Computational study on the reaction of CH3SCH2CH3 with OH radical: mechanism and enthalpy of formation

J of Physical Organic Chem

2017

Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH3SCH2CH3) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔHfo, So and Cp(T)) of 3 corresponding hydroperoxides CH2(OOH)SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6‐311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔHfo298) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods. Isodesmic reactions were used to determine ∆Hfo values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31G(d,p) level theory. Contributions for So298 and Cp(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH3SCH2CH2, CH2(OOH)SCH2CH3, CH3SCH(OOH)CH3, and CH3SCH2CH2OOH are −14.0, −33.0, −37.2, and −32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…CH 3 SCH 2 CH 2 OOH (CSCCQ) with radicals: CH 2 •SCH 2 CH 2 OOH (C•SCCQ) CH 3 SCH•CH 2 OOH (CSC•CQ) and CH 3 SCH 2 CH 2 OO• (CSCCQ•) …”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH₂SCH₂CH₃, CH₃SCH(OOH)CH₃, CH₃SCH₂CH₂OOH, and radicals

J of Physical Organic Chem

2017

Reaction kinetics and thermochemistry of the chemically activated and stabilized primary ethyl radical of methyl ethyl sulfide, CH₃SCH₂CH₂•, with O₂ to CH₃SCH₂CH₂OO•

Int J of Chemical Kinetics

2019

Oxidation of methyl ethyl sulfide (CH 3 SCH 2 CH 3 , methylthioethane, MES) under atmospheric and combustion conditions is initiated by hydroxyl radicals, MES radicals, generated after loss of a H atom via OH abstraction, will further react with O 2 to form chemically activated and stabilized peroxyl radical adducts. The kinetics of the chemically activated reaction between the CH 3 SCH 2 CH 2 • radical and molecular oxygen are analyzed using quantum Rice-Ramsperger-Kassel theory for k(E) with master equation analysis and a modified strong-collision approach to account for further reactions and collisional deactivation. Thermodynamic properties of reactants, products, and transition states are determined by the B3LYP/6-31+G(2d,p), M062X/6-311+G(2d,p), B97XD/6-311+G(2d,p) density functional theory, and CBS-QB3, G3MP2B3, and G4 composite methods. The reaction of CH 3 SCH 2 CH 2 • with O 2 forms an energized peroxy adduct CH 3 SCH 2 CH 2 OO• with a calculated well depth of 34.1 kcal mol −1 at the CBS-QB3 level of theory. Thermochemical properties of reactants, transition states, and products obtained under CBS-QB3 level are used for calculation of kinetic parameters. Reaction enthalpies are compared between the methods. The temperature and pressure-dependent rate coefficients for both the chemically activated reactions of the energized adduct and the thermally activated reactions of the stabilized adducts are presented. Stabilization and isomerization of the CH 3 SCH 2 CH 2 OO• adduct are important under high pressure and low temperature.At higher temperatures and atmospheric pressure, the chemically activated peroxy adduct reacts to new products before stabilization. Addition of the peroxyl oxygen radical to the sulfur atom followed by sulfur-oxygen double bond formation and elimination of the methyl radical to form S(= O)CCO• + CH 3 (branching) is a potentially important new pathway for other alkyl-sulfide peroxy radical systems under thermal or combustion conditions. K E Y W O R D Skinetics, methyl ethyl sulfide, oxidation, thermochemistry 618

Structural and thermochemical studies on CH₃SCH₂CHO, CH₃CH₂SCHO, CH₃SC(═O)CH_3, and radicals corresponding to loss of H atom

J of Physical Organic Chem

2017

CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 are intermediates during the partial oxidation of CH 3 SCH 2 CH 3 in the atmosphere and in combustion processes. Thermochemical properties (ΔH f Investigations of the MES partial oxidation reaction mechanism and kinetics in the atmosphere are helpful in understanding the combustion of sulfur mustard gases. Mansilla et al [7] and Zheng et al [6] experimentally investigated the degradation of MES in the atmosphere. Cao et al [1] have recently done some fundamental computational studies on reactions of MES with OH radical in the atmosphere. To better understand the oxidation process and analyze the kinetics, structural and thermochemical properties of each proposed intermediate and product are required.Vandeputte et al [10] and Zheng et al [8] have developed the thermochemistry and reaction kinetics for the oxidations of dimethyl sulfide [10] and diethyl sulfide, [8] respectively. On the basis of their work, the partial oxidation of MES in the atmosphere would generate intermediates of CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 . [1,7] These aldehydes and ketones are also likely intermediates during the combustion of CH 3 SCH 2 CH 3 . [8,9,11] There is limited available information about the thermochemical properties for these molecules.Besides the importance of intermediate products during MES combustion, CH 3 SCH 2 CHO, CH 3 CH 2 SCHO, and CH 3 SC(═O)CH 3 play important roles in troposphere chemistry. According to Mellouki et al, [12] they are precursors of free radicals and important intermediates of nitrogen oxide transport in the atmosphere. According to Jang and Kamens, these aldehydes and ketones also contribute to the formation of aerosols in the atmosphere through heterogeneous catalytic reactions. [13] Oxidation of compounds containing sulfur, carbon, and hydrogen in the atmosphere results in SO x formation, which is considered an important component of aerosol formations. [14] In this paper, the symbol ("•") represents the radical site located on the preceding carbon or oxygen atom. The molecules and radicals investigated in this study include the following: CH 3 SCH 2 CHO (methylthioacetaldehyde, CAS number: 23328-62-3) with the radicals of CH 2 •SCH 2 CHO, CH 3 SCH•CHO, and CH 3 SCH 2 C•═O; CH 3 CH 2 SCHO (ethyl thioformate, CAS number: 21071-39-6) with the radicals of CH 2 •CH 2 SCHO, CH3CH•SCHO, and CH 3 CH 2 SC•═O; and CH 3 SC(═O)CH 3 (methyl thiolacetate, CAS number: 1534-08-3) with the radicals of CH 2 •SC(═O)CH 3 and CH 3 SC(═O)CH 2 .Geometric structures, standard enthalpies of formation, H─R bond energies, frequencies, moments of inertia, internal rotor potentials, and the entropy and heat capacity values at 298 K and 1 atm are determined in this study. FIGURE 1 Optimized structures of CH 3 SCH 2 CHO, CH 2 •SCH 2 CHO, CH 3 SCH•CHO, and CH 3 SCH 2 C•O (Bond distances in Å; Bond Angles in degrees [°]). A, CH 3 SCH 2 CHO dihedrals: C─S─C─C = −70.3°and S─C─C ═ O = 102.3°. B, CH 2 •SCH 2 CHO dihedrals: C─S─C─C = −66.9°a nd S─C─C═O = 109.0°...