Kinetic and mechanistic studies on the oxidation of nitrite by peroxomonophosphoric acid

The kinetics of oxidation of nitrite to nitrate by peroxomonophosphoric acid in aqueous acid medium have been studied. The observed monotonic fall in rate with increasing pH of the medium has been rationalized on the basis of proton-dissociation equilibria of the substrate as well as the oxidant species. It is found that only HNO₂ reacts with the different PMPA species.     

Kinetic, mechanistic and spectral studies for the oxidation of sulfanilic acid by alkaline hexacyanoferrate(III)

The kinetics of oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium was studied spectrophotometrically. The reaction showed first order kinetics in hexacyanoferrate(III) and alkali concentrations and an order of less than unity in sulfanilic acid concentration (SAA). The rate of reaction increases with increase in alkali concentration. Increasing ionic strength increases the rate but the dielectric constant of the medium has no significant effect on the rate of the reaction. A retarding effect was observed by one of the products i.e. hexacyanoferrate(II) (HCF(II)). A mechanism involving the formation of a complex between sulfanilic acid and hexacyanoferrate(III) has been proposed. The reaction constants involved in the mechanism are evaluated. There is a good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.     

Kinetic and mechanistic studies on the oxidation of arginine and histidine by chloramine-T in hydrochloric acid medium

The oxidation of amino acids by chloramine-T (CAT) in HCl medium at 30°C indicates simultaneous catalysis by H⁺ and Cl^– ions in the HCl concentration range of 0.04–0.12 M. The reaction is first order with respect to concentrations [CAT], [H⁺] and [arginine], but zero order with respect to [histidine]. The rate depends also on Cl^– concentration following 0.7th order. At HCl concentrations >0.12 M, the rate equation is:w=k[CAT] [amino acid]^0.6 and is independent of the [Cl^–]. A suitable mechanism has been suggested.

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-T (CAT) HCl (30°C) H⁺, Cl^– [HCl]=0,04–0,12M. [CAT], [H⁺] [] []. [Cl^–]^0,7. [HCl]>0,12M =k · [CAT][]^0,6 [Cl^–]. .

     

Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: a mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on [CAT]_o and a non-linear dependence on both [SAA]_o and [HClO₄] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [Ru^III] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D₂O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH₃C₆H₄SO₂NH₂Cl⁺) is postulated as the reactive oxidizing species in both the cases.     

Oxidation studies with peroxomonophosphoric acid. II. A kinetic and mechanistic study of dimethyl sulfoxide oxidation in acid and alkaline media

The kinetics of dimethyl sulfoxide (DMSO) oxidation by peroxomonophosphoric acid (PMPA) in aqueous medium at 308 K and I = 0.4 mol/dm³ follow the rate expressions In the pH range from 0 to 2, where k₁ and k₂ are 5.092 × 10^?1 dm³/mol sec and ? 0, respectively; in the pH range from 4 to 7, where k₂ = 8.127 × 10^?3 and k₃ = 2.90 × 10^?3 dm³/mol sec; and in the pH range from 10 to 13.6, where k₄ ? 0, and k₅ = 3.08 × 10^?2 dm³/mol sec. The reaction is interpreted in terms of mechanisms involving an electrophilic and a nucleophilic attack of the peroxomonophosphoric acid species, respectively, in acid and alkaline regions, on the sulfur atom of the sulfoxide molecule giving rise to S-type transition states followed by oxygen-oxygen bond fission to form the products.     

Kinetic investigation of the oxidation of N-alkyl anilines by peroxomonophosphoric acid in anionic surfactant sodium lauryl sulphate

Kinetics of oxidation of N-methyl and N-ethyl aniline by peroxomono-phosphoric acid (PMPA) in aqueous and 5% (v/v) acetonitrile medium respectively have been studied in presence of anionic micelles of sodium lauryl sulphate (SLS) at different pH. Oxidation rate of both the substrates increases up to a certain [SLS] much below the critical micellar concentration (cmc) after which the rate is retarded. Kinetic data have been used to compute the binding constants of both substrate and oxidant with the micelle. A scheme explaining the kinetic data has been proposed.     

