Photolysis of nitroso-compounds. Part IV. 1-Chloro-1-nitrosocyclohexane and other geminal chloro-nitroso-compounds

Detailed studies of the photolysis of 1-chloro-1-nitrosocyclohexane are presented. Photolysis in methanol solutions gave hydrochloric acid, methyl nitrite, 1,1-dimethoxycyclohexane, cyclohexanone, and cyclohexanone oxime. 1-Methoxycyclohexene and 6-hydroxyimino-1-methoxycyclohexene were minor products. Photolysis in aprotic solvents afforded 1-chlorocyclohexene, cyclohexanone, and 1,1-dichlorocyclohexane with small amounts of a-chlorocyclohexanone and 1-chloro-1-nitrocyclohexane at low concentrations whereas at high concentrations substantial amounts of cyclohexanone oxime were found. Evidence based on the variation of product distribution with solvent, concentration, and added radical scavengers is presented, which shows that the primary photochemical step consists in C-NO bond cleavage in all solvents. a-Chloronitrones are postulated as intermediates. The importance of solvolysis and other secondary ionic reactions is emphasised. Other studies of the photolysis of geminal chloronitrosoadamantane, 3-chloro-3-nitrosopentane, and 2-chloro-2-nitrosobutane in alcohols are briefly re-examined in the light of the proposed mechanism. In none of these cases have we found any evidence for a carbonyl-like photoreduction.