Electrochemical conversion of 4-alkyloxytoluenes to cyclic and non-cyclic 4-alkyloxybenzaldehyde acetals. A new approach to liquid-crystalline 1,3-dioxanes

Abstract

4-Ethoxytoluenes bearing substituents in the β-position such as a hydroxy group, a halogen atom, or an ester group were anodically oxidized to give the corresponding benzaldehydes or their derivatives (dimethyl acetals, hydrogen sulphite addition products). The electrochemical oxidation of 4-alkyloxytoluenes in alcoholic solutions in the presence of alkanediols led to cyclic acetals, e.g. 1,3-dioxolanes and 1,3-dioxanes. Various 2,5-disubstituted 1,3-dioxanes were thus prepared, the trans isomers exhibiting liquid-crystalline properties. The ratio of cis and trans isomers formed during the electrolysis was found to be in correspondence with the thermodynamic equilibrium.