97 20. C o m p o s i t i o n o f D e u t e r o - P r o p y l e n e s as a F u n c t i o n o f Temperature 101 21. Deuterium D i s t r i b u t i o n i n Polymers 108 22. F o r m a t i o n o f CH^D and CH. i n the P y r o l y s i s o f 1-Butene i n The p r e s e n c e o f Deuterium 1^9 APPENDIX I I . l a . NMR A b s o r p t i o n Spectrum o f 1-Butene l 8 l l b . NMR A b s o r p t i o n Spectrum o f l- b u t e n e - I ( . - d ^ l 8 l 2. Mass Spectrum o f 1-Butene 18J4. 3. Mass Spectrum o f l - B u t e n e - ^ - d ^ I8I4. 1+. N o r m a l i z e d S p e c t r a o f 1-Butene ( B l a c k ) and l-Butene-I).-d (White) Showing the R e l a t i v e T o t a l I n t e n s i t i e s f o r E a c h Group o f Ions I8I4. - xiv ACKNOWLEDGMENT This inves t i g a t i o n was carried out under the supervision of Dr. W. A. Bryce to whom the author i s greatly indebted. The gas chromatographic apparatus was b u i l t j o i n t l y with Mr. S. A. Ryce whose cooperation i s g r a t e f u l l y acknowledged. The author i s also indebted to the Defence Research Board f o r f i n a n c i a l assistance during the course of t h i s work and to the Standard O i l Company fo r a Graduate Scholarship (1953-54). I N T R O D U C T I O N - 2 - I N T R O D U C T I O N  GENERAL An experimental i n v e s t i g a t i o n i n chemical k i n e t i c s gen e r a l l y involves the design and execution of experiments that provide appropriate data f o r the determination of the rates - and mechanisms of the reactions concerned. In chemical r e actions proceeding by r a d i c a l chains, a spe c i a l task arises i n the determination of the elementary reactions involved i n the mechanism. The thermal decomposition of hydrocarbons often proceeds l a r g e l y by chain mechanisms. In this f i e l d , many i n  vestigations have been undertaken i n which attempts were made to determine the chain mechanism by studying the overall ther mal decomposition of the hydrocarbons. However, i t has been gradually r e a l i z e d that most of the systems studied were pro h i b i t i v e l y complex and that the information obtained was gen e r a l l y not s u f f i c i e n t for the establishment of the elementary steps occurring i n the reac t i o n mechanism. Therefore, i n the l a s t two decades, a change i n approach has taken place. More of the investigations undertaken have been aimed at the study of i s o l a t e d elementary reactions. Considerable knowledge, im agination and experimental s k i l l are required for the design of a system by which an elementary reaction can be studied^ successfully. Data on elementary reactions are of great importance be cause of t h e i r generality. Thus, a knowledge of the rate of recombination of methyl r a d i c a l s can be applied to many systems i n which methyl r a d i c a l s are produced. However, such a "carry over" of data from one reaction system to an other i s c e r t a i n l y not permissible i n a l l cases. In some re action systems, en e r g e t i c a l l y excited "hot" r a d i c a l s may be produced which behave quite d i f f e r e n t l y from the normal species. I f the elementary reaction studied i s the s p l i t t i n g of a molecule (or r a d i c a l ) , the a c t i v a t i o n energy of the re action can be i d e n t i f i e d with the d i s s o c i a t i o n energy of the bond broken, i f the assumption i s made that the a c t i v a t i o n energy of the reverse reaction Is approximately zero. In t h i s way, the study of elementary reactions can provide i n  formation about bond d i s s o c i a t i o n energies and conversely, bond d i s s o c i a t i o n energies determined by other means can be used i n investigations of elementary reactions. I f a s u f f i c i e n t set of data on elementary reactions which might p a r t i c i p a t e i n the decomposition of a hydrocarbon (or i n any other complex reaction) i s available, the f i n a l t est of the usefulness of these data i s to attempt to use them to describe the k i n e t i c behavior of the complex system. This f i n a l t e s t often f a i l s , as i s i l l u s t r a t e d by the ther mal decomposition of ethane, about which considerable con troversy s t i l l e x i s t s . This suggests that more r e l i a b l e i n  formation about elementary reactions i s required, and also that the "carry over" of information has to be done with caution. In the l i g h t of the above considerations, the present i n v e s t i g a t i o n , a study of the o v e r a l l thermal decomposition of 1-butene, might appear to be somewhat out-dated. Yet, there are several j u s t i f i c a t i o n s f or undertaking i t , No systematic i n v e s t i g a t i o n of the o v e r a l l thermal decomposition of 1-butene i s reported i n the l i t e r a t u r e . This applies e s p e c i a l l y to the quantitative determination of the products formed. Subsequently, no reaction mechanism has been postulated or assumed. A considerable amount of information on elementary r a d i c a l reactions i s available i n the l i t  erature. I t was therefore believed that, i f r a d i c a l react ions are involved, i t might be possible to correlate the available information with r e l i a b l e a n a l y t i c a l results for the products of butene decomposition i n a way which would lead to a plausible mechanism for the o v e r a l l reaction. The thermal reactions of a l l higher o l e f i n s are not understood with any certainty. A better understanding of the thermal decomposition of 1-butene would throw some l i g h t on the thermal behavior of these o l e f i n s , since 1-butene can be considered as a good k i n e t i c representative of this group of compounds. SURVEY OF THE LITERATURE  INVESTIGATIONS OF THE DECOMPOSITION OF 1-BUTENE The e a r l i e s t i n v e s t i g a t i o n of the thermal decomposition 36 of 1-butene was made by Wheeler and Wood. 1-Butene was decomposed i n a flow system i n the temperature range between 600 and 700°C. The contact time varied with temperature from 20 seconds for the low temperature range to 10 seconds for the higher temperatures. At room temperature, the composition of the reaction mixtures obtained was; 8 8 $ gaseous products and 12$ liquids, by weight. The gas fraction was analysed separately. The unsatur ated hydrocarbons were separated from the paraffins through bromination, and the bromides were identified further. The paraffins in the gas fraction were shown to be only methane and/or ethane, since no condensation occured at the temperature of dry ice. The relative proportion of methane to ethane then was determined by combustion. The results obtained for the gaseous products are given in Table I. TABLE I. Thermal Decomposition of 1-Butene (Wheeler and Wood) Products In Volume % of Init ial 1-Butene CYEL Ci H 0 C_H, C! PI H_ CH, C H. 4 6 1 + 8 3 6 2 1+ 2 1+ 26 0.9 51+.0 7.6 3.2 0.8 8.1 1.9 1.7 20.0 2 1 + . 5 1I+.2 6.2 37.2 7.1 1.1+ 2.1 19.6 22.3 H . 9 62.1 10.6 The liquids in the reaction mixture were separated roughly by dist i l lat ion, and the fractions were examined further. Cyclohexene, methyl-cyclohexene, cyclohexadiene, raethyl-cyclohexadiene, benzene, and toluene were found to be some of the major products. Wheeler and Wood assumed that three primary reactions Temp. °C 600 650 700 -6- are responsible f o r the formation of the gaseous products. The f i r s t primary re a c t i o n considered i s the rupture of the terminal bond of the 1-butene. This i s followed by "hydrogen- ation of the r a d i c a l s formed". Thus, the r e s u l t i n g products, methane and propylene, are formed i n equal proportions, i n approximate agreement with the a n a l y t i c a l r e s u l t s for the low- 1 er temperatures. It i s not clear whether or not Wheeler and Wood considered the products from the primary s p l i t to be free r a d i c a l s . Since the work was done i n 1930, one year before Paneth and Hofeditz p o s i t i v e l y proved the existence of free methyl r a d i c a l s by the mirror technique, i t must be assumed that the " r a d i c a l s " r e f e r r e d to here were methane and allene. The subsequent hydrogenation was thought to be due to mol ecular hydrogen l i b e r a t e d from the second primary decompos i t i o n r e a c t i o n of the butene, namely, the d i r e c t dehydrogen- ation of butene to butadiene. The t h i r d primary reaction con sidered i s the decomposition of the butene to ethylene, some of the ethylene subsequently being hydrogenated to ethane. The l i q u i d hydrocarbons were believed to originate from the combination of the butadiene with an o l e f i n ; i . e . , cyclo- hexene from ethylene and butadiene, and methyl-eyelohexene from propylene and butadiene, with subsequent dehydrogenation of the c y c l i c compounds so formed. To te s t t h i s assumption, Wheeler and Wood heated mixtures of ethylene and butadiene. At 600°C, a mixture of 1 2 . 8 ^ butadiene and 8?.lf?$ ethylene was prolysed under the same experimental conditions as was the butene. The formation of small amounts of cyclohexene was observed. The dehydrogerrstl'on of the cyclohexene to form the more unsaturated products found, also was investigated by pyrolysing cyclohexene. At 600°C, approximately 9% of the original product was converted to benzene. The molecular mechanisms assumed by Wheeler and Wood ex plain, in a general way, the formation of the main products. However, the experimental evidence clearly is insufficient to warrant an acceptance of the proposed reactions. 12 Hurd and Goldsby have also studied the thermal decomp osition of 1-butene. Analysis of the gaseous products waa made by low temperature •. fractionation in an improved Pod- bielniak type dist i l lat ion column. The analytical results obtained were similar to those of Wheeler and Wood. The authors were interested mainly in the isomerizatioh of the . o 1-butene to 2-butene occurring at temperatures above 600 C, and therefore, a general reaction mechanism was not considered, A more recent investigation is reported by Molera and 22 Stubbs in a survey of the thermal behavior of a number of olefins in a static system. The in i t i a l pressure increase was found to be proportional to the in i t ia l pressure of 1- butene admitted, with a range of in i t i a l pressures from 5>0 to 5°0 mm. Hg. Therefore, an overall f irst order reaction was indicated. The activation energy for the overall re action was determined by an Arrhenius plot of the in i t ia l rate obtained from pressure change measurements. The value found was E=66.i4. kcal./mole, for the temperature range be tween 4\90 and 600°C. Unfortunately, activation energies -8- determined by following the i n i t i a l pressure increase are d i f f i c u l t to interpret without a knowledge of the mechanism involved or of the reaction products formed. Molera and Stubbs also investigated the e f f e c t of n i t r i c oxide on the reaction. Addition of n i t r i c oxide was found to produce an increase i n the rate measured by the i n i t i a l press ure increase. The addition of n i t r i c oxide i n hydrocarbon pyrolysis has been used widely to test f o r the p a r t i c i p a t i o n of free r a d i c a l s . The n i t r i c oxide i s believed to be a very e f f i c i e n t i n h i b i t o r of free r a d i c a l chains. Thus, a decrease i n the de composition rate i n the presence of n i t r i c oxide indicates that the reaction proceeds p a r t l y or exclusively by r a d i c a l chains. Conversely, i f the addition of n i t r i c oxide has no e f f e c t , r a d i c a l mechanisms do not appear to p a r t i c i p a t e i n the reaction. According to t h i s concept, the s l i g h t increase i n rate found by Molera and Stubbs should indicate that rad i c a l chains do not p a r t i c i p a t e extensively i n the reaction mechanism. However, some of the conclusions obtained with the use of the n i t r i c oxide technique are open to doubt, and s t i l l subject to controversy. In the special case of 1-butene, an i n h i b i t o r of r a d i c a l chains i t s e l f , the lack of i n h i b i t i n g a ction of the n i t r i c oxide cannot be'considered as conclusive proof that free radicals do not p a r t i c i p a t e i n the reaction. This question w i l l be dealt, with i n more d e t a i l i n the d i s  cussion of the experimental r e s u l t s . -9- PRIMARY STEP IN THE FREE RADICAL DECOMPOSITION OF 1-BUTENE For a number of years i t has been recognized that the a l l y l r a d i c a l i s s t a b i l i z e d by high resonance energy. This has been substantiated on t h e o r e t i c a l as well as on exper imental grounds. The resonance energy of the a l l y l r a d i c a l has been estimated t h e o r e t i c a l l y by Coulson^ as 15•4 k c a l . / 3 mole and by Orr (quoted by Bolland) as 18.7 kcal./mole. The high resonance energy of the a l l y l r a d i c a l should manifest i t s e l f i n a low value of the d i s s o c i a t i o n energy of the a l l y l - methyl bond as compared with the propyl-methyl bond i n n- butane. The weakest bond i n 1-butene i s thus the allyl-methyli bond, and at s u f f i c i e n t l y high temperatures, the thermal de composition should proceed, at least p a r t l y , with the primary step ( 1 ) , as follows: 1-Butene - CH^ + A l l y l (1) The presence of methyl and a l l y l r a d i c a l s i n the p y r o l  y s i s of 1-butene has been detected d i r e c t l y with the aid of 16 the mass spectrometer by Lossing, Ingold and Henderson. 1- Butene was decomposed at 1000°C i n a f a s t flow system attached to a mass spectrometer. The nature of the apparatus requires r e l a t i v e l y high concentrations of r a d i c a l s for t h e i r p o s i t i v e detection. Since the contact time used i n this method i s a l  so very short (about 0 .8 milliseconds), the temperatures used are considerably higher than those of conventional k i n e t i c investigations. The temperature range studied.in the present in v e s t i g a t i o n i s lower by ij .00 OC. The considerable difference -10- i n temperature reduces the significance of Lossing's r e s u l t s for the present study, since the reaction might proceed by a d i f f e r e n t path at temperatures so much lower. The primary step of the 1-butene decomposition has been studied at lower temperatures (650-770°C) by Sehon and •25 Szwarc. The i n v e s t i g a t i o n was based on the toluene c a r r i e r 30 technique. The main feature of the method i s the use of toluene as a c a r r i e r gas. The r a d i c a l s formed i n the primary decomposition of the compound under invest i g a t i o n are removed by the fas t reaction with toluene. C^EL-CH • R. RH * C H -CH . o 5 3 6 5 2 The r e l a t i v e l y stable benzyl r a d i c a l s dimerize eventually to dibenzyl. The toluene present i n large excess thus acts as an e f f e c t i v e chain i n h i b i t o r . In the p a r t i c u l a r case of 1-butene, the i d e a l i z e d mech anism can be expressed by the equations: CH2= CH-CH2-CR"3 CH2= CH-CH2. + GH^ . (slow) (1) CH V + C,R>-CH., CH, • C,Hr,-CH0. (fast) (2) 3 ° ? 3 4 - 0 3 2 CH = CH-CH. • C.H^-CH — - CH = CH-CH • C.H-CH.(3) d Z 6 3 3 2 3 6 3 2 and chain terminating steps l i k e : 2 C ^ C H g . — (C 6H 5CH 2) 2 ( k ) 2 CH2=CH-CH2. (CH 2=CH-CH 2) 2 etc. According to the above scheme the rate of formation of methane i s equal to the rate of the primary decomposition. The rate of formation of methane can be conveniently measured by separation of the methane from the reaction products at the -11- temperature of l i q u i d nitrogen. In the work described, the non-condensables contained, besides the expected methane, varying amounts of hydrogen (3$ at 935°K increasing to 26$ H at 105l°K). An Arrhenius p l o t of the rate of formation of 2 non-condensables gave a st r a i g h t l i n e . The a c t i v a t i o n energy 13 -1 found was 6l . 5 k c a l . and the frequency factor, A = 10 sec . In separate experiments, i t was shown that packing of the re action vessel with s i l i c a wool had no influence on the rate, i n d i c a t i n g a homogeneous reactio n . The reaction also was shown to be of f i r s t order by a v a r i a t i o n of the p a r t i a l press ure of the butene by a factor of 6. The a c t i v a t i o n energy and frequency factor obtained were i d e n t i f i e d with those of the primary decomposition of 1-butene. The re s u l t s of Sehon and Szwarc provide the only quant i t a t i v e data for the a c t i v a t i o n energy and frequency factor of the primary step i n the free r a d i c a l decomposition of 1- butene. However, i t seems that the i n t e r p r e t a t i o n of the ex perimental r e s u l t s on the basis of the assumed mechanism was done without s u f f i c i e n t proof that the mechanism indeed re presents the major reactions c o r r e c t l y . For example, a s i g  n i f i c a n t amount/jf hydrogen, not accounted for by the mechan ism, was found i n the methane f r a c t i o n , the only gas f r a c t i o n analysed. Also, the amount of dibenzyl, the only other prod uct q u a n t i t a t i v e l y determined, was considerably lower than the t h e o r e t i c a l l y expected amount. The argument that the a c t i v a t i o n energy and frequency factor obtained represent val ues f o r the postulated primary step of the 1-butene decomposition - 1 2 - therefore must be accepted with caution. SUMMARY The investigations r e f e r r e d to above provide the only d i r e c t information on the thermal decomposition of 1-butene available i n the l i t e r a t u r e . A large number of products apparently are formed i n the reaction, but the information available was not s u f f i c i e n t to explain the modes of formation of these products s a t i s f a c t o r i l y . The important question concerning the reaction mechanism, whe ther or not r a d i c a l chains p a r t i c i p a t e , i s also not answered with any c e r t a i n t y . While there i s p o s i t i v e evidence that free r a d i c a l s are o formed i n the p y r o l y s i s of 1-butene at 1000 C, the evidence available f o r the temperature range from $00 to 600°C was not s u f f i c i e n t to warrant a decision on this point. For this reason, possible secondary reactions of the free rad i c a l s produced by a primary s p l i t of the butene molecule w i l l not be reviewed here, although such reactions have been studied. For example, the reactions of methyl r a d i c a l s with 1-butene i n systems where the methyl r a d i c a l s were produced by the photolysis of acetone or by some other means have been investigated. The information about such reactions w i l l be discussed l a t e r i n r e l a t i o n to the ex perimental r e s u l t s from t h i s work. A major d i f f i c u l t y i n past k i n e t i c investigations has been the lack of convenient a n a l y t i c a l methods capable of - 1 3 - providing adequate quantitative analyses. As a r e s u l t , i t has been a practice, i n the past, to postulate mechan isms based on a minimum of quantitative information. In recent years, a number of excellent a n a l y t i c a l methods es p e c i a l l y suited for the analysis of very small quantities of complex mixtures of hydrocarbons have been developed. Some of these methods have been used i n the present work. The objective of the present study was the el u c i d  ation of the mechanism of the thermal decomposition of 1-butene. The i n v e s t i g a t i o n involved the following steps: Choice of a suitable a n a l y t i c a l method to provide s u f f i c i e n t l y accurate a n a l y t i c a l r e s u l t s . Qualitative determination of the compounds present i n the reaction mixtures. Determination of the rates of formation of the products and the rate of butene decomposition as a function of temperature. S p e c i f i c t e s t i n g to determine whether or not r a d i c a l chains p a r t i c i p a t e In the mechanism... Tracing the o r i g i n of the products formed with the use of the deutero-isomer l-butene-4-d^. Correlation of the data and determination of the s i g n i f i c a n t k i n e t i c constants on the basis of a mechanism derived from the experimental r e s u l t s . -14- E X P E R I M E N T A L - 1 5 - E X P E R I M E N T A L METHOD OF PYROLYSIS  APPARATUS AND MATERIALS The 1-butene used was P h i l l i p s Research grade (99 . 8$ ) . The method of preparation of the 1-butene-4-d^ together with proofs of structure and p u r i t y are given i n Appendix I I . The butenes were pyrolysed i n a conventional s t a t i c sy stem. The apparatus used i s represented i n F i g . l a . and V"2 are storage flasks for the 1-butene and l-butene-i^-d^. M-^  and M 2 are mercury manometers. S i s the s i l i c a reaction vessel (300 c c ) . The reaction vessel was heated i n an e l e c t r i c furnace. The system could be evacuated by a mercury d i f f u s i o n pump. FURNACE AND TEMPERATURE CONTROL The heating arrangement i s shown i n F i g . 1 c . The f u r  nace consisted of a quartz tube around which three separate heating c o i l s were wound. The tube was placed i n a small s t e e l b a r r e l and insulated with asbestos wool. Two chrorael- alumel thermocouples were fastened to the top and bottom of the r e a c t i o n vessel. The current f o r the heating c o i l s was supplied through a Sorensen voltage regulator and adjusted fo r a given temperature by a variable transformer ( F i g . l b ) . For f i n e r manual adjustment and manual temperature control, the resistance R^ was used. The current through the three separate heating c o i l s could be adjusted by the resistances -16- Plg.la:Pyrolysis Apparatus Pig.lb P i g . l c C i r c u i t Diagram of Furnace and Reaction Furnace Heaters. Vessel with Thermo couples - 1 7 - R , R and R to obtain the same reading on both therm- 2 3 1+ ocouples. I t was possible to maintain the temperature of the reaction vessel constant to within 1°C. DESCRIPTION OF A TYPICAL EXPERIMENT To shorten the time for admission of a measured quantity of reactant gas into the heated reaction vessel, a pre-expan- sion volume V was used. The pressure of butene admitted i n 3 V (and read on manometer M^), was so chosen as to produce a desired resultant pressure a f t e r expansion of the gas from into the reaction vessel. From V^, the gas was expanded Into the reaction vessel by f u l l y opening the'connecting stop cock T^. After approximately 5 seconds, the pressure on the manometer M^ having become stationary, stopcock T^ was closed. The reaction time was measured from this moment. The pressure of the reaction system could be followed by read ings on the mercury manometer M^. After the desired reaction time ( 1 - 5 minutes) had elapsed, stopcock T^ was opened to the lower g a l l e r y and the reaction mixture expanded through the open stopcock T into the re- 6 ceiving volume V". After a few seconds, T, was closed. The gas trapped In the r e c e i v i n g volume was used fo r analysis, while the remaining gas mixture i n the reaction vessel was pumped out by opening T 5* The volume of the r e c e i v i n g pipette Vh_ and i t s connection to the p y r o l y s i s apparatus varied with the method and purpose i - 1 8 - of the analysis. The i n d i v i d u a l variations w i l l be men tioned i n the discussion of the a n a l y t i c a l methods. METHODS OF ANALYSIS  DIRECT MASS SPECTROMETRY ANALYSIS The mass spectrometer used i n a l l determinations was a 90° sector type instrument. Magnetic scanning and pen re cording were employed. The s e n s i t i v i t y of recording was such that an ion current of 3 x lO" 1^- amps, gave a de f l e c t i o n of 1 cm. on the Leeds and Northrup Speedomax recorder. The ion source and el e c t r o n i c controls have been described by Losslng 18 11 and Tickner, and by Graham, Harkness and Thode. The i n  strument was of the same type as those used by Lossing and associates. To obtain gas samples for analysis, a 300 cc. pipette (provided with stopcock) was attached by means of a ground glass j o i n t to the outer end of stopcock T^ of the pyrolysis apparatus. (See F i g . la.) Direct mass spectrometric analysis showed that the re action mixtures obtained at 1*90 - 550^0 and 1-5 minutes re action time contained; hydrogen, methane, ethane, ethylene, propylene, 1, 3-butadiene and unreacted butene, plus a great many compounds with masses higher than the molecular weight of butene. For convenience, pyroly s i s products with a mol ecular weight greater than that of butene w i l l be referred to as polymers. The molecular masses (parent masses) of the -19- polyraers could be determined by scanning the higher mass range at low electron energies. The existence of a large number of possible isomers, and the lack of complete data on the mass spectra of hydrocarbons i n the to Cg range made the i n  terpr e t a t i o n of the spectra very d i f f i c u l t . Furthermore, the quantitative determination of the l i g h t e r hydrocarbons was made uncertain by the contributions of the polymers to peaks i n the lower mass range. For these reasons, the method of dir e c t analysis was abandoned. LOW TEMPERATURE FRACTIONATION AND SUBSEQUENT ANALYSIS . OF THE FRACTIONS WITH THE MASS SPECTROMETER Since mass spectrometric analysis could not be applied d i r e c t l y , a f r a c t i o n a t i o n of the reaction mixture p r i o r to mass spectrometric analysis was undertaken. 1F> A LeRoy s t i l l ^ was constructed f o r t h i s purpose. The apparatus i s represented i n " F i g . 2 . I t consisted of three main parts; sample pipette V (300 c c ) , f r a c t i o n a t i o n column F and Toepler pump T. The free end of the mercury cut-off C^ was sealed to stopcock T^ of the pyrolys i s apparatus (see F i g . l a ) . The amount of gas sample admitted into the c a l  ibrated volume of the pipette V could be determined by reading the pressure on the mercury manometer M. From pipette V, the gas sample was admitted i n t o the f r a c t i o n a t i n g column, which was cooled with l i q u i d nitrogen. The gases not condensed af t e r a short waiting period (hydrogen and methane) were re moved. For thi s purpose, the mercury cut-off C was opened and -21- the gas pumped out by means of the a u x i l i a r y mercury d i f  f usion pump and the Toepler pump. The amount of coll e c t e d gas was measured i n one of the ca l i b r a t e d volumes of the Toepler pump and then transferred into a pipette f o r mass spectrometric analysis. The f r a c t i o n a t i n g column was then heated, by means of a b u i l t - i n heating c o i l , to a s l i g h t l y higher constant temp erature. The column temperature was adjusted to produce the desired pressure of gas inside the column. The pressure was determined with the McLeod gauge. A pressure of 10-100 microns Hg generally was used, depending on the desired amount of f r a c t i o n to be obtained. The f r a c t i o n then was col l e c t e d by means of the Toepler pump u n t i l the column pressure had f a l l e n o f f to 1-10 microns Hg. In thi s way, a desired number of f r a c t i o n s , or "cuts", could be co l l e c t e d for mass spec trometric analysis. The mass spectrometric r e s u l t s for the fractions of a t y p i c a l run are reproduced i n Table I I . A comparison of the values i n Table II with values ob tained l a t e r by gas chromatographic analysis (see Table V, reaction mixture 55l±.5°C - k min.) shows good agreement be tween the two methods. The analysis by low temperature f r a c t i o n a t i o n had some important disadvantages. The polymers could not be ident i f i e d beyond their molecular masses, since the fr a c t i o n a t  ion i n the high molecular range was not e f f i c i e n t . Complete i d e n t i f i c a t i o n of the polymers was desirable for a better understanding of the reaction mechanism. Also, the results -22- Table II Results from Low Temperature Fractionation and Subsequent  Mass Spectrometric Analysis of the Fractions Analysed mixture produced by pyrolysis of 1-butene ( i n i t i a l pressure 200 mm. Hg) for 4 minutes at 550°C. F r a c t i o n No. Amount of Fract i o n D i s t r i b u t i o n of Volume % Compounds i n Fra c t i o n Volume % 1 26.0 3.5 Hydrogen 22.5 Methane 2 7.3 0.3 Methane 6.5 Ethylene o.5 Ethane 3 6.6 1.8 Ethylene 4.1 Ethane o.5 Propylene 0.2 Butene 4 17.0 13.8 Propylene 1.0 Butadiene 0.8 Butene 5 36.7 0.3 Propylene 1.0 Butadiene 35-4 Butene 6 1.3 0.1+ Butene 0.9 C5IL3, C 5H 8, C 5 H 1 0 7 - 9 6.0 6.0 C6H6» C6H8> C6H10> C ?H 8, C 7H 1 Q, C7H12» c 8 H i 4 99.6 99.6 Composition of Reaction Mixture i n Vol. t Hydrogen 3.5 Methane 22.8 Ethylene 8.3 Ethane 4.6 Propylene 14.6 1,3>'r, Butadiene 2.0 Butene 36.8 Polymers 6.9 99.