Aqueous Acetonitrile Medium Research Articles

Effect of solvent nature on the catalytic activity of iron-containing pyrocatecholsulfonic cationite in the reactions of H2O2 decomposition and benzene hydroxylation

Kinetics of hydrogen peroxide decomposition under the conditions of heterogenous catalysis with iron-containing pyrocatecholsulfonic cationite at 50°C in dimethyl sulfoxide, tetrahydrofuran, dioxane, acetonitrile, and nitromethane was studied. The value of rate constant of hydrogen peroxide decomposition in these solvents was found to diminish with increase of solvent nucleophilicity. At the hydroxylation of benzene in the aqueous acetonitrile medium the formation of phenol was observed. The phenol yield was found to depend on the composition of the binary solvent acetonitrile-water.

Kinetics and Mechanism of the Chromium(VI) Oxidation of Some Primary Alcohols in the Presence of Heteroaromatic N-bases in Aqueous Acetonitrile Media

Heteroaromatic N-bases picolinic acid (PA) and 1,10-phenanthroline (Phen) in MeCN smoothly catalyse the chromium(VI) oxidation of some primary alcohols to the corresponding carbonyl compounds. The depletion of chromium(VI) shows complicated kinetic behaviour involving a fast reaction to ca. 25% consumption followed by a slow one. The Cr(VI)-PA and Cr(VI)–Phen complexes are believed to be the probable reactive electrophiles. The u.v–vis spectrum establishes the formation of a ternary complex and the kinetic data can be rationalized by envisaging its redox decomposition. The low dielectric constant of the medium assists the complex formation and enhances the reactivity. Curvature in the first order plots roughly indicates that chromium(VI) and chromium(V) complexes react at a comparable rate and complicate the kinetic parameters. CH3OH reacts ca. six times faster than CD3OD and this study strongly favours a hydride transfer mechanism. The reactivities of aliphatic alcohols are much greater than benzyl alcohol and this implies the predominance of the inductive effect over resonance effect.

Effect of substituents on the rate of oxidation of anilines with peroxomonosulfate monoanion (HOOSO−3) in aqueous acetonitrile: A mechanistic study

AbstractMechanistic studies on the oxidation of 18 meta‐, para‐, and ortho‐substituted anilines (Ans) by HOOSO−3 in aqueous acetonitrile medium have been performed. The reaction can be characterized by the experimental rate equation, equation image The addition of p‐toluenesulfonic acid (TsOH) retards the reaction. The increase in the reactivity of anilines as the medium is made more aqueous is interpreted. The reaction is enhanced by electron‐donating groups on the amine in the series consistent with the rate‐limiting nucleophilic attack of the amine on the persulfate oxygen. The proposed mechanism involves the conversion of phenylhydroxylamine to nitrosobenzene in a fast step. The ESR study reveals the absence of free radicals in the reaction. Various attempts have been made to analyze the experimental rate constants in terms of LFER plots. Improved correlations are obtained with σ− values and the σ− form of the Yukawa–Tsuno equation. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 649–657, 2005

Ion-Association Analysis between Inorganic Anions and Symmetrical Tetraalkylammonium Ions in Aqueous-Acetonitrile Media by Capillary Zone Electrophoresis

Abstract Weak ion-association equilibrium was analyzed in a water-acetonitrile solution at 25 °C by capillary zone electrophoresis using an ordinary silica capillary. The ion associates examined were formed between some inorganic anions and symmetrical tetraalkylammonium ions, where a series of acetonitrile compositions up to 62.2% (m/m) were investigated. Ion-association constants, Kass, were determined by analyzing the changes in the electrophoretic mobility; the Kass values for most of the anions increased up to about 47% (m/m) acetonitrile, beyond which they remained constant, or decreased slightly. The ion-association equilibrium between tetramethylammonium and bromide ions in aqueous-acetonitrile and in aqueous-ethanol media were compared through the Gibbs free energy of transfer, which revealed that the extent of the equilibrium in aqueous-acetonitrile media is dependent mainly on the increasing instability of Br−. On the other hand, those in aqueous-ethanol media depend on the instabilities of both tetramethylammonium and bromide ions.

