Manganese(III) oxidation of L‐serine in aqueous sulfuric acid medium: Kinetics and mechanism

Kinetics and mechanism of oxidation of L‐serine by manganese(III) ions have been studied in aqueous sulfuric acid medium at 323 K. Manganese(III) sulfate was prepared by an electrolytic oxidation of manganous sulfate in aqueous sulfuric acid. The dependencies of the reaction rate are: an unusual one and a half‐order on [Mn(III)], first‐order on [ser], an inverse first‐order on [H⁺], and an inverse fractional‐order on [Mn(II)]. Effects of complexing agents and varying solvent composition were studied. Solvent isotope studies in D₂O medium were made. The dependence of the reaction rate on temperature was studied and activation parameters were computed from Arrhenius‐Eyring plots. A mechanism consistent with the observed kinetic data has been proposed and discussed. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 525–530, 1999     

Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L‐ascorbic acid

The reduction of Fe(CN)₅L^2? (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H₂A(k₀), HA^?(k₁), and A^2? (k₂), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka₁ and Ka₂, the rate constants are k₀ = 1.8, 7.0, and 4.4 M^?1 s^?1; k₁ = 2.4 × 10³, 5.8 × 10³, and 5.3 × 10³ M^?1 s^?1; k₂ = 6.5 × 10⁸, 8.8 × 10⁸, and 7.9 × 10⁸ M^?1 s^?1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO₄/LiClO₄, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005     

Kinetic studies on the permanganic oxidation of amino acids. Effect of the length of amino acid carbon chain

The kinetic study of the permanganic oxidation of some amino acids (glycine, L-alanine, L-α-amino-n-butyric acid, L-norvaline, and L-norleucine) has been carried out in buffered acid medium at 1 < pH < 3 using a spectrophotometric technique. An autocatalytic effect due to Mn²⁺ ions was found in all cases. The purpose of this work is to study the influence of the length of carbon chain of the above amino acids. For it, structural factors such as steric, inductive, and hyperconjugation effects of the carbon chain were analyzed. It was found that the reactivity of these compounds is not affected by only one factor, but the influence of several factors and the formation of intermediate complexes could be included in these oxidative processes. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 181–185, 1997.     

Kinetics and mechanism of electron transfer reactions in aqueous solutions: Silver(I) catalyzed oxidation of aspartic acid by cerium (IV) in acid perchlorate medium

Silver(I) catalyzed oxidation of aspartic acid by cerium(IV) was studied in acid perchlorate medium. The stoichiometry of the reaction is represented by the eq. (i) Dimeric cerium(IV) species has been indicated and employed in calculations of monomeric cerium(IV) species concentrations. The reaction is second-order and uncatalyzed reaction also simultaneously occurs along with the silver(I) catalyzed reaction conforming to the rate law (ii) where k is an observed second-order rate constant. A probable reaction mechanism is suggested. © 1995 John Wiley & Sons, Inc.     

Kinetic and mechanistic studies of some aliphatic amines' oxidation by sodium N‐bromo‐p‐toluenesulfonamide in hydrochloric acid medium

Oxidations of n‐propyl, n‐butyl, isobutyl, and isoamyl amines by bromamine‐T (BAT) in HCl medium have been kinetically studied at 30°C. The reaction rate shows a first‐order dependence on [BAT], a fractional‐order dependence on [amine], and an inverse fractional‐order dependence on [HCl]. The additions of halide ions and the reduction product of BAT, p‐toluenesulfonamide, have no effect on the reaction rate. The variation of ionic strength of the medium has no influence on the reaction. Activation parameters have been evaluated from the Arrhenius and Eyring plots. Mechanisms consistent with the preceding kinetic data have been proposed. The protonation constant of monobromamine‐T has been evaluated to be 48 ± 1. A Taft linear free‐energy relationship is observed for the reaction with ρ* = −12.6, indicating that the electron‐donating groups enhance the reaction rate. An isokinetic relationship is observed with β = 350 K, indicating that enthalpy factors control the reaction rate. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 32: 776–783, 2000     

Kinetic and mechanistic studies of the oxidation of poly(o‐toluidine) doped with 5‐sulfosalicylic acid

