Selectivity engineering of cation-exchange resins over inorganic solid acids in C-alkylation of guaiacol with cyclohexene

Abstract

Friedel−Crafts alkylation of guaiacol with cyclohexene gives both C- and O-alkylated products, which are commercially valuable. The C-alkylated products are important intermediates for the production of resins, antioxidants, drugs, dyes, polymer additives, agrochemicals, and antiseptic substances. The objective of the current work was to achieve maximum selectivity for the C-alkylated products, using an active catalyst with minimum separation cost. A variety of eco-friendly solid acid catalysts such as sulfated zirconia, Amberlyst-15, Filtrol-24, cesium-modified dodecatungstophosphoric acid (Cs-DTP) supported over K-10 clay (20% w/w Cs_2.5H_0.5PW₁₂O₄₀/K-10), and 20% w/w dodecatungstophosphoric acid (DTP)/K-10 clay were screened to study the effect of their nature of acidity on product distribution. Amberlyst-15 was determined to be the best catalyst to achieve maximum selectivity for C-alkylated product at 80 °C. The O-alkylation versus C-alkylation not only was observed to be highly temperature sensitive, but the nature of the acidic sites also had an important role. Effects of various parameters on rates and product distribution are discussed to deduce the kinetics of the reaction.