The kinetics of oxidation of tryptophan by platinum(IV) was investigated in aqueous perchlorate solutions in the presence of silver(I) catalyst at a constant ionic strength of 2.0 mol dm-3 and at 25°C. The progress of the reaction was followed spectrophotometrically. The reaction did not proceed in the absence of the catalyst. The catalyzed reaction exhibited a first order dependence on both [PtIV] and [AgI ] whereas the order with respect to tryptophan concentration was found to be less than unity. Increasing ionic strength and dielectric constant was found to decrease the oxidation rate. The suggested oxidation mechanism involves formation of a silver(I)-tryptophan intermediate complex in a pre-equilibrium step, which confirmed by both spectral and kinetic evidences. The complex reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step. The final oxidation products of tryptophan were identified as the corresponding aldehyde (indole-3-acetaldehyde), ammonium ion and carbon dioxide.

The kinetics of chromic acid oxidation of one of aminopyrazole formamidine derivatives, namely N,N-dimethylN’-(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.

The oxidation kinetics of fluorenone hydrazone (FH) using potassium permanganate in alkaline medium were measured at a constant ionic strength of 0.1 mol dm−3 and at 25∘ C using UV/VIS spectrophotometer. A first-order kinetics has been monitored in the reaction of FH with respect to [permanganate]. Less-than-unit order dependence of the reaction on [FH] and [OH−] was revealed. No pronounced effect on the reaction rate by increasing ionic strength was recorded. Intervention of free radicals was observed in the reaction. The reaction mechanism describing the kinetic results was illustrated which involves formation of 1 : 1 intermediate complex between fluorenone hydrazones and the active species of permanganate. 9H-Fluorenone as the corresponding ketone was found to be the final oxidation product of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy. The expression rate law for the oxidation reaction was deduced. The reaction constants and mechanism have been evaluated. The activation parameters associated with the rate-limiting step of the reaction, along with the thermodynamic quantities of the equilibrium constants, have been calculated and discussed

The kinetics of chromic acid oxidation of L-tryptophan in H2SO4 medium at a constant ionic strength of 0.6 mol dm3 and 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 fractionalsecond 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.

The kinetics of permanganate oxidation of two substituted azinylformamidines (AznFs), namely N,N-dimethyl-N0 -(pyridin-2-yl)formamidine (Py) and N,N-dimethyl-N0 -(pyrimidin-2- yl)formamidine (Pym), in sulfuric acid were investigated using conventional spectrophotometry. Kinetic evidence for the formation of 1:1 intermediate complexes between the oxidant and substrates was obtained. The reactions of both substrates with permanganate showed similar kinetics, i.e. first order in [MnO4 ]0 and fractional-first-order with respect to both [Azn-F]0 and [H+]. The initial product, Mn2+, was found to autocatalyze the oxidation process. Changes in the ionic strength and dielectric constant of the medium had no significant effect on the rate. The final oxidation products of Py and Pym were identified as 2-aminopyridine and 2-aminopyrimidine, respectively, in addition to dimethylamine and carbon dioxide. A plausible reaction mechanism is suggested and the reaction constants involved in the mechanism were evaluated

The catalytic effect of ruthenium(III) on the oxidation of N,N-dimethyl-N -(4H-1,2,4-triazol3-yl) formamidine (ATF) by hexacyanoferrate(III) (HCF) was studied spectrophotometrically in aqueous alkaline medium. Both uncatalyzed and catalyzed reactions showed first order kinetics with respect to [HCF], whereas the reaction orders with respect to [ATF] and [OH−] were apparently less than unity over the concentration range studied. A first order dependence with respect to [RuIII] was obtained. Increasing ionic strength increased the rate of uncatalyzed reaction and decreased the rate of the catalyzed one Plausible mechanistic schemes of oxidation reactions have been proposed. In both cases, the final oxidation products are identified as aminotriazole, dimethyl amine and carbon dioxide. The rate laws associated with the reaction mechanisms are derived. The reaction constants involved in the different steps of the mechanisms were calculated. The activation and thermodynamic parameters have been computed and discussed.

The catalytic effect of europium(III) on the reduction of thionine dye (Th) by selenous acid has been studied by spectrophotometry in aqueous sulfuric acid solutions at a constant ionic strength of 3.0 mol dm−3 and at different temperatures (283–313 K). A first-order dependence with respect to both [Th] and [EuIII] was obtained, whereas the orders with respect to [SeIV] and [H+] were less than unity. Variation of ionic strength and dielectric constant of the reaction media did not affect the reaction rates. Probable mechanistic schemes for thionine reductions in both the absence and presence of europium(III) catalyst were proposed. The rate laws associated with the reaction mechanisms were derived, and the reaction constants were calculated. The activation parameters of the rate constants of the slow steps of both uncatalyzed and catalyzed reactions along with thermodynamic quantities of the equilibrium constants are computed and discussed. 

The kinetics of the oxidation of an aminotriazole formamidine derivative, N,Ndimethyl-N0 -(4H-1,2,4-triazol-3-yl) formamidine (ATF) by cerium(IV) has been studied spectrophotometrically in aqueous perchloric and sulfuric acid solutions at constant ionic strength of 1.0 moldm-3 . In both acids, the reaction shows first order kinetics with respect to [Ce(IV)], whereas the orders with respect to [ATF] are less than unity. The reaction exhibits negative fractional order kinetics with respect to [H?]. The rates of reaction are not significantly affected by variations of either ionic strength or relative permittivity of the reaction’s media. Addition of cerium(III) product does not affect the rates. Plausible mechanistic schemes for the reactions have been proposed. In both cases, the final oxidation products were identified as aminotriazole, dimethyl amine and carbon dioxide. Under comparable experimental conditions, the oxidation rate in perchloric acid solution is about sixfold higher than that in sulfuric acid solution. The effect of temperature on the rates has also been studied and activation parameters have been evaluated and discussed. The rate laws associated with the reaction mechanisms are derived

The catalytic effect of palladium(II) on the oxidation of L-tryptophan by potassium hexacyanoferrate(III) has been investigated spectrophotometrically in aqueous perchloric acid medium. A first order dependence in [hexacyanoferrate(III)] and fractional-first order dependences in both [L-tryptophan] and [palladium(II)] were obtained. The reaction exhibits fractional-second order kinetics with respect to [H+]. Reaction rate increased with increase in ionic strength and dielectric constant of the medium. The effect of temperature on the reaction rate has also been studied and activation parameters have been evaluated and discussed. Initial addition of the reaction product, hexacyanoferrate(II), does not affect the rate significantly. A plausible mechanistic scheme explaining all the observed kinetic results has been proposed. The final oxidation products are identified as indole-3-acetaldehyde, ammonium ion and carbon dioxide. The rate law associated with the reaction mechanism is derived.

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.