Kinetics and reactivities of ruthenium(III)- and osmium(VIII)-catalyzed oxidation of ornidazole with chloramine-T in acid and alkaline media: A mechanistic approach

Ornidazole is an antiparasitic drug having a wide spectrum of activity. Literature survey has revealed that no attention has been paid towards the oxidation of ornidazole with any oxidant from the kinetic and mechanistic view point. Also no one has examined the role of platinum group metal ions as catalysts in the oxidation of this drug. Such studies are of much use in understanding the mechanistic profile of ornidazole in redox reactions and provide an insight into the interaction of metal ions with the substrate in biological systems. For these reasons, the Ru(III)- and Os(VIII)-catalyzed kinetics of oxidation of ornidazole with chloramine-T have been studied in HCl and NaOH media, respectively at 313 K. The oxidation products and kinetic patterns were found to be different in acid and alkaline media. Under comparable experimental conditions, in Ru(III)-catalyzed oxidation the rate law is −d[CAT]/dt = k [CAT]_o[ornidazole]_o^x[H⁺]^−y[Ru(III)]^z and it takes the form −d[CAT]/dt = k [CAT]_o[ornidazole]_o^x[OH⁻]^y[Os(VIII)][ArSO₂NH₂]^−z for Os(VIII)-catalyzed reaction, where x, y and z are less than unity. In acid medium, 1-chloro-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one and in alkaline medium, 1-hydroxy-3-(2-methyl-5-nitroimidazole-1-yl)propan-2-one were characterized as the oxidation products of ornidazole by GC–MS analysis. The reactions were studied at different temperatures and the overall activation parameters have been computed. The solvent isotope effect was studied using D₂O. Under identical set of experimental conditions, the kinetics of Ru(III) catalyzed oxidation of ornidazole by CAT in acid medium have been compared with uncatalyzed reactions. The relative rates revealed that the catalyzed reactions are about 5-fold faster whereas in Os(VIII) catalyzed reactions, it is around 9 times. The catalytic constant (K_C) has been calculated for both the catalysts at different temperatures and activation parameters with respect to each catalyst have been evaluated. The observed experimental results have been explained by plausible mechanisms. Related rate laws have been worked out.     

Negative- and positive-ion chemical ionization mass spectra of aromatic amines: Surface-assisted reactions involving oxygen

The O₂–N₂ and O₂–Ar negative-ion chemical ionization mass spectra of aromatic amines show a series of unusual ions dominated by an addition appearing at [M + 14]^?˙. Other ions are observed at [M – 12]^?˙, [M + 5]^?˙, [M + 12]^?˙, [M + 28]^?˙ and [M + 30]^?˙. Ion formation was studied using a quadrupole instrument equipped with a conventional chemical ionization source and a Fourier transform ion cyclotron resonance (FTICR) mass spectrometer. These studies, which included the examination of ion chromatograms, measurement of positive-ion chemical ionization mass spectra, variation of ion source temperature and pressure and experiments with ¹⁸O₂, indicate that the [M + 14]^?˙ ion is formed by the electron-capture ionization of analytes altered by surfaceassisted reactions involving oxygen. This conversion is also observed under low-pressure conditions following source pretreatment with O₂. Experiments with [¹⁵N]aniline, [2,3,4,5,6-²H₅] aniline and [¹³C₆]aniline show that the [M + 14]^?˙ ion corresponds to [M + O ? 2H]^?˙, resulting from conversion of the amino group to a nitroso group. Additional ions in the spectra of aromatic amines also result from surface-assisted oxidation reactions, including oxidation of the amino group to a nitro group, oxidation and cleavage of the aromatic ring and, at higher analyte concentrations, intermolecular oxidation reactions.     

