KINETIC STUDIES ON THE GAS-PHASE DECOMPOSITION
OF TRIMETHYLBORANE
DISSERTATION
Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University
, By
JOSEPH ARLAN LOVINGER, B.S.
The Ohio State University
1959
Approved by
Adviser Department of Chemistry ACKNOWLEDGMENT
The author wishes to acknowledge the guidance and suggestions of Professor Frank Verhoek during the course of this study.
The author gratefully acknowledges the financial assistance afforded hy the University Grants-in-Aid, the DuPont
Research Grants-in-Aid, and the General Electric Company for the
General Electric Fellowship. CONTENTS
Page
Part I. THE "TOLUENE CARRIER" TECHNIQUE
I. INTRODUCTION ...... 2
II. APPARATUS AND TECHNIQUES...... 1+
The Furnace...... U The Reaction System ...... 7 Chemicals .’ ...... 9 Procedure...... II Analysis of Methane and H y d r o g e n ...... 13 Low Temperature B a t h s ...... lU
III. RESULTS...... 15
Preliminary Experiments ...... 15 The Effect of Pre-pyrolysis on the Decomposition of Toluene ...... 17 Reaction of Trimethylhorane and Toluene ...... 23 Effect of the Wall on the Pyrolysis of Toluene . . . 23
IV. DISCUSSION...... 27
Part II. STATIC PYROLYSIS OF TRIMETHYLBORANE
V. INTRODUCTION...... 30
VI. APPARATUS AND TECHNIQUES...... 31
The Furnace...... 31 The Reaction S y s t e m ...... 32 Chemicals...... 35 Gas Chromatography...... 36 Procedure...... 37 Analysis of Products ...... ^2 E r r o r s ...... ^
VII. R E S U L T S ...... ^7
iii iv
CONTENTS (contd.)
Page
Trimethylborane...... kj Trimethylborane and Propylene ...... 7^ Trimethylborane and E t h y l e n e ...... 79 Trimethylborane and Azomethane ...... 82 Trimethylborane and Nitric Oxide ...... 8j
VIII. DISCUSSION...... 91
O r d e r ...... 91 Activation En e r g y...... 93 Stoichiometry...... 95 Mechanism...... 101
IX. S U M M A R Y ...... 120
X. SUGGESTIONS FOR FUTURE WO R K ...... 122
Appendix A ...... 125
Appendix B ...... 131
Appendix C ...... 138
Bibliography ...... 1^5
Autobiography ...... 1^7 LIST OF TABLES
Table Page
1. Low Temperature B a t h s ...... ].L
2. Data for Preliminary Experiments for the Reaction of
Trimethylborane and Toluene ...... 16
3. Analysis of Condensable Material from Experiment 15 . . l8
Conditions for the Pre-pyrolysis of Toluene...... 20
5. Data for the Pyrolysis of Toluene...... 21
6 . Data for the Pyrolysis of Trimethylborane and Toluene . 2k
7. Effect of the Wall Coating on the Pyrolysis of Toluene. 25
8. Pyrolysis of 2L-2.6 Micromoles of Trimethylborane at
L68° C ...... 5^
9. Pyrolysis of 97-3 Micromoles of Trimethylborane at
L88° C ...... 55
10. Pyrolysis of 175*1 Micromoles of Trimethylborane at
L8 8 ° C ...... 56
11. Pyrolysis of 2^3.^ Micromoles of Trimethylborane at
k 8 Q ° C ...... 57
12. Pyrolysis of 2kk.7 Micromoles of Trimethylborane at
lf-98°C...... 58
13. Pyrolysis of 95.6 Micromoles of Trimethylborane at
5 0 8 ° C ...... 59
v Vi LIST OF TABLES (contd.) Table Page
]A. Pyrolysis of 239-9 Micromoles of Trimethylborane at
508°C ...... -...... 60
1 5 . Pyrolysis of Trimethylborane in the 229-5 cc Packed
Quartz Flask at U8 8°C 70
1 6 . Pyrolysis of Trimethylborane in the 229-5 cc Packed
Quartz Flask at 50 8 ° C ...... 71
17. The Effect of a Fresh Wall Coating on the Pyrolysis
of Trimethylborane at W 3 8 ° C ...... 73
18. Experiment 21-11. Pyrolysis of Propylene at ^88°C . . 7h
1 9. Pyrolysis of a 1:1 Trimethylborane-Propylene Mixture
at kQQ°C ...... 77
20. Pyrolysis of Trimethylborane and Ethylene at U88°C . . 79
21. Pyrolysis of Trimethylborane and Azomethane in a 110 cc
Quartz F l a s k ...... 83
22. Pyrolysis of Trimethylborane in the Presence of Nitric
Oxide at 1+88°C...... 88
2 3 . Data for the Order Dependence of Trimethylborane . . . 92
2k. Pyrolysis of Trimethylborane at if37°C by Goubeau and
E p p l e ...... 101
25. Mass Spectra...... 135 LIST OF FIGURES
Figure Page
1. High Temperature Core Furnace for the Flow System . . . 5 2. Temperature Distribution of the Core F u r n a c e ...... 6
3. Vacuum System - "Toluene Carrier" Experiments ...... 8
1+. Automatic Toepler Pump and Controls...... 10
5 . Arrhenius Plot for the Pyrolysis of Toluene...... 22
6. Reaction System for the Static P y r o l y s i s ...... 33
7 . Pressure-Time Curves for Some Preliminary Experiments . L8
8. Pressure-Time Curves Showing the Effect of Adding Air to the Reactor Between Experiments...... 50
9 . Pressure-Time Curves Showing Apparent Irreproducxbility at 1j8 8 ° C ...... 51
10. Relationship Between the Observed Pressure Increase and the Moles of Trimethylborane Reacted...... 53
11. Change in Composition for the Pyrolysis of 2^2.6 Micromoles (97*1 mm-) of Trimethylborane at L-68°C. 63
12. Change in Composition for the Pyrolysis of 97-3 Micromoles (^0.7 mm.) of Trimethylborane at L88°C. 6h
1 3 . Change in Composition for the Pyrolysis of 175*1 Micromoles (72.6 mm.) of Trimethylborane at L8S8°C. 65
lL. Change in Composition for the Pyrolysis of 2L3 A Micromoles (101.7 mm.) of Trimethylborane at L88°C 66
15. Change in Composition for the Pyrolysis of 2kb.J Micromoles (102.2 mm.) of Trimethylborane at L98°C 67
16. Change in Composition for the Pyrolysis of 95.6 Micromoles (lj-0.6 mm.) of Trimethylborane at 508°C. 68
vii LIST OF FIGURES (contd.)
Figure Page
17. Change in Composition for the Pyrolysis of 239-9 Micromoles (102.7 mm.) of Trimethylborane at 508°C 69
18. Comparison of the Decomposition of Trimethylborane Alone and in a 1:1 Mixture with Propylene at L88°C ...... 76
19. The Effect of Added Substances on the Pyrolysis of Trimethylborane...... 80
20. Falling-Off of the Rate Constant for Azomethane Ramsperger (20) - . 85
21. Activation Energy for the Pyrolysis of Trimethylborane. 9k
22. Stoichiometry Curves for Hydrogen Formation...... 97
23. Stoichiometry Curves for Methane F o r m a t i o n ...... 98
2k. Tetra-B-methylcyclo-l,3>5>7 boroctane ...... 99 PART I
TEE "TOLUENE CARRIER" TECHNIQUE
1 I. INTRODUCTION
This portion of the work is concerned with attempts to determine the kinetic bond energy of the boron-carbon bond in tri methylborane by use of the "toluene carrier" technique developed by
Szwarc (l) . In this method the compound under study is mixed with a large excess of toluene and the mixed gases passed through a reactor in a flow system.
At the high temperatures at which this method is used, the toluene acts as an excellent radical trap. Thus if a methyl radical is formed it reacts with toluene to give methane and the benzyl radical which is a stable radical at high temperatures and will not undergo any radical reactions except recombination after leaving the reactor. Therefore there can be no radical chain reactions occurring.
The activation energy of the reaction is equated to the kinetic bond energy of the first bond broken.
The "toluene carrier" technique has been applied to the study of the decomposition of dimethylmercury (2 ,3) and dimethyl- cadmium (3). The mechanisms for these decompositions are similar; that for dimethylmercury (2) is as follows:
Hg(CH3) 2 - HgCH3 ♦ CH3 (1)
HgCH3 - Hg + CH3 (2)
CH3 + CgH5CE3 s 0% ♦ CgH5CH2 (3) 3
CH3 ♦ CH3 = CgHg (h)
C6 H5 CH2 + C6 H5CH2 = (c6 h5 ch2) 2 (5)
There have been many estimates of the average bond energy
of the boron-carbon bond in trimethylborane, mostly from thermodynamic
data. These include 8 9.0, 70, 80 and 59 Kcal/mole (^,5,6,7)* It
should be noted that these are the average bond energies for the breaking of all three bonds, i.e., for the reaction
i B'CE3>3 ■ 3 E + aH3-
As is true for other compounds of this type the kinetic bond energy for the reaction
b(ch3) 3 = b(ch3) 2 + ch3
will be larger than the average bond energy. This value has been
estimated as 107 Kcal/mole (6 ). II. APPARATUS AND TECHNIQUES
The Furnace
The furnace is shown in Figure 1. It consists of a 30"
long Alundum Electric Furnace Core, manufactured by the Norton Company,
Worcester, Mass., with a l|r" bore and a pitch. The end plates and
terminal boards are made from 3/8" Transite. Brace rods are ji" steel.
The cover is galvanized iron. Vermiculite is used for the insulation.
The windings are made with 22 gauge Nichrome wire in six separate zones
of equal length along the furnace core. A 2k" length of stainless
steel tubing is centered within the core to help in leveling out the
temperature variations.
The controls for each zone, as also shown in Figure 1,
consist of an Ohmite Rheostat, 25W-1/1, Model H, Series A, a Powerstat,
Model 116, a DPDT switch, and a Westinghouse Portable Ammeter Type PA5.
The output of a Sorensen AC Regulator Model 1001 is used for the power
supply for the Powerstats.
The temperature of the furnace is measured with a Chromel-
Alumel thermocouple, mounted in a double bore quartz tube, and a Leeds and Northrup Potentiometer Model 8 6 6 2 . The temperature distribution of the furnace is shown in Figure 2. Curve II was obtained by lower ing the voltage output of the Sorensen Regulator and leaving all —
a Terminals— Cover bolts To voltage regulator Rheostat i-J L Auto Ai 0 transformer
_ 3 J DPDT switch
yAmmeter
Perspective of Section A (Exclusive of cylindrical covering)
Fig I. High Temperature Core Furnace for the Flow System Temperature, *c. 0 2 6 0 4 6 i. . mprtr Diti i f h Cr Furnace Core the of n tio u istrib D perature em T 2. Fig. 0 6 6 0 0 6 0 8 5 5 ii nsde f nae inches ace, rn fu e sid in n sitio o P 10 Reactor 20 2515 0 3 ON other controls as set for curve I . During the experiments the tem perature variation along the reactor was within £ 3°C. Since this
is a constant heating furnace, there tends to he a day to day drift
in the average temperature.
The Reaction System
The reaction system is shown in Figure 3* It is designed to permit measurable amounts of toluene and trimethylborane to vaporize from the corresponding liquids and pass through a tubular reactor at a measured pressure. The reaction products and unchanged reagents pass into a series of cold traps to remove condensable materials; the non-condensable gases are pushed by a mercury diffusion pump into the chamber of a Toepler pump which in turn collects them in a calibrated gas burette.
The reaction vessel is a quartz tube 25 mm. f 2^ I.D., which carries a smaller tube, 7 mm* + 8$ O.D., down the center. The annular space between the two tubes contains the reacting gases; the inner tube is open at both ends and serves as a well for a movable thermo couple. A cross section of the reactor looks like a doughnut. The overall length is 51 cm. The volume as determined by weighing with water is 22^.5 cc. The reactor pressure is measured on a DuBrovin
Vacuum Gauge from W. M. Welch Scientific Company. The volume of the trimethylborane bulb is 235*7 cc. Capillaries Kl, K2, and K3 serve to control the flow of the trimethylborane, the toluene, and the mixed gases. To fractionation system To vacuum ♦ rSI2 7777ZV///////A To DuBrovin gouge VZ77ZZZ/////ZA To vacuum Furnace and reactor
To vacuum 4 To mercury diffusion pump ^ and auto- SlO€> matic I>epler ^ S ll pomp in series
Toluene weighing bulb 13 Toluene bulb and water bath •" Vacuun
Constant level mercury manometer
Fig. 3. Reaction System Used in the “Toluene Comer- Experiments The ratio of moles Cf toluene to moles of trimethylborane passed through the reactor is determined by the temperatures of the baths used on the respective supply bulbs. The source of each of these compounds is maintained at an equilibrium vapor pressure.
During most experiments the equilibrium pressure in the reactor was reached within three minutes and after this it varied no more than about 0 .2 mm.
All stopcocks except those on the toluene bulbs are lubricated with Apiezon T grease. The stopcocks on the toluene bulbs are lubricated with Dow Corning High Vacuum Grease.
Figure ^ shows the automatic Toepler pump and its controls which consist of two Alco S115 Solenoid valves and a DPDT relay. For the "toluene carrier" experiments the Type I burette is used.
The water bath on the toluene bulb is movable. The tempera ture is maintained by a mercury regulator and a thyratron control circuit.
An ionization gauge located on the main manifold is used to measure the low pressures in the vacuum system.
Auxiliary equipment such as a fractionation train, storage bulbs, tube openers, etc., have been described by Petry (8) and
Coleman (9).
Chemicals
The preparation and purification of the trimethylborane has been discussed by Petry (8) and Coleman (9). The author is indebted to Dr. Coleman for the testing of the purity of the trimethylborane. 10
To vacuum
To high vacuum To vacuum To low vacuum r - Sample tube
Type I
To system Calibrated burette — Type I Thimble
Air solenoid
Vac. solenoid
Vac. solenoid
Electrodes
L _____ JAir solenoid DPDT relay
Fig. 4. Automatic Toepter Pump and Controls 11
The toluene used was treated and purified by several differ ent methods. These are described in Section III.
The hydrogen used for the calibration of the Blacet-Leighton
Apparatus was commercial tank grade (Airco); the methane was Phillips'
Research Grade.
Procedure -6 The system is pumped down to approximately 1 x 10“ mm. All stopcocks are closed. A weighed sample of toluene in a toluene weigh ing bulb is attached to the system at J1 and the connecting lines pumped down. The toluene is distilled into the toluene bulb and the water bath raised to cover the bulb and stopcock. A portion of tri methylborane from the storage bulb is condensed into the trimethyl borane bulb through S12 and SI with the mercury of the constant level manometer lowered. The mercury level is raised and the trimethylborane allowed to vaporize with SI open. A water bath is placed on the tri methylborane bulb, the mercury is raised to the scribed mark, and the temperature and pressure recorded. SI is closed and the water bath replaced by a dry-ice-acetone bath. An ice-salt bath is placed on A, a dry-ice-acetone bath on B and liquid nitrogen baths on C and D.
The diffusion and Toepler pumps are turned on. S6 , S7, S9, and Sll are opened. S3 is opened followed by S2. When the pressure, as measured by the DuBrovin gauge,, is approximately equal to the operating pressure,
Si is opened. When the pressure is approximately 5mm. above the operating pressure, S5 is opened and timing begins. At various times the pressure is recorded. The temperatures of various positions in 12
the furnace are measured and recorded. One-half minute before the end
of the timing period, S2 is closed. At the end of the reaction S3 is
closed. One minute later S6 is closed. The material in B is repeat edly warmed up, condensed and B again evacuated to insure that all the methane and hydrogen are removed. The excess toluene is distilled back into the weighing bulb and reweighed. The temperature and pressure of the excess trimethylborane are measured as before. PVT measurements are made on the gases collected by the Toepler pump and a small sample placed in the thimble (Figure k) for future analysis.
The condensable material in A, B, C and D are distilled into a seal- off tube at J3 and the tube sealed for possible future use.
From the weight difference of the toluene weighing bulb before and after an experiment, the number of moles of toluene used is calculated. By using the ideal gas law, the moles of trimethyl borane used and the moles of methane and hydrogen (non-condensable gases) formed are calculated. The average pressure is calculated by a time averaging. The temperature is found by averaging all measure ments . ,
With a knowledge of the volume (v), the pressure (P), the temperature (t ), the total time (t), and the total number of moles (n) of material passed through the reactor, the contact time (tc) is calculated from the expression
+ Pvt c “ nRT where R is the gas constant. 13
In order to have a simple means of expressing the data, a first order rate constant (k) is calculated by the equation
* = £ (2) assuming the equality
number of moles of _ number of moles of non-condensable gas formed trimethylborane decomposed so that, in equation 2 , a-x (where a is the number of moles of trimethylborane passed through the reactor and x is the number of moles of non-condensable gas formed) is taken to represent the number of moles of trimethylborane issuing from the reactor in the time of an experiment. In view of the difficulties encountered, the experi ments were discontinued without investigating the reliability of equality 3 •
A sample calculation is found in Appendix A.
For those experiments using only toluene the procedure and calculations were almost identical.
Analysis of Methane and Hydrogen
The analysis of the methane and hydrogen mixture was made in a Blacet-Leighton Apparatus for Micro Gas Analysis manufactured by
Arthur H. Thomas Company, Philadelphia, Pa. The procedure used was that of Blacet et al. (10, 11, 12, 13) with the following slight modi fications. Instead of using lead in the heater, potassium dichromate was used since it is easier to see it melt. Because the non-conden sable gas was predominantly hydrogen, nitrogen was used as a diluting gas. Ik
Analysis of pure hydrogen gave 9 9.1 , 99.5, and 100 percent recovery. For pure methane the results were 9 6 .0 and 9 9 .5 percent.
However there were often very erratic results which could not "be explained. The analyses listed in Section III, which are the average of two or more determinations, are probably good within + 2 percent.
Low Temperature Baths
The low temperatures needed in vacuum fractionation were obtained by the use of solid-liquid mixtures of many compounds.
Table 1 lists the bath materials together with the approximate tem peratures obtained.
The fractions obtained in a fractionation are identified by the temperature at which they were condensed and the temperature of the last bath through which they passed. Thus the -80°/-ll8°C fraction contains the material which passed through the -80°C bath but was condensed in the -ll8°C bath.
TABLE 1
LOW TEMPERATURE BATHS
Material t°C
t-Amyl Alcohol -12 Ice-Salt -16 Carbontetrachloride -23 Chlorobenzene -k6 Chloroform -6k Dry-ice-Acetone -8 0 Ethylbenzene -118 Methylcyclopentane -lk 2 Isopentane -155 Liquid Nitrogen -195 Ill. RESULTS
Preliminary Experiments
Table 2 lists the data for the preliminary experiments.
The symbols used are definedin Section II except for n which corresponds to the number of moles of the designated material.
The experiments through ll+ were made with reagent grade toluene. The toluene was fractionally distilled on a Precise Frac tionation Assembly (Model A , Todd Scientific Company) with a 25:1 reflux ratio. A portion of the middle fraction was placed in the vacuum system and dried over phosphorus pentoxide. After thorough degassing the toluene was fractionated through traps at the following temperatures: -12°, -k 6 °, -80°, and -195°C. The toluene trapped at
-80° was used.
Experiment 1^ was made to determine the amount of non- condensables formed from toluene alone. The rate at which the non- condensables were formed in 14 was approximately 10 percent of the . rate at which they were formed in experiment 13 and a still smaller fraction of the rate in 1 2 .
