Anodic Oxidation of Mono-and Disubstituted 1,4-Dimethoxybenzenes

摘要

The electrochemical oxidation of mono-and disubstituted 1,4-dimethoxybenzene derivatives with zero, one, and two benzylic CH_2X groups (X = OAc, CL, OH) (5a—c and 6a—c) has been carried out by using both constant-current and controlled-potential techniques in methanol and in the presence of different electrolytes and working electrodes. Constant-current electrolysis in KOH? methanol solutions yielded mostly the corresponding 1,4-quinone derivatives from 5a—c and 6b, whereas the disubstituted 1,4-dimethoxybenzenes 6a,c underwent side-chain oxidation to form 2,5-dimethoxyterephthalaldehydes. Upon alteration of the medium from the commonly used basic KOH—methanol to neutral LiClO_4—methanol, a new spectrum of products was achieved in most cases, involving novel coupling products from monosubstituted substrates and quinone derivatives from disubstituted ones. Controlled-potential oxidation at the glassy carbon anodes and in a neutral LiClO_4—methanol medium led to more complex mixtures of products, namely, polymers and new coupling products from monosubstituted substrates and quinones and side-chain oxidation (or substitution) products from the disubstituted ones. Three new coupling products were isolated and characterized by X-ray measurements.