In Process Citation

The mild oxidation of bactericidal sulphonamides by hydrogen peroxide in acidic medium at room temperature in daylight, is reported. The oxidation products have been isolated by classical chromatography and purified, and their purity has been determined by HPLC. They have been identified by spectroscopy, chiefly by infrared and mass spectroscopy. An oxidation product not previously reported has been isolated and identified. An oxidation mechanism and the kinetics are discussed.     

Kinetic Studies of Acenaphthene Oxidation Catalyzed by N‐Hydroxyphthalimide

The acenaphthene oxidation with molecular oxygen in the presence of N‐hydroxyphthalimide (NHPI) has been investigated. It is shown that the main oxidation product is acenaphthene hydroperoxide. The phthalimide‐N‐oxyl (PINO) radical has been generated in situ from its hydroxyimide parent, NHPI, by oxidation with iodobenzenediacetate. The rate constant of H‐abstraction (k_H) from acenaphthene by PINO has been determined spectroscopically in acetonitrile. The kinetic isotope effect and the activation parameters have also been measured. On the basis of the results of our studies and available published literature data, a plausible mechanism for the oxidation process of acenaphthene with dioxygen catalyzed by NHPI was discussed.     

Kinetics and mechanism of the oxidation of α-amino acids by n-bromoacetamide

The kinetics of the oxidation of eight α-amino adds by N-bromoacltanude have been studied in aqueous perchloric acid solution. The main products of the oxidation are the corresponding carbonyl compounds. The reaction is of first order with respect to the oxidant and the amino acid. The rate of oxidation decreases linearly with an increase in hydrogen ion concentration. The rate is decreased by the addition of acetamide. The oxidation of deuteriated glycine indicated the absence of a primary kinetic isotope effect. The reaction rate has been determined at different temperatures and activation parameters have been calculated. Hypobromous add has been postulated as the reactive oxidizing species. A rate-determining reaction of the neutral amino add and hypobromous add to give an N-bromo derivative has been proposed. The slow step is followed by a fast decomposition of the N-bromo derivative to yield the ultimate product.     

In Process Citation

The electrochemical oxidation of khelline and amikhelline (chromone derivatives) has been performed by cyclic voltammetry at carbon-paste and polymeric carbon electrodes. The mechanism of oxidation of the two compounds at various pH values has been deduced. The detection limit is 8 x 10(-7)M. A constant-current coulometrie procedure is also described, based on the oxidation of the two chromones with vanadium(V) and backtitration of the excess of oxidant with iron(II).     

A comparative study on direct and indirect electrochemical oxidation of polyaromatic compounds

This study has been performed to investigate the treatment of an industrial wastewater containing naphthalene- and anthraquinone-sulfonic acids, by direct and indirect electrolyses. The direct electrochemical oxidation has been carried out using boron-doped diamond and lead dioxide anodes, while the indirect electrolyses has been mediated by active chlorine electrogenerated on a platinum anode, or by hydrogen peroxide electrogenerated on a graphite felt cathode. For each type of electrolyses the effects of operating parameters, such as anode material, current density, chloride concentration, ferrous ions concentrations have been also investigated. Measurements of Chemical Oxygen Demand (COD) and colour fading have been used to compare the results of different electrolyses. Experimental data showed that the complete COD and colour removals have been obtained only by direct oxidation or by active chlorine mediated electrolyses. On the contrary using electrogenerated hydrogen peroxide the solution has been presented a residual COD and colour. In particular, it found that faster oxidation rate has been obtained by direct oxidation using a boron-doped diamond anodes at low current density.     

Oxidation of ferrocene and some substituted ferrocenes in the presence of horseradish peroxidase

The enzyme catalysed oxidation of ferrocene and some substituted ferrocenes to the corresponding ferricinium ions by hydrogen peroxide in the presence of native or immobilized horseradish peroxidase has been studied. Initial and maximum rates of oxidation have been determined. It was found that the oxidation was independent of the hydrogen peroxide concentration. The oxidation of ferrocene was effected also by horseradish peroxidase in a coupled system with glucose oxidase in the absence of any added hydrogen peroxide.     

Kinetics and mechanism of oxidation of phenylhydrazine and P-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium

Kietics of oxidation of phenylhydrazine and p-bromophenylhydrazine by hexacyanoferrate(III) in acidic medium have been studied. The reactions follow similar kinetics, being first order with respect to both hydrazine and exacyanoferrate(III) and inverse first order with respect to the hydrogen ion. Addition of hexacyanoferrate(II) has no retarding effect on the rate of oxidation. The effects of varying ionic strength, dielectric constant, and temperature on the reaction rates have been investigated. A plausible mechanism has been proposed to account for the experimental results. Benzene and bromobenzene have been identified as the oxidation products.     

