The pyrolysis of dimethyl carbonate

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Authors Olson, Dan Allen Herman, 1913-

Publisher The University of Arizona.

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TEE PYROLYSIS OF DIMETHYL CARBONATE

%y

Dan A. H. Olson

A Thesissmh®tttea to the faculty of the

Department of Chemistryy-'.': "--

in partial fulfillment ofthe requirements.for the degree of

' ■

Master of Science

in the Graduate College Univoreity of Arizona

1938

Approved:Major Profos®or

m* ' ■Date.

/ 9 3 Z

2-

ACOTOWLEDGKEHT

fhe author wishes to express his * most sincere appreciation for the advice and assistance of Dr. lathrop E. Heherts, under whose direction this investigation

TABLE OF CCBtHTTS

latrofluotionPreparation of the MaterialVapor Pressure of Dimethyl CarbonateThe Apparatus and Its Use

The ThermostatThe ThermocoupleThe Compressed Air AgitatorThe Apparatus for following the Pressure Change

Qualitative Analysis of the Products Quantitative Analysis of the Products

Experimental Data Tables of Kinetic Data Discussion and Conclusions

Bibliography

1

Introduction' - '■ ' . / -

Stoichiometric equations, though useful in representing the overall cburse of a reaction, throw little light on the mechanism of the reaction, A determination of the actual steps; takei^hy a reaction from the initial to finalstate is test don# through kinetic studies.

:•! . /:! ‘ ‘Kinetic studies of reaction in the gaseous phase are tobe preferred^to/those in the liquid phase, since our know-

' : /ledge of the Ihwo governing the behavior of gases is much; ' 'more extensive thanrit is for liquids,1 Ihe fundamental Maxwell distribution law gives the distribution at the velocities of the molecules.% From it can be determined the relationships between.the root mean square velocity, the arithmetic mean velocity, and the most probable velocity. Further extensions give us the number of collisions per second per c.c., the mean free path of molecules, etc* From specific heats and band; spectra can be obtained information on the types of motion exhibited by molecules.3

No such quantitative treatment has been made for liquids.1 Furthermore, complicating factors like solvation, association, ionisation, wide variation of dielectric constant, etc., make exact treatment difficult.

However, even in the gaseous phase, treatment of reactions may not be very simple. The quantitative treatment

; * ' . ' ' ' -

of the behavior of gases is usually based on ideal condition®

, :

8

to whleto real gses approach more or less closely, depending upon the attenuation and nearness to critical points. Them* too* the reaction Itself may not follow any single path homogeneously, but be complicated by being in whole or in part heterogeneous due to reaction on the walls of the confining vessel. Again, there may be side reactions* opposing reactions, consecutive reactions, catalysis by the reaction produets, and the like, which reader mathematical treatment very difficult even when the qualitative nature of the reaction is known.

Present knowledge indicates that the more complex molecules are likely to decompose unimoleeularly and homogeneously.4 Since homogeneous animolecular reactions are of particular interest in testing theories of activation by collision* it seems desirable that complex molecules be made the subject for study.

On such considerations* Claudio Alvares-Tostado selected *e8c0g for study.5 He expected it to decompose unimoleeularly and homogeneously because of the feet that dimethyl ether decomposes unimoleeularly at higher temperatures and blmoleeu- larly at lower temperature®. Actually he found that the primary decomposition was catalyzed by the wall of the reaction vessel, although the reaction must be in part homogeneous since the increase in velocity in a packed flask over an unpacked flask was not as great as that of the surface-volume ratio. He concluded that the primary decomposition taking

3

place at 500° gave C02 and (CH^tgO which then decomposed Into

CO, CH4, and Hg. He also eappoeed that ethane was formed in

small amounts hy a side reaction, Dae to lack of time he was not able to make quantitative analyses at various stages of the decomposition, to correlate the analytical data with the kinetic data, and thereby set up a mathematical expression describing the reaction. It was. the purpose of the investigation described in this paper to make the necessary qualitative and quantitative analyses to work out the reaction mechanism. He other work on the deoompecliton of dimethyl carbonate Is known except that of nice and Johnston6 who found that the molecule decomposes Into free radicals at 700°-800e, but did not determine what the producte were.

4

Preparation of the Material

% e dimethyl carbonate used was obtained from the last- man Kodak Company, Tests for chloride were made by hydrolysis in chloride free EaOH with subsequent acidification with HEOg and addition of AgHOg, Considerable precipitate was

formed. Test of the carbonate used by Tostado also revealed the presence of Cl but to a lesser extent• The whole of the carbonate on hand was washed with a 10^ aqueous solution of AgUOg, separated.from the solution and precipitate by use of

a separating funnel and dried with fused. CaClg, It was then refluxed over dry PbO and AgEOg for several hours until 0,4

e,e* of the carbonate gave only the faintest opalescence when tested for CITY The carbonate was decanted off the PbO and fractionally distilled by use of a Glinsky fractionating tower and spiral condenser cooled with ice water. The fraction boiling 860-87.2° at ca. 700 m.m, was collected.

5

The Vapor Pressure of Piciothyl Carbonate

At one stage of the investigation it seemed Sesirafcle to Imew the vapor pressure of MegCOg from about its melting

point to its boiling point* Accordingly an apparatus was set up for determining the.vapor pressure by the Ramsey-Young method.7 later was used as the heating medium and ice for cooling. The temperature was read with a l/lO° thermometer. The following results v/ei^jobtained;

? in sum. T°C.20*5 8.138.0 . 18.185.5 85.8145. . 44.0198. 61.5250. 57.5SOB. 62.4860 ... ■ ' ' : 66.S .407. 70.9477. •75.3546. 79.1612. v 82.4651. 84.4659. 86.5

A graph of the results is given in Figure I. Ho claim is made for high aeoaraey.

yo-t

* 9

6

The Apparatus and Its ffse

One ef the eoaHaeaest methods of studying the kinetics of a reaction is by following the pressure change with time, This was the method used by Tostado in obtaining the results on dimethyl carbonate already mentioned* Later this apparatus mas improved by fihodes® for the study of dimethyl sulfite, The apparatus used for the present investigation is an improvement and simplification of that used by Rhodes, This apparatus possesses the advantages of that used by Rhodes in that:

1. The exact time of introduction of a weighed amount of carbonate can be determined.

2. The reacting gas cones into contact with no surface except pyrex glass, except for about 2 sq. mm. of Hg. and2 sa* ram. of stopcock grease in the cooler part of the apparatus. {Ho stopcock grease was present in Rhodes*b apparatus.)

