The Effect of Ring-Size on the Anodic Oxidation of 'Cyclic Amides' in Methanol

The anodic oxidation of three 'cyclic amides' of type N-acylazacycloalkanes [5- (I), 6- (II) and 7-membered (III) rings] has been studied in methanol under constant current electrolysis, at C anodes and in the presence of various supporting electrolytes, and different concentrations of substrates. Four major products were formed in good yields by all three substrates, namely N-acyl, α-azacycloalkenes, N-acyl, α-methoxyazacycloalkanes, N-acyl, α-methoxy, α'-azacycloalkenes and N-acyl, α,α′-dimethoxyazacycloalkanes. The relative ratios among products and selectivity were found to be highly dependent on the nature of the electrolyte used, and to a lesser extent on substrate concentration. In terms of ring-size effect it was found that the rate of oxidation and current efficiency (yield) was in the order: I > II > III. Also the latter two behaved similarly (but different from I) when various supporting electrolytes were used.