£ - 2 3 - i n Table I I show that the separation of the l i g h t e r hy drocarbons was not complete. For the mass spectrometric analysis of fractions from the pyrolysis of 1-butene, th i s i s of l i t t l e consequence. However, the analysis of the deu- terated reaction products from 1-butene-I^-d^ would have been impossible under the same conditions. Another important disadvantage of the f r a c t i o n a t i o n method i s that i t i s very t ime-c onsuraing. Fortunately, the advent of gas chromatography coincided c l o s e l y with the f u l l r e a l i z a t i o n of the drawbacks of the low temperature f r a c t i o n a t i o n method. ANALYSIS BY GAS CHROMATOGRAPHY INTRODUCTION A survey of thi s r a p i d l y developing f i e l d w i l l not be attempted here. Extensive bibliographies can be found i n many recently published papers. i'9 The separation of gaseous or l i q u i d mixtures by the ad- sorption-elution and p a r t i t i o n - e l u t i o n methods i s effected by passing the mixture i n vapor form c a r r i e d i n a stream of an Inert gas through a column f i l l e d with some "active" material. In the case of adsorption-elution chromatography, the "active" material i s a s o l i d , such as alumina, s i l i c a g el, charcoal, etc. The separation i s then due to d i f f e r  e n t i a l adsorption, as a r e s u l t of which the di f f e r e n t com pounds t r a v e l through the column with d i f f e r e n t speeds, and -21+- emerge from the end separately. In p a r t i t i o n - e l u t i o n chromatography, the active material i n the column i s a s u i t  able l i q u i d with low vapor pressure. The l i q u i d i s supported on the surface of p a r t i c l e s of inactive material, such as c e l l i t e , glass powder, ground f i r e b r i c k , etc., free passage of the c a r r i e r gas and a stationary l i q u i d phase thus being achieved. The separation In t h i s case i s due to d i f f e r e n t i a l absorption of the compounds into the l i q u i d phase, i . e . , differences i n the d i s t r i b u t i o n c o e f f i c i e n t s of the compon ents of the mixture. The compounds leaving the end of the separating column can be detected i n d i f f e r e n t ways. One of the methods comm only used employs a thermal conductivity c e l l mounted i n a balanced bridge c i r c u i t . In t h i s method, the detection i s " effected by passing the c a r r i e r gas alone through one channel of the c e l l (reference channel). The c a r r i e r gas leaving the separating column, carrying the separated compounds, i s passed through the second channel of the c e l l (detection channel). The appearance of a compound other than the c a r r i e r gas i n the detection channel causes an imbalance i n the bridge c i r c u i t . Since the output of the bridge i s fed into a re- corder, the passage of each component of the gaseous mixture through the detection channel produces a peak on the recorder chart. The respective positions of the peaks can be used for q u a l i t a t i v e i d e n t i f i c a t i o n of the compounds. The areas of the peaks are a measure of the amounts of the correspond ing compounds i n the sample. - 2 5 - APPARATUS AND PROCEDURE General The apparatus represented i n P i g . 3 was constructed for the separation of the reaction mixtures obtained i n the but ene p y r o l y s i s . I t consisted of four main parts: Sample admission section, for measuring samples and admitting them into the separating column. Separating column with heater. Thermal conductivity c e l l and detection c i r c u i t . System f o r c o l l e c t i n g the separated f r a c t i o n s . , Helium was used as the c a r r i e r gas. The c a r r i e r gas, supplied from a storage cylinder, passed through a reduction valve, a needle valve and a U-tube p u r i f i e r f i l l e d with char coal and s i l i c a gel into the reference channel of the ther mal conductivity c e l l . Prom there, the gas was directed through either arm or B^ of the bypass into the separating column. The gas leaving the column passed through the second (detection) channel of the thermal conductivity c e l l and then through any one of the traps t-^ to t ^ where the separated compounds could be c o l l e c t e d . The gas then passed through stopcock S to the flow meter and f i n a l l y out to the atmos- 10 phere. When c o l l e c t i o n of the fractions was not required, the gas leaving the detection channel of the conductivity c e l l was not directed through a trap, but bypassed to the flow meter by means of stopcock S . -27- Admlssion of Samples for Analysis Into The Separating System Samples f o r analysis could be admitted to the separating system i n either gaseous or l i q u i f i e d form. For admission of gaseous samples, the reservoir V and the bypass arm were used. The gas sample, withdrawn from the pyroly s i s apparatus by means of a gas pipette, was ad mitted through stopcock S into the evacuated gas reservoir V and the bypass arm B^, the helium stream having been re directed previously through bypass arm B 2. Then, the pressure of the gas sample was adjusted to the desired value by r a i s  ing or lowering the mercury l e v e l i n V. After the pressure was read on the mercury manometer M, stopcock S was closed. The gas sample trapped i n bypass arm B_^  was c a r r i e d to the column by r e d i r e c t i n g the helium stream through B^. The volume of the bypass arm B^ (10.89 c c . ) , was known. After completion of the analysis, a new sample of the same gas could be admitted conveniently in t o bypass arm B^. After r e d i r e c t  ing the helium stream through B^, B^ was evacuated through the vacuum l i n e connection on the two-way stopcock Then a new sample was admitted into B^, by connecting B^ to the gas reservoir V, This arrangement was p a r t i c u l a r l y useful, not only for repeated analyses of a p a r t i c u l a r gas- mixture, but also for repeated determinations of the s e n s i t i v i t y of a stand ard gas. (See section e n t i t l e d : Basis of the Quantitative Determinations.) The admission of l i q u i d samples by means of a syringe and a serum cap has become standard practice i n gas -28- chromatography. A serum cap mounted on a short sidearm sealed to the upper part of.bypass arm was used for th i s purpose. However, the method was used infrequently, i . e . only when an approximate value f o r the retention volume of a l i q u i d standard substance under d i f f e r e n t a n a l y t i c a l con ditions was desired. I t was often necessary to admit large quantities of reaction mixture (containing hydrocarbons i n the range C -C ) into the a n a l y t i c a l apparatus. This was ess e n t i a l 2 7 for the experiments i n which compounds were trapped out and c o l l e c t e d for mass spectrometric i d e n t i f i c a t i o n , and also f o r the quantitative determination of the polymers, which were present i n r e l a t i v e l y small amounts i n the reaction mix ture. For th i s purpose, the hydrocarbon mixture was l i q u  i f i e d at the temperature of l i q u i d nitrogen i n a U-tube. The U-tube was then connected to the bypass arm B^. After the helium stream was directed through B^, the U-tube was heated r a p i d l y , causing a ra p i d evaporation of the sample i n  to the helium stream. Separating Column and Heater Glass columns with a t o t a l length of 1$0 cm. and an i n  ternal diameter of 5 mm. were used. Both ends of the column above the column packing were made of c a p i l l a r y glass tubing with 2 mm. i n t e r n a l diameter i n order to avoid dead space. The column was joined to the gas l i n e by means of two c a p i l l a r y ball-and-socket j o i n t s . -29- The column heater consisted of two concentric pyrex tubes which formed a closed jacket around the column. The heating wire was wound on the outer surface of the inner tube. The temperature was measured by means of a mercury therm ometer, mounted beside the column. The current was supplied through a Sorensen voltage regulator and adjusted to the de s i r e d value by means of a variable transformer. ;For the separation and quantitative determination of com ponents i n the reaction mixture ranging from methane up to and including butene, an alumina packing of the column was used. The aluminum oxide was graded to a p a r t i c l e size of 30-k.O mesh. For the separation and quantitative determination of compounds i n the reaction mixture with molecular weights higher than that of butene, a p a r t i t i o n column with T.C.P. ( t r i c r e s y l phosphate) on cGelite was used. The r a t i o of cGelite to T.C.P. was 2 to 1 by weight. The e S s i i t e (5u,5 Johns-Manvilie Co.) was graded and mixed with the T.C.P. 12 according to the method described by James and Martin. Thermal Conductivity C e l l and Detection C i r c u i t The thermal conductivity c e l l ( F i g . l|.) was constructed from a brass block. The conductivity elements were helixes of platinum wire. The wire of each element had a diameter of 0.005 cm., a t o t a l length of llj. cm., and a t o t a l r e s i s t  ance of 7 Ohms. The ends of each platinum wire were s i l v e r - soldered to the projecting studs of two kovar seals which - 3 0 - Cross-section Side View Side View of Brass Plug Carrying Conductivity Wire Top View Pig. 4 Thermal (actual Conductivity C e l l size) - 3 1 - were soft-soldered to a removable brass plug. Two such brass plugs, one f o r each arm of the c e l l , f i t t e d t i g h t l y into the brass block, completing the gas channels without obstructing them. Vacuum t i g h t connections between the plugs and the c e l l were obtained by means of t e f l o n gaskets. The connections to the gas l i n e were made by copper c a p i l l a r y tubing soft-soldered to brass f i t t i n g s carrying a gas thread of 1/8", and extending into the channel of the c e l l so as to reduce dead space. The conductivity c e l l and the connecting copper cap i l l a r y tubing were submerged i n a thermostated o i l bath. The two platinum wires of the c e l l formed the two arms, and C^, of a conventional Wheatstone bridge. The c i r c u i t diagram i s shown i n P i g . The current, supplied by a storage battery, was regulated to 200 m.A. by means of re sistance R^. Before the beginning of an experiment, when a steady stream of helium was established, the two reference points P^ and P 2 were brought to equal p o t e n t i a l by adjusting the two resistance boxes R^ and R^ to zero d e f l e c t i o n of the galvanometer G. The output of the bridge (points P^ and P ) then was switched to the recorder. A Leeds and Northrup Speed' omax recorder was used. The instrument provided variable s e n s i t i v i t y , from 1 to 20 m.v. f o r f u l l scale de f l e c t i o n , and an adjustable "zero". - 3 2 - ?1 Recorder P2 R 5 F i g . 5 Diagram of Thermal Conductivity Recording C i r c u i t - 3 3 - System f o r C o l l e c t i n g the Separated Components The gas fract i o n s leaving the column could be trapped out of the helium stream and transferred into pipettes f o r mass spectrometric analysis by means of a system of traps and a Toepler pump. The following proved to be the most s a t i s f a c t o r y pro cedure. Prior to the admission of the mixture to be anal ysed, helium was allowed to pass through a l l four traps, which were cooled with l i q u i d nitrogen. Due to i n i t i a l con t r a c t i o n of the helium gas i n the traps, a substantial slow ing down of the helium flow could be observed on the flow meter. After the flow had increased to normal, the helium stream was bypassed through stopcock (Pig. 3 ) , and the traps were shut o f f . Then, the gas mixture to be separated was admitted to the system. In a l l trapping experiments, the gas mixtures were l i q u i f i e d previously i n a U-tube and ad mitted into the helium stream i n the way described e a r l i e r . In t h i s way, the larger quantities of sample necessary f o r trapping could be handled. The gas chromatogram appearing on the Speedomax was observed, and the desired f r a c t i o n trapped by d i r e c t i n g the gas catareanfc through one of the traps. The time l a g between a signal on the recorder and the portion of gas which produced that signal reaching the trap was only about 1 to 2 seconds. Due to t h i s f a c t , i t was possible to trap any portion of a given peak accurately. A t o t a l of four samples could be c o l l e c t e d i n the four traps. To recover the trapped material, stopcock S was connected to the Toepler —31*-- pump, and the helium from a given trap was pumped out. The l i q u i d nitrogen was removed, and the trap allowed to warm up. The gas was c o l l e c t e d and measured by means of the Toepler pump, and then transferred into a pipette for mass spectrometric analysis. Analysis with Gradual Increase of the Column Temperature The v a r i a t i o n of the retention volume-;:- of hydrocarbons belonging to a given homologous series can be expressed by the approximate r e l a t i o n : log r = K.N v c where: r ^ retention volume N- number of carbon atoms. of compound K p r o p o r t i o n a l i t y factor . For constant flow conditions, the r e l a t i o n can be expressed as: '. log r = k.N & t c where: r retention time k p r o p o r t i o n a l i t y factor The expressions hold f o r constant column temperature. The time of analysis thus increases exponentially with the molecular mass of the compounds (belonging to a homologous series) contained i n the mixture to be analysed. The The retention volume of a compound i s defined as the t o t a l volume of c a r r i e r gas that has passed through the detection c e l l from the onset of the analysis t i l l the appearance of the compound i n the detection c e l l . - 3 5 - r e s u l t i n g long duration of the analysis, undesirable i n i t s e l f , i s accompanied by a gradual spreading-out of the recorded peaks. The spreading-out i s due to a gradual d i f f u s i o n of the : gas f r a c t i o n s into the c a r r i e r gas, and increases with the time spent by the fractions i n the column. Low and drawn-out peaks reduce the value of the chromatogram obtained, with regard to q u a l i t a t i v e and quantitative i n t e r p r e t a t i o n . To obviate these d i f f i c u l t i e s i t i s necessary to reduce the time of the chromatographic separation. This can be done either by pre-separation of the.:mixture into two or three fractions or by a gradual increase of column temperature. The second method was adopted, since i t appeared to be f a s t e r and less complicated. The temperature of the column was raised during the analysis by stepwise increases of the voltage across the column heater. This was done either manually or, for series of s i m i l a r analyses, by a timeclock-relay system. The temperature increase could be reproduced within a few degrees i n successive runs. The chromatogram of a reaction mixture taken under the des cribed conditions with the alumina column i s given i n P i g . 6. BASIS OF.THE QUANTITATIVE DETERMINATIONS The s e n s i t i v i t y , S_^ , determined f o r the pure gas i can be defined as: -37- where: A^ peak area produced by gas i on chromatogram n_^  number of moles of gas i . For i d e n t i c a l conditions of analysis ( c a r r i e r gas flow, column temperature, etc.) remains constant over a wide range of values of n^. This forms the basis of the quant i t a t i v e determination. The s e n s i t i v i t i e s of a l l components i n a mixture are determined i n separate experiments using the pure components (gas standards)' alone. The amount of a component i n a gas mixture then i s obtained from: A i n i — S i where: n number of moles of i i n gas mixture i analysed A peak area of gas i i n the chromatogram 1 of the gas mixture S separately determined s e n s i t i v i t y of 1 component i . A discussion of the d i f f e r e n t methods f o r peak area de termination and for computation of the results can be found 8 i n a recent paper by Dimbat and associates. The following procedures were used i n the present i n  ves t i g a t i o n . The exact amount of sample admitted for anal y s i s could be determined as described i n the e a r l i e r section: Admission of Samples f o r Analysis i n t o the Separating System. The peak areas were determined by cutting out the recorded peaks from the chart paper, and weighing them on an analy t i c a l balance. In preliminary experiments, a very s a t i s f a c t o r y -38- constancy of the area/weight r a t i o of the chart paper (Leeds and Northrup) was established. The s e n s i t i v i t i e s of the con stituent gases i n the butene pyrolys i s mixture were determined i n preliminary experiments. A l l s e n s i t i v i t y determinations were done under the same conditions of helium flow (I4.O cc./ min.) and controlled increase of the column temperature as were used i n the analyses of the gas mixtures. Various amounts of each gas standard were used to check the constancy of the s e n s i t i v i t i e s i n the range used i n the analyses. The con stancy of the s e n s i t i v i t y of 1-butene i s demonstrated i n Table I I I . Equally good constancy was obtained for the other components. TABLE III S e n s i t i v i t y of - 1-Butene Amount Analysed S e n s i t i v i t y (moles x 1C-5) ( a r b i t r a r y units) 5.3 14.8 3.5 14.5 1.47 14.8 0.9 14.55 Average sensitivity=ll4 . . 6 7 Maximum deviation=l4\ .8 - Ik..5 = 0.3 Maximum error 0.3 x 100 2.01$ " lIiTo7 = The s e n s i t i v i t i e s required were redetermined at the beginning of each.day of a n a l y t i c a l work. The v a r i a t i o n of the s e n s i t i v i t i e s of the l i g h t hydrocarbons determined over a period of a month i s given i n Table IV. - 3 9 - TABLE IV Var i a t i o n of. S e n s i t i v i t i e s of Light  Hydrocarbons over a Month's Period Compound S e n s i t i v i t y : i n mg. of chart paper per micro-mole of compound Methane 98 91+ 91 96 90 Ethane 136 131+ 135 135 136 Ethylene 125 125 120 12i+ 120 Propylene 161+ 170 160 173 167 Butene 218 210 212 218 218 Prom the res u l t s i n Table IV, i t can be seen that there was l i t t l e v a r i a t i o n i n the measured s e n s i t i v i t i e s over a long period of time. The r e l a t i v e increase i n s e n s i t i v i t y from methane to butene i s larger than the r e l a t i v e increase that could be expected on the basis of the increasing ther mal conductivities of the compounds, ^he increase i n column temperature produces a gradual decrease i n c a r r i e r gas flow. The decrease i n gas flow i s responsible f o r the additional increase i n the s e n s i t i v i t i e s of compounds emerging from the column after a longer time. RESULTS FOR THE PYROLYSIS OF 1-BUTENE  OBTAINED BY GAS CHROMATOGRAPHIC ANALYSIS QUALITATIVE DETERMINATIONS OF THE LIGHT HYDROCARBONS The l i g h t hydrocarbons In the reaction mixture from the -l+o- 1-butene py r o l y s i s were separated by gas chromatographic f r a c t i o n a t i o n . Most of the compounds could be i d e n t i f i e d by retention volume measurements. In addition, a l l chrom atographic fractions were c o l l e c t e d and analysed i n the mass spectrometer. The following compounds were i d e n t i f i e d p o s i t i v e l y : Me thane Pr opyl ene Ethane Butadiene Ethylene 1-Butene Propane (traces) 2-Butene QUALITATIVE DETERMINATIONS OF THE POLYMERS The chromatogram of the polymer compounds contained i n o a re a c t i o n mixture of 1-butene (pyrolysed at 550 C with a reaction time of 5 min.) i s given i n F i g . 7. A p a r t i t i o n column with T.C.P. on cGellite was used for the chromatographic separation. The peaks i n the chromatogram have been indexed according to the nature of the compounds producing them: B C Hydrocarbons k p c $ H C6 Bz Benzene TI Hydrocarbons X Xylene The compounds i d e n t i f i e d by mass spectrometric analysis of the fractions are given i n F i g . 7 under the respective peaks. The mass spectrometric i d e n t i f i c a t i o n was d i f f i c u l t i n some cases. P o s i t i v e l y i d e n t i f i e d were: 120 100 Tl rv«» C 7 H 1 2 U-CH , C 8 H 1 4 • —i i . | - - 8 0 6 0 40 25 Temperature °C Bz H 3 H 2 P 3 B f B 2 C 6 H 10 6 10 Time 50 40 3 0 20 Minutes Fig.7 Gas chromatographic Separat ion of the Polymers. Benzene Toluene Xylene (presumably orthoxylene) Very good evidence, but not a po s i t i v e proof, was obtained for the following compounds: Cyclopentene Cyclopentadiene Cyclohexadiene• The remaining compounds could not be i d e n t i f i e d beyond th e i r molecular formulae. The mass spectra of the i s o l a t e d polymer fractions with a discussion of the mass spectrometric r e s u l t s are given i n Appendix I at the end of t h i s t h e s i s . QUANTITATIVE DETERMINATIONS OF THE LIGHT HYDROCARBONS The gas chromatographic analysis of the l i g h t hydro carbons was done with the alumina column. In a l l determin ations, a gas sample of the reaction mixture of approximately 1.3 cc. at S.T.P. (10.89 cc, at 10 cm. Hg pressure) was analysed. The basis of the quantitative determinations was described e a r l i e r . The re s u l t s for reaction mixtures produced under d i f f e r e n t experimental conditions are presented i n Table V. QUANTITATIVE DETERMINATIONS OF THE POLYMERS The gas chromatographic analysis of the polymers was made with the T.C.P. column. In a l l determinations, the reaction mixture sample analysed was approximately 21 cc. -43- Table V A n a l y t i c a l Results f o r Light Hydffocarbons Time Press we Volume % rain, of ' ;  Reaction Methane Ethane Ethylene Propylene 1-Butene Total System mm, Hg Temperature - 1+93 C 0 198.G 100 100. 1 198.6 0.20 0.10 0 .15 97' 97.5 2 199.0 0.62 0 .13 0.30 0.44 98 99.5 3 199.8 1.25 0.27 0.50 0 .74 95 98.3 1+ 200.0 1.72 0.1+0 0.77 1.14 94' 97.0 5 200.2 2.10 0.56 1.11 1.67 94 99.5 Temperature - 509°C 0 197 100 100. 1 198 1.44 0.21 0.36 0.60 99 101.2 2 199 2.50 0.1+7 0.92 1.34 96 101.6 3 200 3.40 0.72 1.44 2.20 95 102.2 4 202 4 .95 1.06 2.05 2.90 87 98.1+ 5 201+ 5.30 1.35 2.63 3.77 82 95.2 Temperature - 522.2°C 0 199 100 100. 1 201 2 .2 0 .4 0 .7 1.3 93 97.7 2 207 l+.l 0.9 1.7 2.7 86 94.8 3 209 6.2 1.4 2.5 4.0 82 95.7 l± 211 8 .5 1.7 3.4 5.7 76 95.3 5 213 11.0 2 .3 3.9 6.8 69 82.6 -44- Table V (Cont'd) Time Pressure Volume % min. of ; • Reaction Methane Ethane Ethylene Propylene 1-Butene Total System mm* Hg Temperature - 540.6 C 0 202 100 100. 1 209 5.2 1.1 2.2 3 .3 82 • 93.4 2 216 9.7 1.-9 4 . 0 6.1 73 94.3 3 224 13.6 3.1 5.6 8.2 63 93.5 k 5 234 20.0 4 .6 7.9 11 .5 47 91 .0 Temperature - 546°C 0 202 100 100 1 211 Qlo. 1.3 2 .7 71 87.7 2 222 12 .3 2 .7 5 .3 8.3 55 84.1 3 234 16.1 3.7 6 .9 10.6 47 84.2 k 242 18.4 4 . 4 7.4 12.1 39 81.6 5 250 22 .4 4 . 8 8.7 13.6 33 82.5 Temperature - 554.5°C 0 202 • 100 100 . 1 215 8 .4 1.7 3.8 6 .9 68 89.6 2 230 14.I 3.3 6 .5 10 .8 55 90.0 3 241 18.7 4 . 0 8.2 13 .5 40 84.6 4 251 22.6 4 .7 9.0 15.0 35 86.1 5 259 24.9 5 .3 10 .3 15.8 29 85.1 -US- TABLE VI An a l y t i c a l Results f o r Polymers Temp. °C Time min. B, 1 4 8 C. H 2 4 6 P„ 2 5 8 P- C^H 3 5 6 h 6 10 H C H 2 6 8 H C H 3 6 8 Bz C,H 6 6 TI C H 7 8 Temp. °C Timer - min. 1 4 8 P2 ° 5 H 8 3 5 6 H C H 1 6 10 H C, H 2 6 8 H" C H 3 6 8 Bz C,R\ o 6 T l C H 7 8 500 512 2 3 5 1 2 3 5 0.08 0.15 0.17 0.06 0.13 0.26 0.43 0.08 0.15 0.20 0.05 0.15 0.32 0 . 55 0.17 0.28 O.44 0 . I 4 O.24 O.4I 0.65 0.09 0.15 0.15 0.32 0.08 0.17 0.22 0.15 0.28 0.25 0.17 0.28 O.44 0.32 O.48 0.74 0.2ii, O.42 0 .70 0.21 O.42 0.70 0.92 0.09 0.22 0.35 - 0.07 0.19 0.34 0.63 0.07 0.08 0.17 O.O4 0.12 0.18 0.34 529 9& 1 2 3 5 1 2 0.14 0.30 0.48 0.45 0 .33 0.1+2 0.17 O.4O 0.50 0 .65 0.48 0.62 0 .32 0.50 0.70 0.93 0.50 0.78 0.12 0.31 0.48 0.88 0.31 0.58 0.22 0.15 0.21 0.17 0.36 0.75 0.92 0 .55 0.66 O.48 0.70 O.84 0.85 0.66 0.82 0.20 O.4O 0.63 1.08 0.36 0.75 0.20 0.1+1 O.87 0.20 0.50 - 4 6 - Table VI (Cont'd.)  A n a l y t i c a l Results for Polymers Volume jo Temp. °C 544  Time min. 3 5 1 2 3 5 B 1 C H 4 8 0.60 0 .68 o.54 0 .52 0.50 0.30 B 2 C "H 4 6 C H 5 8 0.82 1.30 0.90 1.10 1.05 0.70 P 2 0.91 1.31 0.88 1.05 0.86 0.76 P" 3 C H 5 6 0.98 1.60 0 .85 1.24 1.22 1.24 H l ^ O 0.20 0.18 0.19 0.19 H 2 ° 6 H 8 0.87 1.17 0.80 1.04 0.88 0.97 H 3 ° 6 H 8 0.84 0 .55 0.77 0.60 0.35 . 0.30 Bz C 6 H 6 1.36 2.67 1.10 2.45 2.90 3.70 T l C 7 H 8 0 .95 1.98 0.80 1.62 1.95 2.35 -47- at S.T.P. (325 cc. at $ cm. Hg pressure). The amount of sample was measured volumetrieally. Then, the sample was condensed with l i q u i d nitrogen and analysed as described previously. The r e s u l t s obtained are presented i n Table VI. TOTAL ANALYSIS AND MATERIAL BALANCES Since quantitative determinations of p r a c t i c a l l y a l l components i n the reaction mixtures were made, the ov e r a l l accuracy of the determinations can be examined on the basis of the summation of the volume percentages of the components and, i n more d e t a i l by the computation of material balances. The r e s u l t s for the summation of volume percent for several reaction mixtures are given i n Table VII. The values f o r the l i g h t hydrocarbons and butene were taken d i r e c t l y from Table V. The data given for the polymers were based on Table VI. The data for the polymers were interpolated for a l l cases i n which the reaction temperatures of the reaction mixtures used for the determinations i n Table Vi did not coincide with the temperatures used i n the determinations of the l i g h t hydrocarbons. The r e s u l t s indicate a sat i s f a c t o r y o v e r a l l accuracy, the sum t o t a l of the volume per cent being within±3$ of 100 percent i n a l l cases but one. The computed material balances are given i n Table VIII. The sources of basic data were the same as for Table VII. The values given for carbon represent the percentages of carbon contained i n the respective products, with the t o t a l -k8- Table VII Total Composition of Reaction Mixtures " In Volume % Temp, of Time Volume %  reaction min. Hydrogen Light 1-Butene Polymers Total °C Hydro- Vol. carbons 509 2 0 .25 5.20 96.li, 1.6 103 . 45 5 0.51+ 13.06 82.1 4-03 99.73 522.2 2 0 .44 8.34 86.5 2.73 98.01 5 1.33 14 .01 68.6 6.36 90.30 540.6 2 1 . 2 0 21.70 72 .6 4 .88 100.3 5 2.50 44.00 47.0 9.52 103.0 554.5 2 2.00 35.00 55.0 7.70 99.7 5 4 .23 56.33 28.8 11.06 100.4 - 4 9 - TABLE VIII Mas3 Balances Reaction temg. Reaction time min. CARBON i n l i g h t hydrocarbons i n polymers t o t a l i n reaction products from reacted Butene CARBON % accounted f o r HYDROGEN i n H2 i n l i g h t hydrocarbons i n polymers t o t a l i n react i o n products from reacted Butene HYDROGEN % accounted f o r E'/C RATIO IN PRODUCTS 509 £22.2 i n % of Carbon aa I n i t i a l Butene 2.34 6.33 3.72 10.00 2.27 $.75 4-56 9.18 4.61 12.08 8.28 19.18 2.85 15.35 8.75 25.7 79 95 75 i n % of Hydrogen i n I n i t i a l Butene  0.006 0.014 0.116 0.36 3.08 8.09 5.94 15.51 1.51 3.83 4-60 11.93 2.7 6.28 8.76 22.15 2.85 15.35 8.75 25.7 78 2.0 2.0 100 86 2.1 2 .3 -50- Reaction temp, °C Reaction time min. TABLE VIII (cont'd.) Mass Balances 51+0.6 CARBON i n l i g h t hydrocarbons i n polymers t o t a l i n reaction products from reacted Butene CARBON % accounted f o r HYDROGEN i n H 2 i n l i g h t hydrocarbons In polymers t o t a l i n reaction products from reacted Butene HYDROGEN jo accounted f o r H/C RATIO IN Products 2 5 2 5 i n jo of Carbon i n I n i t i a l Butene 10.65 20.2 18.9 27.8 7.10 15.1+7 12.23 19.8 17.75 35.67 31.13 1+7.6 22.2 1+5.3 36.6 63.5 8o 79 85 75 i n % of Hydrogen i n I n i t i a l Butene 0.32 0.72 0.57 1.26 13.75 1+.77 30.1+ 9.86 23.8 1+2.1+ 7.89 12.31+ 18.81+ 1+0.98 22.2 1+5.3 85 2.1 90 2.3 32.26 36.6 88 2.0 54.90 63.5 86 2.3 carbon i n the i n i t i a l l y introduced 1-butene taken as 100. The values f o r hydrogen were determined i n the same way. The material balance given as "darbon % accounted' for." ex presses the r a t i o : carbon found i n the reaction products carbon i n reacted butene. x The "hydrogen % accounted f o r " was similary derived. I t can be seen that, on the average, only about 80% of the reacted carbon and 88% of the reacted hydrogen i s accounted f o r by the products. The hydrogen to carbon r a t i o found i n the products i s close to the th e o r e t i c a l value, 2. Deviations from the t h e o r e t i c a l value are more pronounced for reaction mixtures with longer reaction times. A l l de viations show values larger than 2.0, r e f l e c t i n g the higher percentage of hydrogen accounted f o r . The probable reason for the discrepancy between carbon and hydrogen accounted for and reacted carbon and hydrogen w i l l be discussed In - the next section, since i t has a bearing on the a n a l y t i c a l r e s u l t s and t h e i r s p e c i f i c use for k i n e t i c purposes. CONVERSION OF THE ANALYTICALLY DETERMINED CONCENTRATIONS  OF THE REACTION MIXTURES TO CONCENTRATIONS IN THE REACTION  VESSEL The conversion of the a n a l y t i c a l l y determined con centrations to the actual concentrations i n the reaction vessel involves the assumption of i d e a l gas behaviour of the reaction mixtures between the temperature and pressure con ditions i n the reaction vessel and the conditions under which a sample of the reaction mixture i s measured and admitted f o r analysis. The volume percent data obtained from the analysis are based e s s e n t i a l l y on a determination of the p a r t i a l pressure p^ of the component i i n a gas sample of the reaction mixture with known t o t a l pressure p : tot P, Vol.