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UBC Theses and Dissertations

Kinetic study of the reaction of O2(1[delta]g) with some olefins and amines Furukawa, Kiyoshi 1971

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A KINETIC STUDY OP THE REACTION OP 0 ( A ) WITH. 2 g SOME OLEFINS AND AMINES by 'KIYOSHI FURUKAWA B . S c , U n i v e r s i t y of I b a r a k i , I960 M.Sc.j " Tokyo I n s t i t u t e of Technology, 1963 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 t h e s i s as conforming to r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA August 1971 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department of The University of British Columbia Vancouver 8, Canada i i . ABSTRACT O^i^hg) was produced i n a discharge flow system and used to study the k i n e t i c s of i t s i n t e r a c t i o n w i t h a number of o l e f i n s , amines and a s u l f i d e . Rate cons-ta n t s were determined f o r the removal of 0?(^"A ) by a s e r i e s of o l e f i n s at a t o t a l pressure of 1.0 t o r r . The values obtained were ; 7 -1 -1 1.1 x 10 1 mol sec by cyclopentadiene by 2,5-dimethylfuran by 2,3-dimethyl-2-butene by 2-methyl-2-butene by cis-2-butene by trans-2-butene. Some c o r r e l a t i o n was found between the i o n i z a t i o n energy of the o l e f i n and the magnitude of the r a t e cons-t a n t . For some of the o l e f i n s the r a t e constants were found to i n crease w i t h i n c r e a s i n g pressure. A d e t a i l e d study of t h i s trend u s i n g 2,3-dimethyl-2-butene, 2-methyl-2-butene and cis-2-butene showed that the i n t e r a c t i o n could be analyzed i n t o the f o l l o w i n g second order and t h i r d order processes : 1 k 0 p( A ) + O l e f i n r_ * hydroperoxide 3.5 x 10 ( 1.6 x 10 1.0 x 10' 3.2 x 10 1.3 x 10 i i i . 1 ko 0 o( A „ ) + O l e f i n 2 q v 0o + O l e f i n 2 g 2 0_( A ) + O l e f i n + 0 o ^ q v 2 0o + O l e f i n 2 g 2 > 2 Prom the k i n e t i c measurements and a determination of the r a t i o of peroxide formed to O^C^A ) removed the 2 g f o l l o w i n g r a t e constants were c a l c u l a t e d : k„ k 0 k 0 r 2q 3q ( Reactant ) ( l m o l " 1 s e c ~ 1 ) ( l 2 m o l ~ 2 s e c ~ 1 ) 2,3-Dimethyl 0.98 x 10 6 0.3 x 10 6 1.26 x 1 0 1 0 -2-butene it 5 9 2-Methyl 1.1 x 10 1 x 10 1.4 x 10 -2-butene The study was extended to i n c l u d e t r i e t h y l a m i n e , diethylamine and d i e t h y l s u l f i d e , where complications are more e a s i l y avoided s i n c e no chemical r e a c t i o n i s observed. For these quenching species the f o l l o w i n g r a t e constants were obtained, Quencher k k (0 ?) k, (Ar) k (He) 2q 3q 1 3q 3q T r i e t h y l - 1 x 10 6 3-5 x 10 1 2 x 1 0 1 0 1.5 x 1 0 1 0 amine 4 8 D i e t h y l - 5-9 x 10 2.7 x 10 amine D i e t h y l s u l f i d e - 8.7 x 10 9 i v . Taking i n t o account some e a r l i e r quenching s t u d i e s conducted i n the condensed phase and the r e l a t i v e e f f i c i e n c i e s of d i f f e r e n t t h i r d bodies, a set of elemen-t a r y processes has been proposed which i n v o l v e s the p a r t i c i p a t i o n of a weakly bound complex between OpC^A ) and the quenchers which d i s p l a y s a t h i r d order quenching process. TABLE OF CONTENTS page Abs t r a c t i Acknowledgement Iv Abb r e v i a t i o n s v L i s t of Tables v i L i s t of I l l u s t r a t i o n s i i x INTRODUCTION 1 The Nature of S i n g l e t Oxygen Molecules 4 Formation of S i n g l e t Oxygen by Energy Transfer 9 R a d i a t i v e L i f e t i m e s 10 Energy P o o l i n g 10 P h y s i c a l Quenching 14 The Chemical Reaction of S i n g l e t Oxygen 19 Sources of S i n g l e t Oxygen f o r K i n e t i c Study 24 Measurement of the S i n g l e t Oxygen Concentra-t i o n 26 EXPERIMENTAL General D e s c r i p t i o n of the Apparatus 29 The Microwave Discharge 32 The D i l u t i o n E f f e c t 36 v i . Plow Rate Regulation 39 Product A n a l y s i s 41 The C a l o r i m e t r i c Detector 43 I n t e n s i t y Measurement 46 Chemicals 47 RESULTS Part A. O l e f i n s Product I d e n t i f i c a t i o n 48 Stoichiometry 56 Order of the Reaction 58 Rate Constants f o r Quenching of A^) by O l e f i n s at 1.0 Torr 64 Rate Constants f o r 2,3-Dimethyl-2-butene 2-Methyl-2-butene and cis-2-Butene 69 Test f o r the P a r t i c i p a t i o n of V i b r a t i o n a l l y E x c i t e d 0 2 ( 1 A g ) 75 Part B. Amines and S u l f i d e T r i e t h y l a m i n e and Diethylamine 80 D i e t h y l s u l f i d e 86 DISCUSSION General Trend i n O l e f i n Quenching A b i l i t y 88 v i i . A n a l y s i s and Comparison with Previous Works 92 2,3-Dimethyl-2-butene 92 2-Methyl-2-butene 95 The Mechanism of "'"A D e a c t i v a t i o n 97 = SUMMARY 106 BIBLIOGRAPHY v i i i . ACKNOWLEDGEMENT to Dr.E.A.Ogryzlo f o r h i s e n t h u s i a s t i c guidance i n the f i e l d of the e x c i t e d oxygen molecule species i n s p i t e of i n e v i t a b l e language t r o u b l e s . to Dr.M.Kasha f o r h i s k i n d v i s i t w i t h us. to Dr.J.T.Herron f o r h i s v i s i t w i t h us to di s c u s s the value of the r a t e constants obtained. to Dr.R.P.Wayne f o r h i s v i s i t w i t h us. to my colleagues f o r t h e i r kindness and h e l p f u l d i s c u s s i o n s . to the people of the workshops and st o r e s f o r t h e i r c o operation. to the U n i v e r s i t y of B r i t i s h Columbia f o r teaching a s s i s t a n t s h i p s . to President.W.Gage f o r U n i v e r s i t y B u r s a r i e s . i x . ABBREVIATIONS The f o l l o w i n g a b b r e v i a t i o n s w i l l be used throughout t h i s t h e s i s . 2,3-Dimethyl-2-butene DMB 2,5-Dimethylfuran DMF •2-Methyl-2-butene MB cis-2-Butene B 0 2 ( 1 A g ) 1 A T r i e t h y l a m i n e TEA Diethylamine DEA X . LIST OP TABLES Table I - Rate Constants ( 1 mol "'"sec ) page f o r the D e a c t i v a t i o n of O^C1!*) 16 2 g Table I I - Rate Constants ( 1 mol~ sec" ) f o r the D e a c t i v a t i o n of 0 ? ( 1 A ) 17 Table I I I - Rate Constants ( 1 mol sec ) f o r the D e a c t i v a t i o n of O^C^A ) 18 2 V g y Table IV - R e l a t i v e R e a c t i v i t i e s of Some O l e f i n s towards S i n g l e t Oxygen 20 Table V - Data f o r 2,3-Dimethyl-2-butene obtained w i t h 0^ Pressure = 1.0 Torr 60 Table VI - " 65 Table V I I - Rate Constants ( 1 mol "^sec 1 ) f o r the D e a c t i v a t i o n of 02('I~Ag) by O l e f i n s at 1.0 Torr of 0 2 68 Table V I I I - Rate Constants : ( 1A + 2,3-Dimethyl-2-butene ) as a f u n c t i o n of Pressure 70 Table IX - Rate Constants : ( 1A + 2-Methyl-2-butene ) as a f u n c t i o n of Pressure 71 x i . , 1 Table X - Rate Constants : ( A + cis-2-butene ) as a Function of Pressure 72 Table XI - The Ratios of I5800 / ] C6340 A 7 6 , 1 Table X I I - Rate Constants : ( A + 2-Methyl-2-butene ) at 4.5 Torr i n the Presence of CH^ Gas 78 Table X I I I - Rate Constants : ( 1A + cis-2-Butene ) i n the Presence of CHjj Gas 79 Table XIV - Rate Constants : ( 1A + Triet h y l a m i n e ) as a Function of Pressure 82 Table XV - Rate Constants : ( XA + Diethylamine ) as a Function of Pressure 83 Table XVI - Rate Constants : ( 1A + D i e t h y l s u l f i d e ) as a Function of Pressure 86 x±X-LIST OP ILLUSTRATIONS page P o t e n t i a l Curves f o r the O-C^A ) 2 g 0 o ( 1 Z + ) and 0 o ( 3 E ~ ) States 5 d S 2 g Contour Surface f o r I T* - E l e c t r o n Wave Functions of the 0 2 Molecule 5 Emission Spectrum of a 10 Torr Stream of Oxygen Containing Op ("'"A ) and 0„("4 + ) at 300°K 11 2 g Flow Diagram of. the Apparatus 31 Diagram of the Micro-Wave Discharge Tube 34 1 Diagram of A Decay along the Reaction Tube 37 Diagram of E l e c t r i c C i r c u i t f o r the Isothermal C a l o r i m e t r i c Detector 44 The Gas Chromatographic Spectrum f o r the Hydroperoxides from the Reaction : 1A + 2-Methyl-2-butene 52 The NMR Spectrum of the Product from the Reaction : XA + 2-Methyl-2-butene 53 x i i i . P i g 10(b). - The NMR Spectrum of the Product from the Reaction : A + 2-Methyl-2-butene 54 P i g 11. - The NMR Spectrum of the Product from the Reaction : A + cis-2-Butene 55 P i g 12. - The Schematic E x p l a n a t i o n of [ "V], [ 1A ] and [ 1A ] f o r d Q R the E v a l u a t i o n of D e a c t i v a t i o n Rates 61 F i g 13- A P l o t of l o g (Rate) a g a i n s t l o g ["'"A ] f o r a F i x e d Concen-o t r a t i o n of O l e f i n s 62 F i g 14. A P l o t of l o g (Rate) a g a i n s t l o g [ 0 1 e f i n ] Q f o r a F i x e d Concentration of ~*"A 63 P i g 15. - The Schematic E x p l a n a t i o n of l o g ["'"A ] , l o g [^ A ] and 1 d Q l o g [ A ] f o r the E v a l u a t i o n K of D e a c t i v a t i o n Rate Constants 67 F i g 16(a). - The P l o t of k as a Function of Pressure f o r 1. DMB, MB and B 71 xiv. F i g 16(b). - The P l o t of k as a Function of Pressure f o r 1 A + MB 72 F i g 17 . - The P l o t of k as a Function of Pressure f o r 1 A + TEA and DEA . 84 F i g 18 . - The P l o t of k as a Function q of. C>2 content i n the Flow at 4.5 Torr f o r 1 A + TEA 85 F i g 19 • - The P l o t of k as a Function of Pressure f o r 1A + D i e t h y l s u l f i d e 87 F i g 20 . - The P l o t of l o g k q as a Function of I o n i z a t i o n Energies f o r 1 A + O l e f i n s 89 F i g 21 . - A Schematic Comparison of Rate Constants by Various Workers f o r 1 A + DMB 93 INTRODUCTION INTRODUCTION I t was i n 1931 that Kautsky and de B r u i j n 1) pro-posed that the e f f i c i e n t quenching of phosphorescence by oxygen r e s u l t s i n the formation of e x c i t e d s i n g l e t oxygen molecules and that these are the r e a c t i v e specie i n a c e r t a i n c l a s s of o x i d a t i o n . r e a c t i o n s . In modern terminology, t h i s sequence Is represented by the f o l l o w i n g equations S Q + hv . T> S 1 : l i g h t a b s o r p t i o n S^ ^ T :intersystem c r o s s i n g T + Q2(3Z ~) — — V *A + S 0 : energy g . •-——' 1A ' + A ^ Products o t r a n s f e r vihere S Q and S^ represent the ground and e x c i t e d s i n -g l e t s t a t e s of an organic dye s e n s i t i z e r , and T i s i t s t r i p l e t s t a t e . ^A represents 02(-'"A ) and A i s some o x i d i z a b l e s u b s t r a t e ( i . e , an a c c e p t o r ) . Somewhat l a t e r , Schoenberg proposed an a l t e r n a t i v e theory i n which the r e a c t i v e intermediates formed i n photochemi-c a l systems were moloxides^). S + hv $ S* S* + 0 2 -> SOO(moloxide) S00 + A —> A 0 2 + S. In photochemical systems, Schoenberg's mechanism i s 2. i n d i s t i n g u i s h a b l e from Kautsky's. K i n e t i c a l l y they give equivalent e x p r e s s i o n s , since no moloxide has been i s o l a t e d or p h y s i c a l l y c h a r a c t e r i z e d , and s i n g l e t oxygen has never been detected i n such systems. In any event, Schoenberg's theory was accepted by workers i n t h i s area u n t i l 1964. Between 1931 and 1964, people i n t e r e s t e d i n upper atmosphere, flame, and gas phase r e a c t i o n s worked w i t h s i n g l e t oxygen, but appeared to be unaware of Kautsky's p r o p o s a l . Consequently the wide-spread formation of s i n g l e t oxygen by energy t r a n s -f e r was not a p p r e c i a t e d . The r e a c t i o n : NaOCl + H 20 2 0* + NaCl + H 20 played an important, r o l e i n the r e v i v a l of Kautsky's theory. A number of workers reported that t h i s r e a c t i o n produces a red luminescence centered at about 6340 A ^' ^ Kahn and Kasha were the f i r s t to a s s i g n t h i s emission to s i n g l e t oxygen molecules. The b a s i s f o r t h e i r a s s i g n -ment was the o b s e r v a t i o n that the emission c o n s i s t s of o a second band at 7030 A. The spacing between the bands i s very c l o s e to the v i b r a t i o n a l spacing i n the oxygen molecule. The formation of s i n g l e t oxygen i n t h i s 5), r e a c t i o n was confirmed by Ogryzlo and co-workers who showed that more than 10 % of the e x c i t e d molecules are formed i n the Ag) s t a t e . In 1 9 6 4 , Poote and Wexler used t h i s r e a c t i o n to provide strong experimental support f o r Kautsky's mechanism ^ \ They found that the same products were obtained i n the same y i e l d i n both s i n g l e t oxygen o x i d a t i o n s 7 8 9 ) and p h o t o x i d a t i o n s 5 5 Before c o n s i d e r i n g these r e a c t i o n s of s i n g l e t oxygen, i t i s u s e f u l to consider the e l e c t r o n i c energy l e v e l s of the oxygen molecule i n some d e t a i l . The Nature of S i n g l e t Oxygen Molecule. The three r e l e v a n t e l e c t r o n i c l e v e l s of 0 2 are shown i n P i g 1. The s i n g l e t d e l t a s t a t e : 0 ? ( 1 A ) l i e s 22.5 Kcal/mol above the t r i p l e t sigma ground s t a t e : 0 2 ( 3 I ~ ) , w h i l e the. s i n g l e t sigma: 0 ( V ) l i e s 37-5 Kc a l g ^ g /mol above the ground s t a t e . Other s t a t e s l i e more than 98 Kcal/mol above ground. These three low l y i n g s t a t e s a l l a r i s e from the same e l e c t r o n i c c o n f i g u r a t i o n which can be w r i t t e n i n the LCAO-MO approximation as: ( a l s ) 2 ( a * l s ) 2 ( a 2 s ) 2 ( a * 2 s ) 2 ( a 2 p ) 2 ( 7 T 2 p ) i , ( 7 r * 2 p ) 2 . To d e s c r i b e these s t a t e s we need to consider only the two e l e c t r o n s i n the antibonding I T* - o r b i t a l s . For two e l e c t r o n problems the s p i n f u n c t i o n s can be f a c t o r e d out ( these are eta,. 