Fumarodinitrile electrohydrodimerization and acrylonitrile electroreduction on liquid gallium: a comparison with mercury

Electrohydrodimerization (EHD) of fumarodinitrile (R) from dilute aqueous solutions of the strong surfactant Triton X-100 takes place both on liquid gallium and on mercury, via a rate-determining homogeneous radical–radical coupling step. However, the potential range over which EHD takes place is much narrower on gallium than on mercury. This behaviour is due to the fact that adsorbed water molecules act as proton donors towards the radical anion R , giving rise to the neutral radical RH , which is immediately reduced to the saturated monomer RH2. Therefore, EHD requires the complete displacement of water molecules from the adsorbed state by Triton X-100; this is more difficult on the hydrophilic gallium than on the hydrophobic mercury. This also explains why, even though fumarodinitrile is much more strongly adsorbed on gallium than on mercury, no appreciable radical–radical coupling takes place in the adsorbed state on gallium. Acrylonitrile is reduced to the saturated monomer on gallium under the same experimental conditions in which it undergoes EHD on mercury. This is also due to the high hydrophilicity of gallium.