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The thermal decomposition of methyl vinyl ether Harris, Jack Edward 1942

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THE THERMAL DECOMPOSITION  OF  METHYL VINYL ETHER  A thesis submitted i n p a r t i a l f u l f i l ment of the requirements f o r the degree of Master of Applied Science.  by, Jack Edward Harris  at THE UNIVERSITY OF BRITISH COLUMBIA 1941 - 1942.  ACKNOWLEDGEMENT  I wish t o thank Dr. Wm. Ure f o r introducing me t o t h i s f a s c i n a t i n g f i e l d of the study of K i n e t i c s , and f o r h i s patient guidance and help during the time spent i n experimental determination of the data herein and i t s subsequent mathematical treatment.  CONTENTS Page 1 2  INTRODUCTION EXPERIMENTAL  2 3 3 8  Preparation of Methyl V i n y l Ether F i r s t Generator Second Generator Removal of Gaseous Samples Reaction Chamber and Pressure Measuring Apparatus Temperature Control  8 10 13  TREATMENT OF DATA - PART I .  13 15 18 . 2 1  Pressure - Time Graphs Order of the Reaction Reaction Rate Constant Energy of A c t i v a t i o n TREATMENT OF DATA - PART II»  24  E f f e c t of the Ratio of F i n a l I n i t i a l Pressures The Reaction Rate Constant Energy of A c t i v a t i o n  31  COMPLICATING FACTORS  31 31 33  Extent of surface Condition of Surface E f f e c t of Wall Reaction on Rate Constant  3&  SUMMARY OF RESULTS MECHANISM OF DECOMPOSITION REFERENCES Appendix  24 23 25  ' 37  v  38 39  INTRODUCTION  This work has been done to supplement and continue that of Gordon Henry Turner as reported by him i n h i s t h e s i s "The Thermal Decomposition of Dimethyl A c e t a l " , now on f i l e i n the l i b r a r y of the U n i v e r s i t y of B r i t i s h Columbia. For an outline of previous studies leading to t h i s present work, 1 r e f e r the reader to the above mentioned thesis.  There he w i l l f i n d a l l the d e t a i l s necessary  for the understanding and appreciation of t h i s t h e s i s . For the most part I have referred to Turner's t h e s i s , when explanations of the d i f f e r e n t phases of t h i s present study,are contained t h e r e i n . Turner found that dimethyl a c e t a l decomposes to give methyl alcohol and methyl v i n y l ether.  I t was thus  considered desirable to study the thermal decomposition of methyl v i n y l ether i n the hope that i t would throw more l i g h t on the decomposition mechanism of the a c e t a l . Although t h i s work has confirmed assumptions made i n explaining the decomposition mechanism of dimethyl a c e t a l , i t has not been completed to the w r i t e r ' s satisfaction.  There are s t i l l complicating f a c t o r s which  could bear further i n v e s t i g a t i o n .  The reader's a t t e n t -  ion w i l l be drawn to these as they are mentioned i n the f o l l o w i n g pages.  EXPERIMENTAL  Preparation of Methyl V i n y l Ether, This preparation was c a r r i e d out a f t e r the method Chalmers ( 1 ) .  of Dr. Wm.  CH OHCH OCH —  (PBr^j —^  CH BrCH 0CH3 —  (NaOH)  2  2  2  2  5  -CHgRrCH^OCH^.CH2CHOGH3.  An excess of the methyl ether of ethylene g l y c o l (8-10 moles) was mixed with two moles of anhydrous e t h y l ether and placed i n a three-necked f l a s k provided w i t h a r e f l u x condenser, s t i r r e r and dropping funnel.  The f l a s k was  cooled i n i c e and water and two moles of phosphorus t r i bromide were added dropwise with vigorous s t i r r i n g .  The  mixture was then warmed on a water bath f o r several hours and allowed to stand over night.  Methyl bromo-ethyl  ether  was separated from the above .by repeated d i s t i l l a t i o n . The methyl v i n y l ether was made by the r e a c t i o n between the methyl bromo-ethyl ether and sodium-hydroxide.  This  was accomplished i n generators attached d i r e c t l y to the apparatus used i n studying the thermal, decomposition. These generators are shown i n f i g u r e s 1 and 2, and are described i n the paragraphs immediately f o l l o w i n g .  