Kinetics of the Oxidation of Methyl Phenyl Sulfide by Hydrogen Peroxide in the Presence of Hydrocarbonate Anion

Abstract

The oxidation of methyl phenyl sulfide in water and water-alcohol mixtures takes place both by a noncatalytic mechanism and with the participation of hydrogen peroxide as catalyst; in the presence of ammonium hydrocarbonate it takes place by a mechanism involving HCO 4 − as a more active oxidant than hydrogen peroxide (>100 times). In water-alcohol media (ethylene glycol, isopropyl alcohol, tert-butanol) the rate decreases in the order H 2 O > EG > IPA > TBA. The reactivity of organic sulfides varies in the following way: MeSPh ≈ EtSPh << Et 2 S. The results were interpreted from the standpoint of a molecular mechanism of oxidation of the sulfide with H 2 O 2 and HCO 4 − through a polar transition state, containing the HOX molecule (X = H, OH, OR) as acid-base catalyst.Recent interest in investigation of the oxidation of organic sulfides arises from the fact that these processes are regarded as the most satisfactory model of the decomposition of ecotoxicants (pesticides) and the active components of chemical weapons; models of yperite are investigated more often than others [1][2][3][4]. Of great interest from the standpoint of the creation of so-called "green" technologies for protection of the environment are systems based on hydrogen peroxide. In weakly alkaline media they can act as a mild oxidant in the un-ionized form [1,4] and as an effective α-nucleophile in the form of the HO 2 − anion [5]. The problem of the low solubility of organic substrates, important for the development of green technologies, is solved by conducting the nucleophilic oxidation reactions in aqueous solutions of surfactants (micellar catalysis) [6-8] and also in microemulsions [9, 10] and water-alcohol mixtures [1,4,8,11]. In oxidation processes hydrogen peroxide is usually activated by various acids, transforming it into highly reactive peroxy acids. Particularly attractive among the activators are hydrocarbonates as readily obtainable and ecologically safe compounds exhibiting maximum activating effect in a weakly alkaline medium [1,4,7,8,11].The reactivity of a series of sulfides in water-alcohol media [1,4,11] and also in the presence of surfactants [7,8] was recently investigated in the H 2 O 2 /OH -and H 2 O 2 /OH -/HCO 3 − systems. In the present work the kinetics of oxidation of methyl phenyl sulfide (MPS) by hydrogen peroxide was investigated both in the absence and in the presence of ammonium hydrocarbonate as activator in water and in water-alcohol mixtures [30 vol.% of the alcohol: isopropyl alcohol (IPA), tert-butyl alcohol (TBA), and ethylene glycol (EG), at 25°C]. The choice of the given sulfide as subject of investigation was determined by the fact that compared with our previously investigated diethyl sulfide [4, 8] it is a model closer to yperite both in 98 0040-5760/05/4102-0098

Oxidation of methyl phenyl sulfide by carbamide peroxide in the presence of activators

“…* Furthermore the reactivity of this substrate has been studied in detail upon its oxidation by aqueous hydrogen peroxide with and without ammonium bicarbonate [6], which permits us to evaluate the oxidation efficiency of carbamide peroxide in similar reactions. _______ *Solubility in 100 g water: 0.313 g Et 2 S, 0.02 g MeSPh, 0.049 g mustard gas.…”

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.…”

“…1 as a Brönsted dependence. In this case, it is more logical to use the true value pK a = 3.9 (closed circles) for HCO 4 − . The open circle corresponds to the apparent pK a = 6.35.…”