The catalytic effect of silver(I) and copper(II) ions on the oxidation of histidine by cerium(IV) in aqueous sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 3.0 mol dm−3 and at 25°C. In both uncatalyzed and metal ions-catalyzed paths, the reactions exhibited first-order kinetics with respect to [Ce(IV)] and [catalyst], and fractional first-order dependences with respect to [His] and [H+]. The oxidation rates increased as the ionic strength and dielectric constant of the reactions media increased. The catalytic efficiency of Ag(I) was higher than that of Cu(II). Plausible mechanistic schemes for both uncatalyzed and catalyzed reactions were proposed, and the rate laws associated with the suggested mechanisms were derived. In both cases, the final oxidation products of histidine were identified as 2-imidazole acetaldehyde, ammonium ion, and carbon dioxide. The activation parameters associated with the second-order rate constants were evaluated

The oxidation kinetics of isosorbide (S) by potassium permanganate in both perchloric and sulfuric acid solutions was investigated spectrophotometrically at a constant ionic strength of 2.0 moldm-3 and at 25 C. In both acids, the oxidation reactions showed a first-order dependence on ½MnO 4 , apparent a less than unit-order dependence with respect to [S] and a fractional-second-order dependence with respect to [H?]. Variation of either the ionic strength or dielectric constant of the reactions media did not significantly affect the oxidation rates. In both acids, the final oxidation product of isosorbide was identified by both spectroscopic and chemical tools as the corresponding monoketone derivative, namely (1S,4S,5R)-4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. Under comparable experimental conditions, the oxidation rate of isosorbide in perchloric acid was lower than that in sulfuric acid. The oxidation mechanism describing the kinetic results was proposed and the rate law expression was derived. The activation parameters of the second-order rate constants were computed and are discussed

The inhibition of the corrosion of mild steel in 0.5 M H2SO4 by vanillin in the presence of various amino acids, typically valine, methionine, cysteine and methylcysteine hydrochloride, are studied using potentiodynamic technique aiming at the elucidation of the mechanism of the corrosion inhibition. The corrosion inhibition of vanillin and amino acids was evaluated, both in their individual presence and in their coexistence. The largest inhibition efficiency has been found in the presence of vanillin and cysteine mixture. To have an insight into the mechanism of the inhibition and probe the adsorption sites of the inhibitor, the inhibition efficiency of a Schiff base, synthesized from vanillin and a selected amino acid, typically cysteine, has been compared with the inhibition efficiency of the vanillin and cysteine mixture. Interestingly, it has been found that the inhibition efficiency of the vanillin and cysteine mixture is much larger than the relevant Schiff base, and that the inhibition efficiency of the latter is much smaller than the inhibition efficiency in the presence of the individual components, i.e., vanillin and cysteine. This points to the blocking of the probable adsorption sites, upon the formation of Schiff base, which is the amino group of cysteine and the aldehydic group of vanillin. The adsorption of the methylcysteine, as an example, in the presence of vanillin was found to follow Temkin isotherm and that the chemical adsorption mode is controlling as revealed from the free energy of adsorption (44.4 kJ/mol).

The electrochemical behavior of nickel, Inconel600, Incoloy800 and 316 stainless steel in different concentrations of HNO3 solutions was investigated using the cyclic voltammetry technique. . All the curves in the anodic cyclic voltammetry are characterized by an anodic dissolution peak (A) followed by a passive region (B), before oxygen evolution. On the other hand incoloy800and 316 stainless steel show an additional dissolution peak (C) and trans passive region followed by oxygen evolution. In the cathodic branch of the CVS there is one cathodic peak in the case of Ni. Inconel600 and Incoloy800.On the other hand, there is an unexpected peak in case of 316 stainless steel.This peak appeared on the anodic branch.All the anodic and cathodic peaks are interpreted. The passivation of Ni was explained based on the formation of NiO. In the alloys the passive layer was mainly composed of Ni+2, Fe+3and Cr+3 in Inconel600, Incoloy800, and Mo+6 in case of 316 stainless steel. The role of Cr+3 and Mo+6ions in the reinforcement of the passive film is explained.

