Kinetics of diethyl sulfide oxidation by hydrogen peroxide and peroxymonocarbonate in the presence of surfactants

Abstract

We have studied the effect of different surfactants on the rate of diethyl sulfide (Et 2 S) oxidation by hydrogen peroxide and peroxymonocarbonate in aqueous solutions. In all the studied cases, the rate of the reaction between Et 2 S and H 2 O 2 decreases as the surfactant concentration increases. The reaction of Et 2 S with HCO 4 − is catalyzed by cationic surfactants and inhibited by neutral and anionic surfactants.A very important endeavor is the search for new systems for rapid oxidation of organic sulfides, which are active components of toxic agents. This task involves solving two fundamental problems: replacing the toxic and aggressive derivatives of hypochlorous acid widely used for disposal of sulfides [1], and selecting solvents that on the one hand make it possible to considerably increase the solubility of toxic sulfides (often practically insoluble in water) and on the other hand to preserve their fast oxidation rate.One promising route to solving the first problem is activation of hydrogen peroxide with formation of peroxy acids, which have high activity in oxidation of sulfides. Bicarbonates [2], silicates [3], nitrites [4], molybdates [5, 6], phthalates [7], and other compounds can be used as the H 2 O 2 activators. Water-alcohol mixtures are used to improve the solubility of the sulfides [2].Recently [8] we studied the bicarbonate-catalyzed oxidation of diethyl sulfide (Et 2 S), modeling 2,2-dichloroethyl sulfide (mustard gas), by hydrogen peroxide in water and in aqueous alcoholic media of variable composition. We established that at pH 7-9, the reaction includes intermediate formation of peroxymonocarbonate:(1)The value of the equilibrium constant for peroxymonocarbonate formation (K (1) ≈ 27) is the same for aqueous and aqueous alcoholic media [2,8]. The rate constant for the reaction (k (2) ) is about 100 times higher than the corresponding value for oxidation of Et 2 S by hydrogen peroxide. In aqueous alcoholic media, the rates of both the catalytic route (with HCO 4 − ) andthe noncatalytic route (with H 2 O 2 ) are slowed down with an increase in the alcohol concentration and in the order HOC 2 H 4 OH > i-PrOH > t-BuOH, but the ratio of the rates is preserved.

Kinetics of the borate anion catalyzed oxidation of diethyl sulfide with hydrogen peroxide in an i-PrOH–H2O medium

“…However it is less effective than derivatives of hypochlorous acid in the decomposition of thioethers. One method for the activation of hydrogen peroxide is its conversion into peroxoacids with the use of such activators as bicarbonates [1,2], silicates [3], molybdates [4,5], nitrites [6] and other compounds.…”

“…The catalytic effect of B(OH) 3 is quantitatively explained by a mechanism which includes the intermediate equilibrium formation of the anions of monoperoxoborate B(OH) 3 (OOH) -(MPB) and diperoxoborate B(OH) 2 (1)…”

Nucleophilic activity of peroxyhydrocarbonate and peroxocarbonate ions relative to 4-nitrophenyl diethyl phosphonate

“…Comparison of these constants with the corresponding constants of other inorganic anions in their reaction with I in the framework of the Brönsted equation indicates that HCO 4 − and CO 4 2− are typical a-nucleophiles. Key words: 4-nitrophenyl diethyl phosphonate, hydrogen peroxide, peroxyhydrocarbonate ion, peroxocarbonate ion, nucleophilicity.In addressing the outstanding problem of eliminating ecologically toxic substances, recent attention has been given to the reactivity of systems containing hydrogen peroxide and its activators, primarily, ammonium and alkali metal hydrocarbonates [1][2][3][4]. Such systems, which fully meet the requirements of green chemistry, are universal and may be used for the decomposition of highly toxic organophosphorus compounds and sulfide derivatives by an oxidative-nucleophilic mechanism since the HO 2 − anion, which is a powerful a-nucleophile [5, 6], and the HCO 4 − ion [1-4], which is an effective oxidizing agent, are both generated in the aqueous H 2 O 2 /HCO 3 − /HO -system.…”

“…This latter value was obtained assuming that the pK a values for HCO 4 − and HSO 5 − are approximately the same. An approximate evaluation of pK a for HCO 4 − as an acid may also be obtained from the pH dependence of the rate of oxidation of several organic sulfides in the H 2 O 2 /NH 4 HCO 3 /HO -system: 2-hydroxyethyl phenyl sulfide [2], diethyl sulfide [3], and methyl phenyl sulfide [4]. In all three reactions in the pH range from about 7 to 9, the rate is virtually independent of pH (pK a > pH, the HCO 4 − anions predominantly participate in the oxidation).…”

“…The midpoint of this range may be taken as the approximate pK a of the HCO 4 − ion. A graphic evaluation gives the following pK a values:~10 [2],~9.8 [3],~9.0 [4]. Thus, we may assume that the pK a for HCO 4 − as an acid (or the pK a for CO 4 2− as a base) is in the range 9.0-10.0.…”