Mechanism of oxidation of DL-methionine by iron(III)-2,2′-bipyridyl in perchloric acid—a kinetic study

Summary The kinetics of oxidation of DL-methionine by iron(III)-2,2-bipyridyl complex in HClO₄ were studied using 20%(v/v) MeOH as solvent. The order with respect to methionine and iron(III) was unity. The rate increased with increased [bipyridyl], but decreased with increased [H⁺]. While the reactive species of the substrate was the zwitterionic form, that of the oxidant was [Fe(bipy)₂-(H₂O)₂]³⁺. At 55 °C E _a and S for the reaction were 50.6 ± 2.5 kJ mol^–1 and –111.4 ± 7.6 JK^–1 mol^–1, respectively.Author to whom all correspondence should be directed.     

Kinetics and mechanism of oxidation of aryl β-styryl ketones by osmium tetroxide in sulphuric acid-acetic acid medium. A structure-reactivity correlation study

Summary Oxidation of aryl -styryl ketones by osmium tetroxide has been studied in H₂SO₄-HOAc medium. The order with respect to osmium is unity in all the cases and the [substrate] order is unity for aryl -styryl ketone and fractional for substituted aryl -styryl ketone. Varying the concentration of [H⁺] at constant ionic strength had practically no effect on the rate; the salt effect is also negligible. Polymerisation did not occur when H₂C- CHCONH₂ was added to the reaction mixture. Increasing the percentage of AcOH decreased the rate. Direct attack at the 58-01 by Os^III in the slow step to give the oxidation product of aryl -styryl ketone, viz. 1-benzoyl-2-arylethane-1,2-diol is suggested and a possible mechanism for the reaction.     

Nucleophilic addition reaction of aromatic compounds with α-chloroglycidates in the presence of Lewis acid

The epoxide 1 obtained by the Darzens condensation reaction of aldehydes with methyl dichloroacetate, reacted with aromatic compounds in the presence of aluminium chloride to afford α-aryl-β-chloro-α-hydroxyalkanoate 3. The intra-molecular nucleophilic addition of epoxide 1′ gave cyclisation compound 4. The scope and limitation of these reaction were studied for various aldehydes and aromatic compounds. The reaction was also studied in the presence of aluminium chloride supported on alumina or silica gel, which is thought to be a mild Lewis acid and harmless for environment.     

Ruthenium(III) catalyzed oxidation of paracetamol by chloramine-T in aqueous alkaline medium – A kinetic and mechanistic pathway

The kinetic study of ruthenium(III) chloride catalyzed oxidation of paracetamol by N-chloro-p-toluene sulfonamide (chloramine-T) in the alkaline medium has been performed. The reaction exhibits second order nature and the effect of the catalyst indicates the occurrence of uncatalyzed reaction simultaneously. Rate is decelerated by hydroxide ions. A plausible reaction mechanism has been suggested and the rate law is derived to account for such experiential observations. The activation parameters have been calculated. No evidence of the participation of free radicals is observed.     

The oxidation of aromatic amines in the presence of “electron-rich” aromatic systems

The oxidation of aromatic amines to the corresponding nitro substituents is performed under mild, nonacidic conditions in the presence of highly nucleophilic aromatic systems such as indoles and furans.     

A multicoincidence study of fragmentation dynamics in collision of γ-aminobutyric acid with low-energy ions

Fragmentation of the γ-aminobutyric acid molecule (GABA, NH(2)(CH(2))(3)COOH) following collisions with slow O(6+) ions (v≈0.3?a.u.) was studied in the gas phase by a combined experimental and theoretical approach. In the experiments, a multicoincidence detection method was used to deduce the charge state of the GABA molecule before fragmentation. This is essential to unambiguously unravel the different fragmentation pathways. It was found that the molecular cations resulting from the collisions hardly survive the interaction and that the main dissociation channels correspond to formation of NH(2)CH(2)(+), HCNH(+), CH(2)CH(2)(+), and COOH(+) fragments. State-of-the-art quantum chemistry calculations allow different fragmentation mechanisms to be proposed from analysis of the relevant minima and transition states on the computed potential-energy surface. For example, the weak contribution at [M-18](+), where M is the mass of the parent ion, can be interpreted as resulting from H(2)O loss that follows molecular folding of the long carbon chain of the amino acid.     

Increases in reaction rates and improvement of current–potential characteristics in the electrochemical oxidation of formic acid

In current-control experiments, perturbing an aqueous solution containing 0.10 M formic acid and 0.50 M HClO₄ by including a small amount of HBF₄ causes more than a 60% increase in the value of the applied current for which low-valued stationary potentials remain stable. The current increases by more than 50% at relevant potential values in potential-control experiments. Current–potential characteristics inferior to those of the HCOOH + HClO₄ solution are obtained with other solutions made by adding small amounts of a strong acid or salt. Properties that exist among the anions present in the latter solutions are possessed by BF₄⁻. Nonlinear behavior exhibited by formic acid oxidation is changed drastically by the presence of a small amount of any one of the anions studied. These results and other arguments support the hypothesis that HBF₄ enhances current–potential characteristics by causing the formation of surface anion complexes possessing OH components at low potentials.     

A new efficient method for the preparation of intermediate aromatic ketones by Friedel–Crafts acylation

Research on Chemical Intermediates - As the most important method to prepare pharmaceutical and chemical intermediate aromatic ketones, Friedel–Crafts (F–C) acylation is used to seek a...     