Synthesis, spectral characterization, catalytic and antibacterial studies of new Ru(III) Schiff base complexes containing chloride/bromide and triphenylphosphine/arsine as co-ligands

A new Ru(III) Schiff base complexes of the type [RuX(EPh₃)L] (X = Cl/Br; E = P/As; L = dianion of the Schiff bases were derived by the condensation of 1,4-diformylbenzene with o-aminobenzoic acid/o-aminophenol/o-aminothiophenol in the 1:2 stoichiometric ratio) have been synthesized from the reactions of [RuX₃(EPh₃)₃] with appropriate Schiff base ligands in benzene in the 2:1 stoichiometric ratio. The new complexes have been characterized by analytical, spectral (IR, electronic, ¹H, ¹³C NMR and ESR), magnetic moment and electrochemical studies. An octahedral structure has been tentatively proposed for all these new complexes. All the new complexes have been found to be better catalyst for the oxidation of alcohols using molecular oxygen as co-oxidant at ambient temperature and aryl–aryl coupling reactions. These complexes were also subjected to antibacterial activity studies against Escherichia coli, Aeromonas hydrophilla and Salmonella typhi.     

Kinetics of oxidation of indigo carmine by N-sodio-N-bromotoluenesulfonamide in acidic buffer medium

The kinetics of oxidation of indigo carmine (IC) by N-sodio-N-bromotoluenesulfonamide or bromamine-T (BAT) in pH 5 buffer medium has been investigated at 30°C using spectrophotometry at 610 nm. The reaction rate shows dependencies of first-order on [IC]₀ second-order on [BAT]₀, fractional order on [H⁺], and inverse first-order on [ρ-toluenesulfonamide]. The addition of chloride and bromide ions, and the variation of ionic strength of the medium have no influence on the reaction rate. There is a negative effect of the dielectric constant of the solvent. Activation parameters have been calculated. A single-pathway mechanism for the reaction, consistent with the kinetic data, has been proposed. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 453–459, 1997     

Facile oxidative conversion of hydrazides of carboxylic acids to corresponding acids,esters and amides using copper compounds

Oxidative conversion of hydrazides of carboxylic acids to acids, esters and amides using Cu salts was studied. Acids were obtained in high yields by using a catalytic amount of Cu(OAc)₂ at room temperature by bubbling oxygen. Hydrazides were converted to esters by the treatment with Cu(OR)Cl or Cu(OR)₂ formed in situ from CuCl₂ and sodium alkoxide. Amides were obtained in high yields by the oxidation of hydrazides with CuCl₂ in the presence of amines.     

Photoredox-enabled 1,2-dialkylation of α-substituted acrylates via Ireland–Claisen rearrangement

Herein, we report the 1,2-dialkylation of simple feedstock acrylates for the synthesis of valuable tertiary carboxylic acids by merging Giese-type radical addition with an Ireland–Claisen rearrangement. Key to success is the utilization of the reductive radical-polar crossover concept under photocatalytic reaction conditions to force the [3,3]-sigmatropic rearrangement after alkyl radical addition to allyl acrylates. Using readily available alkyl boronic acids as radical progenitors, this redox-neutral, transition-metal-free protocol allows the mild formation of two C(sp³)–C(sp³) bonds, thus providing rapid access to complex tertiary carboxylic acids in a single step. Moreover, this strategy enables the efficient synthesis of highly attractive α,α-dialkylated γ-amino butyric acids (GABAs) when α-silyl amines are used as radical precursors – a structural motif that was still inaccessible in related transformations. Depending on the nature of the radical precursors and their inherent oxidation potentials, either a photoredox-induced radical chain or a solely photoredox mechanism is proposed to be operative.

A photocatalytic 1,2-dialkylation of α-substituted acrylates is enabled by a reaction cascade combining reductive radical-polar crossover with the established Ireland–Claisen rearrangement for the synthesis of valuable tertiary carboxylic acids.     