F i r s t Generator. The ether used i n making runs l a , 2a, 3a> 4a, and j?a was made i n the generator shown i n figure 1, The generator G and the column P were f i l l e d with sodium hydroxide p e l l e t s .  With stopcocks S I ,  S3, S3, S6 and S? closed, and S2, S4, S? and S8 open, and whole apparatus as seen i n t h i s diagram was evacuated through the vacuum l i n e • V , which leads through a mercury d i f f u s i o n pump t o a Cenco Hi-vac. Then stopcocks S4, S7 and S8 were closed. About 3 0 m l . methyl bromo-ethyl ether were introduced i n t o the generator through the funnel F and stopcock SI.  On warming the generator on a water  bath, methyl v i n y l ether d i s t i l l e d o f f and passed through the column P i n t o a' gas holder D (approx. 600ml. capacity).  The apparatus was so designed  that any of the bromo-ether leaving G would condense i n the condenser C and run back into P, where i t would be i n contact w i t h sodium hydroxide. A f t e r the r e a c t i o n i n G was complete, S3 was opened u n t i l mercury from the r e s e r v o i r R l had r i s e n above S2. Then both S2 and S3 were closed and the generator, column and condenser were removed by disconnecting the ground glass j o i n t J .  The gas contained i n D now consisted of methyl v i n y l ether together with any permanent gases (which might have been formed from impurities i n the bromoether or from the bromo-ether i t s e l f ) and possibly a trace of the bromo-ether.  The V i n y l ether was frozen  out by immersing the tube T l i n l i q u i d a i r and r a i s i n g the l e v e l i n g bulb LI to increase the pressure i n D. The permanent gases were pumped o f f through S4 and  S8»  Then with only 34 and S? open, the l i q u i d a i r was removed.  Before a l l of the ether had evaporated i n t o  the storage bulb B, S7 was closed and S8 opened t o allow the residue to be pumped o f f . Thus only the middle f r a c t i o n of the gases which had been generated i n G were stored, and the l i g h t e r and heavier f r a c t i o n s were discarded. Second-/. Generator. In spite of the precautions taken i n the above method of preparation, i t was thought that a more e f f i c i e n t type of generator could be devised. the generator shown i n Figure 2 was  Therefore  built.  As before, the whole apparatus was evacuated, and a l l stopcocks closed with the exception of S2.  The  traps Y and Z were immersed i n dry i c e and l i q u i d a i r respectively.  Then, w i t h cold water flowing through  the condenser C and hot water through the jacket H, about 3 0 m l . methyl bromo-ethyl ether were introduced  from F into the sodium hydroxide packed generator G-. The design of t h i s generator was such that any bromoether which evaporated while the pressure i n the apparatus was s t i l l low would be i n contact with sodium hydroxide f o r a longer period of time before passing into the condenserj and that which condensed i n C could run down t o the heated part of the generator. What l i t t l e bromo-ether passed through the condenser was caught i n the dry i c e trap.  Thus only the very low b o i l i n g point  constituents found their way to the l i q u i d - a i r trap. A f t e r the r e a c t i o n was complete, S2 was sealed with mercury and the generator, condenser and dry-ice t r a p were removed. Then S4 and S8 were opened and the permanent gases pumped o f f . On the removal of the l i q u i d a i r , the f i r s t f r a c t i o n of methyl v i n y l ether evaporating was stored i n B. The remainder was taken from the trap to T l by immersing t h i s tube i n l i q u i d a i r .  Then, on the removal of the l i q u i d  a i r from T l , part of the ether was allowed t o evaporate i n t o D and the r e s t was sealed o f f i n T l . The ether stored i n D was used i n a l l of the b-runs, and that stored i n B was used i n the c-runs.  When a  decomposition run was t o be made, the ether was taken to the reaction chamber through S£. A f t e r the run had been completed, titee products of the decomposition were removed  through S3 and stored i n the previously evacuated storage bulbs b l , yz, b3 and b4. Removal of Gaseous Samples,, To remove gaseous samples for a n a l y s i s , the appropriate stopcocks were opened and the gas t o be analysed was pumped . o f f through S9 t o a burette - a Topler pump being used f o r t h i s pumping.  