% i - 1 x .100 P t o t Under assumed ideal gas, or nearly i d e a l gas, behaviour of the reaction mixture: p t o t p t o t f o r conditions f o r conditions i n reaction before analysis vessel and thus, the a n a l y t i c a l l y determined volume percent also should express the concentration conditions i n the reaction vessel. Under the above assumption, i t i s also possible to express the concentration of component i i n the reaction vessel i n mole percent of the o r i g i n a l l y admitted butene: Mole % i s p + AP ° . Vol. i i P o where p i n i t i a l pressure of the ° butene admitted i n the re action vessel AP measured pressure increase i n the reaction vessel at time of withdrawal of the reaction mixture. The percentage of reacted butene can be obtained i n an analogous way: % Butene r e a c t e d g ^ p c - V o l . % Butene x (n.+Ap)/100^xl00 p o -53- These methods of computation were used for the results presented i n Table VIII, giving the material balances. In the table, a c e r t a i n consistent discrepancy between reacted and accounted material was pointed out. This discrepancy could be due to inaccuracies i n the a n a l y t i c a l determinations. Another factor responsible could be the formation i n the re action vessel, of polymer compounds with very low vapour pressures. The&e polymers would condense on the cold walls of the apparatus after expansion of the reaction mixture from the reaction vessel into the sampling pipette. The deposition of yellow t a r r y compounds on the walls of the tubing leading from the reaction vessel to the sampling pip ette could be observed after the apparatus had been i n use f o r several runs. I f the discrepancy i n the material b a l  ances Is explained by the presence of i n v o l a t i l e polymeric compounds, the assumption of i d e a l gas behaviour of the re action mixture i s u n j u s t i f i e d , and therefore, a l l conver sions from concentrations i n the a n a l y t i c a l sample to con centrations i n the reaction vessel w i l l be s l i g h t l y i n error. We believe that the error i s not too serious. For k i n e t i c purposes, only results from reactions i n which the decomp o s i t i o n of the 1-butene had proceeded to but a few percent have r e a l s i g n i f i c a n c e . The error due to polymer formation i n these cases w i l l be very small. The d i f f i c u l t y i n converting concentrations i n a n a l y t i c a l gas samples to concentrations i n the reaction vessel, i n cases where condensation of part of the reaction products -54- might be expected, i s often obviated by the addition of known amounts of a reference gas. The reference gas must be inert to the reaction (generally one of the permanent gases i s used), and i t s a n a l y t i c a l detection should be possible with good quantitative accuracy. The quantitative determination of a permanent gas such as neon was not poss i b l e with the gas chromatographic arrangements used i n this i n v e s t i g a t i o n . A separate mass spectrometric determination of the reference gas i n the reaction mixture was possible, of course. This procedure was used i n only a few pre liminary experiments and, unfortunately, l a t e r discontinued i n the b e l i e f that a l l compounds formed i n the pyrolysis were detectable by the a n a l y t i c a l methods previously des cribed. KINETIC RESULTS FOR THE PYROLYSIS OF 1-BUTENE The methods of the q u a l i t a t i v e and quantitative analysis were described i n the previous sections, and some of the r e s u l t s obtained were given also. In the following sections, the r e s u l t s from the k i n e t i c i n v e s t i g a t i o n of the p y r o l y s i s of 1-butene w i l l be given i n t h e i r proper sequence. KINETIC ORDER OF THE 1-BUTENE DECOMPOSITION The order of the reaction was studied by admitting varying i n i t i a l amounts of 1-butene into the reaction vessel, at a given temperature, and analysing the reaction mixtures -55- Table IX Composition of Reaction Mixtures with Change In I n i t i a l Pressure of 1-Butene Temperature of reaction 522°C Time of reaction 1 minute I n i t i a l pressure mm. Hg 96 ; 200 415 AP/P O.OIO4 O.OIO4 0.011 Volume % Methane 2.20 2.U.0 2.50 n Ethane 0.38 0.1+2 0.45 it Ethylene 0.73 0.80 0.85 ti Propylene 1.32 1.1+0 1.45 ii 1-Butene 94.00 94-50 95.00 Temperature of reaction 556.5°C Time of reaction 1 minute I n i t i a l Pressure mm. Hg 94 I40 195 292 324 AP/P 0.12 0.1 0.1 0.1 0.11 0.11 Volume % Methane 10.0 10.5 10.0 11.0 12.0 12.0 II Ethane 2.0 2.0 2 .0 3.0 3.o 3.0 it Ethylene 4 .5 5.0 4 . S 5.0 6.0 5.0 it Propylene 8.5 8.5 7.5 8.5 8.5 8.5 » 1-Butene 65.0 60.0 65 .0 60.0 60.0 60.0 -56- o b t a i n e d a f t e r one minute r e a c t i o n t i m e . The c o m p o s i t i o n o of r e a c t i o n m i x t u r e s o b t a i n e d a t the temper a t u r e s 522 and 556.5°C f o r v a r i o u s i n i t i a l c o n c e n t r a t i o n s o f 1-butene are g i v e n i n T a b l e I X . The p r e s s u r e i n c r e a s e f o r one minute r e  a c t i o n time i s p r o p o r t i o n a l t o the i n i t i a l p r e s s u r e o f the 1-butene f o r b o t h t e m p e r a t u r e s s t u d i e d . The c o n c e n t r a t i o n o f each compound a n a l y s e d i s f o u n d t o be n e a r l y independent of t he i n i t i a l p r e s s u r e o f the 1-butene. The s l i g h t v a r  i a t i o n s are q u i t e a t random, and must be t a k e n t o r e p r e s e n t a n a l y t i c a l i n a c c u r a c i e s or s l i g h t d i f f e r e n c e s i n the r e  a c t i o n t e m p e r a t u r e . The d e c o m p o s i t i o n o f the 1-butene and the f o r m a t i o n o f the l i g h t h y d r o c a r b o n s show, t h e r e f o r e , a f i r s t o r d e r dependence on the i n i t i a l c o n c e n t r a t i o n o f the 1-butene. The dependence o f the k i n e t i c o r d e r w i t h the time o f r e a c t i o n i s complex, as w i l l be seen i n the subsequent s e c t i o n s . PRESSURE IN CREASE IN REACTION SYSTEM AND ACTIVATION ENERGY  FROM PRESSURE CHANGE The p r e s s u r e change i n the r e a c t i o n system w i t h time f o r s e v e r a l t e m p e r a t u r e s i s g i v e n i n F i g . 8. The p r e s s u r e v s . time f u n c t i o n s show a c h a r a c t e r i s t i c change w i t h temp e r a t u r e . A t low t e m p e r a t u r e s , the f u n c t i o n s have a convex c u r v a t u r e t o the time b a s e . A t h i g h e r t e m p e r a t u r e s , t h e con vex c u r v a t u r e changes t o s t r a i g h t l i n e s and t h e n , a t s t i l l h i g h e r t e m p e r a t u r e s , the c u r v e s assume the r e g u l a r , " f i r s t o r d e r " form. As w i l l be seen l a t e r , t h i s b e h a v i o u r i s p a r  a l l e l e d by the c o n c e n t r a t i o n v s . time c u r v e s of the l i g h t -57-Table X Ac t i v a t i o n Energy From Pressure Increase I n i t i a l Pressure of 1-butene 200 mm. Hg. r Pressure increase a f t e r 1 minute. AP P x 1 0 3 - l o g . AP P T° K 1 ; T 6 .2 2.208 778.1 1.2851 7.18 2.11+1+ 781.1+ 1.2797 8.8 2.056 785.7 1 . 2 7 3 Ik. 1 . 855 792.1 1.2625 17.2 1.766 791+.8 1.2582 18.85 1.725 798.2 1.2528 22.6 1.61+7 802.1+ 1.21+62 3 1 . 1.5095 807. 1.2391 1+1. 1.388 812.3 1.2311 1.292 818.8 1.222 6 1 . 1.216 819.8 1.2198 75 . 1.126 821+.1+ 1.2130 91.1+ 1.06 828.15 1 . 2 0 7 125.5 0.902 835.7 1.197 - 5 9 - 4 J ; +I++ TIT" 4+4+--tj-r 4i: - L : - I . : . 4 4 I T 1 og P/ 111! ±i±\ ! • I • 04 • • • - ::::!:::: .... 1.... 1, ... — :. . 1 ::::]:::: .... 4444 :: 1: : 4 : 444 4 4\ : : : : I : : : : .... 44|::4 ::: • i: • • • ......... 4-441:4; 444 4444 .... 44 -\ 44-4 444- :::: 4 4i44 4 4 4 44 :4 ::::|:.:i: . . . . 1 . . . .  ::::JT::: ::::|:::; ::::):::: 4444 4:44- ::::!::: ::::j::\ .... i — 44J44 \ \ °\ 444 ... :::: 4::|44 ,...|.... ::::):::: ' 4 :::: .... 1.... ....1... 44|44 4 4 44-14 - :::: |::: : - 4~ rrrrr ::::':::: 4444: 4444444 Q : 4::!:::: ; ; ; ; ! ; ; ; ; :4:;|i;:i 4 4 4 4 .4 4 i 4 4 ::::(:::: .... 4 4 4 44-4 - 4 4 I : 4 : :::: |^ 4 • 44|44 ::::!:::: 44:4- i :::: i:::: 44441:444 44i44 :::: 1-5. ......... 4 4 | 4 4 44144 - ....].... TiTTHlT: ::::!:::: .... 444 4 4 | : 4 : 4414::: ::::!:::: .... 1.... 44444444 4444 4 ™;+:::-: i IT. - ::::i:::: ::;:j:::: M :::: i:::: — 1 — :: j:::: :::: ::::!:::: 4.4.|.4:.i 4::j:4: 44J44 "Tni44T4 1 . . . . ::::•:::: 44i:4: ov. ::::):::: :::: j:.:: :.:.: 4444. 4444144 44444 4444 44 ::::::::: - :::: • 4 4 4 4 .... 441:7 ;.' . '.. : 4 4 4 4 ...... . 44 . . . . 1 . . . ::::[.:.::.: ::::!:::: :::: I:::: ::::i:::: ::::!::•: ::::!::.: 4.414 4 \ . ; \ ........ : 4 4 4 4 4444444 4444J44 : : 44: . :: :. •: :•::::: 4 4 4 4 : . 4-4 4-4:4 --444; -..444- :• •: • 744-4444 — .... \ °\ \ \ c • :.4: 4 : 4 4 4 .... . • ..:. • . :::'!.::: ... 4 4 4 • . : : 4 4 . 4 4 -8.0. .: • I 4.444.144 ,,4_.J:,.. • : ; I ... | . ... ! . 4 4 4j '•" • I 4 4 4 4 : ; : : • - : t ~ - T - - : - ::•'!-•:•: : : 4 4 4 4 : 4 44 :.i.:.4.:_.4..::.:44.: 4 4 4 - ! 4 : - - ::...!.:: ' 1: : . ! . . : —r—j—:-—: ~r 4444:|444:4 "•:::•::: 1 •: • 1 • • . ... i \ .... ......... : 4. 4 44447 :••.'!.:::.:.. • • • 1 • : • • • : : • . : 4_4i.i4.i4ji4.44 4 .. r . ::•.:. \ - - : N - : : : : 1 : . • ... i •::::. :-. : :: : • :::' . i... : . : : 4 : . . ..::!:• : •:• '•: • 1 .2 0 1 • 1: .22 :::.:::•• • 1 .2 • • • 4 1 :::. 4 :.: 44I44 .26 4-4- - — i T •1 .28 .. ....... .. r i • • 1/1 XlC 44r - 444 T T 444 444! 4 4 4 : 4 ! . , . , 44j 4444 . . . . . ...... ;4;:4:i: ::::!:::: ] 5." 1 A- atio 11 En ergy fro m :::: In I ......... I t i a 1 Ra .:4444 44144 4^4j4:4;44 444:4 4f44-444 :::: - 6 >4: Pr :..: re I I . . . . re as > 44 w 7 ::::!:::: kcal /mol e: ::::j:::: :...]:... 4.44.:4 :::: i:::: 4 4 4 444 4-444 4.44 4444-- 4 4 iiiiljiii iii; 4 4 ::::!:::: - iipiii i-i • • i l.li ijiip: 4444.] ;444 4444444 -60- hydrocarbons. The pressure increase in the reaction system was de termined for a number of constant temperatures in the temp- o erature range- between £00 a n& £6£ c. The rates of in i t ia l pressure increase are given in Table X. h^e values in Table X were used in an Arrhenius plot for the determination of the activation energy from the in i t i a l rate of pressure increase (Pig. 9). The value obtained for this activation energy is 67 kcal/mole, which compares well with the value of 66.1}. 22 * ' kcal obtained by Molera and Stubbs. RATE AND OVERALL ACTIVATION ENERGY OF BUTENE DECOMPOSITION The concentrations of the light hydrocarbons and the 1-butene as a function of time are given in Table XI. The values are in mole % of the originally admitted 1-butene and represent data from Table V, recalculated under the assump tions described in the section entitled: Conversion of the Analytically Determined Concentrations of the Reaction Mix tures to Concentrations in the Reaction Vessel. The percent age of butene decomposed as a function of time is shown in Fig . 10. The butene decomposition shows a dependence that could have been anticipated from the pressure increase curves. At low temperatures the decomposition is slow and shows an induction period, after which the decomposition increases relatively rapidly. At intermediate temperatures the de composition is nearly proportional to the time of reaction and for the higher temperatures the curves show a concave -61- Table XI Analyses of Reaction Mixtures -- Light Hydrocarbons Components are given i n mole % of the i n i t i a l l y admitted 1-butene. o Temperature 493 C Time min. Me thane Ethane Ethylene Propylene 1-Butene 1 0.2 0.1 0.15 97.5 2 0.62 0.13 0.31 0.44 98.0 3 1.26 0.27 0.5 0.75 96.5 4 1.74 0.1+ 0.78 1.15 95.0 5 2.12 0.57 1.12 1.69 94.5 smperature 509°C Time min. Methane Ethane Ethylene Propylene 1-Butene 1 1.45 0.21 0.36 0.6 99.0 2 2.52 0.ij,7 0.93 1.35 97.5 3 3.46 0.73 l.it-6 2.2k 97.0 4 5.08 1.09 2.1 2.98 90*0 5 5.45 1.39 2.71 3.88 84.6 Temperature 522.2°C Time min. Methane Ethane Ethylene Propylene 1-Butene 1... 2.26 0.38 0.73 1.33 94.0 2 4.27 0.88 1.74 2.81+ 90.0 3 6.48 1.45 2.58 1+.20 85.0 4 9.00 1.80 3.65 6.03 80.5 5 11.8 2.1+7 4.17 7.30 73.5 - 6 2 - Temperature 54-0.6 C Time Methane min. Table XI (Cont'd.) Ethane Ethylene Propylene 1-Butene 1 5 4 1.12 2.29 3.1+6 81+.6 2 10.4 2.03 1+.28 6.53 77.7 3 i 5 . i 3J+4 6.22 9.1 70.0 5 23 .2 5 .35 9.2 1 3 4 55.0 Temperature 51+6°C Time Methane min. Ethane Ethylene Propylene 1-Butene 1 8.3 1.33 2.81 1+.7 71+.5 2 13.6 2.91+ 5 . 8 9.1 60.1+ 3 18 .7 1+.32 8.0 12.3 5 1 + . 5 1+ 22.1 5.23 8.92 1I+.5 1+7.2 5 27.8 6.00 10.8 16.9 1+1.0 Temperature 551+.5°C Methane Time min. Ethane Ethylene Propylene 1-Butene 1 8.93 1.83 l+.l 7 4 5 72.6 2 16.1 3.78 7 4 1 2 . 3 63.1 3 22.1+ 1+.85 9.9 16.2 1+8.1 k 28.1 5.88 11.2 18.7 1+3.0 5 32.0 6 .85 13.25 20.3 37.0 1 -614,- curvature to the time base. F i r s t order rate constants were calculated using the expression: k _. 1 l o g / 100 \ ' t A c / t where t reaction time (sec.) G concentration of butene after t time t (mole %) The r e s u l t s are summarized i n Table XII. Table XII Butene Decomposition, Var i a t i o n of F i r s t Order Rate Constants with Reaction Time k x 10 (sec. ) Time (min.) Temp. (°K) 766° 782° _o 795 811+° 819° 827° 1 1.7 4 -2 10 .3 28 49 54 2 1.7 2 .3 8.8 21 37 41 3 1.8 3 .2 9.1 20 34 43 4 2.1 4 -4 9.0 20 31 35 5 1.9 5-4 10 .3 20 28 33 k (averaged) r.Qk 3.9 9.5 21.8 35.8 1+1.2 The rate constants show some lack of constancy for almost a l l experimental temperatures. This should be l a r g e l y due to the f a c t that the decomposition does not follow a simple f i r s t order behaviour, as was a l r e a d y e v i d e n t from the shape of the decomposition versus time c u r v e s . An a d d i t i o n a l s c a t t e r i n the values of the r a t e constants c o u l d be ex pected from e r r o r s i n the q u a n t i t a t i v e d e t e r m i n a t i o n s . I n a p r e v i o u s s e c t i o n ( B a s i s of the Q u a n t i t a t i v e D e t e r m i n a t i o n s ) , the accuracy of the butene a n a l y s i s was estimated to be with i n 2$ of the measurement. Since the "per cent butene decomp osed" was ob t a i n e d by s u b t r a c t i n g the amount of butene found i n the r e a c t i o n products from the i n i t i a l l y admitted butene, the a n a l y t i c a l e r r o r s w i l l have a r e l a t i v e l y l a r g e e f f e c t on the r a t e constants i n a l l cases where the per cent of de composition was low. An Arr h e n i u s p l o t of the averaged r a t e constants i s shown i n P i g . 11. The a c t i v a t i o n energy o b t a i n e d i s 66 kcal/mole. S i m i l a r p l o t s were c o n s t r u c t e d f o r the r a t e con s t a n t s o btained f o r a g i v e n r e a c t i o n time. The a c t i v a t i o n , e n e r g i e s from these p l o t s are g i v e n i n Table X I I I . Table X I I I A c t i v a t i o n E n e r g i e s f o r the Butene  Decomposition E ' s from Rate Constants f o r t minutes t (minutes) E (kcal/mole) 1 72 2 70 3 69 6k 5 60 E from Averaged Rate • • A Constants 66 -67- Table XSLV Rate Constants for the Formation of the Light Hydrocarbons k B C - 1 5 rate constant sec. x lO-' i n i t i a l concentration of 1-butene (molecules/cc. x 10 ) concentration of light hydrocarbons for 60 sec. reaction time (molecules/cc.x 10"1° Methane Ethane Ethylene Propylene B 250 2^6 241 1.25 .3.56 3.57 5.51 241 13.04 240 20.15 237 21.20 240 24.60 8.4 24.1 24.2 38.I 90.2 140.0 149.0 172.0 246 241 241 240 237 240 250 250 246 241 241 240 237 0.52 0.94 2.71 3.19 4.32 5.50 0 0 0 27 50 89 1.94 44 6.74 9.80 1.7 3.3 6.0 13.4 37.6 46.8 68.8 250 0.39 246 1.46 241 3.25 241 8.35 :2k0 11.90 237 17.60 124.0 2.6 9.9 22.4 57.7 82.6 -log k 4.078 3.618 3.618 3.419 3.046 2.855 2.828 2.760 766.0 782.0 787.2 795.2 813.7 819.0 827.5 828.4 4.752 4.482 4.221 3.873 3.425 3.331 3.163 4.582 4.005 3.650 3.238 3.08k 2.908 766.0 766.0 782.0 795.2 813.7 819.0 827.5 766.0 782.0 795.2 813.7 819.0 827.5 1/1 1.3055 1.2787 1.270 1.2575 1.229 1.2210 1.20Q5 1.2075 3.5 4.454 782.0 1.2787 6.5 4.186 795.2 1.2575 18.8 3.728 813.7 1.229 22.2 3.656 819.0 1.2210 30.4 3.518 827.5 1.2085 38.8 3.412 828.4 1.2075 1.3055 1.3055 1.2787 1.2575 1.229 1.221 1.2085 1.3055 1.2787 1.2575 1.229 1.2210 1.2085 ) - 6 8 - I t should be mentioned that i n a l l cases given i n Tabi>e XIII, the estimated error i s r e l a t i v e l y large (of the order of 5 kcal) since the experimental points generally did not determine the slope of the straight l i n e unambiguously. RATES OF FORMATION AND OVERALL ACTIVATION ENERGIES  FOR THE LIGHT HYDROCARBONS The changes In concentration for the l i g h t hydrocarbons (methane, ethane, ethylene and propylene) with time are graphically represented i n F i g . 1 2 , on the basis of the values given i n Table XX. The concentration curves of the l i g h t hydrocarbons follow the same r e g u l a r i t i e s with increase i n temperature as were pointed out for the pressure increase and f o r the butene decomposition. The rate constants f o r the i n i t i a l formation of the l i g h t hydrocarbons were calculated assuming f i r s t order de pendence on the butene concentration. The re s u l t s are given In Table XIV. The Arrhenius plots f o r the rate constants of the l i g h t hydrocarbons are shown i n F i g . 1 3 . The a c t i v a t i o n energies and pre-exponential factors obtained are given i n Table XV. Table XV Act i v a t i o n Energies of Light Hydrocarbons A 1 / s e c . E kcal/mole 6 0 . 5 6 3 . 6 7 1 . 6 7 0 . 8 . - 6 9 -- 7 0 - FIg.:[2b" TT? o Methane •"Propylene cc Ethylene:; 9 Ethane rap D e p e n d e n c e :j^':,~~J7 ight — Hjpdiro|c air 1&S$B o]T Concentratldna 1 2 3 minutes 7 .1 . : : r -72- TIME AND TEMPERATURE DEPENDENCE IN THE FORMATION OF  POLYMER PRODUCTS The concentrations of the major polymer products as a function of time are given i n Figures lij. and 1 ^ . The data for the plots were taken from Table VI: An a l y t i c a l Results for Polymers. The time dependence of the cyelohexadiehe, benzene and toluene concentrations i s given i n F i g . lij.. A d e f i n i t e r e l a t i o n between the concentration curves of the cyclohex- adiene and benzene can be observed. The rate of formation of the benzene appears d i r e c t l y proportional to the concentrat ion of the cyclohexadiene. The concentration curves of these two compounds follow, q u a l i t a t i v e l y at lea s t , the r e l a t i o n  ships of a consecutive reaction that could be expressed by the following equations: 1 - Butene — • Products 1-Butene + X — Cyclohexadiene + Y Cyclohexadiene — * Benzene + H According to the above reaction sequence the rate of format ion of the cyclohexadiene should decrease gradually with time, due to the decrease i n the butene concentration, u n t i l a point i s reached where the rate of formation of cyclohex adiene Is equal to the rate of formation of benzene. This corresponds to the maximum of the cyclohexadiene concentrat ion. Beyond this point the concentration of the .cyclohexadiene should decrease, with a corresponding decrease i n the rate -73--7k- of formation of the benzene. The experimental curves at the highest temperature ($63°C) show exactly t h i s behaviour. The experimental curves obtained f o r the lower temperatures corr espond q u a l i t a t i v e l y to the e a r l i e r stages of the process described. I t i s , therefore, reasonable to assume that the benzene i s a d i r e c t product of some dehydrogenation reaction of the cyclohexadiene. The data available i n Table VI are not s u f f i c i e n t to provide information as to whether or not the cyclohexene and cyclohexadiene form an analogous p a i r . The concentration of the cyclohexene i s found to be much smaller than that of the cyclohexadiene, even for the shortest re action time analysed. Thus, either the dehydrogenation of the cyclohexene to cyclohexadiene i s a much fas t e r reaction than the dehydrogenation of cyclohexadiene to benzene ( i n the butene system), or the cyclohexadiene i s formed by a d i f f e r  ent mechanism not Involving cyclohexene as an intermediate. The second alternative appears more probable. The toluene concentration shows very much the same time dependence as does the benzene. The concentrations of the cyclopentene and cyclopent- adiene as a function of time are given i n P i g . 1!?. The s i t  uation seems somewhat si m i l a r to that of the cyclohexadiene and benzene, with the difference that at the highest temper ature, the cyclopentadiene curve f l a t t e n s out: i . e . , the compound participates i n further reactions. -75 --16- THERMAL DECOMPOSITION OP 1-BUTENE SENSITIZED WITH MERCURY DIMETHYL Addition of a small amount (5$) of mercury dimethyl to the reactant 1-butene produced a substantial increase i n the rate of the decomposition. The conditions of the ex periment and the results are given i n Table XVI, together with the r e s u l t s from a blank run containing only butene, pyrolysed and analysed under exactly the same conditions. Concentration versus time plots for both experiments are given i n Pi g . 16. The increase i n rate of formation of the polymers was not studied. It can be seen that the addition of mercury dimethyl produces a substantial increase i n the i n i t i a l r a t e . The increase i n i n i t i a l rate of formation for the l i g h t hydrocarbons can be calculated from the re sults i n Table XVI. A c a l c u l a t i o n based on the concentration aft e r one minute reaction time i s given i n Table XVII. Table XVlI Increased Rate of Formation of Light Hydrocarbons i n Sensitized Reaction I t i s i n t e r e s t i n g that i n the sen s i t i z e d reaction, not only methane, but also ethane, propylene and ethylene show greatly Compound Increased Rate Methane Ethane Ethylene Propylene 5.75/0.k33 0. 95/0.083 1. k /0.196 2.2 /0.228 13.3 11 .b, 7.1 9.7 -73 - Table XVI Thermal Decomposition of 1-Butene Sensitized with Mercury-dimethyl Composition of mixture before reaction: 1-Butene 95$ Mercury dimethyl 5$ ("by volume) I n i t i a l pressure i n reaction vessel 209Q8 mm. Hg Reaction temperature 1+92 C Composition of Reaction Mixtures Amount of each reaction product i s given i n mole $ of i n i t i a l 1-Butene. Reaction time min. 1 _ 2 3 .5 •- 10 Pressure mm. Hg 211+.8 216.9 217.9 2 l8 .5 220.9 Methane Ethane Ethylene Propylene Butene Blank run with 1-Butene only, f o r comparison Same temperature and i n i t i a l pressure (199 .5 mm. Hg) / Reaction time rain. 1 2 Z3 5 - : 10 Pressure mm. Hg 199 . 5 199 . 5 199 . 5 201 . 5 20I+.5 Methane 0.1+33 1.7 l+.O Ethane 0.083 - 0 . 5 1 . 1+5 Ethylene 0.196 1.0 2.35 Propylene 0.228 1 .1+ 3.2 Butene 9 5 . 5 95.3 84.2 5.75 6.1+5 6.45 7.35 9.1 .95 1.2 1.5 1.6 2.3 1 .1+ 1.7 1.8 2.15 2.75 2.2 2.75 3.2 3.75 5.15 89. 88.2 85.5 78.6 -79- increased rates of formation. • • • • The discussion of the re s u l t s from the 1-butene decomp o s i t i o n w i l l be postponed u n t i l the results from the p y r o l  y s i s of the 1-buterie-k -d have been described. 3 THERMAL DECOMPOSITION OP 1-BUTENE-k-do The deuterated butene, CH2= CH-CH^CD^, used i n t h i s i n v e s t i g a t i o n was kindly prepared by Dr. L. C. L e i t c h of the National Research Laboratories, Ottawa. The method of prep aration and the proof of structure are given i n the exper imental part of Appendix I I : Deuterium Migration During the Ionization of 1-Butene-k-d^ by Electron Impact. The pre pared compound was found to contain 90% CH^ CH-CH^-CD^ and 10% CK = CH-CH^CD^H. The deuterated butene was pyrolysed i n the same reaction system used for the 1-butene. COMPARISON OP THE PYROLYSES OF 1-BUTENE AND 1-BUTENE-k-d^ The thermal behaviour of the 1-butene-k-d was very 3 s i m i l a r i n a l l respects to that of 1-butene. A l l products formed i n the 1-butene decomposition also were found i n the reaction products of the deuterated butene. The pressure increase with time was i d e n t i c a l for both compounds. The quantitative analysis of the reaction products formed i n the pyrolys i s of both compounds showed no detectable differences - 8 0 - i n the rates of formation of the d i f f e r e n t compounds. The concentrations of the l i g h t hydrocarbons i n the two re action mixtures obtained and analysed under i d e n t i c a l con di t i o n s are given i n Table XVIII. Table XVXII Light Hydrocarbons from the Pyrolyses of 1-Butene  and 1-Butene-U-d for 5 Minutes at 552°C CH .CH .CHrCH 3 2 2 Vol.$ CD .CH .CHsrCH 3 2 Vol. % Methane 2I4..O 2I4..O Ethane 5.3 5.2 Ethylene 8.3 9.0 Propylene 13.0 13.6 The value given for methane formed from the deuterated butene includes a l l deutero-isomers of methane formed i n the p y r o l y s i s . The values for the remaining products of the pyrolysis of the deuterated butene are given on the same basis. I t i s seen that the differences i n the compositions of the reaction mixtures are very small. Differences i n the k i n e t i c behavior of the two compounds could be expected. S i g n i f i c a n t differences i n the reaction rates of normal and deuterated compounds are generally ob served i n cases where the reaction involves processes i n which the respective bonds R-H and R-D are formed and/or broken. The ov e r a l l e f f e c t of such processes, i f they occur - 8 l - i n the system under study, must produce changes i n the rates of formation of the products which are smaller than the l i m i t of detection obtainable with the a n a l y t i c a l method used. The pyroly s i s of 1-butene-i+-d^ sens i t i z e d with 5% Hg(CH^)^ by volume, was studied i n one experiment at l4,92°C . > with one minute reaction time. A substantial acceleration of the reaction was observed. The formation of the l i g h t hydrocarbons had Increased by amounts e s s e n t i a l l y equal to those i n the s e n s i t i z e d decomposition of the non-deuterated 1-butene. ANALYTICAL METHODS USED FOR THE IDENTIFICATION OF  THE DEUTERATED REACTION PRODUCTS The reaction products of the pyroly s i s were separated by gas chromatography. The techniques were analogous to those used for the separation of the 1-butene reaction mix tures. Separation of the i n d i v i d u a l deutero-isomers* could not be achieved. Therefore, the deutero-isoraers of a given compound were c o l l e c t e d i n one f r a c t i o n and analysed on the mass spectrometer. The clean separation of these fractions achieved was of great advantage i n the i n t e r p r e t a t i o n of the mass spectrometric r e s u l t s . The mass spectra of the deutero- Isomers of even simple hydrocarbons often are not known. *• According to the meaning given here to the expression, CH, and CD„H are deutero-isomers. -82- T h e r e f o r e , the mass s p e c t r o m e t r i c ana ly s i s - o f a sample c o n t a i n i n g a number o f d e u t e r o - i s o m e r s can p r e s e n t c o n s i d  e r a b l e d i f f i c u l t i e s . The m o l e c u l a r formulae of the d e u t e r o - isomers c o n t a i n e d i n the f r a c t i o n s o f p r o p y l e n e , butene , and o ther s i n g l y - o r m u l t i p l y - u n s a t u r a t e d hydrocarbons c o u l d be de termined wi thout g r e a t d i f f i c u l t y by s c a n n i n g the mass range at low e l e c t r o n e n e r g i e s . The procedures used f o r the r e m a i n i n g compounds, deutero-methanes , deutero -e thanes and d e u t e r o - e t h y l e n e s , v a r i e d from group to group and w i l l be d e s c r i b e d w i t h the r e s u l t s f o r these compounds. REACTION PRODUCTS FROM THE PYROLYSIS OF 1-BUTENE-k-d , , DEUTERO-METHANES The mass s p e c t r a o f the deutero-methanes p u b l i s h e d 6 by D i b e l e r and M o h l e r were used as s tandards f o r the computat ion o f the a n a l y s i s . S i n c e mass s p e c t r a show v a r i a t i o n s from i n s t r u m e n t to i n s t r u m e n t , the s p e c t r a g i v e n by D i b e l e r were c o r r e c t e d b e f o r e b e i n g u s e d . The c o r r e c t i o n s were based on what i s e s s e n t i a l l y a comparison o f the methane (CH^) spectrum o b t a i n e d by D i b e l e r w i t h the methane spectrum o b t a i n e d w i t h the mass spec trometer used i n the p r e s e n t work. The method by which the c o r r e c t i o n s were a p p l i e d w i l l be i l l u s t r a t e d by t r e a t i n g the case o f CH^D. The s p e c t r a n e c e s s a r y f o r the c o r r e c t i o n are g i v e n i n T a b l e X I X . - 8 3 - Table XIX Mass Spectra Used for Correction of the CR^D Spectrum Mass ' i Ion Intensity  CH.D CH, CH CH D (Dibeler) 4 k 3 (Dibeler) (This (Corrected) Laboratory) 1 7 100 100 16 77.2 100 100 7 4 . 