Novel mesoporous solid superacids for selective C-alkylation of m-cresol with tert-butanol

Abstract

tert-Butylated phenols, which are important precursors in a variety of industries, are usually manufactured by reacting phenol in the presence of liquid acid catalysts, with pure isobutylene or C₄ fraction from naphtha crackers containing isobutylene. These processes suffer from problems associated with the use of highly corrosive liquid acids and also the source of isobutylene. In the current study, alkylation of m-cresol was studied with tert-butyl alcohol (TBA) using sulphated zirconia and three novel superacidic catalysts, namely, UDCaT-4, 5 and 6. The new catalysts UDCaT-4, UDCaT-5 and UDCaT-6 are modified versions of zirconia. Amongst these, UDCaT-5, with 9% w/w sulphate content, was found to be the most active. Effects of different parameters such as, speed of agitation, catalyst loading, reactant ratio (mole ratio of m-cresol to that of TBA), effect of temperature and the recycle of catalyst are discussed. The conversion of m-cresol and the selectivity for mono C-alkylated product at a m-cresol to TBA mole ratio of 3:1, using 0.03 g/cm³ UDCaT-5 at 120 °C under autogenous pressure, were 89% and 90%, respectively. The reaction was carried out without using a solvent to make the process greener and cleaner. The selectivity for the 2-tert-butyl-5-methylphenol was 93%. The reaction mechanism is discussed. A second order rate equation fits the data well. The apparent activation energy was determined as 9.04 kcal/mol.