33 and a$ + 3a f o r the t r i p l e t s t a t e and a3 - 3a f o r the s i n g l e t s t a t e ) . The anti-symme-t r i z e d o r b i t a l wave f u n c t i o n s f o r these s t a t e s are then 10) T r + i ( 2 ) T r! 1^ 1) } T T * (2) T T * (1) } + 1 -1 g /1/2{T T * (1) T T * (2) + +1 -1 g T T ^ C l ) 7 ^ ( 2 ) TT * (1) TT * (2) -1 -1 3v~ /1/2{T T * (1) T T * (2) + +1 -1 F i g 1. P o t e n t i a l curves f o r the 0 o ( 1 A ), 2 g 0 o ( 1 E + ) and 0 o ( 3 E ~ ) s t a t e s . 2 g 2 g F i g 2. Contour surface f o r I T* - e l e c t r o n > wave f u n c t i o n s of the 0„ molecule. 2 (a) gives the shape of the "complex" o r b i t a l s , and (b) gives the shapes of the " r e a l " o r b i t a l s . 5. F i g 2. In these equations the two e l e c t r o n s are i d e n t i f i e d by (1) and ( 2 ) , and T T + 1 and TT_-^ are the "complex" o r b i t a l s shown i n Figure 2(a) which have a sharp o r b i t a l angular momentum of ±fi along the i n t e r n u c l e a r a x i s . An i n s p e c t i o n of these f u n c t i o n s suggests that the two e l e c t r o n s are i n d i f f e r e n t o r b i t a l s i n both E s t a t e s , and i n the same o r b i t a l f o r the A s t a t e ( which i s two f o l d degenerate ). This has l e d some workers"^ to sugges the f o l l o w i n g schematic d e s c r i p t i o n of these s t a t e s i n which the e l e c t r o n s p i n i s i n d i c a t e d by arrows ; ly + © 3 v " © © These f u n c t i o n s can be mis l e a d i n g i f an attempt i s made to i n t e r p r e t them to mean that s t a t e should r e a c t g i n a f r e e r a d i c a l f a s h i o n . A more s a t i s f a c t o r y d e s c r i p t i o n of the oxygen mole-cule can be obtained i f the a l t e r n a t i v e set of " r e a l o r b i t a l s " TT* and TT* shown i n F i g 2(b) are used x : y 7 . i n s t e a d of T T*^ and T T*^. The complex f u n c t i o n s used p r e v i o u s l y are converted to these r e a l o r b i t a l f u n c t i o n s by the equations TT* = /l/2{ T T * + i T T * } +1 x y TT * = /l/2{ T T * - 1 T T * } -1 X y The " r e a l " wave f u n c t i o n s f o r these s t a t e s then become^^ 1L+ = /1/2 { TT*(1) TT*(2) + TT*(1) TT*(2) } g X X y y g /1/2 { TT*(1) TT*(2) - TT*(1) TT*(2) } Vl/2 { TT*(1) TT*(2) + TT*(2) TT*(1) } x y x . y 3 Z ~ = V / 2 { TT*(1) TT*(2) - TT*X(2) T T * ( l ) } An i n s p e c t i o n of these f u n c t i o n s suggests that i n the "'"E* s t a t e and i n one component of the d e l t a s t a t e , O both e l e c t r o n s are i n the same o r b i t a l , while i n the "3 — I JZ„ s t a t e and the other component of the A s t a t e the g g e l e c t r o n s are i n d i f f e r e n t o r b i t a l s . Therefore i n co n t r a s t to the e a r l i e r d e s c r i p t i o n we would be l e d to the f o l l o w i n g schematic r e p r e s e n t a t i o n s of the s t a t e s which i s somewhat d i f f e r e n t from the previous r e p r e s e n t -a t i o n s ; 8 . 1 A g V 0 © © © Such a d e s c r i p t i o n i s of course an o v e r s i m p l i f i c a t i o n , however, there i s reason to b e l i e v e that t h i s l a t t e r schematic d e s c r i p t i o n of these s t a t e s i s more r e l e v a n t i n the d e s c r i p t i o n of s i n g l e t oxygen r e a c t i v i t y . A p e r t u r b a t i o n , such as that caused by the approach of another molecule which breaks down the a x i a l symmetry of 0„, can be considered to mix the E wave f u n c t i o n 2 i 6 w i t h the f i r s t A f u n c t i o n producing new s t a t e f u n c t i o n which i n c r e a s i n g l y resembles the simple r e p r e s e n t a t i o n the A s t a t e i s always s t a b i l i z e d at the expense of 1 ? the Eg s t a t e . The other i n t e r e s t i n g feature of t h i s l a t t e r d e s c r i p t i o n of 0^ i n term of r e a l o r b i t a l s i s that i n s o f a r as "free r a d i c a l " c h aracter can be i d e n t i f i e d w ith unpaired e l e c t r o n s , the "*"E+ s t a t e would not expected S i to d i s p l a y t h i s c h a r a c t e r i s t i c whereas both the A and g O J. the JE s t a t e s would be. 1 + given above 1. 12) Furthermore when such mixing occurs g 9. Formation of S i n g l e t Oxygen by Energy T r a n s f e r . E x c i t e d s i n g l e t s t a t e s of molecules, which are formed whenever l i g h t i s absorbed, are not u s u a l l y quenched e f f e c t i v e l y by oxygen because of t h e i r short l i f e t i m e s ( u s u a l l y <.10 ^ sec ). However, w i t h i n t h i s l i f e t i m e a r a d i a t i o n l e s s conversion process ( i n t e r s y s t e m c r o s s i n g ) can transform the s i n g l e t s t a t e i n t o a t r i p l e t s t a t e whose l i f e t i m e i s u s u a l l y about 10^ times longer. Molecular oxygen i s found to be a very e f f i c i e n t quencher of such t r i p l e t s t a t e s . P o r t e r 18) and Wright are the f i r s t to suggest that such oxygen-induced t r i p l e t - s i n g l e t r e l a x a t i o n i s f a c i l i t a t e d by the f a c t t h a t ' t h e t r i p l e t c h aracter of oxygen makes the over 2) a l l process spi n - a l l o w e d . Even before t h i s , Kautsky had proposed that i n t h i s quenching process s i n g l e t oxy-14) gen was formed. In 1967 Kawaoka et a l presented t h e o r e t i c a l arguments to support Kautsky's pro p o s a l . T h e i r work i n d i c a t e d that 0 2 ( 1 E g ) should be very e f f i c i -e n t l y formed when the t r i p l e t energy of the hydrocarbon exceeds 37-5 Kcal/mol and 0 2 ( 1 A g ) should be e f f i c i e n t l y formed when the t r i p l e t energy l i e s between 22.5 and 37-5 IS) Kcal/mol . In t h i s way a minimum amount of energy needs to be degraded i n t o v i b r a t i o n a l and r o t a t i o n a l motion. R a d i a t i v e L i f e t i m e s . From the i n t e n s i t y of the a b s o r p t i o n band at o 1 3 -12690 A due to the t r a n s i t i o n : 0_( A ) «- 0 o ( Z ) 2 e d & as shown i n F i g 1, a radiative l i f e t i m e of 1.07 hours ( h a l f - l i f e = 45 minutes ) has been c a l c u l a t e d f o r the "*"A s t a t e . S i m i l a r l y , from the a b s o r p t i o n S o 1 + band at 7619 A due to the t r a n s i t i o n : 0. ( E ) •«-3 -0 „ ( I ) the r a d i a t i v e l i f e t i m e of the 1T.* s t a t e has 2 g g been c a l c u l a t e d to be 7 seconds ( h a l f - l i f e = 5 seconds 17) ) . However i n the presence of 0 2, N 2 and C0 2, the r a d i a t i v e l i f e t i m e of Op(^A ) can be shortened appre-16) g c i a b l y . The f o l l o w i n g equation summarizes the q u a n t i t a t i v e r e l a t i o n between the r a d i a t i v e l i f e t i m e ( f ) and the pressure of these gases ( i n atmospheres ) 1.07 hours T =  1 + 3.8P(0 2) + 3.0P(CO 2) + 0.7P(N 2) Energy P o o l i n g . The r a t e constants f o r s e v e r a l processes, i n which two e x c i t e d oxygen molecules pool t h e i r energies to pro-P i g 3 . Emission spectrum of a 10 Torr stream of 1 1 + oxygen c o n t a i n i n g 0 „ ( A ) and 0 „ ( Z ) at 300°K 2 g 2 g ( dotted l i n e ) and 150°K ( s o l i d l i n e ). The spectrum was obtained w i t h an RCA-1P21 photomulti-p l i e r and i s uncorrected f o r i t s s p e c t r a l response \ 11. duce photons with combined energies of both molecules, are comparable with those f o r the pressure induced r a d i a t i v e processes. The process gives r i s e to the 18) v i s i b l e emission bands of oxygen shown i n F i g 3 • The bands at 6340 2 and 7030 8 have been a s s i g n -ed to the process : 0 2 ( 1 A ) + 0 o ( 1 A ) 2 0_( 3Z ") + hv d S 2 g 2 g The i n t e n s i t y of the emission from t h i s process i s found to be p r o p o r t i o n a l to the square of the OpC^A ) c o n c e n t r a t i o n 1 - ^ . The 6340 % peak represents the 0-0 v i b r a t i o n a l band and r a t e constants of 0.14 1 m o l - 1 s e c - 1 2 0 ^ and 0.03 1 mol - 1sec - 1» 2 1^ have been reported f o r t h i s process. The 7030 8 band i s f o r 0-1 band w i t h r a t e constant 0.28 1 mol 1 s e c ~ 1 , 2 ° ^ . In t h i s process, the two O^C^A^) molecules are probably not bound to one 20) another but are simply i n a s t a t e of c o l l i s i o n o o The emission bands at 4800 A and 5200 A dominate the spectrum at low temperature ' . They have been assigned • to the process : OpC1!*) + 0 o ( 1 A ) -> 2 0 o ( 3 E ~ ) + hv ^ g 2 g 2 g The i n t e n s i t y of t h i s emission i s found to be p r o p o r t i o -n a l to the cube of the 0 o ( 1 A ) c o n c e n t r a t i o n . The weak o S bands at 4000 A and 3800 X are assigned to a process 13. 1 + i n v o l v i n g only the E s t a t e s and the emissions S come from 2 0 ( V ) 2 0 0 ( V ) + hv 2 g 2 g The i n t e n s i t y of t h i s process i s expected to be pro-p o r t i o n a l to the f o u r t h power of the C^C^A ) c o n c e n t r a t i o n . A somewhat d i f f e r e n t type of energy p o o l i n g process occurs i n the s i n g l e t oxygen stream which accounts f o r the c o n c e n t r a t i o n dependences of the above emissions : 0 o ( 1 A ) + 0~ ( V ) - 0 o ("4*) + 0 o ( 3 E ~ ) 2 V g' 2 X g y 2 g 2 g This has been c a l l e d "energy d i s p r o p o r t i o n a t i o n " , 23) and was f i r s t suggested by Young . The r a t e 3 -1 -1 24) constant f o r t h i s process i s 1.5 x 10 1 mol sec 5 , which i s comparable wi t h the r a t e constant f o r quenching 1 3 -of 0 o( A ) by 0„( E ). As a r e s u l t of t h i s r e a c t i o n , d g I s a stream of 0 ( A ) always contains a small concentra-1 t i o n of 0o( E ). Because 0 o ( E ) i s r e a d i l y deactivat-d g 2 g ed on the pyrex w a l l , a steady s t a t e c o n c e n t r a t i o n i s q u i c k l y e s t a b l i s h e d i n most flow systems. This steady s t a t e c o n c e n t r a t i o n i s found to be p r o p o r t i o n a l to the square of the O^ C"1"^  ) c o n c e n t r a t i o n . In flow systems l i k e the one used i n t h i s work the r a t i o of 0 ? ( ^ )/0 ? ( 1E^) i s u s u a l l y of the order of 1 0 3 , ^ . 