Carbon Black as an Electron-transfer Catalyst. The Two-phase Dehydrogenation of Hydrazo Nitriles by an Aqueous Solution of Potassium Hexacyanoferrate(III), Using Carbon Black as the Catalyst

The two-phase(aqueous and organic phase) dehydrogenation of hydrazo nitriles by an aqueous solution of potassium hexacyanoferrate(III), using carbon black as the catalyst, was carried out at 40 °C with shaking. In the presence of carbon black, the two-phase dehydrogenation of hydrazo nitriles was accelerated, and the corresponding azo nitriles were obtained in good yields. The catalytic activity of channel blacks was larger than that of furnace blacks. Moreover, the increasing content of phenolic hydroxyl groups tended to increase the catalytic activity of carbon blacks. It became apparent that phenolic hydroxyl groups on the surface of carbon black act as an electron-transfer catalyst in the two-phase dehydrogenation. The reaction scheme was considered to be as follows. In the aqueous phase, phenolic hydroxyl groups on the surface are oxidized by an aqueous solution of K3[Fe(CN)6] to give phenoxyl radicals, and then the carbon black with phenoxyl radicals is transferred into the organic phase, which contains hydrazo nitriles. Subsequently, in the organic phase, the phenoxyl radicals oxidize the hydrazo nitriles to give the corresponding azo nitriles, by which phenolic hydroxyl groups are regenerated. Thus, it was concluded that phenolic hydroxyl groups on the surface are recycled and that carbon black mediates the redox reaction occurring between aqueous and organic phases.