Selectivity engineering in the O- versus C-alkylation of p-cresol with cyclohexene over sulfated zirconia

Abstract

Solid acids are more widely used as heterogeneous catalysts, because they are eco-friendly. This paper reports the results for the Friedel-Crafts alkylation of p-cresol with cyclohexene using solid acids sulfated zirconia, 20% w/w dodecatungstophosphoric acid (DTP) supported on K10 clay and ZnCl₂/K10 (Clayzic). This reaction gave substantial amount of 1-cyclohexyloxy-4-methyl benzene (O-alkylated product) and 4-cyclo-hexyl-4-methyl phenol (C-alkylated product). Both products are of commercial importance as perfume and insecticide respectively. Sulfated zirconia catalyst was shown to be better than others studied in terms of activity and selectivity to the O-alkylated product. The kinetics were studied with sulfated zirconia as catalyst where the rate determining step was the surface reaction between chemisorbed cyclohexene and p-cresol from the liquid phase within pores according to the Eley-Rideal mechanism. The production of O-alkylated p-cresol is favoured at lower temperatures and C-alkylated product at higher temperatures. The best operating temperature is 353 K. The activation energies for O- and C-alkylation are 72.68 and 118.28 kj/mol, respectively.