Electrochemical and spectroscopic studies of ethanol oxidation on Pt stepped surfaces modified by tin adatoms

Ethanol oxidation on platinum stepped surfaces vicinal to the (111) pole modified by tin has been studied to determine the role of this adatom in the oxidation mechanism. Tin has been slowly deposited so that the initial stages of the deposition take place on the step, and deposition on the terrace only occurs when the step has been completely decorated. Voltammetric and chronoamperometric experiments demonstrate that tin on the step catalyzes the oxidation. The maximum enhancement is found when the step is completely decorated by tin. FTIR experiments using normal and isotopically labeled ethanol have been used to elucidate the effect of the tin adatoms in the mechanism. The obtained results indicate that the role of tin is double: (i) when the surface has sites capable of breaking the C-C bond of the molecule, that is, when the step sites are not completely covered by tin, it promotes the oxidation of CO formed from the molecular fragments to CO(2) through a bifunctional mechanism and (ii) it catalyzes the oxidation of ethanol to acetic acid.     

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.     

二氧化硫的电化学氧化过程：Ⅱ.SO2在贵金属电极上的氧化机理

采用计时电位法、计时电流法和稳态极化曲线法研究了ＳＯ＿２在Ａｕ和Ｒｕ两种不同类型贵金属催化剂上的氧化过程，提出了ＳＯ＿２在这两类电极上的氧化机理。     

Thermal-oxidative degradation of high-amylose corn starch

Thermal oxidation degradation of high-amylose (80 %) cornstarch has been studied using thermogravimetry analyser coupled to Fourier transform infrared spectroscopy (TG-FTIR). The linear structure of amylose provides a modal material to understand how the starch microstructure affects on the decomposition mechanisms. Kinetics of the thermal oxidation has been studied using different methods. It is found that the thermal oxidation degradation is more complex than thermal degradation, thermal oxidation degradation kinetics of the starch can be interpreted in terms of multi-step degradation mechanism, the activation energies obtain from Flynn–Wall–Ozawa (F–W–O) method and modified Coats–Redfern method are in good agreement. TG-FTIR and FTIR results confirm that the thermal oxidation mechanism of starch is a process containing long chain scission and glowing combustion.     

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.     

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.     

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.     

Electrochemical Oxidation of Desipramine Drug in the Presence of 4,6‐Dimethylpyrimidine‐2‐thiol Nucleophile in Aqueous Acidic Medium

Electrochemical oxidation of desipramine (DES) has been studied in the presence of 4,6‐dimethylpyrimidine‐2‐thiol (DMPT) as nucleophile in acidic medium by means of cyclic voltammetry, controlled‐potential electrolysis and spectroscopic data, as diagnostic techniques. Voltammetric studies of electro‐oxidation of desipramine were realized in a range of pH 1.0 to 8.0 in the absence and presence of DMPT. The results indicate the participation of the product of electrochemical oxidation of desipramine in the reaction with DMPT with ECEC electrochemical mechanism. However, the voltammetry and coulometry results imply existence of a catalytic (EC′) electrochemical mechanism in parallel with ECEC electrochemical mechanism. The product has been characterized by IR, ¹H NMR, ¹³C NMR and MS methods.     

Facile construction of pyrrolophenanthridone skeleton via a one-pot intramolecular Heck reaction and oxidation

Construction of pyrrolophenanthridone skeleton via a one-pot Pd-catalyzed intramolecular Heck reaction followed by oxidation has been achieved in moderate to good yields. The reaction mechanism has been proposed.     

Comparative studies of reactions of commercial polymers with molecular oxygen,singlet oxygen,atomic oxygen and ozone—II. Reactions with 1,2-polybutadiene

The oxidations of 1,2-polybutadiene by molecular oxygen, singlet oxygen, atomic oxygen and ozone have 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. Crosslinking was observed during all types of oxidation. A new mechanism involving formation of free radicals has been considered in detail. During ozonization of 1,2-polybutadiene, formation of formaldehyde and formic acid were detected. An ozonization mechanism has been proposed.     

Oxidation mechanism of 6-methyl-2,4-dioxopyrimidine with selenium oxide and selenous acid

Analysis of the oxidation mechanism of 6-methyl-2,4-dioxopyrimidine with selenium oxide and selenous acid with the formation of orotic aldehyde has been carried out by the ab initio quantum-chemical method on the 6-31G** basis. The mixed anhydride of acetic and selenous acids is formed with a gain of energy. It possesses high activity and steric accessibility in electrophilic attack on position 5 of the pyrimidine ring. The three-stage mechanism of the oxidation of the methyl group in 6-methyluracil by the mixed anhydride of selenous and acetic acids has been analyzed.     

Enzymatic oxidation of lignin and compounds modeling it. II. A study of the peroxidase oxidation of model compounds of the structural unit of lignin by the chemiluminescence method

An investigation of the radical mechanism of the peroxidase oxidation of monomeric phenols (vanillin, vanillyl alcohol, isoeugenol, and α-quaiacylpropanone) has been made by the chemiluminescence method. It has been established that chemiluminescence is observed in those compounds that contain hydroxy or carbonyl groups on a carbon atom in the α position or have a C=C bond in the β position conjugated with the aromatic ring. The hypothesis has been put forward that peroxide compounds are inhibitors of autocatalytic processes in the oxidation of lignin in the presence of peroxidase.     