5. All gas can be maintained at a uniform temperature with the exception of a small amount in the external capillaries which are heated well above the boiling point of the carbonate by resistance wire wrapped around them.

4.. The pressure produced in the reaction flask by the decomposing carbonate can be read at any desired time without delay.

5. The temperature can be maintained nearly constant over a period of several hours.

f

lia addition the apparatus has the following aivaotages over that asad by Rhodes:

1# Several short runs can be made each day and without the meaessity of dismantling the apparatus between each ram.

2. Duplication of experimental conditions for successive runs is easy to maintain. Hence drifts in the speed of the reaction are easy to detect.

8. The furnace need mot be opened when sample is in- troduced, thereby avoiding the drop in temperature during the irtbial stages of the decomposition.

4. The products can be quickly and easily removed from reaction vessel at any time.

5. The undecompoeed ester can be removed from the reaction products.

6. large amounts of products can be collected for ena-: - ' . . . . '

lysis.7. Final pressures of two atmospheres can be reached.8. The reaction flask can be opened to the atmosphere

at any time between runs for removal of any Eg vapor or for glass blowing without disturbing other parts of the apparatus*

The apparatus consists of the following.

The Thermostat. :The thermostat is the same as that described by Rhodes

with the exception that the heating coils on the bottom of the fumoee were removed and the depth of infusorial earth reduced to about § inch to cut down the temperature gradient.

8

Moreover, the theretostat is not moved or opened at the beginning of the rune* .

The Thermocouple.The five junction, Hichrome-Advance thermocouple for

measuring temperatures nas the same as used by Rhodes. Hie E. Um P. Temperature calibration was taken as correct. The Leeds and Borthrup type K potentiometer was found badly in meed of repair, so a regular Leeds and Borthrup student potentiometer was used instead. It was found to work very well.

The Compressed Air Agitator.The compressed air agitator used by Rhodes was left un

changed. Regulation of the temperature was done manually instead of by use of an automatic thermoregulator. *t was found that by use of a slide wire, heat input could be balanced against radiation and the temperature maintained constant within tl° as long as the external E. M. F. did not vary. As a consequence the relay switch was removed and replaced by a simple single throw switch.

Apparatus For Following Pressure Change, etc.Plate I is a diagram of the apparatus, all glass being

of pyrex. lost of the external tubing is of small bore capillary. A is the thermocouple and B is a tube conducting the compressed air into the furnace. B, I, «T, K, L, P, Q, are stopcocks, L and P being vacuum cocks. C is a bulb provided

f

with two stopcocks and is used to store the gas product® for analysis. It is attached to the mercury pump E by a short piece of rubber tubing. The mercury pump has a bulb of 250o.o. capacity at the top and a leveling bulb attached below. It is comneete# to the small glass mercury trap 0 by glass and rubber tubing. F is a short glass tip whose use will be described later. H is a cooling tube made by bending about 4 feet of 5 mm. tubing to form 4 XT’s and then folding the 0f8 together ®o the whole will fit into a large Dewar jar. The last two and a half U*s are filled with glass beads to increase the surfaee and produce a turbulent flow. This is connected by a series of stopcocks to the reaction bulb M which has about 320 c.o. capacity. The reaction bulb is connected by small capillary to the manometer R of capillary tubing and provided with a leveling bulb clamped to a vertical rack and pinion so a fine and rapid adjustment of the Eg level can be made. The upper portion of the left arm of the manometer is enlarged so that if the Hg thread breaks it can be run up into the enlargement and be brought together again. B is a side arm with attachment (see B Detail) for introducing sample as follows: The ampoule S is made of small shellwall glass by sealing over the end of a three-inch piece.A point about one inch from this end is heated around the circumference until the glass is soft, and then the two ends arc pulled apart until a fine capillary tube connect® then. This ampoule is weighed accurately to l/lO mg. after which

10

the desired weight of dimethyl carbonate Is Introduced through a fine capillary funnel which will pass through the capillary of the ampoule. The ampoule and eantente are put into a EaCX ice mixture at about -15° to freeze the carbonate, a suction pump is attached to the upper, the air is pumped off, the fine capillary sealed through, and the two ends drawn a- part. Both ends are dried thoroughly and rewelghed to l/lO »g. and the exact weight of the carbonate obtained by difference. The ampoule thus filled is put into the. upright tube of H and slipped through a platinum loop sealed in a glass tube containing an iron core, f a s shown. The upper portion of the upright tube is then closed over*

When the temperature is up to the desired value and the external wires hot, cocks P, I, D are closed and the Bg in manometer R is rum up to 0 mark and cock Q, closed. A Cenco Hyvae pump is attached at K and the system evacuated. Then *2 from a cylinder is run in to atmospheric pressure through

K and the system re-evacuated. Cocks J, L, K are then closed. The manometer bulb is lowered until, with cock Q, open, the Hg level in the left arm is at zero. The meter stick from which the pressures are read is adjusted so that its lower, zero end is exactly opposite the lower level of the Hg In the right arm, and clamped in place by means of wing nuts on bolts passing through two slots in the meter stick. Cock G is closed and the Hg in the right arm raised to a level

II

corresponding approximately to the expected initial pressure• fhe whole of H is now carefully heated with a flame• A solenoid, connected to 110 v. circuit with a tap key and resistance in series, is slipped over the arm of E containing the glass-covered iron core T and the circuit closed hy a single tap on the key, thereby causing the platinum loop to strike the capillary of the ampoule a sharp blow and break it. The carbonate at once passes into the reaction flask and a stop watch started. The whole of H is again heated by a flame and then sealed eff from the connecting arm as close to the external heating wires as is feasible. At periodic intervals Q, is opened* the leveling bulb adjusted so the Hg in the left arm is at 0 and the pressure read off the meter stick at the point opposite the level of the Hg in the right arm. Both the time and the eerresponding pressure are recorded.

At the end of the rim the level of the Hg in the left arm of the manometer is run down to the end of the external heating wires, cock Q, is closed, and cocks J and I opened, thus allowing the vapors to pass through the ti tubes S which are cooled by dry ice and alcohol to -80°C. in order to remove UBdeoomposed carbonate. (Although dimethyl carbonate freezes just above zero, it was found that it could not be completely removed by using EaCi ice mixture at -170C.}. Cock D is opened to the system and the gas pumped into E by lowering the leveling bulb and then, after reversing Cock D, it is delivered into the,storage bulb C which has just been evacuated.

