Understanding the kinetics and molecular mechanism of unimolecular gas phase thermal decomposition of the α-ketoester methyl benzoylformate using RRKM and BET theories

Abstract

The RRKM calculation and bonding evolution theory analysis coupled with quantum theory of atoms in molecules have been used to investigate kinetics and molecular mechanism of gas phase thermal decomposition of methyl benzoylformate. The pressure-dependent rate coefficients, by applying different collisional efficiency values, indicated that the atmospheric pressure is in high-pressure limit of fall-off curve and low-pressure limit rate coefficients are in the range of 10−13-10−12 cm3 molec−1 s−1. Temperature dependence of high-pressure limiting of rate coefficient over the temperature range 733 ± 20% K was estimated to be k∞RRKM(CBS-QB3)=2.92×1013s-1exp(227.4kJmol-1/RT) and k∞RRKM(PBE1PBE)=2.67×1013s-1exp(232.8kJmol-1/RT). Topological analysis of electron localization function and electron density at the B3LYP/6-311G(d,p) level reveal that the reaction can be occurred as going through seven turning points defined as methyl benzoylformate 8-CF†FF†TSFC†[CF†]-0: methyl benzoate + carbon monoxide. The molecular mechanism can be categorized in three fundamental sections A) heterolytic rupture of O3C8 bond and detachment of methoxy part; B) formation of O3C7 bond via donation bond formation mechanism; and C) heterolytic rupture of C7C8 bond and detachment of carbon monoxide. The electron density ρ(3,−1)(r) in the region of bond forming and breaking increases and decreases along the reaction course to reflect bond strengthening and weakening, respectively. AIM parameters revealed that so long as chemical bonds are unformed/ruptured, interactions at related BCPs are covalence in nature, otherwise the nature of chemical bonds are strong shared covalence.