The samples taken fromthe burette were stored  over mercury and. microanalysed (2). Reaction Chamber And Pressure Measuring Apparatus. .  Figure 3 shows the method of accomplishing the thermal  decomposition of the methyl v i n y l ether at constant volume, and of measuring the pressure at progressive stages throughout the decomposition. The furnace F, enclosing the decomposition chamber X and the platinum resistance thermometer PR, was brought to the desired temperature, and the whole apparatus as seen i n f i g u r e 3 was evacuated through S 3 , SI2 and S13. Then a l l other stopcocks were closed and S14 was opened u n t i l mercury from the r e s e r v o i r R2 had r i s e n i n t o the U-tube U t o the l e v e l H.  I t w i l l be seen that manipulation  of 310, S l l and S14 leading t o the a i r leaks A l , A2 and A3, and through YB t o a vacuum b o t t l e , made i t possible t o c o n t r o l the mercury l e v e l i n e i t h e r or both of the arms of the U-tube.  9  Ether was l e t into X through Sj> u n t i l the l e v e l i n U showed that the desired i n i t i a l pressure f o r the r e a c t i o n had been reached.  Then Sjp was closed and a i r allowed  i n t o SV (a s t a b i l i z i n g volume) through A l and A2 u n t i l the l e v e l i n U was brought back to H. between the c l o s i n g of  The time which elapsed  and the r e - e s t a b l i s h i n g of the  l e v e l H was recorded together with the pressure read from the manometer M« A i r was l e t into Sv at regular i n t e r v a l s ; and, each time the l e v e l H was re-established by the pressure b u i l d i n g up i n X, the time and pressure were recorded. I t w i l l be seen that each time the l e v e l H was established the pressure i n Sv was the same as the pressure i n X, and therefore the pressure measured by M was i d e n t i c a l w i t h the pressure i n X. Other parts of the apparatus not explained above are l e v e l i n g bulbs to manipulate mercury f o r sealing stopcocks, c a p i l l a r y tubes to retard the flow of gases, and traps to catch w i l d mercury,  l i q u i d products e t c .  Temperature Control. Figure 4.is a w i r i n g diagram showing the methods used to c o n t r o l and measure the temperature. The furnace F l was coupled i n series with a variable resistance R l , an ammeter A and a 110V-j>amp variac V.  Across R l was a secondary c i r c u i t c o n s i s t i n g of another variable resistance R2 and a photoelectric r e l a y (PEC) i n series.  The double throw switch SF was placed i n the  secondary c i r c u i t to accomodate another and s i m i l a r arrangement f o r another furnace. The platinum resistance thermometer PR1 was wired across the center poles of the double throw switch SS another double throw switch SP being placed i n t h i s l i n e to acoompodate the platimum resistance thermometer used i n conjunction with the other furnace.  The side of the ..;  switch SS l e d to t h e wheatstone bridge WC and from there to the galvanometer Gl used with the photoelectric r e l a y . The other side of SS was l e d t o the wheatstone bridge WM and from there t o a second 'galvanometer G2. With the proper adjustment of R l and R2 any desired temperature i n the furnace could be maintained by the correct s e t t i n g of WC, and t h i s temperature could be measured on WM by means of the l i g h t L2 and the scale Sc used i n conjunction with G2. The above method of c o n t r o l l i n g and measuring the temperature i n the furnace was found to be e n t i r e l y satisfactory.  At no time during a run was the temperature  found t o vary more than 0.035<?C on e i t h e r side of the recorded temperature of the run.  TREATMENT OF THE DATA. — PART 1.  .  Pressure - Time Graphs. Experimental t o t a l pressures were plotted as ordinates against time as abscissae. From the curves so obtained, "smoothed" values or the t o t a l pressures corresponding to equal increments of time were tabulated and used i n the following calculations. Graph 1. shows the type of curves obtained when t o t a l pressures were divided by corresponding i n i t i a l pressures and plotted against time.  