Aqueous Perchloric Acid Medium Research Articles

A Study of Micellar Catalyses on Oxidation of Glycine by QDC in the Presence of Sodium Dodecyl Sulphate (SDS) in Aqueous Perchloric Acid Medium

Aims: To study the micellar effect of SDS on the oxidation of glycine by Quinolinium Dichromate (QDC) in perchloric acid medium. Background: Among the amino acids, glycine plays a major role in multiple metabolic reactions, such as glutathione synthesis and one-carbon metabolism. The oxidation of glycine has received importance because it is the major neurotransmitter inhibitor in the spinal cord and brainstem. In the oxidation process of amino acids, highly toxic chromium (VI) compounds are converted into non-toxic chromium (III) by quinolinium dichromate (QDC) oxidant in an appropriate pH value medium. Objective: 1. To study the catalytic role of anionic surfactant (SDS) on the oxidation of glycine by QDC through micellization, evaluation of critical micelles concentration (CMC) in the presence and absence of glycine and other surface properties along with thermodynamic quantities. 2. Determination of rate constant and order of reaction with respect to QDC, glycine, acid and surfactant which will help to study the kinetics of the reaction 3. Analysis of oxidation product by FT-IR and calculation of activation parameters. 4. Synthesis of oxidant (QDC) and its characterization by UV-Visible spectrophotometer and NMR spectroscopy. Results: First-order kinetics was observed with respect to oxidant, glycine and hydrogen ions. The rate of reaction increased remarkably with an increase in the concentration of surfactant (SDS). The kinetic results show that the ionic strength variation does not have any significant effect on the rate whereas the increase in the dielectric constant of the medium shows a remarkable effect on the rate constant. From stoichiometry study, it was found that 2 moles of oxidant (QDC) consumed 3 moles of glycine to produce aldehyde (Formaldehyde). Conclusion: The observed negative value of (ΔS) entropy of activation and positive (ΔH) enthalpy of activation suggests a more ordered activated complex formation and highly solvated transition state. The kinetics of the reaction in a perchloric acid medium is found to be accelerated in the presence of surfactant (SDS). The kinetics of the reaction follow pseudo first-order decay of Cr(VI) species (QDC), a unity dependence of rate on glycine and perchloric acid. The oxidation product formaldehyde was identified by FTIR. NMR spectrum analysis of synthesized QDC shows a resemblance with pure QDC.

WITHDRAWN: Kinetics and mechanism of the reactions of alkanediamine-linked dinuclear platinum(II) complexes with some biorelevant-nucleophiles

The kinetics and mechanism of substitition reactions of dinuclear platinum(II) complexes of the general formula [{Pt(H2O)}2(N,N,N′,N′-tetrakis(2-pyridylmethyl)-N(CH2)n-N](ClO4)4,viz., n = 2 (PtEn); 3 (PtProp); 6 (PtHex); 8 (PtOct) and 10 (PtDec) were investigated in 0.10 M aqueous perchloric acid medium as a function of concentration of l-glutathione (Glu) and dl-penicilliamine (Pen) nucleophiles and temperature under pseudo first-order conditions using UV–visible spectrophotometry. The reactivity data of the dinuclear Pt(II) complexes were compared with those of their mononuclear analogues of the form [Pt(H2O)(N,N-bis(2-pyridylmethyl)-N(CH2)n-CH3](ClO4)2, n = 1 (Ptbpea); 2 (Ptbppa); 5 (Ptbpha) and 9 (Ptbpda) under the same experimental conditions. The observed rate constants for the substitution of the aqua ligands follow the simple rate law: kobs = k2[Nu]. The reactivity of the complexes increases as the chain length of the linker or tail increases except Prop which showed a higher reactivity towards the nucleophiles than the rest of the complexes. The overall trend of reactivity for the dinuclear platinum(II) complexes is PtEn < PtHex < PtOct < PtDec < PtProp. The reactivity of the mononuclear complexes follows the same trend as the dinuclears and increases in the order Ptbpea < Ptbppa < Ptbpha < Ptbpda. In all cases, the mononuclear complexes are more reactive than their dinuclear analogues, which is an indication of the steric retardation on the rate of substitution due to the conformations of the dinuclear platinum(II) complexes. Glu was found to be a better nucleophile than Pen. The relatively small and positive values for the enthalpy of activation, negative values for entropy of activation and the dependence of the second-order rate constants on the concentration of entering nucleophiles supports an associatively activated mechanism.

