Kinetic Study of the Oxidation of Stabilized and the Chemically Activated Secondary Ethyl Radical of Methyl Ethyl Sulfide (CH3SCH•CH3)

Abstract

In order to account for subsequent reactions, collisions, and deactivation, the reaction between activated CH3S CH•CH3 and molecular oxygen is examined using the quantum Rice-Ramsperger-Kassel (QRRK) theory. Under combustion conditions, hydroxyl radicals start the oxidation of methyl ethyl sulphide (CH3SCH2CH3) and MES (methylthioethane). The objective is to identify stable and unstable products of oxidation of activated secondary radical of methyl ethyl sulfide.The thermochemical characteristics of reactants, products, and transition states were investigated using the CBS-QB3 and G3MP2B3 composite and M062X/6-311+G(2d, p) DFT methods. These thermochemical properties are used for the calculations for kinetic and thermochemical parameters. Kinetic parameters are calculated using the thermochemical properties of products, reactants and transition states obtained using under CBS-QB3 method of calculation.It has been found that the reaction between CH3SCH•CH3 and O2 forms an energized peroxy adduct CH3SCH(OO•)CH3 with a calculated well depth of 30.2 kcal/mol at the CBS-QB3 level of theory, under high pressure and low temperature, isomerization and stabilization of the CH3SCH(OO•)CH3 adduct is of importance, and under atmospheric pressure and at temperatures between above 600 ~ 800 K reactions of the chemically activated peroxy adduct become important relative to stabilization. The stabilisation of the CH3SCH(OO•)CH3 adduct is found to be important at temperatures below 500 K, the intramolecular hydrogen shift and isomerization of the CH3SCH(OO•)CH3 adduct are optimal at temperatures between 500 and 900 K, and all subsequent reaction paths are significant at temperatures above 800 K. The optimal temperature for this oxidation reaction to occur under pressures of 1-4 atm is advised to be between 600 and 800 K. With the formation of oxygen-sulfur and oxygen-carbon double bonds as a result of the peroxyl oxygen radical attaching to sulphur, a new pathway for the CH3SCH(OO•)CH3 adduct is observed.