Reductive electron transfer on trichloromethyl derivatives of benzene and pyridine studied by electrochemical methods

The electrochemical reduction of alpha,alpha,alpha-trichlorotoluene (benzotrichloride) and of the corresponding isomeric pyridine derivatives has been investigated by cyclic voltammetry and microcoulometry. Three irreversible diffusion controlled reduction waves have been observed in the voltammetry of the trichloromethyl derivatives and are found to correspond to the progressive two-electron reduction of derivatives where a chlorine atom is substituted by a hydrogen atom. The peak potentials E-p show that reduction of the pyridine derivatives is easier than that of the benzene derivatives with the same number of chlorine atoms, the more positive shift occurring for the 4-substituted compounds. The experimental findings would indicate a concerted electron transfer-bond breaking (C-Cl) mechanism for all the compounds examined, as well as for the chloromethyl and dichloromethyl derivatives formed after Cl/H substitution. Electron uptake appears to be the rate-determining step of the reductive cleavage of these molecules. The effects of the different aromatic rings and of the degree of halogen substitution of the methyl group on the reduction potentials are discussed.