Experiments 15 and l6 were made to determine whether any impurity in the toluene which might have had an effect on the reaction had been removed by reaction in the presence of trimethylborane and were made with toluene reclaimed from 10, 12, and 13. The condensable
15 TABLE 2
DATA FOR PRELIMINARY EXPERIMENTS FOR THE REACTION OF TRIMETHYLBORANE AND TOLUENE
Total *c k x 10^ P time n x 102 n x 10^ n x 105 -1 Exp, mm. min. sec. T°C Toluene b(ch3) 3 CHij. H2 ^Hg sec
5 7 -8o 60 1 3 .6 830 1.015 1 .5^2 3-^5 33-9 6 0 .6 1.67
6 7 .2 0 60 lU.l 835 .9585 1 .1-20 3-83 32.3 67.3 1.91
7 7.15 60 Ik.2 833 . .9516 l.klk 5.51 2 1 .8 78.3 2 .8 1
8 7.17 58| 1 3 .8 833 .9585 1.105 5 .8 1 2 0 .5 79.1 3 .0 6
9 11 .6 0 6b 6 .91+ 83^ 2 .2 I1 1.1+27 3 .8 6 23.3 7 6 .8 3.95
10 11.87 70 6.79 832 2 .5 3 2 1 .1-63 1+-37 27.9 70.7 1+.1+7
12 10.99 60 6.97 831 2 .1 0 1 1.3^1 3-61 29.5 7 0 .1 1+.01
13 1 1 .6 0 60 7 .0 2 833 2 .1 3 0 .853 2 .7 8 23.7 78.1+ 1+.72 ii+ 11.17 100 7-55 833 3A35 0 .0 0 .1+89 1 8 .5 8 1 .1 -
15 12.07 60 6 .9 0 833 2 .1 2 2 1 .3 1 8 1+.33 - - 1 .8 6 l6 1 2 .0 6 80 7 .1 8 831 2.77^ 1 .2 2 0 3 .1+2 -- 3-95 materials from the three experiments were combined and treated
together. They were fractionated in a vacuum through traps at the
following temperatures: -23°, -80°, -118°, and -195°C. The materials
trapped at -80° and -118°C were combined and fractionated through
traps at the following temperatures: -16°, -23°, -80°, and -195°C.
The toluene trapped at -80° was fractionated through the same tem
peratures a second time. The toluene trapped at -8o°C was used for
experiments 15 and l6 . The first-order rate constants for these two
experiments agree with other experiments made at the same temperature.
The condensable material from experiment 15 was fractionated
into several parts in the vacuum system. Each fraction was qualita
tively analyzed by use of the mass spectrometer. Table 3 lists the
results for each fraction.
The Effect of Pre-pyrolysis on the Decomposition of Toluene
A simple calculation using the values of Szwarc (l*+) for the decomposition of toluene showed that if the reaction had been behaving
in the same way as in Szwarc's experiments with pure toluene, no measurable quantity of non-condensables should have been formed in
experiment lU. Szwarc (1,1*0 found that it was necessary to pre- pyrolize his toluene in order to remove all reactive compounds. That
is, he found a correlation between the number of times a sample of. toluene had been passed through the reactor and the first-order rate
constant found for the reaction. It required two or more passes
through the reactor before reproducible rate constants could be 18
TABLE 3
ANALYSIS OP CONDENSABLE MATERIAL PROM EXPERIMENT 15
Fraction Analysis
-l42°/-195°C B(CHj)j, CgHg, CgH^ and some other trace material
-ll8°/-1^2°C b(cHs)3
-8o°/-li8°c Toluene and some other material having large peaks at M/e of 39, ^0, la, k2, hh, 56, 57, 8l and 82
-h5% 8o°c Toluene
-i 6 ° M 5 ° C Toluene 19 obtained. He thus adopted the procedure of pre-pyrolizing his toluene, i.e., purifying the toluene by partial pyrolysis. Therefore the decom position of pre-pyrolized toluene was measured.
Table ^ shows the conditions of temperature and pressure for the pyrolysis of each sample df toluene. The contact times were approximately seven seconds. Besides the reagent grade toluene (RO),
Phillips' research grade toluene (PO, 99-96 mole percent purity) was used. After each pyrolysis the toluene was fractionally distilled on the Precise Fractionation Assembly, placed in the vacuum system, degassed, dried over sodium hydride, and thoroughly degassed again.
The un-pyrolized toluenes were treated similarly.
Table 5 lists the results of the decomposition of the various types of toluene. The first-order rate constants are compared with the results of Szwarc (lh) by means of the Arrhenius graph as shown in
Figure 5 -
Before 18 was made, a large quantity of toluene had already passed through the reactor. Before 22 the reactor had been in contact with air.’ Before 25 the reactor was removed from the system and cleaned with carbontetrachloride, acetone, and distilled water. After each exposure of the reactor to air, large quantities of toluene were passed through it for conditioning.
The experiments show that the reagent grade toluene had a considerable amount of impurities present which decomposed to give non-condensables faster than does toluene itself and that it would be necessary to pre-pyrolize the toluene at least three times before the 20
TABLE k
CONDITIONS FOR THE PRE-PYROLYSIS OF TOLUENE
Starting P Material mm. T°K Product Designation and Symbol
RO 1 1 .2 970 Reagent Grade-single R1 pre-pyrolysis
R1 10.5 973 Reagent Grade-double R2 pre-pyrolysis
R2 1 1 .0 97^ Reagent Grade-triple R3 pre-pyrolysis
PO 10 A ioi+3 Phillips' Research Grade PI single pre-pyrolysis
PI 1 2 .0 10i+0 Phillips' Research Grade P2 double pre-pyrolysis TABLE 5
DATA FOR THE PYROLYSIS OF TOLUENE
Total t CHjj. H2 k x 10^ Type P. time c Toluene Exp. Toluene mm. min. sec. T°K n x 102 n x 105 sec.
18. R1 1 0 .6 0 60 6.73 973 2.105 2.55 2 .1 2
19 R2 1 1 .0 8 60 7.09 972 2.095 1-75 1.35
20 R3 11 .0 9 ' 60 7-20 973 2.052 1.47 1 .0 1
21 R3 11.09 60 7 .2 0 973 2.052 1.52 1 .0 0
22 PO 1 1 .9 0 60 7 .42 972 2.1321 1.09 .698
23 PO 11 .9 8 30 6 .79 1057 1.0814 1 6 .0 21.9
25 PO 11.83 80 7.1+8 986 2.7702 3.61 1.73
26 P2 11.87 80 7 .6 1 986 2:7335 3-44 1.64
30 PI 10.37 75 6.95 986 2.2574 3.33 1 .8 6
31 PI 10.31 80 7 .2 6 1007 2.4366 6 .2 1 3.50
32 PI 10.48 80 7.37 1010 2.4320 7 .3 7 3-84 i- . rhnu Po fr h Prlss f oun. h ln i don from drown is line The Toluene. of Pyrolysis the for Plot Arrhenius 5. Fig- 4 ♦ Log M 0.5 -0 0.5 00 9.3 zocs aa Te oi prin niae te ii o the of limit the indicates portion solid The data. Szworc's h pit idct te ye f oun ue i te experiment. the in used toluene of type identifying the symbols The indicate experiments. points Scwarc's the of range temperature 9.5 -FI 100 P0-o\ 3 R - 0 0 0 -R2 10.5
23
true rate of decomposition for toluene itself could be reached. The
experiments with Phillips' toluene show that little, if any, of the
non-condensables could be attributed to the reaction of an impurity
less stable than toluene.
Reaction of Trimethylborane and Toluene
Table 6 gives the data for the decomposition of trimethyl
borane in the presence of toluene.
Experiments 3^> 35, and 36 show the lack of any certain
effect from pre-pyrolizing the toluene. Experiments 37> 38, and 39
were made to determine the effect of changing the ratio of toluene to
trimethylborane. There is little difference between the first-order
rate constants for 37 and 38 but there is a great increase in the
value for 39* Experiment kl shows that this increase is real.
Experiment was made after the reactor had been exposed
to toluene, as described in the next section.
Effect of the Wall on the Pyrolysis of Toluene
Table 7 lists the data for a series of experiments which
were made to determine whether the coating on the wall formed in the
decomposition of trimethylborane had any effect on the pyrolysis of
toluene. The table also shows the immediate past history of the reac
tor for each experiment. For comparison the first-order rate constant,
as obtained by an extrapolation of the straight .line on the Arrhenius
plot (Fig. 5.)> is about 1.8 x 10 ^ sec. ^ at 81+5°K.
These data show that there is some material formed on the TABLE 6
DATA FOR THE PYROLYSIS OF TRIMETHYLBORANE AND TOLUENE
a b (c h 3)3 CHj^ + Hg t Toluene k x 103 Type P c i CH^ Exp. Toluene mm. sec. T°K n x 102 n x 10^ n x 105 sec. ^
33 PO 12.35 8.79 826-833 2 .0 7 2 1.223 .0913 - ■ “ .849
34 PO 12.24 8 .5 6 842.7 2.7563 1.777 4.87 7 6 .3 2 0 .1 3.25
35 P2 12.55 8 .6 8 842.9 2.7930 1.748 5.43 7 9 .7 1 6 .2 3.51
36 PI 1 2 .6 o 8 .6 8 81+3-2 2.7963 1.792 5.75 8 0 .2 20.4 3.76
37 PI 17-76 7.37 81+5-9 4.7935 1.420 4.72 . 8 3 .0 17.2 4.79
38 PI 12.94 8 .7 8 845.2 2.8390 1.741 6.34 8 1 .4 20.3 4.22
39 PI 12.57 8 .8 9 81+6.7 2.8309 .5563 2.05 8 5 .0 13.9 6.34
4l PI 12.73 8 .9 8 81+5-9 2.84l4 .5207 2.73 - - 5-99
42 PI 17.65 7.30 85k .5 4.7474 1.433 7.45 -- 7.27
43 PI 12.55 8.54 845.3 2.8 2 9 8 1.763 6 .0 0 - - 4.05
44 PI 1 2 .1 9 8.99 844.1 3.5 0 0 1 .6965 3 .0 9 - - 5.04
48 PI 12.25 8.19 845.2 2.874 1.843 5.47 -- 3 .6 8
®The total time for these experiments was 80 minutes except for Exp. 33 which lasted 60 minutes and Exp. 44 which lasted for 100 minutes. TABLE 7
EFFECT OF TEE WALL COATING ON THE PYROLYSIS OF TOLUENE
♦ H2 k x 106 Reactor Treatment Immediately ta Toluene*3 P c Preceding Experiment. Exp. mm. sec. T°K n x 102 n x 106 sec.
^5 1 2 .2 6 8.7^ 8W +.6 2.870 k.h-3 17.7 Exp. kk and two days evacuation0
U6 12.31 8.72 8W5.0 2 .88L- 1.73 6 .8 8 Exp. *4-5 and four days evacuation
b l 11.95 8.8l 8^5 • 7 2 .8 5 9 • 3h 1.27 Placed approximately 20mm. pressure of toluene in reactor several times and left closed. Total time toluene in the reactor was 26 hours Evacuated 3 days.
^9 11.99 8.6 o 8^5 -0 2 .8 5 0 2.29 9.3^ Exp. kQ with toluene and BCCH^)^. Two days evacuation.
®The total time of these reactions was 80 minutes.
^Toluene used was once pre-pyrolized Phillips' toluene.
°During the evacuations of the reactor, the furnace was maintained at approximately 8^5 °K. wall by the reaction of trimethylborane which catalyzes the decom position of toluene. Experiments k6 and k j show that the activity of the wall coating is decreased by reaction with toluene. However, even twenty-six hours' exposure of the reactor to toluene is not. sufficient to inactivate the coating completely, as shown by hf.
Experiment h9 shows that a single experiment with trimethylborane and toluene is sufficient to restore the wall coating to almost its fully conditioned state, which can be taken as the state existing immediately preceding experiment .
Considering the facts that toluene alone deactivated the coating and that the coating is formed quite rapidly by the trimethyl borane, it is apparent that the reaction of toluene in the presence of the wall coating represents at least 10 percent of the non-condensable gases formed in the reaction of trimethylborane and toluene studied at 8^5°K. This 10 percent figure is probably a very low limit.
A single analysis of the non-condensable gases from showed 9 6 .6 percent hydrogen. No analysis was made for the methane. IV. DISCUSSION
Szwarc (l, 1*0 has shown that the pyrolysis of toluene is not a chain reaction. Thus, if the decomposition of the toluene is a homogeneous reaction, the effect of the wall coating must be to provide one hydrogen atom or one methyl radical for each molecule of the non- condensable gases. If this were the correct explanation, then one would expect the wall coating itself to form significant quantities of non-condensable gases in a period of a normal reaction (one or two hours), and to do this even several days after the last trimethylborane experiment, since the activity of the coated wall is retained for this time. This was not found to be true. Thus it appears that the reac tion of toluene and the wall coating is a heterogeneous reaction and also that the age of the wall coating may have an effect on its ability to decompose toluene. No attempt was made to measure the decomposition of toluene on a freshly prepared wall coating. However from the trend in the production of non-condensable gases in going from hj to *t-7 , it is evident that the production of non-condensable gases on a fresh wall coating would be a large fraction of the gases from a trimethylborane- toluene experiment.
Because of the reaction of toluene and the wall coating, this part of the research was discontinued.
27 28
With a knowledge of the effect of the wall coating, the
results of the reaction of trimethylborane and toluene can now be
cleared up somewhat.
Experiments 3h, 35 j and 36 were made to determine the effect
of pre-pyrolizing the toluene. The first-order-rate constants for
these experiments seem to bear no relation to the pre-pyrolizing.
However, an increase in the rate constants is noted, together with
only a slight increase in the temperature. This increase in the rate
constants can easily be explained by assuming that more and more of
the wall coating was formed throughout the three experiments. Thus
the contribution of the non-condensable gases formed by the toluene
as a result of build-up of the wall coating became greater in going from 3h to 3 6 . This type of correction would bring the rate constants more in line with each other.
The high values for the rate constant in 39 and hi can be brought more in line with the value in 38 by assuming a constant production of non-condensable gases from the toluene decomposition
at a given toluene concentration when the wall is coated. Thus the
non-condensable gases from the toluene decomposition constitute a much greater percentage of the total non-condensable gases in 39
and hi than in 3 8. PART II
STATIC. PYROLYSIS OF TRIMETHYLBORANE
29 V. INTRODUCTION
This portion of the work is concerned with a kinetic study of the static pyrolysis of trimethylborane to determine the rate, order and mechanism of the reaction.
Goubeau and Keller (15 ) studied the reaction of trimethyl borane in the presence of boric oxide by placing 0 .06 l moles each of trimethylborane and boric oxide in a 170 cc. bomb tube and allowing six hours for reaction (at 380°C the pressure of the trimethylborane would be approximately 19 atmospheres). Under these conditions the trimethylborane started to decompose, or react with boric oxide, at about 320°C, and at 380°C there was about 2 .5 percent decomposition.
Trimethylboroxin, (CH^BO)^, was the major product. Goubeau and
Epple (16 ) made a study of the products of the pyrolysis of trimethyl borane using bomb tubes and a flow system. In the bomb tubes, experiments were carried out with pressures between ten and fifteen atmospheres and temperatures between 395° and hlO°C. In the flow system, the stream velocities varied between 0 .2 and 50 liters per hour and pressures between .05 and one atmosphere. The temperature range was 390° to V70°C. They found large quantities of hydrogen and methane. They also made a study of the liquid and solid products of the reaction. In both papers, the authors assumed that the reac tion starts with a rupture of a carbon-boron bond and that the initial product is methane rather than hydrogen.
30 VI. APPARATUS AND TECHNIQUES
The Furnace
The furnace and controller are similar to those described by Hembree (17)• The top, bottom, and side constant heaters each have the same type of control as shown in Figure 1 (Section II). A two- inch high copper band is placed on the top heater and Vermiculite placed on the top to reduce heat losses here. The furnace is mounted on a jack so that the furnace can be raised or lowered easily.
Three iron-constantan thermocouples are placed around the reaction flask, one at the top, one at the side, and one at the bottom.
The thermocouples are brought out through the top of the furnace and are silver soldered to heavy copper wires. These solder junctions are placed in glass tubes and act as the cold junctions. Each circuit is connected by a switching arrangement to a Leeds and Northrup Portable
Potentiometer, Model 8662, for measurement of the voltage.
In operation the differences in the temperatures of the three positions around the reactor were no greater than 0.8°C. The variation of the temperatures during the time of a reaction was no greater than
0.6°C. For a series of experiments at the same approximate temperature, the deviation of the temperatures were ± 0.8°C or less. The thermo couples were calibrated at the melting points of tin and lead.
31 The Reaction System
The reaction system is shown in Figure 6 . It is designed to
place a measured amount of trimethylborane in the reactor (D) where
the pressure can be measured as a function of time. After a measured
time interval the reaction mixture is drawn through a series of cold traps to remove all condensable materials and the non-condensable
gases collected in a calibrated gas burette (Type II, Fig. by the automatic Toepler pump (Fig. ^). The condensable materials are then fractionated in the traps and each fraction measured in the gas measuring system.
The high vacuum manifold (not shown) is connected in series to a U-trap at -195°C, a cold finger trap at -80°C, a mercury diffusion pump, another cold finger trap at -80°C, and a Welch Duo-seal pump
(Model lUOO). The low pressures in the high vacuum manifold and con necting system are measured by an ionization gauge located at the end of the manifold farthest removed, from the pumps. The low vacuum mani fold (not shown) is connected in series to a U-trap at -195°C and a
Welch Duo-seal pump (Model 1^05)• The low pressures in the low vacuum manifold and connecting system are measured by a thermocouple gauge located at the end of the manifold farthest removed from the pump. In operation the pressure in the high vacuum manifold is better than
_ z r 1 x 10 mm.j the pressure in the low vacuum manifold is below the
1 x 10' 3 mm. limit of the thermocouple gauge. The dual manifold arrangement proves most useful. It is possible to degas materials or to put on sample bulbs without interfering with the high vacuum. Also when To high vacuum To low To low To storage vocuum vacuum system To high sii vacuum vS5fi S7 V s 1 Furnace auto- mafic H Toe pier pump
JGos measur u “ ing system *jlk— Pt-*. Air S Vocuum i fj— A,r S Vacuum Vacuum— k
Constant level Constant level manometer manometer
Fig. 6. Reaction System for the Static Pyrolysis 3^
materials are to be pumped out of the system, the low vacuum manifold
is used first. By this procedure the problem of adsorption on the
glass walls is kept at a minimum since very little material ever goes
into the high vacuum manifold.
For the reactor (D), two different quartz flasks were used.
The first is a round flask with a capillary quartz-to-Pyrex graded
seal. Its volume as determined by weighing with water is 110.1 cc.; 2 the surface is calculated to be 111 cm. The second is a round flask
packed with short lengths of quartz tubing; for this, the volume
determined by weighing with water is 229*5 cc. and the surface is cal- 2 culated to be 1950 cm. This flask is also connected to the system with a capillary graded seal. The volume of the capillary connections
outside the furnace is approximately 2 cc. Unless otherwise specified,
the reactor used was the 110.1 cc. flask.
The pressure of the material in the reactor is measured on
Pc with the mercury reservoir open to the air. Atmospheric pressure
is measured on Pr after first evacuating the arm through S26. In
early experiments Pc and Pr went directly to open mercury pots. The
change was made so that the length of Pc exposed to the reaction mix-
ture could be degassed between experiments to minimize excessive
sticking of the mercury.
Bulbs M, N, and 0 are calibrated volumes (by weighing with water) of 9.32, 2^.37, and 50.31 cc. respectively. The volume of the cold finger (L) and the manifold of the gas measuring system to a
scribed mark on the constant level manometer is 5«^7 cc. as determined by PVT measurements (in early experiments this volume was 5-^2 cc.). 35
The volume of the trimethylborane measuring bulb (B) and the
manometer line to a scribed mark was calibrated by PVT measurements
and is li8 .8 0 cc.
Bulb A is used for storage of small quantities of trimethyl
borane and is refilled from the storage system as needed. Bulb C,
together with the connecting lines between S9, S10, and Sll, is used
in filling the reactor. This portion of the apparatus is filled with
trimethylborane to a measured pressure, and the evacuated reaction
vessel connected momentarily to it to start the reaction. Bulb I is
used similarly for removal of only a portion of the reaction mixture.
