THEDECOMPOSITION
August, 1955
and there is a wide (15 mm.) induction zone still with no measurable reaction. The surface is at about 400-500° and causes no apparent discontinuity in the thermal wave, which becomes steeper very rapidly with pressure. The composition of the induction zone is almost constant between 100 and 300 p.s.i.g. despite the
OF
ARSINE
777
change in linear rate and the appearance of a flame. The flame consjsts of the reaction between nitric oxide and methane, ethene, carbon monoxide and Hz. Acknowledgment.-The fine thermocouples were made and imbedded by Mr. Don Fuhlhage, and the temperature profiles recorded by Mr. Maynard H. Hunt.
THE DECOMPOSITION OF ARSINE BY KENZITAMARU Frick Chemical Laboratory, Princeton University, Princeton, N . J . Received March 11,1966
Coherent films of arsenic by decomposition of arsine can be laid down on the surface of a reaction vessel if the glass surface is first covered by a coherent film of antimony. On such antimony and arsenic films the kinetics of the decomposit,ion of arsine have been studied by a static method. The reaction is first order with respect to arsine and independent of hydrogen concentration. The apparent activation energy on arsenic surfaces is 23.2 kcal./mole. Arsine decomposes more easily on antimony surfaces than on arsenic surfaces. Decomposition on glass surfaces is much slower. I n the decomposition of a mixture of arsine and deuteroarsine a t 255” intermolecular exchange occurs and the decomposition product contains a large percentage of hydrogen deuteride. When arsine is decomposed with molecular deuterium a t this temperature ?o hydrogen deuteride is found, indicating no exchange between hydrogen and deuterium on the arsenic surface. h a l y s i s of the experimental data suggests the reaction AsH,(a) + AsHl(a) H(a) as the rate-determining step.
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Studies of the decomposition of arsine were first reported by van’t Hoff in his book,l “Etudes de dynamique chimique” published in 1884. He and Kooj found that the decomposition on a glass surface is a first-order reaction. Stock and co-morkers2 t,ried without success to study the decomposition on an arsenic surface covering all the glass surface of the reaction vessel. As the vapor pressure of arsenic a t the reaction temperature was appreciably high, the deposited arsenic recrystallized and sublimed, condensing in the cool parts of the system without covering the glass surface of the reaction vessel and blocking the inlet capillary tubing in four experiments. In spite of this difficulty, the decomposition of arsine on arsenic surface remains one of the interesting catalytic reactions, since the catalyst surface is always renewed by the deposition of fresh arsenic during the reaction and the reaction system itself contains only two elements, one of which is the catalyst for the reaction. Thus we can not only get information about the reaction mechanism and the adsorption and reaction of hydrogen on the clean arsenic surface through this reaction, but also treat this most fundamental reaction from the statist’icalmechanical point of view. Experimental Preparation of Arsine.-Arsine was prepared by adding chemically pure arsenic trichloride to a solution of lithium aluminum hydride3 in ethylene glycol dimethyl ether in a nitrogen atmosphere. As the reaction is fairly violent, the solution of lithium aluminum hydride was cooled with liquid nitrogen as the arsenic trichloride was added. After the arsenic trichloride addition the liquid nitrogen was removed to allow the solution to warm up gradually. The arsine was evolved before the reaction vessel reached room temperature and was condensed in a liquid nitrogen trap. It was purified by distilling several times between solid ( 1 ) J. H. van’t Hoff, “Etudes de dynamique chimigue,” F. Muller and Company, Amsterdam, 1884, p. 83. (2) A. Stock, E. Eohesndia and P. R. Voigt, Ber., 41, 1319 (1908). (3) This hydride and the corresponding deuteride were obtained from Metal Hydrides Incorporated.
carbon dioxide and liquid nitrogen. For the preparation of deuteroarsine, lithium aluminum deuteride of 98% purit,y was used instead of hydride. Apparatus and Procedure.-The experiments were carried out in a static system. A pear-shaped Pyrex reaction vessel attached to a mercury manometer by means of capillary tubing was used. The volume of the vessel was.67 cc. Before the reactant was introduced into the reaction vessel a vacuum of less than mm. was obtained by means of a mercury diffusion pump backed up by a Cenco Hy-Vac oil pump. The reaction temperature was controlled by means of vapor baths, using diphenylamine, acenaphthene, naphthalene and benzoic acid. The course of the reaction was measured by noting the pressure indicated by the manometer a t suitable intervals.4 The content of hydrogen deuteride was determined by a h’ier ratiotype mass spectrometer which measures the ratio of mass 3/mass 2.