Radiation-induced oxidation of solid poly(ethylene oxide). II. Mechanism

The mechanism of γ-initiated oxidation of solid poly(ethylene oxide) (PEO) has been investigated, and an overall reaction scheme has been developed which accounts for most of the experimental observations. Data are correlated on the basis that the oxidation process is the sum of two reactions that are first-order and half-order in rate of initiation. They provide evidence that a significant fraction of the interactions of α-alkoxyalkylperoxy radicals is nonterminating at ambient temperature and yield free alkoxy radicals that are very subject to β scission. The unimolecular decomposition of secondary peroxy radicals, which has been invoked previously for the oxidation of PEO in solution, is not needed to explain the products of the oxidation of PEO in the solid phase. Approximately 90% of the total oxygen consumption has been accounted for by the observed products of oxidation. The radiochemical yield for backbone radical formation in irradiated PEO was estimated to be 6.5 ± 1.5.     

Ring-disk electrode studies of the formation,growth and transformation of iodine films formed during the anodic oxidation of iodide on platinum

The kinetics and mechanism of the formation, growth and dissolution of iodine films on platinum during the electrooxidation of iodide have been investigated using rotating-disk and ring-disk techniques. The dissolution-precipitation mechanism of film formation and a linear growth law for film growth has been confirmed. The iodine film on platinum is believed to be made up of an ionically insulating barrier layer covered by a porous overlayer. The oxidation behavior of iodide and ferrous species shows that the iodine film is predominantly an iodide-ion conductor. Also, a film transformation, responsible for the transient features observed during iodide oxidation has been confirmed. This transformation changes the mechanism of iodide transport through the film from a partly “pore”-type to a Grotthus-type mechanism. The ring current maximum, which occurs at the same instant as the disk current minimum, reveals the mechanism of dissolution of iodine film during the transient period as involving complexation with iodide. Evidence for the mass-transport-controlled component of the potentiostatic transient response has been obtained from the sinusoidal hydrodynamic modulation response.     

Synthesen in der Carotinoid-Reihe 23. Mitteilung Ein Beitrag zur Chromsäure-Oxydation von Polyenen

Chromic acid oxidation of polyenes with terminal β-ionylidene groups has been studied. A number of hitherto unknown and unexpected oxidation products has been isolated. A mechanism for these oxidations is discussed.     

Density functional theory methods as powerful tools to elucidate amino acid oxidation mechanisms. A case study on methionine model peptide

The amino acid oxidation mechanism has been a research focus in recent years. Although various experimental techniques have been employed to address the problem, it is still a great challenge to identify the oxidation intermediates of amino acids. To explore the potential of theoretical methods in helping elucidating amino acid oxidation mechanisms, one-electron oxidation of a methionine model peptide (N-acetylmethionine amide) was investigated by density functional theory (DFT; including TD-DFT) calculations. The theoretical results not only testified the experimentally identified oxidation mechanisms of the peptide to a large extent but also revealed the contribution of protonated species to the peptide oxidation. All of these findings strongly suggest that DFT methodology has great potential in investigating amino acid oxidation mechanisms.     

A study of the reaction of oxygen with graphite: model chemistry

A considerable amount of research has been directed towards the mechanism of oxidation of graphite as a model reaction system and because of its industrial importance. A number of recent studies have been concerned with ab initio molecular orbital calculations on graphite including model chemistry and the reactions with molecular oxygen. This study is concerned with oxidation steps involving the attachment of molecular oxygen to the graphene, the formation of carbon monoxide and, in particular, the subsequent oxidation reactions.     

Ab initio study of oxygen atom transfer from hydrogen peroxide to trimethylamine

Unlike what has been theoretically proposed for ammonia oxidation with hydrogen peroxide, trimethylamine oxidation occurs with a concerted mechanism, which is favored even when an explicit water molecule is added or continuum solvent (water) is simulated.     

Kinetics and mechanism of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate

Kinetics of oxidation of substituted benzaldehydes by 4-(dimethylamino)pyridinium chlorochromate (DMAPCC) in protic solvent system has been studied at 303 K. The product of oxidation has been identified as benzoic acid. A unit order dependence of the reaction with respect [DMAPCC] and [benzaldehyde] has been observed. The reaction has been found to be catalysed by H⁺ ions. Decrease in the dielectric constant of the medium decreases the rate. To study the effect of structure reactivity relationships some para-substituted benzaldehydes were subjected to oxidation kinetics by DMAPCC at four different temperatures and thermodynamic parameters were calculated. The isokinetic plot and Exner plot shows that all the para-substituted benzaldehydes are oxidised by the same mechanism. The Hammett plot is linear with positive ρ value. From the observed kinetic results a suitable mechanism was proposed.     

Low-Temperature Catalytic Oxidation of Sulfide Ions in Aqueous Solutions on a Ni-Oxide System

Catalytic oxidation of sulfide ions in aqueous solutions by air oxygen has been investigated using a Ni-oxide system as a catalyst. The kinetics and the selectivity of the oxidation process were studied by varying the pH, catalyst amount and reaction temperature. A reduction/oxidation mechanism of the reaction has been supposed comprising interaction between the surface active oxygen of the catalyst and HS^– and reoxidizing of the reduced catalyst by the dissolved oxygen. The results obtained show that the Ni-oxide system is a promising catalyst for practical application.