Electrochemical reductions of 2-furoyl chloride, furil and 2-furaldehyde at mercury cathodes in acetonitrile

Cyclic voltammograms for the reduction of 2-furoyl chloride at a hanging mercury drop electrode in acetonitrile containing tetraethylammonium perchlorate exhibit six cathodic waves. Electrolytic cleavage of the carbon- chlorine bond is responsible for the first wave. Controlled-potential electrolyses of 2-furoyl chloride generate the tetramer 1,2-di(2-furyl)ethene-1,2-diol di(2-furoate) as the major product, whereas small amounts of 2- furaldehyde are obtained when a 10-fold excess of glacial acetic acid is initially present in the system. A cyclic voltammogram for reduction of furil at a hanging mercury drop in acetonitrile containing tetraethylammonium perchlorate shows a pair of reversible cathodic waves. Electrolyses of furil at a mercury pool cathode yield 2-furoic acid, 1,2-di(2-furyl)-2-hydroxy-3-cyanopropanone and 1,2-di(2-furyl)ethanone; when furil is electrolyzed in the presence of an excess of 2-furoyl chloride or glacial acetic acid, the principal product is the aforementioned tetramer or furoin, respectively. One irreversible wave is observed when cyclic voltammograms are recorded for the reduction of 2-furaldehyde at a hanging mercury drop in acetonitrile containing tetraethylammonium perchlorate. Bulk electrolyses of 2-furaldehyde produce 3-(2-furyl)acrylonitrile, hydrofuroin, 3-(2-furyl)propionitrile and 3-(2-furyl)glutaronitrile, together with the hydrodimer (2,3-di(2-furyl)-1,4-dicyanobutane) and possibly oligomers derived from the coreduction of 3-(2-furyl)acrylonitrile.