DFT analysis, reaction kinetics and mechanism of esterification using pyridinium nitrate as a green catalyst

The ionic liquid pyridinium nitrate ([H-Pyr](+)[NO3](-)) was synthesized and characterized theoretically and experimentally. Different quantum chemical analyses such as molecular electrostatic potential surface, natural bond orbital and frontier molecular orbital analyses were used for investigation of the electronic properties and chemical reactivity of the title compound. It was found the existence of an interaction between the nitrate anion and the pyridinium cation, expressed mainly by formation of the hydrogen bond O-7 center dot center dot center dot H-11-N-1. The acetic add esterification with 1-butanol was used as a model reaction in order to study the catalytic properties of the [H-Pyr](+)[NO3](-). The influence of various process parameters (catalyst concentration, initial butanol-to-acetic acid molar ratio and reaction temperature) on the acetic acid conversion and reaction rate constant was discussed in details. The obtained experimental data were validated using a pseudo-homogeneous kinetic model. In addition, a plausible reaction mechanism of butyl acetate synthesis catalyzed by the ionic liquid pyridinium nitrate was offered. (C) 2018 Elsevier B.V. All rights reserved.