Reaction Route and Mechanism of the Direct N-Alkylation of Sulfonamides on Acidic Mesoporous Zeolite β-Catalyst

Development of highly active heterogeneous catalysts with strong acidity and mesoporous structure is a highly attractive strategy for organic synthesis. In this study, a mesoporous zeolite beta (HBeta-M) with bulky particle size and strong acidity was synthesized and used in the direct N-alkylation of sulfonamides with alcohols. The strongly acidic HBeta-M had a higher intrinsic activity with initial turnover frequency of 11 X 10(-2) s(-1) than those of H-form mordenite nanosheets (3.3 X 10(-2) s(-1)) and montmorillonite (4.0 x 10(-2) s(-1)) catalysts. The experiment and characterization results demonstrate that there are two parallel reaction routes on the acidic catalysts. One route is the reaction of benzhydrol with p-toluenesulfonamide (route I). Another route is the reaction of dibenzhydryl ether, arising from route I, with p-toluenesulfonamide (route II), which is found in this work. The reaction rate of route I (13 X 10(-3) mol kg(-1) s(-1)) was higher than that of route II (9.8 X 10(-3) mol kg(-1) s(-1)) on HBeta-M, but route II predominantly contributed to the formation of the target product with high selectivity. Hereby, a complete reaction mechanism is proposed in this work.