14. P h y s i c a l Quenching. The r a t e constants f o r the d e a c t i v a t i o n of 1 Z + w i t h a number of d i f f e r e n t molecules have been g determined by s e v e r a l workers using d i f f e r e n t tech-2^5 26 27 28 29) niques 0 ' 3 3 3 . Some of these values are l i s t e d i n Table I . The r e s u l t s obtained by S t u h l 2 g \ et a l resemble those reported r e c e n t l y by 26) 29) P Becker et a l . Young and Black *' r e p o r t e d 10 or 10 J times l a r g e r r a t e constants than the other workers. Since a r a t e constant of about 1 0 1 1 1 m o l - 1 sec 1 i n d i c a t e s quenching on every c o l l i s i o n i t can be seen that the s t a t e i s q u i t e e a s i l y d e a c t i -g vated by some molecules. For the molecules l i s t e d p i n Table I , d e a c t i v a t i o n r e q u i r e s between 10 and g 10 c o l l i s i o n s . I t has been suggested that quench-i n g e f f i c i e n c i e s are r e l a t e d to the b o i l i n g p o i n t of the q u e n c h e r 1 ^ . However the agreement between d i f f e r e n t workers i s not s u f f i c i e n t l y good to support t h i s g e n e r a l i z a t i o n . Another c o n c l u s i o n which has been drawn from the t a b l e i s that the d e a c t i v a t i o n process can be w r i t t e n : 0 9 ( 1 j + ) + Quencher 0 o( 1A„) + Quencher ^ g d g The b a s i s f o r t h i s c o n c l u s i o n i s that t r i p l e t - o x y g e n should be a b e t t e r quencher than s i n g l e t n i t r o g e n i f 0 o(' LZ + ) i s being quenched to the t r i p l e t ground 2 g s t a t e . l4 8 1 + 1 Compared w i t h the Z s t a t e , the A s t a t e g g shows remarkable r e s i s t a n c e to d e a c t i v a t i o n . For comparison, some of the r a t e constants reported by v a r i o u s workers are l i s t e d i n Table I I . These values 2 6 are of the order of 10 to 10 times s m a l l e r than 1 + those f o r O^ C E g ) . However s e v e r a l much more e f f i c i e n t quenchers of the ^ s t a t e have been reported 33) Ogryzlo and Tang used a discharge flow system to determine absolute r a t e constants f o r the d e a c t i v a t i o n of 0„( 1A ) by amines. Foote et a l has shown that 2 g 34) $-carotene i s an e f f i c i e n t quencher i n s o l u t i o n , 35) and H o l l i n d e n and Timmons have s t u d i e d quenching by 2,3-dimethyl-2-butene and 2,5-dimethylfuran. The values obtained i n these l a b o r a t o r i e s are presented i n Table I I I . For amines the r a t e constants show a good c o r r e l a t i o n w i t h the i o n i z a t i o n energies of the quenchers TABLE I . RATE CONSTANTS ( 1 m o l ~ 1 s e c ~ 1 ) FOR THE DEACTIVATION OF 0„( 1Z +). 2 g Gas Becker 2 6- 1 Noxon27"* Arnold 2 5'* S t u h l 2 8 - * Young 2 9'' He ^6 x 10 3 7.2 x 10 5 Ar 9 x 10 3 1.5 x 10 6 1.9 x 10 5 N 2 1.3 x 10 6 1.2 x 10 5 1..5 x 10 6 1.3 x 10 6 3 x 10 8 0 2 ' 9-0 x 10 4 9.0 x 10 4 I 6.6 x 10^ 1.8 x 10 8 C0 2 1.8 x 10 8 1.8 x 10 8 2.«.x 10 7 1.25x 10 8 . 9-0 x 10 9 H 20 ( 3±0.6 )x 10 9 6 x 10 8 1.2 x 1 0 1 0 9 ^ 8 NH 3 1.1 x 10* 1.6 x 10 CH 4 7 6 4.5 x 10' 7-8 x 10 7 C 3Hg 2.2 x 10 C 2H^ 1.2 x 10 8 2.7 x 10 8 H TABLE I I . RATE CONSTANTS ( 1 mol 1 s e c " 1 ) .FOR THE DEACTIVATION OF 0 o ( 1 A D . ) . Gas B e c k e r 2 6 ^ 30) WayneJ F i n d l a y 3 1 ) S t e e r 3 2 ^ Ar < 6 < 1.2 x 10 N2 « 6 . < 4.2 x 10 < 1.8 x 10 < 8.4 x 10 °2 • (1 .04±0.06)x 103 (1 .4±0.1) x 10 3 (1 .31±0.07)x 10 3 (1.23±0.l4)x 10 3 CH|| (8 .4±1.8) x 10 2 C 3 H 8 (1 .45±0.1)x 103 i C 2 H i | ' (1 .2±0.1)x 10 3 NH 3 H 20 (4 (2 .2±1.2)x 10 3 .4+0.6)x 10 3 (8 .4±0.2)x 10 3 co 2 < 5 x 10 (2 .4±0.4)x 10 3 C6 H6 (3 .2±0.2) x 103 RATE CONSTANTS ( 1 m o l " 1 s e c ~ 1 ) TABLE I I I . FOR THE DEACTIVATION OF 0 2 ( 1 A g ) . Compounds Ogryzlo & Tang 3.3) Foote et a l 34) H o l l i n d e n & Timmons 3 Trimethylamine Diethylamine Triethylamine (3.0±0.4) x 10 (2.0±0.2) x 10 ( (1.9±0.1) x 10 7 1.4- D i a z a - b i c y c l o - (1.2±0.1) x 10 2.2.2 octane 2,3-Dimethyl-2-butene 2.5- Dimethylfuran 3-Carotene ^2^5^2^ 1.6 x 10 3 x 10' 6 x 10* 10 (1.8l±0.2) x 10 at 300°K (1.1+0.11) x 10' 1 9 . The Chemical Reaction of S i n g l e t Oxygen. The r e a c t i o n of s i n g l e t oxygen molecules w i t h v a r i o u s o l e f i n s has been i n t e n s i v e l y s t u d i e d , and two types of r e a c t i o n s have been e s t a b l i s h e d . With conjugated c y c l i c dienes s i n g l e t oxygen adds d i r e c t l y to the 1 , 4 - p o s i t i o n . Two examples are shown below. With mono-olefins s i n g l e t oxygen r e a c t s to give the corresponding hydroperoxides with a s h i f t of the 3 7 ) double bond . For example, CH-.\ „CH~> H0C\ CHo \ / • • , i , \ I yC = C + 0 o ( A ) -> VC C — CH-, / \ 2 s / I 3 CH 3 CH 3 H~3C 00H 3 8 ) 3 9 ) • Kopeckey and Reigh and Higgins e_t a l have determined, by competitive methods, the r e l a t i v e r e a c t i v i t i e s of a l a r g e number of o l e f i n s towards s i n g l e t oxygen. They vary widely w i t h the s t r u c t u r e of Table IV Compounds Product A n a l y s i s 3 9 ) Photo-Oxygen-a t l o n NaOCl + H2°2 O l e f i n Disappearance 39) Photo-. Oxygen-a t i o n 0C1 + H 20 2. Photo-Oxygen-a t i o n 3 8 ) 2,5-Dimethylfuran 2 33-Dimethyl-2-butene (1.00) 1i3-Cyclohexadiene 2-Methyl-2-butene 0.024 1- Methylcyclopentene 2- Methyl-2-pentene - 0.019 trans-3-Methy1-2-pentene cis-3-Methyl-2-pentene 1-Methycyclohexene 0.0041 Cyclohexene 0.000048 cis-4-Methyl-2-pentene 0 . 0 0 0 2 6 trans-4-Methyl-2-pentene 0.000047 (1.00) 0.028 0.022 0.0056 0.00024 0.000044 2.4 (1.00) 0.08 0 . 0 5 0 . 0 5 0.04 0.03 0.002 3 . 8 ( 1 . 0 0 ) 0 . 3 0 . 0 6 0 . 0 3 0 . 0 3 0 . 0 3 0 . 0 0 3 (1.00) 0.070 0.0082 0.00018 21. the o l e f i n , a l k y l s u b s t i t u e n t s i n c r e a s i n g the r e a c t i v i t y c o n s i d e r a b l y . In Table IV, the r e l a t i v e r e a c t i v i t i e s of the o l e f i n s are l i s t e d . The f a c t o r s i n f l u e n c i n g the r e a c t i v i t i e s of var i o u s o l e f i n s towards s i n g l e t oxygen have been.discussed by many workers. Kopecky and Reigh 3 8 ^ t r i e d to e x p l a i n the r e a c t i v i t y sequence by usi n g an extreme resonance form of s i n g l e t oxygen, capable of forming a perepoxide, as o r i g i n a l l y proposed by Sharp 40) + V +< 0 - o + + c -> - 0 - 0 0 . c 0 c c \ / / H H-C H-C • • Meanwhile Foote proposed the concerted "ene" 7) mechanism , which can be w r i t t e n as f o l l o w s f o r the -r e a c t i o n w i t h R2C=CH-CH3 ; R 0=0 C + ,0H2<\ 0 - 0-H R' \ H R x / \ R N / > f/ u ; c N H c ~ \ / R \ /H H NCZ^C-H C=C' I H H based on the f a c t that a Markovnikoff-type e f f e c t i s e s s e n t i a l l y absent i n the r e a c t i o n of 1A w i t h o l e f i n s . Secondary and t e r t i a r y hydroperoxides are formed i n nearly. v o n " ) equal amounts from t r i a l k y l s u b s t i t u t e d ethylene '>->p/. Furthermore a solvent has l i t t l e e f f e c t on the r e a c t i o n r a t e constant, i n d i c a t i n g that l i t t l e p o l a r i t y i s 39) developed i n the t r a n s i t i o n s t a t e Hi G o l l n i c k suggested that the perepoxide i n t e r -mediate could be r u l e d out on the grounds that the product r a t i o of hydroperoxides obtained i n the r e a c t i o n of t r i a l k y l s u b s t i t u t e d ethylene w i t h "^A cannot be explained without c o n s i d e r i n g the stereochemical e f f e c t . He found by u s i n g the conformational a n a l y s i s of limonene and the product peroxide d i s t r i b u t i o n s obtained that the r e a c t i v i t y of a l l y l i c hydrogens increased i n the order of CH^- > q u a s i - a x i a l > q u a s i - e q u a t o r i a l : 1A w: :H(CHO. In the r e a c t i o n of "^A i t h t r i a l k y l s u b s t i t u t e d ethylene x • « 3 2 C + A 2 3 00H CH(CH 3) 2 00H 5% a) 95% b) , the f o l l o w i n g stereochemical e x p l a n a t i o n of the product 41) r a t i o of a) to b) was proposed . The hydrogen on the carbon 4 of 2,4-dimethyl-2-pentene i s e c l i p s e d 23. w i t h the double bond so that A cannot make a s i x -membered "ene" r i n g with the hydrogen to form a t e r t i a r y hydroperoxide a ) , while the hydrogen of the two methyl groups on carbon 2 can make the "ene" r i n g e a s i l y because the r e p u l s i v e f o r c e between two methyl groups and the i s o p r o p y l group brings the hydrogen on the methyl group of = CH(CH"3)2 i n t o a s a t i s f a c t o r y p o s i t i o n . 8) Somewhat l a t e r , Kearns et_ al_ obtained evidence f o r a trappable intermediate i n these r e a c t i o n s and argued that t h i s was c o n s i s t e n t w i t h e i t h e r the per-epoxide discussed above or a dioxetene ; C = C + 1A - C C -I I 0 0 dioxetene However Kopecky was able to show that dioxetenes decompose 42) to y i e l d ketones whereas only hydroperoxides are formed i n the r e a c t i o n s under d i s c u s s i o n . In the presence 8) of the azide i o n , F e n i c a l et_ al_ observed the formation of azide hydroperoxide products which they could only e x p l a i n w i t h the exist e n c e of a trappable i n t e r m e d i a t e . However Fcote has i n d i c a t e d that the product r a t i o i s a l s o g r e a t l y a f f e c t e d by the presence of and has suggested that i n the presence of N~ the r e a c t i o n i s complex and that no f i r m c o n c l u s i o n i s p o s s i b l e from 34) t h i s r e s u l t Sources of S i n g l e t Oxygen f o r K i n e t i c Study. S i n g l e t oxygen has been shown to be produced by energy t r a n s f e r i n most photochemical systems when molecular oxygen i s present >'»-'-'» -> > This source of s i n g l e t oxygen has been used by a number of 38 39) workers 2 ' to o b t a i n r e l a t i v e r a t e constants f o r a number of o x i d a t i o n and quenching r e a c t i o n s i n s o l u t i o n . Since 02( 1Ag) has never been- d i r e c t l y , observed as an intermediate i n s o l u t i o n , absolute r a t e constants cannot be obtained without some assumptions. In the gas 31) phase, S n e l l i n g has obtained absolute r a t e constants f o r some quenching process ( see s e c t i o n 6 ) by d i r e c t l y observing the 02(^~Ag) decay. Several very d i f f e r e n t chemical sources of s i n g l e t oxygen have been reported. 1 45) 1) . C l 2 + H 20 2 2 HCl + 0 2( A g) 2) . Transannular peroxide of 9,10-diphenylanthracene + heat 9,10-diphenylanthracene 1 46) + 0 o ( A ) 3) . Triphenylphosphite-ozone adduct + heat - 0 2 ( \ ) + ( C 6 H 5 ° ) 3 P = 0 4 ? ) -25. L i k e the photochemical method, these can a l s o be used to o b t a i n r e l a t i v e r a t e constants f o r r e a c t i o n s i n s o l u t i o n . The presence of 0 (^"A ) i n the a f t e r g l o w from an e l e c t r i c a l discharge i n 0 2 was f i r s t suggested by the 48) mass-spectromemc s t u d i e s of Foner and Hudson . This view was supported by the c a l o r i m e t r i c s t u d i e s 49) of E l i a s et. a l . However d i r e c t s p e c t r o s c o p i c o b s e r v a t i o n of O^ C-'-A ) i n the a f t e r glow was only reported S 50) i n 1964 by Bader and Ogryzlo . The a d d i t i o n of mercury vapour was shown to remove completely the oxygen 49) atoms from the stream J ' . Though the question of other energy r i c h species i n the system i s not completely s e t t l e d , discharged oxygen provides a convenient and steady source of l a r g e concentrations of C^C^A ) f o r k i n e t i c s t u d i e s . In t h i s work, the e l e c t r o d e l e s s microwave discharge was used to produce the s i n g l e t oxygen i n a stream of oxygen at low pressures. 26. Measurement of the S i n g l e t Oxygen Concentration. 1. P h o t o i o n i z a t i o n . 51) Wayne and co-workers have used t h i s technique to determine the quenching r a t e constant f o r Og, , etc The method i n v o l v e s the p h o t o i o n i z a t i o n of 0„("*"A ) by 2 g Argon l i n e s at 1048 and IO67 8 and d e t e c t i o n of the i o n s . The apparatus i s , however, u n s a t i s f a c t o r y when species w i t h low i o n i z a t i o n energies are added to the system and hence the method cannot be used f o r o l e f i n s and amines. 