Data obtained for the kinetics of oxidation of diethyl sulfide (Et 2 S) by hydrogen peroxide in aqueous solution catalyzed by boric acid indicate that monoperoxoborates B(O 2 H)( ) OH 3 − and diperoxoborates B O H OH ( ) ( ) 2 2 2 − are the active species. The rates of the reactions of Et 2 S with B(O 2 H)( ) OH 3 − and B O H OH ( ) ( ) 2 2 2 − are 2.5 and 100 times greater than with H 2 O 2 .The search for new systems to effect rapid selective oxidation of sulfides and sulfoxides is important for solving the problem of the decomposition of pesticides and poisonous substances, whose active components are organic sulfides. Chloramines, commonly used for this purpose, are highly toxic and corrosive [1]. The most ecologically favorable oxidizing agent is hydrogen peroxide, which, however, has only low reactivity by itself. Bicarbonates [2, 3], molybdates [4,5], phthalates [6], and nitrites [7], which form highly reactive peroxo acids upon reaction with H 2 O 2 , are used to activate hydrogen peroxide. Boric acid, B(OH) 3 , which forms peroxoborates upon reaction with hydrogen peroxide under mild conditions, is a promising activator [8-10]. These compounds, in particular Na 2 [B 2 (O 2 ) 2 (OH) 4 ]·6H 2 O [11], are strong oxidizing agents and are used as industrial bleaches. No information is available on the kinetics and mechanisms of oxidation of thioethers by peroxyborates. The chemistry of peroxyborates is complicated. Depending on the ratio of the starting concentrations of B(OH) 3 and H 2 O 2 and the pH of the medium, either peroxoborates [B(O 2 H) n (OH) 4-n ] -(n = 1-4) or polyperoxoborates [B 2 (O 2 ) 2 (O 2 H) n (OH) 4-n ] 2-(n = 0, 2, or 4) are formed [10]. At relatively low concentrations of B(OH) 3 and H 2 O 2 (£1 mol/L) at pH 6-14, the major products are monoperoxoborate B(O H)(OH) 2 3 − (MPB) anions and diperoxoborate B(O H) (OH) 2 2 2 − (DPB)anions. Polyperoxoborates are the major products at higher reagent concentrations.In the present work, we studied the effect of boric acid on the rate of oxidation of diethyl sulfide (Et 2 S), which serves as a model for yprite, by hydrogen peroxide in aqueous solution in a broad pH range to establish the nature of the active species and find optimal reaction conditions. EXPERIMENTALDiethyl sulfide was prepared according to a standard procedure [12]. The working solutions were prepared using doubly distilled water, 35% hydrogen peroxide, and chemically-pure grade samples of boric acid, sodium perchlorate, H 3 PO 4 , and NaOH. 440040-5760/07/4301-0044

It was found that nitrite anions are effective activators of hydrogen peroxide in the reaction with diethyl sulfide. The observed kinetics are consistent with the proposed intermediate formation of peroxynitrous acid (ONOOH). The rate constants for the reaction of diethyl sulfide Et 2 S with the acid ONOOH (k 0 = 1.8×10 3 L/mol×s) and with the anion ONOO -(k -= 6×10 -2 L/mol×s) are respectively 10 5 and three times higher than with hydrogen peroxide.The search for new methods of selective oxidation of thioethers is of great significance for solution of the problem of the decomposition of pesticides and toxic substances in which the active components are sulfides. The hypochlorous acid derivatives widely used for these purposes -chloramines -are extremely toxic and aggressive compounds [1]. It is of great interest to use the ecologically clean hydrogen peroxide, which itself has low reactivity but forms highly active peroxy acids in conjunction with catalysts (bicarbonates [2, 3], molybdates [4], and other compounds). We found that nitrite anions are effective activators of hydrogen peroxide in reaction with diethyl sulfide.In 1901 it was found [5] that in acidic media nitrites are oxidized to nitrates through the intermediate formation of the unstable peroxynitrous acid (ONOOH), which has unusually high oxidizing power. The formation of ONOOH in the H + /HNO 2 /H 2 O 2 system takes place according to the following mechanism [6]:The surge of interest in the chemistry of peroxynitrite (PN) in the last 15 years is due to the discovery of its formation in vivo during the rapid recombination of NO and O 2 & − and its important role in biochemical processes [7]. [According to IUPAC nomenclature peroxynitrous acid has the name hydrogen oxoperoxynitrate, while the peroxynitrite anion ONOO -is oxoperoxynitrate(1-). The usually employed term "peroxynitrite" applies both to the anion and to the acid.] Peroxynitrite is relatively stable in alkaline media, while under physiological conditions it is partly protonated to peroxynitrous acid (pK a = 6.8 [8]), which soon decomposes (k dec = 1.2 s -1 , pH 7.0 at 25°C [8]) with the formation of nitrate. The high reactivity of PN is usually attributed to the formation, during homolysis of the ONO-OH bond, of "hydroxyl-like" radicals, capable of oxidizing even such inert molecules as alkanes under mild conditions [9].Thioethers are oxidized both by peroxynitrous acid and by its anion with the formation of sulfoxides and NO 2 − [10, 11].In the reaction of dimethyl sulfide (Me 2 S) with ONOO -the yield of Me 2 SO and nitrite amounts to 100% on PN, while in 302 0040-5760/05/4105-0302

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