1574
NOTES
the transition of the cyclic sulfides could also be a segregated transition of their C-S-C group. The segregated N + V transition is not exclusive with the C-e-C group; it also appeared in the oxygen nnalogs of the sulfides. The first absorption of vinyl etherll or of furan,l2in the vapor phase, occurs around 49,200 em-'. Such an excitation energy is too high for a s-cis-dienic structure;8 it might therefore be related to a transition of the system of n-electrons of the C-0-C group which is common to both the open and the cyclic molecule. The delocalized orbitals of this quadruplet remain strictly localized within the C-0-C group; they never mix with the n-orbitals of the other ethylenic groups of the molecule, because neither vinyl ether nor furan has a transition that may be related to a sextet. The segregation of the quadruplet of the C-X-C group5 could depend on the intensity of the electrophilic character of the heteroatom, because the localization of the quadruplet is the rule with the highly electrophilic oxygen atom. The localization would ocrur with the sulfur atom only when the n-electrophilic character of the heteroatom is increased above its normal level. This increase could result from the excitation of the sulfur atom. Experimental All the substances were distilled under nitrogen through a 50-plate all-glass Podbielniak column until spectroscopically pure. The ultraviolet spectral absorptions nTere determined with a Ueckmm DK-1 quartz recording spectrometer; all the values were obtained in hexane solution, unless otherwise specified. &ButylVinyl Sulfide.-This substance was prepared in 45% yield by the dehydrohalogenation of t-butyl 2-chloroethyl sulfide's with a boiling solution of sodium hydroxide in 2methoxyethanol, the product of the reaction being removed continuously: b. p. (cor.) 116.5" (760 mm.), n% 1.4610. d2340.832, Amax 234 mw ( E 4,500) and 250 mp ( E 4,700). Anal. C a l d . for CsH12S: C, 62.00; H, 10.41; S, 27.59. Found: C, 62.61; H, 10.45; S,27.08. (11) A J. Harrison, et al., J . Chem. Phys., 18, 221 (1950): 30, 357 (1959) (12) L.W. Piclcett, h'. J. Hoeflichand T. C. Liu, J . A m . Chem. Soc., 75, 4865 :1951). (13) T. P. Davson, ibid., 69, 1211 (1947).
1'01. 64
ethylene platinous chloride and tetradeuterioethylene in several solvents at temperatures between -15 to looo, under a range of partial pressures of ethylenes. Since it necessary to determine the conditions under which the reactions would be homogeneous, me also have investigated the thermal decomposition of this complex, as well as the hydrolysis in 4y0 aqueous hydrochloric acid in the presence of ethylene. Experimental The solvents used were chloroform, acetone, toluene and 4% aqueous hydrochloric acid. The first three were middle fractions obtained by fractional distillation of C . P . reagents. Anhydrous toluene was prepared by shaking with metallic sodium in an all-Pyrex vessel for 15-17 hours at 100'; after thorough removal of hydrogen, a known amount of the solvent was transferred by distillation to a reaction vessel containing a known amount of complex. The aqueous HC1 was prepared by the addition of the required amount of the 38% acid to COz-free distilled water. Very pure ethylene platinous chloride, [Pt(CzHd)C12]2,was prepared by the method of Chatt and Searle,a as modified by Joy and O r ~ h i n . ~The . ethylene was Matheson C.P. grade. The tetradeuterioethylene was obtained from Tracerlab, and contained 95.17, C2D4,3.5% CzHDs and 1.4% C2H3D. 811 reactions were carried out in Pyres vessels provided with break-off seals and appropriate inlet tubes which were sealed with a torch after introduction of known amounts of reagents. All transfer operations were carried out in conventional Pyrex high-vacuum equipment. The vessels, containing known amounts of reagents were vigorously shaken in a constant temperature bath. Analyses of gaseous products were made with a model 21-103 Consolidated Electrodynamics Corp. mass spectrometer. Free platinum in the residues was detected by X-ray diffraction techniques. The thermal decomposition of the complex was studied in constant volume systems and also a t low pressure in allPyrex apparatus. In the experiment at low pressure, gaseous products were continually removed by freezing in liquid nitrogen. In one constant volume system, the reaction was studied in an apparatus similar to that described by Booth and Halbedel,6 so that the rate of pressure rise with temperature could be observed.
