Vol. 59
REMITAMARTT
THE THERMAL DECOMPOSITION OF STIBINE BY I ~ E NTARL4RU ZI F~ickChemical Laboratory, Princeton University, Princeton, A'. J Received May 80, 1966
The decomposit,ion of stibine has been studied by a static method. The decomposition was dependent only upon the partial pressure of stibine, being independent of the partial pressure of hydrogen. The order of the i'eaction W:LR 0.75 at 10" and increased as the reaction temperature became higher, until it became unity at 45'. The actmivationciiei'gy of the reaction was 8.8 kcnl./mole a t 40 cin. stibine pressure decreasing as t,he pressure became lower. The Langniuir rspression is applicable to the result,a, but the calculated constants in theespression have no meaning, as in the case of Stock's results. Stibine decomposition in deuteriuni at 25 did not produce any hydrogen tleuteride, which showed that no exc,hange reaction between hydrogen and deuterium took place on the aiitiniony surface, while the decomposition of the stibine and deuterostibine mixture produced a large amount of hydrogen deuteride. The possibility of capillary condensation of stibine on the ant,imony film has been examined and shown t o be possible under the experimental conditions. The rate-determining step of t,lie over-:dl reaction has been briefly discussed. O
As reported in a series of papers, I tlie decomposition of arsine on arsenic surfaces is a first-order reaction in respect to arsine, while the germane decomposition on germanium surface is zero order. ItJwas suggested that the rat.e-determining step is the chemisorption of arsine in the former case, while in the latter case, it is the desorption of chemisorbed hydrogen from the germanium surface. A s an example of another hydride decomposition, the decomposition of stiliine has been studied. This decomposition was already studied by Stoclc and his collaborators.* They found that the order of the reaction a t 2Fj0 was 0.G in respect t o stibine, and that hydrogen had no effect upon the reactioii rate. Those who have analyzed their data34 explained these facts on the basis of the unimolecular decomposition of stibine in the adsorbed stat'e. Recently, however, it was founds that the data could not be explained on the basis of the Langmuir concept, as the calculatecl constants of the Langmuir expression have no physical meaning. Experimental Preparation of Stibine.-Stibine was prepared by adding antimony trichloride powder to a solution of lithium aluminum hydride in ethylene glycol dimethyl ether in dry nitrogen. As this reaction wax fairly violent, the solution of lithium aluminum hydride was cooled with liquid nit,rogen when the antimony trichloride was added, and after the chloride addition the liquid nitrogen was removed to allow the solution to warm up gradually. The stibine was evolved before the reaction vessel reached room temperature and was condensed in a liquid nitrogen trap. After purification by distilling several times using liquid nitrogen and solid carbon dioxide, the stibine was stored in a liquid nitrogen trap. For the preparation of deuterostibine, lithium aluminum deuteride was used instead of hydride. Apparatus and Procedure.-The experiment was carried out i n a static system. Three pear-shaped Pyrex reaction vessels (A, B and C) attached to mercury manometers by means of capillary tubing were used. Each of the vessels was about G7 cc. in volume. Before the stibine was intro59. (1) (a) K. Tamaru. RI. Boudart and H. Taylor, THISJOURNAL, 801 (1955); (b) P. Fensham, Iothe real situation. In our experiment8s, as mentioned above, t3he Laiigmuir rate equation 2 , though it fits escellent>ly, has the same difficulty, having large bo and a small value of q. The statistical mechanical calculation of tJhe rates of the elementary steps of the decomposition suggest,s, as will be shown iii detail in a later re-
1088
RUSSELL S.HOLLAND AND CHARLES P. SMYTH
port, that, a t higher temperature, the rate-determining step of the over-all reaction is the chemisorption of stibine on the antimony surface, which is first order, but, as the temperature becomes lower, or a t room temperature, the desorption rate of the chemisorbed hydrogen from the antimony surface, having larger activation energy than the chemisorption, becomes slow enough t o be comparable with the chemisorption rate, and the order of the reaction begins to decrease from unity. If the reaction temperature is extremely low, the desorption rate will become rate-determining, and the overall process should be zero order. The experimental region studied corresponds consequently to the transition between the two kinds of rate-determining steps. If this is the case, stibine adsorption on the an-
VOl. 50
timony surface is not in equilibrium a t room temperature during the decomposition as was assumed in expression (2), and it is quite natural, therefore, that the Langmuir expression has no physical meaning in this case. Acknowledgments.-The author wishes to express his thanks to Professor John Turkevich who was kind enough to analyze the samples with his mass-spectrometer. The preceding work was carried out with the assistance of a post-doctoral fellowship kindly provided by the Shell Fellowship Committee of the Shell Companies Foundation, Inc. It also forms part of a program on Solid State Properties and Catalytic Activity supported by the Office of Naval Research N6 onr-27018. For this support we wish to express our appreciation and thanks.