4 15 20.9 86.1 83 1 7 . 7 14 8.8 16.3 12 .4 6 .3 13 4 . 9 8.21 5 .4 3.22 12 2 . 4 6 2 .57 1.6 1 . 4 8 In the d i s s o c i a t i o n pattern of CH^D, some of the mass peaks originate from two d i f f e r e n t ions. For example, the mass l k peak i s produced by CH* and CD +. For these cases, the r e l a t i v e abundances of each contributing ion were est imated by the method of Dibeler and Mohler. I t was assumed that the p r o b a b i l i t y of removing one atom, either H or D, i s equal to the p r o b a b i l i t y of removing one H from CH ; 4 the p r o b a b i l i t y of removing two atoms i s equal to that of removing two H atoms from CR^, and so f o r t h . This assump t i o n i s consistent with the f a c t that the sums of the ions i n CH^ and i n the deutero-methanes are nearly equal. Start ing with the low mass end of the CH D spectrum, the con- % 3 t r i b u t l o n of each type of ion i s computed i n the following manner: Mass 13 r e s u l t s from CH + only, and i s equal to k .90 (Table XIX). As CH + and CD+ are both formed by the d i s s  o c i a t i o n of three atoms, the CD* abundance can be calculated as the difference: CH* i n CH^ (8.21) minus CH* i n CH^D -8k- (k .90) equals 3»31« Further, the t o t a l abundance of ions of mass l k i n CH^D i s 8.80. Consequently, the CH* abundance i s given by 8.80 - 3.31= 5>.49. Continuing i n t h i s manner, the abundances of a l l remaining ions were computed. The correction to Dibeler's spectra then was applied by multiplying the abundance of each in d i v i d u a l ion formed by the loss of i atoms, by the r a t i o : Abundance of C H k + _ ^ ( i n Methane spectrum obtained i n this _ laboratory) Abundance of CH, + ( i n Methane spectrum obtained by Dibeler) The c a l c u l a t i o n of the corrected ion abundances i n the lower mass range of the CH^D spectrum i s given belox*: Mass Ions Corrected Ion Abundances 12 V 2.k6 x 1.6 _ I . 48 2 3 7 ' 13 CH* 4.9 x 5.4 - 3.22 o T l r " 14 CH* CD* 3.31 x 5.4 • 5.49 x 12.4-6.35 d H721 16T3" and so on. The complete corrected spectrum of CH^D i s given i n the l a s t column of Table XIX. The spectra of a l l the deutero-methanes were corrected i n an analogous way. The analyses of the mass spectra of the deutero-methanes from the 1-butene-4-cl^ pyrolysis were computed with the use of the corrected spectra. The method of computation consisted i n successive substraction of the ion contributions of the compounds present, s t a r t i n g with the compound with the highest mass (CD^). In an ide a l analysis, - 8 5 - no residual mass peaks would remain after the contributions of a l l compounds have been subtracted. The r e l a t i v e small- ness of the residuals i n a r e a l analysis i s a measure of i t s accuracy. The residuals from the computations of the deutero- methanes were r e l a t i v e l y small. Only the results for the mercury s e n s i t i z e d reaction are somewaht i n doubt, since the sample contained small amounts of water which i n t e r f e r e d with the analysis. The re s u l t s of the analyses are given i n Table XX. The r e s u l t s for the deutero-methanes from the pyrolyses of 1- butene-k-d show only small variations with reaction time and reaction temperature. The main product, CD^H, con s t i t u t e s approximately 63$ of the methanes. The CD^H most c e r t a i n l y originates from the deuterated methyl group of the CH = CH-CH -CD molecule. Since the deuterated butene also 2 2 3 I n i t i a l l y contained 10$ CR=CH-CH2-CD H, about 63 x 10/90=7% C D 2**2 s k ° u - ^ have been formed together with the 63$ CD^H. It i s seen from the a n a l y t i c a l r e s u l t s that the percentage of OI^H^ found i s much higher, close to 20$ on the average. The methane or i g i n a t i n g from the deuterated methyl group of the butene can be estimated to be at le a s t 75$ ot the methane t o t a l by adding an average value of 5$ the CD 3 to the corrected value for CD H: CD H proportional part from 2 2 CH :CH.CH .CD H 2 2 2 5 CD, k iWo Total - 8 6 - Table XX Deutero-Methanes from the Pyrolysis of 1-Butene-kd, Reaction Temp. Time' OC min. Volume % of t o t a l of Methane 507 2 4 CD 4 3.34 4 .6 CD H 3 6 3 . 6 k . CD H 2 2 2k. 7 21.9 CDH 2.1 3 . CH Total 6.95 100% 6.65 52k 2 k k.9 5.6 62 .5 6 3 . 23.4 22.1 3.8 3.1 5.5 5.5 550.7 2 5 6.k 6 .3 6 0 . k 52 .3 22 .9 2k. 6 k . 8 8.7 5.6 8.2 Deutero-Methanes from the Pyrolysis of 1-Butene-kd Reaction Temp. Time Sensitized with Mercury-Dimethyl Volume % of t o t a l of Methane CD 492 min. 1 '4 CD H 3 1.3k 29 .4 1.36 30 . CD H 2 2 l k . 7 l l l - . l CDH Extrapolated Values f o r Non- Sensitized Reaction Temp. Time ~C 492 min. CD 1 4 2 .5 CD H 3 64 CD H 2 2 CDH. 25.2 1.3 CH Total 4 2 . 52 .5 ' 100%* 3.66 5 1 . " * 50 e.v. Low e l . energies. CH k Total 7.0 100% -87- The main product from the mercury-dimethyl s e n s i t i z e d reaction i s CH , approximately 51$ of the methanes. The CH^ should originate predominately from the methyl groups of the s e n s i t i z e r . A determination of the concentrations of the deutero- isomers i n the reaction mixture of the 1-butene-k-d^ decomp o s i t i o n under conditions of temperature and reaction time i d e n t i c a l with those of the s e n s i t i z e d reaction was not made. The concentrations of the products of the non-sensitized reaction obtained for these conditions were sb small that sp e c i a l procedures would have been necessary f o r the c o l l e c  t i o n and subsequent mass spectrometric analysis of the separ ated products. -The lack of d i r e c t comparative data i s unfortunate. However, semi-quantitative estimates are poss i b l e by extrapolation of the concentrations of the deutero- isomers i n the non-sensitized reaction to the lower temp erature of the s e n s i t i z e d reaction. The plotted concentrations of the deutero-methanes as a function of temperature are given i n F i g . 17. Since the v a r i a t i o n of the concentrations with temperature i s quite small, i t i s believed that no appreciable additional error i s introduced by the extra- polation to ls.92 C. The extrapolated values obtained were corrected to t o t a l 100$. The corrected values for the concentrations also are given i n Table XX. The concentrations of the deutero-methanes for the normal and s e n s i t i z e d reactions were used to calculate the - 8 8 - •:::|::: ::::]::: :!; i H-H- ; 11; I l i l ill!: : : : : ! : : : 14 IT iii: 4:44 l . l l l . 4444L 44 4li4:ii r f i — i - ; ; : ; ; ; ; 4il| 1:44 t ") c fill 44 ;; x V o i % 4:44 ; . . ::: x J tl 3 ri Ur ;fSf- 444 - f 0 M f et Toiti *34; 4-1:1 4H 4;4i4 I l l ; » r * '.V • r w. ITiT : t ; ; P i ; ; 4.44- han< 3: -I- \ — . • -V i\ - • ri L4%: H ii' !ii: ipt iiii- 4 4 4 4 4 ft 1 r TV 144! . ! , . . . : . i i i i l i i ; It!;. • r i • % lf::XJ Si Til! 4-  44 4 4- ;:;;j;;; ! ill! Id:! ::::{::.:;• x-xrr-: : : : ! : : : Iii: x444 .11.14 :::::: : :i 70 4t :::: 1::: ::::(::: i I - I ; ; 444 ilil rill -•••!•• •!':.:: it!! 1xl4 ilil !4!i :-; :: 444 : : ! : ; . . . •:!: 4.1.4 Ilil t • : r iii! :;44: n i l t ; : i • > • i i i i j i i i T T t r r —f) - : : ' ' • : : : : - M\ xl-4-4 1114 14: : . , : t IP' i j i i . 444 i-144: -414 1 144! l i l t j.i.14 t-i l i l:;-p • • X •! 4  44: j i jT ! ! 4 . . . . !!!4 14 fi 14; 4i-iii II Irlf •!' SO 444 i: 44: 4 i i i : ; 4.4 44 44 14 !-l :; • 444- 4 .::::: 41 i l  i:l1:l: 41; 4-44 Jiil j j t i l i t ; 4114 10 44;- :x:xixx i i i i l i i 1 i i i ; 4 44 4 444-1- i-H i 444 !;!;. 444 44 * : .:. i " : : ! j i-i • .4 4 4- :: j:::: :: :: 1: :: ::::!;; 4- 44 4444 444 -44 4-  ::::!:::: ::::):::: x x j x x 444- !:!.: 44: ; ; ! ; r— : 4444 I||! • 1 • • • j • ! ' • ' • • • 1 • 444:4 4-i4t444 — 1 ... 444:4 : 4:: -4 ;;;;!;;;: : : : ; :• x x x ! : : : : : : x ! : : : il x 14 4 ;4-44 444 444441 4 l i l i j i l :*::!:::: x x j x x ::::::::: 4 44.:.; 4. 414 ;:;; 1; 44.4 4444- ;:•::(:::: .4 441.4 4 4 ::;;j:;;: !'-" 4444- 4 444:44 :::: |:::: 44 44 4: xx-ift-: •—-TQr : 4 x 4 4 :4444-::;: h:!.: -xx :::: 1::: • :il-i4:.;4 :::: 4-4-4-4 4 4 4 : 4 ::!:;• •:: j:::: 11 4 i — 44-4-44:4 -4.4-444 :::4:i: • • • • I - . . . : : : : ! : : : : , : : : : i : : : : 444 441 444- .;::: 444: -iii; : . . . 4; 14- It 1 4444-44444 444 44J4 444- . I l l l t i l l l :::: 444 Hi! 14I :!i|;l: :! ! ! ;: 444 ; ; ; ; t i l ! i:!:li-t!4-|: i j l j j 4;ii4: ['::.:• : ; ; : ! : : ;:i:;-j- ffi'i- 4.1;.;: •44 j.;:i:j -|::!x i4-i II Iti-i was i i i t 4 i 1 ': ij~j.gr f 444 i f Ii:F] 4 j :ix xrr!: i : : •| n! 46 -1 iTV - i f i i : 44 4 tffi: ftfT 444 Tiff i ' l t i " M •fffi iliii :|tf!- m ixtt -fix 4i4i4 S i x mi" 1 It! iiit 1:1444.4; i l i l ' 44 5 o;o :_;_H . . : 1 5" 0 *0 : ' • 4J4- 5 4rtt &0 ftf iih 4 R :l444 - ft: I - I T ; ii;4 w -r|-}4 1 ;U : 11 -ftp- Sit uxix 0 O 3U 1. ± t t r •i-lxi--i-t-H -T-H-T- SlifctH :::5x : i . ± 4 f t t f t i :H:tj- : t i t 44 4 ft ift :;:j:n: •i+i-j x .x t X::.n. ; j X1 tjxj: .. .Li... ft; J4:!X f t +4 ± t t t # : ftt ilff i i f f i -Tp4: m - P i u n i i i i m * ,] m i e p; # 4 4 ' ;J4|; TI-TX m # t T 4ffl4 1' 11 ; 11 T -R- + W- + 4: XT X Xfx: 1 1 1 ij 1ft i I f i m Eg ?en i f i a +JH-3(tl i 4ffij4 114 ffli ttt lift --f4-# i #t-t TiTf 4ft 444 ftft:t gSlfiix i i m i i i lit $ pti m f :4i p4 xux ti+: xal In S 4 ft4i •4 ± i 4 4 BE k iSi: -it f-X ft _____ -89- r e l a t i v e increase i n the rate of formation of the i n  dividual deutero-methanes f o r the sen s i t i z e d reaction. The t o t a l increase of methane formation was taken to be 1 3 . 3 - f o l d for one minute reaction time on the basis of previous experiments on the sensiitized r eaction of 1-butene (Table XVII). The c a l c u l a t i o n i s given i n Table XXI. Table XXI Increased Rates of Formation of Deutero-Methanes i n Reaction Sensitized with Mercury Dimethyl (13.3 f o l d increase f o r the t o t a l methanes Compound Ratio of Concentration from Sensitized Reaction to Concentration from Normal Reaction for 1 Min. Reaction Time CD k 1.35 x 1 3 . 3 / 2 . 5 = 7.2 CD3H 30 x 1 3 . 3 / 6 1 J , = 6 .2 CD 2H 2 . 1 4 . 4 x 1 3 . 3 / 2 5 . 2 = 7.6 CDH"3 2.8, x 1 3 . 3 / 1.3 = 28.6 CH 51.7 x 1 3 . 3 / 7 = 98.3 4 I t i s seen that the rates of the CD. , CD^H and CD^H have 4 3 2 2 an approximately equal increase, while the increase of the CDH^ has an intermediate value. The CH^ shows a nearly 1 0 0 - f o l d increase. DEUTERO-ETHANES The mass spectra of CH.CD_, CH- CHD0, and CH_CH D 3 3 3 ^ 25 3 2 obtained by Schi s s l e r , Thompson and Turkevich were used as - 9 0 - standards for the computation of the mass spectrometric analyses. The spectra of the remaining isomers of C^H^D^ and C ^ - ^ ^ a r e n o t k n o w n * Therefore, the analyses had to be computed on the assumption that the C^E^>^ compound present was CH^CD^ and the ^^1^2 W a S C H 3 C H D 2 * The spectra of Schissler and associates were corrected before use,, according to the method described i n the analysis of the deutero-methanes. The analyses then were computed by the same method used with the deutero- methanes. The mass spectra and the r e s u l t s of the analyses are given i n Table XXII. The resolution of the spectra was not s a t i s f a c t o r y . The residuals were considerable, i n d i c a t i n g that the standard spectra used did not re present accurately the spectra of the compounds present In the mixture. Therefore, the an a l y t i c a l r esults are quite uncertain. The main product found i n the deutero-ethanes i s C^E^D^, about 70$ of the t o t a l volume of ethanes. The r a t i o : ° 2 H 3 D 3 / 0 2 H A = l k ' 7 I -91- Table XXII Deutero-Ethanes from the Pyrolysis of 1-Butene-k-d A. Mass spectra of the Ethane f r a c t i o n . Sensitized with Mercury- dimethyl Temp. 507 507 52k 52k 550.7 550.7 492.1 °C Time 2 k 2 k 2 5 1 min. Mass 34 1.02 1.06 1.3 1.27 1.54 1.67 0.75 33 10. 10. 10. 10. 10. 10. 10. 32 ^ 11 .k 10.75 10.9 10.k 10.3 10.8 10.5 31 18.k 17 .8 15.9 19 .3 18.9 18.6 17 .5 30 56. 54. 55.6 55.1 54. 53.3 54.9 29 34.3 31. 4 32.6 32. 28.6 30.3 30.5 28 31)-.7 28.3 37. 2k.k 22. 22.8 39.5 27 13. 12.1 12.2 11 .k 11.2 11.7 15. B. Residuals aft e r subtracting contributions by C J . A , C H D and C2H, D 2 so that peak heights of mass 3k, 337 ^ 3 32 = 0.^. 31 2.6 2.5 0 3.7 2.7 1.5 2.6 30 -1.6 -2. -O.k 0.7 O.k -2. -2. 29 0 - 1 . -0.2 -0.9 -2. -2. - 1 . 27 -0.5 -0.6 -0.6 -0.9 -0.9 - 1 . -0.7 26 -o.9 -0.7 -0.7 -0.8 - 1 . - 1 . -0.7 C. Composition of Deutero-Ethanes i n Volume % of t o t a l of Ethane. Volume %  c 2H 2D k IJT7~ T. 6.4 6.3 77B 8~4 J 4 £79* C 2H 3D 3 69. 71.5 70. 72. 70.6 69. 74.5 67.1* c ? H k D 2 26.3 23.5 23.6 21.6 21.8 22.4 22.3 27.0* q. Total-100% Extrapolated Values for Non Sensitized Reaction k92°C -92- for 2 minutes reaction time at £07 C i s approximately equal to, but s l i g h t l y smaller than the r a t i o : CRD /CD = 18.8 y k obtained e a r l i e r . There are further s i m i l a r i t i e s between the methanes and ethanes. The r a t i o of the tetradeuterated to the tri-deuterated compound increases with temperature for both groups. The r a t i o of C0H. D /C H D i s greater 2 k 2 x 2 3 3 than the r a t i o expected on the basis of the detttero-butenes pyrolysed, as was the case^with the methanes. The concentrations of the ethanes for two minutes re action time as a function of temperature are plotted i n Pig. 18. The extrapolated values for the temperature of k92°C obtained from these plots are given i n Table XXII. A com parison of these values with those f o r the concentrations of the s e n s i t i z e d reaction shows great s i m i l a r i t y . This i s of p a r t i c u l a r i n t e r e s t , considering that the t o t a l increase i n the ethanes formed i n the s e n s i t i z e d reaction, over the ethanes formed i n the normal reaction, was l l . k - f o l d , (Table XVII) i . e . : 10.k x 100 /11 .k =91$ of the ethanes i n the s e n s i t i z e d reaction are due to the action of the mercury-dimethyl. On the basis of the approximate values available, the increase i n rate for the i n d i v i d u a l deutero-ethanes i s calculated i n Table XXITI. -93--9k- Table XXIII Increased Rates of Formation of Deutero-Ethanes in Reaction Sensitized  with Mercury Dimethyl ( l l .k-fold increase for the total ethanes) Compound Ratio of Concentration from Sens Itized Reaction to Concentration from Normal Reaction for 1 Min. Reaction Time. C H D 2 2 k 3.1+ x 11.1+/ 5 .9 = 6.6 7k.5 x ll .k/67.1 =12.2 C H D 2 1+2 22.3 x ll.k/27.0 = 9.1+ The increase in rate is seen to be roughly of the same order. It is questionable whether the variations are real or due to the approximate nature of the analytical de termination. DE UTER 0-E T RYLE NE S The mass spectra of the deutero-ethylenes published by Dibeler, Mohler and de Hanptinne were used as standards for the computation of the mass spectrometric analysis. The spectra were corrected before use according to the method described in the analysis of the deutero-methanes. Since the quantitative determination of the deutero-ethy lenes is also possible by measurements of the parent (mol ecular) peaks at low electron energies, results were ob tained by both methods. The satisfactory agreement between the two independent methods Indicates good accuracy of the 7 -95- r e s u l t s obtained. The r e s u l t s from both methods are r e  presented i n Table XXIV. The main product found i n the deutero-ethylenes Is CH =CH .. Two other products formed i n considerable and 2 2 approximately equal amounts are C H D and C H D. The ^ ^ C. Cm J) r a t i o s of C H D /C H, and C H D/C H increase with temper- 2 2 Z 2 4 2 3 2 4 ature, the f i r s t r a t i o Increasing f a s t e r . The concentrat ions of the deutero-ethylenes for two minutes reaction time plo t t e d i n function of temperature are represented S3, a F i g . 19. The extrapolated concentrations for the temp erature 492°C are given i n Table XXIV.Comparison of these res u l t s with the concentrations for the s e n s i t i z e d reaction shows that the values are p r a c t i c a l l y i d e n t i c a l , as was the case with the deutero-ethanes. Since the increase i n the ethylene formation due to s e n s i t i z a t i o n was approx imately 7.1-fold (Table XVII), approximately 6.1 x 100/7.1 = 86$ of the ethylenes i n the s e n s i t i z e d reaction are due to the action of the mercury dimethyl. On the basis of the values available, the increase of rate for the i n d i v i d u a l deutero-ethylenes i s calculated i n Table XXV. The r e s u l t s indicate that the concentrations of a l l deutero-ethylenes have increased i n nearly equal prop ortions. -9b- Table XXIV Deutero-Ethylenes from the Pyrolysis of 1-Butene-k-d^ Reaction Volume % of total of Ethylene Temp. Time . °C min. 507 2 52k 2 550.7 2 C2HD3 G 2 H 2 D 2 C2H3D 0 ^ 0.76 0.7 1.37 2. 1.3 2.3 2.75 1. 3.6 3.5 18.45 19.25 61.5 18.8 18.8 61.6 22.6 22.7 23.9 23.8 21.k 21.4 22. 21.k 54.6 54. 52.8 52.5 1.89 26.k 22.6 k9. 2.5 25.6 22.8 14.9.2 27.6 28.6 28.k 29.2 23.4 22.6 25.3 25.8 46.3 48. 42.2 41.5 Total 100$ 50 e.v. " low e l . energies ii 11 50 e.v. low e l . energies^ 50 e.v. low e l . energies 50 e.v. low e l . energies 50 e.v. low e l . energies. 50 e.v. low e l . energies. Deutero Ethylenes from the Pyrolysis of 1-Butene-k-d. Sensitized with Hg(CR"3)2. Reaction Volume $ of total of Temp. Time Ethylene °C min. C2HE>3 C 2 H 2 D 2 C ^ D C 2 H k Total 492 0.66 16.6 lk .5 68.3 100$ 50 e.v. 19. 13.8 67.1 low e l . energies Extrapolated Values for Non-Sensitized Reactions" Temp. Time . °C min. C2RD3 C 2 H 2 D 2 C2H3D CpH^ Total 1+92 2 0.1+ 14.7 16.5 68.5 100$ , -97- • T - T ;:;:: iii: Siiit ijii-ii;' iii! !i:|i! i!:S nil i-i i'i 4 !.i'! :i i'i^  ":;;:r::|T;:i:;: 44444 Trrr ilS W llliiil Ilil 1144 ill- iii i i i Lii 14 4444 4114 li Li 3141 -IIS lilllliiili llS 4444 ill 44444444 4 iiiii: iiii ;•;: {iijt Iiii 4 j4;r .1.: ; : 4:141 4 4 4 1 . 4 4 liiiil V •44 4 4 L ii-lll 4 ill: :ii|.iii •Hit ;|4 :;iit 44 o f To y:l ta 14 K iiiliili 4441: Ii lii V i LiiL iiii 441L Etn en ei J " " 4i! 44ii[ 4:1 i i !': ii 11.1.!: 44 il 44444! 44 lil! !': ;4 ilil % ttll iilil Iiliii" - ::::j:::: ::::]:.:: :::: j:: : : : : ! : : : : 4 ir|t Sp 1114 :4 44::4: •:.: !:  i !.: : i ii:4 1I4 Ilil .44 4-4 44|44 4 44 i4: ii44 i i lii.ii ilili 4141 I4444 114 |4444: lili-ii -4444 4144 - •!4-4 44 44 44 i -j;.;-; I44ii; 4 ; 44i!ii •1:1 p. 1111 ;;:+:; 4444: 44-444 4444: 11:|i 4411 444 .4-" ;...:! . ITilj4'4 4444 1-i i-l II !:l- 4: 4 i.ii.i Ll.Ll lis; 441! 1144: iiiii iiii 44 hii.i ii lit): ii 'J : ){!::•;! •' i4 j" i.:44 l!l!; :l|)l i v.v.r iiii - 11H 0 4!44j44 :: i : 4 -il'f; 1111:4 4' lii ilil •111 III) v. Iiiii; _6 .... : : • 1 : i i 1 4:i 4l-|i •T-[-f:- i . ! m 14 1 liiiiii • : 1il44: 141 r* 0 44 \ *• ifffl: 1114 1111:44 •Ii -Iiiii!: 41 1H.L IIS :|:|-i4- 441414 444 44 Hi: i 14-.Mi ]. THi n.j'i- j'! p 1.:i:r i:;: .i:ax :'444: 1-4;!. iiii . : ,.| :; 411 !44 : . . . w iliixi ii : : :"! i : :4- 1 i:4-m-r lilf iiii iLiiii iij.i . . ; . 1 . . . . 1 . . . : ': \: :n j ii'i' 5 r n:. ill! 4 • 41:1  •LLil 4444- • •4:1 .... i:;: r 44 1:;l!4 !4 ; -ilti" ililiH- in.:. iilii: 54 o< ::;: : 4^ IT" : r:: I i ; • 111 44 !-;: :i:l:i:r 4444- 4114 1111 4-4L 444 .... •4-4- ii!: ;.:  :n:.r: :!t!V!:i i:i -;::;-;: t:U:i + H+ :i:|:i:j: Hi!: .1.1  r :: 1: ..... 444 40 j j i : .:: -ill: ;4;:. ...,. : : i : .... 3_ 444 .... •Ill 44 444444 4-4- Iiii :: iii :{:! : . . . -44~ 44 44- T .(.... • 1 — iiii iiliiiiii' . . : . | . : . . ..(.... ::>::. . j i i : ' ! : : . t::: :: i i i i 4 i .... 4-14- 44 i 44-44- Ill: ...... 44 .... -;;4-4---4  4 4:444 4 4 I 4 4 •rr: T : - T IIII4I4 44J44 i 14444 141 ; : : : '.: i::: :rir::r : : ! : : : : 1 • • i • • • • 444 1 44 :::: j:::: :::: j.::: :: j:: 4 4 4::: •ii-lii.;.:. 44 :::: I:::; :: ::::|:::: :: .. 1...: iiliii! i i 1 i i i i -44-i • • i 47414. 4 iiii ...., : : : : ! • : : : r - ! • t' • • • .. . *2l ) 2( - 44444 ::::!:::: 4:444 . . . : I — :: iiiijj^ ii.r" ^ "v. i44 ilili : : : ; ] : : : : ::::i:::: -».< [5] iiii. 4rf4 4 44444444 :: -44--H-n-4 ii 4-4-1: -144: 444 444 414 4i 44 : : : : ! : : : : - 10 : : : : : :: :::: :: ii i:4: 444 i 44:i441 - 44 •444 .44J4.44 .4.4 4 44 141 i ! ; ; : ; ; ;; : 44;J4411 ii iiii 4 41-4 1:! ii iiii 4l!4.i j . r: ; 44 441 l||i ii ': lii! :•]:: .:i i -i-i- -i-i i1 4444 ii 4 ... ::.:{:::! :::: i:: 1 : : : : | : : : : 4il: 44 44 44:- 1  4114 4144: i:i:ii 4.!:. |l 14 !:!j: :i:i.i:: -1-14: Ijjr 1 rr: lii: 114 : ' : 1 LIU •;111 .:1 ii:'4 !-•(•  i4 iiii \] 44*44 414 I P D: •Fl-M nil •ij.il-444 i : : t h i :!+4 5 10 •::!'•"!• :•: c On 4 44-41 \x \SX i i tt A •;•!:  i !::.; 44i|44 :i:4: - 4 4 4 lill ;|J:l.i ~T-n .tri± 4)1 4ILIIL f-i-i t- +' :f 4n*?. ±14 IS iillif i l iiiii! s 4C > G4 ilil i s .<:;::! m t& .ill* i®< 50'" t i on Of 0e j;t Sitii eifs :t!4:r hy P R :ISl -j-j-H- -i-r-ri' liiL :4-•i-i-i-]- 45L )±:i 44- * .i. ii. :!: :p. i 'P' l-i-j- • -i-!-i-j-• i m 4+4 trip •H+L + + +TTF m -t+tt 4444 444:r 444-i-4-t+4-+14+ 4-j-i-t-141 •l-H-i ae Ii 1 :j:i.u:4.;-^ i- m 4444 -hi]:j: 16 Sill: m m Sti -i-f-t-v p+ iiS|i 4444; :±fci: t\# sji liiij: 441L -T-r -:-}-;-:- iHilT 44 :4:.iii. ffllf 4441 •H •+ ii+if m its. m 4444-IfjT in-iS •0.4 4ii-L 14 P 1:|ii: 4tt i l l iffiiil ±I±t m 4:3: m w ijiifii J4ii-4JiS +i-H iiii. : U 4 + ±i:;4: 45444 :i±i:i - 9 8 - Table XXV Increased Rates of Formation of Deutero-Ethylenes i n the Reaction Sensitized with Mercury Dimethyl (7.1 f o l d Increase for the t o t a l ethylenes) Compound Ratio of Concentration from Sensitized Reaction to Concentration from Normal Reaction for 1 Min. Reaction Time C2RT>3 0.66 x 7 . 1 / 0 .k9 =9 .3 C 2H 2D 2 16.6 x 7.1 A4 -7 = 8 . C2H^D 14.5 x 7.1 / 1 6 . 5 = 6 .3 C 2H k 68 .3 x 7.1 /6.8.5 = 7.1 DEUTERO-PROPYLENES Due to lack of data on the spectra of the deutero- propylenes, the analysis was based on measurements of the parent (molecular) peaks at low electron energies. The quantitative estimation of deutero-isomers by measurements at low electron energies was proposed f i r s t by Stevenson 28 and Wagner. The accuracy of the method depends on the assumed equality of the i o n i z a t i o n potentials of the deutero-isomers. It has been shovm by Tickner, Bryce and 32 Lossing that t h i s method can lead to errors as great as 15% i n the estimation of the r e l a t i v e concentrations of CH 4 and CD^. However, there i s evidence that the i o n i z a t i o n potentials of the deutero-isomers of higher hydrocarbons, and e s p e c i a l l y higher o l e f i n s , are s u f f i c i e n t l y close to -99- allow quantitative determinations with good accuracy. In the case of the o l e f i n s , the electron removed at lowest electron energies i s a 5T electron which can be expected to be l i t t l e affected by the deuterium su b s t i t u t i o n . Thus, for both acetylene and ethylene, the i o n i z a t i o n p o t e n t i a l of the non-deuterated compound has been shown to be the same as that of the completely deuterated compound within 0.02 18 e.v. The r e l a t i v e l y good agreement between the re s u l t s from the normal and low electron energy analyses of the deutero- ethylenes i s a further proof for the r e l i a b i l i t y of the low electron energy method for the analysis of unsaturated deutero-rhydrocarbons. The r e s u l t s obtained from the analyses of the deutero- propylenes are represented i n Table XXVI. The main products found are C H , C H D and C H D . The concentrations of the 3 6 ' 3 5 3 3 3 deutero-propylenes for two minutes reaction time p l o t t e d against temperature are represented i n P i g . 20. The extra- o polated concentrations for the temperature I4.92 C are given i n Table XXVI. Since the concentrations of the propylenes changed considerably with temperature, the values obtained by extrapolation must be considered as very approximate. The increased rates of formation of the deutero- propylenes i n the mercury dimethyl s e n s i t i z e d reaction 1are given i n Table XXVII. The C^HgD^, C^L\^>2 & n d °3E$) increases of the same order as those observed for the CHD , 3 the CE£)2* *he deutero-ethanes and the deutero-ethylenes. The increase i n concentration of the C^H^D^ has an -100- Table XXVI Deutero-Propylenes from the Pyrolysis of 1-Butene-k-d 3 Reaction Volume % of t o t a l of Propylene Temp• Time °C min. C_D, H Q GJDJi^ C D H , C DH_ C H Total 3 4 2 3 3 3 3 2 4 3 5 3 6 507 2 3 .9 13 .2 7.9 58 . 17.1 100% 4 ~ 4 -3 18 .6 8 .5 42 .8 25.7 " 524 2 - - - - - 4 4 .1 20.2 10.1 31.4 34 .3 " 550.7 2 4 . 3 17. 8.6 30 .4 39.6 » 5 4 . 1 6 . 9 .4 25 . 4 7 . Deutero-Propylenes form the Pyrolysis of l-Butene -4-cL Sensitized with Mercury-dimethyl ^ Reaction Volume % of t o t a l of Propylene Temp. Time CoD.H? C.D.H. C D H C DH. C H Total °C min. 3 > 2 3 3 3 3 2 4 '3 5 3 6 492 1 2.8 17 .4 7.9 37.7 34 . 100% Extrapolated Values f o r Non-Sensitized Reaction Temp. Time . °C min. C JD. H 0 C D H C D H C DH C H Total 3 4 2 3 3 3 3 2 4 3 5 3 6 492 2 3 .2 6 .0 . 7.3 77 7.1 100% -101- 1 .: I:: .. | ... "444 44 . . . . 1.... I; • i • : 1 of i l 1 Pr e . 444 44-- : ' • -" : :: . ': 1 4 4 ! V. ..(... . ....j... . 4444 — 444J444 -44 444 i' •: _ 4-4 44-4 — 80 _ : : ; : -444 \ iiii|;;i; 44 4  J; 4: . . . . I . . . . 444 1 . . . : : ii;:!:::: j :::: 44.4 444 ..... -j - • .ii'!!' D . 4ii 7( -444 44 4-4- 1: : i 11 1 : !":. -!+;:! -r-r : | :i'!4 i' :HJi: i j-^j- 44 :4x \o 1!.!: .!:ti:i: iii:!: lixlli. .... 1 -1 i - 44 \ :::t;1: 60 44! 14 . .. — \ .[.IT] . . . . 1. .V 444::: 4i .ilil : ;4'-4 !.]!;: :50 +!•! i: \ i-iii. •!:!-H: 1414: - 4444 44 iii- ; H : I+t:: 444 ffl.i. i! 4 .... R ii o\ ::[-..:. :^ r 44  -444 40 - j:ii 4:lti: 44 ... | x x j x x ::::!:::: ::::i:::: 4: 441! iiiiiiii! 4-4-;::: ) _ > 4::i- n : •:: 3C — 1 — 1...'. ••••••••]•••••••• : . : ' 1:: x ........ 44 — 1.... •44 .... .... 444-4444' 4444 4444; :.;_ :::: — ...... ..I.... :: I:::: :rr.—-. 444444 444-44 | | . . . . 1.... 444!: 44; 444: IIHii lit 44il4! 4444H44r ::::!:::: ......... 4444 ,-:.-| :::: 47:4 ; ! : ! _+|+i ;:::::::: — 1 — 4 | : : : : 444444: .... 2C .... j.... :_::-L:.:.:. ::::;;::: i.::. 44J44 iiiiiiii: 4::j:::: .:..,.... ... 4-44: :::: 4444 44;- 4 Tit;! 4:4 i i l i :4: . ..::: — 1 — : : ; : ! ; : : : ::::::::: : : : : i : : : : ::::!:::: ::::]:::: 4ijii4 iii: I4: x x i x x .... m m :•:•i:.:::.-• 1:: 4:4: 4 4 4 : -.44:4 3H 3 % 444 1C -rrr ::::j:::: 4i|4: iii iii ill r4 444 i i p 44 • . " ~ T T : " T : : : : 1:::. ^ ^ * * * | ^ : ; i : ; • :::: .... tijij'-ili ......... * " x | : : : : ::::i:::: 4*44 444J44 WM i r :•:!:: Ii x: i:::|::ii 1, i.iii -.-.:.[rr • ;;.4|;:::i4:: • • • i• • i : : : : : : : : 1: ....|.... i . 4 :::: 1 ;4ij4:i —•—? :!:!:!4:j4:4i: tiff •: .1 AS 441444 I i :i:li:i; 1 Iflt Itlt 44 H i T i i 1 i ! i ; 4 44 5C >0 344! 4: ::::j:c- 4h4i4i4 ,x:x|;::;::. Afiili 1: •:•:•: ii:l5i IX :i± x tft- 50 444 ii.!! ff'T .!•!