12

Several pumpings are necessary to cause a complete evacuation of the eyete*. Korever HcHO, which is one of the produets of pyrolysis condenses in part in U tubes and must he pumped out. Cook 3 is now closed and K opened to the atmosphere.A water pump is attached to cock T which is opened, and any eondensed Hg or vapor in the capillary leading to the manometer is drawn out.

If the amount of condensed ester is to be determined, the dewar containing the freezing mixture is removed from the U tubes. Two tubes in series, one containing CaClg and one Mg(Cl04)2, are attached to F by a short length of pressure tubing; The tubes are evacuated with the Hyvae pimp and filled with Ug* Another tube containing CaClg is attached to a small TJ tube which is connected to I by pressure tubing.This CaClg tube and U tube are evacuated and filled with Hg

and the U tube immersed in dry ice-alcohol mixture. The tip of F is broken off, cock I is opened, and a slow stream of air drawn through the U tubes by applying suction to the CaClg

tube attached to the single XT tube in the freezing mixture.The ester condense® In this XT tube. When the ester is removed from the regular XT tubes this smaller XT tube is raised out of the freezing mixture until only about the lower inch remains immersed. After the ester in the higher part of the tube has melted and recomdeased at the. bottom both arms are sealed off. The weight of the ester is determined by weighing

1#

the tabe eontaining ester and air and them breaking it, removing the ester and reweighing. The amount of ester is obtained by differsme*.

To begin a new run F is resealed, H is resealed on to its side arm from the reaction flask* and the above procedure repeated.

After as much of the products has been collected in C as is desired, it is removed from the apparatus and the gas analyzed on the Orsat gas analysis apparatus.

14

Qualitative Analysis of the Profluotg

Since Tostado5 did not actually make "any qualitative testa for possitl® predmets, it seemed desirable to have some specific evidence of the presence or absence of different products suepeetefl to be formed* In order to obtain products for analysis ampoules containing about.08 gm. carbonate were put into pyrex tubes of about 90 c.c. capacity, 'thsst tubes sere evacuated, sealed off, and the ampoules broken by shaking the tubes violently. These tubes were held in a sheet iron cage and lowered into the furnace which was kept at about 500°C. After several hours the tubes were removed. It was noted that all tubes had some deposit of carbon, especially on the part deepest in the furnace.

Dimethyl other. Since dimethyl ether was to be determined by the method given by Schor&er9 it seemed desirable to determine the lower limit of sensitivity of the method. According a quantity of ether was generated and dissolved in HgSO^ by the method described by Vanino.*0. The gas was regenerated by diluting the acid solution in water and running the gas through a CaClg tube into a gas buret. By continual dilution with air

it was found that when one c.c. of a 5$ mixture was dissolved in a few c.c. of cold water and tested the lower limit was reached for a satisfactory test. At 27° and 70 cm. pressure this corresponds to about 0.0001 gm. ether.

15

It has been shown by Dodge1"1" that dimethyl ether interferes with the test for alcohol, and since Schorger’s method eonverte the ether into alcohol much time was lost and uasmtiefaetory results obtained at the beginning of the experiments because of ignorance of this interference.

Attempts were made to separate the carbonate from the gas by freezing. To determine the effectiveness an ampoule containing about .08 gm. was put into a 90 c.c. tube which was sealed with air in it. The ampoule was broken and the tube immersed in HaCl-lce mixture at -17° for £ hour. The tube was broken open and the gas pumped off while the tube was still immersed. This gas was dissolved in 30 c.o. water.To 20 c.o. was added 5 c.c. of 10$ HaOH and the mixture allowed to stand overnight in a stoppered flask. The 25 c.c. resulting were distilled, 20 c.c. being collected and redistilled into another flask, 15 c.c. being collected. This 15 c.o. was tested for methyl alcohol. A very weak but positive test resulted, showing that the carbonate can be kept back almost completely by freezing.

One of the tubes which had been in the furnace was immersed in HaCl-ioe mixture for half an hour. It was then broken open and the gas pumped off. The gas was run slowly into 25 c.o. water. Twenty c.c. were taken and tested for methoxy with ester linkage. A positive test was given.Since as above remarked, methyl ether would break down and test with this treatment, it would seem to indicate ether is

I#

present in small quantities*A gas sample from the products of one of the regular

kinetic runs was drawn into an evacuated flask. A few c.c. of dilute HaOH containing HgOg was sucked in and the flask shaken

to dissolve ftestrof HCHO, After standing ten minute® or more, the solution was run out, acidified, and the HgO^remaln-

ing destroyed with permanganate. Excess permanganate was added and then destroyed with oxalic acid after about two to three minutea. Schiff's reagent was now added. A definite positive test resulted at onoe. This coloration could he due either to dimethyl ether or dimethyl carbonate if it passed through the U tubes cooled by dry ice-alcohol mixture, f® settle this latter point a 500 c.c. bulb was evacuated, about half a c.c. of carbonate drawn in, and the bulb filled with Wg to atmospheric pressure. This bulb was attached to cock I

by rubber tubing and immersed in water at 45o-50°C* At this temperature the carbonate has a vapor pressure of about 17 ©a. After a few minutes the gas was pumped through the V tubes, cooled in dry ice-alcohol, into another bulb C which had been evacuated. The bulb C was removed, dilute HaOH containing HgOg run in, and the contents thoroughly shaken to dissolve

and hydrolyse any carbonate present. HgOg was added with the

HsOE simply to make conditions more nearly similar to those in the test on the gas sample. The solution was run out and treated a# before, but a negative test was given, indicating

If

that ether is a product.Formaldehyde: One of the remaining tubes was broken

open and the contents shaken with water. Two c.c. were taken and tested for ECHO by the gallic acid test.13 A positive test was given almost at once.

Acetone: Two c.c. of the above solution were taken andtested for acetone.14 The test was negative.

AoeialSehy*®: Five c>c. of the above solution weretested for acetaldehyde.14 The result was that a slight

. ' : ' , \ . .. . - - ' color developed whloh was Insufficient to be considered positive. ■ • ' '-v.'. :• • : ■ : - - : - V

Carbon Monozifie;; A new tube was taken, broken open, and the gas tested for CO by PdClg method.15 A positive test was. given. ..... , * ■ ' •■■■■ -• ■ • : - • • . ' . ̂ ■: y' i - ,

Carbon Dioxide: Considerable white precipitate wasformed when some of the gas was shaken with BaClg. This pre

cipitate dissolved readily in HCl with efferveecenee. Hence COg appears to be present.

