Control of regioselectivity by cation-exchanged sulfonic acid resin catalysts

Abstract

In t-butylation of hydroquinones and condensation of methyl N-phenyl carbamate, cation-exchanged sulfonic acid resin catalysts exhibited significantly better regioselectivity than liquid mineral acid catalysts. This trend was independent of the acid strength of the catalysts and the reaction conditions employed, including choice of solvent. The magnitude of the effect, however, depended on the bulkiness of the substituents. The difference between these heterogeneous and homogeneous acid catalysts was attributed to steric hindrance imposed on fixed protons in the solid catalysts, which caused higher selectivity toward the less-hindered position.