•:•!: .5 -:i+:-|:i-4 /I rv : |-i:-4t!l: 50 rf'rr i 43431 mi 1±j.: :iti4 44 -+44 •i^ii-T-ttff 1 "i:l:H. ++1 1+1:1 !-! i-i t  it: •••i-i!- •!+Fj" - U i j - Hjt m .i.jij Tiff aft XJ:<X 41314 A3. :4ii 1:4 ^i t iffli .l.i.i.L tiff # A3. ttiii , . . . • • iffl: -i :-TT XXtxi :{+!+• 1 sc '1 p >OEi s ,u -••+!-m :4©)t ::ff~l 44-jtft; tiff *a -U4.L Hit -14+ i:|+1: T t T T ff4 -4-+ 14+ 4xi: 335 1 i. 71 Itff H -riff :1± :!" 54 ±1:0: TriT, TlTl lr Hi+ L P ii - Id iii rrr: $ 44 ®% TO # titi: iT1J-i i i i i t llfl: +fff ffp-li:S j-tci: +i+ -fiff ll+l iliff ff|+ •i-i-U 34:4 Oil .Li., 4 1 .i-i-l.l m tH: flit i+t +x X itlt tip !l: m 44 a* m i+tt i4 4F ::4|: i+jr is. 44 ffi .i.i-i j. +H-v T-iit Ail - 1 0 2 - intermediate value and the high value for the C H i s second 3 6 only to the Increase of the CH concentration. k Table XXVII Increased Rates of Formation of Deutero-Propylenes i n the Reaction Sensitized with Mercury Dimethyl ( 9 . 7 - f o l d increase f o r the t o t a l propylenes (Table XVIII) Compound Ratio of Concentration from Sensitized Reaction to Concentration from Normal Reaction f o r 1 Min. Reaction Time. C H D 2 .8 x 9 . 7 / 3.2 = 8 .5 3 2.k C 3H 3D 3 17 .k x 9 . 7 / 6, r 28 C H D o 7.9 x 9 . 7 / 7.3 = 10 .5 3 4 2 C H D 37.7 x 9 .7 /77 '= k . 75 3 5 . C-H, 3k x 9 . 7 / 7.1 * k 6 . 5 3 o DEUTERO-BUTENES The deutero-butene f r a c t i o n separated after pyrolysis of the l-Butene-k-d 3 also was analysed on the mass spec trometer. The mass spectra obtained with 50 e.v. and low electron energies are given i n Table XXVTII, together with the calculated percentages of the isomers found. Unfortunately, no systematic investigation of the. changes In deuterium d i s t r i b u t i o n i n the deuterated butene was made. The idea that the butene Isolated after the re action also should show detectable changes:in the deuterium content occurred too la t e i n the invest i g a t i o n . The - 1 0 3 - Table XXVIII Mass Spectra of Deutero Butenes Low e l . energies 50 e.v. A B C A B C Mass 60 k . 8 k . 8 1 1 . k . 8 4.37 1 0 .k 59 100. 100. 100. 100 . 100 . 100 . 58 1 0 . 10 . 1 3 . 39 . 4 0 . 14-5 - 57 - - 2 . 15 .4 15 .5 20.9 56 7.5 10.9 1 2 . Composition of Deutero Butenes i n 1 Volume % of ..total of Butene A_ B C - Low e l . en. 5o e.v. C, H. D. k 4 k c k H 5 D 3 0 91. 0 8 7 . 5 0 88.2 5.1 82.6 C k H 6 D 2 9 . 8.75 8.8 10.7 C k H 7 D  G k H 8 Total - 3.68 3 . 1.6 100$ 100$ 100$ 100$ A 1-Butene-k-d^ standard B Butene f r a c t i o n i s o l a t e d from reaction mixture obtained from pyrolysis of 1-Butene-k-do s e n s i t i z e d with Mercury- dimethyl at k92°C, 1 minute reaction time. C Butene f r a c t i o n i s o l a t e d from reaction mixture obtained from 1-butene-krdgpyrolysed at 56# C, 3 minutes reaction time. J -104 - Table XXIX Comparison of the Normal and Sensitized Decomposition of 1-Butene-I).-d^ Compound Concentration i n Mole per cent Concentration Ratio (x 10) of I n i t i a l l-Butene -4-d Sensitized to . Unsensitized Unsensitized Sensitized CD4 0 . 1 1 0.7 7 CD H 3 2 . 7 7 1 7 . 2 6 CD 2H 2 1 . 0 9 8 . 3 8 CDH 3 0 . 0 6 1 . 6 2 7 °\ 0 . 3 0 2 9 . 8 1 0 0 0 . 0 5 0 . 3 6 C 2D 3H 3 0 . 5 6 7 . 1 1 3 C2D2Kk 0 . 2 2 2 . 1 1 0 C ^ H 0 . 1 0 0 . 9 9 C 2D 2H 2 0 . 2 9 2 . 3 8 C 2DH 3 0 . 3 2 2 . 0 6 1 . 3 4 9 . 5 7 C 3 V - 0.07 0 . 6 9 C3D3H3 0.II4. 3 . 8 2 7 C 3 D 2 H 4 0 . 1 7 1 . 7 1 0 C 3DH 5 1 . 7 5 8 . 3 5 C 3 H 6 0 . 1 6 7 . 5 ^ 7 C 4 H 8 - 2 7 . 0 -105- analysed deutero-butene from the only f r a c t i o n c o l l e c t e d shows i n t e r e s t i n g changes. The production of isomers with k, 2, and 1 deuterium atoms i s H indicated c l e a r l y . Con sidering the large concentration of the butene i s o l a t e d from the reaction, the amounts of these isomers appear con siderable. The deutero-butene i s o l a t e d from the sensi t i z e d reaction contains G ^ g » presumably 1-butene. • . . . The r e s u l t s from Tables XX -XXVIII concerning comp arisons of the s e n s i t i z e d and normal reactions have been summarized i n Table XXIX. The concentrations of the compounds are given i n mole cf0co of the i n i t i a l l y admitted 1-butene. DEUTERIUM DISTRIBUTION IN THE POLYMERS No systematic i n v e s t i g a t i o n of the deutero-compounds i n the polymer fractions was made. The deutero-isomers con tained i n several polymer fractions of only one reaction mix ture were determined by mass spectrometric analysis of the separated f r a c t i o n s . The r e s u l t s of the analyses with low energy electrons are presented i n Table XXX. The r e s u l t s i n Table XXX indicate the formation of a s u r p r i s i n g l y large amount of deutero-isomers for a given compound. There can be l i t t l e doubt that the re s u l t s are r e a l , since special precautions were taken i n a l l measure ments to reduce the energy of the i o n i z i n g electrons be low a value where a l l remaining peaks due to Ion fragments -106- had completely disappeared. The parent peak with lowest mass measured under such conditions was always that of the completely non-deuterated compound. The concentrat ions of the deutero-isomers of a compound show a char a c t e r i s t i c d i s t r i b u t i o n around a maximum value. The con centrations of the deutero-isomers p l o t t e d against the number of deuterium atoms contained i n the compound are shown i n P i g . 2 1 . Table XXX Deutero-isomers of the Polymers from the Pyrolysis of 1-Butene-k-d 3 Temp, of P y r o l y s i s : 545°C Reaction time: 5 Min. Deutero-isomers i n Chromatographic Fra c t i o n P^ P^ was I d e n t i f i e d i n the analysis of the pyrolysis mixtures from 1-butene as C-jH^, most probably Cyclo-pen- tadiene,-* Mass Compound v o l . : 70 4.08 69 C 5 H 3 D 3 10.9 68 C5%D 2 25.8 67 C ^ D 32 66 S H 6 27.2 Total 100% Appendix I: Qualitative I d e n t i f i c a t i o n of the Polymers. - 1 0 7 - Table XXX (Cont'd) Deutero-isomers i n Chromatographic F r a c t i o n H2 was i d e n t i f i e d i n the analysis of the pyrolysis mix tures from 1-butene as most probably Cyclohexadiene.""' Mass Compound Vol. % 87 C 6HD ? 1.7 86 C 6H 2D 6 3.7 85 C 6H 3D 5 9.1 8k 18 .3 83 C6H^D3 25.7 82 C6H6D2 18.6 81 C 6H ?D l k . 3 80 C6H8 8.6 Total 100 % Deutero-isomers i n Chromatographic Frac t i o n Bz Bz was i d e n t i f i e d i n the analysis of the pyrolysis mix tures from 1-butene as C^H^- Benzene.""" Mass Compound Vol. % 82 C 6H 2D k 3.4 81 -C6H3D3 10 .k 80 C6H^D2 27.6 79 C 6H£D 3k .5 78 C 6 H 6 2k .1 Total 100 % Deutero-isomers i n Chromatographic Frac t i o n T l T l was i d e n t i f i e d i n the analysis of the pyrolysis mix tures from 1-butene as CyHg- Toluene.""" Mass Compound Vol. % 97 C 7H 3D5 6 .5 96 Vl^pb, 16 .8 95 C 7H£D3 26.2 9k C7HV-D2 23 .k 93 C 7H 7D 18 .7 92 C - H Q 8.k Total 100 % Appendix I: Qualitative I d e n t i f i c a t i o n of the Polymers. - 1 0 8 - >•!•••• 44 :::: 4 4 4 4 i 44 liiiii:;! il4i;l iiiijilii j :l;l 41 14 ii i i 4n 44 444 4444444 : : j : : : : :: i:::: t mi ill 44-14 iiiiHii! i i 1 • 1 i i 4 4:4;;; 4 114 4: Iiii 414-4 4-4 44444 c: • Cyc l p p « Len< 3T4J144 4-41- 144 .... 111; 44 :::: a Gyc 4:4:::: ilQh< 4 4 4 : 1 : 1 1 4 sxadi; '::-!:::: 1 i i •: 3ne 4141 44444 4444 Q iiiiliiii I4i4ll444 4 4 4 iii! ;:;:!::::. ::::\ r.:: r sin 1 4 4 4 I :i;!t ""i"i"i IIII- j •:;. • il:4.|l!ii m q j . . :.: il||i;-:;::(:::: iiii. w O J U t wit Iiii. IIII 1 |-l | 1 4.4 4 4 i.;i 4441 i ilil 4441 .Ilil 44J441 :::: ii|4 11. 4.444 4i41 — 1 :.::: j:::: .... . . j . . . . 4-1-4 H- I4ijllir ill! ::.: : : • • ; - 1444144 :::; ::4tl::~ •i : ;' \ef': • 44 i 1 4 4 4144 S|4l: -:-:::'! :ri: re.:.|::::. 411! i n X 4%:: sqoffl ul Bl A' 0- I:S on let a. . ilil Iiii i 1! -lii! :.:;-::!;: j::.:: • ; : : 1 144414:4 tlXJ r:l: u.. iiii Ilil j•:.;-; |:::i.:_:. f •1-11 4 4 4 444 4 lill! 4il 4144 4 ::::i::;: -i--4:: ::::!:::: 44 430 444-11- :::; 4144 44-114- .... .... .... 1 ... . :::: 44441 44 . Ir\^ ... iiii :::: . . . . - -Ii 20 . .... 411 4444|4444 41 :::: :::: i::: 5 4-44 44 -44 •; 144 444 -|44-i l i 44 jlili 4414:: -4|44^  444444 -44|44i — i _ . • • .... 1.... i i ; 14;||4> .... I.... 4 1 1 V • • 1 — \ ( 4J44i :: i:::: ]:.:. r4i44 • • • i — 4 44414444 iiiiliiii •:.: i ::. 444441 .:.: 4 4 4 4-44 4^4.44 \ ... :::: i::.: : ::::i: •: : »44i44 444114 444-4-!": 4-4 :: i:: 4 4 41-444 1 0 . ™ 14 ::::!:::: ::: j:: ;;;;!;;:; 144144 1414 ::: r 44 44114 4  .: :i:: ::: : ::•:!::.: :::: i:::: : : : : I : : : ; ::::|:::: ::::):::: :;;:|;;:; 4-44-4-44 .44441111 ::::i:::i — 44 4 i * • i • • • -::n r:: 1 . . . . ; : 1:41 1 • : : : : i : : : : •441444 it i i i i i vlTtTTIT :::i:::: ilil 4441444 44 — 1 — ::;:!:::: ::::]:;:; 1 . . . : ? 4.4.4.4.1 44 4 414 4 4 ::::|!::: :. .;. .... — ::::|:::: . : . : T : T : T ....(...: 44444 . , ( .... 44 iiii 444 4i ::: : ; 1 -4-4-42 44 :::: ..:: 4.44 4 1.::: * r.oma >::-4|i4 1* 1 - - • -1 • —— 6 . . ; : nr." V til ml •e H T) A1 •il ilil 44 ; i ; : i : : ; 444 : I:: 44 Iiii 41 'iiii 444: 414 Ii 3 01 ne) i:: 44 444 ilil III! lii; Hi 41; 1'|i'l -i'i-i ;i .!:i:!1 •' t-K! !• I T j-i -i i-i-f- Iiii iiii ;•;•:•: 'III! 11 4ij iiii jii $H •41 De Wit e4* ix Di s t ,ti < 11: ifc r r a < J1:1 4441 t : • ; i-i i • fill Hi i-l! i Iiii iii i. Ilil ii.ij II jj lill ilil H i-i-.1 (! 1 ilil 'i l \ :r:'.! iiii. :|- 4ft i illll |lili: iiii ill 444 [.; i i II -'-| i j' •'i'i Hi jj.j 1 jji-i- li 11  i iiii" iiii ill'!' i'iTi lii! :i ri-i-||ii||| 111 ill 1)11: }41 if 4 •;4 Ijii 4pi|l(4 iiii 44 |:|4:|. :f±i1: |:i:i:|: •:•! I > 111! i:i: 4: ;i; • -f t : :|i m l:!l:i •itii tre. i-iti- i-i IT ii'ti. r|tt i i i i Ilil ii-4 441 :j:tii: -1 ii if 11 ±0+4° 4:::1:1: 4 4-14 :|:B: gjl itit 4i |i|l iliji i l l : l-RT •-•44+-4:|;::r . ; x n ; Iiii: Ii |-i 1.1. lit i.U. i-i- i - Ii): fjii l i-" j jjj j j.H Iiii iiii-!•!•!!• ilil 1 H-i Hit 14. 4lJ44 Iiii l i l l -R+t- :!Tt tut i+p i±tt l-i+f I14 j-p-r-liiliil iii 4141 41! -i:| - i_i: il i i lill ill IPi 4111 iiii PI Pli lii m ft Tj+F 4 ' i lit i l w -i-t-f--iii till ijl! Ilil :-f-rf -109- D i s c u s s i o n -110- r D I S C U S S I O N FREE RADICAL VERSUS MOLECULAR MECHANISM A decision as to whether the 1-butene pyrolysis proceeds l a r g e l y by free r a d i c a l mechanisms or by molecular mechanisms i s of primary importance i n the i n t e r p r e t a t i o n of the present r e s u l t s . Some of the experiments were designed s p e c i f i c a l l y to provide information as to the nature of the mechanism. I t was found that the addition of approximately $% by volume of mercury dimethyl to 1-butene and 1-butene-k-d^ produced a large increase i n the rate of the butene decomp o s i t i o n and i n the rate of formation of the products. Mer cury dimethyl i s known to decompose with the formation of methyl r a d i c a l s . Therefore, the acceleration of the butene decomposition must be due to the action of the methyl rad i c a l s from the s e n s i t i z e r bringing about a "forced" free rad i c a l reaction. I f t h i s i s so, several points i n a comparison of the r e s u l t s from the normal and s e n s i t i z e d reactions are s i g n i  f i c a n t : The rate of formation of a l l l i g h t hydrocarbons was greatly accelerated i n the s e n s i t i z e d reaction. For a reaction time of one minute at k93° G» the concentration of the l i g h t hydrocarbon products i n the s e n s i t i z e d pyr o l y s i s had increased 7 - to 13- f o l d over that i n the non- s e n s i t i z e d p y r o l y s i s . -111- In the normal and s e n s i t i z e d decomposition of 1- butene-k-d , the deutero- ;ethanes and deutero-ethylenes 3 were produced i n nearly equal r e l a t i v e proportions, a l  though an estimated 90% of the deutero-ethanes and 86% of the deutero-ethylenes i n the s e n s i t i z e d reaction resulted from the action of the mercury dimethyl. I t i s probable, therefore, that the deutero-ethanes and deu tero-ethylenes were formed i n both cases by analogous mechanisms, I.e. r a d i c a l mechanisms. Thus, the deutero- ethanes and deutero-ethylenes appear to be products of r a d i c a l chains started by the methyl r a d i c a l s . The increases i n concentration of the remaining products i n the s e n s i t i z e d reaction also show ce r t a i n r e g u l a r i t i e s . The concentrations of a large group of deutero-isomers increased by approximately equal amounts, as did the deutero-ethanes and deutero-ethylenes. The remaining compounds showing a much larger increase were methane CH^ and propylene O^H^, both containing no .deu terium. (Table XXIX) I t i s , therefore, reasonable to assume that both these compounds were produced by fast reactions of the methyl r a d i c a l s with the 1-butene-k-d^. This i s e s p e c i a l l y obvious i n the case of CH^. A general inspection of the deuterated products from the normal 1-butene-k-d^ decomposition shows that a wide vari e t y of deutero-isomers was formed. The formation of these products through molecular mechanisms appears improbable. -112- On the basis of these arguments, i t can be concluded that, most probably, the decomposition of 1-butene and 1-butene-kd proceeds l a r g e l y by free r a d i c a l mechanisms. 3 Therefore, the present r e s u l t s w i l l be interpreted on the basis of free r a d i c a l reactions. The extent to which such reactions can explain the experimental re s u l t s q u a l i t a t  i v e l y and qua n t i t a t i v e l y w i l l be a f i n a l test the v a l i d i t y of this assumption, PRIMARY STEP OF THE FREE RADICAL DECOMPOSITION  OF 1-BUTENE The primary step which i s most probably involved i n the free r a d i c a l decomposition of 1-butene i s : CH^ CH-CH0-CH0 -CH = CH-CH .•OH . (1) 2 2 3 2 2 3 The reasons f o r the expected weakness of (the CH :CH.CH -CH ( 2 2 3 bond and evidence for the occurrence of reaction (1) at higher temperatures were given i n the introduction. Also, 26 i t was mentioned that Sehon and Szwarc obtained the 13 values E-j. = 61 .5 kcal/mole and A^ = 10 l/sec for reaction (1) by studying the pyrolysis of 1-butene with the toluene c a r r i e r technique. Some objections to the int e r p r e t a t i o n of the experimental r e s u l t s by which these values for E^ and Aj were obtained were pointed out. However, the value E^= 61 .5 k c a l has received recent confirmation by Lossing, Ingold and Henderson 1 6 and by McDowell, Lossing, Henderson 20 and Farmer. These authors have measured the v e r t i c a l i o n i z a t i o n p o t e n t i a l of the a l l y l r a d i c a l by the electron -113- impact method. The heat of formation of the a l l y l rad i c a l was determined subsequently from appearance pote n t i a l measurements of: A(CH2= CH-CH*, CH2=CH-CH2C1)* A(CH2=CH-CR"2, CH2=CH-CH2Br) A(CH2= CH-CH*, CH2=CH-CH2D and the heats of formation of the a l l y l halides. The three values obtained i n this way for the heat of formation of the a l l y l r a d i c a l agreed within 1 k c a l . The average value obtained was: - AHj (CH2=CH-CH2.) = 32.3 k c a l . The bond d i s s o c i a t i o n energy D(CH^ CHC^-CH^) can be calculated from the above value and the well-known heat of 33 formation of the methyl r a d i c a l according to the equation: . D(CH:CH.CH -C H „ ) =A H S (C H =CS.GH )*AHj(CH.) -AH? (1-butene) 2 3 <- <- 1 3 x 32.3 • 32.5 - (0.03)1 = 6k«-8 kcal./mole. Thus, since f o r the reverse reaction CH^ • CH 2=CH-CH 2—- CH3-CH2-CH=CH2 (-1) should be equal or nearly equal to zero, D(CH2:CH.CH2-CH3) = E^ = 6k.8 kcal/mole. This value i s i n substantial agreement with the value ob tained by Sehon and Szwarc E^= 61.5, considering the l i m i t s of error i n both determinations. A(CH2=CH-CHp, CH2= CH-CH2C1), means the appearance poten t i a l of the CHp=CH-CHp ion i n the mass spectrum of the CH2= CH-CH^l ftolecule. -114- Prom the agreement of these r e s u l t s , i t would appear that the value f o r E can be f i x e d within the limits'-of 1 6l to 6£ k c a l , and that A^ should be i n the neighbourhood ) of 10 ^ l / s e c . Using the above values, the percentage of decomposition of 1-butene due to the primary reaction only, can be calculated for several of the temperatures used i n the present in v e s t i g a t i o n , and the values obtained compared with the experimentally measured t o t a l de composition of the 1-butene. The ra t i o s Ac (total) to Ac (primary) obtained i n t h i s way are given i n Table XXXI. Ac (total) refers to the percentage of t o t a l 1-butene decomposition as measured i n the experiments f o r one minute reaction time (Table XI; and Pig. 10); A c (primary) i s a calculated value f o r the percentage of primary de composition under the assumption: E.^61.5 k c a l , A ± = 1 0 1 3 (column 2 of Table XXXI) and E = 13 6I4..8 kcal/mole, A-^10 (column 3 of the same t a b l e ) . The r e s u l t s obtained indicate that the r a t i o of t o t a l to primary decomposition i s within the l i m i t s of 7.6 to 63. In spite of the considerable uncertainty of the estimate and the wide variations between the values obtained, i t appears that for each butene molecule decomposing by a primary s p l i t to methyl and a l l y l r a d i c a l s , at l e a s t 8 molecules of butene are decomposed by secondary reactions i n i t i a t e d by the methyl and a l l y l r a d i c a l s released i n the primary reaction. - 115 - Table XXXI Ratios of Total to Primary Decomposition of 1-Butene f o r 1 Minute Reaction Time. Temp. Ac (total) A c (total) C Ac (primary) A C (primary) Ej-s 61 .5 kcal E = 6k .8 kcal A-j-- 1 0 1 3 A = 1 0 1 3 493 5.9 50 509 5.9 53 522.2 8 69 540.6 8.6 73 546 9.0 71 554.5 8 ^ 62 Average A c (total) 7i6 63 A c (primary) SECONDARY REACTIONS IN THE  1-BUTENE DECOMPOSITION The secondary reactions occurring i n the 1-butene decomposition should be i n i t i a t e d by the methyl and a l l y l r a d i c a l s released by the primary decomposition. The poss i b l e reactions of the methyl r a d i c a l s w i l l be considered f i r s t , since the methyl r a d i c a l s can be expected to have a greater r e a c t i v i t y than the resonance s t a b i l i z e d a l l y l r a d i c a l s . HYDROGEN ABSTRACTION BY METHYL RADICALS In p r i n c i p l e , methyl r a d i c a l s can abstract hydrogen -116- atoms from any of the four carbon atoms In 1-butene. The weakness of the CH : CH.CH.CH bond due to resonance H s t a b i l i z a t i o n of the r e s u l t i n g r a d i c a l : 1 2 3 4 CH 0 = CH-CH-CH. 2 • 3 suggests p r e f e r e n t i a l abstraction from carbon atoms "3". The bond d i s s o c i a t i o n energy D(CHP=CH-CH-CH,) can be es- E * timated on the basis of recent electron Impact work by 20 McDowell, Lossing, Henderson and Farmer. The authors obtained the heat of formation of the CH-.-CH=CH-CEL r a d i c a l • 2 3 from measurements of the v e r t i c a l i o n i z a t i o n potential of this r a d i c a l produced by the pyrolysi s of l-iodo-but-2-ene and the appearance pote n t i a l of the C^H^ - o n from butene-2. The r e s u l t obtained was: AH° (CH2-CH=CH-CH3) =26+3 kcal The CH -CH=CH-CH r a d i c a l and the CH = CH-CH-CH • 2 3 2 * 3 radical, d i f f e r only by the formally assigned electron d i s  t r i b u t i o n . The two formulae represent two forms of the same resonance hybrid. Therefore: AH° (CH2-CH=CH-CH3)=AH^(CH2= CH-CH-CH3)= 26 i 3 k c a l . The bond d i s s o c i a t i o n energy D(CH2= CH-CH-CH3) then can be H computed from the r e l a t i o n : D (CH •- CH.CH.CH )= AH° (CH = CH.CH-CH )*AH° (H) -AH° (1-bute 2 I 3 f 2 3 1 1 H = 26 • 52 - (-0.03) = 78 k c a l . -117- The r e s u l t obtained i s of twofold i n t e r e s t . F i r s t l y , there i s an appreciable difference between the ac t i v a t i o n energies d>f the two possible primary reactions: 1 - Butene • CHy + CH2=CH-CH"2. E = 63 kcal 1 - Butene-^* H • CH = CH-CH-CH E = 78 kcal 2 ' 3 Secondly, the bond d i s s o c i a t i o n energy D(CH=CH.CH-CH ) i s d H 3 smaller by 15 to 20 kcal than a normal p a r a f f i n i c C-H bond energy, thus confirming the expected p r e f e r e n t i a l hydrogen atom abstraction from the carbon atom i n p o s i t i o n " 3 " . The rates of hydrogen abstraction by methyl r a d i c a l s 34 have been studied by Trotman-DIckenson and Steacie. The methyl r a d i c a l s were produced by the photolysis of acetone. In the actual determinations i s o t o p i c a l l y l a b e l l e d , acetone- was used also. Some of the values obtained by the authors are reproduced i n Table XXXII. Table XXXII Abstraction of Hydrogen Atoms by Methyl Radicals 33 Trotman-Dickenson and Steacie RH % x l ° 6 kcal mole""-'- .cc.sec at l82°C Ethane 10.4 2. 11.3 Ethylene 10.0 2 .9 11.3 Propylene 7.7 12. 10 .8 1-Butene 7.6 34 . 11.2 1-Pentene 7.6 35 , 11.2 The values i n t h i s table r e f e r to the reaction of the methyl r a d i c a l s with hydrogen atoms from the compound RH, i e . with the sura of hydrogen atoms abstracted from any -118- l o c a t i o n i n the molecule. Comparisons of the values ob tained for the di f f e r e n t compounds can be used to obtain information as to which hydrogen atoms i n a given molecule are abstracted p r e f e r e n t i a l l y . Thus, a comparison of the res u l t s for ethane and ethylene with those f o r the res t of the compounds indicates that primary and v i n y l i c hydrogens are abstracted with less ease, and that the difference i s l a r g e l y due to differences i n the ac t i v a t i o n energies. The fact that the values f o r 1-butene and 1-pentene -/are p r a c t i c a l l y i d e n t i c a l indicates that i t i s the hydrogen atoms on carbon atom "3" ( a l l y l i c hydrogen atoms) which are abstracted almost exclusively: 1 2 3 CH2= CH-C^-CH^ 1 2 3 4 5 CH2= CH- CH 2- C^-CH^ The temperature range i n which Trotman-^ickenson and Steacie investigated the abstraction reactions was l80 to 340°C. The extension of these data to the present temperature range of 500 to 5&0oC introduces some uncertainty. The e f f e c t of differences i n the a c t i v a t i o n energies w i l l be reduced at higher temperatures, and abstraction of hydrogen atoms "at random" should become more probable. The abstraction of hydrogen atoms by methyl r a d i c a l s from unreacted butene can be considered to be the reaction responsible for the methane formation i n the pyrolysis of 1-butene. The r e s u l t s from the pyr o l y s i s 'of the 1-butene- 4-cL showed that the deutero-methane formed i n largest amounts -119- was CD^H, presumably o r i g i n a t i n g by the reaction: CD,.* CH = CH-CH_-CD0 • CD H + C, H D . 3 2 2 3 3 k k 3 I t was also found that small amounts of CD^ were found, prob ably o r i g i n a t i n g by the reaction: CD . + CH = CH-CH-CD- - CD, + CH = CH-CH -CD . 3 2 3 k 2 2 2 The methyl r a d i c a l s necessary for the above reactions are supplied only p a r t l y by the slow primary decomposition of the butene. Most of the methyl r a d i c a l s must originate from chain carrying reactions i n which methyl r a d i c a l s are generated. Possible reactions of this type w i l l be discussed i n subsequent sections. However, there are several points with regard to the abstraction reaction which w i l l be con sidered here. The positions from which hydrogen atoms are abstracted are of i n t e r e s t . Depending on the p o s i t i o n from which a hydrogen atom i s abstracted, four d i f f e r e n t C, H r a d i c a l s can k 7 be formed. These are: CH?= CH-CH5-CHQ , CE0= CH-CH-CH, , CH = C-CH--CH ' , CH-CH-CH -CH. c. c. * d. c. . } 2 • c. 3 • 2 3 The four r a d i c a l s can be expected to have d i f f e r e n t properties. An attempt to estimate the r e l a t i v e reaction v e l o c i t i e s of the four abstraction reactions leading to these r a d i c a l s can be made with the use of Trotman-Dickenson and Steacie's values. I f the assumption i s made that the primary hydrogen atoms of. carbon atom "k". 1 2 3 k CH.p= CH—CHg—CH_ -120- behave towards abstraction i n e s s e n t i a l l y the same way as do those i n ethane, and the hydrogen atoms of carbon atoms " l " and "2", as do those i n ethylene, the abstract ion of hydrogen atoms from d i f f e r e n t locations of the 1- butene molecule can be estimated f o r the temperature l82°C from the values i n Table XXXII. Ethane . k x 10 = 2-per Hydrogen atom 2 =0.33 6 ^ Ethylene - k x 10 = 2.9 per Hydrogen A D atom 2.9 -0.72 6 Butene-1 k i v x 10 = 3k Ab Since butene has three primary hydrogen atoms and three v i n y l i c hydrogen atoms, the rate constants for abstract ion of primary hydrogen atoms w i l l be approximately k x 106 = 0.33 x 3 ' 1 Ab and for v i n y l i c hydrogen atoms 6 kAb X 1 0 = 0*72 x 3 = 2.16 The rate constant for t o t a l abstraction from 1-butene i s k^k x 10 = 3k. The c a l c u l a t i o n leads to the r e s u l t that only 3.16 x 100 s 9.3% of the hydrogen atoms abstracted at o ~ 3 i r 182 C are not a l l y l i c hydrogen atoms. In order to estimate the r e l a t i v e rates of hydrogen abstraction from d i f f e r e n t locations of the 1-butene mole cule at the temperature, 5>25°C (an average temperature i n the range studied), the assumption was made that the values E A b = 7 « 6 kcal/mole and A A b= 1 0 1 1 , 2mole 1 . c c . s e c . " 1 from Table XXXII represent abstraction of a l l y l i c hydrogen atoms only. I t was also assumed that the a c t i v a t i o n energies and pre-exponential factors f o r ethane and ethylene could be used -121- f o r the a b s t r a c t i o n r e a c t i o n s o f p r i m a r y and v i n y l i c hy drogen atoms r e s p e c t i v e l y , a f t e r c o r r e c t i n g f o r the a p p r o p r i a t e number o f hydrogen atoms. The v a l u e s o b t a i n e d by s u c h a c a l c u l a t i o n f o r t h e t e m p e r a t u r e , 5 2 5 ° C are g i v e n below: C a l c u l a t e d Rate C o n s t a n t s f o r the A b s t r a c t i o n o f Hydrogen o Atoms from 1-Butene a t £25 C. Hydrogen Atoms k _Ab 18 - i - l P r i m a r y 0.33 x 10 mole , s e c . 18 V i n y l i c O.63 x 10 11 18 A l l y l i c 2.46 x 10 1 1 The v e r y approximate n a t u r e o f t h e e s t i m a t e i s o f c o u r s e w e l l r e a l i z e d . The r e s u l t s of the above c a l c u l a t i o n can be used t o e s t i m a t e the CD„H/CD. r a t i o f o r t h e methanes formed i n 3 k- the d e c o m p o s i t i o n o f the l - b u t e n e - k - d ^ . I f the d i f f e r e n c e i n r e a c t i v i t y o f the CH^ and CD^ r a d i c a l s towards a b s t r a c  t i o n i s n e g l e c t e d and i f H and D atoms are assumed t o be a b s t r a c t e d w i t h e q u a l ease by the ODy r a d i c a l s , the r a t i o o f CD-jH/^p^ o b t a i n e d i s : CD-.H 2.k6 • 0.63 i . _ 9 .4 CD k " 0.33 The a b s t r a c t i o n o f hydrogen atoms by CD^ ( o r CH^) r a d i c a l s i s known t o be f a s t e r t h a n the a b s t r a c t i o n o f d e u t e r i u m atoms. F o r example, i t has been f o u n d t h a t the a b s t r a c t i o n r e a c t i o n (a) -122- CD + HD - CD H + D (a) 3 3 CD 0 • HD CD D + H (b) V 3 26 i s approximately 1.7 times f a s t e r than (b) at 290 C. Therefore, the calculated r a t i o CD^H/CD^s 9.4 i s c e r t a i n l y too low, and should be.corrected upwards. The experiment- o a l l y found r a t i o f o r $2$ C i s CD^H/CD^ = 13, (Table XVIII), The experimental value i s well within the range predicted by the c a l c u l a t i o n . ADDITION OF METHYL RADICALS Methyl r a d i c a l s , besides being capable of abstracting hydrogen from 1-butene, can add to the double bond. CH . • CH= CH-CH-CH «- . (3) .3 2 2 3 5 11 The exothermicity of this r eaction can be estimated, assum ing a l o c a l i z a t i o n i f the methyl group to one of the two carbon atoms p a r t i c i p a t i n g i n the double bond. The two re s u l t i n g r a d i c a l s are: I II CH -CH -CH-CH -CH CH -CH-CH-CH 3 2 * 2 3 ' 2 | 3 CH^ The exothermicity of reaction (3) i s given by: AH?