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

Abstract

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.

Computational Study Investigating the Atmospheric Oxidation Mechanism and Kinetics of Dipropyl Thiosulfinate Initiated by OH Radicals and the Fate of Propanethiyl Radical

“…These compounds play an important role in atmospheric and combustion chemistry, mainly in the formation of aerosols, and elimination of sulfur compounds from crude oil or coal. 1,2 They are also known to participate in global warming, acid precipitation, and cloud formation. 3 The contribution to the atmospheric sulfur burden from natural sources, such as volcanoes, plant and animal decay, marine algae, inland bodies of water, soil, bacteria, and so on, is estimated to be 0.47−2.2 Tmol S year −1 .…”

“…Volatile organosulfur compounds (VOSCs) have been the focus of significant attention in recent years because of their contribution to the atmospheric sulfur budget. These compounds play an important role in atmospheric and combustion chemistry, mainly in the formation of aerosols, and elimination of sulfur compounds from crude oil or coal. , They are also known to participate in global warming, acid precipitation, and cloud formation . The contribution to the atmospheric sulfur burden from natural sources, such as volcanoes, plant and animal decay, marine algae, inland bodies of water, soil, bacteria, and so on, is estimated to be 0.47–2.2 Tmol S year –1 . , Various models have been made to develop a global sulfur cycle, but all of them underestimate the significant amounts of biogenic sulfur needed to balance the global sulfur cycle .…”

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

“…The potential energy diagrams in Figure are based on CBS‐QB3 level potential energy calculations for each species. The enthalpies of formation for the peroxides, radicals, aldehydes, and ketones of MES are from our previous studies . Values for O 2 , OH, and HO 2 are from Ruscic .…”

“…Cao et al have reported on the initiation of CH 3 SCH 2 CH 3 oxidation by OH from three different carbon sites showing similar barriers but different routes and kinetics. Several studies by Song et al have reported on the thermochemical and structural properties of the stable molecules of MES and all of its proposed partial oxidation intermediates, along with the properties of their radicals formed after loss of a H atom from each carbon. This study is on the reaction system of CH 3 SCH 2 CH 2 • + O 2 ; it identifies the reaction pathways and kinetics of sulfuric hydrocarbon partial oxidation and combustion that are initiated by abstraction of a H atom from the methyl carbon site on the ethyl group.…”

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>

“…The potential energy diagram in Figure 4 are based on the CBS-QB3 level potential energy calculations for each species. The enthalpies of formation for the peroxides, radicals, aldehydes and ketones of MES are from our previous work, [53,54] while those of O 2 , OH, HO 2 are from Ruscic et al [56] The total enthalpies of products for each reaction step in Figure 4 are calculated based on the difference between the CBS-QB3 total energies of the reactants and the products.…”