Micelle Catalyzed Oxidation of D-Mannose by Cerium (IV) in Sulfuric Acid

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40°C both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and cerium (IV), which decreased with increasing [H₂SO₄]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (IV) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was the reactive form of cerium (IV). From the kinetic data, micelle-cerium (IV) binding and rate constants in micellar medium were evaluated. The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression: -d[Ce(IV)]=k1Kc1[D-mannose][Ce(IV)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

Choice of a suitable hetero-aromatic nitrogen base as promoter for chromic acid oxidation of dl-mandelic acid in aqueous media at room temperature

Chromic acid oxidation of dl-mandelic acid in the presence and absence of different promoters has been studied in aqueous media under the kinetic conditions [mandelic acid]_T ? [Cr(VI)]_T and [promoter]_T ? [Cr(VI)]_T at 30 °C. The promoters used in this oxidation reaction, picolinic acid (PA), 2,2′-bipyridine (bpy), and 1,10-phenanthroline (phen), are strong chelating ligands which form complexes with most transition metal ions. The reaction is first-order with regard to [H⁺], [mandelic acid]_T, and [Cr(VI)]_T and also has first-order dependence on [promoter]_T. HCrO₄ ^? was found to be kinetically active in the absence of promoters; in the presence of promoters the Cr(VI)–promoter complexes were believed to be the active oxidants. In this path the Cr(VI)-promoter complex in each case undergoes nucleophilic attack by the mandelic acid to form a ternary complex which subsequently undergoes redox decomposition involving 3e transfer as the rate-determining step. Among the three promoters oxidation is much faster with 1,10-phenanthroline.     

Kinetics and mechanism of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) by N-bromosuccinimide in aqueous acidic medium

The kinetics of oxidation of N,N-bis(salicylaldehyde-1,2-diaminoethane) cobalt(II) complex by N-bromosuccinimide (NBS) in aqueous acid and H₂O–MeOH solvent mixtures were studied spectrophotometrically over the 20–40 °C range, 0.1–0.5 mol dm^?3 ionic strength, 2.2–2.8 pH range and 0–40 wt% MeOH–H₂O solvent mixtures for a range of NBS and complex concentrations. The rate shows first-order dependence on both [NBS] and [complex] and decreases with pH over the range studied. The protonated form of N-bromosuccinimide was identified as the main reactive species. An inner-sphere mechanism involving free radicals is proposed.     

Micellar Effect on the Reaction of Chromium(VI) Oxidation of L‐Sorbose in the Presence and Absence of Picolinic Acid in Aqueous Acid Media: A Kinetic Study

The kinetics and mechanism of chromic acid oxidation of L‐sorbose in the presence and absence of picolinic acid (PA) have been studied under the conditions, [L‐sorbose]_T » [PA]_T » [Cr(VI)]_T, at different temperatures. In the absence of PA, the monomeric chromic acid undergoes esterification with the substrate followed by the acid catalysed redox decomposition of the Cr(VI)‐substrate ester through glycol splitting to formaldehyde and the lactone of C₅‐aldonic acid and Cr(IV) which subsequently participates in the faster reactions. In the presence of PA, the Cr(VI)‐PA complex produced in a pre‐equilibrium step experiences a nucleophilic attack by the substrate to produce a ternary complex which decomposes through glycol splitting giving rise to the organic products and Cr(IV)‐PA complex. Both the uncatalysed and PA‐catalysed paths show the first‐order dependence on [L‐sorbose]_T and [Cr(VI)]_T. The PA‐catalysed path is first‐order in [PA]_T and it shows a fractional order in [H⁺]. The uncatalysed path shows a second‐order dependence on [H⁺]. In the presence of the surfactants like N‐cetylpyridinium chloride (CPC, a cationic surfactant) and sodium dodecyl sulfate (SDS, an anionic sulfate), the reaction orders remain unchanged. CPC has been found to inhibit both the uncatalysed and PA‐catalysed paths while SDS shows the rate accelerating effect for both the uncatalysed and PA‐catalysed paths. The observed micellar effects have been rationalised by considering the distribution of the reactants between the micellar and aqueous phases in terms of the proposed reaction mechanism.     

