Kinetic and mechanistic study of the X and XO (X = Cl, Br) reactions with dimethyl sulfoxide

Abstract

The kinetics and mechanism of the reactions of dimethyl sulfoxide (DMSO) with Cl, Br, ClO and BrO have been studied by the mass spectrometric discharge-flow method at 298 K and at a total pressure of 1 Torr of helium. The rate coefficient of the reaction Cl + DMSO → products (1) was measured under pseudo-first-order conditions either in excess of DMSO or in excess of Cl atoms: k₁ = (2.05 ± 0.35) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ (quoted uncertainty includes estimated systematic errors). Both HCl and CH₃ were detected as products of reaction (1) and the branching ratios 0.91 ± 0.15 and 0.10 ± 0.02, respectively, were found for the channels forming these species. For the reaction Br + DMSO → products (2) the rate constants for the HBr and CH₃ forming channels (2a and 2b, respectively) were determined from the kinetics of formation of these products: k_2a = (1.1 ± 0.3) × 10⁻¹⁴ and k_2b = (1.2 ± 0.3) × 10⁻¹⁵ cm³ molecule⁻¹ s⁻¹. For the reactions ClO + DMSO → products (3) and BrO + DMSO → products (4), only upper limits, k₃ < 1.6 × 10⁻¹⁴ and k₄ < 4 × 10⁻¹⁴ cm³ molecule⁻¹ s⁻¹, could be determined.