Hydrocarbons liquid-phase radiolysis

Comparison of the results of vapor- and liquid-phase radiolysis shows that the yields of all products from each hydrocarbon are markedly greater in the vapor phase. As in the liquid phase, polymer is the predominant product, accounting for 83-96% of the hydrocarbon consumed. The 100-e.v. yields (G values) of polymer increase with alkyl substitution from 6 for benzene to 8.7 for ethylbenzene the yield in each case is about five to six times that observed in the liquid phase. 

Horvath, Zs. Ausloos, P Foldiak, G. Comparison between liquid phase photolysis and radiolysis of C3—C4 hydrocarbons mixtures. In Proceedings Fouth Tihany S5unposium on Radiation Chemistry Hedvig, P. Schiller, R., Eds. Akademiai Kiado Budapest, 1977 57 pp. Antonova, E.A. Pichuzhkin, V.I. High Energy Chem. 1977, 11, 201. 

This paper describes a study of the gas-phase x-radiolysis of pure perfluorocyclobutane, including the effects of added N20 and 02 on the reaction. Mixtures of methane and F-cyclobutane were also examined over a broad composition range. The latter experiments were intended to shed light on the radiolysis mechanism of pure perfluorocyclobutane as well as to provide information on the radiolytic behavior of gas-phase fluorocarbon-hydrocarbon mixtures. Related studies on liquid phase mixtures of cyclohexane and F-cyclohexane are currently in progress in this laboratory. 

Tr he stability of aromatic hydrocarbons to radiation has been cited so frequently in the literature that it has come to be accepted (5, 6) as a characteristic of aromaticity, a consequence of electron delocalization. These conclusions are based on the results of irradiations in the liquid phase. That they may not apply to the isolated aromatic molecule, however, is suggested by the few reported studies of the radiolysis of aromatic hydrocarbons in the vapor phase. Such studies have thus far been limited to two compounds—benzene (8, 10, 11) and isopropylbenzene (cumene) (9), and differences in the character of the radiation or the conditions of irradiation preclude a simple assessment of the effect of phase on these systems. 

To provide further information on this point, we have investigated the y-radiolysis of benzene, toluene, ethylbenzene, and the xylenes in the vapor phase and have determined yields of the gaseous products, 4 polymer, and some products of intermediate volatility. These results are compared with those of parallel irradiations of liquid toluene and o-xylene and with published (2, 12) data for the other hydrocarbons in the liquid phase. 

The results clearly demonstrate that aromatic hydrocarbons are markedly less resistant to radiation in the vapor phase than in the liquid G values for their disappearance in the vapor phase (6.3 to 10) are, in fact, not much smaller than those of comparable saturated hydrocarbons. In aromatic liquids neutralization of the ions produced by radiolysis is rapid the excited states, produced either directly or by ion recombination, degrade mostly to the parent hydrocarbon (6). Those chemical reactions which excited species, or radicals derived from them, undergo in the liquid phase should also occur in the vapor and might be enhanced by... 

TJeactions of specific hydrocarbon ions in the liquid phase are difficult to study directly. Ions may be produced in the liquid by direct liquid radiolysis, but the situation is complicated because many other reactive species such as electrons, radicals, and excited states are produced simultaneously. This complex situation may be simplified by producing specific ions in the vapor phase and injecting them by means of an electric field into a liquid or solid matrix. Under such conditions the positive ion is separated from its concomitant electron and is accelerated into the liquid or solid alone. We call this the ion injection method. It shows considerable promise for studying specific ion-molecule reactions in the liquid phase and should allow new types of studies on positive ion trapping in inert matrices to be made. 

Photoionization of the hydrocarbon followed by dissociative electron attachment (Reaction 1) should be considered since the ionization potential of a molecule is less in the liquid phase than it is in the gas phase. For hydrocarbons the ionization potential is 1 to 1.5 e.v. less in the liquid phase (24). The photon energy at 1470 A. is about 1.4 e.v. below the gas-phase ionization potentials of cyclohexane and 2,2,4-trimethylpentane (14). Some ionization may therefore occur, but the efficiency of this process is expected to be low. Photoionization is eliminated as a source of N2 for the following reasons. (1) If photoionization occurred and the electron reacted with nitrous oxide, then O" would be formed. It has been shown in the radiolysis of cyclohexane-nitrous oxide solutions that subsequent reactions of O result in the formation of cyclohexene and dicyclohexyl (I, 16, 17) and very little cyclohexanol (16, Table III). In the photolysis nitrous oxide reduces the yield of cyclohexene and does not affect the yield of dicyclohexyl. This indicates that O is not formed in the photolysis, and consequently N2 does not result from electron capture. (2) A further argument against photoionization is that cyclohexane and 2,2,4-trimethylpentane have comparable gas-phase ionization potentials but exhibit quite different behavior with respect to N2 formation. 

Characterizing the mechanism of the action of amines, the overwhelming majority of tiie authors believe that their basic role reduces to the termination of kinetic oxidation chains on account of reaction (3). Actually, stable radicals (CjH5)2NO have been detected by the method of electron paramagnetic resonance as a result of the interaction with peroxide radicals, formed in the liquid-phase oxidation of a hydrocarbon inhibited with diphenylamine [30]. The interaction of certain secondary amines (Ar2NH) with peroxide radicals, prepared by oxidative radiolysis. 

In liquid hydrocarbon radiolysis, analogies are frequently drawn from gas-phase studies, particularly in regard to ionic processes. We... 

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