Kinetics and mechanism of oxidation of ferrocyanide by N-bromosuccinimide in aqueous acidic solution

The kinetics of oxidation of ferrocyanide by N-bromosuccinimide (NBS) has been studied spectrophotometrically in aqueous acidic medium over temperature range 20–35 °C, pH = 2.8–4.3, and ionic strength = 0.10–0.50 mol dm⁻³ over a range of [Fe²⁺] and [NBS]. The reaction exhibited first order dependence on both reactants and increased with increasing pH, [NBS], and [Fe²⁺]. The rate of oxidation obeys the rate law: d[Fe³⁺]/dt = [Fe(CN)₆]^4–[HNBS⁺]/(k ₂ + k ₃/[H⁺]). An outer-sphere mechanism has been proposed for the oxidation pathway of both protonated and deprotonated ferrocyanide species. Addition of both succinimide and mercuric acetate to the reaction mixture has no effect on the reaction rate under the experimental conditions. Mercuric acetate was added to the reaction mixture to act as scavenger for any bromide formed to ensure that the oxidation is entirely due to NBS oxidation.     

Kinetics and mechanism of the redox reaction between malachite green and iron(III) in aqueous and micellar media

The kinetics of the oxidation of malachite green (MG⁺) by Fe(III) were investigated spectrophotometrically by monitoring the absorbance change at 618 nm in aqueous and micellar media at a temperature range 20–40 °C; I = 0.10 mol dm^?3 for [H⁺] range (2.50–15.00) × 10^?4 mol dm^?3. The rate of reaction increases with increasing [H⁺]. The reaction was carried out under pseudo-first-order conditions by taking the [Fe(III)] (>10-fold) the [MG⁺]. A mechanism of the reaction between malachite green and Fe(III) is proposed, and the rate equation derived from the mechanism was consistent with the experimental rate law as follows: Rate = (k ₄ + K ₁ k ₅[H⁺]) [MG⁺][Fe(III)]. The effect of surfactants, such as cetyltrimethylammonium bromide (CTAB, a cationic surfactant) and sodium dodecylsulfate (SDS, an anionic surfactant), on the reaction rate has been studied. CTAB has no effect on the rate of reaction while SDS inhibits it. Also, the effect of ligands on the reaction rate has been investigated. It is proposed that electron transfer proceeds through an outer-sphere mechanism. The enthalpy and the entropy of the activation were calculated using the transition state theory equation.     

Properties and Extraction for [Ni(NH3)6]2+ of ATPS-a Formed by Aqueous Cationic–Anionic Surfactant Mixtures

The properties and extraction for [Ni(NH₃)₆]²⁺ of anionic aqueous two-phase systems (ATPS-a) that formed in mixtures of cetyltrimethylammonium bromide (CTAB) and excess sodium dodecyl sulfate (SDS) aqueous solutions were investigated. The results showed that the properties and extraction effects were strongly affected by the surfactant concentration, the temperature of system, and the mole fraction of surfactants. The increase of temperature induces narrower phase region and larger phase volume ratio. In addition, [Ni(NH₃)₆]²⁺ was extracted into the surfactant-rich phase with higher distribution coefficient when the liquid crystal had the birefringent properties. Moreover, the distribution coefficient can be improved through reducing the concentration of surfactant from 0.15 to 0.05 mol · L^?1 or increasing mole fraction of CTAB from 21.9% to 23.1%. The results showed that ATPS of cationic–anionic surfactants was efficient for [Ni(NH₃)₆]²⁺ extraction with distribution coefficients of 13.5 when the total surfactant concentration was 0.05 mol · L^?1, mole fraction of CTAB was 21%, and temperature was 34°C.     