K is a small storage tube.
The pressures are measured with the aid of polished stain
less steel plates having etched vernier scales which ride on meter
sticks. The readings are made by sighting on the plate so that the image of the eye is divided by the reference line. In this way parallax is reduced considerably. It is estimated that each reading of a manometer arm is precise to + .2 mm. or better. Because of the sticking of the mercury in the capillaries of PQ and Pr, the precision of the pressure measurements may be considerably less.
All stopcocks were lubricated with Apiezon T except for the following exceptions. For experiments 15-4 and 20-U, S10 was lubri cated with Dow-Corning High Vacuum grease. For experiments 2k~k and
28-l»- stopcocks S8 through S25 were lubricated with Dow-Corning High
Vacuum grease. »
Chemicals
The preparation and purification of the trimethylborane has been discussed by Petry (8) and Coleman (9). The author is indebted to Dr . Coleman for the testing of the purity of the trimethylborane.
The hydrocarbons were all research grade from Phillips'
Petroleum Company. The hydrogen used in the gas chromatography was commercial tank grade.
The azomethane and the nitric oxide were both furnished by
Dr. Jack Calvert to whom the author is greatly indebted.
Gas Chromatography
The apparatus and procedure used in the analyses by gas chromatography are similar to those described by Hembree (17). In order to obtain better temperature control, the Molecular Sieve
(M.S.) and the silica gel (S.G.) columns were made from •£" aluminum tubing, l6 and 8 feet long respectively. The columns were coiled and placed in an oil bath maintained at 75*0 +■ .1°C by a mercury regulator and a thyratron control circuit.
The M.S. column lost its activity, as measured by retention time, rapidly and it was necessary to reactivate it every few months.
The reactivation was carried out by placing the column in a furnace set at about 330°C and passing dry helium through the column for several hours. It is suggested that a drying tube filled with acti vated charcoal and maintained at -195°C placed in the helium supply line might prevent the deactivation.
Two columns not used by Hembree (17) were also made. The packing is Dow-Corning 702 fluid supported on 30-60 mesh firebrick
(Johns-Manville, C22) made according to the directions of Littlewood, 37 Phillips, and Price (l8). The columns are made from Pyrex glass and
are 10 inches long and 6 mm. I.D. and 26 inches long and 8 mm. I.D.
(These columns are referred to as the 10”- and 26"-DC702.)
For analyses of hydrocarbons with molecular weights higher
than 30 a l6 foot Dowtherm A column, borrowed from Mr. V. Wiley of
The Ohio State University Research Foundation, was used.
In all cases the carrier gas was helium at a flow rate of
25 cc. per minute.
During the later part of the investigation, the ten millivolt
Brown recorder was replaced by a Daystrom-Weston recorder with 2.5,
1 0, and 50 millivolt ranges.
For standardization purposes, mixtures of hydrogen and methane and of ethane, ethylene, and helium were made and used through
out the investigation. Every time an unknown sample of the non-con densable gases was analyzed, two samples of the hydrogen and methane
standard were analyzed, immediately before or immediately after the
unknown. Inthis way corrections could be made for the changing activ
ity of the M.S. column. The non-condensable gas was analyzed only for methane; the hydrogen was found by difference. This was done since the
sensitivity for hydrogen, using helium as the carrier gas, is very poor.
The S.G. column was very stable and was calibrated only once a week or even less.
Procedure
The system is pumped down to 1 x 10 ^ mm. through the high vacuum manifold. Stopcocks SI, S2, S.6g. ahd S8 are closed; S3 and S7 are left open. S5 is slowly opened and the trimethylborane pressure
in Bulb C and the sub-manifold allowed to increase to a predetermined
value and S5 closed. S7 is closed and the excess trimethylborane in
the sub-manifold is condensed back into A by use of a -195°C bath on A.
The trimethylborane located in C is transferred to B through S2 and
then S2 is closed. The trimethylborane is allowed to vaporize and SI
is opened. A water bath at room temperature is placed on B and the
mercury level adjusted to the scribed mark. The temperature and
pressure of the trimethylborane are recorded. The trimethylborane is
transferred to C and S7 closed. While the trimethylborane in C is
attaining temperature equilibrium at room temperature, the temperature
of the furnace is measured and recorded. The zero points on Pc and Pr
are recorded. S9, S10 and Sll are closed. S8 is opened. Timing for
the experiment starts when S10 is opened and closed rapidly. The pressure as read on Pc is read and recorded (this is usually within
six seconds of the time at which S10 is opened). The trimethylborane which did not enter D is transferred back into B and measured as before. S8 is closed and S9 is opened to the high vacuum for a few minutes. At various times the pressures measured at Pc and Pr and the furnace temperatures are recorded. Near the end of the reaction period liquid nitrogen baths are placed on E, F, G, and H. Stopcocks
Sll and S13 are opened and all others closed.
For the experiments for which analyses of the non-conden
sable gases are to be made, only a portion of the reaction mixture is taken. The end of the experiment is chosen by a certain pressure 39 reading. When this pressure is reached, S10 is quickly opened and
closed, and the pressure recorded. The Toepler pump is started. Slk,
SI6 , Sl8 and S20 are opened in this order and the non-condensable
gases collected in the calibrated burette (Type II, Fig. *0 by the
Toepler pump. When it appears as if most of the non-condensable gases have been collected, SI1)- is closed and the bath removed from E. After
the trap is warmed up to room temperature, the -195°C bath is replaced on E and Slk reopened. This procedure is repeated, if necessary to insure the complete removal of all the non-condensable gas. When all the non-condensable gas is collected, S20 is closed and three sets of
PVT measurements made on the collected gas. A portion of the gas is placed in a sample tube for later analysis.
For the experiments for which the non-condensable gases are not measured, the total sample is removed. The end of the experiment is chosen for a definite time. At the end of the experiment S10 is opened, followed quickly by Slit-, Sl6 , Sl8, S19, and S22 (to the high vacuum). After five minutes S10 is closed. SI1)- is then closed and the condensable material treated as above to insure the complete removal of the non-condensable gases.
In either case, after the non-condensable gases are removed,
Sll, S13, and S20 (or S19) are closed and the baths removed from F,
G, and H in order to have all the condensable material in E. The condensables are then vacuum fractionated through traps, E, F, G, and
H at -80°, -lk 2 °, -155°, and -195°C respectively for forty seconds.
The material collected in H is transferred to the gas measuring system kO
by condensation in the cold finger (L) (this -155°/-195°C fraction is
hereafter referred to as the C2 's). With S25 closed the material is
vaporized and PVT measurements made. The C2 's are then transferred
directly to a gas chromatography lopp (17) at J3 and then analyzed.
The remaining material is fractionated through traps at
-80°, -ll8°, and -195°C. The -80°/-ll8°C fraction is transferred to
the gas measuring system and allowed to vaporize. To determine whether
all the trimethylborane has been removed, a -8o°C bath is placed on L.
If the pressure of the material drops almost instantly to 0.5 mm. or
less, it is assumed that all the trimethylborane has been removed.
If the pressure drops slowly, the material is fractionated, repeatedly
if needed, until the pressure does drop instantly. The material is
then vaporized and PVT measurements made. This fraction was collected
from several experiments and stored in K.
The material collected at -195°C in the second fractionation
(corresponding to a -118°/-155°C fraction originally) is then trans ferred into the gas measuring system and PVT measurements made.
The material remaining in the -80°C trap is generally dis
carded .
For the experiments with propylene and trimethylborane, a
large sample of the mixture was prepared in advance and placed in A.
The procedure is the same as above except that after measuring the mixture in B and transferring to C, the mixture is allowed to stand overnight to assure composition equilibrium.
For the experiments with azomethane and ethylene, the trimethylborane is measured as usual and placed in C. The second ■ material is placed in the system from a storage tube attached at J2 and measured in the gas measuring system. After measuring, this material is also transferred to C and the mixture allowed to stay overnight to assure composition equilibrium.
For the experiments with nitric oxide the procedure is slightly different since nitric oxide is considered to be a non- condensable gas. A sample tube of nitric oxide is placed at J2.
Stopcocks S10, Sll, S12, and S23 are opened; all others are closed.
The stopcock on the sample tube is opened until the desired pressure of nitric oxide is in the reaction flask. S10 is then closed as is the sample tube and the excess nitric oxide pumped out. The procedure after this operation is then the same.
In all cases, except for nitric oxide, the number of moles of each sample or fraction is calculated from the PVT data assuming the material obeys the ideal gas law.
For those experiments in which only a portion of the reac tion mixture is taken, the fraction removed for analysis (f) is cal culated from the equation
where P^ is the pressure in the reaction flask immediately before a sample is removed and Tf is the pressure immediately after the sample is removed. The total number of moles of an individual fraction (nt) is given by the equation k2
where n is the number of moles of the fraction found in the portion of
the reaction mixture removed.
Analysis of Products
The non-condensable gases are analyzed by use of the
Molecular Sieve Column as described above. For several experiments,
portions of these gases were analyzed by the mass spectrometer. In
no case was there evidence for anything but hydrogen and methane.
From the gas chromatography, the amount and thus the percentage of
methane in the sample is calculated. The total number of moles of
methane is calculated and the hydrogen determined by difference.
The method for the separation of the Cg fraction was tested
on a known mixture of trimethylborane, ethane, and ethylene. The
C2 (-155°/-195°C) fraction was 101 percent of the calculated amount of the ethane and ethylene; this is well within experimental error. When this fraction was chromatographed on the 26"-DC702 column no evidence for trimethylborane was found (sensitivity of trimethylborane is £ approximately .03 x 10 moles per mm. of peak height on the 10 mv. range). The -l42°/-155°C fraction from this mixture was also examined on the 26"-DC702 column and here, no evidence for any ethane or ethylene was found.
In spite of the above evidence for the efficient separation of trimethylborane and the two hydrocarbons, mass spectrometry of the
Cg's from some experiments showed the presence of trimethylborane. A comparison of the number of moles of the Cg fraction with the sum of the number of moles of ethane and ethylene found by gas chromatography shows that the number by gas chromatography was usually lower than that found by the PVT measurements. Only in three cases was this difference greater than 015 x 10-^ moles. It is felt that the major cause of this discrepancy was the incomplete transfer of the Cg's from the gas measuring system to the chromatography loop; the presence of trimethyl- borane in the C2 's also accounted in part for the discrepancy.
The percentage composition of the C2 's was determined for ethane and ethylene from the data obtained from gas chromatography.
The number of moles of these two materials was determined, after assuming that the C.£ fraction was pure ethane and ethylene, by multi plying the number of moles of the Cq's (n^'s) found in the PVT measure ment by the fraction composition, i.e.,
n' " c2*6 ^ 6 ■ "«2's ti1 + n 1 = “C g ’s N c 2H 6 ^ C2H6 C2^ where n is the number of moles of the material indicated, n ’ is the number of moles as found by gas chromatography, and mole fraction of ethane in the C2 ’s as determined from gas chromatography.
In experiments 2^-2 and 11-3 an extra peak in each was observed from the gas chromatography of the C2 's. The peaks do not correspond to trimethylborane, acetylene, oxygen or nitrogen.
Portions of the -ll8°/-155°C fraction from the early experi ments were analyzed by mass spectrometry. The samples were almost pure trimethylborane, with a very slight trace of some higher molecular weight material. This fraction was, therefore, taken to be pure trimethylborane. The -80°/-ll8°C fractions always showed evidence for tri-
methylhorane when the samples were examined on the DC702 columns. In
addition three other peaks were found. On the 10"-DC.702 column operat
ing at about 28°C, the retention times for these peaks were about
10.5, 26, and kS minutes. The last peak was very small. This fraction
was collected from several experiments, and samples of the first two
peaks were isolated by means of gas chromatography and examined in
the mass spectrometer. The mass spectra for these two peaks together with those of some samples of the total -80°/-ll8°C fraction for indi
vidual experiments can be found in Appendix B. The material present in
this fraction was not identified.
The material remaining in the -80°C trap was usually dis carded. In a few early experiments the material was placed in the gas measuring system where it had a pressure of about 2 mm. at room temper ature but it appeared to be a vapor pressure of a liquid or solid, that is, the material was not completely vaporized. The mass spectra of two samples of this material showed peaks at masses above 150. A spectrum can be found in Appendix B .
A sample calculation of an experiment can be found in
Appendix C .
Errors
The measurement of the number of moles of trimethylborane placed in the reactor is based on the difference of two different sets of PVT data. It is estimated that the value of the number of moles of trimethylborane initially in the reactor is precise to + 1 percent or better. The precision of the measurements of the total non-condensable
gases was very good and there was less than 1 percent variation in the calculated amount for an individual experiment. The error in the number of moles of methane and hydrogen includes the error in the measure of the total non-condensable gases as well as the error in the analysis by gas chromatography. The error in the methane of the non- condensable gases depends upon the size of the non-condensable sample.
It is estimated that for non-condensable samples larger than 50 x 10 moles, the error in the methane is •+- 3 percent or less. For non-conden- -6 sable samples less than 50 x 10~ moles, the error in the methane -ft increases considerably, so that for samples of about 10 x 10 " moles, the error may be + 10 percent or even more. The errors in hydrogen will be similar since hydrogen was found by difference.
The percentage error in the number of moles of the frac tion may be quite large because of the presence of trimethylborane in the sample as described above. In all probability, there was no more than 0.5 x 10"^ moles of trimethylborane in the sample. The precision of the analyses of the C2's by gas chromatography is very good and it is possible to measure very small quantities of the C2 's. The value for the mole fraction of ethane (N_ „ ) listed in the tables is there- fore quite reliable and is not affected by the possible presence of trimethylborane in the Cg's as measured by PVT data. The individual values for the number of moles of ethane and ethylene, however, are in error because of the contamination of the sample with trimethylborane.
The error in the number of moles of unreacted trimethylborane b6
is caused mainly by its presence in the -80°/-ll8°C fraction and the -6 C2 's. At most I believe there is less than 2.0 x lO- moles error in
the unreacted trimethylborane.
The percentage error in the -80°/-ll8°C fraction is probably
very large, since the sample is very small and the presence of even -6 0 .5 x 10 moles of trimethylborane can cause as much as a 50 percent
error.
In addition to the above errors, there is an additional one
common to all the measurements of material in the reaction mixture for
those experiments in which only a portion of the reaction mixture was
removed. This is the error introduced because of the error in f, the fraction removed (equations 1 and 2). This error is estimated to be no more than + 2 percent and may be considerably less. VII. RESULTS
Trimethylborane
A series of preliminary experiments on the pyrolysis of trimethylborane was made in a Pyrex cylindrical vessel approximately
23 inches long and one inch in diameter. The furnace used was similar to the one described in Section II. The temperature of the furnace was about 500° +• 10°C. Reactions were made with an initial trimethyl borane pressure of about 15 mm. The pressures were measured with a
10 mm. bore U-manometer. These experiments showed fair reproducibility of the pressure-time curves. After two experiments the reaction vessel was removed and examined. It had a dark yellowish brown coating. At the entrance to the vessel the coating was yellow and gave the appear ance of being a viscous liquid.
Two experiments were made at about 6 lO°C in a cylindrical
Vycor reactor. The pressure increases for these reactions were so rapid it was necessary to estimate the initial pressures by equating them to the pressures of the trimethylborane in the cutting flask after a portion had been placed in the reactor. For this reason the initial pressures are uncertain.
Figure 7 shows the pressure-time curves for several of the preliminary experiments. The two experiments at 500°C were allowed to Pressure Increase, mm. 0 4 32 4 2 0 i. Pesr-ie Curves Pressure-Time 7 Fig. 0 8 0 4 ie mi nutes Time, or fo oe rlmnr Experiments Preliminary Some 120 160 proceed overnight. The pressure increases for these two experiments
were approximately 1.3 times the initial pressures. The curves for
the reactions at 600°C show 100 percent pressure increases in less
than one minute. The reaction with an initial pressure of 20 mm. of
trimethylborane shows a pressure increase of about 195 percent.
Figure 8 illustrates the effect of admitting air to the cylindrical Pyrex reactor between experiments. The experiment for curve 1 was made in a reactor coated with the dark products of previous reactions ("conditioned") with an initial pressure of lit- mm. of tri methylborane. After this experiment air was admitted to the hot reactor for one minute and then the system was evacuated. Three experi ments were then made in succession with 15 mm. of trimethylborane.
These experiments gave curves 2, 3? and k in this order. These experi ments show that there is some material formed on the wall of the reactor upon admission of air which greatly changes the mode of reaction of trimethylborane. Because of this effect, whenever a reactor came in contact with air, at least four portions of trimethylborane were placed in the reactor before experiments were resumed.
Early experiments in the system shown in Figure 6 with the capillary manometers in open mercury reservoirs showed irreproducibility of the pressure-time curves. Figure 9 shows pressure-time curves for two experiments showing the greatest difference in the pressure-time curves at the same temperature. These curves also show an eight-minute initial period where the pressure did not change. After changing the capillary manometers to the design shown in Figure 6 , the variations in the pressure-time curves decreased considerably. Also a small 50
12
9
a
§c
2? 3
a§ . 3
0 Time, hours
Fig. 8. Pressure-Time Curves Showing the Effect of Adding Air to the Reactor Between Experiments Fig. Pressure-Time Showing Curves Irreproducibility Apparent 9 at 6 E
Pressure increase- 60 100 20 80 40 20 Time, minutes 40 488°C. 8060 5l 52
pressure increase was noted within the first 3 minutes of the experi
ment. Thus, the variations in the pressure-time curves and the lack
of an initial pressure increase in the early experiments were probably
due to increased sticking of the mercury in the capillaries caused by
adsorption on the glass of part of the reaction mixture.
The first series of experiments at 488°C and i+0.7 mm. initial pressure of trimethylborane (Table 9 and Fig. 12) showed that the per centage composition of the reaction products varied with the percentage decomposition of the trimethylborane. For this reason and because of the apparent irreproducibility of the pressure-time curves, the decom position was studied by measuring the number of moles of the different species present after varying lengths of time of reaction.
Figure 10 shows further evidence of the lack of a uniform relationship between the pressure change observed and the moles of trimethylborane reacted. The curves are drawn using the data for vario’ s series of reactions (Tables 9> 11> and lh) by plotting the total pressure change for a given reaction against the number of moles of trimethylborane found to decompose in that reaction. The value for the total pressure change is the difference between P-^ and P^ in the tables; the value for the micromoles of trimethylborane reacted is the
" A b (c h 3)3 ." The three curves show very definitely that the relation ship between the pressure change and the number of moles of trimethyl borane reacted is a function of both the initial concentration of trimethylborane and the temperature of the reaction.