(CH .) + A H° (1-butene )-AH°( I or II) The bond d i s s o c i a t i o n energies necessary for the comput ation of AH° (j) andAHj(IT) are not known. However, for the • purpose of the estimate the following d i s s o c i a t i o n energies were assumed: - 1 2 3 - D C C H ^ . C H ^ C H . C H ^ C H ) 94 Seal H D(CH2.CH.CH.CH3) 97 kcal H CH, 3 The d i s s o c i a t i o n energies were chosen on the basis of the 33 known d i s s o c i a t i o n energies of the lower hydrocarbons: D (CH^-H) 104 kcal D (CpH^-H) 98 kcal D (CH3CH2CH2-H) 98 kcal D ( C H ^ H C H ) 94 kcal •H using: 1 A H ° (n-pentane) -35, kcal 1 33 one obtains: f A H ° (2 methyl-butane) - 36 .9 " A H ° ( H ) 52 " A H ° (I) 7 kcal A H ° ( I I ) 8.1 kcal « The exothermicity of the reaction can then be obtained with the use of.the known values f o r : 33 A H ° ( C H ) 32.5 kcal A H ° (1-butene) 0.03 " Exothermicity of reaction forming ( I ) 25.5 kcal ' " 11 " " (11)24.5 kcal On addition of the a c t i v a t i o n energy of the methyl r a d i c a l addition reaction of 2-5 k c a l , (for the o r i g i n of this value see subsequent discussion) the excess energy contained i n the -12k- addition product C^ H_._ . w i l l be roughly 27 to 30 k c a l . p 11 The reverse decomposition of the addition product (C H .) w i l l depend on the p o s s i b i l i t i e s for d i s t r i b u t i o n 5 11 of the excess energy into the d i f f e r e n t degrees of freedom and de-activation by c o l l i s i o n . At the elevated temper atures of the experiments ($00-560°C), the l i f e of the addition product w i l l be very short, and the reverse re action can be expected to take place with high p r o b a b i l i t y . I f this i s exclusively the case, the addition reaction w i l l not be important i n the mechanism of the 1-butene de composition. However, the p o s s i b i l i t y that the r a d i c a l s also can decompose to form products d i f f e r e n t from methyl and 1-butene must be considered. Therefore, i t i s of i n t e r e s t to discuss some of the available iforraation on the addition reaction i t s e l f , and also to consider some of the possible modes of decomposition of the addition product C .H . 5 II The addition r e a c t i o n of methyl rad i c a l s to o l e f i n s has been subject to a number of investigations, most of which also deal with the subsequent polymerization of the o l e f i n s induced by methyl r a d i c a l s . This work w i l l not be considered here, since further polymerization of the addition product C H Is highly improbable at the high temperatures used 5 II i n the present i n v e s t i g a t i o n . However, the results from 21 a recent study by Mandelcorn and Steacie i n which Only the addition reaction was studied (as f a r as t h i s was possible) are relevant. -125- By comparing the experimental r e s u l t s obtained from the photolysis of acetone alone, and i n the presence of an unsaturated hydrocarbon, Mandelcorn and Steacie were able to deduce the rate of addition of methyl radicals to the unsaturated hydrocarbon. Some of the values obtained by the authors are given i n Table X X X I I I . E N J i s the act i v a t i o n ° Ad energy f o r the addition reaction and i s the act i v a t i o n energy for the recombination of the methyl rad i c a l s to ethane. Since E 0 ~ 0, E N J , ~|E.r~ E A ,. P A J and P^ re f e r to 2 Ad 2 Ad Ad 2 the s t e r i c factors for the addition and methyl r a d i c a l re combination reactions. Table X X X I I I Addition of Methyl Radicals to Unsaturated Hydrocarbons - Mandelcorn and  Steacie Hydrocarbon E.- £ E 2 10^ x P / P li ke al A a ^ c 2 H k 7 5 C 3H 6 6 3 C 2 H 2 * " • Unfortunately, experiments with 1-butene were not per formed. However, propylene and 1-butene can be expected to behave very s i m i l a r l y towards addition. On the basis 3k of these data and data f o r the abstraction reaction , a rough estimate can be made of the r e l a t i v e rates of the two competing reactions. The r a t i o of the rates for propylene at 5>00°C ^ s given by: - 1 2 6 - R -7700/1.987 x 773 A b s t r a c t i o n _ 3«e  R " -6000/1.987 x 773 A d d i t i o n 3.e = 1/3 The r a t i o o f the r a t e s f o r 1 -butene , assuming t h a t 1- butene behaves i d e n t i c a l l y l i k e p r o p y l e n e towards a d d i t i o n , i s t h e n : R -7600/1.987 x 773 A b s t r a c t i o n 8.e R " -6000/1.987 x 773 A d d i t i o n 3.e 1 /1 .1 The r e s u l t s i n d i c a t e t h a t the a d d i t i o n r e a c t i o n w i l l be about as f a s t a s , or f a s t e r t h a n the a b s t r a c t i o n r e a c t i o n i n o the temperature range around 500 C . On the b a s i s o f these c a l c u l a t i o n s , t h e r e f o r e , the a d d i t i o n r e a c t i o n must be of importance f o r the mechanism o f the butene d e c o m p o s i t i o n , p r o v i d e d of course t h a t the subsequent d e c o m p o s i t i o n o f the u n s t a b l e a d d i t i o n p r o d u c t O ^ H ^ a l s o produces o t h e r s p e c i e s than the o r i g i n a l m e t h y l r a d i c a l s and 1 -butene . There i s an a lmost complete l a c k o f d i r e c t k i n e t i c d a t a on the p r o p e r t i e s o f the C^H r a d i c a l s . A l s o , s i n c e 5 11 the a d d i t i o n p r o d u c t s i n q u e s t i o n are formed w i t h an excess energy of the order o f 30 k c a l , t h e i r b e h a v i o u r c o u l d not be p r e d i c t e d from a s t u d y of the p r o p e r t i e s of r a d  i c a l s c o n t a i n i n g no excess e n e r g y . T h e r e f o r e , the d i s c u s s i o n must be l i m i t e d to o n l y one of the f a c t o r s d e t e r m i n i n g the p o s s i b l e d e c o m p o s i t i o n r e a c t i o n s of the C H r a d i c a l s , 5 11 - 127 - namely the bond d i s s o c i a t i o n energies involved i n the various possible modes of decomposition. The modes of decomposition, together with calculated bond d i s s o c i a t i o n energies of the ruptured bonds, are summarized i n Table XXXIV. The reactions l i s t e d do not include modes of de composition i n which the products formed indicate that a re-arrangement has taken place. For example, reactions of the type: CH -CH -CH-CH-CH CH -CH-CH + .CH -CH 3 2 - 2 3 3 2 2 3 were not considered. Although such reactions are possible, e s p e c i a l l y since the C^H^^ r a d i c a l carries excess energy, they appear to be less l i k e l y than the straight decomposit ion reactions considered i n Table XXXIV. The a c t i v a t i o n energy of a decomposition reaction Is equal to the bond d i s s o c i a t i o n energy of the bond ruptured plus the a c t i v a t i o n energy for the reverse reaction. Since i n a l l cases considered i n Table XXXIV the reverse reaction i s the simple addition of a r a d i c a l to the double bond of an o l e f i n , the ac t i v a t i o n energy of the reverse reaction can be expected to be i n the order of 3-6 kcal for a l l cases considered. Therefore, the bond d i s s o c i a t i o n energies given are a good measure of the ac t i v a t i o n energies for the decomposition reactions. - 128 - Table XXXIV Decomposition Reactions of the CVH . Radicals 5 11 Radical Decomposition Reaction Calculated Bond Dissociation Energy (la) CH3-CH2-CH-CH"2-CH3 (lb) "- (11a) CH -CH-CH--CH-d > d jj CH ( l i b ) (11c) CH -CH-CH-CH -CH + H 38 kcal 3 2 3 CH3-CH2-CH=CH2 + CH^. 25.5 CH =CL-CH„-CH + H 35 2 1 2 3 CH 3 CH2=CH-CH2-CH3+ CH^. 2k .5 CH2= CH-CH^ + CH^CH^ 23 The bond d i s s o c i a t i o n energies and standard heats of formation used f o r the computed res u l t s i n the table are l i s t e d below: D (H-H) D(CH3-H) D(C2H^-H) D(CQHc,.CH.C0H[r) 2 5 H 2 5 D(CH,..CH0.CH.CH0-H) CH, 10k kcal 103 " 98 " 9k » 97 " Currently accepted values A r b i t r a r i l y chosen plaus i b l e values, (see page 123) AHf methane " e thane " propylene " 1-butene " n-pentane " 2-methyl-butarte " 2-pentene - 1 7 . 9 kcal at 25 C - 2 0 . 2 k . 9 - 0 .03 -35 - 3 6 . 9 - 7 2-methyl-1-butene - 8.7 -129- The results in Table XXXIV show that reactions in volving, the elimination of a hydrogen atom require higher energy than those involving the elimination of an alkyl group. Thus, a prediction based on the activation energies only, indicates that reactions where the split t i n g of an alkyl group occurs will be faster. Reaction l i e is of particular interest, since i n this case, the alkyl rad i c a l formed is not methyl. Therefore, i f this reaction takes part i n the mechanism of the 1-butene decomposition, propylene and ethyl radicals should be formed. The ethyl radicals can be expected to react further, either forming ethane by hydrogen abstraction from unreacted butene, or decomposing to ethylene and hydrogen atoms. In the pyrolysis of 1-butene-k-d^, the corresponding reactions would be: CD • CH = CH-CH -CD CH -CH-CH -CD 3 2 2 3 -• 2 | 2 3 CH CD + CH=CH-CH2-CD CH D,CD • C H D 2 3 4 5 2 .CH -CD 2 3 CH 5CD • D 2 2 The above reactions can be used to explain the observed. - 1 3 0 - formation of propylene-d , ethane-d , ethane-d and 3 3 k ethylene-d 2 i n the pyrolysi s of the 1-butene-k-d^. Accord ing to the reaction sequence assumed above, the concen trations of the products should obey the equation: C 2H 3D 3 • C 2H 2D k • C 2H 2D 2/C 3H 3D 3 - 1 On examining the re s u l t s for any given experimental con ditions (Table XXVIII), i t i s found that the r a t i o f o r the concentrations considered i s not equal to 1 but close to 2.k on the average. Therefore, i t must be concluded either that the proposed mechanism i s not correct or that ethane- d 3 and -d^ and ethylene-d 2 also are formed by some other reactions. The second alternative i s considered more l i k e l y . On the basis of reaction ( l i e ) one should expect that i n the se n s i t i z e d decomposition of l-butene-k-d 3 the formation of CQR\. should be greatly accelerated: Hg(CH 3) 2 — Hg • 2CH3 CH, • CH~=CH-CHo-CD0 • CH0-CH-CH -CD - CH = CH-CH • CH CD„ 3 2 2 3 2 | 2 3 2 3 2 3 . CH 3 ( l i e ) This, i n fact, i s the case. The increase of the C form ation was found to be k 7-fold, second only to the increase of the CH^ formation (Table XXIX). The corresponding increase of the C H D and CpH D formation was only 11 to 3 3 3 2 1 2-fold. This r e s u l t can be explained i f i t i s assumed again that the deutero-ethane and deutero-ethylene are formed not only as a re s u l t of reaction ( l i e ) but also by some other reactions, and that these reactions do not - 1 3 1 - receive such a d i r e c t enhancement i n the sen s i t i z e d decomposition as does reaction ( l i e ) . Such reactions w i l l be discussed i n subsequent sections. The formation of non-deuterated butene i n the sen s i t i z e d decomposition of l-butene-k-d^(Table XXIX) can be explained on the basis of reaction (lb) of Table XXXIV. Hg(CH ) — Hg + 2CH 3 2 3 CH_ + CH = CH-CH -CD CH -CH -CH-CH -CD — ~ CH -CH -CH=CH + CD 3 2 2 3 3 2 2 3 3 2 2 (lb) Since the formation of non-deuterated butene was observed only i n the se n s i t i z e d decomposition i t i s almost c e r t a i n that t h i s product must have been formed by the proposed mech anism. I t i s i n t e r e s t i n g to note that 2.7% C, H was formed. 4 8 The non-deuterated butene together with CH^ (2.9%) are the two products formed i n by f a r the largest amounts i n the sen s i t i z e d reaction (Table XXIX). The results also indicate that reaction (lb) Is almost as fa s t as the hydrogen abstraction reaction by methyl r a d i c a l s ( 2 ) . CR\ + C. H D • CD + C H (lb) . 3 4 5 3 3 4 8 CH + C. H D„ CH, + C H D (2) 3 k $ 3 4 5 4 3 Besides explaining the formation of non-deuterated butene, reaction (lb) indicates the main source of CD^ ra d i c a l s i n the se n s i t i z e d decomposition. Thus, the i n  creased formation of CD3H and CD^ i n t h e s e n s i t i z e d reaction should be due l a r g e l y to hydrogen abstraction reactions of the CDo r a d i c a l s released by ( l b ) . -132- The possible occurrence of reaction (Ic) and the almost c e r t a i n occurrence of reaction (lb) are considered as strong evidence that at higher temperatures the addition of a free r a d i c a l to the double bond of an o l e f i n i s not in v a r i a b l y inactive for the mechanism: i . e . , the addition product does not exclusively decompose to y i e l d back the o r i g i n a l r a d i c a l and o l e f i n . The newly formed bond i n the addition might be retained and the addition product decompose with the s p l i t t i n g of a new bond leading to the formation of a new o l e f i n and a new r a d i c a l . Such disproportionation reactions might be of considerable importance i n mechanisms of the thermal decompo s i t i o n of o l e f i n s . REACTIONS OF THE FREE RADICALS STABILIZED BY ALLYL-TYPE  RESONANCE • It was noted e a r l i e r that as a r e s u l t of hydrogen 1 abstraction from 1-butene by free r a d i c a l s , four d i f f e r e n t C^H^. r a d i c a l s could be formed. These were: I II III IV CHP=CH-CH0-CH0 CH=CH-CH-CH- CH = C-CH_-CH_ CH=CH-CH - An approximate c a l c u l a t i o n indicated that about 10% of the abstraction reactions should lead to the formation of the resonance s t a b i l i z e d r a d i c a l I I . No evidence from the experimental r e s u l t s can be obtained f o r the formation of ra d i c a l s I I I and IV, while the formation of I was indicated by the presence of r e l a t i v e l y small amounts of CD, and -133- C 2 H 2 Dk f o u n d i n t h e l-^utene-k-d^ p y r o l y s i s . Since the rad i c a l s I, I I I , and IV are formed only with low p r o b a b i l i t y , the subsequent fate of these r a d i c a l s In the butene system w i l l not be considered further, on the assumption that the contribution of these reactions to the ove r a l l mechanism i s r e l a t i v e l y unimportant. The discussion w i l l be l i m i t e d to the possible fate of the resonance s t a b i l i z e d r a d i c a l GE^ CHj-CH-CH^ only. Since the a l l y l r a d i c a l formed i n the primary step of the 1-butene decomposition i s also a s t a b i l i z e d r a d i c a l , the reactions of these two free r a d i c a l s w i l l be treated together. Prom the several possible modes of decomposition of the two radic a l s the following reactions appear most l i k e l y : .CH = CH-CH-CH -CH=CH-CH=CH • H 2 3 2 2 CH2=CH-CH2 -CH2=C = CH 2* H The bond d i s s o c i a t i o n energies of the bonds ruptured i n the d i s s o c i a t i o n can be estimated from the heats of formation of the a l l y l and CH2=CH-CH-CH^ r a d i c a l quoted e a r l i e r . D(CH 2:CH.CH.CH 2-H)=AH£ 1,3 Butadiene +AH^ H -AHf CH2:CH.CH.CH3 = 2 6 . 3 + 5 2 - 2 6 kcal/mole = 52 .3 kcal/mole D(CH2.C.CH2) = AH° Allene + AH° H - AH° CH2:CH.CH2 H = k6 + 52 - 32 kcal/mole - 66 kcal/mole -134 - The a c t i v a t i o n energies f o r the decompositions considered above are equal to the bond d i s s o c i a t i o n energies plus the a c t i v a t i o n energies f o r the reverse reactions. The reverse reaction i n both cases i s the addition of a hy drogen atom to an unsaturated hydrocarbon, and therefore, of the order of a few kcals only. Thus, the bond d i s  s o c i a t i o n energies can be taken as good representatives of the a c t i v a t i o n energy f o r the decomposition. Since the frequency factors of the decomposition reactions are not known and can not be estimated, the rate constants can not be calculated. I t i s reasonable to assume that the reactions w i l l have frequency factors of the same order of magnitude. I f t h i s i s the case, the decomposition of the CR"2= CH-CH-CH^ r a d i c a l should be faster than that of the a l l y l r a d i c a l . Assuming that the frequency factors have a value i n the neighbourhood of 13 the "normal" value of 10 l / s e c , the decomposition of the Cj^H- r a d i c a l w i l l be s u f f i c i e n t l y f a s t to constitute one of the reactions by which the CE^CH-CH-CH^ r a d i c a l i s removed from the reaction system, while the decompos i t i o n of the a l l y l r a d i c a l w i l l be much too slow to re present any appreciable f r a c t i o n of the reactions of t h i s r a d i c a l . Part of the a l l y l r a d i c a l s w i l l be eliminated by hydrogen abstraction reactions leading to the formation of propylene. - 1 3 5 - Since both r a d i c a l s considered can be expected to be r e l a t i v e l y unreactive due to their high degree of s t a b i l i z a t i o n , i t i s reasonable to assume that t h e i r steady state concentration should be r e l a t i v e l y high. Therefore, chain terminations should occur by recomb in a t i o n reactions of the a l l y l and CH2=CH-CH-CH^ r a d i c a l : 2 CH2=CH-CH2. — G 6 H 1 Q 2 CH2= CH-CH-CH 3—~ CQ\I CHQ=CH-CH0. • CH=CH-CH-CH,—-C„IL n d d c. • } ( yd C y c l i z a t i o n and further dehydrogenation of the dimeriza- t i o n products could lead to the c y c l i c polymers i d e n t i f i e d . i n the experimental r e s u l t s . I t i s , therefore, of intere s t of e s t a b l i s h i f a l l , or at least an appreciable part, of the polymers found were formed as a re s u l t of the chain termination reactions considered above. Since the rate of primary decomposition of the 1-butene i s not known, only a very uncertain estimate can be made. Assuming that the a c t i v a t i o n energy f o r the primary step i s E-j= 6 l . £ kcal/mole and the frequency factor i s A^ = 10"*"3 l / s e c , the rate of primary decomposition can be calculated and com pared with the measured >amount of polymers formed. Some of the values obtained i n this way are given below. The amount of polymers formed afte r two minutes' reaction time i s found to be larger than would be expected I f the polymers were products of chain termination steps. This i s p a r t i c u l a r l y the case when i t i s considered that the - 1 3 6 - Table XXXV Ratios of Polymer Formation to Primary Decomposition of -the 1-Butene Temp. Reaction Calculated Polymers % Polymers °C " Time Primary Formed ^Primary De- (Minutes) Decomposition % composition 509 2 .5k 1.6 3 522 2 l . k 9 2.7 1.93 5k0 2 3.55 k . 9 1.38 55k 2 6.61 7 .7 1.16 calculated primary decomposition i s a maximum value i . e . the primary reaction i s , most probably, slower. (See Table XXXI). The gradual r e l a t i v e decrease i n the polymer formation with increase i n temperature i s probably due to the decomposition of the polymer intermediates at" the higher temperatures. It appears that some of the polymer formation re sulted from reactions other than free r a d i c a l recombination followed by c y c l i z a t i o n and dehydrogenation. Some Indication to the nature of these reactions i s given by the fa c t that the polymers formed i n largest amounts were i d e n t i f i e d as c y c l i c hydrocarbons: cyclopentene, cyclopentadiene, cyclohexadiene, benzene, toluene, etc. This suggests that reactions i n which c y c l i z  ation occurs, as a natural consequence are involved. Polymer i z a t i o n reactions i n which the intermediates have structures that are favourable f o r c y c l i z a t i o n are the addition react ions of the a l l y l and CH"2= CH-CH-CH^ r a d i c a l to unreacted - 137 - butene. For example, the following reactions are possible: .CH2-CH=CH-CH3 «- CH2=CH-CH2-CH3 • CH^CH-CHg-CH-j 0 H o CH-CH- CH j CH2-CH-CH2-CHo CHp-CH-CHp-CHo I 1 * OH, — I I CH 2 CH 3 CHo CH-CHo CH \ C H CHp-CH-CHo-CHo CHp-CH. 1 I \ D \ CH 2 CH CHp-CH + .CH2CH3 CH XCH J Cyclopentadiene + H and: CH2=CH-CH2. + CH2=CH-CH2-CH3-* CH2-CH-CH2-CH3 CH 2 ^H 2 CH | CHp-CH, • CHp-CH-CH^-CHo I II „ „ I I 2 3 CHp CH C 2H^. CHp CHp CH 2 ' . X C H etc. In the above reactions c y c l i z a t i o n occurs as an i n t r a  molecular addition reaction i n which the free r a d i c a l end adds to the double bond, both functional groups being on the same molecule. Some of the results from the mass balance (Table VIII) can be used as support f o r mechanisms of thi s type. The r a t i o of the t o t a l hydrogen contained i n the polymers plus the' molecular hydrogen (H2) to the t o t a l carbon contained i n the polymers for d i f f e r e n t experimental conditions i s - 138 - given belowi: Table XXXVI Ratios of Hydrogen Gas Plus Chemically Bound Hydrogen i n Polymers to Chemically Bound Carbon i n Polymers. Reaction Time Minutes H/C 509 509 522 522 540.6 540.6 2 5 2 5 2 1.33 1.33 1.24 1.44 1.43 1.36 1.38 1.37 2 5 I t i s found that the H/C r a t i o remains r e l a t i v e l y unaltered with the experimental conditions, the average r a t i o being about 1 .4 . Although the t o t a l hydrogen gas (H^) found i n the reaction mixtures i s included i n the above r a t i o s , the r a t i o s s t i l l f a l l f a r short of the H/C r a t i o of the reactant 1-butene, which i s equal to 2 . Since i t also was found that the H/C r a t i o of the t o t a l products was close to the t h e o r e t i c a l value 2 , i t follows that the low hydrogen content of the polymers i s not compensated for by H^ ,but by the saturated hydrocarbon products, mainly methane and ethane. This then indicates that the unsat urated polymers were formed (from the o r i g i n a l butene) by mechanisms i n which very l i t t l e molecular hydrogen was produced. Therefore, the formation of the polymers i s l i m i t e d to two types of reactions: either the (molecular) polymerization of some highly unsaturated products of the butene p y r o l y s i s , e.g. acetylene, allene, etc., or re actions of the type (8) and (9) where e f f e c t i v e -139- dehydrogenation of the c y c l i c polymer occurs mainly by the release of methyl and ethyl free r a d i c a l s . The f i r s t alternative must be considered as very u n l i k e l y since no acetylene or allene were found i n the products, even i n concentrations below 0.1%. The H/C r a t i o s for the products of several a p r i o r i possible reactions are given i n Table XXXVII. Table XXXVII Hydrogen to Carbon Ratios i n Polymer Products Resulting from Various Reactions H/C of ' Polymer Product a) CH^ CH 2 + CH2= CH-CH CH £ ^G(^E1o 1 .67 b) 2 CH2=CH-CH2. " " ^ ^ O 1 .67 c) CH = CH-CH-. + CH = CH-CH-OHr—C H 2 2 2 3 7 12 1.72 d) 2 CH 2 = CH—CH—CH^ — " " ^ 8^1k 1.75 e) CH=CH-CH0+ CH= CH-CH-CH — C,H + 2 2' 2 - 3 6 9 CH^ 1 .50 f) 2 CH2= CH-CH-CH^ ~~~ C 6 H 8 + 2CH 3 1.34 g) CH2= CH-CH2. + CH2= CH-CH2-CHyC^Hg * C 2H 5 1 .6 CH^ 1 .66 h) 0H2=CH-CH-CH3 * OH2=CH-0H2-OH3-06H • 2CH 3 1 . 5 — w CH + 3 C 2H 5l.k Prom the calculated H/C ra t i o s i t i s evident that only reactions e, f, g, and h come close to the experimentally found r a t i o , H/C= l . k . These res u l t s also suggest that the polymers were formed by a l l y l and CH2=CH-CH-CH^ ra d i c a l recombination reactions, and by reactions of the type ( 8 ) and ( 9 ) , and that i n both cases, free methyl, -lkO- and possibly ethyl r a d i c a l s were released by the polymer molecules. The assumed l i b e r a t i o n of free methyl and ethyl r a d i c a l s by the polymer intermediates also provides an explanation f o r the "induction" periods for the 1-butene decomposition and the formation of l i g h t hydrocarbons o observed at the lower temperatures — k90 to $10 C (Pig. 10 and 12a,). The induction period can be con sidered to be a r e s u l t of a gradual build-up of the concentration of polymer intermediates. Since the polymer intermediates react further, releasing free a l k y l r a d i c a l s , the rate of butene decomposition w i l l increase i n the induction period as the concentration of the polymer intermediates increases. PYROLYSIS OF 1, 5-HEXADIENE In the previous section i t was suggested that the resonance s t a b i l i z e d a l l y l and CH2=CH-CH-CH^ r a d i c a l , besides p a r t i c i p a t i n g i n chain termination reactions by ra d i c a l recombination, might be involved i n polymerization reactions with unreacted 1-butene, and also that i n the course of the e f f e c t i v e dehydrogenation of the polymers formed i n t h i s way, free a l k y l r a d i c a l s would be released. Since according to this view, the resonance s t a b i l i z e d r a d i c a l s are capable of p a r t i c i p a t i n g i n a number of com plex reactions, i t was thought of int e r e s t to examine the - l k l - p y rolysis of l , 5-hex adiene, ( d i - a l l y l ) . The d i s s o c i a t i o n energy of the central bond i n 1,5-hexadiene has been estimated to be around kO to kk kcal/mole: 20,29 D(CH2:CH.CH2-CH2.CH:CH2) = kO - 1+k kcal/mole. The weakness of the central bond suggests that the primary step i n the pyr o l y s i s should be the decomposition to free a l l y l r a d i c a l s : CH = CH-CH -CH -CH=GH - 2CH =CH-CHp. Indeed, the decomposition of 1,5-hexadiene to a l l y l r a d i c a l s has been observed d i r e c t l y , with the use of the 16 mass spectrometer. Lossing and co-workers detected a good y i e l d of a l l y l r a d i c a l s i n the pyrolysis of 1,5- o hexadiene at temperatures above 700 C. The high temper atures used are necessitated by the very short contact time of the flow system used by the authors and the r e l  a t i v e l y high concentrations of a l l y l r a d i c a l s required for t h e i r p o s i t i v e i d e n t i f i c a t i o n . I t appears reasonable o to assume that at 550 C, also, 1,5-hexadiene w i l l decompose by a free r a d i c a l mechanism involving theformation of free a l l y l r a d i c a l s i n the primary step. Therefore, the pyrolysis of 1,5-hexadiene can be used to obtain some indications of the reactions of a l l y l r a d i c a l s . For this purpose, an experiment was performed i n which 1,5-hexadiene at an i n i t i a l pressure of 100 mm. Hg was pyrolysed .at 550°C i n the same s t a t i c system as was used fo r the pyrolysi s of the butenes. The products formed -Ik2- afte r one minute reaction time are given i n Table XXXVTII. Table XXXVIII Products from the Pyrolysis of 1,5-Hexadiene . . o Temperature, 550 C — Reaction Time, 1 Minute I n i t i a l Pressure of 1,5-Hexadiene, 100 mm. Hg Composition of Reaction Mixture Volume % 1,5-Hexadiene 15 Cyclohexene 1 Benzene 10 Toluene 2 Cyclohexadiene k C 5 H 6 k Propylene kO Ethylene 10 Ethane 1 Methane 7 The reaction mixture was analysed d i r e c t l y on the mass spectrometer without previous f r a c t i o n a t i o n . Since some of the components (C^H^ and others i n smaller quantities) could not be i d e n t i f i e d , the computation of the mass spec trometric r e s u l t s was only approximate. The quantitative r e s u l t s given should be considered as in d i c a t i n g the order of magnitude only. The analysis did not include a determination of the amount of hydrogen formed. A comparison of the results f o r 1,5-hexadiene with the r e s u l t s of the 1-butene pyrolys i s at 550°C shows that the ov e r a l l decomposition of 1,5-hexadiene i s much faster than that of the 1-butene. The large number of products observed i n the reaction mixture of the 1,-5-hexadiene pyrolysis indicates that the a l l y l r a d i c a l s produced i n the primary -143- step induce a number of secondary reactions. The mech anism appears to be complex. Some of the reactions can be suggested by analogy with the observations from the butene system. For example, the formation of propylene and benzene can be explained on the basis of the reactionss (CH2=CH-CH2-)2-~ 2 CH2* CH-CH . CHP= CH-CH?. + CH— CH-CH2-CH0-CH=CH — - CH = CH-CH + 2 d* d d d 2 2 3 CHp=CH-CH-CH -CHfCH CH = CH-CH-CHP- CH=CHp—* CHp-CH*CH,,-CH -CH=CH * CH CH CH II I CH CH X C H £ 2 Benzene * H^ 1,3-Cyclohexadiene + H With regard to the 1-butene system, the following conclusions can be drawn from the 1,5 hexadiene pyrolysis o experiment. At temperatures around 550 C and a pressure of the reactant gas of 100 mm. Hg, a l l y l r a d i c a l s can engage i n a number of complex reactions, leading to the formation of l i g h t hydrocarbons and unsaturated C^, C^ and C hydrocarbons mainly of c y c l i c nature. The CH2=CH-CH-CH3 r a d i c a l presumably can undergo analogous reactions. These conclusions are i n agreement with the reactions proposed i n the previous section. ADDITION REACTIONS OF HYDROGEN ATOMS It was suggested i n the previous sections that several -lkk- reactions could lead to the formation of hydrogen atoms. These were: C H ^ C I ^ — GH 2=CH 2+H (£) CH2= CH-CH-CH3 — - CHp= GH-CH=CH2+ H (6) CH = CH-CH-CH • CH = CH-CH=CH + H (7) 2 2 2 2 2 CH= CH-CH + 1-Butene —• C y c l i c unsaturated 2 - 2 hydrocarbon+ A l k y l r a d i c a l s + H (8) CH = CH-CH-CH + 1-Butene—Cyclic unsaturated -> hydrocarbon + A l k y l r a d i c a l s • H ' ( 9 ) The hydrogen atoms produced by these reactions could react with the 1-butene according to the scheme: H + CH = CH-CH -CH — * CH -CH-CH -CH — — J CH -CH=CH + CH 2 2 3 - £ 2 2 3 3 2 3 (10) H + CH = CH-CH2-CH — * CH2-CH-CH2-CH3 CE= CH^ C^-CH (11) 3 JJ 3 H + CH2= CH-CH2-CH 2 CH2= CH-CH-CH^ + H 2 (12) In the corresponding reactions of l-butene-k-d^, deuterium atoms w i l l be involved also. These should originate mainly from reactions (5) and ( 6 ) . Reaction (10) i n this case should lead to CD., rad i c a l s and CH D-CH=CH . 