Dividing by the i n i t i a l pressures  f a c i l i t a t e s comparisons of f r a c t i o n a l increases i n pressure from one time to another during a given run, or from one run to another f o r a given time. Each curve w i l l be seen to turn upwards at the beginning.  The length of time f o r which t h i s was noted  varied from curve t o curve and seemed t o depend upon the temperature and i n i t i a l pressure and upon the c o n d i t i o n of the r e a c t i o n chamber.  For r e l a t i v e l y high temperatures  and f o r high i n i t i a l pressures the e f f e c t was nearly indisoernable because of the more rapid increases i n t o t a l pressure due t o the main r e a c t i o n .  It is difficult,  therefore t o c a l c u l a t e the dependence of t h i s "induction" period upon temperature and (ore) pressure.  Experiments  with a i r proved that i t was not due to the heating of the  ether from room temperature to the temperature of the run. This takes an immeasurably short time. Order of the Reaction. Graph I I . shows  J . 2 — plotted against time, where Pf "Pt  p  Q  i s the i n i t i a l pressure, p^ i s the f i n a l pressure and  P  t  i s the t o t a l pressure at time t . The i n i t i a l pressures  were calculated from the f i n a l pressures by d i v i d i n g by 2.2 . This value was determined by introducing methyl v i n y l ether into the cold r e a c t i o n chamber, measuring the pressure, heating u n t i l the decomposition was complete and then measuring the f i n a l pressure. The value 2.2 i s an average of several runs made i n t h i s manner. The f a c t that the curves i n Graph I I . approach l i n e a r i t y shows the decomposition r e a c t i o n to approximate an o v e r a l l second order r a t e . I f the r e a c t i o n were second order the r a t i o s t  \^-/^.  tl/2  and , 3/4 should be 1/3 and 3 r e s p e c t i v e l y ! where t i / 4 , •fcl/2  * l / 2 and ^3/4 are the times necessary f o r decomposition of 1/4, 1/2 and 3/4 of the ether r e s p e c t i v e l y .  Table 1  shows that the above r a t i o s would indicate an approximately second order r e a c t i o n .  From t h i s we may conclude that the  main r e a c t i o n i n the thermal decomposition of methyl v i n y l ether i s d e f i n i t e l y second order.  ief  O >  /o  Jo  Run: 2b " 433°C  o  7  Jo Jo  ...  .  Run l b / c> 423 °C .• /o /o  ^.  b -  • -  Run 3b 4I3°U  >  °/  2o :  . :  •j  •'  /  •<  •  1 ;  .  :•  VI  1  Run 4b 403 °G i  / (/  1  •  Q/  o/ o/ o/ 9 / of / </  I  Run 6c > 390°Q  / / G/ • •ClT-  .  •  •.  i  5 I  •  O / V  -  - •  . —  ••  i  GRAPH I I .  -  •«<  X  (< • • •  °0  10  .2©  J0  time i n minutes  ;40  • i  TABLE 1  t  Run  T°C  la  400 423  5a 2a 3a 4a  403 413  lb  423 433  6c  390 403  2h•,  3c  \/2  .41  423 430 439  4b 3b 5b  l/4  .37  .35 .37 .35 .36 .39 .36 .36  414  .31 •  A9  414 ! . 3 6 .44 414  t  l/2  2.70 3.99 2.88 3.13 3.03  3.24 2.60 3.25  3.24  3.14:  423 453  .28 ,33  413  .41  3.53 3.53 2.99 3.13 2,95  averages  .35  3,15  5c 1c 2c 4c 7o  Reaction rate constants (kg) were calculated for each run by use of the formula-  §=L  (.  t  p  f  - p  t  p  f  ) ——(appendix - p;  (1))  Q  where S i s the r a t i o of f i n a l to i n i t i a l pressures determined as described above. Values f o r kg calculated i n t h i s manner did not show any d e f i n i t e dependence upon temperature.  This was assumed  to be p a r t i a l l y due to what I have, f o r convenience, termed the "induction" period. As w i l l be seen i n the following example (chosen to show t h i s e f f e c t ) , the determination of an exact constant f o r the rate of the main r e a c t i o n was almost impossible - at l e a s t by t h i s method. Since values of kg so calculated were i n most cases constant over considerable periods of time, i t was decided that the main decomposition r e a c t i o n was d e f i n i t e l y second order.  