Tables 8 through lU give the data for the pyrolysis of trimethylborane. The symbols used have the following significance: | 40 | Fig. Relationship10. the Pressure BetweenObserved Increase the and Pressure increase 60 20 oe o TrimethylboraneMoles of Reacted irmls ofMicromoles 0 80 40 B(CH 3 ) 3 □ 488*0, 488*0, □ 508*G, A O 488*C., 97.3 * I0“* I0“* * 97.3 488*C., O reacted 299.9 x 10“* 10“* x 299.9 2414 * I0~*2414 moles 120 males moles
53 t a b l e 8
PYROLYSIS OF 21+2.6 MICROMOLES (97-1 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT b6B°C
Exp. 20-3 23-3 19-3 25-3 21-3
P^,mm. 97 A 97-2 96.1 97.6 97.2 time,min. 30.0 1+5-0 60.0 75.0 90.0
B(CH3)3-i 2M+.0 21+3-2 21+0.8 21+1.8 21+3.1
B(CH3)3-t 217.9 190.2 167.9 11+1.5 109.2 ab(ch3) 3 26.1 53-0 72.9 100.3 133.9
.2 .6 c 2h6 0.0 .1 .3 C2HI). 1.5 2.0 3 A 3.6 l+.o
N02H6 .000 .061+ .01+9 .076 .138
-8o°/-ii8°c 2.2 1.7 2.2 1.9 2.8
VJ1 4=- TABLE 9
PYROLYSIS OF 97-3 MICROMOLES (1*0.7 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT 488°C
Exp. 29-9 30-9 25-9 5-3 6-3 22-9 3-9* 24-9
Pi,mm. hi. 6 ho.h 39-7 41.5 4o.3 - 41.6 39-8 4l.0
P^,mm. h3-3 h-5.6 49-7 -- 62.8 79-3 78.6 time,min. 13.2 18.8 23.9 32.5 37-5 43.7 75.0 79-2
B(CH3)3-i 97-h 97-0 96.6 97-5 97.2 97.1 95.7 98.2
B(CH3)3-t 93-3 79.3 71.8 58.7 52.7 49.4 15.0 14.4 ab(ch3) 3 k .l 17-7 24.8 38.8 44.5 47.7 80.7 83.8
CH^ 3.8 9-3 19.5 - - 56.6 117 117
5.4 15-5 24.2 -- 44.6 56 55 c2e 6 0 0 0 0 .1 .2 .6 V 2.8 CgHl^ .8 1.6 1.4 2.6 3.0 3-2 J 2.8 NC^6 .000 .000 .000 .000 .029 .047 - .173 -8o°/-ll8°C 1.1 1.4 1.8 1.6 1.8 1.0 - 1.3
- - nrec. 104 107 119 155 191 191 121 -- 147 188 ncal. 101 109 191 aDuring this experiment, the furnace temperature reached 495°C. The value for B(CH3)3~t includes the -80°/-ll8°C fraction. The experiment is used only to confirm 24-9. TABLE 10
PYROLYSIS OF 175-1 MICROMOLES (72.6 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT H88°C
Exp. 2-3 27-2 25-2 18-2 2k-2 17-2 26-2 3-3
P-j^mm. 72.8 72.2 72.5 71.8 72.9 73.2 72.7 73-1
P^.,mm. - - 80.0 88 A 99-6 113 A H 9 . 5 - time,min. - 5-0 10.0 lk.9 19.5 28.0 36.1 H2 .H 50.0
B(CH3)3-i ’ 17^.9 176 A 175.2 175.2 175.5 rjk.6 17H.I 175.2
B(CH3)3-t j 171-7 1 6 k.2 155.3 135.2 111.2 82.7 68.2 H9.6
Ab(ch3) 3 3-2 12.2 19.9 ko.o 6H.3 91.9 105.9 125.6
CHj^ -- 3k.0 68.5 117 138 - > 33.5 % - - J 35.5 50.3 65 72 — C 2H6 .0 .0 .0 .0 .2 • 3 .5 .7
CqH^ A .7 2.1 3.0 k.3 HA 5.1 k.6
.000 .000 .008 0 3 .070 .090 * 2 * 6 .000 . k .137 -8o°/-il8°C 1.1 1.7 2.0 2.1 2.9 1.9 2.2 2 A nrec. -- 193 210 237 272 287 - ncal. _ - 193 217 2 kO 271 286 - TABLE 11 PYROLYSIS OF 2hJ>.k MICROMOLES (101.7 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT 1*S8°C
Exp. 19-11 17-11 9-10 6-10 1+-10 7-10 2-10
PjL,mm. 100.8 101.9 101.2 101.8 102.7 102.0 101. U
P-t^mm. 100.8 101.9 H A . l 112.0 136.6 151.0 202.1 time,min. 5.0 7-0 12.5 17.0 27.5 36.75 81.9
B(CH3)3-i 2I+1.9 214-2.7 214-14-. 6 2143.8 2I4.5.I 2h2.9 2h3.0
B(CH3)3-t 236.8 239.8 223.5 207.1 15^.7 1114.7 8 A a b (c h 3)3 5.1 2.9 21.1 36.7 9 0 .4 128.2 2314.6
C% i.oa 2a 10.6 28.14 10l4 170 395
2 8 .U 60 70 814 h 2 l.la 2a l l A .2 C2H6 \ 0 trace .1 2.5 c .21 y .26 J j 1.3 2.6 3.5 3-1 2.0 NC 2H 6 - - .000 .000 .029 .058 .5514
-8o°/-ll8°C - - 1.3 2.0 1.0 1.5 1.1 nrec. 239 2kk 2h8 268 3214 360 ^93 ncal. 2k2 2l+3 252 268 326 360 I48I4
^ h e analyses of these samples vess very poor and the results are only approximate although the sum of hydrogen and methane is good. TABLE 12
PYROLYSIS OF 2M+.7 MICROMOLES (.102.2 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT l+98°0
Exp. 6 -1+ 7-1+ 8-1+ 3 -h
P^,mm. 1 0 1 .8 1 0 2.1+ 1 0 1 .7 10 3 .0
time,min. 1 0 .0 13-5 1 7 .0 2 0 .0
B(CH3)3-1 21+5.0 21+5.0 2I+I+.1 21+1+.6
B(CH3)3-t 20U.5 177-3 151.3 1 2 5 .6 ab(ch3) 3 1+0 .5 67.7 9 2 .8 1 1 9 .0
C #6 0 .1 • 3 • 3
C r£k 3-3 1+.7 5-3 1+.8
NC2H6 .015 .021+ .01+5 .067
-8o°/-ll8°c 1.9 2 .8 2 .7 1.7
VJ1 00 TABLE 13 PYROLYSIS OF 95.6 MICROMOLES (1*0.6 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT 508°C
Exp. 22-10 20-10 15-10 18-10 13-10
P^,ram. 1*0.9 1*0 .1 1*0 .0 1*0.9 1*1 .1
Pt,mm. - ^3-3 1*9.8 5 8 .0 7^.9
time,min. 2.5 5-0 9-95 1^.75 29.75 b (c h 3)3-i 95.6 95-8 95-3 95.5 95.6
B(CH3)3-t 9 1 .2 81*.7 6 7 .2 53-0 19.1* ab(ch3 ) 3 i*.i* ll.l 2 8 .1 1*2.5 7 6 .2
c % - 5-0 1 9.O 39-1 91.5
h2 - ll.l 2 7 .2 1*0.3 6 3 .I
C 2H6 0 trace .1 .1+ > .26 C 2^-b J 1 .0 2.9 3-2 i*.o - .000 .000 .031 ,0 9 7 C2H6 -8o°/-ll8°C .82 1 .1 1 .1 l.'l .8
nrec. - 103 117 137 179
n cal. - 103 119 135 17^ \J] VO TABLE Ik PYROLYSIS OF 239-9 MICROMOLES (102.7 mm.) OF TRIMETHYLBORANE IN A 110 cc. QUARTZ FLASK AT 508°C
Exp. 3-11 5-11 31-10 28-10 10-11 7-11 2lt—10
1 0 2 .3 1 0 2 .U 1 0 2 .2 1 0 2 .2 1 0 2 .2 1 0 2 .7 1 0 2 .0
P^mm. 103 .h 103-5 1 1 2 .1 123.7 llt-8 .2 1 6 0 .I 1 8 6 .1 time,min. 3 .0 3-0 5.6 7-9 1 2 .0 13.9 2 3 .0
B(CH3)3-i 2it-0 . 2 239-3 23 9 .9 239-5 21)0 .1 2it-0 .it- 238.3
B(CH3)3-t 2 3 0 .2 230.7 2 0 6 .1 1 8 0 .1 1 3 1 .6 109.1 ^7-9
Ab(ch3) 3 1 0 .0 8 .6 33-8 59.^ 108.5 131.3 190.it
CH^ 1+.1 2 1 .7 ^9-9 - 162 280 V 7 -8 h2 J it-.6 2 7 .1 52.7 - 9it 106 C2H6 .0 .0 trace .1 •3 • 5 1.5
CgHlj. .5 .6 3-0 it- .8 6.7 7-1 5.6 nc2H6 0 .000 .000 .021 .Oit-7 .069 .208
-8o°/-ii8°c .5 .3 .8 l.it- .3 • 9 2.5
nrec. 239 2U0 259 289 - 373 it-it-3
ncal. 2k3 21+2 263 290 - 375 if-35 6i
P-pinm. = initial pressure of trimethylborane in mm.
Pt,mm. ■ final pressure at end of experiment in mm.
time,min. = total time of reaction in minutes
BCCH^^-i = initial number of micromoles of trimethylborane
BCCHgJg-t = number of micromoles of trimethylborane at time t
= number of micromoles of trimethylborane reacted in time t
CH^ = number of micromoles of methane at time t
H2 = number of micromoles of hydrogen at time t
Cj^Hg s number of micromoles of ethane at time t
= number of micromoles of ethylene at time t
NC2Hg = mole fraction of ethane as determined by gas chromatography
-80°/-ll8°C s number of moles of the -80°/-ll8°C fraction at time t
nrec = sum of all material recovered and measured
nca^_ a calculated number of moles of gas at time t =
[B(CH3)3 -r| x !i .
For those experiments in which no value for P^. is given, the
total reaction mixture was removed. In these experiments methane and
hydrogen were not measured. For those experiments in which a value for P.j. is given, only a portion of the reaction mixture was removed
(usually more than 90 percent). For these experiments ncal> is calcu lated. A comparison of nrec< and ncap. shows that the material measured included practically the whole of the reaction mixture and that the material which did not pass through a trap at -80°C was a very small percentage of the reaction mixture. 62
The values for the number of moles of methane, hydrogen,
ethane, and ethylene formed and of trimethylborane reacted are plotted against time as shown in Figures 11 through 17. The ethane and ethylene curves are located at the tops of the graphs and the ordinate scales for these are at the right side of each graph.
A group of experiments was made in the 229.5 cc. packed quartz flask at k88° and 508°C. These reactions were made at pressures corresponding to those used in the unpacked vessel so that the initial concentration of trimethylborane in both reactors was the same. The data for these experiments are given in Tables 15 and l6 . Each experi ment has two columns of data. The column labeled "a" contains the actual experimental data as measured. The column labeled "b" is found by multiplying the values in "a" by the average of the initial number of moles of trimethylborane for experiments in the 1 1 0 .1 cc. reactor at the same conditions of temperature and pressure and dividing by the initial number of moles of trimethylborane for the experiment. This procedure is approximately equivalent to multiplying by which simply constitutes a volume correction. This method was adopted so as to make corrections for slightly different concentrations and to be able to ignore the volume outside the furnace. The data from the
"b” columns are shown on the appropriate graphs for direct comparison with the results in the unpacked vessel. Except at h88°C and 101.7 mm. initial pressure of trimethylborane, the data show that there is no surface contribution and, therefore, that the reaction is homogeneous.
No explanation can be given why the data at k88°C and 101.7 mm- initial Moles x 10 63 Moles Fig. 12. Change in Composition for Pyrolysis the of 97 3 Micromoles (40.7 mrn.) i WH »i"* of Trimethylborane at Time, minutes 40 i 489°C. reacted — 4 d * 61* Moles Moles O 160 120 0 8 0 4 i. 3 Cag i Cmoiin o te yoyi o 175.1 of Pyrolysis the for Composition in Change 13. Fig. irmls 726 m) f rmtybrn t 488°C. t* Trimethylborane of mm.) 6 2 (7 Micromoles 20 ie minutes Time, O..B(SfcUi*..t»£icUiiti . K ;H t lid i l n to C;:Hc K ! i I ) iG tu i i tu iG ) I H liic —— loimiic Hj i . K G] 44*-*4r**«p- oi m # > r j m i i c » i - 4 4 0 6 0 8 Moles 6£ Moles M 240 200 120 160 40 80 0 i 1 Cag i Cmoiin o te yoyi o 24. Mirmoles icrom M 43.4 2 of Pyrolysis the for Composition in Change 14 Fig 117 m) f rmehloae 488,,C. t a ethylborane Trim of mm.) (101.7 20 Time, minutes 40 f h » blachanid •*...ijrflfewi lo blachanid per » h f In# in e m m ♦ OH -ft r*tw 1 •— OjH» ♦ • X CaH, formed- - formed- X CaH, fk. H orrreij Hj 00 ti 8060 66 Moles is o Moles x 140 100 120 0 4 0 6 0 6 20 0 i. 5 Cag i Cmpsto fr he yoyi o 244.7 of Pyrolysis e th for position Com in Change 15. Fiq. co ls 122m. o Tiehloae t #C. 8 9 4 at Trimethylborane of mm.) (102.2 oles icrom M 10 ie minutes Time, 20 0 3 67 Moles 100 40 60 o e 20 i. 6 Cag i Cmoiin o te yoyi o 9. Micromoles M 95.6 of Pyrolysis the tor Composition in Change 16. Fig. (4Q6mm) of Trim ethylborane a t t a ethylborane Trim of (4Q6mm) Time, minutes 20 i croe snol indicall syntool! cartoned Tie oeprmotrtr peeked ontvrvthr foreiperim + Ggh + QgiieX »■ f )rm .. 4 o 68 *o Moles X 240 200 120 160 40 0 6 i 1 Cag i Cmoiin o te yoyi o 299 Micromoles 239.9 of Pyrolysis the for Composition in Change 17 Fig (102.7 mm.) of Tri methylborane at at Tri methylborane of mm.) (102.7 . Time, minutes f .. 20 -I .. O C*mturmid m * C + c«l i l a fin cH« tfe. 40 4 * 69 Moles S TABLE 15 PYROLYSIS OF TRIMETHYLBORME IN THE 229-5 cc. PACKED QUARTZ FLASK AT l£ft°C Exp. 13-12 10-12 20-12 17-12 a b a b a b a b P-j^Him. 40.8 1+0.4 1 0 1 .6 10 2 .2 P^-,nnn. 14-9.6 5 1 .8 126.3 150.7 titne,min. 2 0 .0 2 5 .2 2 0 .1 3 0 .0 b (c h 3)3-i 2 0 1 .6 97-3 2 0 0 .8 97-3 498.5 243.4 499.5 243.4 B(CH3)3-t 159-2 7 6 .8 144.5 7 0 .0 369.6 180.5 2 5 6 .1 9 2 .8 ab(ch3) 3 42.4 20-5 56.3 27.3 1 2 8 .9 6 2 .9 243.4 1 1 8 .6 c % 32-9 15-9 44.3 21.5 1 3 1 .0 64.0 306 149 h2 42.7 2 0 .6 57-5 27.9 101.7 49.7 156 76 .1 .4 c2h6 .00 .00 .1 0 .0 • 3 • 9 4.8 ^2^4 3-8 1 .8 4.1 2 .0 7-8 3-8 9.9 .00 .019 .032 .082 -80°/-ll8°C 2 .8 1.4 2 .6 1.3 2 .2 1 .1 1 .8 .9 nrec. 21+1 253 613 730 ncal. 2l+5 257 620 737 TABLE 16 PYROLYSIS OF TRIMETHYLBORANE IN A 229-5 cc. PACKED QUARTZ FLASK AT 508°C Exp. 6-1 . . 23-12 26-12 a b a b a b Pj^mm. UO-5 1 0 2 .9 1 0 3 .6 P^mm. 55-7 135.2 157.6 time,min. ll.l 8.9 1 3 .0 b (c h 3)3-i 199.3 95-6 1*91.0 239.9 1*91-5 239.9 B(CH3)3-t 1 3 2 .2 63 A 335-8 l6i*.i 2l*2 .0 1 1 8 .1 6 b(ch3) 3 6 7 .1 3 2 .2 155.2 75.8 21*9.5 1 2 1 .8 CHij. 53 A 2 5 .6 152 71* 297 11*5 h2 70.9 3**.o 131* 65 195 95 c2H6 .1 0 • 3 .2 1.0 .5 CgHlj. 6.73 3-2 11.6 5 .7 ll*.5 7-1 NC2H6 .012 .029 .061* -8o°/-il8°c 2 .0 •9 1.3 .6 1.7 .8 nrec. 265 635 752 ncal. 274 6k 5 71*8 72 pressure indicate a higher percentage reaction of the trimethylborane in the packed reactor than in the unpacked one. Experiment 10-11 provides some information on the decomposi tion of the wall coating at 508°C. The reaction mixture from this experiment was removed from the reactor as for an experiment to remove the total sample. The reactor was then closed for 101 minutes. After this time, the non-condensable gases were collected by the Toepler pump and measured. There was 19.2 x 10"^ moles of non-condensable gases. The time in which these gases were formed was the; 101 minutes plus the actual time of collection with the Toepler pump. Analysis by gas chromatography showed the gases to be about 1^ percent methane and 86 percent hydrogen. A group of three experiments was made to determine the effect of a freshly prepared wall coating on the decomposition of trimethyl borane. These experiments were made by placing a portion of trimethyl borane in the reactor for a definite time for "conditioning." The reactor was then evacuated for a few minutes and a second portion of trimethylborane was placed in the reactor. After reacting a certain time, the reaction mixture was removed and analyzed as before. Table 17 lists the data for these experiments. For comparison, the table also includes values for the number of moles of the various species as determined from Table 9 and Figure 12 which are for the reaction of 9 7 .3 micromoles of trimethylborane at i+S8°C. The row listed as "eond. time" indicates the time of reaction for the first portion of trimethylborane used for "conditioning." The value for is in TABLE 17 THE EFFECT OF A FRESH WALL COATING ON THE PYROLYSIS OF TRIMETHYLBORANE AT 1*88°C Exp. 16-3 2 -2 6 -2 Data from Fig. 10 and Table 9 Cond. time,min. 1 0 .0 3 0 .0 6 0 .0 39-3 39-2 39-^ 1*0.7 1*0 .7 1*0.7 - 5 6 .2 5 8 .2 time,min. 2 7 .0 29.3 3 0 .0 27.0 29.3 3 0 .0 B(CH3)3_i 9 8 .6 96.9 97.9 97-3 97-3 97.3 B(CH3)3-t 66.5 60.5 5 9 A 65.7 6 1 .8 6 0 .8 &b(ch3) 3 32.1 36.1* 38.5 31.6 35-5 36.5 ch4 - 33.0 35-9 - 3 1 .0 31)-.5 h2 - 3^-7 35.2 - 33.0 3^.3 c2h6 0 .1 .1 0 0 0 C2H14. 2.7 2.9 2.7 2 .2 2.3 2 .1* .015 .028 .029 .000 .000 .000 -8o°/-ii8°c 1.7 1 .6 1.5 1.7 1 .7 1.7 nrec. - 133 135 ncal. - 139 li*6 considerable error because of the sticking of the capillary manometer, and thus the value for ncai. is also in error. A comparison of these data shows that the wall coating has little effect on the decomposition of trimethylborane. Trimethylborane and Propylene Experiment 21-11 was made with propylene alone in a condi tioned reactor at *t8 8°C. The reactor had been evacuated for two days at WS8°C. Table l8 gives the data for this experiment. TABLE 18 EXPERIMENT 21-11. PYROLYSIS OF PROPYLENE AT *t8 80C P^,mm. 1 0 1 .0 2 .0 Pi,mm. 1 0 1 .0 -118°/-195°C less C2H^ 237.7 time,min. Uo.o 425°/-ii8°c 1-3 C3H6-i 2*6-5 nrec. 21+h- CH^ 4 H2 3-0 ncal. 2*l4 The symbols have the same significance as before. The ethylene was determined by gas chromatography and subtracted from the total -ll8°/-195°C fraction. The value for -ll8°/-195°C less probably represents the total unreacted propylene although it may contain some hydrocarbons. The’ 425°/-ll8°C fraction was placed on the Dowtherm A column, but no peaks were found. This experiment shows that there is only a small amount of decomposition of propylene at U88°C in a trimethylborane conditioned flask. 75 Two experiments were made at U88°C with trimethylborane and propylene in a 1 to 1 mole ratio. Figure 18 shows the pressure-time curves for these reactions together with curves for reactions with approximately the same concentration of trimethylborane. The corre sponding curves show that the reactions with propylene have much greater rates of pressure increase and reduced pressure induction times than for reactions in the absence of propylene. The reaction mixture, after the removal of the non-condensable gases, was fractionated for it-0 seconds through traps at -80°, -1^5 °* -155°> and -195°C. The material contained in the -195°C trap (-155°/-195°C #l) was analyzed on the silica gel column and contained ethane, ethylene, and a small amount of propylene. After removal of this material the fractionation was continued for four minutes. The material not passing through the -80°C trap was discarded. The three other fractions were measured and placed on the Dowtherm A column for qualitative analysis. Table 19 gives the data for these experiments. The analyses on the Dowtherm A column showed the presence of trimethyl borane, propane, propylene, isobutane, butene-1 and/or isobutene, butene-2-trans and butene-2-cis. In addition 21-1 also showed three very small peaks which were probably due to hydrocarbons. The saturated hydrocarbons were present in only small amounts. The major portion of the trimethylborane was found in the -1^5°/-155°C and the -80°/-l1»-5oC fractions. The major portion of the propylene was found in the -l1t-5°/-155°C fraction. If the fractions which contained the trimethylborane are considered to be pure trimethyl borane, the decompositions are approximately *4-7 and 6 l percent in 21-1 0 6 12 18 24 Time, minutes 2 1 - I j 168.5 x I0"6moles B(CH3)3 168.5 x IO '6moles C3H6 26-1; 96.7 x IO“® moles B(CH3)3 96.7 x I0'6 moles C3H6 2 4 -2 j 175.5 x KT6 moles B(CH3)3 24-9* 98.2 x 10'6 moles B(CH3)3 Fig 18. Comparison of the Decomposition of Trimethylborane Alone and in a hi Mixture with Propylene at 488°C. 77 TABLE 19 PYROLYSIS OP A 1:1 TRIMETHYLBORANE-PROPYLENE MIXTURE AT i)88°C Exp. 21-1 26-1 Pi,trnn. 138.5 80.9 P^.,mm. 213.0 130.8 time,mln. 20.0 26.0 B(CH3)3-i 168.5 96.7 C3H6 -i 168.5 96.7 CH^ 253 150 h2 133 95 -155°/-195°c #1 26.9 17-6 -155°/-195°C #2 6.2 7.2 -ll5°/-155°C 39-8 21.9 -8o°/-ll{-50C 50.6 16.3 8.2 3-8 c 2 18.1 ll.l nrec. 510 308 ncal. 518 313 78 and 26-1 respectively. The decomposition determined from the graphs at approximately the same initial concentration of trimethylborane and time of reaction are 21 and 29 percent respectively. It is also quite evident that a very large fraction of the propylene decomposed. These data show quite definitely that the mode of decomposition of trimethyl borane is different in the absence and presence of propylene and that the decomposition of the two materials is much greater in a mixture of the two than for each individually. The effect of a freshly prepared wall coating, formed by the pyrolysis of trimethylborane, on the pyrolysis of propylene was deter mined in experiment 15 -1+. The procedure used was to place about 100 mm. of trimethylborane in the reactor at 488°C and to allow it to react for 20 minutes. The reaction mixture was then removed and the reactor evacuated for U.5 minutes. Propylene at 101 mm. pressure (approximately 21-0 micromoles) was then placed in the reactor for 30 minutes. In this time the pressure increased by 2 mm., as compared with no measurable pressure increase in i+0 minutes with an aged wall coating (Table 1 8 ) . The reaction mixture was removed and the conden sable material qualitatively analyzed on the Dowtherm A column. The following were identified: ethane and/or ethylene, propylene, butene-1 and/or isobutene, butene-2-trans, and butene-2-cis. Because of the large amount of propylene present, a small quantity of propane, if present, would have escaped detection. The substances identified correspond to the major hydrocarbon products formed in the reaction of propylene and trimethylborane. Thus the freshly prepared wall coat ing produces the same products as trimethylborane itself in the decom position of propylene. 