Kinetics of oxidation of diols by ozone in aqueous solution

The kinetics of the oxidation of diols by ozone was investigated by a spectrophotometric method in the temperature interval of 277–304 K. The activation parameters of the reaction were determined.     

Kinetics and mechanism of oxidation of phosphorus oxyacids by pyridinium hydrobromide perbromide

Oxidation of three lower oxyacids of phosphorus, viz. phosphinic, phenylphosphinic and phosphorous acids by pyridinium hydrobromide perbromide (PHPB), is first-order with respect to both oxyacid and PHPB. There is no effect on addition of acylonitrile and pyridinium bromide. On oxidation, deuterated phosphinic and phosphorous acids exhibit substantial kinetic isotope effects. The effect of solvent composition on reaction rate indicates that the transition state is more polar than the reactants. Reaction rates were determined at different temperatures and the activation parameters calculated. Alternative mechanisms, involving the two tautomeric forms of the oxyacid, have been formulated and it has been concluded that the reaction proceeds through the pentacoordinated tautomer. Transfer of a hydride ion from the oxyacid to PHPB, in the rate-determining step, has been proposed.     

Kinetics and mechanism of the oxidation of some vicinal and non-vicinal diols by tetrabutylammonium tribromide

Kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers, by tetrabutylammonium tribromide (TBATB) has been studied. The vicinal diols yield products arising out of glycol-bond fission, while the non-vicinal diols produce the hydroxycarbonyl compounds. The reaction is first-order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to diols. The reaction fails to induce the polymerization of acrylonitrile. There is no effect of tetrabutylammonium chloride on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The oxidation of [1,1,2,2-²H₄] ethanediol shows the absence of any primary kinetic isotope effect. Values of solvent isotope effect, k(H₂O)/k(D₂O), at 288 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutan-1-ol are 3.41, 0.98 and 1.02 respectively. A mechanism involving a glycol-bond fission has been proposed for the oxidation of vicinal diols. Non-vicinal diols are oxidised by a hydride-transfer mechanism, as they are monohydric alcohols.     

Kinetics and Mechanism of the Oxidation of Somethioacids by Benzyltrimethylammonium Tribromide

The oxidation of thioglycollic, thiolactic and thiomalic acids bybenzyltrimethylammonium tribromide proceeds through the formation of asulfenium cation in the slow step.     

Kinetics and mechanism of oxidation of thiocarbohydrazide in the free state and in its metal complex and thiocarbohydrazone by chloramine-T and dichloramine-T

Kinetics of oxidation of thiocarbohydrazide (TCH) in the free state and as its metal complex, and as a hydrazone by chloramine-T (CAT) in aqueous HClO₄ medium, and by dichloramine-T (DCT) in 1:1 (v/v) water-methanol medium in the presence of HClO₄ have been studied. Rates of oxidation of TCH in the free state and in metal complex by CAT were determined. The rate law for the oxidation of TCH at high [H⁺ ] and for complex oxidations were identical to that for CAT oxidations. The conversion of TCH into its hydrazone changed the order in [H⁺] from a positive to a negative value, probably signalling the change of reaction site. The rate law for oxidation under these conditions was determined. Addition of the reduced product of the oxidants had no effect on the rate of oxidations. Variation in ionic strength of the medium had little positive effect, while decrease in dielectric constant of the medium decreased the rate in both the oxidations. Oxidation processes generally follow a Michaelis-Menten type of mechanism. Constants of the rate limiting steps have been calculated at different temperatures and these constants have been used to calculate the activation parameters from the Arrhenius plots. The proposed mechanisms are supported by investigations with HOC1 under identical reaction conditions. Metal complexation of the substrate decreased the reactivity, while conversion of TCH into its hydrazone changed the rate dependence on [H⁺].     

Kinetics and mechanism of oxidation of anisole and substituted anisoles by acid bromate in acetic acid-water mixture

Oxidation of anisoles by acid bromate has been studied in acetic acid-water system in the presence of sulphuric acid. The reaction is first order each in [anisole] and [Br(V)]. The rate of reaction increased with increase in [H⁺] and percentage of acetic acid. The products of oxidation have been identified as ortho and para hydroxyanisoles. From the effect of [H⁺] and [acetic acid] on rate, H ₂ ⁺ BrO₃ has been established as the reactive species. Anisoles having electron-donating substituents in the benzene ring accelerate the rates and vice versa with a Hammett ρ value of −0.6. A mechanism involving the attack of H ₂ ⁺ BrO₃ on ortho/para position of the anisole in the rate-determining step has been proposed.     

Kinetics and mechanism of oxidation of N-substituted phenothiazines by chromium(VI)

The kinetics of oxidation of N-acetylphenothiazine (NAPT) by Cr(VI) in 80% acetic acid-20% water (v/v) mixture is first-order each in [NAPT] and [Cr(VI)]. The reaction is catalysed by added acid with a third-order dependence in [HCIO₄], Increase in polarity of the solvent medium decreases the rate. The oxidation is insensitive to variations in ionic strength as well as added acrylamide. Oxidations of phenothiazine (PT) and N-methylphenothiazine (NMPT) under similar conditions are found to be very fast. However kinetic investigations with NMPT in an acetic acid-sodium acetate buffer show first-order dependence each in [NMPT] and [Cr(VI)] and a fractional-order dependence in [H⁺] in the pH range 1.80-3.09. Increase in polarity of the medium increases the rate. In both the cases, the corresponding sulphoxides are identified as oxidation products. Based on the kinetic results, mechanisms for oxidations are proposed.     

Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-²H₂]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.     

Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO₄ medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]_o and zero-order with respect to [CAP]_o. The fractional-order dependence of rate on [H⁺] suggests complex formation between CBT and H⁺. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.     

Kinetics and mechanism of the oxidation of diols by pyridinium bromochromate

The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: k_obs=a+b[H⁺]. The oxidation of [1,1,2,2-²H₄]ethanediol exhibited a primary kinetic isotope effect (k_H/k _D=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 285–290, 1998.     

Cr(VI) oxidation using cetylpicolinium dichromate: Kinetics of oxidation of benzaldehydes with a green protocol

Oxidation kinetics of benzaldehyde and some of its ortho- and para-monosubstituted derivatives have been studied using cetylpicolinium dichromates, a class of novel phase transfer oxidants, in dichloromethane medium. The rate of reaction is first order with respect to oxidant and fractional order with respect to the substrates. The Michaelis–Menten type oxidation was observed with respect to the substrates. Benzaldehydes are found to be oxidized to their corresponding acids. The mechanism of oxidation reaction has been suggested based on the solvent isotope effect, Hammett plot, and thermodynamic study. The solvent isotope effect (k_CHCl3/k_CDCl3 = 1.57) indicates the involvement of hydrogen exchange with the medium during oxidation reactions. A strong influence of specific solute–solvent interactions on the rate of the reaction is observed. Both the electron-withdrawing and electron-releasing substituents on the substrates accelerate the rate of reaction.     

Kinetics and mechanism of oxidation of some basic amino acids with bromamine-T

Kinetics of oxidative decarboxylation of arginine, glutamine, histidine and lysine by bromamine-T (BAT) was investigated in acid and alkaline media at 30° and 20° fespectively. The form of the rate law at low concentrations of HClO₄ has been worked out. Proton inventory studies in H₂O-D₂O mixtures with Arg as a probe have been made. The rate increases in the order: His > Lys > Arg > Glu - NH₂. In alkaline media, the rate shows a first order dependence on [BAT]₀ and is fractional in [S] and [OH].p-Toluene sulphonamide retards the rate. Mechanisms proposed are consistent with the experimental rate laws.     

Kinetics of oxidation of glycylglycine by bromamine-T in acid medium

The kinetics of oxidation of a typical dipeptide glycylglycine (GG) by bromamine-T have been studied in HClO₄ medium at 40°C. The rate shows first-order dependence on [BAT]₀ and is fractional order in [GG]₀ which becomes independent of [substrate]₀ at higher [GG]₀. At [H⁺ ] > 0.02mol dm⁻³, the rate is inverse fractional in [H⁺ ] but is zero order at lower [H⁺ ] (≤0.02 mol dm⁻³). Variation in ionic strength or dielectric constant of the medium had no significant effect on the rate. The solvent-isotope effect was measured and = 1.45. Proton inventory studies have been made. The reaction has been studied at different temperatures (308-323 K) and activation parameters have been computed.     

Kinetics of oxidation of dioxanes by ozone in aqueous solutions

The kinetics of oxidation of dioxanes by ozone was investigated by a spectrophotometric method in the temperature interval of 281-311 K. The activation parameters of the reaction were determined.     

Kinetics of Oxidation of Phosphinic, Phenylphosphinic and Phosphorous Acid by Benzyltrimethylammonium Chlorobromate

The oxidation of lower phosphorus oxyacids by benzyltrimethylammonium chlorobromate (BTMACB) proceeds by a mechanism involving a hydride-ion transfer from oxyacids to the oxidant in the rate-determining step.     

Kinetics and mechanism of the oxidation of some thioacids by benzyltrimethylammonium dichloroiodate

The oxidation of thioglycolic, thiolactic, and thiomalic acids by benzyltrimethylammonium dichloroiodate (BTMAIC) to the corresponding disulfide dimer, is first-order with respect to each the thioacid and BTMAIC. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The reaction failed to induce polymerization of acrylonitrile. The reaction rate increases with the increase in the concentration of zinc chloride. Addition of benzyltrimethylammonium chloride enhances the reaction rate. Suitable mechanism has been proposed. © 1996 John Wiley & Sons, Inc.     

Efficient method for the oxidation of aldehydes and diols with tert-butylhydroperoxide under transition metal-free conditions

An efficient, mild, and simple protocol is presented for the oxidation of aldehydes and diols to carboxylic acids utilizing 70% aq TBHP as oxidant and t-BuOK as additive. The oxidation of aldehydes could be achieved by two methods under aqueous medium. Excellent yields of products were obtained in short reaction times. Notably, the products were isolated by simple filtration technique and do not involve chromatographic separation. These reactions may prove to be valuable alternatives to traditional metal-mediated oxidations. Oxidation does not require any transition metals or organic solvents in reaction, making this protocol green.