Since averaging values such  as those i n table 2 would not give good r e s u l t s , the r e a c t i o n rate constants used f o r f u r t h e r c a l c u l a t i o n s were obtained from the formula k  2  2  2  »• ^ » ti/g  —(appendix  (2))  P f  The constants obtained i n t h i s manner are tabulated i n table 3. These values showed better agreement f o r runs at the same temperature and showed a temperature  relationship  TABLE 2. Run 1c 414°C  min. 0 2 .4 6 8  10  12 14  16 18  20 22 24 26 28  30 32 34 36 38  40 -  P cm.  2z  fc  zl03  7.00 7.55  5.0  8.20  5.0 6.7 7.1 8.5  8.85 9.50  10.15  10.70 11.05  11.30  11.50  ll.6o  11.75 11.90 12.05 12.15 12.50  12.40  9.4 9.5  9.4 9.1  8.7 8.4 8.3 8.3 8.2 • 8.2  12.70  8.1 8.1 8.1 8.1  12.85  8.2  12.50  12.60  Pf * 15.40  e f f e c t of induction period  TABLE 3  t  Run la 5a 2a 3a 4a  T°G 400 423 423 430  439  l/2  fc  Remarks  8.65' 2.90 2.48  .0359 .0105 .0273 .0428  p^ too low.  9.52 5.27 9.25 2.78 1.85  .0081 .0110 .0185 .0183 .0269  •21.10 2 2 . 1 0  „0022 .0031 .0075 .0093 .0112 .0200 .0111  Po cm 13.30 6.32 10.95  9.40 9.40  2  mm _~  4.40  proven unreliable by Po/Pf-Pt *• v s  4b 3b 5b  lb 2b  6c 3a 5c  le  2c 4c 7c  403  413 414  423  433 390 4o3  414 414  423  433 413  12.90 17.20 5.85 19.60 20.10 15.05  21.65 17.40 7 . 6 8 7.00 15.30 15.80 8.10 10.50 4,75 6.O7 14.95  Po too low.  •  as seen i n Graph I I I . I t w i l l be noticed that the points i n t h i s graph congregate i n zones, and that the averages of points w i t h i n each zone show a d e f i n i t e trend from zone to zone. Energy of A c t i v a t i o n . The energy of a c t i v a t i o n (E) f o r a second order reaction i s given by the equation k  =  2  1  2  AT / : e" |§r  from which we may derive* E = 2.303R  l o g i o k _ RT_ — (appendix(3)) "T*T ~~ 2 . . d-^r2  and since RT i s r e l a t i v e l y small compared with E, •E  * - 2.303R  Thus p l o t t i n g l o g line.  1 0  k  d  l Q  k  g l O 2 = const. d-L. . •T a g a i n s t _ l _ should give a s t r a i g h t ^  2  This however was not the case.  But on p l o t t i n g  logj_0 kg against T the s t r a i g h t l i n e i n Graph IV. was obtained - i n d i c a t i n g the r e l a t i o n s h i p E = 2.303R  £J^glp_kg_ d T  2  — PTL --.-(appendix ( 4 ) )  • O.IT - 0.992 T 2  = 48,300 cals at 430°0 and 44,600 cals at 400°C.  1  1 l!  22t  i. Am  4>>U  >  4.4.0 •  • i:  C jC • •  r  4p (J  C a; CO W/ L ; '  /@  A •  / o  o]  a  a  ro  1 C  > !  ;• ob  'O jC A~\ Pi  'I  "b  41U  GRAPH i CI. :  c - /b a——a  !o o ol  b~—b  R HIS. R ins.  400 7  / -;-<§>-fc> pyo  '  T]le double < s i r c l e s ar< i averages , The p t s . v ?  xrylng widf sly from t.le trend hi ive not  -b< j-e-n—:i-nc-l-ud-f jd—i-n—t-he—i  XV Hi  ago a •  I  7 on ()•  1' ,  ;  -  ..  ....  I  ; kgXlO  2  2^  ...  .  .  .....  |  440  \  "  GRAPH IY. ••• •  •  •  •  .  :-I  •  4p0 \ o il.  420 -  T  , e  |;|  G  \  3\ \ ,  410  t :  . . lit  ' • ii  I x  •  Z O O  < l  ;  f •  >3 - '  '  •  c J -1 ° 10 2 S  k  " C  N » J c  <y  L  • ' ".  c  J  •  c  J  i  The fact that the o v e r a l l reaction was proven to approximate a second order rate would indicate that, although t h i s l a s t equation may give values of the a c t i v a t i o n energy which are of the r i g h t order of magnitude, the equation i t s e l f could hardly be expected t o hold over any reasonably large range of temperatures.  ': TREATMENT OF THE DATA — PARTII. E f f e c t of the Ratio of F i n a l t o I n i t i a l Pressures, The dependence, or apparent dependence of the a c t i v a t i o n energy upon temperature was thought to be due to the condition of the reaction chamber.  I t w i l l be remembered  that the r a t i o s of f i n a l to i n i t i a l pressures were taken as 2,2 f o r every run.  I f , however, the pressure - time  curves are extrapolated t o zero time, the actual values of t h i s r a t i o very and 2,2 i s just  an average.  