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 selecti vity of the hydrogenation of acetophenone to 1-phenylethanol over Rane y nickel catalysts has been studied. In the solvent sequence: cyclohex ane, 2-propanol, 2-propanol-water, 2-propanol-water+sodium hydroxide, the maximum yield in phenylethanol observed over Raney nickel rises fr om 82.4% to 99.5%. The very high selectivity in 1-phenylethanol observ ed in the later solvent is attributed to the presence of water at the catalyst surface which diminishes strongly the adsorption at the aroma tic ring of acetophenone and of 1-phenylethanol; the formation of cycl ohexylmethylketone and of l-cyclohexylethanol arising from the hydroge nation of this ring being diminished too. The addition of sodium hydro xide improves also the selectivity, the acid catalysed hydrogenolysis of the C-OH bond is prevented. In the best solvent mixture, i.e., 2-pr opanol-water+sodium hydroxide, the unpromoted Raney nickel is as selec tive as the chromium doped catalysts, the later ones being slightly mo re reactive. (C) 1997 Elsevier Science B.V.