Kinetic Study of Complex Formation of by 2‐Nitroso‐1‐naphthol with Cobalt (II) Ion in Presence of Cetyltrimethylammonium Bromide Surfactant

The kinetic complex formation of 0.001 M 2‐nitroso‐1‐naphthol (NAPH)with 0.01 M cobalt (II) ion (Co²⁺) in aqueous in presence of 0.02 M NaOH at 30°C in aqueous and/or in and 0.002 M cetyltrimethylammonium bromide (CTAB) have been studied using spectrophotometer at 430 nm. The present data showed that the reaction is first‐order with respect to [Co²⁺]_T and NAPH. Also, k _obs have constant values within concentration 0.015–0.05 M of NaOH and decreases with increase of concentration of CTAB to 0.002 M, then, k _obs have constant values up to 0.005 M. The rate of the reaction in the presence of micelles has been explained with the pseudo‐phase model of the kinetics. Association constants of Co²⁺ and NAPH to CTAB micelle have been calculated. The activation parameters ΔH* and ΔS* have been obtained. The increase of reaction rate with sodium benzoate (C₇H₅O₂Na) also has been discussed.     

Kinetics and mechanism of interaction of dipeptide (glycyl–glycine) with ninhydrin in aqueous micellar media

The rates of reaction between ninhydrin and dipeptide glycyl–glycine (Gly–Gly) have been determined by studying the reaction spectrophotometrically at 70°C and pH 5.0 in aqueous and in aqueous cationic micelles of cetyltrimethylammonium bromide (CTAB). The reaction follows first‐ and fractional‐order kinetics, respectively, in [Gly–Gly] and [ninhydrin]. The observed rate constant is affected by [CTAB] changes and the maximum rate enhancement is ca. three‐fold. As the k_ψ ? [CTAB] profile shape is characteristic of bimolecular reactions catalyzed by micelles, the catalysis is explained in terms of the pseudo‐phase model of the micelles (proposed by Menger and Portnoy and developed by Bunton and Romsted). The presence of inorganic salts (NaCl, NaBr, Na₂SO₄) does not reveal any regular effect but the data with organic salts (NaBenz, NaSal) show an increase in the rate followed by a decrease. The kinetic data have been used to calculate the micellar binding constants K_S for Gly–Gly and K_N for ninhydrin and the respective values are 317 and 69 mol^?1 dm³. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 643–650, 2006     

Effect of Cationic Micellar Aggregates on the Kinetics of Dextrose Oxidation by N-Bromophthalimide

The effect of cationic micelles of Cetyltrimethyl ammonium bromide (CTAB) on the kinetics of oxidation of dextrose by N-Bromophthalimide were studied at 40°C. The reaction follows fractional-order and first order kinetics, with respect to [dextrose] and [NBP], respectively. CTAB strongly catalyze the reaction, and typical k_obs and [CTAB] profile was observed, that is, with a progressive increase in [CTAB], the reaction rate increased, reaches a maximum value then decreased. Results are treated quantitatively in terms of Berezin's Model, which is applicable to bimolecular micellar catalyzed reaction. There is a negative effect of mercuric acetate and phthalimide. The influence of salts on the reaction rates has also been seen. The activation parameters as well as other parameters were calculated and suitable mechanism consistent with the experimental findings has been proposed.     

N‐bromosuccinimide oxidation of dipeptides and their amino acids: Synthesis,kinetics and mechanistic studies

Dipeptides (DP), namely valyl–glycine (Val–Gly), alanyl–proline (Ala–Pro), and valyl–proline (Val–Pro) were synthesized by classical solution phase methods and characterized. The kinetics of oxidation of amino acids (AA) and DP by N‐bromosuccinimide (NBS) was studied in the presence of perchlorate ions in acidic medium at 28°C. The reaction was followed spectrophotometrically at λ_max = 240 nm. The reactions follow identical kinetics, being first order each in [NBS], [AA], and [DP]. No effect on [H⁺], reduction product [succinimide], and ionic strength was observed. Effects of varying dielectric constant of the medium and addition of anions such as chloride and perchlorate were studied. Activation parameters have been computed. The oxidation products of the reaction were isolated and characterized. The proposed mechanism is consistent with the experimental results. An apparent correlation was noted between the rate of oxidation of AA and DP. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 376–385, 2006     

Mechanistic investigation of oxidation of metronidazole and tinidazole with N-bromosuccinimide in acid medium: A kinetic approach