2. Mass Spectrometer. Though the mass spectrometer has been used to study the k i n e t i c s of 0 (''"A ) - o l e f i n r e a c t i o n s by f o l l o w i n g product formation J ', the mass spectrometer i s very i n -s e n s i t i v e to OoC^A ) i n a flow system 52,53) a n d hence cannot e a s i l y be used f o r quenching s t u d i e s . 3.. E l e c t r o n Paramagnetic Resonance Spectroscopy. S e v e r a l workers have used E.P.R to measure O-f^A ) 2 g 3S 54 55 56) m a flow system ->-'iy >-J-J>-J s a n ( j the technique undoubt-edly has great p o t e n t i a l . However c a l i b r a t i o n s must be c a r r i e d out at each pressure used, so that absolute con-c e n t r a t i o n can be obtained. I t i s worth n o t i n g that the measurement of the O-C^A ) a b s o r p t i o n cannot be 2 g accomplished with a V a r i a n E-3 spectrometer because of the l a r g e magnetic f i e l d necessary to observe 27-the t r a n s i t i o n at about 9550 MHz i n the x-band. For t h i s reason, we could not use the instrument i n the present study. 4. Chemical t i t r a t i o n . Some workers have used the r e a c t i o n s ; i "52) 1A + 2,5-dimethylfuran -*• Product J ' 1A + 2,3-dimethyl-2-butene -> Product 9) to t i t r a t e "*"A . However i t must be assumed that the p h y s i c a l quenching by these species i s n e g l i g i b l e and that the r e a c t i o n product i s i n e r t . This may not be t r u e . 5. Isothermal c a l o r i m e t r i c d e t e c t o r . This method i n v o l v e s measuring the heat l i b e r a t e d to a c o i l of c o b a l t wire when i s d e a c t i v a t e d on the surface ^9)^ j n present study i t was used to o b t a i n the absolute c o n c e n t r a t i o n of -'-A i n the flow system. 6. L i g h t emission. I t has been shown that the emission at 6340 A i s i 19) p r o p o r t i o n a l to the square of XA c o n c e n t r a t i o n This emission i s hence a very s e n s i t i v e method of monitoring the -^A c o n c e n t r a t i o n which i s independent of other gases present i n the stream or of the absolute 70) pressure and temperature ' • 28. Though i t measures only the r e l a t i v e c o n c e n t r a t i o n along the tube, i t i s p o s s i b l e to convert these readings i n t o absolute values i f a s i n g l e absolute value of OgC^Ag) i s determined by some other method ( such.as'#5 above ). EXPERIMENTAL EXPERIMENTAL. General D e s c r i p t i o n of the Apparatus. D e t a i l e d d e s c r i p t i o n of i n d i v i d u a l components of the apparatus are given i n l a t e r s e c t i o n s of t h i s chapter. However, i t i s u s e f u l to begin with a few general comments about the major components of the flow system shown somewhat s c h e m a t i c a l l y i n Pig.4. Oxygen i s admitted to the apparatus through an Edwards needle valve at the p o i n t shown i n the diagram. The stream passes over a drop of mercury, then through the micro wave c a v i t y where the discharge produces the ex-c i t e d molecules, and a mercuric oxide deposit recombines the atoms. The oxygen.then flows through s e v e r a l l i g h t traps i n t o the o b s e r v a t i o n tube which was 100 cm long and 4.9 cm i n diameter. A m u l t i p l e j e t i n l e t was used to introduce the o l e f i n s and amines i n t o the stream A second set of i n l e t s was used i n some experiments to add Ar and He both a f t e r the discharge. The absolute c o n c e n t r a t i o n of O f ^ A ) was determined w i t h a c a l o r i -2 g metric d e t e c t o r at the end of the observation tube. The r e l a t i v e c o n c e n t r a t i o n of the species along the o b s e r v a t i o n tube was determined by measuring the i h t e n s i ' . o ty of the 6340 A emission band with a red s e n s i t i v e 30. p h o t o m u l t i p l i e r . The vacuum pump which had a nominal c a p a c i t y of 3001/minute provided a flow of about 3-5 l i t e r s / s e c at 1-5 t o r r r e s u l t i n g i n a r e a c t i o n time of about 0.6 seconds between the i n l e t j e t and the end of the observation tube. The apparatus used i n t h i s work i s very s i m i l a r to t h a t used by many other workers f o r the study of atom r e a c t i o n s . The only s i g n i f i c a n t d i f f e r e n c e l i e s i n the f a c t that the r a t e constants being s t u d i e d i n t h i s work are somewhat smaller than those p r e v i o s l y encountered i n discharge-flow experiments. Conse-quently i t became necessary ""to introduce la r g e amount of the r e a c t a n t i n t o the oxygen stream. Under such c o n d i t i o n s s e v e r a l p h y s i c a l changes were noted i n the flow p a t t e r n and some time was spent c o r r e c t i n g f o r the e f f e c t . This i s discussed i n s e c t i o n 2 of t h i s chapter. The l i g h t emissions monitored i n t h i s work are a l s o somewhat weaker than those observed p r e v i o u s l y . This r e q u i r e s some care i n the c o n s t r u c t i o n and use of the p h o t o m u l t i p l i e r and d e t e c t i o n system. P i g 4. Plow diagram of the apparatus. n - C 4 H | 0 Edwards Needle Valve Hg MANOMETER Photomultiplier Capillary Or i f ice Amines Olefins Edwards . Needle Valve Precision Pressure Gauge •j Discharge I F i l te r slits Co Wire to trap a pump 32. The Microwave Discharge. The e l e c t r o n i c a l l y e x c i t e d molecules used i n t h i s study were obtained i n an e l e c t r i c a l discharge produced by a Raytheon micro-wave generator ( model CDM-10 ) w i t h a maximum power output of 100 watts. Though "1/4 - wave" c a v i t i e s are used i n most l a b o r a t o -r i e s f o r d i r e c t i n g the r a d i a t i o n i n t o the gas stream, we found that a simple commercial C-type c a v i t y bent around the discharge tube was most e f f i c i e n t at pro-ducing "'"A i n the present system. Atoms were removed from the stream by the method 49) f i r s t d escribed by E l i a s e_t aJL . A drop of mer-cury was l o c a t e d a few inches before the discharge and t h i s was heated to produce a mercuric oxide r i n g a f t e r the discharge. The atoms recombined on t h i s surface q u i t e e f f i c i e n t l y , however, some d i f f i c u l t y was encountered i n o b t a i n i n g a stream which was both atom-free and steady i n i t s "*"A c o n c e n t r a t i o n . I t was found that i f a small gas flame kept the drop of mercury warm while the discharge was on, not only were atoms completely e l i m i n a t e d at the pressures between 0.5 and 3-5 t o r r , but the "'"A c o n c e n t r a t i o n was steady and almost twice as l a r g e as i t was i n previous systems. With the l a r g e r amount of HO formed i n such a system 33. i t was found necessary to increase the length of • tubing before the r e a c t i o n tube. The discharge arrangement used f o r most experiments i s shown i n F i g 5- At pressures between 3-5 and 5-5 Torr a d e t e c t a b l e .amount of atomic oxygen was c a r r i e d i n t o the o b servation tube. Since t h i s i s probably because atoms are simply swept over the mercuric oxide at high pressures, the f o l l o w i n g remedy was used. Only s u f f i c i e n t 0 2 was passed through the discharge to b r i n g the pressure to 2.0 Torr, and a d d i t i o n a l 0 2 was then added a f t e r the discharge to b r i n g the pressure i n t o the range 3-5 to 5-0 Torr. Argon and helium could a l s o be added e i t h e r before or a f t e r the discharge "i i n the high pressure experiments. To minimize the l i g h t emission from the d i s c h a r g e , the e n t i r e r e g i o n was painted b l a c k . A f t e r encounter-i n g some d i f f i c u l t y w i t h black laquers that have a high graphite content, "CIL" - f l a t black p a i n t was used and found to absorb very l i t t l e microwave power and not r e s u l t i n any a r c i n g or overheating. To prevent the pyrex ( or quartz ) discharge tube from c o l l a p s i n g , compressed a i r was used to c o o l the discharge. Some care had to be taken to keep the c o o l i n g F i g 5. Diagram of the micro-wave discharge tube. coolant air / \ Microwave Electrode Al plate to shut off the light from the fIQmey D.8 mm T Hg drop Flame Py rex G l a s s Fig 5 35. a i r stream constant to ensure a steady A concent-r a t i o n since t h i s v a r i e d somewhat with temperature of the discharge. The pumping speed through the discharge appears to be s i g n i f i c a n t since i t was found that the ''"A flow l e a v i n g that r e g i o n v a r i e d g r e a t l y when d i f f e r -ent rotary-pumps were used. Pumps wit h a " f r e e - a i r " c a p a c i t y l e s s than 50 l i t e r s / m i n u t e were found to be very u n s a t i s f a c t o r y . In t h i s study a Welsh Scien-t i f i c Duo-Seal Model 1376 r o t a r y pump with a " f r e e -a i r " c a p a c i t y of 300 l i t e r s / m i n u t e was used. This provided a flow v e l o c i t y of about 10 cm/sec through the discharge r e g i o n at room temperature. 36. The D i l u t i o n E f f e c t . An example of the decay of "*"A at a pressure of 1 t o r r i s shown i n F i g 6. The uppermost l i n e shows the decay i n the absence of any a d d i t i v e s . The lower s o l i d l i n e gives the "*"A c o n c e n t r a t i o n along the tube when about 100 micro moles/sec of cis-2-butene i s added at the i n l e t nozzle ( zero on the s c a l e ). I t can be seen that t h i s l i n e c o n s i s t s of two d i s t i n c t regions l a b e l l e d a & b on the f i g u r e . To determine whether the "a" r e g i o n i s due to a p h y s i c a l - d i l u t i o n e f f e c t , c hemically i n e r t butane was added to the stream i n place of cis-2-butene. The "'"A c o n c e n t r a t i o n along the tube i n the presence of 100 micro moles/sec of butane i s given by the dotted l i n e . I t can be seen that i n the "b" r e g i o n the slopes of the l i n e s are i d e n t i c a l i n the absence of a d d i t i v e and the presence of butane, i n d i c a t i n g that the butane does not quench s i n g l e t oxygen. However the i n i t i a l drop of the "a" r e g i o n s t i l l occurs. This i s c l e a r l y due to the d i l u t i o n of 1A by the a d d i t i v e s . This e f f e c t was O R S7) apparently not recognized by Kubo J 3 J 1 ' , s ince he used the drop of ^A i n t h i s r e g i o n to c a l c u l a t e constants which are about 2 orders of magnitude l a r g e r F i g 6. Diagram of A decay along the r e a c t i o n tube. 38. than these obtained by other workers. I t would appear tha t such d i l u t i o n - e f f e c t s have not been common i n d i s -charge flow systems because such l a r g e concentrations of a d d i t i v e s were not necessary i n previous s t u d i e s . In t h i s work the quencher flow o f t e n approaches 40 % of the t o t a l gas flow and hence such p h y s i c a l e f f e c t s become very important. Not only i s the "'"A d i l u t e d , but a l s o the flow r a t e and pressure are a f f e c t e d . Consequently i t was found u s e f u l to add an equivalent amount of i n e r t species to the "'"A stream when o b t a i n i n g the r e f e r e n c e -l i n e , i . e , the decay of t h i s species i n the absence of the quencher. In every case,- the reference gas used was one w i t h a s i m i l a r molecular weight, so that the flow p a t t e r n was i d e n t i c a l i n both cases. 