Selective electrocarboxylation of bromostyrene at silver cathode in DMF

The electroreduction behavior of bromostyrenes 1 in DMF has been detected by cyclic voltammetry (CV) on GC and Ag electrodes. Under the atmospheric pressure of CO₂, selective electrocarboxylation of 1 was carried out in an undivided cell at Ag cathode under potentiostatic conditions, with the corresponding vinyl-benzoic acid methyl ester 3 as the principal product, accompanied by styrene 2. Moderate to good electrocarboxylation yields were obtained by preparative electrolysis. Synthetic parameters such as supporting electrolyte, applied potential, electric charge, and temperature, were found to influence the carboxylation efficiencies. Both CV and electrolysis confirm that the positions of C-Br and C=C groups strongly affect the electrocarboxylation. Higher yields were obtained by changing from ortho to meta to para isomers.