I t i s -time  that the difference between these values and the average was never more than -give percent, but the f o l l o w i n g c a l c u l a t i o n s show that t h e i r use i n place of the average gives a constant value f o r the a c t i v a t i o n energy while having l i t t l e e f f e c t upon the other data. Using the i n d i v i d u a l values of Pf and the P 's from Po 0  extrapolation of the pressure - time curves, i t was found that the curves i n Graphs I and I I were not noticeably s h i f t e d , and that the approximation of an o v e r a l l second  order rate was indicated as before. Table 4. shows the values of s=p /p and the e f f e c t they have f  0  on. previously calculated data. The blank spaces i n table 4 correspond t o curves which could not be extrapolated to zero time. The Reaction Rate Constant. Table j>. gives the values of kg calculated by use of the formula kg = l/pot^yg.  (appendix (2))  This table includes only runs f o r which the pressure time curves could be extrapolated to zero time. With the exception of kg f o r run 4b , the values i n columns a and b check quite c l o s e l y , but i t w i l l be seen that those i n column b show more r e g u l a r i t y than those i n column a. Energy of A c t i v a t i o n . Under t h i s heading i n part I i t was explained t h a t , f o r a second order r e a c t i o n , the energy of a c t i v a t i o n i s given by the equation <i( loglG-k?) • E - -2.3Q3R a)lt ~ constant. and p l o t t i n g l o g k g against 1/T should give a s t r a i g h t 1 Q  l i n e . Graph V. shows t h i s c o n d i t i o n f u l f i l l e d f o r the reaction rate constants i n column b, table 3» The slope of the l i n e i n Graph V. i s - 3 , 0 0 0 , giving E = 24,900  calories.  This value would appear to be extremely low and i s d e f i n i t e l y not i n agreement with that previously c a l c u l a t e d .  TABLE A  NOTE - s<=2.2 f o r (a) columns and. i s v a r i a b l e f o r (b) columns. e  Rum T c:  6e 390 l a 400 4b 403 3c 403 3b 413 5b 414 l c 414 5c 414 7c 413 l b 423 2a 423 5a 423 2c 423 3 a 430 4e 433 2b 433 4a 439  c m  Po (a) m 21.10  13.30 12.90 15.05 17.20  5.85 7.00 17.40 6.07  19.60 10.95  f  (A)  C>)  (  20'. 95 46.40  2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2.2 2,2 2.2 2.2 2.2  2.22  22.10  29.25  12.40 16.80 5.90 17.10 19.33  15.80 9.40 10.40 19.22  28.40 33.10 37.85 12.85 15.40 38.30  13.35 43.12 24.10  13.90 34.75 20.70  23.10 20.10 44.22 9.40 : 9 . 8 0 20.65  2.2  t  3/4  ^1/2  (a&b)  6,32  10.50  Jl/4  s  p em  2.29  2.23 2,18 2.24 2.24  (a)  (b)  21.15  .31  .31  *  5.93  9.52  21.65  5.27 9.25 15.30  7.68  14.90 2.78  8,65 4.40 8.10  2.22 2.30 2.09  (b)  2.90 4.75  1.85 2.48  T  £7$i 12.60  .35 ; " 3 6  .19 .36  7.27  .36  2.79  .36  4.50 1.75 3.20  averages  .28  .39 .44 ; . 3 0  .41  .35  .37 .41 .28 .35 .33  .34  .36  .34  .35  .37  .33  .35  .33  (a)  (b)  3.03  2.57  2.60 3.53  3.00  3.14 3.24  2.51  3.53 2.95  3.72  3.13 3.24 3.13  3.23 3.28 3.34  3.15  3.11  3.25 3.99 2.70 2.99 2.88  3.21  TABLE 5. 2 . 2 f o r (a) columns and i s v a r i a b l e f o r (b) columns. Run  6c 4b 3b 3c  lb  4©  2:b  4a  T°C  390 403  413 414  423 433 433 439  kg (a)  (b)  .0022 .0081 .0110 .0073 .0183 .0200 .0269 /0428  .0022 .0136 .0093 .0081 .0185  .0214  .0298 .0339  S8 i  ,..0027-  .0026'  'j -  *0025"  'i  O  0024  -  I T°C  ....  ..  •:  •  i  ..  o/ Q/Q  i • ••  GRAPH V.  • • : •  •  •  '  <•> • ; - - •  t  ^-N  H  .  .  ,.  C C• og k 10 2  k  To obtain the best value f o r the energy of a c t i v a t i o n i t was decided t o use a l l of the i n d i v i d u a l values f o r kg and l o g  solve f o r the slope  $S  l c f e L by the method of l e a s t  squares. Thus ^iog  1 0  k  2  - r i  • b,  m  %]0&L  where the slope m =  d{1  d(^(  Yl  r ^io£l0^1 (  /-TT 2  )_T ' Z j f ^ = -8,500  Prom t h i s we have: s  - -8,500  x(-2.303)(1.985)  - 38,800 calories.  Although p l o t t i n g the r e a c t i o n rate constants f i r s t c a l c u l a t e d against l/T does not show any d e f i n i t e trend (Graph V I . ) , the a c t i v a t i o n energy c a l c u l a t e d from these by the above method i s obviously the best value obtainable from the data i n hand. On consideration of the work of Turner and of the r e a c t i o n rates i n t h i s t h e s i s , i t w i l l be seen that 5 8 , 8 0 0 c a l o r i e s i s reasonable f o r the energy of a c t i v a t i o n i n the thermal decompdjsition of methyl v i n y l ether.  