Synthesis of kyotorphin precursor by an organic solvent-stable protease from Bacillus licheniformis RSP-09-37

The synthesis of the analgesic dipeptide kyotorphin precursor (Bz-Tyr-Arg-NH 2) was studied under kinetically controlled conditions in 10–90% (v/v) aqueous-acetonitrile media at −20 °C using a novel protease obtained from the cell free supernatant of a Bacillus licheniformis mutant strain (RSP-09-37). α-Chymotrypsin (CT) was used for comparison. The conditions for maximum yield of kyotorphin precursor synthesis were optimized using CT by varying the type of nucleophile (amide and ester), nucleophile concentration and nucleophile to acyl donor ratio. The nucleophile (Arg-NH 2) at a concentration 400 mM and nucleophile to acyl donor ratio 1:40 was found to be optimum for kyotorphin precursor synthesis. The protease from B. licheniformis RSP-09-37 was stable even at 90% acetonitrile concentration and allowed for a significantly higher synthesis over hydrolysis ratio (S/H ratio) of 15.6 compared to only 3.0 found for CT at −20 °C.

Determination of direct orange 8 in effluent using a polypyrrole modified electrode

Electrochemical studies of direct orange 8 were carried out with a bare glassy carbon electrode (GCE) and a polypyrrole-coated GCE in aqueous acetonitrile medium using voltammetric techniques. One reversible couple around 0.3 V due to the redox reaction of the phenol group, one reduction peak around −0.4 V due to reduction of the azo group and one oxidation peak around 1.0 V due to oxidation of the amino group were observed. Chronocoulometric studies revealed dye adsorption on the GCE. A square-wave stripping method was developed for the determination of the dye at pH 13.0, and a linear calibration equation obtained. The reproducibility in the measurement of peak currents was confirmed from the RSD value 2.8% at 0.001 mg mL−1 concentration. A comparison of the stripping voltammetric method with the UV-Vis spectrophotometric method was made. The determination limits are wider and the RSD value is lower in the stripping voltammetric method. The concentration of the dye present in dye effluent was determined using this method.

Carboxylate-substituted radicals from phenylselenide derivatives. Designs on models for coenzyme B12-dependent enzyme-catalyzed rearrangements.

Laser flash photolysis (266 nm) of alpha- and beta-phenylselenyl esters, carboxylic acids, and carboxylates in aqueous acetonitrile media gave the corresponding radicals by homolytic cleavage of the phenylselenyl groups. In the beta-substituted systems, acid and carboxylate radicals reacted in intramolecular reporter reactions with approximately equal rate constants. For the alpha-substituted systems, an ester- and carboxylic acid-substituted radical reacted in an intramolecular reporter reaction with the same rate constants, but the analogous alpha-carboxylate radical, a radical anion, reacted an order of magnitude less rapidly and with an activation energy that is 3 kcal/mol greater than that found for analogues. A kinetic titration of the equilibrating alpha-acid and alpha-carboxylate radicals gave pKa = 4.6. The results indicate that alpha-ester and alpha-carboxylic acid radicals are unlikely to be appropriate models for alpha-carboxylate radicals, the intermediates formed in a large subset of coenzyme B12-dependent enzyme-catalyzed reactions.

Catalytic Activity of Tetraarylporphyrins in the Oxidation Reactions of Saturated Hydrocarbons

The oxidation of cyclic hydrocarbons by potassium peroxymonosulfate catalyzed by the iron and manganese complexes of tetra-(4-N-butylpyridinium)porphyrin, tetraphenylporphyrin, and mixed porphyrins containing phenyl and butylpyridyl substituents was studied in an aqueous acetonitrile medium. The test catalysts were dissolved in the reaction medium or adsorbed on layered aluminosilicates. It was found that the immobilization of metal complexes on layered aluminosilicates, as well as the bromination of porphyrins, decreased the activity of catalysts in a number of cases, although it improved their stability. The addition of pyridine in an equimolar amount with respect to metal complexes to the reaction mixture increased the activity of dissolved manganese complexes. An increase in the number of butylpyridyl meso-substituents in a porphyrin molecule improved the catalytic activity of a metal complex.