3 2 2 - The deutero-propylenes i s o l a t e d from the reaction mix tures of the 1-butene-k-d py r o l y s i s contained con- 3 siderable amounts of monodeutero-propylene (up to 60% of the t o t a l propylene at the low temperatures, f a l l i n g o f f to 30$ at the highest temperature). The observed formation of monodeutero-propylene thus suggests the possiblr occurrence of reaction (10). It should be mentioned here that the mass spectrometric analysis of -111-5- the molecular hydrogen obtained as a reaction product from the pyrolysis of the 1-butene-k-d^ revealed the presence of varying amounts of HD besides the R^. A quantitative estimate could not be made, due to the lack of gas standards (pure HD and D^). Support for the occurrence of disproportionation reactions of the type suggested (10) can be found i n a study of simi l a r systems. In an investigation of the 29,31 p y r o l y s i s of propylene, Szwarc found as major products of the reaction, methane and hydrogen, which were roughly i n the r a t i o , 2:1. Other products formed i n r e l a t i v e l y large concentrations were ethylene and allene. Assuming that the primary process i n the propylene decomposition i s the formation of hydrogen atoms and a l l y l r a d i c a l s , Szwarc explained the formation of methane according to the following reaction sequence: CH2= CH-CH^ — - CH2=CH-CH2.+ H ( l ) H+CH2=CH-CH3 — - H 2 + CH2= CH-CH2 (2) H+GH2=CH-CH3 — - CH2=CH2+ CH . (3) CH 3 # + CH2= CH-CH3 CHk+ CH2= CH-CH2. (k) Reaction (3) i s analogous to reaction (10) which i s assumed to pa r t i c i p a t e i n the 1-butene p y r o l y s i s . The two alternative mechanisms f o r the formation of methane are: a d i r e c t molecular decomposition of the propylene to methane and acetylene, or the dir e c t primary s p l i t of the propylene to v i n y l and methyl r a d i c a l s , followed by reaction ( k ) . The molecular decomposition to methane and acetylene appears improbable since the general -146- evidence presented by Szwarc strongly supports a free r a d i c a l mechanism. Also, the formation of methyl r a d i c a l s by a primary s p l i t of the propylene molecule could not account for a l l the methane formed, since reaction (1) should be considerably faster than (5) : C H 2 = C H - C H - — - C H 2 = C H - C H 2 . + H (1) CE£ C H - C H ^ • C H 2 = C H . + C H . (5) Another example for the occurrence of a reaction analogous to reaction (10) i s found i n the pyrolysis of toluene: H + C 6 H 5 - C H 3 — C 6 V C H 3 . The above reaction was proposed o r i g i n a l l y by Leigh 14 and Szwarc, i n an attempt to account f o r the observed formation of methane, and confirmed l a t e r by Blades 2 and Steacie. On the basis of the evidence quoted, i t seems j u s t i f i a b l e to assume that hydrogen atoms can i n i t i a t e disproportionation reactions of the discussed type and w i l l generally do so i n systems containing propylene, butene or other higher o l e f i n s . The occurrence of disproportionation reactions i n the butene system w i l l depend on the concentration of hydrogen or deuterium atoms. The r a t i o s of monodeutero- propylene to t o t a l molecular hydrogen (H2+HD+D,-)) formed under d i f f e r e n t experimental conditions i n the pyrolysis of l-butene -4-cL are^given'"'below. -147- T a b l e X X X I X R a t i o o f C-H_J) t o T o t a l M o l e c u l a r H y d r o g e n 3 P R e a c t i o n T e m p . R e a c t i o n T i m e c->HrrD °C M i n . 3 5 T o t a l M o l e c u l a r H y d r o g e n 522 2 12 540 2 7.6 554 2 7.1 I f i t i s a s s u m e d t h a t a l l o f t h e m o n o d e u t e r o - p r o p y l e n e was f o r m e d b y t h e d i s p r o p o r t i o n a t i o n r e a c t i o n (10) i n w h i c h d e u t e r i u m a toms w e r e i n v o l v e d , t h e r a t i o s o b t a i n e d w o u l d i n d i c a t e t h a t r e a c t i o n (10) i s m o r e t h a n s e v e n t i m e s f a s t e r t h a n t h e a b s t r a c t i o n r e a c t i o n (12): D ' + C H = C H - C H - C D , — r , CH D - C H = C H + CD (10) 2 2 3 1 2 2 3 D + CH = C H - C H - C D » HD + C , , H , , D , (12) 2 2 3 H- 4- J A l t h o u g h t h e r e l a t i v e r a t e s o f r e a c t i o n s (10) a n d (12) c a n n o t be p r e d i c t e d w i t h a n y c e r t a i n t y o n t h e o r e t i c a l g r o u n d s o r f r o m i n f o r m a t i o n a v a i l a b l e i n t h e l i t e r a t u r e , i t a p p e a r s t h a t t h e d i f f e r e n c e o f t h e r e l a t i v e r a t e s o b  t a i n e d i s . e x c e s s i v e . F o r e x a m p l e , S z w a r c ' s r e s u l t s f r o m t h e p y o p y l e n e p y r o l y s i s , t o g e t h e r w i t h t h e i n t e r p r e t a t i o n r e p r e s e n t e d b y r e a c t i o n s (1) t o ( 4 ) » g i v e t h e r e s u l t t h a t t h e d i s p r o p o r t i o n a t i o n r e a c t i o n i s o n l y a b o u t t w i c e as f a s t as t h e a b s t r a c t i o n r e a c t i o n f o r t h e p r o p y l e n e s y s t e m , The d i s p r o p o r t i o n a t i o n r e a c t i o n (10) i s d i f f i c u l t t o r e c o n c i l e w i t h t h e l a r g e d i f f e r e n c e i n t h e r a t e s o f f o r m a t i o n o f m o n o d e u t e r o - p r o p y l e n e a n d t o t a l h y d r o g e n . -Ik8- Therefore, although such a reaction seems very probable, the experimental evidence i n the present work i s not s u f f i c i e n t to e s t a b l i s h i t s p a r t i c i p a t i o n with cer t a i n t y . MECHANISM OF THE THERMAL DE- .COMPOSITION OF 1-BUTENE AND 1-BUTENE-k-d^ The reactions discussed i n the previous sections are summarized i n a mechanism; for the decomposition of 1-butene-k-d^ given on the next page. The proposed mechanism has several important c h a r a c t e r i s t i c s . The thermal decomposition i s assumed to proceed by a com plex free r a d i c a l mechanism. The i n i t i a t i n g reaction i s considered to be the primary decomposition of the butene to methyl and a l l y l r a d i c a l s . There are no long chains, but the secondary reactions are numerous. Methyl r a d i c a l s are generated by several reactions: the primary decomposition ( l ) , the release of methyl rad i c a l s i n the e f f e c t i v e dehydrogenation of the polymers (8) and ( 9 ) , and the reaction of the hydrogen atoms with 1-butene (10). Ethyl r a d i c a l s are generated by the methyl r a d i c a l disproportionation reaction with 1-butene (3)> the release of ethyl r a d i c a l s i n the e f f e c t i v e dehydrogenation of the polymers (8) and ( 9 ) , and the hydrogen atom disproportionation reaction with 1-butene (11). F i n a l l y , hydrogen atoms are generated -> by the unimolecular decomposition of the ethyl r a d i c a l s -149- CH2=CH-CH2-CD3 —-CH2=CH-CH2.+ CD^ (1) CD-. + Butene-d, —-CHD + C. H, D . (2) 3 3 *3 4 4 3 CD^. + Butene-d 3 : — ~ ° \ * C l i E ^ 2 CD^.* Butene-d^ — ~ C V ^ . + (3) CD-CH.+ Butene-d —«• CH_CD • C. H. D . (4) 3 2 3 3 3 4 4 3 CD,-CH . * Butene-d_ —-CH DCD + C H D . (4a) 3 2 3 2 3 4 5.2 CD 3CH 2. —-CH 2CD 2 • D (5) CH = CH-CH-CD, — - CH0= CH-CH=CD + D (6) 2 * 3 2 2 CH=CH-CH -CD . — CH = CH-CH=CD + H (6a) 2 2 2 2 2 CHQ=CH-CH0.* Butene-d —*CH 0= CH-CH + C.H.D.,. (7) 2 2 3 . 2 3 4 4 3 CH=CH-CH0.+ Butene-d 0 — - CH 0?CH,CH„D + C. H .D . (7a) 2 2 3 d 2 4 5 2 - CH?= CH-CH„.+ Butene-d — - A d d i t i o n Product — * Cyc l i c ^ d 3 or C, Hydro carbon • CH,. and/ or CD3-CH2.-:5 (8) CH = CH-CH-CD • Butene-d — - A d d i t i o n Product — - Cyc l i c d ' .3 , j or C, Hydro carbon + CH . and/or CD .CH^ 3 (9) D + Butene-dj—-CH 2D-CH=CH 2 + CD^. (10) H + Butene-d^—-CH^-CHsCHg + CD3. (10a) D • B u t e n e - d 3 — - CH2= CHD • .CH2-CD3 (11) H + Butene-d^—-CH 2=CH 2 + '.CHg-CD^ (11a) D + Butene-d,—-DH + C. H. D . (12) 3 4 4 3 H + Butene-d 3—-H 2 + C^H^D^, (12a) 2 CH 2 3CH-CH 2.—"C 6H 1 Q (13) .—Polymers (14) GH2=CH-CH2.+ CH2= CH-CH-CH3 — C i \ Z 2 CH= CH-CH-CH,. —-C.H . d 3 6 14 -150- ( 5 ) » the unimolecular decomposition of CH = CH-CH-CH,. 2 • 3 and CH2= CH-CH2-CH2. ra d i c a l s (6), and possibly, the dehydrogenation of the polymers. Chain termination i s assumed to occur by the recom bination of the resonance s t a b i l i z e d a l l y l and CH"2 CH-CH-CH^ r a d i c a l s . A very large number of reactions has been included. The large number of reaction products and the deuterium d i s t r i b u t i o n i n the products can be explained only on the basis of a complex mechanism. Since the majority of the experimental re s u l t s were obtained from pyrolysis ex periments i n which considerably more than 1 or 2% of the butene was decomposed, i t can be argued that the complex i t y of the reaction products i s l a r g e l y due to secondary reactions involving the reaction products themselves. While t h i s might be the case f o r these experiments, i t should be noted that the reaction mixtures obtained from experiments i n which only 1 or 2% of the o r i g i n a l butene was decomposed showed the same large number of products, and the deutero-isomers i n the products were equally numerous. The decomposition of the butene, therefore, i s c e r t a i n l y a complex reaction under the present conditions. The large number of proposed reactions therefore seems j u s t i f i e d . The reactions (1) to (15) were chosen on the basis of the discussion given i n the previous sections. The arguments used were based mainly on a qu a l i t a t i v e examination of the experimental r e s u l t s . Semi-quantitative or quantitative - 1 5 1 - support could be given for only some of the proposed reactions. Thus, the proposed mechanism requires further quantitative confirmation. Unfortunately, great d i f f i c u l t i e s are encountered i n an attempt to v e r i f y the mechanism further. Some of these d i f f i c u l t - ies should be mentioned. The most useful procedure for the v e r i f i c a t i o n of a proposed mechanism with the ex perimental r e s u l t s i s to compare the rates of formation of the products as a function of reaction time and temperature. Generally, the r e l a t i v e rates of formation for the reaction time t — - o are e s p e c i a l l y s i g n i f i c a n t . The mechanism then can be v e r i f i e d by observing constant re l a t i o n s between the rates of formation of given comp ounds i n accordance with the predictions of the mechan ism. The use of th i s procedure for the system i n question i s made very d i f f i c u l t by the large number of products to be considered. The numerous reactions are so i n t e r  connected that a high uniform accuracy i n the quantitative determinations of v i r t u a l l y a l l products, including the polymers, i s required. Such accuracy cannot be ex pected considering the complex nature of the analyses. Moreover, i n most of the rel a t i o n s the rates of formation of p a r t i c u l a r deutero-isomers should be considered. However, i t was noted e a r l i e r that the quantitative determinations of some of the deutero-isomers were only approximate. - 152 - Some of the results from the quantitative analyses of the deuterium isomers which undoubtedly were accurate also have not been explained. For example, i t was found that the deutero-methanes from the l-butene-k-d^ con tained CHD^ and Cp^Dg i n the r a t i o : CHD^/CHgDg = 3 (from Table XX) Roughly the same r e s u l t was found for the deutero-ethanes: C 2HgP 3/C 2H kD 2= 3 (from Table XXII) Since the 1-butene-k-d^ was found to contain i n i t i a l l y only 10% of bi-deuterated product (l-butene-k-d 2), the above r a t i o s should have been expected to be not equal to 3 , but equal to 10. The reason for the discrepancy i s not understood. The d i f f i c u l t i e s outlined above apply equally when attempts are made to interpret some of the k i n e t i c con stants obtained from the 1-butene p y r o l y s i s . The over a l l a c t i v a t i o n energy of the butene decomposition was determined as well as the ac t i v a t i o n energies f o r the formation of the l i g h t hydrocarbons. I f a steady state treatment could be applied to the proposed reaction mechanism, some k i n e t i c significance possibly could be given to such r e s u l t s . However, the reactions assumed to p a r t i c i p a t e i n the mechanism are too numerous. Attempts to express even the essential features of the mechanism were not successful. Even i f a steady state treatment - 1 5 3 - could be derived on the basis of the proposed mechanism, i t i s questionable whether the experimentally obtained figures for the a c t i v a t i o n energies, etc., should be associated with the derived expressions. Thus, the general r e s u l t s c l e a r l y indicate that some of the "primary" products formed i n the decomposition are very reactive and p a r t i c i p a t e further i n the reactions. The e f f e c t of these products should be small at low temperatures and short reaction times since under such conditions t h e i r concentration i s too low and s t i l l i n the process of being b u i l t up. The induction period observed i n the butene decomposition (Fig. 10) i s an i n d i c a t i o n of such a process. At higher temperatures the e f f e c t of subsequent reactions of such products should be noticeable very soon; even during the f i r s t minute i n t e r v a l . Thus a change of k i n e t i c pattern can be expected to take place for the d i f f e r e n t reaction temperatures influencing the composition of the reaction mixtures obtained even afte r the shortest sampling time (1 minute). To allow for such changes i n a mathematical treatment would be a formidable task. . . . In view of the d i f f i c u l t i e s outlined above i t seems that additional quantitative support for the proposed mechanism w i l l be very d i f f i c u l t to obtain. Therefore, the reactions proposed represent, at best, a plausible mechanism fo r the complex decomposition of the 1-butene, providing a general q u a l i t a t i v e picture of the processes involved. -154- SIGNIFICANCE OF SOME OF THE FINDINGS  AND SUGGESTIONS FOR FURTHER EXPERIMENTAL WORK The mechanism proposed to account f o r the major reactions of the 1-butene decomposition makes extensive use of two types of reactions, both involving free r a d i c a l s and 1-butene. These are: the abstraction of hydrogen from the butene by free r a d i c a l s and the addition of free r a d i c a l s to the double bond of the butene followed by rapid decomposition of the addition product. The l a t t e r r eaction r e s u l t s i n disproportion ation when the addition product decomposes to form prod ucts d i f f e r e n t from the i n i t i a l r a d i c a l and 1-butene. It was shown that at least q u a l i t a t i v e l y , a large number of reaction products observed can be explained on the basis of the addition-disproportionation reaction which should be c h a r a c t e r i s t i c of o l e f i n i c compounds. It must be mentioned that while the addition of free a l k y l r a d i c a l s , e s p e c i a l l y the methyl r a d i c a l , to unsaturated hydro carbons has been subject to considerable study at low temperatures (below 300°C), mechanisms involving addition products as intermediates have been considered to be of importance at higher temperatures only r a r e l y . Since the occurrence of such reactions i s strongly supported by the r e s u l t s of the present investigation, a complete proof for the extensive p a r t i c i p a t i o n of such reactions i n the mechanism of o l e f i n decomposition c e r t a i n l y seems - 1 5 5 - .worthwhile. In this way, a class of reactions of seemingly great importance that hitherto has found l i t t l e consideration w i l l be established. The following r e l a t i v e l y simple experiments are suggested as a means for obtaining additional ex perimental evidence. In the mercury-dimethyl s e n s i t i z e d decomposition of 1-butene-k-d^, It was found that aside from the greatly increased formation of CH and CH D, or i g i n a t - k 3 ing presumably by the reactions: H g ( C H 3 ) 2 — Hg + 2 CH3. - CH + C H D CH . + CH = CH-CH-CD k k ^ 3- 3 ^ 1 3 CH,D + C, HJD . j> k p 2 the formation of non-deuterated propylene also had received a great acceleration. This was explained by the reaction: CH + CH = CH-CH-CD CH -CH-CH-CD - CH = CH-CH + CD -CH . 3 2 . 2 3 ' 2 6H > 3 2 3 3 2 This reaction also was suggested b^y the formation of propylene-d 3 i n the normal (non-sensitized) decomposition of the 1-butene-k-d : 3 CD„ + CH = CH-CH -CD — - CH -CH-CH -CD —-CH=CH-CD • .CH CD . 3 2 .2 .3 ' 2 6D 2 3 2 3 2 3 The possible occurrence of t h i s reaction could be i n  vestigated e a s i l y i f the HgtCD.^)^ se n s i t i z e d pyrolysis of CH= CH-CH -CH were studied. According to the above 2 2 3 assumed reactions, the formation of propylene-d^ should be -156- observed. The suggested experiment also should lead to the formation of CTL..CH -CH=CH i n analogy with the 3 2 2 observed formation of CRV= CH-CH-CH. i n the Hg(CH ) 2 2 3 3 2 s e n s i t i z e d reaction of the l-Butene-k-d^ for which the reaction, C H CH.,. + CH =CH-CH0-CD CH -CH-CH -CD CH -CH - CH=CH + CD . 3 2 2 3 2 2 3 3 2 2 3 was assumed. Thus, the HgCCD^)^ sen s i t i z e d decomposition of the CH2= CH-CH^-CH^ should provide a d e f i n i t e answer , • regarding the reactions described above and possibly provide clues for some of the remaining reactions. Since Hg(CD 3) 2 i s now r e a d i l y available commercially, the ex periment seems e a s i l y f e a s i b l e , and involves only a dup l i c a t i o n of the a n a l y t i c a l techniques already used. A q u a l i t a t i v e study of the suggested mechanism leading to the c y c l i c polymers could be made i f the pyrolysi s of 1-butene or 1-butene-k-d i n the presence of small amounts 3 2k of 1,5-hexadiene or mercury-diallyl were studied. At temperatures around k90°C where the normal decomposition of the butene i s very slow, the mentioned s e n s i t i z e r s should decompose appreciably under formation of a l l y l r a d i c a l s . The increased supply of a l l y l r a d i c a l s should lead to increased formation of the c y c l i c hydrocarbons such as cyclopentadiene and cyclohexadiene, with a simultaneous increase i n the rate of butene decomposition. I f 1-butene- k-d-j i s used, a simultaneous increase of the CHD^ and CH^.CD^ formation also should be observed, i n accordance - 157 - with the proposed reactions (8) and (9). A further extension of the in v e s t i g a t i o n by means of further refinement of the accuracy of the a n a l y t i c a l techniques does not seem worthwhile. The complex be haviour of the system under the conditions studied most probably would defeat any attempts for the derivation of s i g n i f i c a n t k i n e t i c constants such as pre-exponential-. factors and a c t i v a t i o n energies of the elementary re actions involved. It i s c e r t a i n that the reaction could be studied under conditions for which the mechanism i s less complex. For example, the use of a flow system operated at very low percentages of t o t a l decomposition would be more suited for a further study of the butene p y r o l y s i s , e s p e c i a l l y with the help of gas chromatographic a n a l y t i c a l techniques. PYROLYSIS OF 1-BUTENE IN THE PRESENCE OF.DEUTERIUM The formation of methane i n the pyrolysis of 1- butene i n the presence of deuterium has been studied 5 recently by Danby, S p a l l , Stubbs and Hinshelwood. Vary ing i n i t i a l amounts of 1-butene were decomposed i n the o presence of D^ at 5&0 C. The i n i t i a l pressure of 1- butene was varied from 3 to 100 mm. Hg, while the i n i t i a l pressure of the deuterium was kept constant at 100 ram. Hg i n a l l experiments. The methane formed after k -158- minutes reaction time was separated and analysed f o r deuterium content on the mass spectrometer. The methane was found to contain, besides CH^, varying amounts of CH D. A plot of the res u l t s obtained by 3 Danby and co-workers i s reproduced i n F i g . 22. A gradual decrease of the CH D/CH r a t i o with increase ; 3 / k of the i n i t i a l concentration of the 1-butene i s a prominent feature i n the r e s u l t s . The authors assumed that at 560°C, the temperature of t h e i r experiment, 1-butene decomposes by a molecular mechanism. The assumption was based mainly on the fact that n i t r i c oxide has no i n h i b i t i n g e f f e c t on the 1-butene de- 21 composition, (Molera and Stubbs) . The isotopic mixing, i . e . the CH^D formed, was assumed to occur without the p a r t i c i p a t i o n of free methyl r a d i c a l s i n the reaction. Therefore, as Danby and co-workers point out, the assump- 23, 35 t i o n i n sim i l a r investigations that isotopic mixing i s an i n d i c a t i o n f o r the p a r t i c i p a t i o n of free r a d i c a l s i n the reaction, i s open to doubt. However, since the r e s u l t s of the present invest i g a t i o n strongly favour a free r a d i c a l mechanism, i t i s pertinent to show that the r e s u l t s obtained by Danby and co-workers can be interpreted on the basis of free r a d i c a l reactions. A clue f o r the p a r t i c i p a t i o n of methyl r a d i c a l s i n the 1-butene decomposition i n the presence of deuterium as studied by Danby and co-workers i s the observed gradual decreas.e of CH D/CH with increase 3 k lii: \ \ \ : i:~:. .... . , iiii! -tliit l l l i ! 4 4 i i E 1 exp. -Kfin: lit;: .... ii.j.; IT:: : : : T 14'4 4 4 -i:t"r: .44 :iXi'4'- 4444- . . . 4144 aii Iiii .Iiii F i P ,:.:•:: ail- i l l .. .*: •' c ::.:: 444: IS -• • • • 1144 44 Iii i!;li :;ai: : : : . ; • ; • : • : : .. 4444 H; i iii 4:I4:|: 8 j !T| i i i .Iii.:: ["LI:!: S H I 444:4 / 444 4 4444 441441 - TIT!' j • T f : I T L !nt.i : 44444 4444: 4444: 444: 4 4 t i n 1- : • J ill: 4 : : ; . : : " • • ] - i j : : i Iii:!' T ; i ; ' in::! 4!::ii : : : : : .;•;:!:! iiiiii. !!4!!4i. "IT""' 4444 Iiiiii! 6 .frit .j.j.p. H i i :!:::: '.;T:"i •Hi; ! ! ! ! : / ! ! ilil .:.U.|. •;•:•; :. 4444 ! n ! 44: ai.i! 44 iTH.:: :Hrl: Iiii 4!!! iiii 1144: .:•• Iiii. Ilji Iiii! 1 f IE 144 1 4 ;•*• JTfl. 'tf.i i lilt ::!1 i: .i.f-L. li4 ' S i iiiiii- •|t:;:; T44 Iii] ' i44i 1444 I|!!I 4 iii 4.4. !04i! 4444 44- 4 SHi .1:4: 1 :-l: ... . - •r—r- :.i::: •••it;. :;:;:::: : : ; T III!!!!!! Ijij- 444!!! lililpl 4::! :|:!.i :. :'/4i44!;: •IT f! 41 iiiri .1:1:!:! •iti-j' -ill: :.-:: 111: T;::;- 4 4 : : : : ! : : : : : : : : i : : : : C H 3 D < sale . . . . 1 . . . . - H T - li-j'-l •44 : : : 44 4 4 4 4 J44 -ii-x" - i~T — I—- I:—;!"~ BX '; iZl 42 iiiil '! Iii. / ,„ - - •iii! 4:4 44 4"' :::.:!:::::.: r • l4il it;;: 4;'Hr iiit 4!TJf iiii iiii •:::tr: i l l • • • • 1 : ! ! ! ji;:r 444:1' ::r:x "Pr!T aa 4 4 it 441! 4 44] 4 4 44 4 4 ' ' JTS - lljf If 111 ilil :i:i Iiii -j.i M. :i!i.!4 : -i4 :!:: ! i : : : : i : : : - i i i i l - " : ' : : : : :::t:::; _ •_• 1 — J::!::: i i i : : ! : : ! : : ! : - 4-144- III! 2 0 4 0 :::: i:::: ::::;::.£ i O — 444 44? 10 : : : : ; : : : : 1( t^ n 1 smi Hi :::: j. :: T I ... . . . . — - l l l l l i T i ! 1 It 144 IIIIITI; 44-4-44-4 i l l 41!!!! ! ! ! : TTTi : : : : 444 : ! : i i!:;! i i ! : ! : : ! ! ::::{:::: U -1 : : : : 444;- . 1 . . . . : : : : CH • • ::::; ~v. . . . . . . . . . . . . ^ . . . . : : : : — 1 — : : : : ; : : : : : : : : . . . . ; 1 "( (CH 4 :.: • ) . . . III ....... !! • ! ! : ! ! : — j — : : : : ! : : : : ::::(:::: 44 4 4 j4'r4 •44 4444-TiTifiiiT — i . : .(Jj L /* ( iiiiii r t ^ i i i — 1 — 4-41-4444 . . . . 1 . . . 4 _ ,...V44: -: | v4; "!"'.::'~ '•' 11'. • • • - . - - • • - • • • ! • • • • ::."{:::: T : . . 1.... -r : : : : :i::l:!!! i-rrriTii-r ; : : : ! : : : : •444 ! 1 \!!!!!! P...1.UI • • • • i ^J-0 • .4  Li-!.i_i.i : : : : ; : : : : ':A\A\ |S:4 4-4-4 4-444 : ; : . : . . ; . . : : : : ! : : : : 44!!.j44;_ liljili! I P i r t p 4 ::::i:::: . . . 1. . . . 4-444 i i4 44 : : : : ; : : : : ... I 4rii'i4i44 . . . . 1 . . . . .... j ... . 4i44 4 4:4 . . . i . . . . 4 i 4 • ' . 2 \ ; ! ! : ! j ! : : : 44|44 : : ! : ! ! ! ! ! | ! :!:l:::: ill 4444- l l 4T4[7-H . . . : . . . . \ \ \ :::4.:rii" . . . , | . : i . I::!::!! i i i i ! ! ! ! i i ! : ! ! : : : : : ; : : : m l!!i 4444. : : : : . . . . 1 . . . . . . . . . 444 44 44 . . . . : : . : I • • • • 144 44-44144 : : : : | x * 1 ! ! ! : ' ! ! ! : •:::i!::i ' : : : l : : : : lllljli:: ! : ! ! . . . . 4 4 4 1 44 4 4 -•. i i u . . . . . . : " 1:. 44 41 i ? n 44 0 u% Q i ! T r i e 0 1 r NT r l i f l Ifi- TTr 4:4j:i4li i: i 1 i!ir 141 14! fr fit V: • :!.•::.: 1 c 4 .u.:C !-f : t- o f Iu1 , fir tin •f. : i: i i : : ; i 4;l 4!i - m lllj mi 44 iii! iji! • ill :H 11 Ilil •Tij' 1 ].. ;4-t'tf I'M A iii! IH m S. ^ Eo up i!3 on i i i o f th 4 Ca 4ii)l 4iP m » 'Si •mis 4t3 or 1 C » f 4 44-1-!-4+4 ! : ; ! _L:.j.L WW |la en id ee G 0 H 4 f Iii m n th eli s i ^ i ^ o f i i m -er le- i i i  ir P Iiii iiii 0 m -iii 2li: wi i # M Lte .10 iii: 01 •itj Llr ie;< 144 ill! «s fell jDfci lil> fea an d w kit ! !!il iiii iiiiii :n:i.i. iiii -j-i.j.. !';-t I iiii: -160- of the i n i t i a l concentration of the pyrolysed 1-butene. This r e s u l t can be interpreted on the basis of the two competing reactions: C H 3 + D 2 C H 3 D + D k D C H 3 * C k H 8 — CH k 4 C kH ? k B I f the methyl r a d i c a l production i s assumed to be proportion a l to the butene concentration, the following equations can be written: d(CH,D) , " x (where=(B) = concentration of 1-butene) d(CHo) " 3 = k x(B) - k B(CH 3)(B) - k D(CH 3)(D 2) Assuming a steady state one obtains: '(CH,) - k l ( B ) a r i d : k B(B) • k D(D 2) d(CH3D) k^iB) (B2) dt = K B(B) + k D(D 2) d(CH k) _ k g ^ C B ) 2 dt " kg(B) + k D(D 2) If s u b s t i t u t i o n !^ B _ i s m a d f e . 1 _ P dt " (B) + 1 ( D 2 ) d(CH3D) k 1 ( B ) ( D 2 ) i d(CH k) _ k-^B) P 2 dt ~ (B) • 1(D 2) II -161- The ra t i o s of CH^D/CH^ f o r the i n i t i a l stages of the reaction i n function of various i n i t i a l concentrat ions of the 1-butene can be obtained from equations I and I I i f a plausible value for p i s assumed. A value for k /k - p can be estimated with the use of known B D data f o r the abstraction of hydrogen atoms from 1-butene and deuterium by methyl r a d i c a l s . For the abstraction 3k from butene, Trotman-Dickenson and Steacie give: klg/k^ x 1 0 1 3 = 210 cc.^ molecules"^ s e c . " at 253°C and E = 7.6 kcal/mole B where k refers to the methyl r a d i c a l re-combination to 37 ethane. For the abstraction from D^, Whittle and Steacie give: k y / k ^ = kk . 9 cc.^ molecules'"^ sec. for 290°C and ED = 1 1 * ^ kcal/mole Since E^ = 0, the above data can be used for a c a l c u l a t i o n of k B / k D at 560°C. The r e s u l t obtained i s : k B / k D = 2.5 at 560°C Of course, the r e s u l t i s only approximate. Since the kg obtained represents i n essence only abstraction of a l l y l i c hydrogen atoms from the 1-butene, the value for kg should be corrected upwards by a factor of at lea s t l . k . (See calculations of k on pagel20). Thus, the B c a l c u l a t i o n leads to a value f o r p i n the order of: P = k B/ kD = k The value p = 5 was Used i n the subsequent c a l c u l a t i o n s . -162- Substituting into equations 1 and 11 the values: p = 5, = 100 mm. Hg, and varying i n i t i a l pressures for B , values f o r the r a t i o of the i n i t i a l rates, r (CH^D) /r(CH^) i n function of the i n i t i a l concentration of the butene were obtained. These values are plotted i n P i g . 20(b), together with the experimental values for the r a t i o CH^D/CH^ found by Danby and co-workers after k minutes' reaction time. I t can be seen that the calculated values f o r the r e l a t i v e I n i t i a l concentrations approximate the experimental curve wel l . Thus, the experimentally found v a r i a t i o n of CH^D/CH^ can be explained by a free r a d i c a l mechanism. The procedure of comparing the calculated i n i t i a l ' rates r (CH^Dyr (CH^) with the r a t i o of the concentrat ions, CH^D/ GB^ obtained aft e r four minutes reaction time implies the unwarranted assumption that the con centration of the 1-butene has remained e s s e n t i a l l y unchanged. According to the experimental re s u l t s des cribed e a r l i e r i n this work (for example, F i g . 