Oxidation of α-substituted cyclohexanols by nitric acid
The influence of α-substituents on the oxidative cleavage of cyclohexanol by nitric acid in the presence of copper(II) and vanadium(V) ions has been investigated. Following the initial oxidation to give the cyclohexanone, further reaction, leading to ring opening of the ketone, requires at least one α-hydrogen. Thus 2,2,6,6-tetramethylcyclohexanol is converted to the corresponding ketone whilst 2,2,6-trimethylcyclohexanol is oxidised to a mixture of dicarboxylic acids. The mechanisms of the oxidations are discussed and enolisation is shown to be the key to oxidative cleavage. For ketones that can give two alternative enols, reaction occurs predominantly via the more stable tautomer.