39. Flow Rate Regulation. The main oxygen flow through the system was con-t r o l l e d u sing an Edwards needle valve and the flow r a t e was determined from the pressure d i f f e r e n c e across an o r i f i c e using a manometer f i l l e d w i t h mercury. This manometer was c a l i b r a t e d by known flow r a t e s d e t e r -mined by c o l l e c t i n g the q u a n t i t y -of gas passing through the system i n a given time. In the case of l i q u i d o l e f i n s and amines some of the l i q u i d was vapourized i n t o a w e l l evacuated v e s s e l of 1.256 l i t e r s which was then opened to the flow system.. The flow of reactant was a l s o c o n t r o l l e d by an Edwards needle v a l v e , but the pressure d i f f e r e n c e across the o r i f i c e was measured wi t h a Wallace & Tiernan FA-141 gauge. The use of t h i s gauge and greaseless stopcocks avoided the r e - e v a p o r a t i o n of the compounds d i s s o l v e d i n grease and o i l . The gauge was c a l i b r a t e d by measuring the pressure change i n the storage bulb f o r a given time. In the case of l e s s r e a c t i v e o l e f i n s , such as cis-2-butene, the gauge was c a l i b r a t e d by u s i n g an e x t r a bulb of 24.578 l i t e r s f i l l e d w i t h these o l e f i n s . A p r e c i s i o n pressure gauge made by Texas Instrument Co ( # 145 ) was used to measure the pressure change of t h i s 40. storage bulb. In general, the less reactive olefins required a greater flow to remove a given amount of singlet oxygen. Separate capillaries had to be prepared for each range of quencher flow -4 -6 which varied between 10 to 10 moles/sec. Product A n a l y s i s . The r e a c t i o n products were c o l l e c t e d i n a trap at l i q u i d n i t r o g e n temperature at the end of the c y l i n d r i c a l r e a c t i o n tube, and separated by a V a r i a n Aerograph 90-P3 gas chromatography using 3 feet of PVA on c e l i t e at 55°C. At the o u t l e t of the gas chromatograph, a product ( u s a l l y an organic hydro-peroxide ) was accumulated i n a s p i r a l pyrex tube of 5 mm o.d. at dry i c e temperatures. By breaking t h i s s p i r a l tube, the product was d i s s o l v e d i n t o an NMR quartz c a p i l l a r y tube w i t h s p e c t r a l grade carbon t e t r a -c h r o l i d e . For a very v o l a t i l e ' " o l e f i n ( such as c i s -or trans - 2-butene ) a d r y - i c e bath was used i n s t e a d of l i q u i d n i t r o g e n to c o l l e c t only the hydroperoxide, which was d i s s o l v e d d i r e c t l y i n t o the NMR c a p i l l a r y without p a s s i n g through the gas chromatopraph. 9) The recent work of P i t t s e_t aJL i n d i c a t e d that the e f f i c i e n c y of a l i q u i d n i t r o g e n trap was s u f f i c i e n t to c o l l e c t a l l hydroperoxides formed i n the stream. The t r a d i t i o n a l KI t i t r a t i o n of peroxides was found to be u n s a t i s f a c t o r y i n the presence of 2 , 3-dimethyl - 2-butene because I ? was r e l e a s e d by t h i s o l e f i n even when the 42. peroxides were absent. Hence the peroxides c o l l e c t e d i n our work were analysed q u a n t i t a t i v e l y by the r e a c t i o n 2+ 3 + : -00H + 2 Fe •*• • 2 F e J + 0 2 58) according to the w e l l developed S h e l l procedures The S h e l l method was e n t i r e l y i n s e n s i t i v e to the r e s i d u a l 3+ o l e f i n , and the r a t i o of Fe formed to H 20 2 consumed became e x a c t l y two moles to.one as long as the procedures were fo l l o w e d r i g o r o u s l y . In a d d i t i o n , i t was found necessary to double the recommended q u a n t i t y of fe r r o u s ammonium s u l f a t e to t i t r a t e a l l the peroxides formed by the r e a c t i o n . Fe(SCN) 3 i n methanol had i t s strongest o ab s o r p t i o n at 3200 A i n the v i s i b l e r e g i o n . The absorbance was c a l i b r a t e d w i t h a known amount of f e r r i c i o n using a Cary 14 spectrometer. The S h e l l method was u n f o r t u n a t e l y inadequate f o r a n a l y s i n g peroxides when dienes were present. 43. The C a l o r i m e t r i c Detector. The absolute c o n c e n t r a t i o n of the s i n g l e t d e l t a molecules was determined by the i s o t h e r m a l - c a l o r i m e t e r technique . This c o n s i s t s of the d e a c t i v a t i o n of ''"A on an e l e c t r i c a l l y heated wire known as a d e t e c t o r . The l i b e r a t e d heat by the "*"A i s then matched by an appr o p r i a t e decrease i n the current through the w i r e , the d i f f e r e n c e p r o v i d i n g an accurate measurement of the "^A c o n c e n t r a t i o n . The de t e c t o r c o n s i s t s of a h e l i c a l l y wound s p i r a l of platinum w i r e , e l e c t r o p l a t e d w i t h c o b a l t . The platinum wire was e l e c t r o p l a t e d i n a sa t u r a t e d s o l u t i o n of c o b a l t n i t r a t e ( prepared by d i s s o l v i n g c o b a l t n i t r a t e i n water and then adding 50 cc of the concentrated ammonia wi t h 5 g of ammonia s u l f a t e ). A 6 v o l t automobile b a t t e r y was used f o r e l e c t r o p l a t i n g . F i g 7. shows the c i r c u i t of the d e t e c t o r . In the absence of "^A , the bridge was balanced a l l o w i n g the r e s i s t a n c e ( R ) of the de t e c t o r to be determined and the current ( i ) was measured using a potentiometer. The "'"A was then passed over the d e t e c t o r , and the bridge was re-balanced by decreasing the c u r r e n t . Since the r e s i s t a n c e of the de t e c t o r remained unchanged, the temperature of the de t e c t o r was a l s o maintained at F i g 7- Diagram of e l e c t r i c c i r c u i t f o r the i s o t h e r m a l c a l o r i m e t r i c d e t e c t o r . 1 fi p r e c i s i o n 10K fi 6V Leads to Detector C o i l 10K ft max Decade Box 100 ft loo ft i 50 ft | P potentiometer t e r m i n a l C common - " G galvanometer " T tapping key " 45. a constant v a l u e , and the current ( 1 ) was again measured. The flow r a t e i s given by : - 1 A flow (mol/sec) = ( i 2 - i 2 ) R / k E where E = energy l i b e r a t e d per mol ( 22.4 Kcal ) of A, k = 4.18 c a l sec w a t t " 1 . 1 This equation gives the absolute flow of A provided that a l l the "^A i s d e a c t i v a t e d on the metal s u r f a c e . , i o However since a measurement of 6340 A emission before and a f t e r the d e t e c t o r could be "used to determine the f r a c t i o n of; "'"A d e a c t i v a t e d on the c o i l s , the method could be .used even when only a f r a c t i o n ( P.) of the "*"A was removed from the stream. In that case 1 2 2 A flow = ( i - i ) R k E F I n t e n s i t y Measurement. The 6340 8 band was i s o l a t e d with a Kodak i n t e r -ference f i l t e r and was detected i n a l l cases using a RCA 7265 p h o t o m u l t i p l i e r . The s i g n a l was chopped at 82.5 Hz and fed to an EMC Series-240 l o c k - i n ampli-f i e r . The output from the l o c k - i n a m p l i f i e r was recorded w i t h a 10 mV Leeds and Northrup r e c o r d e r . o The r e l a t i v e i n t e n s i t i e s of the 5800 A and 6340 8 bands were measured w i t h an RCA 1P21 p h o t o m u l t i p l i e r tube. A Zeiss v i s i b l e i n t e r f e r e n c e f i l t e r was used to i s o l a t e these bands. ^ The c o n c e n t r a t i o n of "^A i n the discharge stream ' 19 24) was c a l c u l a t e d from the r e l a t i o n ' '. I n t e n s i t y of 6340 A band 1 2 const x [ A ] Therefore the r e l a t i v e c o n c e n t r a t i o n of "'"A can be c a l c u l a t e d from the square root of the 6340 X emission i n t e n s i t y . 47. Chemicals. The oxygen used i n t h i s work was the Matheson extra-dry'gradej and argon was obtained from Canada L i q u i d A i r L t d . "Pure" grades or research grades of P h i l l i p s o l e f i n s were used f o r 2-methyl-2-butene, cis-2-butene n-butane, n-pentane and n-hexane. D i f f e r e n t grades d i d not y i e l d r e s u l t s that d i f f e r e d s i g n i f i c a n t l y i n the present experiment. 2,3-Dimethyl-2-butene was 99 + % pure, and was obtained from the A l d r i c h Chem-i c a l Co. Triethylamine was obtained from the A l d r i c h Chemical Co., and diethylamine was from Eastman Organic Chemical L t d . The chemicals mentioned above were used without f u r t h e r p u r i f i c a t i o n . RESULTS i '48. RESULTS. Part A. ' O l e f i n s . Product I d e n t i f i c a t i o n . S everal workers have shown that "*~A r e a c t s w i t h 2,3-dimethyl-2-butene ( DMB ) to form e x c l u s i v e l y the 6 9 57) peroxide shown below . There appears to be no question that only t h i s product i s observed f o r t h i s r e a c t a n t i n both the gas phase and i n s o l u t i o n . In case of the r e a c t i o n of "'"A wi t h 2-methyl-2-butece ( MB ), previous workers c h a r a c t e r i z e d only the 7) products f o r the r e a c t i o n i n s o l u t i o n . The f o l l o w -i n g two hydroperoxides were i d e n t i f i e d , and found to 7) occur i n the y i e l d s shown . CH CH C CH 2 = C CH CH 3 00H CH 3 00H I I ( 46 % ) I ( 54 % ) To determine whether the same products are formed i n the gas phase, the products were trapped under con-d i t i o n s s i m i l a r to those used i n the k i n e t i c s t u d i e s . The gas chromatographic spectrum of the products trapped at 77°K are shown i n F i g 8. The peaks on the r i g h t hand side of the spectrum are due to unreacted MB and tr a c e i m p u r i t i e s . Peak (a) & (b) are true product peaks, which might be composed of hydroperoxides (I) & ( I I ) . I f the products were hydroperoxides, by the r e d u c t i o n these hydroperoxides would be converted to a l c o h o l s . To confirm that these products were per-oxi d e s , the mixture was reduced w i t h the reagent : NaBHjj + K^O. The gas chromatographic spectrum of t h i s reduced mixture again showed two peaks due to the r e a c t i o n products, however, they were now s h i f t e d t o -wards s h o r t e r r e t e n t i o n times as i s c h a r a c t e r i s t i c of a l c o h o l s . The two peroxide products were c o l l e c t e d separate-l y and analyzed w i t h a 100 mHz-NMR spectometer. The s p e c t r a f o r these two products are shown i n F i g 9(a) and F i g 10(b). In F i g 9 ( a ) , a s i n g l e t peak at 8.75T i s the a b s o r p t i o n due to the methyl group whose adjacent carbon atom i s not conbined with any hydrogen atom(-H). The quartet between 4T and 5? i s c h a r a c t e r i s t i c of the 50. 59) group H2C=CH- . Hence the NMR spectrum of product (a) i s c o n s i s t e n t w i t h ( I ) . For product (b) the spectrum shown i n F i g 10(b) shows a doublet peak at 8.75.T and a s i n g l e t peak due to CH^- at 8.3x. These absorptions are c o n s i s t e n t with the presence of the f o l l o w i n g molecular fragments ; CH3 ,c- -c = c-/ I H CHo doublet at 8.75x s i n g l e t at 8.3T f o r CH 3- f o r CH 3~ • The a b s o r p t i o n at 1.7T i s c o n s i s t e n t w i t h the presence of the -00H group i n ( I I ) . A quartet at 5.6T and the. ab s o r p t i o n at 5-2x are a l s o c o n s i s t e n t with the f r a g -ments ; 00H H v I \ - C - CH 0 C= I 3 / H H a quartet at 5.6T the a b s o r p t i o n at 5.2T The a b s o r p t i o n at 6.6r which i s seen i n both F i g 9(a) and F i g 10(b) i s that of an i m p u r i t y . From the r e l a t i v e peak areas on the gas chromatogram ( detected w i t h a thermal c o n d u c t i v i t y c e l l ) shown i n F i g 8, the y i e l d s " of the products (a) and (b) i n the gas phase r e a c t i o n ' a r e 66 % and 33 % r e s p e c t i v e l y . In the case of cis-2-butene ( B ), only the f o l l o w -i n g hydroperoxide has been c h a t a c t e r i z e d i n s o l u t i o n 51. H„C = CH CH CH_ 2 | 3 OOH In order to determine whether the same product i s formed i n the gas phase, the peroxide was trapped by the technique described i n the experimental s e c t i o n ( see page 41). The 100 mHz NMR spectrum of t h i s product i s shown i n F i g . 11. A doublet due to the CH^- group at 8.8T, and -OOH band at 2.4T and peaks between 4x and 5T due to K^C = CH- are c o n s i s t e n t w i t h the above hydroperoxide which i s contained i n 60) the l i q u i d phase r e a c t i o n The gas chromatographic spectrum f o r the hydroperoxides from the r e a c t i o n : ~*"A + 2-methyl-2-butene F i g 9 ( a ) . The NMR spectrum of the hydroper-oxide j CH I 3 „ CH 3 C — — — C H = CH 2 > OOH F i g 10(b). The NMR spectrum of the'hydro-peroxide j CHo = C ———. CH CHT I I 3 CH 3 00H The NMR spectrum of the hydrope oxide, H2C = CH CH CH 3 00H 56. Stoichiometry. 