Stereoselective hydrogenation of p-tert-butylphenol over supported rhodium catalyst

Abstract

p-tert-Butylcyclohexanol is used as an intermediate for manufacturing esters with lower carboxylic acids, which are important in perfumery, soap and detergents manufacturing. Stereoselective hydrogenation of p-tert-butylphenol (PTBP) to cis and trans-p-tert-butylcyclohexanol (PTBCH) has been carried out by using supported metal catalysts such as rhodium supported on carbon (2% Rh/C), Raney nickel, nickel supported on silica (20% Ni/SiO₂), and palladium supported on carbon (5% Pd/C). Among the variety of catalysts used 2% Rh/C exhibited 100% conversion of PTBP and 100% selectivity of the cis-isomer of PTBCH when methanesulphonic acid was used as the co-catalyst. The reaction was 100% selective towards the product. The effects of various parameters on the rates of reaction were studied systematically and a kinetic model was built. The reaction was found to be kinetically controlled. The formation of cis-isomer was explained theoretically.