Metronidazole (MTZ) and tinidazole (TNZ) belong to nitroimidazole group of drugs used to treat infections such as ameobiasis, giardiasis and trichomoniasis. The kinetics of oxidation of MTZ and TNZ with _N-bromosuccinimide (NBS) in perchloric acid medium has been investigated at 308 K. A 1:1 stoichiometry has been observed in both MTZ and TNZ cases. The oxidation reactions of both MTZ and TNZ follow the same rate law, -d[NBS]/dt = [NBS][Sub][H⁺]. However, in case of MTZ, at higher concentrations of H⁺ (0.006–0.01 mol dm^?3), the rate law obtained is -d[NBS]/dt = [NBS][MTZ][H⁺]^?1. Accelerating effect of [Cl^-] and retardation of the added succinimide on the reaction rate have been observed in the case of MTZ. The reactions were examined with reference to changes in concentration of added neutral salt, ionic strength and dielectric permittivity of the medium. The overall activation parameters have been evaluated from the Arrhenius plot. The reactive oxidizing species of NBS have been determined. The main oxidation products were identified by IR and ¹H NMR spectral analyses. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced.     

Kinetics and mechanism of oxidation of (aqua-2-aminomethyl-pyridine) chromium(III) by N-bromosuccinimide

Summary The kinetics of oxidation of (aqua-2-aminomethyl-pyridine) Cr^III by N-bromosuccinimide (NBS) in aqueous solution to yield chromium(VI) has been studied spectrophotometrically over the 25–40 °C range. The reaction rate is first order with respect to both [NBS] and [Cr^III], and increases with increasing pH between 7.6 and 8.6. The thermodynamic activation parameters were calculated. The experimental rate law is consistent with a mechanism in which the deprotonated [Cr(L)₂(OH)]²⁺ was considered to be the most reactive form compared to its conjugate acid. It is assumed that electron transfer takes place via an inner-sphere mechanism.     

Kinetics and mechanism of oxidation of β-Alanine by <Emphasis Type="Italic">N</Emphasis>-bromophthalimide in the presence of Ru(III) chloride as homogenous catalyst in acidic medium

The kinetics of Ru(III) chloride-catalyzed oxidation of β-Alanine (NH₃ ⁺CH₂CH₂COOH, β-Ala) by N–bromophthalimide (NBP) in aqueous perchloric acid medium was studied at 35 °C. The rate law followed a first-order and zero-order dependence with respect to [NBP] and [β-Ala], respectively. The reaction followed first-order kinetics with respect to [Ru(III)] chloride at a range of low concentrations while the order changed from first- to zero-order at high concentration of [Ru(III)] chloride; demonstrating the catalytic effect for the oxidation of β-Ala by NBP. The rate decreased with increase in acidity. Chloride ions positively influenced the rate of the reaction. Neither phthalimide (NHP) nor Hg(II) influenced the reaction rate. Ionic strength (I) and dielectric constant (D) of the medium had no significant effect on the rate. Activation parameters of the reactions were determined by studying the reaction at different temperatures (30–50 °C). The colorimetric, FTIR, and GC-MS techniques were used to identify methyl cyanide (CH₃CN) and CO₂ as products of the reaction. In the reaction, approximately 2.3 moles of NBP oxidized one mole of β-Ala. A reaction scheme of the oxidation of β-Ala by NBP in the presence of Ru(III) chloride was found to be in consistent with the rate law and the reaction stoichiometry.     

Thermodynamic characteristics of alanine-18-crown-6 ether complexes in binary water-acetone solvents

The formation of 18-crown-6 ether (18C6) complexes with D,L-alanine (Ala) in mixed wateracetone solvents with 0.0, 0.08, 0.17, 0.22, and 0.30 mole fractions of acetone (T = 298.15 K) was investigated by means of calorimetry. Thermodynamic characteristics of the reaction of the molecular [Ala18C6] complex formation (Δ_r G°, Δ_r H°, and TΔ_r S°) were calculated on the basis of calorimetric data. Analysis of solvation contributions of reagents into the enthalpy of the [Ala18C6] formation reaction showed that the changes in the reaction energy when the solvent composition is varied are determined by the changes in the solvate state of 18C6.     

