Gamma radiolytic oxidation of cyclohexane

Abstract

The liquid-state yields of cyclohexanol and cyclohexanone obtained by the gamma radiolytic oxidation of cyclohexane have been measured, both in the absence and presence of sulphur, and the radical scavenger, iodine. In the absence of these additives the yields of ketone and alcohol are similar and it is suggested that the major part of these products is accounted for by a mechanism involving the formation and disproportionation of cyclohexylperoxy radicals. The presence of iodine reduces the yields of both the alcohol and the ketone, as predicted by the disproportionation mechanism, the low residual yields at high iodine concentration suggesting that non-radical processes do not make any important contribution. This conclusion is further substantiated by a kinetic analysis of the results. In the presence of sulphur the yield of ketone is greatly reduced while that of alcohol is much less affected. This is attributed to preferential formation of the cyclohexanol by the reaction of sulphur intermediates with oxidizing radicals and products. Solid-state yields of both alcohol and ketone are lower than those obtained in the liquid, this being attributed to a lower equilibrium concentration of oxygen in the solid, and possibly to a reduced mobility of both oxygen and radicals at low temperatures. The relatively greater reduction in the alcohol yield is attributed to a steric effect imposed by the solid lattice leading to inhibition of cyclohexylperoxy radical disproportionation. The validity of vapour phase chromatography as a method of analysis in such studies is also discussed.