Hydremiaj Ho specific test was made for Eg. It was ob-- : ' ' ' ' - r ..' ' - ' - : . ' ' r\ Vserved, however, that water vapor condensed out in the capillaries of the Great when the gas was passed:through;the heated CuO tube, for the determination of Eg. . 1

Methane: Ho specific test was made for methane. After■■ ■ ‘ ; ' . . . ■the determination of COg, Eg, CO in the Great there always re

mained about 25fj of the original gas volume which was determined

as methane by eeabmstion with exygea.Ethanet Ho specific tests were made for ethane, which

eight easily he present through the eombira tion of methyl mil** eale. fostado claims to have fornid ethane ae a product to the extent of a few per cent. Initial Onset analyses indicated the presence of ethane,in this investigation hut it was later discovered that this was Sue to CO not completely removed by oxidation by CuO.. When a different CuO tube was used the per cent of ethane came out consistently aero,

Illumlnants: The presence of illuminants was not ous-peeted until late in the investigation when teats in which Brgwas absorbed indicated the presence of unsaturated compounds. Specific testes on the gas products showed that acetylene was was absent. Moreover, when the gas was passed into a pipet containing fuming HgSO^ in the Orsat, a small amount was absorbed, This was not due to the solubility of other substances because more than four passings of the gas into the pipet ̂did not increase the amount absorbed. The illuminant was assumed to be ethylene.

Water: To determine whether or not water is a product,the U tubes were opened and powdered, anhydrous cobaltous chlor lie put in. When the products of the packed flask run were pumped through, a small portion of the eobaltous chloride turned pink. This would seem to indicate some water, but in very small amounts. Specific test with ester shewed that it does not color eobaltous chloride.

IS

Carbon: As remarked above, a carbon deposit was ebservedin the tubes heated to obtain products for qualitative analysis. Moreover, in the kinetic- runs it was observed that the pyres flask took on a yellowish-brown hue which became progressively darker the longer the flask was used.

Other products; Whenever the gas products were dissolved in water a peculiar persistent sweetish odor was given off the solution. Hone of the products identified have a similar odor. What this substance is is not known. »' '

20

QnantltatlTe Analysis of tho Reaction Products

For the purpose of making quantitative analyses» the IT.S. Bureau of Mines Great apparatus for gas analysis17 was set up. Several modifications of the procedure were found necessary on account of poor totals and poor reproducibility of results {except for absorbables) which were obtained when the procedure given was used. This does not necessarily reflect adversely upon the Bureau of Mines method, but may simply be due to characteristics of the particular apparatus used.

A discussion of the more important modifications follows:1. Absorbables. Absorbables include C02, HCHO and (CH3)20.

Instead of the 50$ KOH recommended by the Bureau, approximately one normal HaOH was used. %iis was due to the fact that the apparatus was used jointly by Fitzhugh who studied the pyrolysis of dimethyl sulfite.18 Stronger BaOH interfered seriously ' : ' ' ■ " ■ ■ - : ' . : : ' . - , ' ^ - with his determinations of S02 gravimetrically from the solu

tion from the alkali pipette, The only disadvantage in the use of dilute BaOH is that it is more short lived. The supply of alkali for toe pipette was at all times kept under a gas mixture consisting approximately of 20$ Eg, 35$ CO, and

45$ natural gas, which contained about 82$ methane and 13$ ethane. . ■ . . . ■ .

2i Hydrogen and Carbon monoxide. Hydrogen and; carbon monoxide were determined by fractional combustion by Chp at

21

500®. Si® Bureau’s pamphlet calls for a single combustion with two passings each way at 10 c.c. per ■taut®. A single combustion was found sufficient for the removal of hydrogen but a second one was necessary completely to remove carbon monoxide. $he 00% formed from the first combustion was ab

sorbed before the second one was made. It is known that CuO absorbs CO and that CO is not completely oxidized unless it is removed as soon as formed.19 This may account for the necessity for a second combustion.

Any CO undetermined here will be determined as ethane in the combustion plpet. This explains the source of ethane which feetado reported and which was found in the earlier analyses of this investigation.

3. Methane. Originally methane was determined as the Bureau’s pamphlet directs. It was found by Fitzhugh,18 however, that the freshly reduced CuO absorbed the oxygen added at the rate of 2 c.c. per hour, thus throwing the readings off for the combustion of methane. To obviate the need for running the oxygen through the CuO tube, about 10 c.c. Eg

were run into the left side of the manifold before the addition of oxygen, passed through the CuO tube to flush out the methane, and then mixed with the gas sample in the gas buret. The cocks leading to the CuO tube, now filled with Bg* were then closed.

The pamphlet calls for two combustions over the platinum filament with several passings of the gas the first time, and once the second time. When this was done, it was found that

\

the per cent of methane was almost invariably considerably less than the per cent of original gas sample remaining after the removal of absorbables, % and GO, thus indicatingIncomplete combustion* 1© obtain good results, it was necessary to make three combustions and to pass the gas over the platinum filament at least ten times in each case.

Formaldehyde, Formaldehyde was determined iodometrical- ly,*2 A sample of the gas was measured in the gas buret of the Great and delivered Into an evacuated bulb. A measured amount of standard 0.01H I2 was rum in from a buret together with enough 0.15H HaOH to produce a straw colored solution after considerable shaking. After standing for about ten minutes the solution was run into a flask and the bulb rinsed1several times with distilled water. %he solution was acidified and the remaining 1% titrated with standard 0.01H Thiosulfate. The formaldehyde equivalent to the Ig

used can then be calculated and its per cent of the gas sample obtained. In general values of only 0.2$ to 0.5$ were obtained.

Dimethyl ether. Though no quantitative determination of dimethyl ether was made, evidence that it is present only in small amounts, other than that obtained colorimetrieally, is the following: In one of the Orsat analyses total absorbablescame out 32.35$. This would include C02, HCHO, dimethyl etherand some carbonate. (Methyl carbonate was present since in

this case HaCl-ice at was asei to eool the U tefcoe.It was later shown to pass through at this temperature by a method similar to that used to prove that the carbonate does not pass through the tf tubes when they are cooled with dry lee and alcohol. This method has already been described under the qualitative tests for dimethyl ether.) A gas sample of 52.1 c.c.

24

Illuminantet Illuminante were determined by absorption in fuming H2S04 .

Ester: The method of determining undeepmposed ester hasalready been described, $he method.did mot seem highly accurate.

