2725
NOTES
been calculated and are compared in Table I11 with the experimental values4 and the values for water. It is seen that the theory correctly predicts the decrease which is observed experimentally on going from water to benzene. Acknowledgments. The author wishes to thank Dr. Y. Marcus for valuable discussions and Mrs. X, Bauman for technical help.
Mass Spectrometric Study of the Production
carbon ions prevented investigation of the rate of production of WCN. The presence of these molecular ions suggests the occurrence of the reaction
CHBNNCHB + CHsNH2
+ HCN
(1)
The rate of reaction 1 was shown to be dependent upon the surface to volunie ratio of the reactor. Table I presents the data for the deterniiiiation of the rate of this heterogeneous production of nzethylaiziine from azomethane at a surface to volume ratio of 5.7 cni.--I. An activation energy of 10.6 += 0.2 kcal. is obtained by a least-squares fit of a first-order treatment of these data.
of Methylamine from Azomethane'
by Morton E. Wacks
Table I : The Temperature Dependence of the Rate of Production of Methylamine from Azornethane
National Bureau of Standards, Washington, D.C. sOs84 (Receiaed A p r i l 6 , 1964)
Fhile following the thermal decomposition of azomethane in a flow system with a mass spectrometer an ion a t m/e = 31 was noted. This ion was identified as the methylamine molecular ion. The ion appeared when a mixtuire of helium and azomethane was passed through a heated flow reactor used in conjunction with a time-of-fligh t mass spectrometer. This flow system and reactor, similar to that described by Herren,% was constructed for the purpose of studying the thermal production and reactions of organic radicals with a time-oi-flight mass spectrometer. The pinhole in the fast reaction chamber of the mass spectrometer was replaced with a quartz cone which extended 2 mni. into the heated quartz flow reacbor. The sampling leak in the quartz cone was 125 p in diameter and 2 cm. from the ionizing electron beam of the mass spectrometer. The flow rea,ctor was a 20-cm. long quartz tube of 0.7-cm. i.d. This was heated by a multitapped heater capable of attaining uniform reactor tenipertttures in excess of 750". The temperature profile was adjusted to keep variations a t less than = k 2 O over a 15-cni. length of the reactor. The production of this ion at mle = 31 was found to b-e linearly dopendent upon the partial pressure of azomethane for a tenfold variation with some slight deerease from linearity observed at partial pressures of azoniethane above 10 1.1. The production of this ion was also observed to increase with increasing temperature. The ion was identified by ionization efficiency studies and mws spectral data as being the C€LNH,+ ion produced from ionization of methylamine. A mass peak at m / e = 27 corresponding to the HCNf ion from HCX was also observed. Interference from hydro-
632.8 632.8 632.8 632.8 654,5
654.5 697.3 697.3 697,3 754.8 754.8
1 44 1 23 2 53 2 64 0 57 0 97 2 95
1 05 3 67 1 78 1 78
1 25 1 25 1 25 1 25 1 20 1 25 1 25 1 20 1 20 1 20 1 20
0 13 0 12 0 23 0 24 0 07 0 12 0 52 0 18 0 63 0 48 0 49
30 9 30 9 30 30 29 29 28 27 27 25 25
3 10
7 7
3 15 3 14 3 04 4 45 4 20 6 89 6 89 6 77
5 5
11 95 12 28
9 9
5 5 3
Methylamine has not been found as a product of the homogeneous thermal decomposition of azomethane.3 The production of azoniethane during the gas phase photolysis of inethylainine has been r e p ~ r t e d . ~ However, Eiiiinett and Harkness5 concluded, on the basis of vapor pressure measuremeiits, that methylamine was an intermediate in the catalytic decomposition of azoinethane. Furthermore, the other products of the initial rapid decomposition step were H2, Fe4N, and C when the catalyst was a doubly promoted synthetic amnionia catalyst. The final products of this catalytic decomposition included S Hs from the decomposition of the methylamine intermetliate. Only small amounts of ethane and nitrogen were found. (1) This research was supported in part by TX'ADD. (2) J. T. Herron, J . Res. Satl. Bur. Std., 65A, 411 (1961). (3) 4 bibliography of earlier studies of the t,hermal decomposition of aeomethane can be found in the paper by W. Forst and 0. K . Rice, Can. J . Chem., 41, 562 (1963). (4) J. V. Michael and W.A. Noyes, Jr., J . Am. Chem. Soc., 85, 1228 (1963). ( 5 ) P. H. Emmett and R. W. Harkness, ibid., 54, 538 (1932).
