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

• Published in: Journal of molecular liquids 2019-03, Vol.277, p.241-253
• Main Authors: Tankov, Ivaylo, Yankova, Rumyana
• Format: Article
• Language: English
• Subjects: DFT; Homogeneous catalysis; Kinetics; Mechanism; Pyridinium ionic liquids
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2018.12.087

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 O7⋯H11N1. The acetic acid 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. [Display omitted] •DFT study of the ionic liquid [H–Pyr]+[NO3]− was shown for the first time.•A value of 4.635 was obtained as a difference between LUMO and HOMO orbitals.•Hydrogen bonds affected the [H–Pyr]+[NO3]− reactivity.•Anion and cation were related to donor and acceptor activity, respectively.•Presence of [H–Pyr]+[NO3]− improved substrate conversion and rate constant.