Effect of surfactant micelles on the kinetics of oxidation of D‐fructose by cerium(IV) in sulfuric acid medium

Kinetics of the oxidation of D ‐fructose by cerium(IV) has been investigated both in the absence and presence of surfactants (cetyltrimethylammonium bromide, CTAB, and sodium dodecyl sulfate, SDS) in sulfuric acid medium. The reaction exhibits first‐order kinetics each in [cerium(IV)] and [D ‐fructose] and inverse first order in [H₂SO₄]. The Arrhenius equation is found to be valid for the reaction between 30–50°C. A detailed mechanism with the associated reaction kinetics is presented and discussed. While SDS has no effect, CTAB increases the reaction rate with the same kinetic behavior in its presence. The catalytic role of CTAB micelles is discussed in terms of the pseudophase model proposed by Menger and Portnoy. The association constant K_s that equals to 286 mol^?1 dm³ is found for the association of cerium(IV) with the positive head group of CTAB micelles. The effect of inorganic electrolytes (Na₂SO₄, NaNO₃, NaCl) has also been studied and discussed. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 18–25, 2006     

硫酸溶液中胶束催化Ce(IV)氧化D-甘露糖

Kinetics of D-mannose oxidation by cerium (IV) was studied in a sulfuric acid medium at 40℃ both in absence and presence of ionic micelles. In both cases, the rate of the reaction was first-order in D-mannose and in cerium(Ⅳ), which decreased with increasing [H2SO4]. This suggested that the redox reaction followed the same mechanism. The reaction proceeded through formation of an intermediate complex, which was proved by kinetic method. The complex underwent slow unimolecular decomposition to a free radical that reacted with cerium (Ⅳ) to afford the product. The catalytic role of cationic cetyltrimethylammonium bromide (CTAB) micelles was best explained by the Menger-Portnoy model. The study of the effect of CTAB also indicated that a negatively charged species was reactive form of cerium (Ⅳ). From the kinetic data, micelle-cerium (Ⅳ) binding and rate constants in micellar medium were evaluated.The anionic micelle of sodium dodecyl sulfate plays no catalytic role. The oxidation has the rate expression --d[Ce(Ⅳ)]= k1Kcl[D-mannose] [Ce(Ⅳ)]dt Different activation parameters for micelle catalyzed and uncatalyzed paths were also calculated and discussed.     

Kinetics and mechanism of the reduction of μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] by dithionate ion

The kinetics and mechanism of the reduction of the μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] complex, [Fe₂adi], by dithionate ion, S₂O₆ ^2?, have been investigated in aqueous perchloric acid at 29 °C, I = 0.05 mol dm^?3 (NaClO₄) and [H⁺] = 5.0 × 10^?3 mol dm^?3. Spectrophotometric titrations indicated that one mole of the reductant was oxidized per mole of oxidant. Kinetic profiles indicated first-order rate with respect to [Fe₂adi] but zeroth-order dependence on [S₂O₆ ^2?]. The rate of reaction increased with increase in [H⁺], decreased with increased dielectric constant, but was invariant to changes in ionic strength of the medium. Addition of small amounts of AcO^? and Mg²⁺ ions did not catalyse the reaction. A least-squares fit of rate against [H⁺]² was linear (r ² = 0.984) without intercept. The reaction was analysed on the basis of a proton-coupled outer-sphere electron transfer mechanism.     

Ruthenium(III), osmium(VIII) and ruthenium(III) + osmium(VIII) catalysed oxidations ofi-propanol by N-bromosuccinimide in basic solution

Summary The oxidation ofi-propanol (IPA) by N-bromosuccinimide (NBS) in basic solution was investigated separately in the presence of Ru^III, Os^VIII and Ru^III + Os^VIII ions. The order in [IPA] was found to be 0.7, 0.5 and 0.3 respectively in the above three cases in the concentration range studied. The order in [NBS] was unity in the presence of Ru^III chloride but was found to be zero in the case of Os^VIII and Ru^III+Os^VIII catalysis. The order in [metalion] was found to be nearly unity in all the three catalysed reactions. Increase in [^–OH] increased the rate of reaction while addition of succinimide retarded the rate of reaction. Decrease in dielectric constantsof the medium decreased the rate of oxidation. The pseudo first order rate constants (k), zero order rate constants (k₀) and the formation constants (k_f) of the substrate-catalyst complexes and the thermodynamic parameters have been evaluated. Suitable mechanisms in conformity with the experimental observations have been proposed for the three catalysed reactions.