Results and Discussion A. Stability of Complex.-It was found that the
solid complex is fairly stable below about 130°, but decomposes rapidly and irreversibly a t temperatures above 160". The estimated half-lives at 130 and 172" were 4.5 days and 1.7 hours, respectively. The gaseous products in experiments STABILLTY AND CATALYTIC ACTIVITY carried out at constant volume and nearly atmosOF PLATINUM ETHYLENE CHLORIDE pheric pressure, contained 40-50% ethylene and a mixture of chlorinated products, among which BY A. ,3. Gow, JR.,AND HEINZHEINEMANN were CH2=CHC1, 1,2-C2H4Cl2, C2HaC1, 1 , l The M . W . Kellogg Co. Research & Development Department, CzH4C12and HC1, in decreasing order of concenJersey Czty 9, N . J . tration. The residues consisted of free platinum Received February 86, 1960 and platinous chloride. In the experiment carried Evidence for the low-temperature homogeneous, out at low pressure at 180", the gaseous product liquid phase hydrogenation of ethylene in acetone contained over 98% ethylene, and the residue conand toluene solutions of ethylene platinous chloride sisted almost entirely of platinous chloride. These has been reported by Flynn and Hulburt.' This experiments clearly shorn that the primary thermal suggested that the ethylene in this complex might decomposition reaction results in the formation of react in the same manner as ethylene adsorbed on ethylene and platinous chloride, and that subseplatinum and other metals, and be capable of ex- quent reactions result in the formation of free changing its hydrogens with tetradeuterioethylene, platinum and chlorinated hydrocarbons. as in the heterogeneous exchange between CzH4 Hydrolysis of this complex in 4-qlG aqueous hyand C2D4 on nickel-kieselguhr, reported by drochloric acid in the presence of ethylene was Douglas and Rabinovitch. We have, therefore, (3) J. Chatt and M. L. Rearlo, "Inorganic Syntheses," Vol V, M c studied the homogeneous H-D exchange between Graw-Hill Book Co., I n c , New York, N. T..1957, pp. 210-215. (1) J. E.Flyn.2 and H. M. Hulburt, J . A m . Chem. Soc., 76, 3393 (4) J. R. Joy and M. Orchin, private communication. (1954). (2) J. E. Douglas and 8.S. Rabinovitch, ibid., 74, 2186 (1952).
( 5 ) H. (1946).
S. Booth and H. S. Halbedel, J. Am. Chem. S o r , 68, 2652
NOTES
Oct., 1960 incipient after 1 hour a t looo, and led to the formation of appreciable quantities of free platinum, carbon dioxide and ethane and smaller amounts of methane. The dilute solutions used made analysis of the aqueous phase impractical, and it was not possible to determine the reactions which had occurred. Since the presence of carbon dioxide and saturated hydrocarbons among the products has not been reported in previous investigatioiis6.7 of the hydrolysis of this complex, it would be of interest to study the reaction in more concentrated solutions, so that an analysis of the aqueous phase could be made. With these data, the nature of these reactions could be better understood. B. H-D Exchange.-No H-D exchange was observed under the conditions Reaction temp., O C . Reaction time, hr. Solvent Chloroform 4% HCl 4% HC1 Acetone Toluene Toluene Toluene
24 2'7 100
- 15 - 8 20 50
0.25 17 1 1 28 36 12
1375
panied by exchange and raises the question whether there is a major difference between the system as used in our experiments and in their work. In all of the experiments, replacement of complexed ethylene by tetradeuterioethylene had essentially reached equilibrium within 15 minutes, indicating that mass transfer between phases was not rate-controlling. We believe that studies of the H-D exchange between C2H4 and CzDl on platinum at temperatures below 50" and the homogeneous deuteration of ethylene in solutions of ethylene platinous chloride may furnish the necessary data to enable one to draw conclusions concerning the similarity of the chemical behavior of ethylene complexed with platinum salts with that of ethylene adsorbed on platinum. DIFFUSION OF METHYL RADICALS I N T H E GAS-PHASE PHOTOLYSIS OF AZOMETHANE' BY SIDNEYTOBY School of Chemistry, Rutgers, the State Univei situ, New Brunswick,
N . J.