Determination of ascorbic acid in bulk and vitamin-C tablets using manganese (III) in aqueous acidic perchlorate media

Determination of ascorbic acid in bulk and vitamin-C tablets using manganese (III) in aqueous acidic perchlorate media

Kinetics and oxidation of thiocarbohydrazide by hexacyanoferrate(III) in aqueous perchloric acid medium

Hexacyanoferrate(III) [HCF(III)] was used to oxidize thiocarbohydrazide (TCH) in an aqueous perchloric acid (HClO4) medium, and the reaction kinetics were studied spectrophotometrically at 420 nm while keeping a constant ionic strength of 1.0 mol dm−3 and modulating the temperature between 298K and 318K. The stoichiometry of the reaction among TCH and HCF in the HClO4 medium is 1:2. The reaction has a lower than unit order in both TCH and HClO4 and is of the first order in HCF. The impact of varying the ionic strength and dielectric constant of the medium on the rate has been investigated. The effect of temperature on the reaction rate was studied, and different activation parameters of reaction Ea, ΔH#, ΔS#, ΔG#, and log10 A were calculated. The products of oxidation were analyzed by simple qualitative analysis. On the basis of the collected data, the rate law has been derived, and a probable mechanism has been proposed.

Kinetics and mechanistic studies for the oxidation of N-Benzylhydroxylamine by a CoIII-bound bridging superoxo complex in perchloric acid medium

In aqueous perchloric acid medium (pH = 0.522 – 1.3) , N–benzylhydroxylamine ( two electron reductant) reduces the one electron oxidant, superoxo ligand in [(dien)(en)CoIII(O2)CoIII(en)(dien)](ClO4)5 (1) to the corresponding hydroperoxo complex, [(en)(dien)CoIII(HO2)CoIII(en)(dien)]5+ (2) and itself gets oxidised to PhCH2NO following both proton coupled electron transfer (PCET) path and an electron – transfer (ET) reaction. The kinetics, stoichiometry and reaction mechanism clearly indicate that oxidation of PhCH2NHOH occurs through the formation of an intermediate, benzyl derivative of aminoxyl radical (PhCH2NHO•). In the presence of excess PhCH2NHOH over 1, the reaction obeys first-order kinetics and rate of the reaction increases with [PhCH2NHOH]. The reaction rate, however, decreases with increase in [H+] and the plot of 1/ko with [H+] is linear with a small but noteworthy intercept. It is also remarked that the reaction rate remarkably decreases with increasing proportion of D2O replacing H2O in the solvent. Therefore, an H-atom transfer (HAT) from PhCH2NHOH to the bridging superoxide in 1 seems reasonable at the rate determining step.

Substrate Inhibition in Ruthenium(III) Catalyzed Oxidation of Propane-1,3-diol by Periodate in Acidic Medium: A Kinetic Study

Ruthenium(III) catalyzed oxidation of propane-1,3-diol by potassium periodate was studied in aqueous perchloric acid medium. Orders of reaction with respect to concentrations of oxidant, substrate, acid and catalyst were determined. First order in oxidant and catalyst concentrations, and inverse fractional order in acid medium were observed. In addition, substrate inhibition (i.e. a decrease in reaction rate with an increase in substrate concentration) was observed. Effect of addition of salt and solvent was studied. Based on the studies of temperature variation, Arrhenius parameters were calculated. Plausible mechanism was also proposed based on observed kinetics.