Oxidation of Ethylbenzene with Dioxygen in the Presence of Iron(III) Tris(acetylacetonate)-Based Catalytic Systems: 1. Mechanism of Ethylbenzene Oxidation with Dioxygen Catalyzed by Fe(III)(acac)<Subscript>3</Subscript>

The catalytic activity of Fe(III)(acac)₃ (Cat) in ethylbenzene oxidation with dioxygen is studied. 1-Phenylethyl hydroperoxide (PEHP), acetophenone (AP), and methyl phenyl carbinol (MPC) are the main products of the process throughout the Cat concentration range examined. Phenol (Ph) is formed in much smaller amounts. The highest PEHP selectivity, S _PEHP = 65%, is observed at an ethylbenzene conversion of C ≈ 2% at low [Cat] values. PEHP and the other main oxidation products (AP and MPC) form by parallel reactions at any Cat concentration. Depending on [Cat], AP and MPC form by parallel or consecutive reactions. When [Cat] is high enough, AP results from MPC oxidation. At the initial stages of the reaction, the MPC selectivity (S _MPC = 50%) exceeds the PEHP selectivity (S _PEHP = 25–30%). The mechanism of ethylbenzene oxidation catalyzed by Fe(III)(acac)₃ and the role of active complexes in its steps are considered.__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 354–359.Original Russian Text Copyright © 2005 by Matienko, Mosolova.     

Ruthenium(III)-catalyzed and uncatalyzed kinetic studies on the oxidation of sulfanilic acid by chloramine-T in perchloric acid medium: a mechanistic approach

The kinetics of the oxidation of sulfanilic acid (SAA) by sodium N-chloro-p-toluenesulfonamide (CAT) in the presence and absence of ruthenium(III) chloride have been investigated at 303 K in perchloric acid medium. The reaction shows a first-order dependence on [CAT]_o and a non-linear dependence on both [SAA]_o and [HClO₄] for both the ruthenium(III)-catalyzed and uncatalyzed reactions. The order with respect to [Ru^III] is unity. The effects of added p-toluenesulfonamide, halide, ionic strength, and dielectric constant have been studied. Activation parameters have been evaluated. The rate of the reaction increases in the D₂O medium. The stoichiometry of the reaction was found to be 1:1 and the oxidation product of SAA was identified as N-hydroxyaminobenzene-4-sulfonic acid. The ruthenium(III)-catalyzed reactions are about four-fold faster than the uncatalyzed reactions. The protonated conjugate acid (CH₃C₆H₄SO₂NH₂Cl⁺) is postulated as the reactive oxidizing species in both the cases.     

Kinetics and mechanism of the ruthenium(III)-catalysed oxidation of aliphatic acids by peroxodiphosphate in acetate buffers

Summary The kinetics of oxidation of aliphatic acids (AAs), such as propionic acid, butyric acid, isobutyric acid and valeric acids, by peroxodiphosphate (PDP) using ruthenium(III) as catalyst in aqueous H₂SO₄ at constant ionic strength and different acidities were studied. The ruthenium(III)-catalysed oxidation is first order in [PDP] and fractional order in [AA]. The order with respect to [Ru^III] is fractional. An analysis of the rate dependence upon [H^–] suggests that H₃P₂O ₈ ^– is the active oxidizing species in the oxidation. A mechanism consistent with the rate law is proposed.     

Oxidation of some catecholamines by sodium N-chloro-p-toluenesulfonamide in acid medium: A kinetic and mechanistic approach

The kinetics of the oxidation of five catecholamines viz., dopamine (A), L-dopa (B), methyldopa (C), epinephrine (D) and norepinephrine (E) by sodium N-chloro-p-toluenesulfonamide or chloramine-T (CAT) in presence of HClO₄ was studied at 30±0.1 °C. The five reactions followed identical kinetics with a first-order dependence on [CAT] _o , fractional-order in [substrate] _o , and inverse fractional-order in [H⁺]. Under comparable experimental conditions, the rate of oxidation of catecholamines increases in the order D>E>A>B>C. The variation of ionic strength of the medium and the addition of p-toluenesulfonamide or halide ions had no significant effect on the reaction rate. The rate increased with decreasing dielectric constant of the medium. The solvent isotope effect was studied using D₂O. A Michaelis-Menten type mechanism has been suggested to explain the results. Equilibrium and decomposition constants for CAT-catecholamine complexes have been evaluated. CH₃C₆H₄SO₂NHCl of the oxidant has been postulated as the reactive oxidizing species and oxidation products were identified. An isokinetic relationship is observed with β=361 K, indicating that enthalpy factors control the reaction rate. The mechanism proposed and the derived rate law are consistent with the observed kinetics.     

