Kinetics Of Chromic Acid Oxidation Research Articles

Chromic Acid Oxidation of Methylaminopyrazole Formamidine in Sulfuric Acid Medium: A Kinetic and Mechanistic Approach

The kinetics of chromic acid oxidation of one of aminopyrazole formamidine derivatives, namely N,N-dimethyl-N’ -(5-methyl-1H-pyrazol-3-yl) formamidine (MAPF)in sulfuric acid solutions has been investigated at constant ionic strength and temperature. The progress of the reaction was followed spectrophotometrically. The reaction showed a first order dependence on [chromic acid] and fractional-first order dependences with respect to [MAPF] and [H+]. Increasing ionic strength and solvent polarity of the reaction medium had no significant effect on the oxidation rate. Addition of AgI, PdII and RuIII catalysts was found to enhance the reaction rate and the order of catalytic efficiency is: AgI > RuIII > PdII. The final oxidation products of MAPF are identified by spectral and elemental analysis as methylaminopyrazole, dimethylamine and carbon dioxide. A spectral evidence for the formation of chromium(III) product was obtained. A reaction mechanism adequately describing the observed kinetic behavior is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the rate-determining step of the reaction, along with thermodynamic quantities of the equilibrium constants, are presented and discussed.

Ruthenium(III)-catalyzed oxidation of alginate and pectate biopolymers by chromic acid in aqueous perchlorate solutions: a comparative kinetic study

The kinetics of chromic acid oxidation of alginate and pectate carbohydrate biopolymers in aqueous perchlorate solutions was studied in the absence and presence of ruthenium(III) catalyst at a fixed ionic strength of 2.0 mol dm−3 and a temperature of 298 K. Both uncatalyzed and Ru(III)-catalyzed oxidation reactions were followed spectrophotometrically. Both the reactions exhibited first-order dependence on [Cr(VI)], less than unit order with respect to the biopolymer concentration and fractional second order with respect to [H+]. The catalyzed reactions were first order in [Ru(III)]. No significant effect of ionic strength or dielectric constant of the medium was observed. Addition of Mn(II) inhibited the oxidation. Probable mechanistic schemes for the oxidation reactions are proposed, and the rate laws associated with these mechanisms have been derived. In both cases, the final oxidation products were characterized by spectroscopic data and microanalysis as mono–keto derivatives of the biopolymers. Under comparable experimental conditions, the oxidation rates of alginate were found to be lower than those of pectate for both the uncatalyzed and Ru(III)-catalyzed paths. The activation parameters with respect to the slow step of the mechanisms have been computed.

Kinetics and mechanistic approach to the chromic acid oxidation of l-tryptophan with a spectral detection of chromium(III) product

The kinetics of chromic acid oxidation of l-tryptophan in H2SO4 medium at a constant ionic strength of 0.6moldm−3and at 25°C have been investigated spectrophotometrically. The reaction exhibits a 3:2 stoichiometry (tryptophan:chromic acid). The reaction shows a first order dependence on [chromic acid], a fractional-first order dependence on [tryptophan] and fractional-second order dependence on [acid]. Increasing ionic strength and dielectric constant had no significant effect on the oxidation rate. The final oxidation products of tryptophan were identified as the corresponding aldehyde (indole-3-acetaldehyde), ammonium ion and carbon dioxide. A spectral evidence for the formation of chromium(III) product was obtained. The experimental results suggest formation of an intermediate complex between the protonated tryptophan and chromic acid which decomposes in the rate-determining step to yield the products. The mechanism of such reaction has been proposed. The thermodynamic parameters with respect to the first step of the suggested mechanism were evaluated and discussed.

Kinetics and mechanism of oxidation of chondroitin-4-sulfate polysaccharide by chromic acid in aqueous perchlorate solutions

The kinetics of chromic acid oxidation of chondroitin-4-sulfate polysaccharide as sulfated carbohydrates at a constant ionic strength of 4.0moldm−3 has been investigated, spectrophotometrically. The reaction kinetics showed a first-order dependence in chromic acid and fractional-first-order kinetics with respect to the chondroitin-4-sulfate concentration. The influence of [H+] on the reaction rates showed that the oxidation process is acid-catalyzed. Added Mn2+ ions indicated the formation of Cr(IV) as intermediate species. A kinetic evidence for formation of 1:1 intermediate complex was revealed. The kinetic parameters have been evaluated and a tentative reaction mechanism in good consistent with the kinetic results obtained is discussed.

Kinetics and mechanism of oxidation of poly(vinyl alcohol) macromolecule by chromic acid in aqueous perchloric acid

The kinetics of chromic acid oxidation of poly(vinyl alcohol) (PVA), a synthetic polymer, in perchlorate media at a constant ionic strength of 1.0 mol dm −3 has been studied spectrophotometrically. A first-order reaction in chromic acid and a fractional order with respect to PVA concentration were observed. The reaction was found to be acid catalyzed. Kinetic evidence for the formation of an intermediate complex between the chromic acid and PVA is presented. A mechanism consistent with the kinetic results is suggested.