79 These propylene experiments were made with the purpose of determining whether there is any radical chain character to the trimethylborane pyrolysis. The results show that the two substances react strongly with each other, but the retardation in rate on addition of propylene, which would be expected if the trimethylborane decomposition involves chains, does not occur. Trimethylborane and Ethylene One experiment was made with a mixture of trimethylborane and ethylene. Table 20 gives the data for this experiment.(10-4). TABLE 20 PYROLYSIS OF TRIMETHYLBORANE AND ETHYLENE AT U88°C time,rain. 15.0 A B(CH3 ) 3 6k.k B(CH3)3-i 2k6.2 c2h6 .k CgHi^-i 11.7 1-k B(CH3)3-t 181.8 -8o°/-ll8°c 2.9 Figure 19 shows the pressure-time curve for this experiment and also for ^-10 which was made with 2h5 .1 micromoles of trimethyl borane at h88°C. A comparison shows that in 10-lt- the period of accelerating rate of pressure increase is much shorter than in h-1 0 . The rate of pressure increase, once the maximum rate is reached, is slightly greater in 10-1+ than in h-10. This, however, may only be another case of irreproducibility as reported before. From Figure ik, which is for the pyrolysis of 2^3 .6 micromoles of trimethylborane at E E i. 9 Te fet f de Sbtne o -h Prlss f Trimethylborane of Pyrolysis -the on Substances Added of Effect The 19. Fig. Pressure increase 32 24 2 - 24-4 24-4 10-4 i 10-4 20-4; -Oi 4-IO i 17 I“ mls C2H4 moles I0“* x11.7 x 246.2 4. x 0* oe B(CH3)3 moles 10"* x 241.5 m NO mm. 2 m. NO mm. 6 3. x 0* oe B(CH3)3 moles 10"* x 232.8 4. x 0* oe B(CH3)3 moles 10"* x 245.1 A ie minutes Time, IO • oe B(GH3)3 moles ~• x 84 - 4 , 4-10 -4 24 x 80 81 488°C, the number of micromoles of ethylene and ethane formed and of trimethylborane reacted in 15 minutes are 1.8, 0.0, and 28.5 respec tively. Thus it is apparent that the reaction of trimethylborane and ethylene is not the same as the initial reaction of trimethylborane alone. However, if it is assumed that the decomposition of trimethyl borane in the presence of ethylene proceeds at the maximum rate, Figure 14 shows that 69 micromoles of trimethylborane would decompose at this rate in a fifteen-minute period. However, another interpre tation is to assume that the pressure curves for 10-4 and 4-10 both bear the same relationship to the decomposition of trimethylborane. In this case a superposition of the curves shows that they nearly coincide if zero time for 10-4 is made 6 minutes for 4-10. In other words, the pressure induction period has been shortened by 6 minutes by the addi tion of ethylene. With this correction of starting time, Figure 14 shows in 21 minutes less 6 minutes (15 minutes) a decrease in trimethyl borane of 53 micromoles (58 at 21 minutes less 5 at 6 minutes) and an increase in ethylene and ethane of 3 and 0 micromoles respectively in that fifteen-minute period. This compares with a decrease of 3*3 micromoles for ethylene and an increase of O A micromoles for ethane in experiment 10-4. The true analysis probably lies somewhere between the above two cases. If the assumption of maximum rate is more likely, the comparison of 64.4 and 69 micromoles shows that there is no induction period and no change in the maximum rate of decomposition caused by the addition of ethylene. If the change in zero time is more nearly the correct interpretation, the comparison of 6k.1* and 53 micromoles shows that the presence of ethylene has accelerated the rate of decomposition of trimethylborane, while shortening the induction period by 6 minutes. Trimethylborane and Azomethane Three experiments were made with mixtures of azomethane and trimethylborane. The data for these experiments are shown in Table 21. The interpretation of these experiments is carried out as follows for the reactions at k88°C. Using the value for the first-order rate constant, k, as given by Ramsperger (19)* it was calculated that at 1*88°C more than 99 percent of the azomethane would have reacted in a few milliseconds; thus it is assumed that after 3 minutes 100 percent would have reacted, even if the pressure were in the falling-off range. Next it is assumed that the azomethane decomposed to give nitrogen and two methyl radicals. It was also assumed that the forma tion of ethane and ethylene was due completely to the reaction of these methyl radicals formed by the azomethane. Therefore the number of moles of methyl radicals available to react with trimethylborane, A, would be given by A . 2(CH3)2N2 - aCgHg - 2 0 ^ . (l) At k88°C it is necessary to allow for the fact that trimethylborane itself reacts. The trimethylborane reacting by itself was estimated by determining the number of moles of trimethylborane reacting (n^) at k88°C and 1*0.7 mm. pressure at the maximum rate from the straight line portion of the curve in Figure 12 and correcting for the differ- 83 TABLE 21 PYROLYSIS OF TRIMETHYLBORANE AND AZOMETHANE IN A 110 cc. QUARTZ FLASK Exp. 11-3 9-3 20-1 T°C i@e 188 315' time,min. 3.0 5.0 50.0 B(CH3)3-i 91.1 93.5 236.1 (CHjJgNg-i b.9 5-0 11.2 B(CH3)3 -ta 85.2 81.9 220.0 C2HJ4. 2.3 2.1 .9 -8o°/-ii8°c 1.5 1.5 5-1 A* 2.b 2.8 18.0 B b.7 7.7 0.0 c 7.1 10.5 18.0 D 6.2 11.6 16.3 aThe -ll8°/-155°C fraction identified previously as the trimethylborane would also contain any unreacted azomethane. ^See text for meaning of A, B, C and D. 8^ ences in initial concentration by the equation B r corrected moles of B(CH ) reacting = n | — ~ I (2) 3 3 97 L 97 • 3J ' where 97-3 is the average of the initial number of moles of trimethyl borane in the series at hO.J mm. pressure and n^ is the initial number of moles of trimethylborane in the experiment. Now the assumption is made that the methyl radicals available to react with trimethylborane each react with one trimethylborane molecule, so that the number of moles of trimethylborane removed by reaction with these methyl radicals is also A. Thus the total number of moles of trimethylborane expected to react is given by C and C = A + B. (3) The value for the number of moles of trimethylborane reacted, D, at it8 8°C is equal to "ABCCH^)^" given in the table. At 315°C the procedure is slightly different since the azomethane is not completely reacted. Ramsperger (20) studied the decomposition of azomethane at 290°C and 330°C at various initial pressures in the range at which the first-order rate constant, k, is falling off. To find the value of k at 315°C, Ramsperger's data is plotted on a log-log plot as shown in Figure 20. It is assumed that the trimethylborane is ,as effective as the azomethane in collisional activation so that the pressure is taken to be 8.0 cm. initially. The values of log k at 8.0 cm. pressure were then plotted against l/T°K, _k 0 and the value of k - 8.00 x 10 sec. at 315 C was determined. With this value of k, it is calculated that 9 0 .9 percent of the azomethane is decomposed after 50 minutes or that .909 x 1 1 .2 x 10 ^ = 1 0 .2 x 10 ^ 20 20 .121 * KT3 n O 603*K 02 2 4 10 30 100 Pressure, cm. Fig. 20. Falling—Off of the Rate Constant for Azomethane [Rompsberger (20)] 86 moles of azomethane is decomposed in 20-k. Also it is assumed that none of the trimethylborane would decompose by itself at this temperature. The value for the number of moles of trimethylborane reacting in the experiment, D, is given by "ABCCH^Jg" plus the number of moles of unreacted azomethane (l.O x 10"^). The values of A, B, C, and D in micromoles are also listed in Table 21. A comparison of C and D for each experiment shows that with the assumptions made, all the reacting trimethylborane can be accounted for without attributing any radical-chain character to the pyrolysis. Therefore it is apparent that methyl radicals are not involved in any chain process with trimethylborane and that no radicals formed in the reaction of methyl radicals and trimethylborane can start chain processes. The only assumption which would lead to serious errors in this treatment is the one assuming that azomethane decomposes by ch3nnch3 ---- > 2CH3 + n2 . (10 However, it has been well established that 1+ does occur. The assump tion that the trimethylborane at 1+88°C is decomposing at the maximum rate represented by the straight line portion of Figure 12 is supported by experiment 10-Ij- and by the fact that at the onset of this straight line portion of the curve, only one micromole of ethylene is present, compared with the 2.3 micromoles in these two experiments. Also the initial pressure increases observed were greater than in any experi ment with trimethylborane alone at a comparable concentration. If the assumption that the trimethylborane at 1+88°C is decomposing at the maximum rate is not correct it is possible to assume that the trimethylborane in 11-3 and 9-3 is reacting as if no azomethane were present and that an extrapolation of the curve for trimethylborane reacted in Figure 12 can be used to determine the number of micromoles of trimethylborane reacting in 3 and 5 minutes. The extrapolation leads to values of 0.8 and 1.7 respectively as the number of micromoles of trimethylborane reacting, B, at 488°C. These values together with the values for the number of micromoles of available methyl radicals, A, lead to the values of 3-2 and k.$ for the number of moles of trimethylborane expected to react, C, compared with 6.2 and 11.6 micromoles reacted, D, as found in 11-3 and 9"3 respectively. With a comparison of these figures, it is evident that, if there is a chain process occurring, the chain lengths are no more than three. This is assuming that radical chains started by the reac tion of methyl radical and trimethylborane would be fast reactions. Trimethylborane and Nitric Oxide Two experiments were made with mixtures of nitric oxide and trimethylborane. Table 22 lists the data for these experiments and also the data taken from Figure 1^ at 25 minutes. Figure 19 shows the graph of pressure increase against time for the two experiments together with the curve for ^-10 which was made with 2^5 micromoles of trimethylborane at l488°C. The differences in the curves for 2k-b and h--10 are slight and are no more than those found in any series of experiments made. Experiment U-10 was made while the capillary manometer was in an open mercury pot, and thus the capillary could not 88 TABLE 22 PYROLYSIS OP TRIMETHYLBORANE IN THE PRESENCE OF NITRIC OXIDE AT l*8d 0C Exp. 28-lt From Fig. lit PN0 -i,mm. 2.0 6.1 0 P.^-total, ram. 102. it 102.it time,rain. 25.0 25.0 25.0 B(CH3)3-i 2kl.5 232.8 2k3.k B(CH3)3-t 15k.6 173.0 l6 8 .it Ab(ch3) 3 86.9 59-8 75.0 .2 .1 c 2h 6 1.9 c 2% ^•3 5-k 3-3 -8o°/-il8°c 2.28 2.9 - ing of the mercury. Experiment 28-k is peculiar in that this was the only experiment in which a pressure decrease was noted and that it took at least 12 minutes for the pressure to start a rapid increase. The differences in the initial number of moles of trimethylborane are too small to account for these differences. The relationship between the curves for 28-k and 1+-10 or 2k-k is quite similar to the relation ship between the curves for the preliminary experiments made before and after admitting air to the reactor, as illustrated in Figure 7 . One possible explanation is the use of Dow-Corning High Vacuum Grease (a silicone product) on the stopcock on the reactor for 2k-k and 28-^, since silicone greases are known to creep. If the creepage occurred prior to the experiment the surface effect may have been quite different. A portion of the non-condensable gases from 28-k was chromatographed on the Molecular Sieve column. Nitrogen, hydrogen, and methane were observed. The presence of nitrogen indicates that the nitric oxide was reduced some time during the experiment. Thus it may be that the nitric oxide is oxidizing the surface or in some other way changing the surface similarly to the air. If oxidation occurred, all the nitric oxide might have been used up by the time the trimethyl borane was added and therefore there would be no inhibition. It is also possible that the nitric oxide reacted rapidly with the trimethyl borane in a molecular reaction, similarly to the oxidation of trimethylborane by oxygen as reported by Petry (8), Petry and Verhoek (2l), and Coleman (9)• Here again no nitric oxide would be 90 present to inhibit the chain decomposition of trimethylborane if it occurred. The initial pressure decrease in 28-k could also be explained by a reaction of nitric oxide and trimethylborane. If nitric oxide was present during the reaction it may have acted in 2k-k similar to the way it acted with ethane as reported by Staveley (22). He reported that the initial rate of the ethane decomposition was greatly inhibited by small amounts of nitric oxide at 620°C. However, after the nitric oxide was all removed by reac tion, there was a slight acceleration of the rate over that for ethane alone. He measured the rates by following pressure changes. In the case of trimethylborane, however, experiments 19-11 and 17-11 (Table ll) show that although there is no measurable increase in pressure, there is decomposition of trimethylborane in the early parts of the reaction. Thus pressure cannot be used as a criterion of initial rate of reaction. Since 28-^ contained three times as much nitric oxide as did 2k-k, it would take longer for the nitric oxide to be removed. This may explain why the percentage decompositions listed in Table 22 -seem to be inconsistent. The reaction of trimethylborane and nitric oxide deserves further study. VIII. DISCUSSION Order From the shape of the curves for trimethylborane reacted against time as shown in Figures 11 through 17 it is evident that the decomposition of trimethylborane is a complex reaction and that no simple order (or rate expression) will describe the reaction. During the early period of the reaction, the reaction shows an accelerating rate. Then a period of apparently constant rate of reaction sets in, followed by a small falling off of the rate. This behavior is typical of an autocatalytic reaction. The period of constant rate would indi cate a zero order dependence if the reaction were simple instead of complex. Table 23 lists the temperature, T°C, the initial number of moles of trimethylborane, ni, the rate of disappearance of trimethyl borane at the maximum rate, Rm , in micromoles per minute, and the rate of disappearance divided by the initial number of micromoles of trimethylborane, — , in reciprocal minutes, for each of the series of ni experiments with trimethylborane in the 110 cc. quartz flask. From the data for the experiments at k88° and 508°C it is seen that a 2 .5 fold increase in the initial amount of trimethylborane has a large effect on the maximum rate. However, at W38°C, the values for _! are constant; this indicates that the maximum rate has a first i order dependency on the initial concentration of trimethylborane. R However, at 508°C, the values of —2 are not constant but differ by ni about 25 percent, being larger at the higher concentration. An explanation for the difference at 508°C probably lies in the experi mental difficulties. As noted before, the reactions showed an initial period of no observable pressure change. In most series the variations in the length of this period were small and random. However, in the series at 508°C with 95-6 micromoles of trimethylborane the "pressure induction period" was increasingly long in going from small amounts of reaction to large amounts of reaction, that is, the greater the time of reaction, the greater was the "pressure induction period." No explana tion can be given for this behavior, and it must be noted that the experiments were not made in the order listed in Table 13. If some corrections for this increasing "induction period" were made, the rate, R Rm , and — would be larger and thus the results at 508 C would be more ni in line with a first order dependency. TABLE 23 DATA FOR THE ORDER DEPENDENCE OF TRIMETHYLBORANE i Rm , micromoles m , min. Series T°C micromoles min. n^ 1 1*68 21*2.6 1.83 .00755 2 lf88 97-3 1.85 .0190 3 1*88 175.1 3-20 .0183 l* 488 21*3.1* 4.63 .0190 5 498 244.7 7.65 .0312 6 508 95-6 3.30 .031*5 7 508 239.9 11.2 .01*67 93 Activation Energy The activation energy,A Ea, of a simple reaction is found by plotting the log of the specific rate constant, k, against the reciprocal temperature in degrees Kelvin. From the Arrhenius equation - A E log k ■ ------■+■ log s (l) 2.303RT v ' where s is the frequency factor and R is the gas constant. The slope — A. E of the line is -----2 . The significance of A E „ in a process where 2.303R a a single step in the mechanism controls the rate is that A E a is the activation energy of the rate controlling step. In those reactions in which the rate expression has the form Rate = Ife. h rA]m [B]n = kM"^]* (2) "3 kJ where k^ and kj are the specific rate constants for the individual steps in the mechanism, and m and n are the orders with respect to the concentrations of A and B respectively, A E Q has the following rela tionship to the activation energies E. and E., of the individual steps: A E a . Z E. - % Ej . (3) i 3 For those cases in which the rate is given by a complex relationship, such as Rate - kifAplB] 11 f k2 [A]P[B]9 (1) where m and p and/or n and q are not equal, there is no simple significance to the A E a obtained from the Arrhenius graph. R The values of the log of ~ listed in Table 23 are plotted nl against the reciprocal temperature as shown in Figure 21. The best 9h ZO 1.6 1.2 .81— 1.25 1.30 1.35 j o ! T*K i Fig. 2L Activation Energy for the Pyrolysis of TrimethyIborone 95 straight line is drawn through those points for n.^ of about 2k0 micromoles. The slope of this line leads to the value of 53-1 Kcal. per mole for A E a . The value for the frequency factor is calculated to he 1 x 1011 sec.-1. Thus the rate expression for the steady state decomposition of trimethylhorane is JS = 1 x 1011 exp.