Kinetic and mechanistic studies of indigocarmine oxidation by chloramine-T and chlorine in acidic buffer media

Oxidations of indigocarmine (IC) by chloramine-T (CAT) and aqueous chlorine (HOCl) in acidic buffer media, pH 2–6, have been kinetically studied at 30°C using spectrophotometry. The CAT reaction rate shows a first-order dependence on [IC]₀ and an inverse fractional order on [p-toluenesulfonamide]. The effect of [CAT] on the rate is strongly pH dependent with a variable order of 1–2 on [CAT]₀ in the pH range 6–2. The chlorine reaction rate follows first-order in [IC]₀ and [HOCl]₀ each in the pH range 6–2. Addition of halide ions and variation of ionic strength of the medium have no influence on the reaction rate. There is a negative effect of dielectric constant of the solvent. The kinetics of the IC oxidation with CAT at pH 6 and of that with HOCl at pHs 2–6 are similar suggesting similarity in their rate determining steps. A two-pathway mechanism for the CAT reaction and a one-pathway mechanism for the HOCl reaction, consistent with the kinetic data, have been proposed. Activation parameters have been calculated using the Arrhenius and Erying plots. © 1995 John Wiley & Sons, Inc.     

Kinetic and mechanistic studies of oxidation of alanine and phenylalanine by sodium N-chlorobenzene sulfonamide (chloramine-B) in hydrochloric acid medium

The kinetics of oxidation of alanine and phenylalanine by sodium N-chlorobenzene sulfonamide (CAB) has been investigated at 30°C in two ranges of acid concentrations. The reactions follow identical kinetics for both amino acids. At low acid concentration (0.03–0.10M), simultaneous catalysis by H⁺ and Cl^? ions is noted. The rate shows a first-order dependence on [CAB], but is independent of [substrate]. A variation of the ionic strength or the dielectric constant of the medium or the presence of the added reaction product benzene sulfonamide (BSA) has no pronounced effect on the rate. At [HCl] > 0.2M, the rate is independent of [H⁺], but shows a first-order dependence on [CAB] and a fractional-order dependence on [amino acid]. The addition of BSA or Cl^? ions, or a change in the ionic strength of the medium has no influence on the rate. Upon decreasing the dielectric constant of the medium, the rate increased, indicating positive ion–dipole interaction in the rate-determining step. The reaction was studied at different temperatures, and activation parameters have been computed. Rate laws in agreement with experimental results have been derived. Suitable mechanisms to account for the observed kinetics are proposed. The rate constants obtained from the derived rate laws as [H⁺], [Cl^?], and [substrate] vary are in excellent agreement with the observed rate constants, thus justifying the proposed rate laws and hence the suggested mechanistic schemes.     

Kinetic studies on the oxidation of ascorbic acid by technetium(VII)

The pertechnetate ion oxidizes ascorbic acid in strong acid medium to form red species. A reaction mechanism has been developed which correctly predicts all the experimental facts. The results obtained support the postulate according to which the red species corresponds to a complex formed between Tc(V) and dehydroascorbic acid. The rate constants and Arrhenius parameters have been investigated.     

Kinetic and mechanistic aspects for the tartaric acid oxidation by vanadium(V) in sulfuric acid medium

Tartaric acid oxidation by vanadium(V) in sulfuric acid medium was investigated spectrophotometrically at 760 nm and 30°C by appearance of the vanadium(IV), as vanadyl. The reaction rate was determined under pseudo-first-order conditions with an excess of hydroxyacid over the oxidant concentration. The oxidation showed a first-order dependence with respect to vanadium(V) concentration and fractional orders with respect to tartaric acid and sulfuric acid concentrations, with no control and with constant ionic strength. The reaction rate is enhanced by an increase of ionic strength, and slightly reduced by a decrease of the dielectric constant of the medium. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 1998 John Wiley & Sons, Inc. Int J Chem Kinet: 30: 55–61, 1998.     