The oxidation of isosorbide (S) by chromic acid (CrVI) has been studied in aqueous perchlorate solution at a constant ionic strength of 3.0 mol dm-3 and temperature of 25 C. The course of the reaction was followed spectrophotometrically. The reaction exhibited first-order dependence on [CrVI], less than unit order with respect to [S], and fractional-second-order dependence with respect to [H?]. Variation of the ionic strength or dielectric constant of the medium had no significant effects on the oxidation rate. Addition of MnII inhibited the oxidation rate. The oxidation product of isosorbide was identified as the corresponding monoketone derivative, namely (1S,4S,5R)- 4-hydroxy-2,6-dioxabicyclo[3.3.0] octan-8-one. A mechanism for the oxidation is proposed, and the corresponding rate-law expression has been deduced. The activation parameters associated with the second-order rate constant are presented and discussed

The effect of increasing the concentration of chloride ions as pitting corrosion agent on the potentiodynamic anodic polarization curves of nickel(Ni), Inconel 600, Incoloy 800 and 316 Stainless steel (SS) in 0.1M HNO3 solution at a scan rate 1.0 mV sec-1 was studied. The pitting corrosion potential varied with the logarithmic of the molar concentrations of chloride ions in case of Ni and Inconel 600 according to S-shaped curve. This behavior was explained according to re-passivation, propagation and continued propagation of the pits formed. In case of Incoloy 800 and 316SS a broken lines were observed according to re-passivation and propagation of the pits formed. It is found that,316SS is more resistance to pitting attack due to the presence of Mo in their chemical structure. The effect of the increasing concentration of some inorganic anions such as the sodium salts of chromate, tungstate, molybdate, phosphate dibasic and carbonate to inhibit the pitting corrosion was investigated. The values of the pitting corrosion potential were shifted to more positive values indicating the inhibiting action of these anions toward the pitting corrosion.

Kinetics of chromium(VI) oxidation of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), in perchlorate solutions was investigated at a constant ionic strength of 2.0 mol dm3 and at 25 oC. The progress of the reactions was followed spectrophotometrically. The reactions showed a first order dependence on [Cr(VI)] and fractionalfirst order dependences with respect to hydrogen ion and fluorene derivatives concentrations. Under comparable experimental conditions, the order of the oxidation rates of the fluorene derivatives was: Fl > Fl-I > Fl-Br > Fl-Cl. The mechanism of the oxidation reactions was suggested and the rate-law expression was derived. Values of the rate constants of the slow step along with the equilibrium constants were calculated.

Oxidation kinetics of fluorene (Fl) and its halogenated derivatives, namely, 2,7-dichlorofluorene (Fl-Cl), 2,7-dibromofluorene (Fl-Br) and 2,7-diiodofluorene (Fl-I), by permanganate ion in both perchloric and sulfuric acid media have been investigated using conventional spectrophotometric technique. In both acidic media, the reactions manifested first order kineticsin [permanganate] and less than unit order each in [reductants] and [acid]. Increasing ionic strength had no effect on the oxidation rates. Oxidation rates of fluorenes in perchloric acid were higher than those in sulfuric acid and the order of the oxidation rates was: Fl > Fl-I > Fl-Br > Fl-Cl. Final oxidation products were identified by GC/MS and FT-IR analyses in all cases as 9H-fluorenone derivatives. Reaction constants as well as activation parameters of the second order rate constants were also evaluated

Kinetics of hexacyanoferrate (III) (HCF) oxidation of fluorene (Fl) in organic alkaline medium has been studied by spectrophotometric technique at a constant ionic strength of 0.15 mol dm-3 and at a temperature of 25°C. The reaction showed a first order kinetics with respect to [HCF] and fractional-first order dependences on both [Fl] and [OH- ]. The oxidation rate was increased with the increase in the ionic strength of the reaction medium. The oxidation mechanism was suggested which involves formation of a 1:1 intermediate complex between fluorene and HCF species in a pre-equilibrium step. The final oxidation product of fluorene was identified by spectroscopic and chemical tools as 9H-fluorenone. The appropriate rate law expression was deduced and the reaction constants involved in the mechanism were evaluated. The activation parameters of the rate constant of the slow step along with the thermodynamic quantities of the equilibrium constants were evaluated and discussed.

The electrochemical behavior of nickel, Inconel 600, Incoloy 800 and 316 stainless steel electrodes in different concentration of NaOH solution was investigated using the cyclic voltammetry technique (CV). All the curves in the anodic branch of the CV are characterized by anodic dissolution peak (A), passive region (B), anodic dissolution peak (C) before oxygen evolution. In the case of the cathodic branch of CV there is one reduction peak (D) in case of Ni electrode but there are two reduction peaks (D and E) in case of the three alloys used. All these peaks are explicated. The effect of chloride ion as a pitting agent on the cyclic voltammetry and the potentiodynamic anodic polarization of Ni ,Inconel 600, Incoloy 800 and 316 SS electrodes in NaOH solution was investigated. As the concentrations of the chloride ions increase the change of the amount of the anodic charge Δqa increases and the values of the pitting corrosion potential are shifted to the more negative direction indicating the breakdown of passivity and the imitation of the pitting corrosion. At one and the same Cl- ion concentration, the resistance to the pitting attack decreases in the following order: 316SS > Inconel 600 > Incoloy 800> 316 SS. This order depends on the chemical composition of these alloys.