- SitiOO Sec>-1 (5) n1 RT The value of It should also be noted that the plot of Rm itself would lead to the same value of A E a since the straight line was drawn through the points with the same initial number of moles of trimethyl- borane, i.e., at the same initial concentration. Stoichiometry From Figures 11 through 17 the following can be seen: 1 . Ethylene is a minor product appearing in the early stages of the pyrolysis. It reaches a maximum value and then decreases in amount. 2. Ethane does not appear until late in the reaction and is formed in only small amounts. 3. Hydrogen is formed in large amounts in the early portions of the reaction but at a decreasing rate in the later portions. it-. Methane is produced in ever increasing amounts during the reaction. 96 Figure 22 shows the moles of hydrogen produced as a function of the moles of trimethylborane reacted for reactions at i)-880C and 508°C. From the curves at approximately 97 micromoles of trimethyl- d n r r o borane initially, the values of the initial slopes, ------, are dnB(CH3) 3 one for both temperatures. As the initial concentration increases, the initial slope decreases. At ^88°C and 2^3 micromoles of trimethyl borane initially the slope is only 0 .7 - In all cases, the slope decreases as the trimethylborane is reacted, indicating that in the later stages of the reaction, hydrogen is being produced at a lesser rate with respect to the rate of decomposition of trimethylborane than in the initial stages of the reaction. This may mean that the hydrogen itself is being removed from the system by some reaction or that the reaction sequence producing hydrogen has become less important in the later stages of the pyrolysis. Figure 23 shows the moles of methane produced as a function of the moles of trimethylborane reacted. For methane, the initial dnCHo slopes, ----— =2— , of all the curves are 0.5. At each temperature dnB(CH3) 3 and concentration the slopes increase as more trimethylborane is decomposed. In each case, the slope approaches 2 when a large por tion of the trimethylborane has reacted. This large increase in the slope probably means that the initial products of the reaction undergo further reactions which produce methane. The stoichiometry for the pyrolysis in the early stages is therefore 2 B(CH3')3 ---- > 2 I 2 + CHI). + [B 2C 5 H 103 . <» Mfcromoles of Hydrogen Formed at 508^0. Micromoles of Hydrogen Formed at 488°G. ID n “1 3 3 o o O o a % I A i O o << Fig. 22. Stoichiometry Curves for Hydrogen Formation Micromoles of Methane Formed at- 508°C. 0 0 3 250 200 150 100 50 0 i . 3 Socimty uvs o Mtae Formation Methane for Curves Stoichiometry 23. Fig. 50 Micromoles of Trimethylborane Reacted 100 il jrml o 8(CH$)s mjcromolM of tiol 7. I 6 5 9 I | .3 '7 S 4 . 3 inaiooi 150 200 100 0 0 2 150 50 Micromoles of Methane Formed at 98 99 This stoichiometry is only for the lowest pressure studied (approxi mately Ul mm. of trimethylborane initially). As the pressure increases the stoichiometry for hydrogen production decreases. We may thus make more precise items 3 and h of the summary on page 95 by substituting: 3'.a. Initially one mole of hydrogen is formed per mole of trimethylborane decomposing for ^1 mm. initial pressure. 3'.b. At the higher pressure, 101 mm., less than one mole of hydrogen appears per mole of trimethylborane decomposing. 3'.c. Toward the end of the reaction, only about 0.2 mole of hydrogen is formed per mole of trimethylborane decomposing. h-*.a. Initially one-half mole of methane is formed per mole of trimethylborane decomposed, at both pressures. h'.b. Toward the end of the reaction, nearly 2 moles of methane are formed per mole of trimethylborane decomposing. The stoichiometry found is quite different from that proposed by Goubeau and Epple (l6 ). They suggest that the reaction starts with a splitting out of methane and that the boron-containing residue' initially forms the tetramer "tetra-B-methylcyclo-1,3,5,7 boroctane" (Fig. 2b) . This compound was found among the products of the decom position. CHo— B— CHq -*-B— CHo 3 I 2 I 3 CHo CHp I I CH^— B— CHp— B— CHg Fig. 2b. Tetra-B-methylcyclo-1,3,5>7 boroctane 100 They further suggest that the boroctane can condense by splitting out methane from the methyls attached to the borons to form polycyclic polymers. The polycyclic polymers then split out methane with a change in the ring structure to form (BCH)X polymers and then hydrogen is split out to form boron-carbon polymers. With the scheme proposed by Goubeau and Epple there should be one methane formed for each trimethylborane reacting in the initial reaction and more should be formed as the initial products further decompose. Wo hydrogen should be formed in the initial reaction and hydrogen should become more important as the decomposition of the initial products proceeds, i.e., the ratio of hydrogen produced to trimethylborane decomposed should.increase but it should never be greater than .5 . These conclusions based on the scheme of Goubeau and Epple are quite different from the results of this investigation. It should be noted that the pressures used by Goubeau and Epple were much higher than those used in this investigation. Table 2k shows the data for three experiments made by Goubeau and Epple in a flow system at ^37°C at one atmosphere. At the fastest stream velocity, which would correspond most nearly to the initial reaction, the ratio of the methane formed to the trimethylborane reacted is very close to the 0.5 found in this investigation; the ratio of hydrogen produced to the trimethylborane reacted is O.8 5. When the flow rate was decreased the methane ratio increased to over 1 .1; the results for hydrogen are variable. The results for these three experiments by Goubeau and Epple are in agreement with the results of this investigation. 101 Goubeau and Epple do not report any ethane or ethylene or any other hydrocarbon products. In the present investigation, no acetylene was found even though the Cg's were frequently analyzed for acetylene by gas chromatography. If small amounts of propylene were present they would have escaped detection. TABLE 2k PYROLYSIS OF TRIMETHYLBORANE AT 1*3 7°C BY GOUBEAU AND EPPLE b(oh3) 3 Flow Initial CH^ p rate b(ch3) 3 reacted H2 b(ch3) 3 b(ch3) 3 at. l/hr ccm. ccm. 0.9^ 1+ 2100 150 0.55 0.85 0.9^ 2 1780 i(40 1.12 0.70 O .85 1 1100 3^0 1.13 0.86 Mechanism There are several ways by which trimethylborane might start to decompose. One way would be to assume that the initiating reac tion breaks only one bond in the molecule, forming free radicals. In trimethylborane there are only two bonds that can break— the carbon-boron and the carbon-hydrogen bonds. By analogy with hydrocarbons and metal alkyls, one would predict the break to occur at the boron-carbon bond. However, if the boron-carbon bond is considerably more stable than the carbon-carbon bond, the break could occur at the carbon-hydrogen bond. There is some reason to expect 102 that the "boron-carbon bond is quite strong. First, the electro negativities of boron and carbon are quite similar and therefore the bonds between boron and carbon would be expected to be similar in strength to the carbon-carbon bonds. The fact that the boron in trimethylborane is electron deficient could further strengthen the carbon-boron bond since hyperconjugation would impart some double bond character. Together with the strengthening of the boron-carbon bond by hyperconjugation, the hydrogen-carbon bonds would be weakened compared to the carbon-hydrogen bonds in hydrocarbons. The extent of this strengthening and weakening remains to be determined. After the initial free radicals are formed, they would react further. In hydrocarbon chemistry, there are five types of radical reactions which are generally accepted: 1. Combination reactions' CHg ♦ CHg ------CgHg 2. Abstraction reactions CH3 RH * CH^ ♦ R 3. Disproportionation reactions CgH5 * CgHj---- » C2H^ + C ^ g Ij-. Decomposition reactions in which olefins usually are formed RCH2CH2 -----* R f CH2 - CH2 5. Addition reactions ch3 rch=ch2 ---- > rchch2ch3 or RCH(CH3)CH2 When abstraction reactions occur in hydrocarbon chemistry, the radical usually abstracts a hydrogen (equation 2). There are a few cases in which radical abstraction has been suggested. For example Henkin and Taylor (23) have studied the reaction of hydrogen atoms produced by a diseharge-tube method with azomethane. They suggest the reaction H CH3MCH3 CHj^ + , which would be a methyl abstraction reaction. Further, the reaction of methyl abstraction has been suggested (2^, 25 ) for ch3 + ch3cocf3 c2h6 + cf3co though it is likely that this involves a preliminary addition to the double bond. One additional type of reaction might occur with boron' compounds. This would be a displacement reaction such as H «■ (CH^gBCHg ------? (CH^) gjBH + CHg or ch3 + C2H5b(ch3)2 ----> (ch3)3b .+ . The author knows of no instance in which this type of reaction has been proposed. However, the vacant p orbital on the boron may make this type of reaction very probable. If hydrogen atoms or methyl radicals are formed in the pyrolysis of trimethylborane, there is no reason not to expect that these species can abstract from trimethylborane by the reactions 10l+ Evidence for reaction 2' is found in the results of the reactions of azoraethane and trimethylborane in which the total amounts of methyl radicals formed are not accounted for by ethane and ethylene. The only apparent way to remove the excess methyl radicals appears to be by reaction 2 '. The following mechanisms, employing radical reactions, have been considered in attempting to explain the initial stoichiometry, 2B(CH3) 3 --- > 2H2 + CH^ + B2C5H10 , (3 ') with the requirement that there are no chain reactions such as are frequently observed in hydrocarbon chemistry. In all cases the mechanisms were discarded. I". Assume that the first bond to break is the carbon- hydrogen bond, b(ch3) 3 y b(ch3)2ch2 + h , (V) and then the H abstracts by H 4> B(CH3) 3 ---- > H2 + B(CH3)2CH2 . (1 ’) The B(CH3)2CH2 may then decompose to form an olefin type compound by the reaction b(ch3)2ch2 ch3 + ch3b:ch2 (5') followed by an abstraction by the methyl radical, CH3 + B(CH3) 3 --- * GH^ + B(CH3)2CH2 . (2 ’) This possibility is excluded since 5' and 2' constitute a chain reaction; furthermore, hydrogen is not formed in the 1:1 ratio required. II. If we again start with reactions. V and 1’ 105 B(CH3) 3 ► H -f B(CH3)2CE2 (If') H«.B(CH3) 3 ► H2f B(CH3)2CH2 (!') followed by the decomposition reaction b(ch3)2ch2 ---- h ♦b ( c h 3)(ch2) 2 , (6 ') a chain reaction is again set up. III. If the first bond to break is the boron-carbon bond, b(ch3) 3 > b(ch3) 2 + ch3 , (7 ’) the CH3 can react by the abstraction reaction CHg ★ B(CH3) 3 — » C% B(CH3)2CH2 . (2 ') The B(CH3) 2 can then decompose, forming an olefin type compound, by b(ch3) 2 --- > h * ch3b:ch2 (8') and then hydrogen, H2, can be'formed by the abstraction reaction h-*b(ch3) 3 > h2 ♦ b(ch3)2ch2 '. (1 ’) For this scheme to be correct, it would now be necessary for the 2 B(CH3)2CH2 radicals and the CH3B-CH2 to form 2 hydrogen molecules and one-half methane molecule to obtain the correct stoichiometry, and to do this without forming any hydrogen atoms or methyl radicals, for these would start chain reactions. IV. Again starting with a rupture of the boron-carbon bond b(ch3) 3 ---- > b(ch3) 2 +c h 3 (7’) followed by an abstraction 0H3 * B(CH3) 3 ---- + B(CH3)2CH2 , (2 ') the B(CH3)2CH2 could react with B(CH3) 3 by a replacement reaction, such as B(CH3)2CH2 ♦ B(CH3) 3 — ^ (CH3)^BCH^B(CH3) 2 4 CH3 . (9') But 2' and 9' constitute a chain reaction. io6 V. Starting again with 7' and 2' the B(CH3)2CH2 could possibly displace a hydrogen atom by B(CH3) 2CH2 ♦ B(CH3) 3 ------► (CH^gBCHgCH^CH^g +H (10') followed by H-t-B(CH3) 3 *- H2 > B(CH3)2CH2 . (I1) Here again a chain reaction is set up by l1 and 10'. Although there is no reason to expect hydrogen atoms not to undergo the abstraction reaction 1 ', that possibility is now considered. VI. Starting by rupturing the carbon-hydrogen bond, B(CH3) 3 H + B(CH3)2CH2 , ■ (h') followed by the displacement reaction h * b ( c h 3) 3 > h b ( c h 3 ) 2 + c h 3 , (11'.’ ) and then the abstraction reaction CH3 + B(CH3) 3 ---- ► CH^ «► B(CH3)2CH2 , (2 ’) it would then be necessary for the 2 B(CH3)g£H2 radicals and the HB(CH3) 2 to form one-half of a methane -and three hydrogen molecules to establish the correct stoichiometry. In the above discussion, it has been shown that by the use of normal types of free radical reactions, as well as an unusual one, there is not a logical sequence of reactions which will explain the initial stoichiometry observed for the pyrolysis of trimethylborane without forming chain reactions. These mechanisms have all assumed that the boron-containing radicals also reacted by rapid radical reactions. The azomethane experiments indicate, however, that the B(CH3)2CH2 radicals, if they are formed by reaction of methyl radicals 107 and trimethylborane (and there is every reason to believe that they are), must be quite stable toward decomposition reactions which form methyl radicals or hydrogen atoms, and react slowly, if at all, with trimethyl borane. Otherwise, the azomethane experiments should have shown con siderable chain character. Thus it is necessary to consider mechanisms in which hydrogen and methane are formed, in part at least, by non radical reactions or in which the boron-containing radicals undergo slow reactions. The problem now is to determine the structure of the boron- containing residue, B2C^H10. If the residue exists as a single species the following structures can be drawn which satisfy the valence requirements of all the atoms: 1 . C?2 HC CH 2 . HB BCEL C H = CH 3. CHg-CHj, B — CH^ — B ch2— ch2 108 To the author's knowledge these structures have no known counterparts in boron chemistry. The boroctane (Fig. 2k) reported by Goubeau and Epple (16) has methylene bridges (-B-CH2-B-); these methylene bridges have also been reported by Harrison, et al. (26 ) who prepared dimethylenetetraborane by the reaction of ethylene with decaborane, King structures involving boron have also been reported by Winternitz (27)• He heated tri-n-amylborane under reflux and found hydrogen, "trans-3-pentene," and the heterocylic compound HpC— CHo 7 I HpC HCCHp \ / 3 B I c5Hn in a 1:1:1 molar ratio. On heating tri-n-hexylborane he found a small quantity of the compound CH0 CHP \ i CHo CHCHq \ / B . I c 6h13 Hydrogen and trans-3“hexene were also formed. Although ring structures have been proposed in boron chemistry, it is clear that structure 3, above, would have no stability since the boron bonds would all be highly strained from the normal planar trigonal bonds. 109 Structures 1 and 2 involve carbon-carbon double bonds, where originally not even single carbon-carbon bonds were present. The only case with which the author is familiar, for the formation of carbon- carbon double bonds where no carbon-carbon bonds were originally present, is the formation of styrene in the pyrolysis of toluene as reported by Blades et al. (28). Structure k can be visualized as having two three-centered bonds formed by the combination of the sp^ orbitals from each of the methylene carbons on a boron together with the p (or possibly a sp^) orbital from the same boron. Another description of structure k is that it contains resonating forms of the type h 2c h2c+ 'CH,2 Tables 9, 10, 11, 13, and ll- show that the boron-containing products are mostly found on the walls or as highly condensed polymers since the sum of methane, hydrogen, ethane, and ethylene account for better than 96 percent of the reaction products present as gases in the reactor. That is, if the number of moles of methane, hydrogen, ethane, ethylene,and unreacted trimethylborane are subtracted from the calculated number of moles of material present in the reactor at the end of the experiment (nc a l ), less than if percent of the reaction mixture remains to be accounted for by material which may contain boron. If the boron-containing products were found mainly in the gas phase, there should have been a larger amount of material not accounted' for by the major components of the reaction mixture. The species would not have sufficiently low vapor pressures at the temperatures used in the present investigation to remove them from the gas phase. Goubeau and Epple (l6 ), for instance, report that the tetra-B-methylcyclo-1,3,5,7 boroctane, B^CqH^, has a vapor pressure of 11 mm. at 25°C. Hence if B2C^H^q is formed in the gas phase it must rapidly polymerize to high molecular weight polymers which remain on the walls. The formation of ethylene early in the reaction, before any ethane is formed, probably indicates that there is a carbon-carbon bond within the boron-containing species. The usual mechanism for the formation of ethylene in the pyrolysis of metal methyls involves the formation of ethyl radicals which decompose to form ethylene and a hydrogen atom. In all cases ethylene is a minor product compared with the ethane. The ethyl radicals are formed by methyl radical addition to followed by a decomposition reaction forming CrjHtj which: in turn decomposes to form ethylene. The ethane is formed by methyl radical combination. In the presence of added hydrogen, little or no C2’s are found because of the reaction of methyl radicals and hydrogen. In the present investigation, the ethane is a very minor product compared with the ethylene, at least until very late in the reaction; thus it is evident that the mechanism usually applied to ethylene production does not apply in the pyrolysis of trimethylborane. The only other logical explanation for the ethylene production would be the decomposition of some material containing a carbon-carbon bond. Ill Thus, if the horon-containing products contained any carbon-boron structures similar to those proposed for B^^H-lq (page 107) these products might decompose to form ethylene. Since no ethane is formed early in the reaction it is evident that the concentration of methyl radicals is small. If there were a large concentration of methyl radicals, some ethane should have been formed early in the reaction by a combination reaction. It cannot be argued that methyl combination will not occur at the temperatures used in the present investigation, since the reactions with azomethane (Table 2l) showed considerable ethane formed. It should be noted that the sum of ethane and ethylene (Tables 8 to 1*0 increases as the reaction proceeds; the ethylene, however, reaches a maximum value. Thus it appears that the ethane is formed by some type of hydrogenation reaction of ethylene. The following two reaction mechanisms are now proposed: I . Starting with a rupture of the carbon-hydrogen bond, b (ch3) 3 ----- b(ch3)2ch2+ h , (V) followed by an abstraction reaction, h + b ( c h 3) 3 h2 + b(ch3)2ch2 , (1 ') a displacement reaction can then follow b(ch3)2ch2 +b(ch3) 3 ---- (CE3)^CE2B(CE3) 2 + ch3 . (9T) The methyl radical could then abstract CH3 + B(CH3 ) 3 ---- ► CH^ ♦ B(CH3 )2 (CH2) (2 ’) and a wall reaction can occur (CH3)^BCH^B(CH3) 2 ---- *- B2C5H10 + 2H2 . (12’) 112 II. Start with a rupture of the carbon-boron bond b ( c h 3) 3 ----> b(ch3)2 ^ch 3 (7 -) followed by an abstraction CH3 +B(CH3) 3 ----> CH^ B(CH3)2CH2 . (2-) The B(CH3) 2 can decompose to form an "olefin," b ( ch 3 ) 2 ------» h + c h 3 b : c h 2 , ' (8') and the hydrogen can then abstract H 4 B ( ch3) 3 ------► h2 + b ( c h 3 ) 2 ch2 . (1*) The reactions of B(CH3)2CH2 are then the same as in I, so that S', 2 ',and 12’ follow. These mechanisms are therefore similar except for the mode of initiation. The following discussion is for mechanism I, but it is applicable to mechanism II with only slight modifications. Reactions S' and 2 1 now constitute a chain reaction. However, it has been specified that the B(CH3)2CH2 does not undergo rapid radical reactions but is stable and reacts at rates similar to the rates of molecular reactions. The sum of reactions S', 2 ’, and 12' is 2B(CH3) 3 ----2H2 + CH^ + b2C5Hio > which gives the correct ratios for hydrogen and. methane formation during the initial stages of the pyrolysis. Thus for the mechanism to predict the correct initial ratios reaction S' must be more rapid than the initiation reaction 1'. Also reaction 12’ must be very rapid compared with reaction S' so that the rate of hydrogen production is also controlled by S'• 113 With this mechanism, the autocatalytic behavior observed is also explained. In reactions 9' and 2' there is no net loss of B(CH2)2CH2 . Obviously, the initiating reaction !