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.

Kinetic investigation on the hexachloroplatinate(IV) (HCP) oxidation of L-histidine (His) catalyzed by zirconium(IV) has been performed in sulfuric acid medium at constant ionic strength and temperature. The reaction has been followed spectrophotometrically. A first order dependence on [HCP] and fractional-first order dependences with respect to [His], [acid] and [Zr(IV)] are obtained. Increasing ionic strength and dielectric constant decreases the oxidation rate. On the basis of the experimental results, a suitable mechanism has been proposed. The reaction is suggested to proceed via formation of zirconium(IV)-histidine intermediate complex, which reacts with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step to give rise to the oxidation products which are identified as the corresponding aldehyde (2-imidazole acetaldehyde), ammonium ion and carbon dioxide. The appropriate rate law is deduced and the activation parameters are evaluated and discussed.

Kinetic investigations of Pt(IV) oxidation of L-asparagine catalyzed by transition metals with different valencies, namely Ag(I), Pd(II), Cr(III) and Zr(IV), were studied spectrophotometrically in sulfuric acid medium at constant ionic strength and temperature. The reaction was first order in [Pt(IV)], while the orders with respect to the concentrations of Asn, sulfuric acid and transition metal were less than unity over the concentration range studied. The rate constants decreased with increasing ionic strength and dielectric constant, while increasing temperature enhanced the rate. The order of catalytic efficiency was: Ag(I) [Cr(III) [Pd(II) [Zr(IV). A mechanism involving the formation of a complex between the catalyst and substrate is proposed. Oxidation by Pt(IV) is suggested to take place by an inner-sphere mechanism in which Pt(IV) is reduced to Pt(II) on the catalyst-bound substrate in a onestep two-electron transfer process. The oxidation products of Asn were identified as a-formyl acetamide, ammonium ion and carbon dioxide. The rate law associated with the reaction mechanism was deduced. Activation parameters of the reactions were evaluated and discussed

Kinetics of hexachloroplatinate(IV) (HCP) oxidation of L-histidine (His) in H2SO4 medium has been investigated in the absence and presence of silver(I) catalyst at constant ionic strength 2.0 mol dm-3 and temperature 25 C. The progress of both uncatalyzed and silver(I)-catalyzed oxidation reactions has been monitored spectrophotometrically. Both uncatalyzed and catalyzed paths show first-order dependence on [HCP] and fractionalfirst-order dependence each on [His] and [acid]. The catalyzed path is first order in [AgI ]. Increasing ionic strength and dielectric constant decreases the oxidation rates. The catalyzed reaction has been shown to proceed via formation of a silver(I)-histidine intermediate complex, which 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 histidine were identified as the corresponding aldehyde (2-imidazole acetaldehyde), ammonium ion and carbon dioxide. The mechanisms of these reactions have been proposed and the appropriate rate laws are deduced

The anticorrosion characteristics of sulfachloropyridazine (SCP) as an eco-friendly inhibitor for the corrosion of mild steel in 0.5 M H2SO4 solution has been studied, for the first time, using potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). The possible synergistic effect of halide ions on the inhibitive effect of SCP has been investigated. Thermodynamic calculations indicated that SCP adsorption on steel surface obeyed Langmuir adsorption isotherm. Electrochemical measurements showed that the SCP acted mainly as an anodic inhibitor. Halides significantly promoted the inhibition performance of SCP through the pre-adsorption on the electrode surface which is positively charged under the present conditions.