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.

The kinetics of oxidation of alginate (Alg) and pectate (Pec) carbohydrate biopolymers was studied by spectrophotometry in aqueous perchloric and sulfuric acid solutions at fixed ionic strengths and temperature. In both acids, the reactions showed a first order dependence on [Ce(IV)], whereas the orders with respect to biopolymer concentrations are less than unity. In perchloric acid, the reactions exhibited less than unit orders with respect to [H+] whereas those proceeded in sulfuric acid showed negative fractional-first order dependences on [H+]. The effect ofionic strength and dielectric constant was studied. Probable mechanistic schemes for oxidation reactions were proposed. In both acids, the final oxidation products were characterized as mono-keto derivatives of both biopolymers. The activation parameters with respect to the slow step of the mechanisms were computed and discussed. The rate laws were derived and the reaction constants involved in the different steps of the mechanisms were calculated

Silver(I)-catalyzed oxidation of two amino acids (AA), namely L-asparagine and L-histidine, with platinum(IV) as hexachloroplatinate(IV) ion (HCP) has been investigated in perchloric acid solutions at constant ionic strength of 2.5 mol dm
3 and at 25 C. The courses of the oxidation reactions were followed spectrophotometrically. The kinetics of oxidation of both amino acids by HCP are identical, being first order in [HCP] and fractional-first orders with respect to [AA], [H+ ] and [Ag(I)]. The rates of both reactions decrease with increasing ionic strength and dielectric constant of the media. Addition of small amounts of Cu(II) and Al(III) increases the rates of reactions. Raising temperature enhances the rates. Amino acids are oxidized to form the corresponding aldehydes, ammonium ion and carbon dioxide. The rate law associated with the reaction mechanism is deduced. Activation parameters of the catalyzed oxidation reactions have been evaluated and discussed

The kinetics of chromium(VI) oxidations of iota- and lambda-carrageenans biopolymers have been investigated in aqueous perchlorate solutions at a constant ionic strength of 4.0 mol dm-3 and a temperature of 35 oC. The progress of the reactions was followed spectrophotometrically. The reactions showed a first-order dependence in [CrVI] and fractional-second order kinetics with respect to the concentrations of carrageenans. The influence of hydrogen ion concentration on the oxidation rates showed that the oxidation processes were acidcatalyzed. Increasing ionic strength of the reactions decreased the rates. Kinetic evidence for the formation of 1:2 complexes between chromium(VI) and carrageenans were revealed. The activation parameters of the rate constants along with thermodynamic parameters of the equilibrium constants were computed and discussed. A plausible oxidation mechanism consistent with the kinetic results has been suggested. An isokinetic relationship for some redox reactions involving chromium(VI) as an oxidant was examined. The tendency for formation of coordination polymer complexes between the formed biopolymer precursor chelating agents and some metal cations was investigated.

In aqueous alkaline medium, the kinetics of oxidation of pectate biopolymer (Pec) by hexacyanoferrate(III) (HCF) has been studied spectrophotometrically under the conditions, [Pec] >> [HCF], at a constant ionic strength of 1.0 mol dm-3 and at 25 oC. The reaction showed first order dependence on [HCF], whereas the reaction orders with respect to both [Pec] and [OH- ] are less than unity. The oxidation rate was found to increase with the increase on the ionic strength and dielectric constant of the reaction medium. Initial addition of reaction product, hexacyanoferrate(II), did not has any significant effect the oxidation rate. Based on the kinetic results, a plausible mechanistic has been proposed which involves the formation of a 1:1 intermediate complex between HCF and the deprotonated pectate species in a pre-equilibrium step. The rate law associated with the oxidation mechanism is derived and the reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to the slow step of the mechanism along with the thermodynamic quantities of the equilibrium constants are also calculated and discussed.

Kinetic investigation on the oxidation of one of the aminotriazole derivatives, namely N,N-dimethyl-N’- (4H-1,2,4-triazol-3-yl) formamidine (ATF) by permanganate ion in alkaline medium has been performed at a constant ionic strength of 0.1 mol dm-3 and at 25 oC. The progress of the reaction was followed spectrophotometrically. Both spectroscopic and kinetic evidences reveal formation of a 1:1 intermediate complex between the oxidant and substrate. The influence of pH on the oxidation rate indicated that the reaction is base-catalyzed. The reaction shows first order dependence with respect to [MnO4 - ], and fractional-first order dependences on both [ATF] and [OH- ]. Increasing ionic strength and dielectric constant did not affect the reaction rate. Addition of small amounts of alkali-metal ion catalysts was found to accelerate the oxidation rate and the order of effectiveness of the ions was: Li+ > Na + > K + . The final oxidation products of ATF were identified as 3-aminotriazole, dimethyl amine and carbon dioxide. A plausible reaction mechanism consistent with the kinetic observations is proposed, and the reaction constants involved in the different steps of the mechanism have been evaluated. The activation parameters with respect to the slow step of the reaction, along with thermodynamic quantities of the equilibrium constants are calculated and discussed.

Kinetics and mechanistic investigations of copper(II)-catalyzed oxidation of L-asparagine (Asn) by hexachloroplatinate(IV) (HCP) was performed in alkaline medium at a constant ionic strength of 0.2 mol dm-3 and at 25 oC using a conventional spectrophotometric technique. A first order dependence in both [HCP] and [CuII] and fractional-first order kinetics with respect to both [Asn] and [OH- ] were observed. Increasing ionic strength and dielectric constant increases the oxidation rate. The proposed mechanism indicated that the reaction proceeds via formation of copper(II) _ asparagine intermediate complex, which reacts with the oxidant in the rate-determining step to give rise to the oxidation products which were identified as αformyl acetamide, ammonia and carbon dioxide. In this context, platinum(IV) is reduced to platinum(II) by the substrate in a one-step twoelectron transfer process. The rate law associated with the reaction mechanism is deduced. Activation parameters of the reaction have been evaluated and discussed.