Kinetic and mechanistic studies of Rh(III)-catalysed oxidation of D-xylose and L-sorbose by N-bromoacetamide in perchloric acid medium

The kinetic and mechanistic studies of homogeneously Rh(III)-catalysed oxidation of D-xylose and L-sorbose by Nbromoacetamide (NBA) in perchloric acid medium were carried out at 40 °C. The reactions were first-order with respect to each of [NBA], [Rh(III)] and [H⁺] and zero-order in [sugar]. Variation of [Cl_?] showed positive effect while variation of [Hg(OAc)₂] showed negative effect on the rate of the reactions. Addition of acetamide (NHA) had a negative effect on the rate of the reaction. The rate of the reaction was unaffected by the change in ionic strength (??) of the medium. Various activation parameters were calculated with the help of pseudo-first-order rate constant, k₁, obtained at four different temperatures. The mechanisms involving RhCl₄(H₂O)₂ ^?, as reactive species of rhodium(III), and H²OBr₊, as reactive species of NBA, are proposed which find support from the spectrophotometric evidence and activation parameters, especially the entropy of activation.     

Citric acid oxidation by vanadium(V) in sulfuric acid medium: Kinetic and mechanistic study

The citric acid oxidation by vanadium(V) in sulfuric acid medium at 303 K is reported. The reaction rate was determined spectrophotometrically by monitoring the formation of vanadium(IV) at 760 nm. The oxidation showed a first‐order dependence with respect to vanadium(V) concentration and fractional order with respect to citric acid concentrations, with no control and with constant ionic strength. The reaction is also first order with respect to sulfuric acid concentration with no control and of fractional order at constant ionic strength. The reaction rate is enhanced by an increase of ionic strength and increased by a decrease of the dielectric constant. The activation parameters were calculated based on the rate constants determined in the 293 to 313 K interval. The proposed oxidation mechanisms and the derived rate laws are consistent with the experimental rate laws. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 566–572, 2000     

Kinetic and mechanistic studies on the oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion

The kinetics of oxidation of pyrrolidine by bis(hydrogenperiodato)argentate(III) complex anion ([Ag(HIO₆)₂]^5?) was studied in alkaline medium, with reaction temperatures in the range of 15.0–30.0 °C. The experiments indicated that the oxidation follows an overall second-order reaction, being first-order in both Ag(III) and pyrrolidine. The observed second-order rate constants, k′, decreased with increasing [IO₄ ^?] but increased slightly with increasing [OH^?]. The influence of ionic strength on the reaction rate was also investigated. The oxidation resulted in oxidative deamination of pyrrolidine, giving 4-hydroxybutyrate as the product. A reaction mechanism is proposed which includes an equilibrium between [Ag(HIO₆)₂]^5? and [Ag(HIO₆)₂(OH)(H₂O)]^2?; these two Ag(III) species are reduced by pyrrolidine in parallel rate-determining steps. The rate equation derived from the proposed mechanism can explain the experimental observations. The rate constants of the rate-determining steps, together with the associated activation parameters, were calculated accordingly.     

Kinetic and mechanistic studies of the iridium(III) catalyzed oxidation of sulphanilic acid by diperiodatocuprate(III) in aqueous alkaline medium

The effect of La₂O₃, K₂O and Li₂O on the properties and catalytic performance of silica-supported nickel catalysts for the hydrogenation of m-dinitrobenzene was investigated. The catalysts promoted with La₂O₃, Li₂O and K₂O showed better catalytic performance than the catalyst without promotion, especially the ones co-promoted with La₂O₃ and K₂O or Li₂O.     

Kinetics and mechanism of oxidation of sulfanilic acid by periodate ion in aqueous medium

Results of kinetic studies of the sodium metaperiodate oxidation of sulfanilic acid in aqueous medium are discussed. A mechanism for the formation of azobenzene-4,4-disulfonic acid, isolated and characterized as its S-benzylisothiuronium derivative, is proposed.

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. -4,4- , S- .

