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The oxidation of organic sulfides (thioethers) plays an important role in biochemical transformations and in the chemistry of the atmosphere and natural waters. Dimethyl sulfide (Me 2 S), generated by oceanic phytoplankton, is an important source of sulfur in the atmosphere [1,2]. Its oxidation in the gas phase to the oxides of sulfur leads to the formation of acid rain [2]. In biosystems the oxidation of methionine, which plays a key role in the transfer of unpaired electrons, leads to the destruction of proteins and peptides [3]. Sulfides are also active components of pesticides and toxic substances the utilization of which requires a search for new effective oxidizing systems.Particularly attractive among the large number of the various reagents used for the oxidation of sulfides [2, 4], both in economic and ecological respects, is hydrogen peroxide. The mechanisms of oxidation of thioethers, particularly dimethyl sulfide, by hydrogen peroxide have been studied well experimentally [2, 5, 6] and by quantum-chemical methods [7,8]. The ab initio calculations in [8] indicate that the slow stage of the reaction includes cleavage of the O-O bond in H 2 O 2 and the formation of an S-O bond.However, the oxidation of sulfides by hydrogen peroxide takes place slowly. One promising way of activating H 2 O 2 is to convert it into peroxo acids [9][10][11]. An effective activator may be boric acid, B(OH) 3 , which in reaction with hydrogen peroxide gives peroxoborates [12]. Recently we showed [13,14] that the monoperoxoborate B(OOH)(OH) 3 -(MPB) and diperoxoborate B(OOH) (OH) 2 2-anions formed at pH 6-13.5 are 2.5 and 100 times respectively more active than hydrogen peroxide in the oxidation of diethyl sulfide.2 0040-5760/11/4701-0002

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The DFT method was used to study gas-phase chlorination reactions CH 4 + HOCl (1) and CH 4 + HOCl + H 2 O (2). These reactions entail singlet-triplet (s®t) preactivation of HOCl and terminate in a reverse t®s transition. At 298 K, the barrier DG t ¹ for reaction (2) is higher than for reaction (1) by 1.5 kcal/mol, while the singlet transition state TS s -2 lies higher than TS t -2 by DG ¹ = 21.4 kcal/mol. The reactions of alkanes (RH) with chlorine in the gas phase and in acid media such as Cl 2 -CH 3 CO 2 H-H 2 SO 4 have a radical chain mechanism initiated by light or thermally [1]. In superacids, electrophilic chlorination of RH by Cl + ions takes place [2]. In previous work [3, 4], we were the first to study the chlorination of alkanes by hypochlorous acid in water: (1) RH + HOCl ® RCl + H 2 O. The kinetic equation -(d[RH]/dt) = k[RH][HOCl] holds in three chlorinating systems, namely, Cl 2 /H 2 O, Cl 2 + Hg 2+ /H 2 O, and HOCl/H 2 O. The values of k are equal for equal [HOCl] and identical for reactions in the light and dark. The primary and tertiary C-H bonds in isobutane (CH 3 ) 3 CH are chlorinated in parallel to give (CH 3 ) 2 CHCH 2 Cl and (CH 3 ) 3 CCl. (CH 3 ) 2 CHCH 2 Cl is further chlorinated, while (CH 3 ) 3 CCl is rapidly hydrolyzed to give (CH 3 ) 3 COH. A similarity was found in the substrate selectivity and kinetic isotope effect (KIE) (c-C 6 H 12 /c-C 6 D 12 ) for reaction (1) and the reaction RH + OH • ® R • + H 2 O in the gas phase. Thus, the ratio of the rate constants ethane : propane : isobutane is 0.14 : 1 : 3.6, while the KIE = 2.9 ± 0.2 for HOCl in water at 70°C and 0.24 : 1 : 2.1 and KIE = 2.6 ± 0.2 for OH • in the gas phase at 25°C. We note that the reaction of RH + OH • in water is complicated by a cage effect [4,5] and is not suitable for comparison with reaction (1).These findings permit us to exclude species Cl • , Cl 2 , Cl + , Cl -¼Hg 2+ , and Cl + ¼OH 2 as possible reagents and conclude that reaction (1) proceeds as a molecular chlorination by HOCl and begins with reagent preactivation entailing the conversion of singlet HOCl into triplet HO • Cl • , while the C-H bond is broken by the action of the OH • group of the HO • Cl • diradical [4].In the present work, for a comparison with the kinetic data for reaction (1) in water and to check the hypothesis of a singlet-triplet preactivation of the reagent, we studied the mechanism of the chlorination of methane by HOCl molecules in the gas phase by the density functional (DFT) method for variants with a bimolecular (reaction (1)) and trimolecular reaction (with the participation of a water molecule)(2) RH + HOCl + H 2 O ® RCl + 2H 2 O.