10), more than h a l f of the 1-butene i s decomposed after k minutes at 550 C. Therefore, a refinement can be introduced i n the c a l c u l a t i o n by taking account of the va r i a t i o n of the butene concentration with time. I t was found that the 1-butene concentration decreases approximately by a f i r s t order law with time at temp eratures around 550°C ( F i g . 10), Therefore, one can write: - 1 6 3 - = k B and (B) = (Bo)e" k t (where (Bo) = i n i t i a l concentration of the 1-butene). I f t h i s time dependence of the butene concentration i s intro duced i n equations I and I I , one obtains: d(CH-D) k . ( B o ) e ~ k t ( D p ) I 3 _ = _1 2_i>_ I ( a ) (Bo)e" k t + ( D 2 ) I d(CH k) _ k ^ B o ^ e - 2 ^ dt ( B o j e " k t + ^(D2S?: 11(a) Upon integration of 1(a) one obtains: k^-Dg) log (CBLD) ^ k.p (Bo) • ( D 2 ) | .(Bo)d- kt + (D )1 (after t seconds) Prom the experimental r e s u l t s given i n Table XII, an approximate value f o r k can be chosen: k 5£k°C = 33 x 1 0 " k l / s e c . = k Introducing the above value i n the equation, the r a t i o ( C H 3 D ) A i can be calculated for a reaction time of four minutes, f o r d i f f e r e n t i n i t i a l pressures of the 1-butene, In order to compare the values thus arrived at with the experimental results obtained by Danby and co-workers, a value for the constant factor k-^  was calculated by putting: ( C H 3 D ) A l * = ( C H 3 D ) A l where (CH^DJAi " represents the number obtained from the c a l c u l a t i o n f o r four minutes' reaction time and an -16k- I n i t i a l concentration Bp = 20 mm. Hg, and the CH^D'on the r i g h t hand side represents the experimentally obtained concentration of the CH^D by Danby and co-workers for the p y r o l y s i s of butene with 20 mm. i n i t i a l pressure. The value for k_^  obtained i n t h i s way was: k x = 7.78 x 1 0 _ k sec. " 1 The values f o r Cp^D calculated by t h i s second method are plo t t e d i n F i g . 20 (a). I t can be seen that the calculated points follow the general trend of the experimental curve well. Thus, the experimentally found v a r i a t i o n of the CH^D and CH, concentrations as a function of the i n i t i a l butene concentration can be predicted on the basis of a free r a d i c a l mechanism. Therefore, the conclusion of Danby and co-workers that Isotopic mixing can occur to the ex tent observed i n t h e i r experimental results without part i c i p a t i o n of free methyl r a d i c a l s Is open to doubt.' I t i s also important to note that i f the above conlusions are correct, the n i t r i c oxide c r i t e r i o n f o r the existence of r a d i c a l chains as used by Molera and Stubbs and Danby, S p a l l , Stubbs and Hinshelwood can not be applied to the 1-butene system. - 1 6 5 - L I T E R A T U R E C I T E D 1. AMERICAN PETROLEUM INSTITUTE, Selected Values of Phys i c a l and Thermodynamic Properties of Hydrocarbons and Related Compounds, Pittsburgh, Carnegie Press, 1953. 2. BLADES, A. T. and STEACIE, E. W. R., Can. J. Chem., 32, 1142 (1954). 3. BOLLAND, J. L. and GEE, G., Trans. Faraday S o c , 45, 244 (1946). 4. COULSON, C. A., Proc. Roy. Soc. (London), A 164, 383 (1938). 5. DANBY, C. J. , SPALL, B. C , STUBBS, F. J. and HINSHELWOOD, S i r C y r i l , Proc. Roy. Soc. (London), A 228, 449 (1955). 6. DIBELER, V. H. and MOHLER, F. L., J. Research N.B.S., §6, 441 (1950). 7. DIBELER, V. H., MOHLER, F. L. and DE HEMPTINNE, M., J. Research N.B.S., 53, 107 (1954). 8. DIMBAT, Martin, PORTER, P. E. ,an'd, STROSS, F. H., Analyt. Chem.,. 28, 290 (1956). 9. EGGERTSEN, F. T., KNIGHT, H. S. and GROENNINGS, S., Analyt. Chem., 28, 303 (1956). 10. FREDERICKS, E. M. and BROOKS, F. R., Analyt. Chem., 28, 297;, (1956). — 11. GRAHAM, R. L., HARKNESS, A. L. and THODE, H. G., J. S c i . Instr., 24, 119 (1947). 12. HURD, C. R. and GOLDSBY, A. R., J. Am. Chem. S o c , 56, 1812 (1934). — 13.V JAMES, A. T. and MARTIN, A. J. P., Biochem. Journal, 50, 681 (1951). 14. LEIGH, C. H. and SZWARC, M., J. Chem. Phys., 20, 403 (1952). — 15. LEROY, D. J., Can. J. Research, B 28, 492 (1950). 16. LOSSING, F. P., INGOLD, K. U. and HENDERSON, I. H. S., J. Chem. Phys., 22, 621 (1954). -166- 17. LOSSING, P. P., INGOLD, K. U. and HENDERSON, I. H. S., J. Chem. Phys., 22, 1489 (1954). 18. LOSSING, P. P. and TICKNER, A. W., J. Chem. Phys., 20, 907 (1952). 19. LOSSING, F. P., TICKNER, A. W. and BRYCE, W. A., J. Chem. Phys., 20. MCDOWELL, C. A., LOSSING, P. P., HENDERSON, I. H. S. and FARMER, J . B., Can. J. Chem., 34, 345 (1956). 21. MANDELCORN, L. and STEACIE, F. W. R., Can. J. Chem., 32, 474 (1954). 22. MOLERA, M. J. and STUBBS, P. J., J. Chem. S o c , 1952, 381. 23. RICE, P. 0. and VARNERIN, R. E., J. Am. Chem. S o c , 76, 324 (1954). 24.. ROTHSTEIN, Eugene and SAVILLE, R. W., J. Chem. S o c , 1952, 2987. 25. SCKESSLER, D. 0., THOMPSON, S. 0. and TURKEVITCH, J., Discussions Faraday S o c , 10, 40 (1951). 26. SEHON, A. H. and SZWARC, M., Proc. Roy. S o c (London), A 202, 263 (1950). 27. STEACIE, E. W. R., Atomic, and Free Radical Reactions, N.Y., Reinhold, 1954, p. 537. 28. STEVENS ON, D. P. and WAGNER, C. D., J. Am. Chem. S o c , 72, 5612 (1950). .29. SZWARC, M., J. Chem. Phys., 17, 284 (1949). 30. SZWARC, M., J. Chem. Phys., 17, 431 (1949). 31. SZWARC, M. and SEHON, A. H., J. Chem. Phys., 18, 237 (1950). 32. TICKNER, A. W., BRYCE, W. A. and LOSSING, P. P., J . Am. Chem. S o c , 73, 5001 (1951). 33. TROTMAN-DICKENSON, A. F., Gas Ki n e t i c s , London, Butterworths, 1955. 34. TROTMAN-DICKENSON, A. F. and STEACIE, E. W. R., J. Chem. Phys., 19, 169 (1951). -167- 35. WALL, L. A. and MOORE, W. J., J. Am. Chem. S o c , 73;, 2840 (1951). 36. WHEELER, R. V. and WOOD-, W. L., J. Chem. S o c , 1950, 1819. 37. WHITTLE, E. and STEACIE, E. W. R., J. Chem. Phys., 21, 993 (1953). -168- A P P E M D I X I QUALITATIVE INVESTIGATION OF THE POLYMER PRODUCTS FORMED IN THE PYROLYSIS OF 1-BUTENE -169- A P P E N D I X .il QUALITATIVE INVESTIGATION OF THE POLYMER PRODUCTS FORMED IN THE PYROLYSIS OF 1-BUTENE The reaction mixture from the pyrolysi s of 1-butene contained a large number of compounds with molecular weights higher than that of butene. For convenience, these products are referred to as polymers,. As was described, i n the main text, the polymers were separated by gas chromatography and the c o l l e c t e d fractions analysed with the mass spectrometer. This appendix presents the results from the mass spectrometric in v e s t i g a t i o n . The mass spectrum of a given compound varies to a small extent from instrument to instrument. The ob served variations are generally small, amounting to a few percent of the r e l a t i v e ion i n t e n s i t y f o r a given mass number. Thus, i n the majority of cases, s a t i s f a c t o r y i d e n t i f i c a t i o n of a pure compound can be achieved by a ^  simple comparison of i t s experimentally-obtained spectrum with the published spectra of isomeric compounds. The polymer products were i d e n t i f i e d by comparing the ex perimentally-obtained mass spectrum of each gas chrom atographic f r a c t i o n with the mass spectra of compounds l i s t e d i n the Catalogue of Mass Spectral Data published by the American Petroleum I n s t i t u t e . A l l the mass spectra o r i g i n a t i n g from this laboratory were taken with £0 e.v. energy of the i o n i z i n g electrons. -1.70- A t y p i c a l gas chromatogram showing the fractions contain ing the polymer compounds i s represented i n Pig. 7 of the omain text. In the following sections, the mass spectrometric results are given i n the order i n which the fractions appear i n the chromatogram. Fractions B, B^ + B2, Pi Peak B re s u l t s from unreacted 1-butene. Peak B^ B£ contains two hydrocarbons: 1,3 butadiene and a butene, pre sumably 2-butene. The i d e n t i f i c a t i o n of these hydrocarbons was effected using fractions separated i n the alumina column, where peak Bi • B2 was resolved into the two peaks of the constituent gases, due to a better separation achieved with the alumina column i n that range. No attempt was made to i d e n t i f y peak P]_. Fra c t i o n P2 A comparison of the mass spectrum of P2 with that of cyclopentene i s given i n Table I. The spectrum of P 2 was recalculated on the basis: Ion i n t e n s i t y f o r mass 68 (parent peak) = kl.. It can be seen that the two spectra f i t quite c l o s e l y except at mass 67 . The mass spectra of l , 3 - p e n t a d i e n e ^ e ^ l , k - p e n t a d i e n e } ^ l T p e n t y n e ^ d ^ and 2 methyl -1 ,3 b u t a d i e n e ^ c ^ the only other mass spectra available for compounds with the molecular formula C ^ H Q , give a much less s a t i s f a c t o r y -171- Table I Comparison of the Mass Spectrum of Fraction P 2 with That of Cyclopentene Mass Ion Intensity Ion Intensity of F r a c t i o n P2 of Cyclopentene 1\ a/ 69 2 2 68 k l k l 67 83 100 66 5-7 7 65 7.6 5 6k 0.3 0.5 63 2.5 2.6 62 1.6 1.8 61 0.8 1.08 5k 1.3 1 53 2k.3 23 52 1.7 l . k 51 3.2 2.8 50 2.1 1.8 k9 0.3 0.35 k2 11.6 8.k k l 22 19 1+0 16 16 39 30.2 30 correspondence. I t i s concluded, therefore, that the gas present i n f r a c t i o n P 2 i s cyclopentene. Frac t i o n Po The mass spectrum of the f r a c t i o n P^ i s given i n column two of Table I I . The recorded ion currents for masses 8k and 66 were i d e n t i f i e d as parent peaks by scanning at low electron energies. The spectrum at 50 electron volts also indicated the presence of two compounds: C^H^ (parent mass 66), present i n large amounts, and C^ H-^ g (parent mass 8k), -172- present i n : trace amounts. The i d e n t i t y of the C^H-j^ compound could not be established. The contributions of this compound to the. spectrum were estimated on the basis of the spectrum f o r 1-hexene (column three of Table II).. "Since the spectra of a l l hexenes are quite s i m i l a r , the error should not be large. In columns four and f i v e of the table, the only two available spectra f o r compounds with the molecular formula C 5 % 2 a r e g i v e n * A comparison of the spectra, e s p e c i a l l y for masses where contributions from the hexenes are not to be expected (underlined), reveals a close s i m i l a r i t y of the P3 spectrum to that of cyclopentadiene. It i s concluded> therefore, that the gas present i n f r a c t i o n P3 i s cyclopenta diene . Fracti o n H - Attempts to i d e n t i f y the components i n f r a c t i o n H were not successful. This was due to the small amounts of f r a c t i o n H present, and also to the proximity of f r a c t i o n H to f r a c t i o n P3. The mass spectrometric analysis showed that the compound present i n the highest concentration had the molecular C ^ H - ^ Q . The spectrum showed some resemblance to that of cyclohexene, but a positive i d e n t i f i c a t i o n could not be made. -173- Table II Mass Spectra of Fr a c t i o n P ^ , Trans-2-pentene-k-yne (CH^-CH CH-C CH) and Cyclopentadiene Mass ' Ion Intensity Contributions Ion Intensity Ion of Fra c t i o n of C/iL on of 1(h)Intensity P o the Basts of CH .CH:CH.C:CH' of Cyclo- 2 1-Hexene 3 pentadiene 8k 70 69 68 67 66 65 6k 63 62 6 r 60 56 55 5k 53 52 5 i 5o k2 k l kO 39 38 37 2.8 o . i 5 2.2 1.27 8.27 100 51 3.8 8.9 r~ Id 0 7 5 5 10 l 1.58 0.318 3TIH" 1.9 8.k 37 k k ^ 1 1 ^ 2.8 1.9 8 . 5 5 . 5 7.k 10 0.8 5 5.k 100 k8 11 9 2.k 11 10 l . k k5 69 20 12 6 .5 100 39.5 8 9.5 c~ l 5  J7b2 0.72 0.72 0 . 36 3Tb2 2 7 T H 1 . k5 30. k k l . 6  12.7 T ^ k -17k- Fraction The mass spectrum of f r a c t i o n IL^  i s given i n Table I I I . Table III Mass Spectrum of Fract i o n IL^  Mass Ion Mass Ion Mass Ion Intensity Intensity Intensity 0.7 70 o .5 56 1.8 10.1 69 o.k5 55 2.7 8.1 68 1.85 $k 3 .5 1.6 67 32.k 53 k . 2 k 66 l . l 52 1.1 0.6 65 2.8 51 2.1 2.15 50 1.2 etc. 83 82 81 80 79 78 77 The only parent peak detected at low electron energies was at mass 82 . The spectrum i s obviously that of a hy- . drocarbon with molecular formula C^R^. The spectra of cyclohexene and 1, 5 hexadiene could not be f i t t e d , either separately or i n combination, to the spectrum of R^. Fractions and The mass spectra obtained for the separately c o l l e c t e d and analysed fractions and are given In Table IV. For comparison, the spectrum of 1,3 cyclohexadiene i s given i n column four. The three compounds have very similar spectra. I t i s probable that a better agreement would have resulted but f o r the interference of compounds present i n trace quantities i n fractions and H-^ . -175- Table IV Mass Spectra of Fractions and and 1,3 Cyclohexadiene Mass Ion Intensity Ion Intensity Ion Intensity. of H 2 of H - of 1 , 3-cyclp- • 3 hexadi ene 1>,S) 80 60 5i 59 79 100 100 100 78 11,5 26.6 19 77 k l kk 38 76 0.8 l 0.8 75 1.6 2.38 k . 9 7k 2.0 2.8 2.2 53 10 13 7 52 12.3 16 l k 51 15.6 21 19 50 9.85 13.8 12 The presence of a compound with parent mass 82 ( C ^ H ^ Q ) i n f r a c t i o n and a compound with parent mass 96 ( C y l i ^ ) i n f r a c t i o n could be detected e a s i l y by meas urements at low electron energies. I t i s concluded that H p and H are composed of cyclohexadienes; presumably the two isomers, 1,3 and l , k cyclohexadiene. Frac t i o n Bz The trapped f r a c t i o n , Bz. was p o s i t i v e l y i d e n t i f i e d with the mass spectrometer as benzene. Fractions T The three small peaks following the benzene peak were c o l l e c t e d together. A r e s o l u t i o n of the mass spectrum was not attempted. At low electron energies, the parent peaks for masses 96 ( c y i ^ ) , 9k ( C^IL^), and 110 ( C 8 H l k ) , were found. By analogy with the benzene group, the C y H 1 0 could be expected to be methyl cyclohexadiene. -176- F r a c t i o n TI The mass spectrometric analysis of the TI gave positi v e i d e n t i f i c a t i o n of Toluene. Trace quantities of a compound with parent mass 1 0 6 ( C Q H ^ Q) also were found. Fract i o n X-^  Table V gives a comparison •of ; the upper mass spectrum of f r a c t i o n X^ with that of o-xylene. The spectrum of X was recalculated on the basis: 1 ion Intensity for mass 106 = 5 l . A l l three xylenes have si m i l a r spectra, but the spectrum of X^ i s most sim i l a r to that of o-xylene. I t i s con cluded that f r a c t i o n X^ consists of xylene, most probably o-xyxlene. Table V Mass Spectra of Fraction X 1 and O-Xylene  Mass Ion Intensity Ion Intensity of X of O-Xylene -Ho) 106 51 51 105 18 * 22 10k 3 2.k 103 5 5 102 1.3 1.1 -177- APPENDIX I LITERATURE CITED Catalogue of Mass Spectral Data, American Petroleum I n s t i t u t e , Mass (a) 127 (b) 178 (c) 2k2 (d) 271 (e) 330 (f) 331 (g) k36 (h) 936. Lossing, F. P., National Research Council, Ottawa. Private communication. - 178 - A P P E N D I X I I DEUTERIUM MIGRATION DURING THE IONIZATION OF  l-BUTENE-k-d3 BY ELECTRON IMPACT""" Reproduction of paper-by ¥. A. Bryce and Paul Kebarle: Can. J. Chemistry, 3_k_> l2A-9 (1956) . -179- A P P E N D I X II  DEUTERIUM MIGRATION DURING THE IONIZATION OP 1-BUTENE-k-d, BY ELECTRON IMPACT INTRODUCTION Migration of hydrogen atoms along the carbon skeleton i n ionized hydrocarbon molecules has been proposed to account f o r the appearance of such fragments as CHj^ i n the mass spectrum of propane and CH^ i n the spectrum of cyclohexane. These peaks can not be accounted for by 13 isotopic contributions from C . Evidence for rearrange ment of hydrogens p r i o r to d i s s o c i a t i o n of the corres ponding molecule ions has" been reported by several workers (1, 2, 8 ) . Some migration of deuterium atoms i s reported i n a recent paper on the mass spectra of deuterated but anes (5). Migration of atoms and isomerization of ionized molecules has been r e f e r r e d to by McDowell (k) i n an int e r p r e t a t i o n of mass spectra based on excited molecular states. Processes of t h i s type are of special i n t e r e s t because of the insight they provide into the nature of bonding forces i n molecular i o n i c states. The present study of the mass spectrum of 1-butene-k-d arose i n connection with mass spectral analysis of the pyrolysis products of this compound and of the l i g h t isomer 1-butene. -180- EXPERIMENTAL The 1-butene used f o r purposes of comparison was Research Grade (99.88$)' obtained from the P h i l l i p s Petroleum Company, B a r t l e s v i l l e , Okla. The deuterated butene was kindly prepared f o r us by Dr. L. C. L e i t c h of the National Research Laboratories, Ottawa, according to the following method: hY CCl Br •• CH = CH-CH CI COUCH -CHBr-CH CI, 3 2 2 3 2 2 Zn CCl,CH„CHBrCH„Cl ^ CD CH_CH=CH . 3 ^ ^ CHyjOOD 3 2 2 The product was shown by analysis to be almost 100$ C=C hydrocarbon. A preliminary mass spectrometric analysis using 10 v o l t electrons gave an uncertain r e s u l t but Indicated that the sample was better than 90$ 1- butene-k-d^. Conclusive proof of the p u r i t y of the com pound was obtained by analysis with a Varian high res olution nuclear magnetic resonance (NMR) spectrometer. The NMR spectrum of the 1-butene i s shown i n Pig. 1(a). The peaks l a b e l l e d a, b, c, and d are proton resonance absorption peaks for the hydrogens located on the carbons as follows: CH2=CH—CH2—CH^ a b e d The t h e o r e t i c a l r e l a t i v e i n t e n s i t i e s of the two groups of peaks f o r 1-butene can be expressed as (a*b)/(c*d) = (2*l)/(243) = 3/5. The actual r a t i o found by measuring the area under the - l 8 l - >- UJ h- z (a) (b) F I E L D S T R E N G T H F I E L D S T R E N G T H P i g . l a NMit A b s o r p t i o n Spectrum o f 1-Butene l b NMR A b s o r p t i o n Spectrum o f l - B u t e n e - 4 - d 3 -182- peaks was 3/5 .8. P i g . 1(b) shows the NMR spectrum of the deuterated butene. The i d e n t i t y of the a and b peaks with those shown i n F i g . 1(a) i s obvious. The d peak of the CR^ group i n 1-butene has completely disappeared i n the deu terated compound. Deuterium atoms, having an even number of nucleons, do not exhibit NMR absorption. The r e l a t i v e i n t e n s i t i e s of the groups i n CH=CH-CH~CD, e.d b c^ d 3 should be (a*b)/(c-d) = (2+l)/(2+0) = 3/2. The observed r a t i o was 3/2.26. The complete absence of a 'd' branch i n the spectrum of the deuterated compound was taken as conclusive evidence that the methyl group was completely deuterated, within the s e n s i t i v i t y of detection of the a n a l y t i c a l method. The r e l a t i v e i n  t e n s i t i e s of the a, b, and c branches demonstrate the absence of deuterium i n the groups to which these peaks correspond. As a check on the resu l t s obtained by NMR a com parison of the in f r a r e d spectra of the two butenes was made using a Perkin-Elmer double beam spectrophotometer. A complete i n t e r p r e t a t i o n of the spectra obtained has not yet been achieved but a preliminary band assignment confirms the results obtained by NMR. -183- The mass spectrum of the l i g h t butene i s presented i n P i g . 2 and that of the deuterated compound i n F i g . 3« P i f t y - v o l t electrons were used i n obtaining these spectra. The i n t e n s i t y of the larg e s t peak i n each spectrum i s assigned a value of 100 i n the usual way. Normalized spectra for both compounds are presented i n F i g . k . Here the t o t a l ion i n t e n s i t i e s for the C^, C^, C^, and groups of ions are p l o t t e d on a scale such that the C ion i n t e n s i t i e s are k made equal. The s o l i d peaks are f o r the undeuterated com pound. A detailed study of the fragmentation pattern of the deuterated butene at low electron energies was not made but a few preliminary re s u l t s showing the i n t e n s i t i e s of various fragments as a function of electron energy are pre sented i n Table I . ^he r e l a t i v e i n t e n s i t i e s " at 50 electron volts are also shown. Results obtained for the pyrolysi s of the two butenes . provided an i n t e r e s t i n g basis for comparison of the thermal and electron-impact modes of d i s s o c i a t i o n . The results given i n Table II show the d i s t r i b u t i o n of the p r i n c i p a l products f o r the pyrolysi s of 100 mm. of each hydrocarbon o i n a s t a t i c system for 5 min. at 552 C. The analyses were performed by gas chromatography, using both adsorp- t i o n - e l u t i o n and p a r t i t i o n - e l u t i o n methods. DISCUSSION The mass spectrum of the l i g h t butene shows c l e a r l y that -18k- • 1111 • L ± L • I I I I . 4 0 M A S S Fig.2 Mass Spectrum of 1-Butene l O O r l l l l i I, I Fig.3 Mass Spectrum of l-Butene-4-d 3 too 4 8 0 • i 6 0 o - I < 4 0 n n 20 f ION G R O U P Fig.4 Normalized Spectra of 1-Butene (black) and l-Butene-4-d3 (white) Showing the Relative Total I n t e n s i t i e s for Each Group of Ions -18$.- Table I Variation of Ion Intensity with Electron Accelerating Potential for CD^CR^CHCHg, Electron Accelerating Ion Intensity (Arbitrary Potential (volts) Units) . 4 l 42 43 44 13 .0 1.0 3.0 5.0 2.0 15 .0 4 .0 8.0 14 .0 6.0 17 .0 12.0 20.5 32.0 16.0 50.0 74.3 ^7 .0 99.3 59.0 Table II Pyrolysis Products f o r the Two Butenes  After 5.0 Min. at 552 cT ~ CH3CH2CHCH2 CD3CH2CHCH2  (vol.#) (vol.#) Methane 24.0 24.0 Ethane 5 .3 5 .2 Ethylene 8 .3 9.0 Propylene 13 .0 13.6 the most abundant fragment produced by electron impact i s the C^H^ ion, formed presumably as a consequence of the preferred rupture of the CHj- CH^HCH^ bond. This ion would be expected to have the a l l y l structure, CH^HCEL,, but by rearrangement could assume structures such as CH2CH2CH or CH^CH^C. A.-C^H^ fragment i s also r e l a t i v e l y abundant. The spectrum of the deuterated compound i s markedly d i f f e r e n t from that of the l i g h t isotopic molecule. The chief difference i s seen i n the C, group of peaks. - 1 8 6 - The C H* ion (mass k l ) , which might well be expected 3 5 to be the most abundant 3-carbon fragment, accounts for only 19$ of. the t o t a l ion i n t e n s i t y . The greater part of the ion i n t e n s i t y comes from higher masses. Sev er a l possible formulas can be written f o r each of these ions, but the contributions of some of these to the i o n i c i n t e n s i t i e s w i l l be n e g l i g i b l e . Since the k2 peak from 13 1-butene i s only s l i g h t l y greater than the C isotopic • peak the contribution of ions equivalent to C^H^ can be neglected. This includes ions such as G^H^D* (mass kk) and C^H^D*(mass k3). In addition since the mass kO peak from 1-butene i s quite small, ions equivalent to C^H^ w i l l make r e l a t i v e l y small contributions to the low energy spectrum. Therefore, ions C^HD^ (mass k 3 ) , C^D^ (mass k 2 ) , and C^RT^ (mass kl) can be neglected. Thus, the greater part of the ion i n t e n s i t y comes from C^H^D^ (mass kk), C^H^Dg (mass k 3 ) , C^H^D* (mass k 2 ) , and (mass k l ) . I t i s therefore apparent that migration of the deuterium atoms from the CD^ group to the r e s t of the carbon skeleton must have occurred. Rearrangement of hydrogen atoms sim i l a r to the rearrangements observed i n the deuterated butene w i l l , of course, occur i n the l i g h t compound but cannot be detected by the present method. The r e l a t i v e i n t e n s i t i e s of the ions of masses k l to kk (Table I) provide some insight into the r e l a t i o n s h i p between the energy of the i o n i z i n g electron and the -187- extent of the migration process. At the lowest electron energy the c-^$* * o n m a ^ e s a comparatively small con t r i b u t i o n to the t o t a l ion i n t e n s i t y . The contribution increases markedly with increasing electron energy. This can be seen from Table I I I i n which the v a r i a t i o n of the C ^ D * (42) • C^D*'* (43) .• C ^ D * (44) to C (4D Table III Var i a t i o n of Ratio of the Sum of Masses 42, 43 and 44 to  Mass 4 l with E l e c t r o n Energy Electron accelerating p o t e n t i a l 42 * 43 * 44 (volts) 41 13.0 10.0 15.0 7.0 17.0 5.7 50.0 3.0 i n t e n s i t y r a t i o Is presented as a function of electron accelerating p o t e n t i a l . It i s apparent that deuterium migration i s the less probable the higher the energy of the i o n i z i n g electron, a consequence presumably of the shorter l i f e t i m e s of ions i n higher energy states. At lower electron energies the l i f e t i m e s of the ions are s u f f i c i e n t , perhaps several vibrations long, to permit extensive rearrangement of the atoms attached to the carbon skeleton. The r e l a t i v e i n t e n s i t i e s of the ions of masses li2t 43, and 44 remain approximately constant f o r a l l electron energies. This indicates that the migration mechanism does not depend -188- on the energy of the i o n i z i n g electron hut i s the same fo r a l l energies once Ionization of the molecule has occurred. The factor c o n t r o l l i n g the extent of migration i s the l i f e  time of the ion, as suggested above. It can be seen from F i g . k that the t o t a l i n t e n s i t i e s of the ions of a given carbon-number group are the same i n the two butenes even though the d i s t r i b u t i o n of i n t e n s i t i e s and the numbers of fragments observed within the groups are d i f f e r e n t . This s i m i l a r i t y i n group i n t e n s i t i e s shows that deuteration does not have any appreciable e f f e c t on the p r o b a b i l i t y of C - C bond rupture. A similar lack of e f f e c t i n the thermal decomposition of the parent molecule i s shown by the d i s t r i b u t i o n of pyrolysis products f o r the two isotopic compounds given i n Table I I . The present work confirms the res u l t s reported by Stevenson and Wagner (8) and bears out t h e i r p r e d i c t i o n that rearrangement of H and D atoms would be more extensive i n o l e f i n i c than i n p a r a f f i n i c hydrocarbons. This i s presumably a consequence of the less l o c a l i z e d character of the bonding i n the o l e f i n i c parent molecule-ion. The v a r i e t y of three-carbon fragments formed i s evidence of the existence of a number of d i f f e r e n t modes of decomp o s i t i o n of the ionized molecules. The existence of such modes has been re f e r r e d to by Rosenstock et a l . (7) i n attempting to calculate the mass spectra of polyatomic molecules from a s t a t i s t i c a l b a s i s . Migration of deuterium - 189 - atoms, with the r e s u l t i n g changes i n configuration, r e s u l t s i n tran s i t i o n s between various c l o s e - l y i n g energy le v e l s of the given io n i c state. Such tra n s i t i o n s are equivalent to the crossing of the corresponding potential energy surfaces. The o v e r - a l l decomposition pattern of the molecule-Ions w i l l depend on the d i s t r i b u t i o n of the ions among the various accessible energy states. In formation i s not yet available to permit the evaluation of the p r o b a b i l i t i e s of the transitions referred to above. Lennard-Jones and Ha l l (3) have considered the p r o b a b i l i t y of e x c i t a t i o n to various electron states i n n-octane by ca l c u l a t i n g the density of po s i t i v e charge over the octane ion but l i t t l e i s known about the p r o b a b i l i t y of t r a n s i t i o n between c l o s e - l y i n g configurational states i n polyatomic molecules. The extensive migration of isotopic hydrogens ob served i n the present work casts some doubt on the re l i a b i l i t y of the "fragmentation indices" calculated by Magat and V i a l l a r d ( 6 ) to describe the p r o b a b i l i t y of bond rupture i n the d i s s o c i a t i o n of hydrocarbons by electron impact. The necessity f o r caution i n i n t e r  preting the results of mass spectral analyses where deu terium migration can occur i s obvious. -190- APPENDIX I I LITERATURE CITED 1. BRINTON, R. K. and BLACET, P. E. I., J. Chem. Phys., 17, 797 (1949).. 2. LANGER, A., J . Phys. & C o l l o i d Chera., jgj., 6l8 (1950). 3. LENNARD-JONES, S i r J . and HALL, G. G., Trans. Faraday S o c , ILQ, 581 (1952). 4. McDOWELL, C. A., Applied Mass Spectrometry, Inst, of Petroleum (1954)• 5. McFADDEN, W. H. and WAHRHAFTIG, A. L., J. Am. Chem. S o c , 78, 1572 (1956). 6. MAGAT, M. and VAILLARD, R. I., J. chim. phys., 1^ 8, 385 (1951) . MAGAT, M., Discussions Faraday S o c , 10, 114 (1951). 7. ROSENSTOCK, H. M., WALLENSTEIN, M. B., WAHRHAFTIG, A. L., and EYRING, H., Proc. Natl. Acad. S c i . U.S., 3_8, 667 (1952) . 8. STEVENSON, D. P. and WAGNER, C. D., J. Chem. Phys., 12, 11 (1951)• 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0062153/manifest

Comment

Related Items