Total gas volumes The total amount of gas collected was. ■ ■ ■ ■ : v ;determined by measuring successive portions of the gas volume

In the gae buret. By running mercury into the sample bulb, the last few c.c. of gas could be forced over into the buret. In each case the volume, temperature, and barometric pressure were recorded*

25

A nttmtier of kinetic runs and corresponding analyses were made. In some of the rune the U tubes were cooled with ice and salt mixture which did not complete remove the ester* thus giving high absorbablea and throwing She percentages of the other product# off. fhem^ toot the analytical procedure in connection with the use of the Great was not completely worked cut in earlier analyses, giving poor reproducibility. For these reasons only the analytical results of runs made after the experimental technique had been worked out will be given. •' .- * Using a sample of about 0.2020 gm. ester, four runs weremade to complete decomposition at 540 C. The kinetic data are given in Table I and a graph given in Figure 2. The time is given in the first column, and the corresponding pressures in columns 2, 4, 6, and 8 for each run? Columns 3, 5, 7, and 9 give the change in the pressure per minute for certain portions of the reaction. The initial pressure was determined by extrapolation to zero time. These may be considered quite accurate because the curve is almost linear for the first few minutes. The ratios of the final to the initial pressure sreas follows: p

Run 20

26

Since it appears that one molecule of dimethyl carbonate decomposes into four molecules, it was expected that CO^,

Hg, CO, and CH^ would each total 25$. Actual analysis of runs 3 and 4 gave:

- - . . ' ' v. : : ? V / -i •'Bun 3 Run 4

$ Decomposition 100 100Initial ester 0.2024 gnu 0.2013 gm.

. is . ' $ ■■■ . ■ ■ ■;COg 25.8 ga.i°2H4 *S •**£ 26.8 27.6=0 , 26.1 26.2

'v: Cl, ■ 22.9 22.5, *9t.l 99.9 100.1

HCHO 0.214*Ester usdee. ■ . --- ••• ' 'Gas vol. ohs. 242 c.c. 20?*4 * #.

- : Gas. vol. calc. 239 c.c. 238 c.c.. The value given for GOg in. actually the total absorbable#

which includes HCHO and (CHg)gO. Since the error in determining

the ebeorbables is of the erder of magnitude of the per cent H

by four. For Run 3 the agreement can be seen to be excellent. $he low result for the gas volume observed in Run 4 la probably due to leakage through the cooks of the sample bulb.

faking the 4 to 1 ratio as indicative of a complete reaction, three runs were then made to three quarters decompo- elties. For each run, therefore, the reaction was allowed to proceed until the pressure developed was 3.25 times the initial, pressure determined by extrapolation, fhe kinetic data are given in Table II, and a graph is given in Figure 3.

Analysis of the product® gave: .

deeomp. from volume ratio 79.7 Total ester 0.6056 gm.

*co2 26.4c2H4 - 1.0*2 24.4CO 24.1ch4 24.1Total 100J0ECHO 0.169#

Ester undec. .0810 gm.Gas vol. obs. 569 c.c. at 25° and 70.0 cm.Gas vol. calc.for total deeomp. 714 c.c. at 25° and 70.0 em.

le products cannot be removed instantaneously, the

28

reaction actually wont slightly beyond three quarters decomposition. To determine the true degree of decomposition, the volume which the 0.6059gm enter would occupy at 25° and 70.0 cm. was calculated and multiplied by four. This is the volume which would result if the reaction had gone to completion. By dividing the observed volume by this, volume and multiplying by 1 0 0, the true per cent was obtained.

Two series of runs to half decomposition were also made.The decomposition was allowed to proceed until the pressure developed was 2.5 times the initial pressure determined by extrapolation.

The kinetic data of the first of these is given in Table Ill and graphed in Figure 4. The analysis of the mixed products of the four rune gave:

% deoomp. from volume ratio 54.8 Total ester 0.8089 gm.

C02%n2COGH4TotalmemoEster undec. 0.3636 gm.Gas vol. obs. 523 o.c. at 25° and 70.0cm.Gas vol.calc.

for total decomp. 955 at 25° and 70.0 cm.The next series to half decomposition consisted of two

28.8.8

' 23.822.4 '23.4 99.2

0.243#

g#

runs. The kinetic data are given in Table IY and graphed in Figure 4. A composite analysis gave:

S& decomp* from volume ratio 63*6■Total, ester - 0.4030 gm.

GQg 32.6GeS* .6H 2 21.9GO 21.9% 23.3Total 100*3ECHO 0.135$Ester undec. 0,1544 gm.Gas vol. oh®. 250 c.c. at 25® and 70.0 cm.Gas vol. ealc. fortotal decomposition 476 c.c* at 25° and 70.0 cm.

The weight of ester was then reduced to about 0.1010 gm., and three runs made to infinite time at 540°C. The kineticdata are given in Table V and graphed in Figure 5. The following ratios of the final pressure to the initial pressure were obtained, the initial pressure being determined by extrapolation:

Run Po Pf K1 17.7 69.6 . 3.932 18.3 67.8 3.703 66.2 17.9 5.67

Run 3 was made with a new bulb which was first seasoned, by making several runs in it and discarding the products..

Considerable variation in the ?f to P0 ratio Is observed.

ihai

30

faking the ratio as 5.7 and using the new bulb runs were made to three quarters decomposition and to half decomposition as before. Kinetic data and graphs are given in fables VI and VII and Figure 6 . In addition a run to infinite time was made with the same initial pressure in a packed flask. She kinetic data and graph are included in fable VIII and Figure #*

lack of time prevented analysis of any runs at this lowerpressure.

31

Tables of Kinetle Data

She following symbols are used in tabulation of the data; t is the time in minutes measured from the moment

of the breaking of the ampoule.P is the pressure produced in centimeters of

t ' 'mercury at the time t.P is the change in pressure per minute between the

value of P adjacent to it and just below it.

The temperature was 540°C.

gglgll

sassgs

tsgggŝ

igssss

KssPS'

0̂'m

to22£3455£678

TABLE ITotal Decomposition

Run 1 Run 2 3 Run0^2018g. 0 .201^ . 0.2024m. 0.20134.1 34.4 . 33.8 33.0.3f.3

38.1 37.637.139.240.2 39.9 41.5.41.4: 43.6■42^7 :;i.s

46,5 1.4

49.8 1.4

58.260*?

