A Comparative Study of Nickel and Cobalt Catalysts in the Hydrogenation of Substituted Acetophenones. Dependence of Hydrogenation Rate and Adsorption Strength on Substituents and Solvents

Abstract

Abstract The difference in the nature of nickel and cobalt catalysts has been investigated by a comparative study of the competitive hydrogenation of substituted acetophenones. The electronic and steric effects of substituents and the effects of solvents on the adsorption strength of acetophenones are greater for the reactions over R-Ni than for those over R-Co. On R-Co catalyst acetophenones substituted with electron attracting groups (3-methoxyl, 3-hydroxyl, and 4-fluoro groups with σ0>0) are adsorbed more strongly than those with electron donating groups (2-, 3-, and 4-alkyl and 4-methoxyl groups with σ0<0). Over R-Ni catalyst the adsorption of acetophenone is greater than that of any substituted acetophenones. The rates of hydrogenation over R-Ni are more susceptible to the effects of substituent and solvent than those over R-Co. Over both R-Ni and R-Co the rates of hydrogenation of unsubstituted acetophenones are greater than those of substituted acetophenones with either electron donating or electron attracting groups.