Polarographische und voltammetrische Untersuchungen an symmetrischen Methin-, Azamethin- und Phosphamethincyaninen in Acetonitril

Polarographic Investigations on Symmetrical Methine-, Azamethine-, and Phosphamethinecyanine dyes in Acetonitrile Solution The reduction and oxidation behaviour of six symmetrical methine-, azamethine-, and phosphamethine dyes with different heterocycles in MeCN solutions has been investigated by menas of dc- and ac-polarography (DME, MDE and rotating Pt-electrode) and cyclic triangular wave voltammetry. The reduction and oxidation mechanism has been found to be of the type ec with the reduction and oxidation step being reversible to irreversible. Reduction and oxidation potentials, transfer coefficients, and specific currents have been measured and compared with known properties of methinecyanines, carbocyanines, and triazacarhocyanines.     

Sorption and sensing characteristics of polyvinyl alcohol films impregnated with CaCl2

Selective methanol oxidation to formaldehyde over polycrystalline copper has been studied with the use of in situ XPS combined with mass spectrometry. It has been shown that the copper surface completely covered by methoxy groups exhibits low activity in methanol oxidation, whereas the metallic copper with sub-oxide oxygen is active in the selective oxidation of methanol to formaldehyde. The concentration of the sub-oxide oxygen species seems to correlate with the rate of formaldehyde production. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computational modeling of the mechanisms of the free radical-chain reaction of alkanes with oxygen. The oxidation of isobutane,n-butane,and isopentane

A general computational method for obtaining complete solutions of time-dependent kinetic equations has been developed and applied to free radical-initiated reactions of alkanes with oxygen. The method has been applied to the low-temperature, peroxide-initiated oxidations of isobutane and isopentane. Using available independently measured and estimated values for the rate constants and activation parameters for each of the 20 proposed reaction steps for the oxidation of isobutane, the rates and products have been calculated for both the liquid phase and gas phase in the range of 100°–155°C. The calculated rates and products of oxidation agree with published experimental values. The oxidation of isopentane was examined by a 32-reaction model. The rate constants were estimated using values for the appropriate rate steps in the oxidation of n-butane and isobutane. The calculation of the oxidation rate and products agree with our experiments.     

Low-temperature heterogeneous oxidation of sulfide ions on a higher Co oxide system in aqueous medium

Low-temperature heterogenous oxidation of sulfide ions on a higher Co oxide system in aqueous medium has been studied. The effects of pH, temperature and catalyst amount on the kinetic parameters as well as on the selectivity of the oxidation process were investigated. An oxidation mechanism has been proposed based on the results of kinetic investigations and on the data obtained by IR and XPS spectroscopic studies of Co oxide before and after sulfide ion oxidation.     

Surface and interface engineering in transition metal–based catalysts for electrochemical water oxidation

A tremendous effort has been provided in last two decades to develop efficient transition metal–based heterogeneous catalysts for the electrochemical water oxidation. Several approaches such as composition modulation, heteroatom doping, morphological development, particle size tuning, surface area enhancement, and control over electronic structure have been explored for the designing of the materials with improved water oxidation activity. As the electrochemical process is a surface phenomenon, surface structure plays a crucial role in controlling the water oxidation activity. Rational engineering of the catalyst surface by composition modulation, crystal facet tuning, and generating functional overlayer has been reported to enhance the water oxidation activity. Heteroatom doping, cationic and anionic deficiencies, and ultrathin 2D morphology are also found to promote electrochemical performance. In addition, engineering in the interface provides intrinsic improvement of the catalytic activity and stability for the electrochemical water oxidation. Although, surface and interface engineering of the catalyst has come out as the major factors in the electrochemical water oxidation, no dedicated review is available in this field. In this review, we have described the strategies of improving water oxidation activity of the catalysts by surface and interface engineering. The progress in this field discussed in detail; the challenges have been identified and addressed to attain a clear understanding in this field.     

Effect of inclusion complex on nitrous acid reaction with flavonoids

The kinetic of the nitrous acid reactions with quercetin and catechin has been studied using spectrophotometric method in aqueous solution. The results show that these antioxidants participate in oxidation reactions with nitrous acid which is derived from protonation of nitrite ion in mild acidic conditions. Corresponding o-quinones as relatively stable products were detected by spectrophotometric techniques. pH dependence of the reactions has been examined and the rate constants of reactions were obtained by non-linear fitting of kinetic profiles. The effect of β-cyclodextrin on the oxidation pathway was another object of this study. It is shown that β-cyclodextrin has an inhibitory effect on the oxidation reaction. The rate constants of oxidation reactions for complexed forms and their stability constants were obtained based on changes in the reaction rates as a function of β-cyclodextrin concentration.     

