Selective hydrogenation of acetophenone on chromium promoted Raney nickel catalysts .3. The influence of the nature of the solvent

The influence of the nature of the solvent on the activity and selectivity of the hydrogenation of acetophenone to 1-phenylethanol over Raney nickel catalysts has been studied. In the solvent sequence: cyclohexane, 2-propanol, 2-propanol-water, 2-propanol-water+sodium hydroxide, the maximum yield in phenylethanol observed over Raney nickel rises from 82.4% to 99.5%. The very high selectivity in 1-phenylethanol observed in the later solvent is attributed to the presence of water at the catalyst surface which diminishes strongly the adsorption at the aromatic ring of acetophenone and of 1-phenylethanol; the formation of cyclohexylmethylketone and of l-cyclohexylethanol arising from the hydrogenation of this ring being diminished too. The addition of sodium hydroxide improves also the selectivity, the acid catalysed hydrogenolysis of the C-OH bond is prevented. In the best solvent mixture, i.e., 2-propanol-water+sodium hydroxide, the unpromoted Raney nickel is as selective as the chromium doped catalysts, the later ones being slightly more reactive. (C) 1997 Elsevier Science B.V.