Kinetics of oxidation of glycylglycine by bromamine-T in acid medium

The kinetics of oxidation of a typical dipeptide glycylglycine (GG) by bromamine-T have been studied in HClO₄ medium at 40°C. The rate shows first-order dependence on [BAT]₀ and is fractional order in [GG]₀ which becomes independent of [substrate]₀ at higher [GG]₀. At [H⁺ ] > 0.02mol dm⁻³, the rate is inverse fractional in [H⁺ ] but is zero order at lower [H⁺ ] (≤0.02 mol dm⁻³). Variation in ionic strength or dielectric constant of the medium had no significant effect on the rate. The solvent-isotope effect was measured and = 1.45. Proton inventory studies have been made. The reaction has been studied at different temperatures (308-323 K) and activation parameters have been computed.     

Kinetics of oxidation of ethylenediamine tetraacetic acid by aromatic N-bromamines in buffer medium

Kinetics of oxidation of disodium ethylene-diamine-tetraacetic, acid (EDTA) by bromamine-B (BAB) and bromamine-T (BAT) was investigated at 30°C in acetate buffer of pH 5. The oxidation behaviour is similar, with a first-order dependence of rate on [oxidant] and fractional orders in [EDTA] and [H⁺]. The influence of the reaction products, halide ions, ionic strength and dielectric constant of medium on the rate has been studied. A possible mechanism is suggested.     

One-Pot Direct Oxidation of Primary Amines to Carboxylic Acids through Tandem ortho-Naphthoquinone-Catalyzed and TBHP-Promoted Oxidation Sequence

Biomimetic oxidation of primary amines to carboxylic acids has been developed where the copper-containing amine oxidase (CuAO)-like o-NQ-catalyzed aerobic oxidation was combined with the aldehyde dehydrogenase (ALDH)-like TBHP-mediated imine oxidation protocol. Notably, the current tandem oxidation strategy provides a new mechanistic insight into the imine intermediate and the seemingly simple TBHP-mediated oxidation pathways of imines. The developed metal-free amine oxidation protocol allows the use of molecular oxygen and TBHP, safe forms of oxidant that may appeal to the industrial application.     

Absolute Configuration Assignment from Optical Rotation Data by Means of Biphenyl Chiroptical Probes

A non-empirical approach for the assignment of the absolute configuration of chiral 2-alkyl-substituted carboxylic acids and primary amines by [α]_D measurements has been developed. The method requires the conversion of the chiral acids or amines into the corresponding 4,4′-disubstituted biphenylamides or biphenylazepines, respectively. In these derivatives a central-to-axial chirality transfer induces a preferred torsion in the biphenyl moiety revealed by the sign of the biphenyl A band in the ECD spectrum. By 4,4′-substitution on the biphenyl moiety a redshift of the A band is obtained, leading to an increase of its relative contribution to optical rotation. This allows to reliably establish a direct correlation between the [α]_D sign, the biphenyl twist and, then, the substrate absolute configuration. This approach thus constitutes a really practical and reliable method to assign the absolute configuration of chiral carboxylic acids and primary amines by simple and straightforward [α]_D measurement, readily obtainable by a routine instrumentation like the polarimeter.     

Direct conversion of secondary phosphine oxides and H‐phosphinates with [Di(acyloxy)iodo]benzenes to phosphinic and phosphonic amides

The reaction of [di(acyloxy)iodo]benzene with secondary phosphine oxides or H‐phosphinates in the presence of primary or secondary amines allows one to obtain phosphinic or phosphonic acids amides in the one‐pot process. We take advantage of the strong acylating system DAIB/R₂P(O)H to phosphinylation of amines. However, the reaction mechanism is multipathway and causes yields of phosphinic or phosphonic acids amides to be moderate. When the concentration of amines is low, the intermolecular process plays a main role leading to the formation of carboxylic amides through mixed phosphoric–carboxylic anhydride, and also in the low concentration of amines, tetrahydrofuran effectively competes with the amines in the nucleophilic attack on the acylating intermediates. © 2009 Wiley Periodicals, Inc. Heteroatom Chem 20:81–86, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20514     