45.0 1.347.0 1.348.9 1.3

55.2 1.2

59.9

43.044.245.7 ■. • • • -47.048.2 49.550.711:154.1

t-v,.-

1.2- 45.5 1.5 47,4

1.2 50.6m m'.1,3:;:;;:55.5

■ 11:1

63,6 -V'.: 59.6 : v 66.4- " •• ‘ :66.0

66.068,0 66.1 ' 64.9 72.173.0 70.9 69.6 77.177*1 -v 76.7 . . 74.0 85.781.5 80.0 77.8 86.506*4 83.5 84.0 : 90.089,0 87.0 8S.2 92.892.0 M m 89.0 95.5'98.4M m .v:. v '93.3 91.1104,0 100.8 98.8 104.8

107.0 104.8 110.0115. . r 116.0 . 109.8 V 116.2117,8 114.9 113.0 ; ; 115.5121.9 121.7 118.1 119.0125.0 124.6 121.3 120.8134,6

136.7 135.5

V -

SSSSSSgSSSggSgSKSKPS

'0

33

fiBLE IX

t0Li

3i

Hun 1 - Hun 2 Enn 30.2018 gm. 0.2020 gm. - 0.2018 iP 3P. ' ' ' ■ - P ■88.1 34.4 35.0

• 88.8 36.937.7 36.3 37.508.4 37.0 38.288%0 37.7 38.8■ ,v • 38.7 . 39.440.7 39.8 40.240.942.9 ' 42*4 41.7

K -S3.155.35919#&.#54.0 65.974.488.093.4 98.1 102.2196.0108.0110.4112.7114.0

45.048.2

'4-4 * .. • . ? '

56.058.4

64.566.6

104.5107.1 108.9,111.1 111.0

l56.588 T60,965.073.381.688.4 93.8

El108.9111.8113.5118.98

MILE III

0.2019Dgm.P A p

70,2 VV4.#

SO53&353640 f®,i4 H 82.8

One Half Run 2

0^2023

0,2021 mP A P

0 35.0 35.6.... 35.1 34.12 36.5 36.5 ■ 37.8 • 38.93 37.5 38.3 40.3 *4 38.9 40.8 43.2 ': • 44.05 40.5 43.0 1.7 45.3 - 46.56 42.3 1.4 44.7 2.0 47.4 1-9 48.97 43.f 1.4 46.7 1.6 4# j U # 51.48 45.1 1.4 48.3 1.8 #1^3 53.29 46*5; 1.8 50.1, 1.8 53.2 :.2 ;o 56.010 48.0 1.4 51.9 1.7 55.0 jl*8 58.011 49.4 1.2 53.5 1.7 56.9 i.g 60.012 50.t 1,4 55.2 1.8 58.6 l;7 62.015 52.0 1.3 : 57.0 1.4 60.0 x.*4 74.014 53.3V 1.3 58.4 1.4 61.5 1;5 65.715 54.4 1.3 59.8 1.4 63i0; 1.-5 67.420 60.3,r 1.3 67.0 1.2 71.1 1.6 74.925 45.f> 73.2 1.0 82.52® • • ... - >• ■" 85.2

Run 4 0.2026 m . P A p

2.5*2.4 2.8 2.8 2.8 * 2.0

• 2 . 0 '2%02.0leti:?'1.5

78.383.084.0

1.0rI#?5 87 *75

One Half DecompositionTABLE 17 .

Run 1 Run 20.2017 ga. 0.2013 gm

t i? A-B - P A po : •34.7 : 33.82 .. 37.1 . *7.0 .3 38.3 .4 39.4 . 40.25 ■ . 40.7 . 42.5g. • ■ 42 3 . 45.07 45.0 2.3 47.4-8 47.3 2.2 49.59 : 49.5 2.3 • 51&8 .10 : . 51.8 2.1 ‘ 54.1 1.911 53.9 2.2 56.0 2.112 56.1 2.1 58.1 1.913 52.2 2.0 60.0 1.8M . ■." €0.2 2.0 61.8 1.715 ’ ■•.'22. 2 '-1.8 63.5 1.620 71.3 71.725 79.0 78.630 85.5 . 84.5 " '31 86.75 - ;. .

ggggas

ggasgg

ssgsgK

SBggss

ssss:

O

, *

: ■

-V i '

H . '

> *.

36

TABLE VTotal Decomposition

0.1004t P0 17.72 19.73 20.74 21.95 23.16 24.37 -V'K - 23 48 23.79 : #7#10 . 28.911 go.0}2; ■ ■ 31*913 32.0

Ron 2 0.1015 &m.

Run 30.1006 i

v-'-;

w a34.0

Is38.039.089.740.041.3

1.1 l.l •1a 1 1*0 1*0 1.0 1*0 1*0 1*0 1*0 1*0 1*0 1*0

18.3 20.2 21.8 22*823.224.2:2 * 226.0.1?:?28.7

i i33*0 33* #34.83* #36.4II43.2':rv- «

1.0.9

1.0.91.01.0y:!.81.0

i i•8

a:

P17.920.221.4 1.322.1 1.023.7 1.024.7 1.025.7 1.026.7 1.027.7 •1.028.7 : .929.6 ' ,8 .30.431.232.032.7

36.3

39.3

46.4 44*0; . , : 42.1---49.2 ■ . 47.5:l!:::-:: 44.651.6 49.5 46.853.8 . 51.6. 49.155.6 53.757.1 55.5 _ ■ •58.4 56,8 ;; 53.161.4 56.065.0 ■ ' ■ 61.5 V I:':-' 58.063.9 62.7 58.864.6 63.4 60.069.6 67.8 66.2

TABLE VItoree Fourths BeooepttSitlon

16BO25m86404660656065VOf58084

0.1008 gtaA

52*0 54*5 56*8 88*1 41 E45*:i:4 4 ?47*249.049*950.951.7..52*3

Run 20.1007 m.