     

Kinetic and mechanistic studies of oxidation of arginine,histidine, and threonine in alkaline medium by N-chloro-N-sodio-p-toluenesulfonamide

The kinetics of oxidation of arginine, histidine, and threonine by chloramine-T (CAT) have been investigated in alkaline medium at 35°C. The rates are first order in both [CAT] and [amino acid] and inverse fractional order in [OH^?] for arginine and histidine. The rate is independent of [OH^?] for threonine. Variation of ionic strength and addition of the reaction product, p-toluenesulfonamide, or Cl^? ions had no effect on the rate. A decrease of the dielectric constant of the medium by adding methanol decreased the rate with arginine, while the rates increased with histidine and threonine. The solvent isotope effect was studied using D₂O. (k_obs)/(k_obs) was found to be 0.55 and 0.79 for arginine and histidine, respectively. The reactions were studied at different temperatures, and activation parameters have been computed. The oxidation process in alkaline medium, under conditions employed in the present investigations, has been shown to proceed via two paths, one involving the interaction of RNHCl (formed rapidly from RNCl^?), with the amino acid in a slow step to form monochloroamino acid, which subsequently interacts with another molecule of RNHCl in a fast step to give the products, p-toluenesulfonamide (RNH₂), and the corresponding nitrile of the amino acid (R'CN). The other path involves the interaction of RNCl^? with the amino acid in a similar way to give RNH₂ and R'CN. Mechanisms proposed and the derived rate laws are consistent with the observed kinetics. The rate constants predicted using the derived rate laws, as [OH^?] varies, are in excellent agreement with the observed rate constants, thus justifying these rate laws and hence the proposed mechanistic schemes.     

Ruthenium(III) catalyzed oxidation of sulfanilic acid by diperiodatocuprate(III) in aqueous alkaline medium. A kinetic and mechanistic approach

The kinetics of ruthenium(III) catalyzed oxidation of sulfanilic acid by diperiodatocuprate(III) (DPC) in alkaline medium at a constant ionic strength of (0.50 mol dm⁻³) has been studied spectrophoto-metrically. The reaction between sulfanilic acid and DPC in alkaline medium exhibits 1: 4 stoichiometry (sulfanilic acid: DPC). The reaction is first order with respect to [DPC] and [Ru^III] and has less than unit order both in [sulfanilic acid] and [alkali]. The active species of catalyst and oxidant have been identified. Intervention of free radicals was observed in the reaction. The main products were identified by spot test and IR. Probable mechanism is proposed and discussed. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed. Thermodynamic quantities are also determined.     

Investigation of the electro-oxidation and oxidation of catechol in the presence of sulfanilic acid

The electrochemical oxidation of catechol (1) in the presence of sulfanilic acid (2) was investigated. Some electrochemical (EC) techniques such as cyclic voltammetry and controlledpotential coulometry were used. The oxidation reaction of catechol (1) with periodate in the presence of sulfanilic acid (2) was also investigated spectrophotometrically. The results indicate that the o-quinone derived from catechol participate in Michael addition reaction with sulfanilic acid (2). In addition, according to the ECE mechanism, the observed homogeneous rate constant (k _obs) for the reaction ofo-quinone derived from catechol (1) with sulfanilic acid (2) has been estimated by digital simulation of cyclic voltammograms.     

Kinetic and mechanistic studies on the oxidation of Norfloxacin by Chloramine‐B and N‐Chlorobenzotriazole in acidic medium

The kinetics of oxidation of Norfloxacin [1‐ethyl‐6‐fluoro‐1,4‐dihydro‐4‐oxo‐7‐(l‐piperazinyl)‐3‐quinoline carboxylic acid] by chloramine‐B and N‐chlorobenzotriazole has been studied in aqueous acetic acid medium (25% v/v) in the presence of perchloric acid at 323 K. For both the oxidants, the reaction follows a first‐order dependence on [oxidant], a fractional‐order on [Norfloxacin], and an inverse‐fractional order on [H⁺]. Dependence of reaction rate on ionic strength, reaction product, dielectric constant, solvent isotope, and temperature is studied. Kinetic parameters are evaluated. The reaction products are identified. The proposed reaction mechanism and the derived rate equation are consistent with the observed kinetic data. Formation and decomposition constants for substrate–oxidant complexes are evaluated. ©1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 153–158, 1999