Protonation of poly(o‐toluidine) base form (POT‐EB) with 5‐sulfosalicylic acid (SSA) was proved experimentally and computationally. Molecular mechanics (MM+) calculations showed that the potential energy (PE) of the optimum molecular geometric structure of SSA‐doped POT is 4.703 × 10³ kcal mol^?1 or at least three orders of magnitude higher than the PE of the molecular geometric structure of the same matrix. These calculations indicate that the optimization of this matrix is necessary for understanding the stability. Dark green coloration (λ ～800 nm) after addition of SSA into POT‐EB matrix (dark blue, λ ～600 nm) revealed that the SSA was working as a protonating agent to convert POT base form (POT‐EB) to salt form (SSA‐doped POT). The change of the dark green color of SSA‐doped POT to dark brown (λ ～500 nm) after addition of oxidant (K₂CrO₄) was due to the highest oxidized form of the matrix obtained (the quinoid one), which undergoes a hydrolysis reaction to produce p‐hydroquinone (H₂Q) by a mechanism similar to Schiff‐base hydrolysis. Kinetic parameters of the oxidation reaction were deduced employing a computer‐aided kinetic analysis of the absorbance (A) at ～800 nm against the hydrolysis time (t) data. The results obtained indicate that the rate controlling process may be governed by the Ginstling–Brounshetin equation for three‐dimensional diffusion (D4). The proposed mechanism for the oxidation of SSA‐doped POT matrix is also supported by MM+ calculations. Activation parameters for the rate of the oxidation process of acid‐doped POT matrix have been computed and discussed. © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 260–272, 2003     

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     

Kinetic studies on the oxidation of uranium(IV) in nitric acid solution

The kinetics of oxidation of U(IV) in nitric acid solution by nitrous acid and air oxygen have been studied. The effects of concentrations of U(IV), nitric acid, hydrogen ion and nitrous acid in aqueous solution or oxygen in gas on the oxidation rate have been examined. The oxidation rate increases with increasing temperature and the activation energies are 47 kJ mol^–1 for nitrous acid and 91 kJ mol^–1 for oxygen. The mechanisms for both oxidation reactions are discussed.     

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 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^–]. .

     

Delayed autocatalytic behavior of Mn(II) ions at a critical ratio: The effect of structural isomerism on permanganic oxidation of L‐norleucine

The kinetics of the permanganic oxidation process of L ‐norleucine, L ‐leucine, L ‐iso‐leucine, and L ‐tert‐leucine in strong acid medium has been investigated using a spectrophotometric technique. Conclusive evidences have proven autocatalytic activity of Mn(II) for these reactions in strong acid medium analogous to weak acid medium, but in the former, ratio of Mn(II) to amino acid concentration must reach a certain amount for autocatalytic phenomenon to emerge, which we call “critical ratio.” This critical ratio depends on the nature of the amino acid employed. Thus considering “delayed autocatalytic behavior” of Mn(II) ions, rate equations satisfying observations for both catalytic and noncatalytic routes have been presented. Kinetic data in a noncatalytic pathway have been fitted to a biparametric equation including inductive, steric, and hyperconjugation correction effects, and it is determined that by shifting the side branch on a carbon chain toward an α‐carbon atom (adjacent to amino acid's functional group) and also adding branches to the α‐carbon atom, the reaction rate in the noncatalytic pathway decreases. Inductive and steric hindrance factors in amino acid's carbon chain are effective on processes' rate both in catalytic and noncatalytic pathways. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 1–11, 2006     

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.     

Kinetic studies on the periodate oxidation of an iron(II) oxime‐imine complex

The iron(II) complex of H₂L (H₂L=3, 14‐dimethyl‐4, 7, 10, 13‐tetraazahexadeca‐3,13‐diene‐2,15‐dione dioxime, Coord. Chem. Rev., 33, 87 (1980)) is oxidized by periodate very rapidly in the range pH 2.0–7.0, and the kinetics of the reaction has been followed by stopped‐flow spectrophotometry at 30°C and ionic strength I=0.20 mol L⁻¹ (NaClO₄). The reaction is found to follow a simple second‐order kinetics as −d/dt [Fe^II(H₂L)²⁺]=k [Fe^II(H₂L)²⁺] [I(VII)], giving [Fe^III(L)]⁺ and IO₃⁻ as the final products. The reaction has been proposed to occur through a H‐bonded transition state formed probably between the protonated oxime group of the ligand and the oxygen atom on the periodate species, followed by an electron transfer from Fe^II centre to I^VII in a rate‐determining step. The I^VI species thus generated reacts in a fast step with another Fe^II complex. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 23–28, 1999     