88^38 i 6t s a

IS49.550.851.852.8

Run 30.1011 gm.

p- A P . P ^ P T ,17.3 - 17.5 17.819.1 19.8 20.0. 20.2 20.9 21.1 .21.1 21.9 22,3 :

■ •*' V : 22.1 .7 22.8 .8 23.1■ 22.8 .8 23.6 .8 24.0 -23.6 .7 • 24.4 .8 25.0■ ■ 24.5 V *8 ■ 28*2 g8 25.726.1 .8 26.0 .7 26.5' 26.9 >5 26.7 .7 ; 27.6% * .7 29^4 y *8 28.4•• 29.1 .9 28.2 .6 29.228.0 - .4 ' • ■ 28.8' .7 30.028.4 *9 • ' 29.5 .7 30.6- 29 *1 ' 50*2, 31.5

.91*0

.7

.81.1

I38.040.745*048.847.048*450*051.252.255.153.7

38

TABLE VIIOne Half Decomposition

Run 1 Run 2 Run 3' 0.1020 gm. 0.1013 gm* 0.1020 gm.

t P Zxp P ^ P P /&P© ' 17.7 1.0 17.9 17.92 5 19.7 1.0 20.2 20.53 20.7 1.1 21.4 21.84" ’ ‘ 21.8 1.0 22.5 1.2 23.25 22.8 1.0 23.7 1.1 24.2 1.36 ’ 23.8 .9 • 24.8.- , .9x ■ 25.6 1.07 . % 24.7 ;$ 25.T 1.0 28.5 1.08 ‘ . 25.3 - .9 .• ' 26.7 1.0 27.5 1.09" 2S.2 .9 - 27^7 ;8 28.5 1*010 27.1 .8 " 28.5'-/:i9: - 29.5 1.011 : 27.9 .7 • ' 29;4;- ' 30.4 •9■IS- 28.6 .7 31.4 .913 29.3 .8 ' - 31.2 .8 ■ ■ 32.114 30.1 .7 33.115 30.8 ’ • 32.8':v:::v''- 33.9 ' •• '.2d 34.1 . - 36.3/ 37*8 - -25 ■ :3f.2;., 39 ̂6 .. 41*027 - . ‘ . - 42.1 1 ..29 ■' • . ' . ' . 42*1 .30 ’ 40.0 *% 41.6 ‘ ' .;; :

"SEil°5SSS"§

"88°"K5gps'or

o":,

1

St) X3 20 JLJ- **> »•* *

p:

D je*t*r* T ^z. _2 T d /?***} 3

yÔ

/f

afa-t/e ma

P&**rj

j z m or

y/*,x Tmi/rMT

y y y , l □ Z « e r > y y Z< # e .

i

B

40

Discussion and Conclusions

As the graphs indicate there is considerable variation in the velocity of the reaction for different runs. In some cases duplication of runs was almost exact, as Figures 3 and 4 (right) show. On the other hand, as can be seen in Figures 4 (left), 5 (right), and 6 , the reaction went progressively faster for other runs. In addition several cases were observed in which the reaction slowed down. Figure 7 and Figure 5 (left) being examples. Moreover, the velocity of the first run of a day invariably proceeded more slowly than the last run of the day before. The run in the packed flask shows clearly a more rapid rise in pressure during the early stages of the reaction than in an unpacked flask# All these facts indicate some heterogeneity in . the reaction.

Inspection of the tables shows that in many cases the change in pressure per minute is strictly linear over a period of several minutes in the earlier part of the reaction. Such pressure variations are characteristic of zero order reactions, which take place on the wall of the reaction bulb.

At one time an apparatus was used in which the ester was introduced into the reaction bulb through a stopcock. The temperature was 510*0. After a few runs were made, the reaction suddenly stopped. Though the ester was heated for half an hour, no pressure change was observed. This behavior was repeated for five runs* To force a reaction, the

4 1

temperature had to he raised to 550*0. where peculiar curves were obtained, one of which is given in part in Figure 8 .The behavior observed was presumably due to stopcock grease washed into the system by the ester and seems to us to be proof that .the initial decomposition of dimethyl carbonate is heteregeneon#.

The reaction graphed in part in Figure 8 proceeded for ten hours, so practically all ester must have been decomposed. Hence, any ester passing through the XT tubes which were

O ' 'cooled to -17 C. with ice and salt was negligible. Analysis of the products gave:

C08 23.2*2 27.3eo 23,2% 1.13ch4 23.30Total 97.13

When the per cent of CO and CH4 is corrected on the assumption that the ethane is due to CO, we have

co2%

23.20= 2 27.3000 . 24*88ch4 24.43

99.26Total

Ae has already been shown, dimethyl ether appears to he a product of the reaction. It would seem plausible, therefore, that the initial, heterogeneous decomposition ef dimethyl carbonate in given by the equation

(CHgigCOg --5 (CEgigO+COg

Hinsehlwood and Askey20 have shown that dimethyl ether decomposes homogeneously and unimoleeularly at temperatures , from 422°C. to 552*0. provided the initial pressure is above 800-400 mm. The products were and CO, with ECHO asan intermediate product.

Furthermore, Fletcher22- has shown that formaldehyde decomposes homogeneously and bimoieculariy from 510° to 607° when the initial pressure was between 30 and 400 mm. The products were CO and Ho. - .

In the present investigation it has been shown that for- maldehyde is a preduet of pyrolysis and that neither formaldehyde nor dimethyl ether accumulate to any appreciable extent. The latter is to be expected since the temperature at which the decomposition of the carbonate was studied was 540®C. Moreover, the analytical data shows that COg, CO,

H2, and CH4 are the principal products of pyrolysis, each

being present to the extent of approximately 25^. It thus appears that the principal decomposition of dimethyl carbonate can be represented very nearly by the three consecutive reactions

42

43

(CHg} gC Og—— {CHg} gO COg

(CE3)20 — > H m o V C H 4m m o — > h 2+ go

That c62> CO, Hg, and CII4 are not present to the extent©f exactly 25$ is probably due to site reactions which are un- q.ueetionably present. Carbon ant ethylene are among the produets formed, and water may also be. Prom the hiis tic data for the peeked flask run, it will be observed that a decrease in pressure of 7.9 cm. resulted over the period from 17& hours to 48 hours. When the flask was removed from the furnace, the glass tubes used to pack the flask and the flask Itself were observed to be very dark yellowish-brown in color. The same color resulted with the unpacked flask, but to a lesser degree. Hinshelwood and Askey21 found that dimethyl ether gives neither ethylene nor water. Hence It appears that the products of pyrolysis undergo reaction at the temperature used* In addition, of course, dimethyl carbonate may decompose by some side reaction to give products other than those already indicated.

Inspection of the analyses brings out the following facts: 1. During the early stages of the reaction C02 is

present to more than 25$ of the gas volume and decreases with time to less than 25$. 2. Eg and CO both begin at less than

25$ and increase to greater than 25$ with their ratio remaining

44

nearly constant. S. The per cent of CH4 Is nearly constant*

In addition It will be observed that in the case of the decomposition to 52.5^ completion, the per cent of CH^ is

greater than the per cent of either Hg or GO.

faking the mechanism as postulated and assuming that both tCH3)gO and ECHO accumulate to the extent of 1 , 3 analysisshould give

: ■ ' . 3 5Abeorbables 20.6 includes COg, (CHglgO,

Hg 23.4 • • -• ' :* -CO 23.4CH4 2 M

100.0

This is in good agreement with the values obtained for the decomposition to 54.8^ completion. However, in no case was there any evidence that either the ether or formaldehyde was present to more than a third, af that assumed eteve*

The ethylene formed is probably produced by the reaction

sch4 — * c2h4,h 2

which ha® teen studied by CanteloSS who passed CH4 through a hot tube at 600°C*

Bone and Coward24 have observed that methane decomposes to give carbon and hydrogen.