Received February $7, 1060
Solid phases were present in the experiment in acetone and that in toluene a t 20". I n the former, we believe that the solid phase consisted of a 2 and trans-Pt(C2H4)zClz; mixture of [Pt(C2H4)C12] in the latter, the white solid phase was believed to be the cis-form of Pt(C2H&Cl2, as described by Chatt and Wilkins.8 The partial pressure of ethylene in the experiment in acetone at -8" was approximately 600 mm., while that in the experiment in toluene at 20" was approximately 900 mm. According to Chatt and Wilkins,* the dissociation pressure of the trans-form of the diolefin complex is approximately 1 atmosphere a t -6". These data make the presence of this species in both experiments probable. In addition, the bright canary yellow color of both solutions, characteristic of the trans-form of the diolefin complex, substantiates this belief. In toluene a t loo", a suspended phase always appeared after 15 min., and H-D exchange was incipient at the end of 2 hours, and approximately 60y0 complete after 17 hours. This suspended phase was invisible to the naked eye and could only be detected by means of the Tyndall effect. X-Ray diffraction indicated the presence of free platinum in the residues obtained after all gases and solvents were removed at the end of these experiments. Since the initial C2H4/CzD4 ratio was nearly unity in these experiments, the greater proportion of C2H4and C2HSD in the recovered ethylenes indicated that the solvent was involved in the H-D exchange, which apparently took place heterogeneously on the platinum. This observation is of considerable interest, as it would indicate that the homogeneous hydrogenation of ethylene reported by Flynn and Hulburtl was not accom1 6 ) J. S. Anderson, J. Chem. Soc., 971 (1934). (7) J. R. Joy and M. Orchin, Unpublished Thesis, University of Cincinnati, Cincinnati, Ohio. 18) J. Chatt and R. G. Wilkins, J . Chem. Soc., 2622 (1952).
Some years ago Hill2 performed some calculations on the difficult subject of radical diffusion. Taking acetone vapor as his model, he considered the effect of a photolyzing beam concentric with, but of smaller diameter than, a cylindrical photolysis cell. Attempts by Nicholsona to use Hill's results to explain the drrhenius curvature encountered below about 80" in the gas-phase photolysis of acetone met with little success. The situation has been reviewed by no ye^.^ drrhenius curvature also is encountered in the gas-phase photolysis of azomethane.6 The system is simpler than the acetone photolysis because the CH3N2- radical is too shortlived to react (unlike the corresponding acetyl radical) and because the Arrhenius curvature occurs below - lo", when more than 99% of the methyl radicals dimerize rather than abstract from azomethane. Some experiments in which a reduced light beam was used5 afforded the opportunity of testing Hill's expression for the mean radical diffusion distance. The photolysis of azomethane (a) may be represented by
+ hv +2CH3 + Nz (0) 2CH3 +CzH6 (1) CH, + B +CII, + -CHzN2CH$ (2) CH3 $- A-wall + CH4 + -CH2XzCH3 (3) CH3 + A +CH3A(4) A
together with reactions involving higher substituted hydrazines6 which may be neglected for present purposes. The mean square CHX diffusion distance, X2, (1) This vork was supuorted in part by a Cottrell Grant from t h e Research Corporation. (2) T. L. Hill, J . Chem. Phys., 17, 1125 (1949). (3) A. J. C. Nicholson, J. A m . Chem. Soc., 7 3 , 3981 (1951). (4) W. A. Noyes. Jr., THISJOURNAL,65, 925 (1951). ( 5 ) S. Toby, J . A m . Chem. Soc., 82, 3822 (1960). (6) M. H. Jones and E. W. R. Steacie, J . Chem. Phys., Zl, 1018 ( 1953).