Experimental Results Arsine Decomposition on a Glass Surface.When arsine was heated to 302” in a Pyrex glass vessel, using the diphenylamine vapor-bath, a pi’essure increase of 1.7% was observed in 47 hours. It decomposed as shown in Table I, when the TABLE I DECOMPOSITION O F ARSINEON Grd.ss Time, hr.
0
4.33 16
Total P A ~ H ~ ,Time, pressure, om. cm. hr.
39.2 40.3 43.65
39.2 37.0 30.3
25.5 37.66 44.75
AT
350”
Total Phs&, pressure, om. o m .
45.35 48.05 48.85
26.9 21.5 19.9
reaction temperature was raised to 350” using an electric heater. It was a first-order reaction in respect to arsine. In this case the arsenic which deposited as a reaction product did not cover the glass surface but arsenic crystals were observed in tthe cool capillary tubing as well as in the reaction vessel, and no marked acceleration of the reaction by arsenic was recognized. Thus, as the vapor pressure of arsenic a t this temperature is appreciably high (ca. 2.3 mm. a t 350°), it required a dif(4) After the reaction the pressure increased stoichiometrically that is, up to 3/2, within the experimental error.
KENZITAMARU
778
ferent technique to cover all the glass surface with arsenic for experiments on the decomposition of arsine. Arsine Decomposition on Antimony and Arsenic Surfaces.-Arsine was found to decompose fairly fast on an antimony surface formed by decomposition of stibine. All the surface of the reaction vessel, consequently, could be covered by arsenic, depositing arsenic on the antimony surface a t temperatures where its vapor pressure, or mobility, is negligibly small. The antimony film on the glass surface was prepared in the way described by Stock and co-workers6 in their experiments on the decomposition of stibine, except that the stibine was prepared in our case by the reaction between antimony trichloride and lithium aluminum hydride as in the preparation of arsine. The decomposition rate of arsine on the antimony surface became slower as arsenic covered the surface, and finally it reached a practically constant rate as shown in Fig. 1. This constant reaction rate was considered to be the decomposition rate of arsine on the arsenic surface, and thus the kinetics of the decomposition on the arsenic surface could be studied.
VOl. 50
c
0
50
100
150 200 250 300 Time (hr.). Fig. 3.-Decomposition of arsine at 218'.
the partial pressure of arsine against time. It is obvious that the reaction is first order in respect to arsine, and the velocity constants are 0.0887 and 0.0062 hr.-I a t 278 and 218", respectively The dependence of the initial reaction rate upon various initial pressures of arsine at 254" is shown with circles in Fig. 4. On the other hand, when 48.3 cm. arsine was decomposed a t this temperature, the rate of the reaction was plotted against the partial pressure of arsine, and is shown as triangles in Fig. 4. I n this experiment the benzoic acid, used for the vapor-bath, changed its boiling point gradually. The reaction rates were corrected taking the temperature coefficient 'of the reaction rate into consideration. In Fig. 4 we can see that the reaction rate is independent of the partial pressure of hydrogen and is proportional to that of arsine.
0.02 0.04 0.06 0.08 0.10 0.12 0.14 Amount of deposited arsenic (g.), Fig. 1.-The relation between the rate of decomposition of arsine and the amount of deposited arsenic on the antimony film a t 254'. 0
The results of the decomposition of arsine on arsenic surfaces a t 278 and 218" are shown in Fig. 2 and Fig. 3, respectively, plotting the logarithm of
10 20 30 40 50 Pressure of arsine (cm.). Fig. 4.-Dependence of the decomposition rate of arsine upon pressure a t 254'. 0
0
5
15 20 25 30 Time (hr.). Fig. 2.-Decomposition of arsine a t 278'. 10
(6) A . Stock, F. Gomslkq qnd H, Heynemctnn, Eer., 40, 632 (1907).
The temperature coefficient of the reaction is shown by the plot in Fig. 5 . It obeys the Arrhenius equation, from which an apparent activation energy of 23.2 kcal./mole is obtained. Exchange Reactions between Arsine and Deuteroarsine and between Hydrogen and Deuterium on Arsenic Surfaces.-When 31.7 em. of arsine and 24.0 cm. of deuteroarsine were introduced into the reaction vessel to decompose a t 255", a large
THEDECOMPOSITION OF ARSINE
August, 1955
779
Infrared Absorption Spectra of AsH3 and Isotopic Molecules.-It is shown in Fig. 6 (i) and (ii) that AsH3 and AsDa have the following absorptions'
- 1.0
AsHa, cm.-' AsD3, cm.-' -1.5
2060 1490
2120 1531
906 652
2185 1578
1003 716
(2120)9
HowardlO calculated the normal vibration frequencies of AsH3 and tried t o assign the absorption bands of AsH3 to fundamental vibrations. He also calculated the fundamental frequencies in cm. of NH3 and its isotopic molecules. Figure G must be the first observed absorption of the AsH,D, isotopic molecules, where x y = 3 and x # 0 a n d y # 0.
