Quantum mechanical and reaction dynamics investigation of butyl acetate synthesis in the presence of pyridinium hydrogen sulfate

Abstract

The thermodynamic and kinetic aspects of the mechanism of butyl acetate synthesis catalyzed by the diprotic ionic liquid pyridinium hydrogen sulfate ([H–Pyr]+[HSO4]−) were investigated using density functional theory (DFT) at B3LYP/6-311 + G(d,p) level of calculation. Electronic structure and geometry for individual molecules (substrate, catalyst) were clarified using molecular electrostatic potential surface, natural bond orbital analysis and atoms in molecules theory. The DFT results elucidated the catalytic cycle, which involved the formation of a transition state via substrate-BAIL interaction. Hydrogen bond interactions were found to exist throughout the process of the catalytic cycle, which are of special importance for stabilizing the transition state. Thus, a mechanism involving cooperative hydrogen bonding for BAIL catalyzed butyl acetate synthesis was established. Based on the above mechanism, the calculated thermodynamic parameters were validated by the subsequent kinetic study. Such results may provide fundamental insights into the design of ionic liquid-based homogeneous catalysts for esters production.