sc  j 1 :\ ' ' J  '  '  '  00° f)  The ob lia.ue_li.ne s show the s t r a i g h t l i n e trend by the met hod of lees t  I  squares -j  a l i o 1510^2.1 _ _ 8,500 d  />f  00 i 1  (D  . O ' ...  .  .  • .......  f. CD  O .  o  o I 1,  _.0.02-4_  |i •  o  C'  GO  -  •  O o ...... -QQ-2rJ)  GRAPH Y I . o  .x" . ' .  J •  c  ...  ! . . . .  . . .  f\ -  c!>' c> «  r -1 o g k 1 0  J 2  f\ C» 1  -  <  c% «  J  -  -  COMPLICATING FACTORS. -In a d d i t i o n to the runs previously discussed, four runs were made with a r e a c t i o n chamber packed with glass tubing to give a surface 6.25 times as great as that of the unpacked chamber. The information gained from these runs threw more l i g h t onto f a c t o r s such as:(I)  The e f f e c t of extent of surface.  (ii)  The e f f e c t of condition of surface.  To study these e f f e c t s , four runs (2a,2c,8c, and 11c) a l l made at 423°C were considered as f o l l o w s . Extent of Surface. Graph V H . shows that there i s a r e a c t i o n dependent upon the extent of surface which tend to suppress the b u i l d i n g up of pressure due t o the main r e a c t i o n . Thus we have the branching of the two sets of ,-lines - the lower branch In each set showing the r e s u l t of adding to the extent of surface i n contact w i t h the decomposing ether. This may be taken as an i n d i c a t i o n of a free r a d i c a l mechanism ( 3 ) . Condition of Surface. The condition of the walls of the r e a c t i o n chamber i s by f a r the most important f a c t o r . Reference to Graph V I I . shows that the extent of surface does not have much e f f e c t upon the general shape of the pressure - time curve, while the number of runs previously made i n a chamber (whether  1  -  1  1  i  •  •  2.25  I 3  Run 8 ct 4 2 3 c . Run 2 £L 423 °C.  2 4  Run 11ci 423°c; Run 2 c : 423°C  -  e  '  _4_  1-T75  3  -  = = = = =  ==a  1  - ~  "  1.50  Pt/P  .  0  ^  ;  ...  .....  .  CffiAPH V I I . 1.25  -  l.do c  10  a)  30  4  time i n mj.nutes. w to  packed or not) Is of great importance i n t h i s respect. On comparing the values of t , . (table 6 . ) we f i n d 1/2 a good index t o the dependence on w a l l conditioning of what must be the combining of f r e e r a d i c a l s on the w a l l s . ( 4 ) . I f we assume a chain mechanism involving free r a d i c a l s , we'-may conclude that the combining of these r a d i c a l s on the chamber walls terminates the chain and slows up the decomposition.  As more and more runs are made i n a given  chamber, the walls become conditioned i n such a manner that the free r a d i c a l combination i s slowed up. This leads t o a f a s t e r o v e r a l l decomposition rate. E f f e c t of Wall Reaction on Hate Constant. The e f f e c t s of both extent and condition of surface are seen i n table 7.  Increased surface decreases the rate  constant as seen by comparing the constants f o r 8c and 11c with those f o r 2'c and 2a r e s p e c t i v e l y .  Conditioning of the  surface also increases the rate constants as seen by comparing kg f o r 8c with that f o r 11c. 2c and 2a do not show t h i s e f f e c t .  The constants f o r  This may be due to t h e i r  not being accurate enough and to the extent of surface of the unpacked chamber not being great compared with the i n i t i a l pressures. L i t t l e has been said and l i t t l e can be said about what has been previously termed the "induction period". A study of the pressure - time curves shows that t h i s period at the  TABLE 6  Runs at 423°C.  Run  no. of previous runs  * l  kg /  8c  0  20.38  .0029  . 2c  ' 1  P. 10  .0112  11c  3  ' 8.55  .0069  8.65  .0105  4.40  .0359  2.78  .0185  2a 3a i*  5  Remarks.  2  packed with glass tubing.  packed with glass tubing  TABLE 7  Runs at 423°G.  Run  Packing  8c  yes  0  .0029  2a  no  1  .0112  11a 2a  No. of. previous runs  .0069  yes no  3  .0105  beginning of each run v a r i e s with i n i t i a l  pressure,  condition of surface, temperature and extent of surface. These f a c t o r s are w r i t t e n i n the order of t h e i r e f f e c t i n i t i a l pressure being most important.  