•' is still proceeding and therefore there is a continual increase initially in the BCCH^JaCHg concentration, so that the rate of disappearance of trimethylborane accelerates. The volatile products formed by the B(CH3)2CH2, either during the reaction or upon removal of the reaction mixture from the furnace, may be contained in the material which did not pass through the trap at -ll8°C. The BCCH^rjCHg could dimerize by the reaction 2B(ch3)2ch2 ---- » (ch3)2bch2b(ch3) 2 (13') which could be reversible. This reaction would also be a termination reaction. As shown in Appendix B, the 2 samples isolated from the -80°/-ll8°C fraction contain boron, methyl groups (CH^), and methylene groups (CH2). The material formed by the reactions of B(CH3)2CH2 must disappear by the formation of high polymers either in the gas phase or on the wall for the reasons described above. Thus the B^^H^q formed in 12' must not remain as such, but must polymerize rapidly. Also, to account for the very rapid increase in the amount of methane being produced per mole of trimethylborane disappearing, it is necessary to propose that the B ^ H p o polymer decomposes rapidly with the formation of methane or methyl radicals, followed by a slow decomposition yielding hydrogen, similar to the proposals of Goubeau and Epple. Experiment 10-11 at 508°C showed that the material nil- remaining on the wall of the reactor after removal of the reaction mixture decomposed to form 86 percent hydrogen and lU percent methane. Thus hydrogen is the major product of the slow reaction of the wall material remaining after removal of the reaction mixture. If reaction 12' occurs on the wall, the decrease in the initial stoichiometry for hydrogen as the pressure increases might be explained, in part, by a change in the rate of diffusion to the wall. The rate of diffusion might be sufficiently decreased in order to allow a portion of the (CH^jjBCH^CCH^p to decompose homogeneously by reactions similar to those of trimethylborane itself, thereby reducing the amount of hydrogen formed per mole of trimethylborane reacted. The following series of reactions is given to illustrate some of the possible reactions of the higher molecular weight boron compounds with the final formation of tetra-B-methylcyclo-1,3,5,7 boroctane, which is the boron-containing compound identified by Goubeau and Epple (l6 ) as being formed in the pyrolysis-of trimethyl borane. Starting with ( C H ^ g B C H ^ C H - ^ have an abstraction by a methyl radical, (CH^gBCHgBfCH^g * CH 3 (CH^^BCHgBCCH^CHg * CH^ , (l^ ') followed by a displacement reaction with trimethylborane, (CH^gBCH^CH^CHg + B(CH3) 3 -- > (CH^2BCH2B(CH3)CH2B(CH3)g + CH^ (l5f) The product from 14' can now react with (CH3)2B(CH2) by 115 CH3BCHgB(CH3) 2 (CH3)^C H 2 *'(CH3)^BCH2B(CH3)CH^B(CH3) 2 ---* CHg ♦CHg. (l6 ‘) CHgBCH-^B (CH3)g It is now possible that the product of l6 ' could lose a hydrogen atom from one of the methyl groups attached to the terminal borons, either by an abstraction reaction or a primary split. If this occurs, it is entirely possible that the two ends could react together by a displacement reaction to form the boroctane CHQB -0 H o -B -CH„ 3I 21 3 CHo CHo I I ch3b-ch2 -bch3 If the BgC^H-^Q formed on the wall as a high molecular weight product has any structural, similarity to the BgC^H-^Q structures shown on page 107, i.e., if it has the -CHg-CHg- grouping, the formation of ethylene is possible by the rupture of 2 bonds which is not unlikely on the surface. Once ethylene is present in the reaction mixture from the pyrolysis of trimethylborane, additional reactions become possible. These are the reactions of trialkylboranes and olefins which have been studied by Koster (29). He was able to carry out reactions of displacement and of addition: B (cnH2n+1^3 * cmH2m * •B^GnH2nl-1^2^CmH2mtl^ + cnH2n (IT1) and B (cnW 3 ,(!.H 2.— ' b(ciim » 2‘cm W • <18'> He did not, except in one or two instances, isolate the mixed alkyls, but found the disproportionation products. 116 Mixed alkyls have "been shown to disproportionate rapidly at temperatures well below 100°C (30, 31). Roseriblum (32) has shown that tri-n-butylborane decomposes at 125°C to form butenes and dibutyldiborane which in turn decomposes readily at temperatures where it exhibits measurable vapor pressures. No mention is made of the products of the dibutyldiborane decomposition. Combining the above results, the following reaction series is possible in the reaction mixture after ethylene is formed. First have an addition of trimethylborane across the double bond in ethylene B(CH3)3 + CgHi,. --- <*• (CH3)^BC3H7 (19') followed by (CH3)2B(C3Ht) ----► ( C H ^ H * C3H6 . (20') Since dibutyldiborane is decomposed at relatively low temperatures, it is probable that the (CS^)^E will decompose very rapidly at the temperatures used in the present investigation. Thus reactions 1 9 ', 2 0 ' together with the decomposition of dimethylborane will also catalyze the pyrolysis of trimethylborane. The experiments with propylene, Section VII, show that propylene reacts very rapidly with trimethylborane so that very little propylene would be present in the reaction mixture and its formation would go undetected. If instead of an addition to the double bond, the reaction were of the displacement type, i.e., B(CH3)3 + C2Hu --- ► B(CH3)2C2H5 + CH2 (21') followed by B(CH3)2C2H5 ---- * B(CH3)2H ♦ CjjH* , (22') the autocatalytic behavior would still be present. 117 Experiment 10-4, which was the experiment with added ethylene, showed that there was a net loss of ethylene during the reaction without a corresponding formation of ethane. Thus reaction 19' occurs or reaction 21' is not followed by 22'; these two would not account for a loss of ethylene. Once a large concentration of hydrogen is present it is possible for the methyl radicals 'to react with hydrogen by CH3 4 H2 ---- ► 4 H . (23 ') The hydrogen atoms can then combine, I + HtM » H2 + M (third body) , (24') abstract, H + B(CH3) 3 — H2 + B(CH3)2CH2 , (1C) or add to the ethylene present, . (25’) The effect of these four reactions would be to reduce the apparent rate of formation of hydrogen with respect to the rate of disappearance of trimethylborane, as was found. Earlier in this discussion it was brought out that there are no radical chain reactions in the decomposition of trimethylborane. Several investigators have reported that trialkylboranes initiate the polymerization of vinyl compounds (33*34,35)- The alhyls used were ethyl and butyl. Fordham and Sturm (33) studied the use of triethyl- and tributylborane as catalysts in the copolymerization of methylmethacrylate with acrylonitrile and styrene. They compared the copolymers formed with copolymers formed using lauroyl peroxide and 2 ,4 dichlorobenzoyl peroxide as the catalysts, which are typical 118 initiators for free radical polymerization. The copolymer composition obtained with the boranes was the same as that using the other initiators and they concluded that the trialkylboranes are radical initiators. They carried out reactions in the bulk and in n-hexane solutions at temperatures up to 50°C. Furukawa, Tsuruta, and Inoue (3*0 used triethylborane to catalyze the polymerization of several vinyl compounds at 20°G. They report that vinyl chloride could be polymerized even at -30°C. With no evidence reported they suggested ionic polymerization. The experiments were carried out under a nitrogen atmosphere. Ashikari (35) also reports the polymerization and copolymerization of vinyl compounds using triethyl- and tributylborane as catalysts. Ashikari (36 ) and Furuhawa and Tsuruta (37) report that the presence of oxygen greatly increases the rate of polymerization when trialkylboranes are used as catalysts. Furukawa and Tsuruta also report that hydrogen peroxide also increases the rate, even though hydrogen peroxide alone did not cause polymerization under similar conditions. In view of the high temperatures needed to decompose trimethylborane as reported herein it seems unlikely that the trialkylboranes themselves could be decomposing at the low tempera tures reported in the polymerization studies. It is more likely that most of the work has been carried out in the presence of some oxygen. Petry (9 ) and Petry and Verhoek (21) have reported the formation of a peroxide from the low-pressure oxidation of trimethylborane. This 119 peroxide was shown (9) to undergo radical decompositions at 25°C. Abraham and Davis (38) also report the formation of a peroxide from the oxidation of tributylborane. It is my contention, therefore, that the radicals initiating the polymerizations were not from the trialkylborane but from a peroxide formed because of the presence of oxygen. If this is not the answer it is equally probable that there are reactions between the boranes and the olefins used forming mixed boranes which in turn might decompose at the low temperatures used in the polymerization studies. Thus the radicals, if any are present, would not be from the trialkylborane but from some other reaction product. IX. SUMMARY The "toluene carrier" experiments in the flow system show that in the pyrolysis of trimethylborane, some material is formed on the walls of the reactor which catalyzes the decomposition of toluene, presumably by a heterogeneous process. The results of the study of the pyrblysis of trimethylborane in the static system can be summarized as follows: 1. The rate of decomposition of trimethylborane is autocatalytic showing an acceleration initially, a period of steady rate, and then a slight falling off. 2. The steady rate, Rm , has a zero time order, but is first order with respect to the initial concentration of trimethylborane. The rate law for the steady rate is -S = 1 x 1011 (exp. - 53.iAQP.) sec.“^- H ■ RT 3. At the low pressures (about 4l mm.), the ratio of the hydrogen being formed to the trimethylborane decomposing in the early part of the reaction is one; at the high pressures (about 101 mm), the ratio is slightly less. At both pressures the ratio is below 0.3 near the end of the reaction. it-. At both pressures, the ratio of the methane being produced to the trimethylborane decomposing is 0.5 initially and the -120 121 ratio rapidly increases as the reaction proceeds so that near the end of the reaction the ratio is nearly 2 . 5. The overall stoichiometry at the low pressure for the initial reaction is 2B(CH3) 3 ---- ► 2H2 + CH^ + [B2C5 H10] . 6 . Ethylene is formed early in the reaction and shows a maximum in its concentration during the reaction. 7. Ethane is not found until late in the reaction and probably is formed by the hydrogenation of ethylene. 8 . The reaction is homogeneous. 9. The reaction mechanism doesn't involve free radical chain reactions of the rapid type. Wo mechanism which satisfactorily explains the results has been found. X. SUGGESTIONS FOR FUTURE WORK The following is a list of suggestions for possible future research on the pyrolysis of trimethylborane: 1. Study the initial rate and the primary products of the pyrolysis. This could best be accomplished using a flow system. The reactions should be carried out using very short contact times and small percentage decompositions. Since only a small percentage of reaction should be allowed, it will be necessary to measure the amounts of trimethylborane before and after the experiment with a very high degree of accuracy. The most convenient way to measure the trimethylborane would be by use of PVT data. Thus a pressure multi plying device, such as a transducer, should be used to obtain the greatest accuracy in the pressure measurement. To insure complete separations of the products from the trimethylborane, a Ward still could be used. 2. Use deuterated and undeuterated trimethylborane in the flow system to determine whether the hydrogen, methane, and ethylene are coming from inter- or intramolecular reactions. The deuterated trimethylborane could be made by using commercially available deuterated methyl iodide to prepare the Grignard reagent used in the reaction with boron trifluoride to form deuterated trimethylborane. 122 123 One complication in a study of this type is the problem of exchange. Thus.it would he necessary to show that there is no exchange in the trimethylborane, i.e., no reactions such as b(ch3) 3 4 b(cd3) 3 ---- > b(ch3 )2 (cd3) + b ( c d 3)2 (ch3) . It will also be necessary that exchange does not occur among the products themselves or among the products and trimethylborane. 3. Study the unidentified products of the reaction including the boron-containing products. The low molecular weight products could best be formed in a flow system using a vessel with a very high volume to surface ratio. Thus a large percentage of the low molecular weight products based on • the trimethylborane decomposed could be removed from the hot reactor. The separation of these products could best be accomplished by gas chromatography. By the use of mass spectra, infrared and ultraviolet spectra, chemical analysis, and chemical reaction, if needed, the identity of the products could probably be established. For the non-boron-containing products, an initial separation could easily be made by forming the ammonia adducts of the boron-containing products. 1. Study the effect of nitric oxide to determine how it is reacting and whether there might be some inhibition in the initial rate. 5 . Make a complete, study of the reaction of ethylene and trimethylborane to determine the mechanism of the reaction. This type of study would be very valuable not only in understanding the trimethylborane pyrolysis, hut in understanding the mechanisms of the disproportionation reactions frequently encountered in "boron chemistry. 6 . Study the effect of added hydrogen to determine whether hydrogen is really being removed by a reaction or if by some chance the mechanism of the reaction has changed so as to produce very little hydrogen. APPENDIX A CALCULATIONS FOR A FLOW SYSTEM EXPERIMENT The following is given to illustrate the data collected and the calculations made in an experiment on the pyrolysis of trimethyl- borane using the "toluene carrier" technique. The data are for experiment 3 6 . Experiment 36 The toluene and its weighing bulb are weighed before and after the experiment. The grams and the number of moles of toluene used are calculated. The toluene is single pre-pyrolized Phillips’, weight toluene * bulb before= 86.5 8 6 2 grams weight toluene ♦ bulb after = 8^.0099 grams weight toluene used s 2.5763 grams moles toluene used n 2.7963 x 10”^ The pressure and temperature of the trimethylborane in its bulb (volume is 2 35-7 ml.) are measured before and after the experi ment. The number of moles of trimethylborane used is calculated. before after P,mm. 577-8 1+35-5 T,°K 300.96 301.26 n 7-257 x 10_3 5 rU6k x 10"3 moles of trimethylborane used * (7 .257-5 .U61)-) x 10 3 = 1.793 x 10“3 The pressure in the reactor is measured on the DuBrovin gauge at frequent intervals after the start of the experiment. 127 P,mm. time, min. P,mm. time, min. 1 10.20 u 1 2 .6 0 23! 11.90 1 1 2 .6 0 30 12.20 4 1 2 .6 0 35 12.30 2 1 2 .6 0 39| 12 >0 3 1 2 .6 0 i+if 12.50 k 1 2 .6 0 50! 12.50 5 1 2 .6 0 5^ 1 2 .6 0 6 12 .6 0 58 1 2 .6 0 7 1 2 .6 0 62 | 1 2 .6 0 8 1 2 .6 0 68 1 2 .6 0 10 1 2 .6 0 72 1 2 .6 0 13 12 .6 0 76 1 2 .6 0 15 1 2 .6 0 79! 1 2 .6 0 i9i 12.55 80 average P a 1 2 .6 0 During the reaction, the EMF of the thermocouple is measured at various positions in the furnace. position EMF,mv. position EMF,mv 5! 23.55 16 23.70 6 .59 17 .69 7 .66 18 .65 8 .65 19 .63 9 .60 20 .61 10 • 57 21 .60 11 .60 22 .61 12 .61 23 .61 13 .67 2k .5^ 1^ • 71 2 h \ • 51 15 .70 average EMF a 2 3 .6 2 mv. T a 81*-3.2°K At 79:30 the trimethylborane flow was stopped. At 80:00 the toluene flow was stopped. The contact time, tc, is calculated as .22k5 x 12.60 x 80.0 x 60 tc s {2 .7 9 6 + .179) x 10"2 x 6 2 .3 6 x 6 ^3 .2 a 8 .6 8 sec. 128 During the period of the reaction, the Toepler pump had been collecting the non-condensable gases in the calibrated burette. After the end of the experiment, the condensable materials are thoroughly degassed to insure complete removal of the non-condensable gases. After the non-condensable gases are collected, three or more sets of PVT measurements are made at different settings of the mercury in the calibrated burette. P,mm. V,ml. t°c n x 10 101.1 10.73 28.90 5.76 126.3 8 .6h 28.90 5-79 218.6 h .96 28.90 5.76 h-39.0 2.h5 28.90 5.71 average 5-75 The value for the first order rate constant is calculated as * . iog f V.TgU lEL?