Oxidation of indole‐3‐acetic acid by peroxomonosulphate: A kinetic and mechanistic study

AbstractKinetics of oxidation of indole‐3‐acetic acid (IAA) by peroxomonosulphate (PMS) in aqueous acetonitrile medium has been investigated. The reaction follows a total second order, first order each with respect to [IAA] and [PMS]. The rate of the reaction was not affected by added [H+]. Variation of ionic strength (μ) had no influence on the rate. Increase of percentage of acetonitrile decreased the rate. Absence of any polymerization indicated a nonradical pathway. Activation and thermodynamic parameters have been computed. A suitable kinetic scheme based on these observations is proposed. The reactivity of PMS towards IAA was found to be higher than that with peroxodisulphate. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 569–574, 2002

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

AbstractThe catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)2/HQ/FePc wan investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV‐VIS, IR., XPS spectroscopy and cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyclohexene catalysed by Pd(OAc)2/HQ/FePc was elucidated.

Determination of endosulfan by stripping voltammetry

The electroreduction and adsorption of endosulfan was studied in aqueous and acetonitrile media. The optimum experimental conditions were derived at a stationary glassy carbon electrode by differential-pulse and square-wave stripping voltammetric techniques and used for the determination of endosulfan in soil samples. The best determination limit (ng ml–1 and lower) for endosulfan in a soil sample was obtained with the square-wave stripping technique in an aqueous acetonitrile medium.

Polarography of n‐Butyl 3‐Mercaptopropionate In Water and its Mixtures With Methanol, Acetonitrile and Dioxane

AbstractThe polarographic behaviour of n‐butyl 3‐mercaptopropionate (R‐S‐H) at the DME in aqueous methanol, acetonitrile and 1,4‐dioxane has been investigated in presence of 0.1 M KNO3 and 0.01% thymol. The effect of pH, concentration of RSH and drop time, on the wave characteristics and the mechanism of the reaction occurring at the surface of the mercury drop have been studied. Well‐defined reversible and diffusion controlled anodic waves were obtained in aqueous (pH=3.8) 40% v/v methanol (pH=3.86) and 40% v/v acetonitrile (pH=2.94). In 40% v/v dioxane a well‐defined irreversible anodic wave was obtained at pH=8.1. Mathematical and analytical evidence was obtained to show that the anodic wave of RSH at the DME in aqueous 408 v/v methanol, 40% v/v acetonitrile and 40% v/v dioxane is due to formation of a mercury complex RSHg. The linearity of id with RSH concentration provides a rapid and precise method for the determination of RSH, down to 0.4 mM in aqueous methanol, acetonitrile and dioxane medium

Oxidimetric determination of thiourea—xanthate and thiourea3-dithiocarbamate mixtures

A convenient and accurate method has been developed for the analysis of thiourea—xanthate and thiourea—dithiocarbamate mixtures by oxidimetric titration of the mixture with iodine monobromide first in acetonitrile medium and then in acidic aqueous acetonitrile medium. The end-points can be detected both visually and potentiometrically. The methods are rapid and have wide applications.

Volumetric determination of tetraalkyl thiuram disulphides

A method for the volumetric determination of tetraalkyl thiuram disulphide is developed. It is based on its reaction with potassium cyanide in aqueous acetonitrile medium, when the corresponding tetraalkyl thiuram monosulphide and thiocyanate are formed. The former is removed by extraction with benzene and the latter converted into cyanogen bromide, which is estimated iodometrically.