2,3-Dimethyl-2-butene ( DMB ). To determine the r a t i o of peroxide formed to -6 s i n g l e t oxygen removed, a flow of 7-1 x 10 mol/sec of 1A at a t o t a l pressure of 1.0 t o r r was e s t a b l i s h e d i n the presence of a flow 8.8 x 10 ^ mol/sec of n-hexane to c o r r e c t f o r the " d i l u t i o n - e f f e c t " ( see page 36 ). The n-hexane was then replaced by an equal flow of DMB which consumed " a l l " the "'"A i n a di s t a n c e of about 90 cm. The peroxide and unreacted DMB were trapped out f o r a p e r i o d . o f 15 minutes and the amount of peroxide present was determined by t i t r a t i o n w i t h ferrous ammonium s u l f a t e . The flow of peroxide was thus determined to be 4.1 x 10 ^mol/sec. Therefore, at 1.0 t o r r the r a t i o ; 2-Methyl-2-butene ( MB ). In a s i m i l a r experiment w i t h MB, 8.3 x 10 mol/sec 1 -5 of A was consumed when about 2 x 10 mol/sec of MB Peroxide formed = 0.6 removed was added to the system. From the amount of peroxide 57. c o l l e c t e d , the formation r a t e of peroxides was deter-_7 mined to be 9-0 x 10 mol/sec. R1 = 9.0 x 10 _ 1/8.2 0.11 cis-2-Butene ( B ) An attempt was made to trap an organic peroxide i n t h i s r e a c t i o n , but the q u a n t i t y c o l l e c t e d was n e g l i -g i b l y s m a ll under c o n d i t i o n where "^A was s i g n i f i c a n t l y removed. The upper l i m i t f o r the formation r a t i o of peroxide was t h e r e f o r e l e s s than the e r r o r which i s about 1 %. "R1 = Peroxide formed < 0.01 "^A removed 58. Order of the Reaction. In the presence of reactant ( Q ), the concentration of singlet oxygen i s considered to decrease i n the reaction tube according to the following sequences : ° A > — ^ V °2< 39 O^Ag) + Q ^ °2(\] + Q > where k i s the rate constant for loss of singlet oxygen i n the w reaction tube. This i s expressed i n terms of the following equation, d ih ] , , R, = - 3 — » k T i ] + k [1A ] m [ Q ] n ... (1) 1 d t wL q J q L q J In the absence of reactant, the concentration of singlet oxygen can be described by the reaction : o 2 ( \ ) k " ) o 2 (V ) , governed by the rate equation : d ih ] 1 R 2= - — — = ...... (2) d t The difference between (2) and (1) gives the relation : 1 m n d { [ \ ] - [ \ ] } R - R = k [XA f [ Q ] n = 2 3 q d t 59. d t It can be seen that ["'"A R ] plotted In Fig 12 represents the difference between the other two curves which represent [^"A ^] and [^"A ]. An example of the calculation of [^"A R ] from intensity measurements i s given i n Table V. Since the quencher i s , i n some cases, consumed, i n i t i a l slopes ( R Q ) were used to obtain R at a known concentration of quencher [ QQ ]. The results of these measurements with Q = DMB, MB and B are shown i n Fig 13 and 14. In Fig 13 when log R q i s plotted as a function of log [^ A ] at a fixed [ Q ], the slopes of the lines yield "n". Within experimental error, the points f a l l on lines with a slope 1 indicating a f i r s t order dependence on [^ A ]. The Fig 14 where ["^A ] i s fixed and R Q i s plotted against [ Q ] on a log - log scale, the data i s also consistent with a f i r s t order dependence on olefin concentration for a l l three olefins. In the present experiment, every measurement was made i n the room temperature ( 25 ± 4 ) °C . 60. TABLE V. cm / I , / I x - / I 2 1.1 x 10 1.1 x 10 mol/sec of mol/sec of • n-hexane 2 33-dimethyl -2-butene 0 7.56 7.5.9, . 0 10 7.25 > 2.693 6.96 2.638 0 .055 20 7 .06 2.657 6.41 2.532 0 .125 30 6.84 2.615 5.91 2.431 0 .181 40 6.66 2.581 5.515 2.348 0.233 50 6.56 2.561 5.20 2.280 0.281 60 6.39 2.528 4.84 2.20 0.328 70 6.27 2.504 4 .50 2.121 0.383 80 6 .05 2.460 4 .223 2.055 0.405 90 5.99 2.447 4 .025 2.006 0.441 The schematic e x p l a n a t i o n of [ A^], ["'"A ] , and ["'"A ] , f o r the e v a l u -q 5 R a t i o n of d e a c t i v a t i o n r a t e . F i g 13- A p l o t o f . l o g (Rate) against l o g [ 1A ] f o r a f i x e d ' c o n c e n t r a t i o n of o l e f i n s . A P l o t of log..(Rate) against l o g [ O l e f i n ] Q f o r a f i x e d c o n c e n t r a t i o n of "^A . T T l o g ( O l e f i n ) 64. Rate Constants for Quenching of A by Olefins at 1.0 Torr. —6 1 A concentration of 2.6 x 10 mol/liter of A was found to be conveniently maintained i n our flow system. For the . determination of rate constants, this concentration of ^"A was established at the inlet jet of the quencher. Since the time/cm along the observation tube does not change much with pressure, the flow of "'"A remained f a i r l y constant as well and was normally 9.3 x 10~6 mol/sec. This i s about 5 % of the t o t a l 0 2 flow at 1.0 Torr. The flow of quencher introduced into the oxygen stream -4 -6 had to be varied between 10 and 10 mol/sec to produce a measurable quenching rate. In Table VI, the results of a typical experiment are recorded and some of the calculations are shown. The quencher i s DMB. In calculating rate constants, the following procedures were used. From (1) of page 58, - In [^Al = { k + k [ Q ] } t + const ...(3) From (2) on the same page , - In [V,] = k t + const (4) L d J w The difference of (3) to (4) gives the relationship ; In [ 1A d] - In [ 1A q] = k [ Q ] Q t This equation w i l l be valid under at least two conditions (1) when the process i s chiefly physical quenching of "^A rather than reaction, and 65. Table VI l o g [ A d] r l r l l o g [ A ] l o g [ A ] 4 n cm J l l o g I1 J2 " l o g l 2 l o g Ij/12 ( A r b i t r a r y u n i t ) 1.74 of n x 10~ 6mol/sec 1.74 x -hexane of 2,3-butene 10 ^mol/sec -dimethyl-2-0 7 .60 7.57 5 7 .385 0.8687 7-215 0.8582 0.0102 10 7 .205 0.8576 6.78 0.8312 0.0264 20 7 .075 0.8496 6 .115 0.7864 0.0632 30 6 .935 0.8410 5.51 0.7412 O.O998 4o 6 .81 0.8331 4.95 0 .6946 0.1385 50 c .Co - " _> 0.8215 4.48 0.6513 0.1702 60 6 .46 0.8102 3.985 0.6004 0.2098 70 6 • 35 0.8023 3.63 0.5599 0.2424 80 6 .215 0.7934 3.385 0.5295 0.2639 90 6 • 03 O.7803 3.14 0.4969 0.2834 66. (2) when the I n i t i a l rate ( R ) i s measured ( before a significant change i n [ Q ] occurs ). The data i s plotted In Fig 15. The dotted line represents the difference between the other two lines i n Fig 15 ( last column In Table VI ), and gives the logarithm of the relative "'"A concen-tration removed by the quencher alone, which equals k t [ Q ] . The slope of the line i n Fig 15 i s therefore equal to 2.303/k [ Q ]. The curvature at long reaction times i s undoubtedly due to the significant consumption of quencher along the reaction tube. How-ever the i n i t i a l slope can be used to evaluate k, using the equation ; ( S 1°P e W i a l = 2 - 3 0 3 / k C Q ]o The use of this technique made i t possible to determine the rate constants for the removal of "'"A by some olefins. The results thus obtained are l i s t e d i n Table VII. The schematic e x p l a n a t i o n of l o g [ A^], l o g ["'"A ] and' "log [^A^] f o r the D q & R e v a l u a t i o n of d e a c t i v a t i o n r a t e constants. ONVa V 0 1 7 2 9 PAllSN'31N|6o| o 68. Table V I I . O l e f i n s k ( 1 mol~"1"sec "*") I o n i z a t i o n * at 1.0 t o r r of energies ( eV ) 0 2 flow. Cyclopentadierie 1. ,11 X 10 7 8. • 93: 2,5-Dimethyfuran 3. • 52 X 6 10 2,3-Dimethy1-2-butene 1, .5 X 6 10 8. .3 1 - M e t h y l - l - 5. .04 X •10-5-• cyclopentene.. 2-Methyl-2-butene l , .0 X 10 5 8. .67 1J 3-Cyclohexadiene 2, .90 X 10 5 cis-2-Butene 3. .2 X 4 10 9. .13 cis-2-Pentene 2, • 52 X 4 10 9. .11 1 - M e t h y l - l - 1, .26 X 4 10 cyclohexene 4 10 trans-2-Butene 1, .26 X 9. .13 2-Methylbutadiene 1. . 20 X 4 10 2-Hexene '8. .4 X 10 3 9. .16 * Rosenstock.H.M, Herron.J.T and Draxl.K, NSRDS-NBS 26. 69. Rate Constants for DMB, MB and B as a Function of Pressure. Using the same technique described i n the previous section, rate constants were determined for DMB, MB and B at several pressures between 1 and 5 torr. The results of individual determinations are l i s t e d i n Table VIII, IX and X. The average values at each pressure were calculated and these are plotted as a function of pressure i n Fig 16(a) and (b). It can be seen that the rate constants increase with increasing pressure. Assuming that the processes consist of a combination of second and third order reactions where .[ M ] i s the third body concentrations, the following values of and can be obtained from the slopes and inter-cepts i n Fig 16(a) and (b). k + ( Olefins ) k 0 ( 1 mol~ sec. ) k 0 ( l 2mol 2sec 1 ) B MB DMB ( 1.3 ±0.45 ) x 10 ( 0.32 ±0.2 ) x 10! ( 3.6 ± 0.7 ) x 10 ( 8.1 ± 1.8 ) x 10* ( 1.3 ± 0.11 ) x 10: ( 1.5 ± 0.6 ) x 108 Table VIII. RATE CONSTANTS : ( A + DMB ) AS A FUNCTION OF PRESSURE. Torr k ( 1 mol sec" ) x 10' 1.1 1.6 ± o.4 2.0 2.0 ± 0.5 3.0 2.1 ± 0.06 4.5 2.5 ± 0.3 Table IX. RATE CONSTANTS : ( A + MB ) AS A FUCTION OP PRESSURE. Torr k ( 1 mol" sec ) x 10' 1.2 1.0 ± 0.1 2.0 1.9 ± 0.1 3.0 2.6 ± 0.2 4.6 3.5 ± 0.06 72. Table X. RATE CONSTANTS : ( 1A + B ) AS A FUNCTION OF PRESSURE. -1 -1 -4 k ( 1 mol sec ) x 10 1.0 t o r r of 0 2 flow 4.0 t o r r of plus cis-2-butene ( 0 2/Ar = 1/2 ) plus cis-2-buten.e 3.97 ( 1.5 t o r r ) 3.56 ( 1.3 t o r r ) 5.36 ( 4.5 t o r r ) 6.26 ( 4.3 t o r r ) •Pig 16(a). The p l o t of k as a f u n c t i o n of pressure f o r 1A + DMB, MB and B. P r e s s u r e ( t o r r ) P i g 16(b). The p l o t of k as a f u n c t i o n of pressure f o r "^A + MB. 0 I 2 3 4 _ 5 Torr Pressure Fig 16(b) 75. Test for the Participation of Vibrationally Excited 0 ( A ) . In view of the observation by Gray and Ogryzlo that the stream of singlet oxygen molecules coming from a microwave discharge contains an anomalously large concentration of vib-rationally excited species, i t i s possible that the rate con-stants obtained i n this system are i n error or the pressure dependence of the rate constants i s due to their presence. To test these p o s s i b i l i t i e s , the relative amount of CLC^A )v~® and 0 O ( 1 A ) v = 1 had to be monitored. This ratio 2 g 2V g y was determined by the emission from the following processes : 0^\)V"° + OAh)^1 - 2 C U V ) + 5800 A OAhj^0 + O^h)^0 •> 2 0 9 ( V ) + 6340 A 2 g 2 g 2 g Since the intensities of o [ O / A ) V = 0 ] [ O / A ) V = 1 ] the 5800 A emission const x o and 6340 A emission const x I6340 Hence the above intensity ratio i s a measure of the 76. relative 0 2( 1A g)^° , 0 2 ( 1 A g ) v - 1 concentration. The variation i n this ratio i s given i n Table XI. Table n . W ^ O Torr I5800 / I6340 15S00/ I6340 20 cm after 70 cm after i n l e t nozzle in l e t nozzle 1.0 2 x 10" 2 1.6 x 10~ 2 -2 2.0 2.1 x 10' 3-0 1.8 x 10~ 2 1.5 x 10 - 2 ^•5 2.0 x 10 2 1.6 x 10" 2 77. It can be seen that there i s no significant change i n 1 v=l this ratio with pressure, suggesting that 0 ?( A ) i s not related to the pressure-dependence of rate constants. A somewhat different experiment provided more positive 1 v=l evidence against the involvement of A g) i n the reaction observed. The 0 2 ( 1 A g ) v = 1 - O 2 ( 1 A g ) v = 0 spacing i s about 1556 cm-"1'. Since methane has a fundamental vib-ration frequency near to that i n CLC^A ) , a small amount of the gas was introduced after the discharge i n an attempt to remove vibrationally excited singlet oxygen. The concentration of 1 0 vibrationally excited A ) ( determined by 58OO A emission ) was found to drop to one third of the normal value. However, as shown i n Table X I I and X I I I , with experimental error, the absolute values of rate constants were not influenced by the change i n Op(^A )v~~'". 