SuMftARY. OF RESULTS ,The f o l l o w i n g i s a tabulated summary of the r e s u l t s of t h i s work on the thermal decomposition of methyl v i n y l ether. 1.  The o v e r a l l rate of decomposition i s second order.  2.  An increase i n surface lowers the r a t e .  3. "Conditioning" the walls increases the r a t e . 4.  There are three main f a c t o r s (a) the main decomposition. (b) the induction period dependent upon I . i n i t i a l pressure. I I . condition of surface. I I I . temperature of decomposition. IV. extent of surface. (c) a free r a d i c a l mechanism dependent upon I,  condition of surface.  I I . extent of surface. 5.  The a c t i v a t i o n energy i s approximately c a l o r i e s per mole.  |^ 000 ?  MECHANISM OF DECOMPOSITION I t i s d i f f i c u l t t o propose a mechanism f o r the decompo s i t i o n u n t i l analyses of the intermediate and f i n a l produots have been completed.  Following, however, are  equations giving what appear t o be l i k e l y steps i n the decomposition (1)  CH3-0-CH=CH  CHj + CH C0H.  2  2  —-5^"  (2)  2CH^ + CO.  CH^ + CH3-0-CH=CH — C H 2  CH (3)  + CH -0-CH=CH .  4  + CO * C H .  2  2  2  2  CgH^ + CH^-0-CH=CH — j ~ C H '  (4)  4  2  6  5  + CH ~0-GH=CH . 2  2  C H£ + GO -t GgH^. 2  C H^ + CHj —*« C^Hg. 2  Equation (4) i s presumably the reaction terminating the chain.  This would be dependent upon the extent and  condition of the surface of the r e a c t i o n chamber ( 3 )  REFERENCES.  (1) P r e p e r a t i o n of Ethers of V i n y l A l c o h o l - Win. Chalmers. Canadian Journal of Research  7, 464-71  (1932).  (2) The Thermal Decomposition o f Dimethyl A c e t a l - G. H. Turner. - a t h e s i s , U.B.C. ( 1 9 4 1 ) .  (3) The A l i p h a t i c Free R a d i c a l s . - F.O.Rice and K.Rice.book, Johns Hopkins (1935)•  (4) On the Polymerization of Ethylene and Propylene by Free A l k y l R a d i c a l s . - Beech and Rust ( S h e l l Development, J . Chem. Phys.j 9 - 480 ( 1 9 4 1 ) .  ( 3 ) Reference ( 3 ) .  APPENDIX Symbols used i n the f o l l o w i n g derivations are as l i s t e d below -  •  p  Q  =  i n i t i a l pressure.  p  f  =  f i n a l pressure*  p^ =  t o t a l pressure at time t .  p^l=  pressure of undecomposed ether at time t .  s  r a t i o of f i n a l to i n i t i a l pressure.  =  * l / 4 » - i / 2 and t = 1/4, 1/2 and 3/4 l i f e respectively. ' t  3  (1)  /  4  To obtain the r e a c t i o n rate constant from the pressure - time data.  dt  V ' = k dt. 0  d  P +  tr  but  P  _ 1  1  IT \  - s p . giving  f  0  +  P * P s(p -p T). •n Pf~Pt ' s-1 and at zero time t  t t  0  t  f?)  m  J)Q  •  »  o  «  •  •  from equations, ( 1 ) , (2) and (3) kj,t—5=5L - s - l Pf~Pt Pf-Po thus  k? - ^ — ( ^ r - - ™ T H «  *  • * •• » • i j5 )  (2) To obtain the reaction rate constant from the h a l f l i f e . From part; (1) pt.  for t  l  /  -  2  V ^.  P-fct " l/2po and p =  t±  t  then  ...simly;  P  t l / 2  = Pf- ( ^ l ] | = (( 1-^(|-) )bf•  p  t  i  /  ^  ((1-5=1(1)  P  t  5  A  -  (( 1 ^ ( 1 )  P o  ))p . f  Thus, from the calculated values f o r the t o t a l pressures at t y , t y 1  4  1  and t^/4 the values, of t-j^/4, t-jy  2  and 2  - ^3/4  can be read from the pressure - time curves. k  1  " dt 2 P To get the r e a c t i o n rate constant i n terms of the h a l f l i f e , we integrate the above equation as p goes from p t o o 0  1  —p  Q  and % goes 0 t o t-jy . k from = 2  2  Po°l/2  but p  G  » P-^, therefore s k„ =  2 " Prtx/g  and  f o r s=2.2  v  k  2  „ „  - 2.2 ~ r-r V l / 2  (3) The a c t i v a t i o n energy. For a second order r e a c t i o n 1/2 _ E kg = AT e RT F 1 l n k ~ - £7=r + I n A + j i n T 2  (1)  d i f f e r e n t i a t i n g ( l ) w i t h respect t o l/T ' ;  d(lnkg) _ E d(|) ~ ~ *  T 2 '  E = - R i U n k g i _ RT. T = - R 2H2iio^i(2»303)  -  T (4) D i f f e r e n t i a t i n g (1) i n part (3) with respect t o E = d(LMk:) 2 PRT  RTg  = 2.303- R AilO£ k l 2„ HT. dT 10  2  T  d  

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