MICROWAVE ADSORPTION AND MOLECULAR STRUCTURE I N LIQUIDS. X. THE RELAXATION TIMES OF NINE HETEROCYCLIC RIOLECULES1i2 BY
RUSSELL 8. HOLLAND3 AND CHARLESP. SMYTH
Contribution from the Frick Chemical Laboratory, Princeton University, Princeton, N .
J.
Received Moa, 8 0 , la66
Measurements of dielectric constant and loss a t wave lengths of 1.21, 3.22, 10.7 and 33.3 em. and 577 m. haye been carried out a t temperatures from 1 to 60" upon pyridine, ?-picoline, pyrrole, pyrrolidine, quinoline, isoquinoline, thiophene, tetrahydrofuran and furan in the pure liquid state and upon dilute solutions of pyridine in heptane. The critical wave lengths and molecular relaxation times calculated from these results, together with the results in the literature for toluene, are shown, with one exception, to be consistent with the molecular sizes and shapes and the viscosities of the liquids. The Debye relationship between molecular relaxation time, molecular radius and liquid viscosity is shown to apply satisEactori1.v to the closely related molecules of pyridine, ?-picoline and toluene, in contrast to its failure for dilute solutions when measured viscosities are used. The relation of the molecular relaxation times calculated for these three liquids to the molecular sizes and shapes indicates that the effect of internal field upon the molecular relaxation time obtained by Powles and by O'Dwyer and Sack as a first order approximation is more nearly correct than the Debye relationship or the supposedly mora exact second order approximation of O'Dwyer and Sack.
The program of investigation carried out in this Laboratory upon the relation between dielectric relaxation and molecular structure has encompassed a variety of comparatively simple polar organic r n o l e c ~ l e s , ~most - ~ ~ of which are more or less flexible or nearly spherical. Nine heterocyclic compounds, all but two of which are aromatic in character, have been selected in the present work to demonstrate the behavior of rigid molecules. Five of the compounds have fivemembered rings, two have six-membered rings, (1) This research has been supported in part by the Office of Naval Research. Reproduction, translation, publication, use or disposal in whole or in part b y or for the United States Government is permitted. (2) This paper represents a part of the work submitted by Mr. R. 8. Holland t o the Graduate School of Princeton University in partial fulfillment of the requirements for the degree of Doctor of Philosophy. (3) Procter and Gamble Fellow in Chemistry, 1953-1954. (4) W. M. Heston, Jr., E. J. Hennelly and C. P. Smyth, J. A m . Chem. Soc., 70,4093 (1948). ( 5 ) H. L. Laquer and C. P. Smyth, ibid., 70,4097 (1948). (6) E. J. Hennelly, W. M. Heston, Jr., and C. P. Smyth, ibid., 7 0 , 4102 (1948). (7) W. M. Heston, Jr., A. D. Franklin, E. J. Hennelly and C. P. Smyth, ibid., 74,3443 (1950). (8)A. D. Franklin, W. M. Heston, Jr., E. J. Hennelly and C. P. Smyth. i b i d . , 72,3447 (1950). (9) A. J . Curtis, P. L. McGeer, G. B. Ratlimann and C. P. Stnyth, ibid., 74,644 (1952). (10) F. H. Branin, Jr., and C. P. Smyth, J. C'hem. Phye., 20, 1121 (1952).
and two are a fused riiig system of two six-memhered rings. All 11nve been measured as p1.m liquids, and, in addition, pyridine has been 111vestigated as a polar solute in heptane solution. Purification of Materials.--n-Heptane from the PhilJips Petroleum Co. was used as solvent without purification. The pyridine used was "spectro grade" from the Eastman Kodak Company and the ypicoline and tetrahydrofuran were from Brothers Chemical Company, while the other six compounds were from Matheson, Coleman and Bell, Inc. The pyridine was refluxed for 48 hours over barium oxide and fractionated. The quinoline and isoquinoline were refluxed for 48 hours over barium oxide and fractionated a t reduced pressure. The pyrrole, thiophene, r-picoliile, tetrahydrofuran, pyrrolidine and furan were fractionally distilled, t,he two latter substances immediately before use. Boiling points or melting points and refractive indices found for the sodium-o line are tabulated below for comparison with the literature values. Substance ?+Heptane Pyridine Pyrrole Pyrrolidine Furan Thiophene Quinoline
B.p.,
OC.
114.4-114.7 84.3 (756 mm.) 31 83.5-83.8 M.p. - 19-20
y-Picoline 143,8 (752 iiitu.) Tetra hydrofuran 64,545
Lit. h.p., OC.
115.3 129.7 88.5 31-32 84.1 R3.g. -19.5 143.I G5-GG
?LZ0D
1.3881 1.5096 1,5097 1.4385 1.4222 1.5281 1.6202 (24.9') 1.503'3
Lit. n%
1.3878 1.5096 1.5035 1.4431 1.4216 1.5285 1,6245 (24.9') 1 ,5029