— 1 8 .6 8 I U-793 - -0575) x 10 = 3 .7 6 x 1 0 sec . The non-condensable gases are transferred to a thimble and then to the Blacet-Leighton apparatus for analysis. The volumes and temperatures at each step are recorded. The volumes listed are all in microliters. Nitrogen is added to increase the volume of the sample. Analysis of First Sample Vp, #36 = 52.1*0, 52.hO, 52.hO at 300.96°K V 2 , N2 = h0.05, hO.05, h0.05 at 3 0 0 .96°K Vp + V 2 = 9 2.h5 at 300.96°K 129 The sample is allowed to react with a potassium hydroxide- copper oxide head. v3 = 5 0 .50 , 5 0 .50 , 5 0 .5 0 at 3 0 1 .96°K V3 b 50.39 at 300.96°K Therefore V of H2 = Vx t V2 - V3 ■ 92.k 5 - 50.39 « ^2.06 at 300.96°K. h2 .o6 Therefore there is ^2'ko x =80.2 percent hydrogen. Add excess oxygen, ignite with combustion coil and dry with a phosphorus pentoxide head. Vi* = 69.25, 69.25, 69.25 at 302.36°K Ahsorh the CO2 with a potassium hydroxide head (moist). V5 = 58.55, 58.55, 58.55 at 3 0 2 .36 °K Therefore the volume of carhon dioxide, which is equated to the volume of methane, is V of CH^ a Vi^ - V5 ■ 69.25 - 58.55 = 10.70 at 302.36°K (v^ - v5)' = 1 0 .6 6 at 3 0 0 .96°k Therefore there is x 100 = 20.3 percent methane. Analysis of Second Sample Vx = ^9-35, ^9-35, ^9-35 at 302.66°K V 2 = h5.3 0, 54-5-25, ^5.30, 1-5.30 at 302.66°K V-l t V2 s 9I4-.65 at 302.66°K V3 = 55-10, 55-10, 55-10 at 303.26°K Vg =55.00 at 302.66°K = 8 1.6 0 , 8 1.6 0 , 8 1 .6 0 at 3 0 3 -66 ok 130 v5 - 71A5, 71.45, 71.45 at 303.66°K - v5 = 10.15 at 303,.66°K (V^ - V5)‘ = 10.13 at 302.66°K Therefore the percentage hydrogen and methane are hydrogen; 9 k ‘& ~ x 100 = 8 0 .2 ^9-35 methane; x 100 = 2 0 .5 * 49-35 The averages are 80.2 percent for hydrogen and 20.4 percent for methane. The calculations for all gas samples are made assuming ideal gas behavior. APPENDIX B MASS SPECTRA This appendix includes mass spectra of several samples of material obtained from the pyrolysis of trimethylborane. The spectra were made on a General Electric Analytical Mass Spectrometer operating with an ionization voltage of 75 volts. The author is indebted to Mr. Charles Weisend for the preparation of the spectra. The samples listed follow: A. The sample of all material not passing through the trap at -80°C from experiment 3~9- This experiment was made with 95-7 micromoles of trimethylborane at approximately U88°C. The time of reaction was 75 minutes; 80 percent of the trimethylborane was decomposed. B. The -80°/-ll8°C fraction from experiment 6-10. This experiment was made with 21+3*8 micromoles of trimethylborane at A88°C. The time of reaction was 17 minutes; 15 percent of the trimethylborane was decomposed. C. The -80°/-ll8°C fraction from experiment 25-9- This experiment was made with 9 6 .6 micromoles of trimethylborane at lf-88°C. The time of reaction was 23-9 minutes; 25.6 percent of the trimethyl borane was decomposed. D. The first unidentified peak obtained by gas chromatography of the -80°/-ll8°C fraction collected from several experiments. E. The second unidentified peak obtained by gas chromatog raphy of the -80°/-ll8°C fraction collected from several experiments. F. A gas chromatography "blank." 132 133 The -80°/-ll8°C fractions used to obtain sample D and E were collected from many experiments made at different temperatures and initial amounts of trimethylborane. Samples D, E, and F were obtained by placing a small U-trap equipped with stopcocks at the exit of the thermoQonductivity cell on the gas chromatography system. During the time the sample was collected the trap was maintained at -195°C. The trap was then trans ferred to the vacuum system and the helium removed. The samples were then transferred to small bulbs and the spectra made. These samples may have been contaminated with mercury during the vacuum transfer. The values listed in the table are the peak heights of the given peaks in arbitrary units. On the instrument used, the only measure of the mass of a given peak is the magnet current at which the peak appears. Since the electo-magnets have considerable hysteresis, a given mass can appear at several different values of the magnet current. For this reason the masses assigned to the peaks may be in error. At masses below 100 the error may be about * 2; at higher masses the error may be considerably more. Considering the possible errors in the mass assignment, it is evident that the columns listed in the table can be shifted with respect to each other, as well as with respect to the mass assignment. Three masses, however, are fairly well established by comparison with the back ground spectrum made immediately before making the sample spectrum. These masses are 18 (watei), 28 (nitrogen) and kh (carbon dioxide). The masses near 100 are defined somewhat by their relationship to the mercury (Hg8-^) peaks. 13k From the peaks at mass 11 for samples B, C, D, and F it is concluded that boron is present in the samples. The peaks at mass 15 indicate the presence of methyl groups. Since samples B and C (and probably A) are mixtures of compounds, little additional informa tion can be gained from their mass spectra. Samples D and E, however, may be pure compounds since they were separated by gas chromatography from the -80°/-ll8°C fractions. For each of these samples (D and E) there are large peaks at masses of 89 and 88 with the 89 peaks being larger. At masses of 75 and 7^ additional large peaks are also found with the 75 peaks being larger. There is a mass difference of ll+ between these groups of peaks indicating the presence of a methylene group (CHg). Large peaks are also found at masses 6 l and 60 with mass differences of 28 compared with the peaks at 89 and 88 thus indicating 2 methylene groups. In sample D, large peaks are found at masses 50 and 1+9 indicating the presence of boron (mass ll) in the sample by comparison with theofil and 60 peaks, Thus, at least 2 compounds in the -80°/-ll8°C fraction contained boron, methyl groups and methylene groups. 135 TABLE 25 MASS SPECTRA Mass •A B c D E F 11 9.5 8 9 18.5 1*1 12 -- - 11.5 ll* 12 13 5.5 -- 10.5 33 - - ll* 1* 6 5 9 21*.5 2l* 15 - 3 3 30.5 37 1* 16 12 9 9 18 12 32 16 + - 2 2.5 - - - 17 - 3 2 72.5 2 1+6 18 ll* 16 7 278 22 178 23 - -- - 8 - 2h --- - 25 - 25 1* 5.5 5 8.5 92 - 26 2l* 21 23 12 95 k 27 63.5 1*1 .5 1*1* 22.5 173 - 28 81* 33 19 52 212 129 29 16 1* l* ll* ll - 31 - 2 8 -- - 32 7 2 - - 5 27 33 - 5 - - 53 - 3^ - - - - 10 35 5 3 l* - - - 36 38 21* 33 19 33 - 37 90 61 81* 1+3.5 22l* - - 31* - - - 7 - 38 11.5 17.5 19.5 15-5 573 - 39 29.5 1*1*.5 1+7 - 78 - 1+0 39 95-2 58 8 175 k 112.3 89 2 1 2 .2 2l* 1*2 3 1*2 25-5 1 6 .5 16 1+5-5 126 3 1*24 71 30 33.5 158 31+ - 1*3 10 6 3 - 10 - i*3t - -- - 87 - 1*1* - 3 10 100 17 138 - 1*5 _- 8 7 253 1*6 1* 2 3 - 55 - - 1+7 3 5 6.5 13 27 - 1*7+ 10 15 9-5 - 101 1*8 29 26 . 27 28 287 - 1*9 1*6 29 1*6 .5 1*0.5 1*62 - 50 51 1+3 57.5 25.5 378 - - 51 98.5 8.5 93-6 1+.3 683 - 52 9 1 0 .5 27 5 1+3-5 - 53 13 - 12 9-5 73 136 TABLE 25 - Continued Mass A B C D E F 534 3 3 3 15 7 - 5ll- k it 12.5 28 - 55 k.5 7 5 - 2k - 56 11 8 5 - 78 - 57 7 3-5 7-5 37 - - 58 - 7 . 16 26 Ill - 59 13 . 15.5 31 36 207 - 60 28 23 52 50.5 368 - 61 ^3 . 2 - 63.5 520 - 62 22.5 9-5 20 25.5 2lt-0 - 63 37 13-5 28 25.5 282 - 6k 55-5 10 20 9 136 - 65 103 16 31.5 11 211 - 66 5 - - lit 8 - 67 -- 8 lit.5 - 68 2 1.5 k 9.5 15-5 - 69 3 3 6.5 21 38 - 70 k.5 7 11.5 31.5 8it.5 - 71 8 5-5 12 51 151 - 72 12.5 7 18 kk 133 - 73 13.5 8 27 75 165 - Ik 19 12.5 3^.5 119 125 - 75 23 7.5 18 llt-7 200 - 76 3^.5 7-5 2k 7.5 72.5 - 77 21 22 123.2 7-5 - 78 15 k 8 7-5 8 - 79 11 ll 2 6.5 9 - 80 2.5 21.5 k - 13 - 81 3 k 7 lit lt8 - 82 6 k.5 10 22 108 - 83 9 3.5 8 27.5 Ikk - 8it 10.5 5 10 15 100 - 85 9 7 lit-.5 19 153 - 86 _ 12 37 77 22 228 - 87 10.5 131 28lt 63 856 - 88 28.5 182.5 It09-5 203 2,720 - 89 7^.5 15 50 itoit-- 3,819 - 90 112.3 10 30.5 28It- 151 - 22 16.5 13.5 - 91 23 7 s’ 914 - -- “ 6 92 28.5 - 3 - 9 93 16 - - - 7 -- — - - 10 9^ k s ’ “ 95 k -- - 6 96 5 - -- 8 137 TABLE 25 - Continued Mass AB c D E F 97 8 3 5 98 9-5 - 5-5 - 68 - 99 11 6.5 17 69 115 - 99* 2b 27 6 i+.5 119 159 61+ .5 100 bo 93-6 201.2 162 89 115 loot -- -- 21k 159 101 — - - 92 399 81 101* 39 115.1+ 21+6 .8 207 1,529 206 102 15 8.5 - ^7 2,205 1+3.5 103 30.5 - - 18 - ioi+ ' 33-5 - - 23.5 - - 109 1.5 - 3 - - - 110 2.5 - 1+ - - “ 111 7.5 3 7 - ill “ 112 17.5 3 8.5 “ 7 - - 113 26.5 7.5 11.5 - - lib 37-5 9 27 - - - 115 1+8 - 32 - - - 116 5b - 2 - - - “ 117 55 - “ - - 118 20.5 - - - - — “ 119 3.5 - - - - 120 3 - — •* 121 2 - - - *■ 122 3 - - — “■ m. 123 6 - “ -— 12b li+ - 1.5 » - ~ 125 3b - 2.5 - - — 126 70 - 3 - 127 7I+.9 - 5 -— 128 11 - 5 - “ — 129 3 - 2.5 - - - 3 • 135 — 136 2.5 - 6 - •• 137 3 - 11+ - 138 29.5 - - •* — “ 139 1+8 - - ll+O 35-5 - “ — •■ 11+1 3-5 - - — "" 153 1.5 - — 15 ^ 2 - — —* 155 3 - • •“ 156 5 - - 157 8.5 - 158 6.5 - ~ APPENDIX C CALCULATIONS FOR AN EXPERIMENT IN THE STATIC SYSTEM The following is given to illustrate the data collected and the calculations made for an experiment on the static pyrolysis of trimethylborane. The data are for experiment 7“H . Experiment 7-11 The EMF for each of the three iron-constantan thermocouples is measured just before placing the trimethylborane in the reactor. position EMF.mv. side 2 7 .9 7 top 27.98 bottom 2 7 .9 6 furnace temperature is 508.2°C The trimethylborane is measured in bulb A before placing a part in the reactor and again after. Pressure, volume, and temperature are measured and the number of moles is calculated. B(CH_)_ before B(CH_ ) 0 after o 3______2------P = 21*6.3 mm. P = 15^.2 mm. V = 1*8.80 ml. V = 1*8.80 ml. T - 300.1°K . T = 300.3°K n = 6k2 .3 x 10 _b n = 1*01.9 x 10“b number of moles placed in the reactor ■ B ^ H ^ ^ - I = 21+0 .1+ x 10 ^ The pressures are measured on PQ and Pr just before and just after placing the trimethylborane in the reactor and also at various times as shown below. The pressure of the material in the reactor, P as, and the increase in pressure, A P , are then calculated. D t, min.:sec. Pr,mm. Pc,mm. Pgas,mm. AP,mm. 155.7 156.9 0 259.6 102.7 0:30 259.6 102.7 0 139 140 min.:sec. Pr ,mm. Pc,mm. PgasJmm* AP,mm, 1:00 259.6 102.7 0 1:30 259-8 102.9 .2 2:00 259.9 103.0 • 3 2:30 260.3 103-4 • 7 3:00 261.0 104.1 1.4 3:35 263 .O 106.1 3.4 4:04 265.0 108.1 5.4 4:49 268.0 111.1 8.4 5:37 272.0 115.1 12.4 6:10 275.0 118.1 15.4 6:37 278.0 121.1 18.4 7:09 281.0 12k.1 21,4 7:30 155.7 8:00 286.0 129.1 26.4 8:43 290.0 133.1 30.4 9:23 29k. 0 137.1 34.4 9:58 297-0 i4o.i 37-4 10:32 300.0 143.1 40.4 11:06 303.0 146.1 43.4 1 1: Uo 306.0 149.1 . 46.4 12:36 3H.0 154.1 51.4 13:14 31!+.0 157.1 54.4 13:56 317.0 160.1 57-4 155.7 165.0- 8.1 At 13:56, a portion of the reaction mixture was removed. The value of Pc was read immediately after this removal. The fraction of the mixture removed, f, is f - l6 0 .1 - 8.1. . 0.9494 160.1 The non-condensable gases are collected in the calibrated burette by the Toepler pump, and PVT measurements made at three different positions of the mercury. The number of moles is calculated. 1 2 JL P,mm. 214.2 308.7 402.2 V,ml. 21.08 14.58 11.19 t°C 24.4 6 24.4 24.4 n 243.3 x 10 242.5 x 10 242.5 x 10 average n = 2h2.& x 10"^ 141 Experiment 7-11 Continued Thus the total number of moles of non-condensahle gases is n = ■ -4 x 242.8 x 10~6 = 255-7 x 10"6 . .9494 A portion of these non-condensable gases is placed in a sample tube and then into a gas chromatography sample loop at the following conditions: P = 139.8 mm. V * 5 *44 ml. (volume of sample loop) t = 24.6°c = 297.8°K n = 41.0 x 10"° moles. The material in the loop is placed on the Molecular Sieve column. The peak height of the methane peak is measured to be 129.6 mm. Two samples of the standard hydrogen and methane mixture are also measured in the loopSc.and placed on the M.S. column. The fraction of this mixture which is methane is 0.497* The sensitivity is calcu lated as moles of methane per millimeter peak height. The data are as follows: 1 2 P,mm. 1 6 9 .2 146.2 V,ml. (sample loop) 5-44 5*40 t ° c 2 5 .0 2 5 .0 ^otal 49.3 x 10"6 42.3 x 10"6 nCH^ 24.6 x 10"6 21.1 x 10"6 Peak height,mm. 122.8 105-3 Sensitivity, £°le£ .200 x 10"6 .200 x 10“6 mm. Therefore the number of moles of methane in the non-conden sable gas sample placed on the M.S. column is 1^2 Experiment 7-11 Continued .200 x 10"^ x 129.6 = 25.9 x 10"^. The fraction of the sample which is methane is fCH . 21 :9 ..Z. .10 . 0.632 k hl.O x 10“° The total number of moles of methane that was present in the reactor, nC H ^ 1S riQg = .632 x 255.7 x 10~6 = 162 x 10”6 k and the total number of moles of hydrogen, n„ , is, by difference, u2 s (256 -162 ) x 10"6 = 9^ x 10“6 . Two samples of the standard ethane (.0836), ethylene (.092k), and helium (.82k) mixture are measured in the gas chromatography sample loops and placed on the silica gel column. The data are as follows: P,mm. 148.7 1^1.8 V,ml. (sample loop) 5.1*4 5-^0 t°c 2 5 .5 25.5 1+3 .k x 10"6 Ul.l x 10"6 ntotal 3.63 x 10"6 3.kk x 10"^ 4.01 x 10”6 3 .8 0 x 10~6 nG2Eh Peak height of C2Hg,mm. 56.3 53*9 Peak height of 02^ , 1™ . 39*8 37*8 Sensitivity,CgHg , S O M .06 U-5 x 10"6 .0638 x 10"6 mm. Sensitivity, CoHi,., moles #101 x 10-6 .101 x 10"6 mm 143 Experiment 7-11 Continued Average sensitivity of C2Hg « .0641 x 10~^ 5°7e.s, mm. Average sensitivity of CoHi, a .101 x 10"^ ^ H mm. The condensable material is then fractionated through traps at -80°, -142°, -155°, and -195°C for 40 seconds. The -155%195°C fraction, identified as the C2's, is transferred to the gas measuring system and measured as follows: P = 2b .J mm. V - 5 .V7 ml. t = 25.3°C , n = 7 .2 6 x 10"° thus the moles of C2's in the reactor, n^, |g, is n_ , = — i-r x 7 .2 6 x 10"6 - 7.6 x lO-6. C2's 79594 The C2's are transferred from the gas measuring system to a loop and then placed on the silica gel column. The number of moles and the mole fractions (N) of ethane and ethylene in the C^'s, assuming the sample to contain only these, are calculated as follows: Peak height of s 7-2 mm. Peak height of ■ 61.7 mm. nQ^gg =7 .2 x .0641 x 10"^ ■ .46 x 10"^ n„ „ = 6 1 .7 x .101 x10"6 s 6 .2 1 x 10"6 C2nlj. ^CgHg ■ -o65 V i " -931 Thus the total number of moles of ethane, and ethylene, in the reactor are ll& Experiment 7-11 Continued n _ s .069 x 7-6 X 10 ^ = .5 x 10 ^ c2h6 and nC2Hi). " x 10"6 * 7,1 x 1 0 "’6 ' The remaining material is now fractionated through traps at -80°, -118°, and -195°C. The -80°/-ll8°C fraction and the unreacted trimethylborane, the -ll8°/-195°C fraction, are each measured in the gas measuring system and the total amount of each in the reactor, n^, is calculated. The data are as follows: 0 m -P 1 -8o°/-ll8°C on on P, mm. 2.8 1 3 0 .7 V, ml. 1^.79 t°C 2 5 . b 25 .k n .83 x 10"6 1 0 3 .6 x 10"6 C nt .9 x 10"6 1 0 9 .1 X 10 The calculations for all the samples are made assuming ideal gas "behavior. BIBLIOGRAPHY 1. Szwarc, M., J. Chem. Phys., 1J, (19^9). 2. Gowenlock, B. G., Polanyi, J. C., and Warhurst, E., Proc. Roy. Soc. (London), A2l8, 269 (1953). 3 . Price, S. J. W., and Trotman-Dickenson, A. F., Trans. Faraday Soc., 2 2 , 939 (1957). k . Skinner, H. A. and Smith, N. B., ibid., £1, 19 (1955). 5. Tannenbaum, S. and Schaeffer, P. F., J. Am. Chem. Soc., 77. 1385 (1955). 6 . Long, L. H. and Norrish, R. G. W., Phil. Trans. Roy. Soc. (London), Ser. A, 2*kL, 587 (19^9). 7 . Quarterly Technical Report, Univ. of Utah, Subcontract M 3“l8l-26 of Contract NOA(S) 52-1023 C, March,. 1955. 8. Petry, R. C., Ph.D. dissertation, The Ohio State University, 1958. 9. Coleman, J. E., Ph.D. dissertation, The Ohio State University, 1959. 10. Blacet, F. E. and Leighton, P. A., Ind. Eng. Chem., Anal. Ed., 2, 266 (1931). 11.: Blacet, F. E. and MacDonald, G. D., ibid., 6 , 33**- (193*0 • 12. Blacet, F. E. and Volman, D. H., ibid., % Uk (1937). 13. Blacet, F. E., Sellers, A. L., and Blaedel, W. T., ibid., 12, 356 (19**0). lk. Szwarc, M., J. Chem. Phy., 16 , 128 (19^-8) . 15. Goubeau. J. and Keller, H., Z. anorg. u allgem. Chem., 2 6 7 . 1 (1951). 16. Goubeau, J. and Epple, R., Chem. Ber., 22, 171 (1957). 1^5 1 ^4-6 17. Hembree, G. H., Ph.D. dissertation, The Ohio State University, 1958. 18. Li tlewood, A. B., Phillips, C. S. G., and Price, D. T., J. Chem. Soc., 1180 (1955). 19. Ramsperger, H. C., J. Am. Chem. Soc., l£, 912 (1927). 20. Ramsperger, H. C., ibid., l£, 11-95 (1927). 21. Petry, R. C. and Verhoek, F., ibid., 7 8, 61l6 (1956 ). 22. Staveley, L. A. K., Proc. Roy. Soc. (London), Al62, 557 (1937)• 2 3 . Henkin, H. and Taylor, H. A., J. Chem. Phys., 8, 1 (191-0) . 2l. Sieger, R. A. and Calvert, J. G., J. Am. Chem. Soc., j6 , 5197 (195*0 • 25. Smith, R. M. and Calvert, J. G., ibid., 'jQ, 231-5 (1956). 26. Harrison, B. C., Soloman, I. J., Hites, R. D., Abstrs. of Papers, 135th ACS Meeting (Boston), 38 M (1959). 27- Winternitz, P. F., ibid., 19M (1959)- 28. Blades, H. B., Blades, A. T., and Steacie, E. W. R., Can. J. Chem., 22, 298 (195*0. 2 9. Koster, R., Ann., 618, 31 (1958). 30. Parsons, T. D. and Ritter, D. M., J. Am. Chem. Soc. j 6 , 1710 (1951-). 31. Hennion, G. F., McCusker, P. A., and Rutkowski, A. J., ibid.. 8 0, 617 (1958). 32. Rosenblum, L., ibid., 77. 5016 (1955). 3 3 . Fordham, J. W. L. and Sturm, C. L., J. Polymer Sci., 22> 503 (1958). 3l. Furukawa, J., Tsuruta, T., and Inoue, S. ibid., 26 , 23I (1957). 35* Ashikari, N., ibid., 28, 250 (1958). 3 6 . Furukawa, J., Tsuruta, T., ibid., 28, 227 (1958). 37. Ashikari, N., ibid., 28, 61.1 (1958). 3 8. Abraham, M. H. and Davis, A. G., Chem. and Ind., 1622 (1957). autobiography I, Joseph A. Lovinger, was "born in Detroit, Michigan, on November 22, 1928. I received my secondary education in the public schools of Detroit, Michigan, and my undergraduate training at Wayne State University which granted me the Bachelor of Science in Chemistry degree in 1951* In September, 1951* I entered The Ohio State University where I specialized in kinetics under Professor Frank Verhoek. While in residence I held teaching and research assistantships. For the year 1953~5^ I was the General Electric Fellow. I was also the recipient of a scholarship from the DuPont Research Fund.