Inhibition Effect of {Cationic Surfactant-Ascorbic Acid} Premicellar Aggregation on the Rate of Hexacyanoferrate(III) Oxidation of Ascorbic Acid: A Kinetic Study

The kinetics of oxidation of ascorbic acid by acidic hexacyanoferrate(III) have been investigated in presence of cationic surfactant viz. cetyltrimethylammonium bromide (CTAB). An inhibition effect of CTAB (below its critical micelle concentration) on the rate of oxidation has been observed. The spectrophotometric and kinetic data support a 1:1 premicellar association between substrate and surfactant. A mechanism has been proposed and a rate law consistent with kinetic results has been derived.     

团聚铂纳米粒子电极在甲醇氧化中的电催化特性

用H2还原法并以Nafion作为稳定剂合成团聚的Pt纳米粒子，附载于玻碳表面制备电催化剂.透射电子显微镜（TEM）和扫描电子显微镜（SEM）表征结果指出,团聚Pt纳米粒子的平均尺寸约为400 nm.运用电化学循环伏安法(CV)和原位傅立叶变换红外反射光谱（in situ FTIRS）研究甲醇的氧化过程，发现团聚Pt纳米粒子电极具有较高的电催化活性.原位FTIRS研究结果检测到甲醇在所制备的电催化剂上氧化的中间体为线型吸附态CO物种，其红外吸收给出异常红外效应的光谱特征.     

Comparative studies of reactions of commercial polymers with molecular oxygen,singlet oxygen,atomic oxygen and ozone—I. Reactions with cis-1,4-polybutadiene

The oxidation of cis-1,4-polybutadiene by molecular oxygen, singlet oxygen, atomic oxygen and ozone has been studied using u.v. and i.r. spectroscopic methods. Some possible implications of the results of oxidation in the presence of singlet oxygen (parallel free radical oxidation) and atomic oxygen (formation of NO₂ and its reaction with polymer) are discussed. Chain scission was observed during all types of oxidation. A new mechanism involving opening of double bonds and formation of biradicals has been considered in detail.     

Highly efficient aerobic oxidation of oximes to carbonyl compounds catalyzed by metalloporphyrins in the presence of benzaldehyde

Highly efficient oxidation of oximes to carbonyl compounds by molecular oxygen with benzaldehyde as an oxygen acceptor in the presence of metalloporphyrins has been reported. The simple structural manganese porphyrin showed an excellent activity for the oxidative deoximation reactions of various oximes. Moreover, different factors influencing oximes oxidation, that is, catalyst, solvent, and temperature, have been investigated. A possible mechanism for the deoximation reaction has been proposed.     

Kinetics of oxidation of some disaccharides in ammoniacal medium

Kinetics of oxidation of lactose, maltose, cellobiose and melibiose has been studied by hexacyanoferrate(III) in the presence of ammonia. A general mechanism involving the formation of intermediate enodiol anion has been suggested. The effects of dielectric constant and salts have been studied in detail. The oxidation products have been characterised by descending paper chromatography. Compensation effects have been observed.     

二氧化硫的电化学氧化过程Ⅲ．SO_2在聚钴卟啉膜电极上的氧化机理

采用循环伏安法、稳态法、计时电位法等研究了ＳＯ＿２在聚钴卟啉膜电极上的电化学氧化过程，并和ＳＯ＿２在贵金属电极上的行为进行了比较。     

Electrocatalytic activity of cobalt phthalocyanine stabilized by different matrixes

The behavior of cobalt phthalocyanine complexes incorporated inside an hydrotalcite-like clay (HT) or a sonogel-carbon composite has been investigated in order to develop chemically modified electrodes suitable for use as amperometric detectors. The electrocatalytic oxidation process of cysteine at this new electrode has been studied by cyclic voltammetry. For comparison, the oxidation of cysteine catalyzed by the cobalt phthalocyanine complex as a redox mediator, either dissolved in solution or entrapped inside the HT structure, has been followed by polarography. The sonogel-carbon composite electrode is stable and its response is repeatable. Cysteine oxidation is actually induced by the electrogenerated Co(III) complex, and the relevant anodic peak current varies linearly with cysteine concentration within the range 9.0x10(-4) to 1.0x10(-2) mol L(-1).