Gas chromatographic analysis of C1–C20 carboxylic acids esterified in aqueous solutions as isobutyl esters

Summary C₁–C₂₀ carboxylic acids have been esterified in aqueous solutions with i-butanol. Gas chromatographic analyses have been performed from a single chromatogram. It has been established that esterification in the concentration range of [H₂O]/[i-BuOH]=0.01–10.3 can be utilized for the quantitative determination of these carboxylic acids.The presence of water does not interfere in the range of [H₂O]/[i-BuOH]=0.01–1.03.In the cases of [H₂O]/[i-BuOH]>1.03, anhydrous sodium sulfate has been used for binding the water, in an amount of [Na₂SO₄]_anh./[H₂O]0.2.     

Kinetics and mechanism of oxidation of chloramphenicol by 1-chlorobenzotriazole in acidic medium

Chloramphenicol (CAP) is an antibiotic drug having a wide spectrum of activity. The kinetics of oxidation of chloramphenicol by 1-chlorobenzotriazole (CBT) in HClO₄ medium over the temperature range 293–323 K has been investigated. The reaction exhibits first-order kinetics with respect to [CBT]_o and zero-order with respect to [CAP]_o. The fractional-order dependence of rate on [H⁺] suggests complex formation between CBT and H⁺. It fails to induce polymerization of acrylonitrile under the experimental conditions employed. Activation parameters are evaluated. The observed solvent isotope effect indicates the absence of hydride transfer during oxidation. Effects of dielectric constant and ionic strength of the medium on the reaction rate have been studied. Oxidation products are identified. A suitable reaction scheme is proposed and an appropriate rate law is deduced to account for the observed kinetic data.     

Mechanism and kinetics of the 2,2′-bipyridyl catalysis of the chromium(VI) oxidation of malic acid

A spectrophotometric study of the kinetics and mechanism of the oxidation of malic acid (Mal) by chromium(VI) catalyzed by 2,2′-bipyridyl (bpy) in aqueous acidic medium was conducted in a temperature range of ～298 to 313 K. This reaction was found to be pseudo-first order with respect to Cr(VI) and first order with respect to malic acid. Under the conditions of the pseudo-first order ([Mal]_o ? [Cr(VI)]_o), the observed rate constant (k _obs) increased with the increase in [H⁺] and [bpy]. There was a weak negative salt effect. Based on the experimental results, a possible reaction mechanism for this oxidation catalyzed by bpy is proposed. The rate equation derived from this mechanism can explain all the experimental phenomena.     

Studies on transition metal nitrido and oxo complexes. Part 161. The nature of the oxoruthenates involved in some rutheniumcatalysed organic oxidations

Summary Electronic spectroscopy has been used to ascertain the nature of the oxoruthenates present in a number of organic oxidations catalysed by ruthenium complexes reported in the literature. The utility of oxoruthenates as catalysts with [Fe(CN)₆]^3– as co-oxidant for the conversion of primary alcohols to carboxylic acids and secondary alcohols to ketones has been assessed.     

Synthesis of novel dibenzo-2,6,9-triazabicyclo[3.3.1]nonanes from <Emphasis Type="Italic">o</Emphasis>-tosylamino- and <Emphasis Type="Italic">o</Emphasis>-mesylaminobenzaldehydes

Condensation of o-tosylaminobenzaldehyde with γ-aminobutyric, 4-aminophenylthioacetic, and p-aminobenzoic acids and β-alanine gave 6,12-epimino-5,11-ditosyl-5,6,11,12-tetrahydrodibenzo[b, f]-1,5-diazocines with carboxyl-containing substituents at the bridging N atoms. The structures of three products were examined by X-ray diffraction analysis. Condensation of o-mesylaminobenzaldehyde (prepared by the McFadyen-Stevens reaction) with NH₄OAc and primary amines afforded 6,12-epimino-5,11-dimesyl-5,6,11,12-tetrahydrodibenzo[b, f]-1,5-diazocine derivatives.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2165–2171, October, 2004.