Thermochemistry and Reaction Kinetics of Secondary Ethyl Radical of Methyl Ethyl Sulfide, CH<sub>3</sub>SCH•CH<sub>3</sub>, with <sup>3</sup>O<sub>2</sub> to CH<sub>2</sub>SCH(OO•)CH<sub>3</sub>

Abstract

The quantum Rice-Ramsperger-Kassel (QRRK) theory is used to analyze the reaction between the activated CH₃S CH•CH₃ and molecular oxygen to account for further reaction and collisional and deactivation. hydroxyl radicals initiate the oxidation of Methyl ethyl sulfide (CH₃SCH₂CH₃) and MES (methylthioethane) under combustion conditions. The CBS-QB3 and G3MP2B3 composite and M062X/6-311+G(2d, p) DFT methods was used to study the thermochemical properties of reactants, products and transition states. These thermochemical properties are used for the calculations for kinetic and thermochemical parameters. Under high pressure and low temperature, isomerization and stabilization of the CH₃SCH(OO•)CH₃ adduct is of importance. Under atmospheric pressure and at temperatures between above 600 ~ 800 K reactions of the chemically activated peroxy adduct become important relative to stabilization. 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. Kinetic parameters are calculated using the thermochemical properties of products, reactants and transition states obtained using under CBS-QB3 method of calculation. At temperature below 500 K, Stabilization of CH₃SCH(OO•)CH₃ adduct is of importance. Temperature of 500-900 K, is optimal for intramolecular hydrogen shift and the isomerization of CH₃SCH(OO•)CH₃ adduct. At temperature above 800 K, all of the subsequent reaction paths are of importance. For a reaction to move forward under pressure 1-4 atm, the recommended optimal temperature is between 600-800 K. A new pathway for the CH₃SCH(OO•)CH₃ adduct is observed, the attachment of peroxyl oxygen radical to sulfur followed by carbon-sulfur bond dissociation and formation of oxygen-sulfur and oxygen-carbon double bonds.