Kinetic Studies of Chromic Acid Oxidation of Glyoxal

AbstractThe kinetics of chromic acid oxidation of glyoxal is reported. The reaction is first‐order in glyoxal and indicates a gradual change from a first‐order to a zero‐order dependence on acidity. The kinetic nature of this reaction has been studied and the rate law is consistent with a proposed mechanism as follows; rate = kKb, K[Cr+6][Gx][H+]/(l+0.238[H+]) at 25°C. The product analysis indicates that formic acid is the oxidation product under similar kinetic condition.

Kinetics and mechanisms of oxidations by metal ions. Part IX(1) Oxidation of phenylphosphinic acid by chromic acid in perchlorate medium

The kinetics of chromic acid oxidation of phenylphosphinic acid to phenylphosphonic acid has indicated the formation of an anhydride between HCrO4− and phenylphosphinic acid in its active PhP(OH)2 and inactive PhPH(O)OH forms. The ambiguity about the reactive form of phenylphosphinic acid arises from the fact that protonation of the anhydride leads to the same transition state which disproportionates in the rate-determining step to phosphonium ion and chromium(IV). These, through different reactions in the fast step, yield phenylphosphonic acid and chromium(III) as the final products. That HCrO4− is the reactive species of chromium(VI) is confirmed by the fact that k0 is independent of the inital [CrVI] where k0 is defined by the Equation k0=kobs[CrVI]/[HCrO4−]; kobs is the pseudo first-order rate constant with respect to chromium(VI) ([Phenyl-phosphinic acid]≫[CrVI]).

Kinetics of Chromic Acid Oxidation of Some Hydroxy Acids

Kinetics of Chromic Acid Oxidation of Some Hydroxy Acids

A search for resonance effects in the kinetics of chromic acid oxidation of a series of benzaldehyde and substituted benzaldehydes. A reinvestigation

The kinetics of oxidation of a series of meta and para substituted benzaldehydes by chromic acid has been re-investigated in acetic acid water mixture with a view on the search for resonance effects of para substituents. The overall order of the reaction is two, first order in each reactant at constant acidity. The products of oxidation were found to be the corresponding carboxylic acids. Hammett's reaction constants (ρm) and (ρp) for meta and para substituents were calculated separately and found to be 0.851 and 1.23, respectively. The reason for the higher ρp value with respect to ρm is discussed. The resonance parameters for para substituents were calculated and discussed.

Kinetics of Chromic Acid Oxidation of Serine, Methionine and Cysteine

Kinetics of Chromic Acid Oxidation of Serine, Methionine and Cysteine

Kinetics and mechanism of oxidation of some aldoses by chromic acid in perchloric acid medium

The kinetics of chromic acid oxidation of d-galactose, d-mannose, l-arabinose, and d-xylose have been studied in perchloric acid media. The reactions show first-order dependence on both chromium (VI) and aldose concentrations. The order with respect to hydrogen-ion concentration in each reaction is complex, and the hypotheses for the mechanism of acid catalysis have been tested. Different activation parameters have been evaluated. Aldoses are oxidized mainly to the aldonic acids when the aldose substrate is in excess. A tentative reaction mechanism has been suggested.

Kinetics of the Oxidation of Aliphatic Aldehydes by Chromic Acid

The kinetics of chromic acid oxidation of propanaldehyde, butyraldehyde and isobutyraldehyde in aq. acetic acid have been studied. The product of the oxidation is the corresponding carboxylic acid. The reaction is of first order with respect to each the acid chromate ion, HCrO4 ⊖, and the aldehyde but of second order to hydrogen ion. The rate increases with proportion of acetic acid in the solution. The activation parameters for the oxidation and enolisation reactions have been evaluated. The rate of enolisation under similar condition is less than that of oxidation. A mechanism in which the first step is the rapid reversible formation of a chromate ester followed by a hydrideion transfer in the rate determining step has been suggested.

Kinetics of chromic acid oxidation of phenanthrene and 3-substituted phenanthrenes

Kinetics of chromic acid oxidation of phenanthrene and 3-substituted phenanthrenes

Kinetics of the Chromic Acid Oxidation of Glycollic and Benzilic Acids

Abstract The kinetics of chromic acid oxidation of glycollic and benzilic acids have been studied. Catalysis by H+ ions has been noticed in both cases of oxidation. The results show that the logarithm of the rate constants increases with increase in the proportion of acetic acid in the mixture. Ionic strength decreases the rate of oxidation. Pyridine catalyzes the oxidation of glycollic acid whereas the catalysis in the case of benzilic acid is negligible. The energy of activation and entropy of activation have been calculated. Both kinetics and spectrophotometric results indicate the formation of intermediate chromium (VI)-hydroxycarboxylate complex in each case. The complex finally decomposes to give reaction products. Glycollic acid initially produces glyoxylic acid which subsequently gives formic acid whereas benzilic acid is oxidized to benzophenone.