&
-
M
+
-2.0
-2.5 1.8
1.9 2.0 2.1 103. of the decomposition rate upon ternperature.
I/T
Fig. 5.-Dependence
x
amount of hydrogen deuteride was detected in the reaction product. During the reaction the reactants were pumped out to analyze, by infrared absorption analysis, whether any exchange reaction had taken place between arsine and deuteroarsine. The infrared spectra were taken with a Perkin-Elmer, Model 21, infrared spectrometer, using a 10-cm. cell a t gas pressures of about 20 cm. The results are shown in Fig. 6. I n the figure (i) is the absorption spectrum for pure arsine and (ii), that for 98% pure deuteroarsine, and (iii), for the mixture of these two compounds and decomposition products after 65 and 10.5% decomposition, and (iv) was obtained putting approximately equal amounts of arsine and deuteroarsine mixtures in the compensating cell. The infrared spectrum for the products from the reaction vessel was slightly different from that of a mixture which was not subjected to the high temperature of the reaction vessel. 31.9 cm. of arsine was allowed to decompose with 35.2 cm. of deuterium on an arsenic surface at 255" for 24 hours and the decomposition product was analyzed by means of the mass spectrometer. Practically no hydrogen deuteride was found in it. This experiment also shows that the reaction between hydrogen and deuterium on arsenic surfaces does not take place appreciably at this temperature. Areas of the Arsenic and Antimony Surfaces.The surface area of the arsenic in the reaction vessel was measured a t liquid nitrogen temperature by means of krypton adsorption.6 The result was 4.8 X lo3 cm.2, which means the roughness of the surface is approximately 50. The area of the antimony surface before being covered by arsenic was also measured and found to be the same area as that of the arsenic surface, that is, 4.8 X lo3cm.2. (6) R. A. Beebe, J. B. Beckwith and J. M. Honig, J . ilm. Chem. Soc., 67, 1554 (1945).
(ii) AsDa
(iii)
, I , 1,
, I
.
I .
I
,
I
,
I ,
2000 1500 1200 900 800 700 Wave numbers, em.-*. 4 6 8 10 12 14 Wave length, p. Fig. 6.-Infrared spectra of arsine and deuteroarsine: iii (upper) 65% decompn.; iii (lower) 10.5%; iv, 10.5%.
Discussion A first-order rate of decomposition is compatible with a diffusion-controlled process. Because of the long time intervals, up to 350 hours, in which the first-order constant is obtained, calculations of diffusion velocities through any practicable values of the stationary layer indicate that the diffusion process is so fast that it does not affect the over-all rate of reaction. The possible consecutive processes involved in the (7) These absorptions were reported by Lee and WuS as 2122, 2185, 906 and 1005 cni.-l for AsHs, and 1534, 660 and 714 c m - 1 for AsD3. ( 8 ) E. Lee and C. K. Wu, Tranu. Faradag SOC.,86, 1366 (1939). (9) The absorption in the AsDa curve at 2120 cm.-' falls exactly
in the position corresponding to the strong absorption of AsHn, and according to Lee and Wu, this absorption can be considered to be due t o the presence of a small amount of the light compound in the deliteride. (10) J. B. Howard, J . Chem. P l y e . , 8,208 (1935).
780
G. R. F'RET"M.~N AND C. A. WINKLER
VOl. 50
decomposition of an arsine molecule at an arsenic surface include
The calculations suggest also that, a t very low temperatures, a zero-order reaction would result, the arsenic surface being largely covered with AsH(a). AsHs(g) = AsHa(a) (1) The quantitative evaluation of this mechanism and AsH8(a) = AsHz(a) H(-As) (2) that of other hydrides already studied, including AsH2(a) = AsH(a) H(-As) (3) GeH4 and SbH3, will be separately communicated. AsH(a) = As H(a) (4) Acknowledgment.-This work was carried out on 2H(a) = Hdg) (5) a post-doctoral fellowship kindly provided to where reaction (1) is the physical adsorption and Princeton University by the Shell Fellowship Comthe reaction (5) is the desorption of physically ad- mittee of the Shell Companies Foundation, Inc., sorbed hydrogen. Theoretical considerations of New York City. We wish to express our apprecithe total sequences of the reactions lead to a con- ation of this support. The work in question is clusion that either reaction (1) or (2) can be com- also a part of a program of research supported by patible with the experimental results as the rate- the Office of Naval Research N6onr-27018 on Solid determining step of the over-all reaction. Because State Properties and Catalytic Activity. Aclmowlthe physical process of adsorption (1) is in general edgment is made also to this research project for more rapid than the process of chemisorption (2), facilities used and for consultation with workers stage (2) or the chemisorption of arsine is actually in the project, and to Dean Hugh Taylor for rate determining in the experimental region studied. advice and assistance.