Volume 68, Number 9
September, 1964
SOTES
2726
Henkin and Taylor6 found methylamine as a product in the high teniperature reaction of azomethane with atomic hydrogen. They estimated an energy of activation of 8 kcal. for the production of methylamine by the intermediate reaction CH3NH-NHCH3
+ H --+ CHsSH2
+ CH3NH
(2)
A scheme for reaction 1 consistent with the above is as follows: (a) surface adsorption of azomethane giving an intermediate similar to dimethylhydrazine, (b) intramolecular hydrogen rearrangement and breaking of the N-X bond, (c) desorption of products. Azomethane exists in the trans form’ and therefore step a probably proceeds by adsorption at one nitrogen atom followed by isonierizatioii and adsorption a t the other nitrogen atom. Aroniatic cis-trans isonierizations in azo compounds have been reported8; however, inforniation is lacking for the aliphatic compounds. Hutton and Steelgrecently reported the production and isolation of the cis form of azomethane in solution. The energy for this isomerization is not reported. It is probably in the 2-5 kcal. range on the basis of available data for N2F2.’0 The sorption energies for azomethane, methylamine, and hydrocyanic acid on quartz or carbonized quartz are not known. The surface behavior of “3 and CH3NH2 has been shown to be almost identical” while the available iiiforniation on S H 3 indicates that the sorption energies are a strong function of the surface coverage, varying from 5 to 20 k ~ a 1 . ~ ~ , ~ ~ There are several choices available for the rate-deterniining step of reaction 1. On the basis of the above discussions, the work of Henkin and Taylor (reaction 2), and the fact that azomethane is known to isomerize in basic solution to fornialdehyde methylhydrazone (CH2=K-NHCH3)g it is felt that step b is rate-deterniining and that the activation energy of 10.6 0.2 kcal. is associated with this step. The over-all rate determining reaction perhaps follows the path shown in reaction 3 H CH3-K-X-CH3
I 1 s* s*
I I I s* s*
+ H2C=N-N-CH3
H HCGS
l s* The Journal of Physical Chemistry
X-CH3
i s*
(6) H. Henkin and H. A. Taylor, J . Chem. Phys., 8, 1 (1940). (7) G. Hersberg, “Infrared and Raman Spectra,” D. Tan Kostrand Co., Inc., Princeton, K. J., 1945, p. 357. (8) E. Fischer, J . Am. Chem. Soc., 82, 3249 (1960). (9) R . Hutton and C. Steel, ibid., 86, 745 (1964). (10) G. T. Armstrong and S. Rlarantr, J . Chem. Phys., 38, 169 (1963). (11) S. T’oltr and S. Weller, J . P h y s . Chem., 62, 574 (1958). (12) J. Bastick, Compt. rend., 247, 203 (1958). (13) A. Clark, V. C. F. Holm, and D. M.Blackburn, J . Catalysis, 1, 244 (1962).
Diffusion of Sodium-22 in Molten Sodium Nitrate at Constant Volume
by 11. K. Nagarajan, L. Nanis, and J. O’M. Bockris Electrochemistry Laboratory, University of Pennsyleania, Philadelphia, Pennsylvania 19104 (Received April IO, 1954)
According to a hole theory of liquids, the total enthalpy of activation for diffusion, AHtot*,consists of two terms1n2:the energy required to form a hole in the liquid, AH,,*, and the energy of activation needed for the particle to jump into an adjacent hole, AH,”. At constant volume, the total number of holes in 1 mole of liquid remains constant over the temperature range considered so that AHj* = -R(b In DldllT).. Hence, the energy of hole formation is AH,,* = AH^,$* - AH,*
(3)
=
b In D
b In D
On the basis of data8 for the viscosity of normal liquids a t constant volume, Bockris, et u Z . , ~ concluded that the predominant term in AHtot* is the energy to forin a hole, i.e., AH,,* and that AH,* contributes very little (-loyo) to the total enthalpy of activation for transport. A microjump model5 of transport considers the essential step in transport to be jumps each of length much smaller than the interparticle distance and hcnce (1) A (2) J Chem (3) A
H
\/
S* represents the active adsorption site on the quartz surface, probably an Si-0-H group.
Bondi, J Chem P h y s , 14, 591 (1946) O ’ M Bockris, S Yoshikawa, and 9 R Richards. J P h y s 68 1838 (1964) Jobling and A S C Lai+rence, Proc R o y Soc (London), A206, 267 (1951) (4) J 0’11 Bockris, E H Crook, H Bloom, and N E Richards, zhad, A255, 558 (1960) ( 5 ) R A Swalin, Acta M e t , 7, 736 (1959)
