The kinetics of oxidation of L-asparagine (Asn) by hexacyanoferrate(III) (HCF) has been investigated in alkaline medium in the absence and presence of silver(I) catalyst at a constant ionic strength of 0.5 mol dm−3 and at 20°C. The progress of both uncatalyzed and silver(I)-catalyzed oxidations was followed spectrophotometrically. Both reactions showed a first order dependence with respect to [HCF], whereas the orders with respect to [Asn] and [OH− ] were less than unity. The catalyzed reaction exhibited a first order dependence in [AgI ]. Increasing both ionic strength and dielectric constant of the reaction medium increased the rate of uncatalyzed reaction and did not affect significantly the rate of catalyzed reaction. Addition of the reaction product, HCF(II) to the reaction mixture had no affect on the rate. Appropriate reaction mechanisms for both uncatalyzed and catalyzed oxidations explaining all of the observed kinetic results has been proposed. The catalyzed reaction has been shown to proceed via formation of a silver(I)-asparagine intermediate complex, which reacted with the oxidant by an inner-sphere mechanism leading to decomposition of the complex in the rate-determining step to yield the final oxidation products which were identified as α-formyl acetamide, ammonia, and carbon dioxide. The rate law expressions associated with the reaction mechanisms were derived.

In aqueous alkaline medium, the kinetics of oxidation of methylaminopyrazole formamidine (MAPF) by hexacyanoferrate(III) (HCF)has been studied spectrophotometrically under the conditions, MAPF >> HCF at a constant ionic strength of 0.1 mol dm-3 and at 25°C. The reaction showed first order dependence on [HCF] while it exhibited fractional-first order kinetics with respect to [MAPF] and [OH- ]. The oxidation rate increased with increasing ionic strength and dielectric constant of the reaction medium. Addition of small amounts of some divalent transition metal ions accelerates the oxidation rate and the order of catalytic efficiency was: Cu(II) > Ni(II) > Zn(II) > Co(II) > Cd(II). The suggested mechanism involves formation of a 1: 1 intermediate complex between HCF and the deprotonated MAPF species in a pre-equilibrium step. The final oxidation products were identified as methylaminopyrazole, dimethylamine and carbon dioxide. The appropriate rate law was deduced. The reaction constants involved in the mechanism were evaluated. The activation and thermodynamic parameters were determined and discussed.

The kinetics of oxidation of N, N-dimethyl-N’-(pyridin-2-yl) formamidine (Py-F) by cerium(IV) was studied spectrophotometrically in aqueous perchloric acid solutions at a constant ionic strength of 1.0 mol dm-3 and at 20°C. The reaction showed first order dependence with respect to [Ce(IV)] and less than unit order with respect to [Py-F]. The reaction exhibited negative fractional-first order kinetics with respect to [H+ ]. The rate of reaction was not significantly affected by variation of either ionic strength or dielectric constant of the reaction medium. Addition of cerium(III) product did not affect the reaction rate. A suitable mechanistic scheme for the oxidation reaction has been proposed. The final oxidation products were identified as 2-aminopyridine, dimethylamine and carbon dioxide. The activation parameters have been evaluated and discussed. The rate law associated with the reaction mechanism was derived.

The kinetics of oxidation of iota- and lambda-carrageenans as sulfated polysaccharides by cerium(IV) was studied spectrophotometrically in aqueous perchlorate solutions at a fixed ionic strength of 2.0 mol dm-3 and a temperature of 25 oC. The reactions showed a first order dependence on [CeIV], whereas the orders with respect to each carrageenan concentration were less than unity. The reactions exhibited fractional-first order kinetics with respect to [H+ ]. Increasing ionic strength increased the oxidation rates. The oxidation products of carrageenans were characterized by elemental analysis and IR spectra as their diketo-acid derivatives. The oxidation products were found to have high tendencies to form coordination polymer complexes with some metal cations such as BaII, CdII, PbII and AgI . Kinetic evidences for the formation of 1:1 complexes were revealed. Plausible mechanistic scheme for cerium(IV) oxidations of carrageenans were proposed. The activation parameters with respect to the slow step of the reactions were evaluated and discussed. The rate laws have been derived and the reaction constants involved in the different steps of the mechanisms were calculated. The activation parameters associated with the ratedetermining step of the mechanism along with thermodynamic quantities of the equilibrium constants were computed and discussed.

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.