Kinetics and mechanism of oxidation of l‐ascorbic acid by peroxomonophosphate in aqueous acid medium

The kinetics of oxidation of l ‐ascorbic acid (H₂A) by peroxomonophosphate in acid aqueous medium has been studied. The stoichiometry of the reaction corresponds to the reaction as represented by the equation (1) where A is dehydroascorbic acid. The reaction is second order versus first order with respect to each reactant. The rate is retarded by hydrogen ion concentration. A plausible reaction mechanism has been suggested. The derived rate law (2) from such a mechanism accounts for all experimental observations: (2) Such pH dependence is somewhat different from that observed in the case of metal ion oxidants. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 41–16, 2013     

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 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.     

Kinetics and mechanism of oxidation of antimony(III) by keggin‐type 12‐tungstocobaltate(III) in aqueous hydrochloric acid medium

The reaction between Sb(III) and [Co^IIIW₁₂O₄₀]^5? proceeds with two, one‐electron steps; formation of unstable Sb(IV) is the slow first step followed by its reaction with another oxidant in a fast step. The reaction rate is unaffected by the [H⁺] as there are no protonation equlibria involved with both the reactants, whereas the accelerating effect of chloride ion is due to the formation of an active chlorocomplex of the reductant, SbCl₆^3?. Increase in the ionic strength and decrease in the relative permittivity of the medium increases the rate of the reaction, which is attributed to the formation of an outer‐sphere complex between the reactants. The activation parameters were also determined and these values support the proposed mechanism. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 35: 9–14, 2003     

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     

Kinetics and mechanism of the picolinic acid catalysed chromium(VI) oxidation of ethane-1,2-diol in the presence and absence of surfactants

The kinetics and mechanism of the Cr^VI oxidation of ethane-1,2-diol in the presence and absence of picolinic acid (PA) in aqueous acid media have been carried out under the conditions: [ethane-1,2-diol]_T [Cr^VI]_T and [PA]_T [Cr^VI]_T at different temperatures. The micellar effect on the title reactions has been studied in order to substantiate the suggested mechanism. Under the experimental conditions, ethane-1,2-diol is predominantly oxidised to hydroxyethanal and the kinetic contribution from the glycol splitting path is negligible. In the absence of PA, the simple alcohol oxidation mechanism, involving one —OH group, operates. In the PA-catalysed path, a Cr^VI–PA cyclic complex has been proposed as the active oxidant. In the PA-catalysed path, the Cr^VI–PA complex is the subject of nucleophilic attack by the substrate to form a ternary complex which subsequently experiences a redox decomposition (through 2e transfer) leading to hydroxyethanal and the Cr^IV–PA complex. The Cr^IV–PA complex then participates further in the oxidation of organic substrate and ultimately is converted into the inert Cr^III–PA complex. It is striking to note that the uncatalysed path shows a second-order dependence on [H⁺], while the PA-catalysed path shows a zeroth-order dependence on [H⁺]. Both the uncatalysed and PA-catalysed paths show first-order dependence on [ethane-1,2-diol]_T and on [Cr^VI]_T. The PA-catalysed path is first-order in [PA]_T. All these observations (i.e. dependence patterns on the reactants) remain unaltered in the presence of externally added surfactants. The effect of the cationic surfactant (i.e. cetylpyridinium chloride, CPC) and anionic surfactant (i.e. sodium dodecyl sulfate, SDS) has been studied both in the presence and absence of PA. CPC acts as an inhibitor and restricts the reaction to aqueous phase, while SDS acts as a catalyst and the reactions proceed simultaneously in both aqueous and micellar phase, with an enhanced rate in the micellar phase. The observed micellar effects have been explained by considering the preferential partitioning of the reactants between the micellar and aqueous phase. The applicability of different kinetic models, e.g. the Menger–Portnoy model, Piszkiewicz cooperative model, pseudo-phase ion exchange (PIE) model, has been tested to explain the observed micellar effects.