45

. CH4 — > C 4-282

They found, however, that the rate was very slow at temperatures helow ?O0®C* enlees a very large surface was exposed to the gas. This reaction would aeeeuat for some of the carbon formed as well as a portion of the increase in Eg. They have

also shown that ethylene gives carbon and methane in the neighborhood of S80®6#

c2k4 **> ̂ 4 CH4

In this manner some of the methane would be restored.Carbon dioxide maybe removed by the reaction

COg + C — ) 2C0which is known to proceed slowly below 800°C. ,2^ or. by thereaction . ' • . . ' . .' : • ■

COg^Hg — » CO + EgO

which is favored by heat.2^It may be that a 'water gas* reaction is also present

C + H 20 — > C04-H2

This series of reactions, known to proceed sore or lees rapidly at the temperature used, provide a means of increasing the percentages of CO and Eg and reducing the percentage of

Y/hat reaction causes the decrease in the volume is not• V

46

definitely known. However, a reaction such as Hgf CO— >C4 HgO

would have this effect. In any case, the reaction does Involve the deposition of carton.

An estimate of the overall order of the reaction can be obtained from the following consideration®s For a first order reaction, the ratio of the time for three quarters decomposition to that for half deeowpesitlon is 2 . For a second order reaction this ratio is 3.

It will he observed that Hun 8 in Table II and Run 4 in Table III proceeded at about the same rate. Hence

4 * T0.T5 '28 2.6These runs were at the higher initial pressure.

Again, Run 3 in Table VI and Run 1 in Table VII, both at the lower Initial pressure, show about the same speed* Per this case

Bti

— IL.83.26 2.3

which is in good agreement with the former value. These value® indicate that the overall reaction is therefore between a first and a second order.

1, An apparatus has been described which is suitablefor the study in the gaseous phase of substances which are liquids at ordinary temperatures. . :

2. Kinetic data have been obtained for the decompesl- ti@n of dimethyl carbonate at 540°C. and at initial pressures of about 17.7 cm. and 34.0 cm.

g. Qualitative analyses have been made indicating that the products are C02, CO, Eg* CH4 » c2̂ 4» HCHO, (CHsJgO^ C,H20, and some unknown substanee. Acetylene, acetaldehyde*

\ ■ ■ ' -acetone and ethane are absent.4. Quantitative analyses have been made to determine

the ratio of the components of the products at three stages of the decomposition.

5. Evidence has been given to show that the reaetien Is in part heterogeneous and in part homogeneous.

6 . A mechanism has been postulated to account for the facts, but not entirely successfully.

7 . It has been shown that side reactions involving the products take place. Known reactions are given which w i n produce results which are in qualitative agreement with the facts.

48

Bibliography

1. Hlnehelwood, C. B.Kinetics of Chemical Change in Gaseous System#. BrflE4 •» P • 2 *

2. Jellinek, Karl .: ' . . . . ' - • ' ' - , ■ 'Lehrbuch flerPhyBikalischen ohemie I. Band (1914).p. 207 ff.

5. Hlnehelwoofl, C. II.Op. cit., p. 19.

4. ‘ Hlnshelwood, C. I?.Op. cit.. p. 187.

B. Alvares-Tostado, Claudiothermal Decomposition of Dimethyl Carbonate. Master's Thesis, University of Arizona, 1955.

6 . Rice, F. 0 . and Johnston, V. R.J. A. C. S. 56, 214 (1934). .

7. Findlay, AlexanderPractical Physical Chemistry. 6th Ed., p. 65.

8 . Rhodes, H. D.Thermal Decomposition of Dimethyl Sulfite. Master's Thesis, University of Arizona, 1936.

9. Bchorger, A. V/.The Chemistry of Cellulose and Wood. 1st Ed., p. 527.

49

10. Vanino, LudwigPraperatlve Chcmie, Tol. II, 2nd Ed., p. 49.

lie Lodge, Barnett F.Analytical Ed. lad. and Eng. Chem., Vol. 4, Ho. 1* p.28 (1932).

12. Treadwell, F. P., and Hall, T. H.Analytical Chemistry, 7th Ed., Vol. II, p. 589*

13. Weston, $*. E.A Sehome for Detection of Organic Compounds, 3rd Ed., p* 47. . . .

14. Weston, F. E*Op. cit., p. 46. .

15. Treadwell, E. 2. and Hall, T. H.Analytical Chemistry, 4th Ed., Vol. I, p. 506, footnote.

16. Snell, F. 0, and Snell, C. T.Colorimetric Methods of Analysis, Vol. II, p. 1 (1937).

17. Fieldner, A. C.; Jones, G. W.; and Holbrook, V/. F.The Bureau of Eines Orsat Apparatus for Gas Analysis. Technical Paper Ho. 320, U. S. Department of Commerce.

18. Fitfchugh, Andrew F. , . .The Pyrolysis of Dimethyl Sulfite. Master's Thesis, University of Arizona, 1936. .

19. Lunge, GeorgeTechnical Gas Analysis. Revised By H. R. Ambler, 1934. pp. 145, 146.

:Udi*53

20. Hinshelwoofl , C. II., anS Aslcey, P. J*Homogeneous Reactions Involving Complex Molecules. .Kinetics of Decomposition of Gaseous Dimethyl Ether. Pros. Roy. Soc. A 115, IS27, p. 215.

21. Fletcher, C. J. 1£.The Thermal Decomposition of Formaldehyde. Free. Boy. See. A 146, 1934, p. 367.

22. Cantelo, R. C.The Thermal Decomposition of Methane. J. Phys. Chem. 28, 1924, p. 1036.

24. lone, V/. A., and Coward, H. P.The Thermal Decomposition of Hydroearhons. I. J. Chem. Soc. 93, 1908, p. 1197.

26. Kendall, .Tames .Smith’s Inorganic Chemistry, 2nd Revised Ed., p. 570

26. Partington, J. R. .Textbook of Inorganic Chemistry, 4th Ed., p, 687. .

50

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