A kinetic study of the aqueous phase oxidation of di-μ-oxo-bis(L-cysteine)-oxomolybdenum(V) by molecular oxygen

The molecular oxygen-mediated decomposition of the binuclear complex, prepared from oxomolybdate(V) and L-(+)-cysteine, was studied spectrophotometrically at pH 3.5–5.6. The formation of MoVI was detected. The effects of pH and [O2] on the decomposition kinetics are given by the equation:

Kinetic study of the oxidation of L-threonine by MnO4? ions

A self-catalytic effect attributed to Mn²⁺ ions was observed when studying the oxidation of L-threonine by permanganate ions. The process obeys the rate equation:

Spectrophotometric studies on oxidation of some primary alcohols by 2,2′-bipyridinium chromate. A kinetic study

Some primary alcohols were oxidized by 2,2-bipyridinium chromate (BPC) in the presence of oxalic acid and TsOH giving aldehyde as major product. The reactions were carried out in 80% MeCN-DMF (v/v) medium under varied experimental conditions. The rate depends on the first power of the concentration of BPC and fractional power on the concentrations of alcohol, oxalic acid and TsOH.     

Density,viscosity and electrical conductivity of isobutyric acid–water with added ions in the critical regions

Density, viscosity and electrical conductivity of the six concentrated binary ionic mixtures of isobutyric acid–water with X M [KCl] at the critical concentrations were measured as functions of temperature (ΔT = T ? T _c ≤ 2 K) and at various compositions, X, in the critical regions. The molar volumes have been calculated from their densities. The molar volume data dependence of viscosity and conductivity has been fitted to an equation similar to the Vogel–Tammann–Fulcher (VTF) based on the free volume model. The concentration of ions (K⁺, Cl^?), dependence of the Vogel temperature, the intrinsic volume and the transport properties are primarily governed by the existence of intermolecular interactions.     

Pentafluoroperbenzoic acid as the efficient reagent for Baeyer–Villiger oxidation of cyclic ketones

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Can large active-space CASSCF calculation make sense to the reaction analysis of iron complex? A benchmark study of methane oxidation reaction by FeO+

A methane oxidation reaction by FeO⁺ cation was theoretically investigated based on the density functional theory (DFT) and the complete active-space self-consistent field (CASSCF) method as well as the coupled-cluster singles, doubles, and perturbative triples (CCSD(T)) to explore the active-space dependency to computational analyses in such strongly correlated reaction systems. A small active-space CASSCF(5e in 5o) calculation, which only includes five 3d orbitals of the Fe atom in the active-space, showed remarkable difference both in energy and geometry compared to those computed by the DFT and CCSD(T) methods. Interestingly, a large active-space CASSCF(17e in 17o) calculation, which includes almost all the valence orbitals gives a qualitative agreement with either the DFT or the CCSD(T) results in the first half part of the reaction, although it varies from them in the latter half part. Therefore, it is indicated that the active-space dependency is serious in some part of the reaction and the small active-space CASSCF might lead a wrong discussion. We further investigated the optimized geometry of the intermediate complex with the small and the large active-space CASSCF methods as well as the CCSD(T) method, and found that the CASSCF(5e in 5o)-optimized geometry is considerably different from the others. In consequence, a small active-space CASSCF/CASPT2 calculation does not really work for such a strongly correlated reaction system even qualitatively, and a sophisticated assessment using the large active-space CASSCF/CASPT2 method will be indispensable. © 2018 Wiley Periodicals, Inc.     

Reversal of chemoselectivity in Diels-Alder reaction with alpha,beta-unsaturated aldehydes and ketones catalyzed by Brønsted acid or Lewis acid

[reaction: see text] High chemoselectivity was observed in the Diels-Alder reaction of alpha,beta-unsaturated aldehyde and alpha,beta-unsaturated ketone with cyclopentadiene. Using Tf2NH as catalyst, the reaction gave Diels-Alder adduct derived from alpha,beta-unsaturated ketone as a major product. On the other hand, bulky Lewis acid, B(C6F5)3, gave mainly the cycloadduct of alpha,beta-unsaturated aldehyde and cyclopentadiene.     

Regioselective Friedel–Crafts deacylations of polycyclic aromatic ketones in the pyrene series

1,3,6,8-tetrabenzoylpyrene (1,3,6,8-Bz ₄ PY) and 1,3,6-tribenzoylpyrene (1,3,6-Bz ₃ PY) were synthesized and their crystal structures were determined. The Friedel–Crafts deacylations in PPA of 1,3,6,8-Bz ₄ PY (at 120–200 °C) and of 1,3,6-Bz ₃ PY (at 80–160 °C) have been studied. The mono-deacylation of 1,3,6-Bz ₃ PY was regioselective and led to three dibenzoylpyrenes in the following order of relative amounts: 1,8-Bz ₂ PY > 1,6-Bz ₂ PY > 1,3-Bz ₂ PY. 1,3,6,8-Bz ₄ PY was resistant to deacylation at 120–160 °C. The deacylations of 1,3,6,8-Bz ₄ PY at 200 °C gave the polycyclic aromatic ketone (PAK) 8H-dibenzo[def,qr]chrysen-8-one (DBCO) via an intramolecular Scholl reaction. Two plausible pathways of the Friedel–Crafts deacylation of 1,3,6,8-Bz ₄ PY to give DBCO are proposed. A density functional theory (DFT) B3LYP/6-311(d,p) computational study of the conformational spaces of 1,3,6-Bz ₃ PY and 1,3,6,8-Bz ₄ PY was performed. The estimated energy barriers of formation of dibenzoylpyrenes by deacylation of 1,3,6-Bz ₃ PY increase in the following order: 1,8-Bz ₂ PY < 1,3-Bz ₂ PY < 1,6-Bz ₂ PY. A mechanism of the Friedel–Crafts deacylation of 1,3,6-Bz ₃ PY in PPA via the respective O-protonated ketone and σ-complexes is presented.