- Evidence for a Linear Sulphurane Intermediate in the Oxidation of Sulphoxide by Persulphoxide
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Oxidation of 18O-labelled dimethyl sulphoxide by dimethyl persulphoxide produced by photosensitised oxygenation of dimethyl sulphide proceeded via a linear sulphurane intermediate.
- Akasaka, Takeshi,Ando, Wataru
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- Mechanism of sulfone formation in the reaction of sulfides and singlet oxygen: Intermediacy of S-hydroperoxysulfonium ylide
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H-D exchange was observed in the methyl group during the formation of sulfones in the reaction of dimethyl sulfide-d6 or thioanisole-α,α,α-d3 with singlet oxygen in aprotic solvents. No exchange was observed in the sulfoxides obtained. The proton in the sulfones was shown to come from adventitious water, since the oxidation of C6H5SCH3 in the presence of D2O lead to the formation of sulfones with monodeuteriation. The 16O2-18O2 tracer study demonstrated no oxygen scrambling in the sulfones. All the results indicate that the sulfones are formed intramolecularly via an intermediate possessing one activated proton exchangeable with trace water, a suggested structure for which is S-hydroperoxysulfonium ylides (RS+(OOH)CH2-). Kinetic isotope effects (k(H)/k(D) = 2-4) observed for methyl protons in the sulfone formation suggest that the rate-determining step is the intramolecular proton abstraction in the persulfoxides (RS+(OO-)CH3) generating S-hydroperoxysulfonium ylides. The conversion of the ylide intermediates to sulfones is shown to be facile on the basis of PM3 theoretical calculations.
- Ishiguro, Katsuya,Hayashi, Masaki,Sawaki, Yasuhiko
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p. 7265 - 7271
(2007/10/03)
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- A Mechanistic Study of the Reaction of OH with Dimethyl-d6 Sulfide. Direct Observation of Adduct Formation and the Kinetics of the Adduct Reaction with O2
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A pulsed laser photolysis-pulsed laser-induced fluorescence technique has been employed to study the detailed mechanism for the reaction of OH radicals with deuterated dimethyl sulfide .Equilibration of pulsed laser-generated OH with a (CD3)2S-OH adduct has been directly observed, thus confirming the existence of this controversial weakly bound species.Elementary rate coefficients for adduct formation and decomposition and, therefore, the equilibrium constant for OH + (CD3)S (CD3)2SOH have been determined as a function of temperature.From tte temperature dependence of the equilibrium constant over the relatively narrow temperature range 250-267 K, a 258 K adduct bond strength of 13.0 +/- 3.3 kcal mol-1 has been obtained (second law method).Alternatively, an entropy change calculated using standard statistical mechanical methods and ab initio theory (for determining the (CD3)2S and (CD3)2SOH structures) has been employed in conjunction with an experimental value for the equilibrium constant at a single temperature to obtain a 258 K adduct bond strength of 10.1 +/- 1.1 kcal mol-1 (third law method).Experiments in the presence of O2 confirm the previously reported dependence of the OH + DMS-d6 rate coefficient on the O2 partial pressure and are consistent with the previously proposed four-step mechanism involving hydrogen abstraction, addition of OH to the sulfur atom, and adduct decomposition in competition with an adduct + O2 reaction .The rate coefficient for the adduct + O2 reaction is found to be (8 +/-3 ) x 1E-13 cm3 molecule-1 s-1 independent of pressure (100-700 Torr of N2) and temperature (250-300 K).
- Hynes, A. J.,Stoker, R. B.,Pounds, A. J.,McKay, T.,Bradshaw, J. D.,et al.
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p. 16967 - 16975
(2007/10/02)
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