GLASSY-CARBON SURFACE EFFECTS ON THE ELECTROREDUCTION OF AROMATIC CARBONYL-COMPOUNDS .1. BENZALDEHYDE

The voltammetric behaviour of benzaldehyde on a glassy carbon electrode (GCE) in DMF and aqueous media is reported and the distinct electrode effect of the GCE when compared with a mercury electrode under identical conditions is discussed. In DMF, on the GCE also, benzaldehyde undergoes one-electron reductive dimerization as in the case of mercury. But even in the presence of protonating agents such as o-cresol and benzoic acid, one-electron dimerization predominates on the GCE whereas two-electron reduction is noticed on mercury. The interaction of benzaldehyde radical anions with acidic functional groups on the GCE leads to a higher surface concentration of radical anions and hence faster dimerization. On a partially polished GCE in DMF as well as on a well-polished GCE in neutral aqueous media, a new time-dependent surface pre-wave is noticed. Evidence indicates that this pre-wave is due to the strong interaction of acidic functional groups with the reactant, benzaldehyde. Constant potential electrolysis indicated the formation of a dimer even in aqueous media. Very strong blocking effects were also noticed on the GCE in alkaline media.