Self-catalyzed esterification of 2-hydroxyisobutyric acid: A simple method to produce methyl 2-hydroxyisobutyrate

Abstract

In this paper, we first propose a method to produce methyl 2-hydroxyisobutyrate (HBM), which is an essential chemical in semiconductor manufacturing processes, through esterification of 2-hydroxyisobutyric acid (HBA) with methanol without adding any catalyst or solvent. We found that molecular HBA efficiently catalyzed its own esterification, and methanol successfully served as both a reactant and solvent. Significant HBA conversion (ca. 87%) with no byproducts was achieved via self-catalyzed esterification at a reaction temperature of 120 °C and reaction time of 48 h. In comparative experiments using Amberlyst-15 and Nafion NR50 catalysts, ca. 80% and ca. 93% of HBA conversion were obtained at 90 °C for 6 h, respectively. A kinetic study of the self-catalyzed esterification demonstrated that the reaction order relative to HBA was two, and the activation energy was 44.1 kJ mol−1. Based on the kinetics, we suggest a possible reaction mechanism, where the molecular HBA catalyzes the reaction (rather than the protons generated by dissociation of HBA). Thus, self-catalyzed esterification of HBA with methanol could be a promising method to produce HBM.