Electrohydrodimerization of 4-chloro-3-formyl-2H(1)-benzopyrans in ethanolic solutions: a comparative study

Abstract

The electrochemical reduction of two β-chlorovinylaldehydes, 4-chloro-3-formyl-2H(1)-benzopyran and β-chlorocinnamaldehyde, was studied in buffered ethanolic solutions. The protonated form of the aldehydes was reduced at pH < 5.00 in a single two-electron step while two- and three-step reductions were observed in the pH range 5.00-7.00 and at pH > 7.00, respectively. It was found that hydrogenoly- sis of the carbon-chlorine bond takes place first, in preference to that of the carbon-carbon double bond and that of the aldehydic group. Macroscale electrolysis of 4-chloro-3-formyl-2H(1)-benzopyran and its substituted compounds in 60% (v/v) ethanol + water mixtures afforded head-to-tail electrohydrodimers whereas the macroelectrolysis of β-chlorocinnamaldehyde gave only oily products.