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THE REACTION OF ACTIVE NITROGEN WITH METHYLAXIINE' BY G. R. FREEMAN A N D C. A. WINKLER Contribution from the Physical Chemislru Laboratory, McGill University, Monlreal, Caruida Received March Id. 1966
Plctive nitrogen reacted with methylamine to produce hydrogen cyanide, hydrogen and a polymer, with smaller amounts of ammonia and C2 hydrocarbons. The rates of methylamine destruction and hydrogen cyanide production increased with increasing temperature, while polymer formation increased with decreasing temperature. Comparison of the maximum rates of hydrogen cyanide production from methylamine and from ethylene during reaction with active nitrogen indicates that methylamine undergoes both ammonia and hydrocarbon type reactions.
The relative extents of reaction of ammonia and hydroxide solution were cooled to lo", and mixed in a flask, ethylene with active nitrogen2 indicated that a t nitrogen was bubbled through the mixture and the gas stream passed through a condenser cooled with Dry Ice least two reactive species are present in active into a similarly cooled receiver containing potassium hynitrogen. It appeared that ammonia reacted with droxide pellets. About 10% of the recovered methylamine only one of these while ethylene (and presumably was removed by distillation under vacuum and diwarded, and the residue distilled twice, with rejection each time of the other hydrocarbons, e.g., propylene,ja p r ~ p a n e , ~ blast 20% to remove traces of water. Infrared analyses? b ~ t a n e ,etc.) ~ reacted with the other or both. of the final distillate showed that it contained 98.7% Since methylamine might be expected to undergo methylamine and 1.3% ammonia The amount of methylamine passed into the reaction both ammonia and hydrocarbon type reactions, it vessel was estimated from the change in pressure in a storage was obviously of interest to examine the reaction vessel of known volume. Condensable products of the of active nitrogen with this compound. reaction were collected in a trap containing 10 ml. of standard sulfuric acid, immersed in liquid nitrogen, and their Experimental base content determined by titration to methyl red endThe apparatus used was essentially the same as that described in earlier papers.686 The molecular nitrogen flow rate was 9.2 X 1 0 - 6 mole/ sec., corresponding to a pressure of 1.43mm. in the reaction vessel. In several experiments, the reaction vessel was surrounded by powdered Dry Ice. While the wall temperature may be assumed to have been approximately -78", the temperature of the gases in the reaction vessel, as indicated by a glass encased thermocouple, was about -5' during the active nitrogen-methylamine reaction. To obtain methylamine, equal volumes of 25% methylamine solution (C.P.Fisher Scientific Co.) and 50% sodium
(1) Financial assistance froin the National Rewarch Council of Canada. (2) G. R . Freeman and C. A. Winkler, THISJOURNAL,59, 371 (1955). (3) (a) G. S. Triok and C. A. Winkler, Can. J . Chem., SO, 915 (1952); (b) I?.Onyszchuk, L. Breitman and C. A. Winkler, ibid., 32, 351 (1954). (4) R. A. Back and C. A. Winkler, ibid., 32, 718 (1954). (6) J. H. Creenblatt and C. A. Winkler, Can. J . Rea., B87, 721 (1949). (6) H. Blades and C. A. Winkler, Can. J . Ch~m.,49, 1022 (1951).
point of the excess acid after it had been allowed to melt in the trap. The presence of hydrogen cyanide did not affect the titration. Ammonia was determined by infrared analysis. The condensable reaction products were collected in an evacuated bulb immersed in liquid nitrogen, then distilled into an evacuated 10 cm. absorption cell. The wave numbers of the absorption peaks used were 968 cm.-* for ammonia and 2930 crn.-l for methylamine. The hydrogen cyanide content of the condensable products was determined by the Liebig DBnighs method.B In some experiments, these products were also analyzed for cyanogen. To do this, condensable products were collected in a trap containing 20 ml. of 0.5 N silver nitrate solution and 0.5 ml. of 6 N nitric acid, immersed in liquid nitrogen. The cyanogen was flushed out of the melted solution with nitrogen (1 hr.), and the cyanogen removed from the nitrogen stream by bubbling it through potassium hydroxide (7) We are indebted to the Central Research Laboratory, Canadian Xndustries (1954) Ltd., McMasterville, Que., and to Ayerst McKenna and Harrison, Ltd., Montreal, Que., for the infrared analyses reported in this paper. (8) I. M. Kolthoff and E. B. Sandell, "Textbook of Quantitative Inorganic Analysis," The Macmillan Co., New York, N. Y., 1946.