78 Table X I I . RATE CONSTANTS : ( A + MB ) AT 4.5 TORR IN THE PRESENCE OF CH^ GAS. Torr -1 -1 -5 k ( 1 mol sec ) x 10 1.3 0.95 ( + Ar ) 1.2 0.92 C + C H. ) 2 4 1.3 0.995 ( '+ CH 4 ) 4.7 3.47 ( + CH 4 ) Table X I I I . RATE CONSTANTS ; ( 3"A + B ) IN THE PRESENCE OF CH^ GAS -1 i -4 k ( 1 mol s e c " 1 ) x 10 Torr k 4.3 6.43 ( + CHi, ) 4.5 , 4.73 ( + CH^ ) 80. Part B. Amines and S u l f i d e . T r i e t h y l a m i n e and Diethylamine. In pa r t A of t h i s s e c t i o n , r e s u l t s were reported that i n d i c a t e a t h i r d order quenching process f o r some o l e f i n s . I t was d i f f i c u l t to be a b s o l u t e l y c e r t a i n that such observations were not, i n some way, caused by com p l i c a t i o n s from the r e a c t i o n products. Hence a s i m i l a r study of the quenching by amines and a s u l f i d e was undertaken to e s t a b l i s h whether such t h i r d order was observable i n a system where r e a c t i o n does not occur. The experiments were conducted i n the same manner as those f o r o l e f i n s and data was t r e a t e d i d e n t i c a l l y . The present r e s u l t s are shown i n Table XIV and XV. The presence of methane gas i n the stream d i d not change the values of the r a t e constants at 4.0 t o r r i n the case of 1 v = l die t h y l a m i n e , v e r i f y i n g that the presence of 0„(. A ) i s not important. As i n the case of o l e f i n s , the l i n e s i n F i g 17 can be analyzed by assuming that the experimen-t a l quenching constants can be decomposed i n t o second and t h i r d order components, i . e , k = k 2 + k [ M ] 81. The values of k 2 and k 3 q obtained from Pig 17 are —1 —1 2 —2 —1 Amines k 2 ( 1 mol sec ) ( 1 mol sec ) Triethylamine ( 0.88 ± 0.12 ) x 106 ( 4.1 ± 0.15 ) x 10 1 0 Diethylamine ( 0.49 ± 0.11 ) x 102* ( 3.0 ± 0.9 ) x 108 To determine what role the third body plays i n the quenching process, argon or helium was added to the stream to determine whether these third bodies are as effective as 0^ i n increasing the quenching rate. Fig 18 shows a plot of the rate constants for triethylamine against the percentage of oxygen i n the stream. Assuming k 0 [ M ] = k» [ Ar ] + k" [ He ] + k 0 [ 0 o ] 3 3q 3q 3q 2 the data i n Fig 18 yield values of k i 2 x 10 1 0 3q k'3'q = 1.5 x 10 1 0 k 3 q = 3.5 x 10 1 0 82. Table XIV. Torr ' k ( 1 mol sec ) 0 o mol % 1.0 3.15 ' 100 2.0 ' 5 . 2 9 " 2.0 5.29 11 3.0 7-37 3.0 ' 7-22 11 4.5 - 1 0 . 9 8 11 4.5 10.81 " " 6.14 22 ( + He ) " 6.59 " " 7.70 44 ( + He ) 7.56 " 6.36 22 ( + Ar ) " 6.99 " 7.71 44 ( + Ar ) " 8.06 11 • 83. Table XV. DIETHYLAMINE, 1.0 Torr .4.0 Torr 6.43 x 10^ l.mol """sec 1 1.32 x 10 5 1 mol 1 s e c ~ 1 ' 4 5 7.56 x 10 " 1.02 x 10 1.26 x 10 5 " + C H 4 5 1.10 x 10 " + CH„ The p l o t of k as a f u n c t i o n of pressure f o r 1A + TEA and DEA. 1 C H CD i o ° 5 CD ° if) O E a o — @ -o T r i e t h y l a m i n e D i e t h y l a m i n e 1 2 3 P r e s s u r e ( t o r r ) t 4 The p l o t of k^^ as a f u n c t i o n of content i n the flow at 4.5 t o r r f o r "'"A + Triethylamine 0 2 m o l % 86. D l e t h y l s u l f i d e . 34) Foote and co-workers have reported that d i e t h y l s u l f i d e quenches "^"A i n s o l u t i o n w i t h a r a t e 6 i —1 constant of 6 x 10 M~ sec . A comparison of our r e s u l t s w i t h t h i s value could y i e l d i n f o r m a t i o n which i s u s e f u l f o r determining the mechanism of the gas phase quenching processes. The r e s u l t s of measure-ments w i t h d i e t h y l s u l f i d e at two pressures are shown i n Table XVI. This data i s p l o t t e d i n F i g 19. The quenching appears to be e n t i r e l y t h i r d order with 9 2 -2 -1 k_ = 8.7 x 10 1 mol sec 3q . Table,XVI. Torr k ( 1 mol "'"sec 1 ) x 10 ^ 1.0 0.575 o. 585 4.5 II 2.70 2.70 The p l o t of k as a f u n c t i o n of I q • pressure f o r A + D i e t h y l s u l f i d e . T DISCUSSION. 88. DISCUSSION General Trend i n O l e f i n Quenching A b i l i t y . In view of the complex trends i n r e a c t i v i t i e s and quenching constants evident from the pressure-dependence s t u d i e s , i t seems u n l i k e l y that the o v e r - a l l ^A quench-i n g plus r e a c t i v i t y constants reported i n Table VII would show a simple c o r r e l a t i o n with some molecular 6 1 ) parameter. However Tang has found a reasonably good c o r r e l a t i o n between the quenching f o r a l i p h a t i c amines and t h e i r i o n i z a t i o n energies. To see whether a s i m i l a r c o r r e l a t i o n occurs f o r o l e f i n s , such a p l o t i s presented i n F i g 2 0 . I o n i z a t i o n energies are not a v a i l a b l e f o r s e v e r a l of the spec i e s . I t can be seen that i f cyclopentadiene i s ignored there does appear to be some c o r r e l a t i o n between these q u a n t i t i e s . Since cyclopentadiene forms an endoperoxide r a t h e r than a hydroperoxide, t h i s species might be expected to show anomalous behavior. To account f o r such a c o r r e l a t i o n , Ogryzlo and Tang have proposed that the d e a c t i v a t i o n of A proceeds v i a a "charge t r a n s f e r " complex. In g e n e r a l , the f o l l o w i n g r e l a t i o n s h i p has been proposed f o r 6 2 ) -"charge t r a n s f e r " r e a c t i o n s . . '• ' 1 W = ( I - E - Q ) F i g 20. The p l o t of l o g k as a f u n c t i o n of i o n i z a t i o n energies f o r "'"A + O l e f i n s . @ Cyclopentadiene 1 — i — 1 — r — r ~ — r — i — i — 1 — i — 8 . 2 8 . 6 8 . 8 9 . 0 9 .2 Ionization Energy 90. where W = a measure of the extent of charge t r a n s f e r i n the complex, E = e l e c t r o n a f f i n i t y of the acceptor ( 0 i n t h i s case ), 2 Q = a term p r o p o r t i o n a l to the coulombic i n t e r a c t i o n between the donor and the acceptor, I = i o n i z a t i o n energy of the donor ( the o l e f i n i n t h i s process ). E i s constant f o r a f i x e d acceptor, and Q i s u s u a l l y considered to be small and almost constant f o r a s e r i e s of s i m i l a r donors . Therefore the r e l a t i o n s h i p between W and I i s expected to be and u s u a l l y found to be l i n e a r . When the energy l e v e l of "*"A i s cl o s e to t h a t of the "charge t r a n s f e r " complex, the mixing of both s t a t e wave f u n c t i o n s ( "'"A - o l e f i n and the CT complex ) i s expected. Since the t r a n s i t i o n between the CT-state and ground i s not s t r o n g l y f o r b i d d e n , one might expect a r e l a t i o n s h i p such as the f o l l o w i n g between the t r a n s i -t i o n p r o b a b i l i t y ( i . e , r a t e constant ) f o r the quenching and W (. the amount of charge t r a n s f e r i n the complex ). l o g k = const x W 91. However, t h i s argument i s r e l e v a n t only to the b i m o l e c u l a r quenching process which, according to the a n a l y s i s presented i n the next s e c t i o n , sometimes makes a minor c o n t r i b u t i o n to the quenching constants at 1.0 t o r r . 92. Analysis and Comparison with Previous Works. DMB. A schematic comparison of rate constants obtained by various workers i s given i n Pig 21, where k r = the second order rate constant for chemical reaction, k 2q = the second order quenching rate constant, k ^ = the third order quenching rate constant. In our previous experiments, the value of ( k^ + + [ M ] ) for the removal of "^A by DMB was found to be ( 1.6 ± 0.4 ) x 10 6 1 mol - 1sec - 1 at 1.0 torr. Since the ratio of peroxide formed to "^"A removed was 0.6, the value of k r i s ( 1.0 ± 0.3 ) x 10^ 1 mol-"'"sec-1, which agrees well with the result of two different measurements by Herron and Huie 5 2 T h e i r values were ( 1.0 ± 0.3 ) x 10^ and 0.86 x 10^ 1 mol-"'"sec-1 at 25 °C. According to their report, there i s no pressure-dependence of the rate constants for chemical reaction between "'"A and olefins i n this pressure-52) range . I f this i s true, i t can be concluded that the pressure -dependence of rate constants reported here i s due to a third order quenching process. From the slope i n Pig 16, the value of q p —2 —1 k^ was determined to be ( 8.1 ± 1.8 ) x 10 1 mol sec . I f the chemical reaction i s independent of pressure, the difference between the intercept ( k^ + ) at 0 torr and k^ ( 1.0 ± 0.3 ) P i g 21. A schematic comparison of r a t e constants by various workers f o r -""A + DMB. 2 . 5 H CD o K 2 . 0 i o Q) W 1 .5H O E <>i i . c H CM 0 . 5 H kr-4- k 2q + k 3q [iVl] Timmons k2q -f k3q [iVl] f^-k2q + kr kr 1 kr ( Herron and Huie) kr ( P i t t s e t a l ) O 1 2 3 4 P r e s s u r e ( t o r r ) 94. x 10^ 1 mol "^sec-1 w i l l give the bimolecular quenching rate constant k^ for deactivation of "^A by DMB. As shown i n Fig 21, k^ = 0.3 x 10 1 mol s e c . Our results on the stoichiometry of the reaction of "^A q) with this olefin are i n conflict with those of Pi t t s et a l , who concluded that the physical quenching of of "4\ by DMB was negligible i n the pressure range 1 - 1 0 torr and the rate 5 -1 -1 constants for chemical reaction i s 10 1 mol sec . This value i s about an order of magnitude smaller than ours and the S"2 64) values obtained by Herron and Huie ' I t i s d i f f i c u l t to account for this discrepancy. An assessment of their work would require an examination of the details of their experiments which have not been published yet. Hollinden and Timmons reported a determination of the rate constant k ( = k + k„ + k~ [ M ] ) for the q r 2q 3q removal of A^ by DMB, using E.S.R to follow the "*"A concen-tration. Their value of ( 1.8 ± 0.2 ) x 106 1 mol/sec - 1 obtained at 300 °K and 0.5 torr i s somwhat higher than our vlaue. The results of our work and those of previous workers are summarized i n Fig 21. 95. MB. The value of ( k + k„ + k [ M ] ) f o r r 2q 3q 1 R -1 d e a c t i v a t i o n of A by MB was ( 1.0 ± 0.1 ) x K r 1 mol sec 1 at 1.0 t o r r . Since the r a t i o of hydroperoxides formed to removed was 0.11, k f o r r e a c t i o n of r 1 4 - 1 - 1 A w i t h MB i s 1.1 x 10 1 mol sec , which i s i n reasonable agreement w i t h the r e s u l t of Herron and 52) 4 -1 -1 Huie . T h e i r value was 11 < 10 " 1 mol sec •. The slope of the l i n e f o r MB i n P i g 16(b) gives the value of k^ = ( 1.3 ± 0.1 ) x 109 l^nol" 2sec"" 1 for the •termolecular quenching r a t e constant. Since the i n t e r c e p t i s w i t h i n experimental e r r o r of k f o r 4 r e a c t i o n ( 1.1 x 10 ), i t would appear that k_ 4 q f o r t h i s species i s somewhat s m a l l e r than 10 . Because of the s c a t t e r i n the r e s u l t s , a more accurate estimate of t h i s constant cannot be made from the data. T r i e t h y l a m i n e and diethylamine. I t i s of i n t e r e s t to compare the present r e s u l t s 33) w i t h those obtained by Ogryzlo and Tang f o r the same processes. At 300°K and 2.25 t o r r they obtained 7 - 1 - 1 6 -1 values of 1.9 x 10 1 mol sec and 2.0 x 10 1 mol sec ^ f o r the "*"A quenching w i t h t r i e t h y l a m i n e and d i e t h y l a m i n e , r e s p e c t i v e l y . Our present pseudo second 96. order r a t e constants at 2.0 t o r r are 5.3 x 10 1 mol "'"sec-"1" and 8.0 x 10^ 1 mol "*"sec 1 f o r quenching of "*"A by t r i e t h y l a m i n e and d i e t h y l a m i n e , r e s p e c t i v e l y . What i s p a r t i c u l a r l y s i g n i f i c a n t i n t h i s comparison i s that Tang evaluated the r a t e constants without c o r r e c t i n g f o r the " d i l u t i o n e f f e c t " ( see page 36 ) and had d i f f i c u l t y i n determining the flow r a t e of the quenchers. Some very recent measurements done by Herron and Huie i n d i c a t e a quenching r a t e constant f o r t r i e t h y l a m i n e equal to 2. x 10^ 1 mol "^sec-"1"' which i s i n good agree-ment wit h our present pseudo second order r a t e constant ( 3-15 x 10 6 ) at 1.0 t o r r . 97. The Mechanism of A D e a c t i v a t i o n . The most d i f f i c u l t problem r a i s e d by the r e s u l t s r e p o r t e d i n t h i s study i s the mechanism of the t h i r d order quenching of "'"A . In proposing a d e t a i l e d mechanism f o r the d e a c t i v a t i o n of ^A , there are at l e a s t four experimental observations which must be considered. 1) . The p h y s i c a l quenching process d e a c t i v a t e s ''"A v i a both "bimolecular" and "te r m o l e c u l a r " processes. 52) 2) . The experiments of Herron and Huie have shown that the chemical r e a c t i o n i s second order and shows no t h i r d order process at these high pressures. 3) . The t h i r d p o i n t i s that argon and helium are almost e q u a l l y e f f e c t i v e as the t h i r d body and oxygen i s almost twice as e f f e c t i v e as argon or helium. Hence i t i s u n l i k e l y that the t h i r d body [ M ] i s d i r e c t l y i n d u c i n g the i n t e r s y s t e m c r o s s i n g : 98. 1 M 3 [ Q • A ] ^ [ Q . o 2 r since 0^ could a l l o w the process to occur w i t h the "conservation of s p i n " and t h e r e f o r e should be very much more e f f i c i e n t than the low molecular weight i n e r t gases. 34) 4). The f o u r t h o b s e r v a t i o n i s that Foote et_ al_ determined the absolute r a t e constant f o r 1A . + d i e t h y l s u l f i d e 6 i i i n s o l u t i o n ( = 6 x 10 M sec ). Since the s o l u t i o n i t s e l f may be considered to provide a very l a r g e t h i r d body c o n c e n t r a t i o n , .the pseudo second order constant measured i n the gas phase should not exceed that observed i n the l i q u i d phase. The f o l l o w i n g set of elementary r e a c t i o n s c o n s t i -t u t e a mechanism which i s c o n s i s t e n t w i t h the above observations ; 1 k l s +• Q r k -1 C* k 2 \ 4 r — * A  C* [1],[2] Product [3] 0„C 3E ) + Q [4] 2 £ k 3 ^ C* + M , 7 C + M [5][6] C k4 v 0-(V) + Q [7] r 2 g C* represents a " c o l l i s i o n complex" which i s formed on every encounter between ''"A and Q, and which has a r e l a t i v e l y short average l i f e t i m e because of r a p i d r e d i s -s o c i a t i o n ( T = l/k_- ] L ) . The c o n c e n t r a t i o n of C* i s then given by - J - [ A ] [ Q ] k - l i n our pressure range. This complex may undergo one of two unimolecular processes represented by equations 3 and 4 or may be s t a b i l i z e d by a c o l l i s i o n w i t h any t h i r d body M to a. "bound complex" C. To p r e d i c t a high pressure l i m i t to the quenching r a t e the r e d i s s o c i a t i o n of t h i s complex given by equation 6 ( governed by k_^ ) must be i n c l u d e d . To be c o n s i s t e n t w i t h the l a c k of a t h i r d order r e a c t i o n the complex C must be capable of unimolecular r e l a x a t i o n to the ground s t a t e ( Q + 0 2 ) but must not be able to undergo r e a c t i o n to hydroperoxides at a s i g n i f i c a n t r a t e . Assuming a " s t e a d y - s t a t e " c o n c e n t r a t i o n f o r C 3 100. we o b t a i n the pseudo second order r a t e constant k± k ^ k 3 k 1 [ M ] k = — ± _ ( k' + ko ) + exp k k _ l { k _ 3 [ M ] + k 4} Comparing t h i s with the equation used to analyze the data k _ = k^ + k ? n + k o n [ M ] , Lexp " K r ^ K 2 q + * 3 q l k--1 k-[ - l k k k k„ = 3 1 3q k _ 1 ( k _ 3 [ M ] + k 4} At the r e l a t i v e l y low pressure used i n our study, i f k^ >> k_ 3 [ M ] , k l k_ = k-j . 3q k 3 -1 At high pressure or i n a condensed phase where kj, << k_ 3 [ M ] 101. i . e , the r a t e constant becomes "pseudo-second order and equal to k l k 3 k 4 k - l k - 3 (a) When the quencher i s d l e t h y l s u l f I d e , .6 k l k 3 1 i k, k - l k - 3 6 x 10 . . . Foote et a l 34) (b) (c) k. k„ < 10" -1 9 x 10' experimental values d e t e r -mined i n t h i s study The r a t i o of (a) to (c) gives (d) V k-3 6.7 x 10 -5 -4 Since [ M ] i s 5.8 x 10 m o l / l i t e r at 4.5 t o r r , i n the pressure range between 1 and 5 t o r r the assumed i n e q u a l i t y ; k^ >> k [ M ] , which can be w r i t t e n ; k, >> [ M ] , -^3 becomes on s u b s t i t u t i o n w i t h r e l a t i o n s h i p (d) -4 -5 6.7 x 10 >> 5.8 x 10 102. which i s c o n s i s t e n t w i t h our a n a l y s i s . I f we take k-^  as 1 0 1 1 which i s order of c o l l i s i o n frequency, the f o l l o w i n g r e l a t i o n s h i p would be obtained 10 6 x k 2 < k from (b) 11 k 3 = k_x. from ( a ) / ( c ) 5 Then, 10 k 2 < k^ i s found. I f k^ occurs on every 11 as i n 3 c o l l i s i o n ( i . e , k * 10 ), k_ 1 * 1 0 1 2 , 67) which i s acceptable f o r a s l i g h t l y s t i c k y c o l l i s i o n As a r e s u l t , we can see that 10 6 k 2 < 10 k 3 = k 1 and the value of k 2 could be"" 10^ which i s not unreasonable . The value of k^ and k^ w i l l probably not be too d i f f e r e n t . I f k^ = k^ , we o b t a i n from (a) and (b) k 3 _ _ i > 60 . k-3 I f the energy removal i n r e a c t i o n 5 i s l e s s e f f i c i e n t ( i . e , k^ i s considerably smaller than c o l l i s i o n frequency ), then k would be s m a l l e r . 103-I t i s worth no t i n g that our mechanism resembles 68) one proposed by P o r t e r to e x p l a i n t h i r d order atom recombination r e a c t i o n s . In f a c t the t h i r d order quenching and atom recombination processes do have s e v e r a l features i n common. The constants l i e i n the 9 2 -2 -1 v i c i n i t y of 10 1 mol sec , and s l i g h t d i f f e r e n c e s i n the e f f i c i e n c i e s of various t h i r d bodies are observed. A "negative a c t i v a t i o n energy" i s observed i n atom recombination and i t would be i n t e r e s t i n g to determine whether t h i s i s a l s o true f o r the t h i r d order quenching process. However, i t i s not obvious why the weakly bound complex C i s not able to give the r e a c t i o n products but 3 -only r e l a x e s to E . The only e x p l a n a t i o n we can suggest at the moment i s that the c o n f i g u r a t i o n of the weakly bound complex i s not s a t i s f a c t o r y f o r the forma-t i o n of an "ene" r i n g and t h e r e f o r e cannot r e a c t to produce a hydroperoxide. On the other hand, the more l o o s e l y bound.complex C* may be capable of assuming the co r r e c t c o n f i g u r a t i o n and hence more r e a d i l y produces the hydroperoxide. There do not appear to be many other systems i n which induced e l e c t r o n i c r e l a x a t i o n has been shown to 104 . r e q u i r e a t h i r d body. C a l l e a r ejfc a l found a very >n i i 65) 3 s i m i l a r phenomenon i n the d e a c t i v a t i o n of H (6 P Q) by NH^ molecule Hp. (6 3P_) + NH 0 k 2 v H (6 1S ) + NH_ & o 3 > g o 3 H (6 3 P ) + NH-3 + M g o 3 ^ 3 ^ H g NH* + M When M = , He or Ar, the values reported were 10 2 -2 -1 k 3 ( N 2 ) = 6.8 x 10 1 mol sec , 10 2 -2 -1 k^( He or Ar ) = 3-4 x 10 1 mol sec , r e s p e c t i v e l y . In t h e i r work the pressure range stu d i e d was between 0 and 800 t o r r , and they found no evidence f o r a decrease i n the value of k . For the "'"A d e a c t i -3 v a t i o n we had to assume the presence of an upper l i m i t which the r a t e constant i n the gas phase cannot exceed 34 ) because Foote et a l have reported an absolute value f o r one r a t e constant i n the l i q u i d phase. I t w i l l be of i n t e r e s t to examine the r a t e constants f o r "'"A d e a c t i -v a t i o n at high pressure and to see whether such an upper l i m i t does occur. I t was u n f o r t u n a t e l y not p o s s i b l e to extend our pressure range beyond 5 t o r r i n the present study. A new method which i s able to supply "'"A at 105. r e l a t i v e l y high pressures would probably be very v a l u a b l e . W I t i s i n t e r e s t i n g that the t e r m o l e c u l a r r a t e constant i n C a l l e a r ' s work i s c o n s i s t e n t w i t h other t e r m o l e c u l a r r a t e constants such as those f o r atom recombination. Some of our constants are small and i t may be that these low values are a s s o c i a t e d w i t h very weakly bound complexes where the removal of energy comparable to kT i s d i f f i c u l t . F urther d i s c u s s i o n of these values does not seem warranted i n the absence of some independent i n f o r m a t i o n about these processes. SUMMARY. 106. SUMMARY. I t i s c l e a r from the r e s u l t s described i n t h i s t h e s i s that o l e f i n s can remove O^C^A ) by both chemical and p h y s i c a l processes. Furthermore i t appears that the p h y s i c a l quenching can proceed v i a a t e r m o l e c u l a r process. S i m i l a r r e s u l t s w i t h amines and d i e t h y l s u l f i d e i n d i c a t e that the phenomenon i s f a i r l y general and that the process i n c l u d e s the p a r t i c i p a t i o n of a t h i r d body whose nature i s not too important. This has l e d us to propose that the t h i r d body i s r e q u i r e d f o r the s t a b i l i z a t i o n of a weakly bound complex between "*"A and the quencher. In view of the magnitudes of the r a t e constants described i n the a n a l y s i s presented i n the d i s c u s s i o n , i t i s very u n l i k e l y t h a t such complexes can be trapped or observed.spectro-s c o p i c a l l y . As f u r t h e r i m p l i c a t i o n of t h i s study, i t w i l l be very i n t e r e s t i n g to l e a r n whether a t h i r d order p h y s i c a l quenching process i s observable i n other s p i n - f o r b i d d e n processes, such as o 2(V) * o2(V) 0( 1D ) - 0 ( 3 P ) BIBLIOGRAPHY. » BIBLIOGRAPHY. 1. H.Kautsky and H.de B r u i j n , Naturwissenschaft. 19, 1043 (193D 2. A.Schoenberg, Ann. .5_l8, 299 (1935) 3. L . M a l l e t , Compt.Rend. l8_5, 352 (1927) 4. H.H.Selinger, Analyt.Biochem. 1, 60 (I960) 5. R.J.Browne and E.A.Ogryzlo, Proc.Chem.Soc.April, 117 (1964) 6. C.S.Foote and S.Wexler, J.Am.Chem.Soc. 86, 3879 (1964) i b i d 86, 3880 (1964) 7. C.S.Foote, S.Wexler and W.Ando, Tetrahedron L e t t e r s . 46, 4111 (1965) 8. . 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M.Sc. t h e s i s , U n i v e r s i t y of B r i t i s h Columbia C.D.Wagner et a l , Anal.Chem. 19_, 976 ( 1 9 4 7 ) Dyer.John.R, i n " A p p l i c a t i o n of Absorption Spectro-scopy of,. Organic Compounds", P r e n t i c e - H a l l , I n c ( 1 9 6 5 ) G.O.schenk,H.Eggert and W.Denk, Ann. 5 8 4 , 177 ( 1 9 5 3 ) C.W.Tang ( 1 9 7 0 ) , "Quenching of 0 2 ( 1 A g ) by Amines" B.Sc.Honors Thesis U n i v e r s i t y of B r i t i s h Columbia L.E.Orgel, Quart.Rev. 8_, 422 ( 1 9 5 4 ) J.M.Murrel, i n "The Theory of the E l e c t r o n i c Spectra of Organic Molecules", p 2 7 2 - 2 7 3 -London.Methuen & Co ( 1 9 6 3 ) J.T.Herron and R.E.Huie, J,Chem.Phys. 5 1 , 4l64 ( 1 9 6 9 ) J.T.Herron and R.E.Huie, P r i v a t e Communication. 66. A.B.Callear and J.McGurk, Chem.Phys.Letters. 7_ , 491 (1970) 67. M.I.Christie, A.J.Harrison, R.G.W.Norrish and G.Porter, Proc.Roy.Soc. A231, 446(1955) 68. G.Porter, Disc.Farad.Soc. 33, 198 (1962) 69. R.J.Brovme (1969), "Halogen Afterglows and Excited Molecular Oxygen". Ph.D.Thesis. The University of B r i t i s h Columbia. 70. S.J.Arnold (1966). "Excited Molecules i n Gaseous Flow System". Ph.D Thesis. The University of B r i t i s h Columbia. APPENDIX. APPENDIX. The Error Analysis of Rate Constants. Errors involved i n rate constants were analyzed by the graphical method described i n the text book by Shoemaker and Garland. In the next page, an example for DMB i s shown. The difference between the two slopes or intercepts of the limiting lines was taken as the estimate of twice the limit of error i n the slope or intercept of the best straight line. Unfortunately the source of errors i n the present experi-ment has not been sufficiently clear yet. Particularly i n the case of olefins, i t was seldom possible to control the errors , not only by adjusting the flow rates of gases carefully but also by choosing the wall condition properly. P r e s s u r e ( t o r r ) 

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