Oxidative Degradation of Methyl Green Dye by Cyanide Ion in Aqueous Perchloric Acid Medium; Kinetics, Thermodynamic and Mechanistic Approach

Oxidative Degradation of Methyl Green Dye by Cyanide Ion in Aqueous Perchloric Acid Medium; Kinetics, Thermodynamic and Mechanistic Approach

Kinetics and Mechanism of Oxidative Conversion of Methionine to Sulfone by Chloramine-B in Acid Medium

Background: Methionine, Met, is one of the sulfur containing amino acids required in the human body by certain biochemical reactions. Since Met is not biosynthesized in humans, it needs to be supplied externally in diet. Met is highly susceptible to oxidation. Objective: The oxidation of Met to its sulfone by CAB in aqueous perchloric acid medium at 323 K has been kinetically studied. Method: Effect of varying ionic strength, solvent composition, dielectric constant has been determined. Effect of reduction product of Chloramine-B (CAB), benzenesulfonamide, on the reaction rate has also been investigated. Conclusion: The experimental rate law obtained is: rate = k׀ [CAB] [H2O]. Activation parameters have been evaluated using Arrhenius and Eyring plots. A mechanism consistent with the observed kinetic data has been discussed. A rate law has been derived based on the mechanism. Keywords: Chloramine-B, kinetics, mechanism, methionine, oxidation, rate law, reduction, sulfone.

Palladium(II)-catalyzed oxidation of l-tryptophan by hexacyanoferrate(III) in perchloric acid medium: a kinetic and mechanistic approach

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. Palladium(II)-catalyzed oxidation of L-tryptophan by hexacyanoferrate(III) in aqueous perchloric acid medium has been investigated. The effect of temperature on the reaction rate has been studied and the activation parameters have been evaluated and discussed. The final oxidation products are identified as indole-3-acetaldehyde, ammonium ion and carbon dioxide.

Kinetics and Mechanism of Cerium(IV) Oxidation of Fosfomycin Disodium Salt: An Antibiotic Drug in Acid Perchlorate Solutions

The kinetics of the oxidation of fosfomycin disodium salt by cerium(IV) in an aqueous perchloric acid medium at constant ionic strength, I = 1.10 mol dm−3, has been investigated spectrophotometrically at 25°C. The reaction is of first order in cerium(IV) concentration, fractional order in both fosfomycin and H+ ion concentrations. The active species of oxidant is found to be Ce(OH)3+. Based on the experimental results a suitable mechanism is proposed. The reaction constants involved in the different steps of the reaction mechanism and the activation parameters with respect to the slow step of the mechanism are determined and discussed.

Oxidation of an antibiotic drug – fosfomycin disodium salt by chromium(VI) in aqueous perchloric acid medium – A kinetic and mechanistic study

Oxidation of an antibiotic drug – fosfomycin disodium salt by chromium(VI) in aqueous perchloric acid medium – A kinetic and mechanistic study

Spectroscopic investigation on kinetics, thermodynamics and mechanism for electron transfer reaction of iron(III) complex with sulphur centered radical in stimulated biological system

Electron transfer reactions of biological organic sulphides with several metal ions to generate sulphide radical cations are a great concern in biochemical process. To understand the mechanism, a stimulated biological system having model compounds, iron(III)-bipyridyl complex with thio-diglycolic acid (TDGA) was investigated. Spectroscopic study reveals the kinetics and thermodynamics of the reaction in aqueous perchloric acid medium. The reaction follows first and fractional order of 0.412 with respect to [Fe(bpy)3]3+ and TDGA, respectively. The oxidation is insensitive to variation in [H+] but slightly decreases with increase in ionic strength ([I]). Addition of acrylamide, a radical scavenger has no effect on the rate of the reaction. The high negative value of ΔS# (−74.3±1.09JK−1mol−1) indicates the complex formed has a definite orientation higher than the reactants. Based on the above results, a suitable reaction mechanism for this reactionis proposed.

Kinetics and mechanistic study of manganese(II)-catalyzed cerium(IV) oxidation of thiamine hydrochloride in aqueous perchloric acid medium by stopped flow technique

The kinetics of the manganese(II)-catalyzed oxidation of thiamine hydrochloride by cerium(IV) in aqueous perchloric acid medium at a constant ionic strength of 1.10 mol dm−3 was studied spectrophotometrically at 15, 25, 35, and 45 °C by the stopped flow technique. The reaction between thiamine hydrochloride and cerium(IV) in the acid medium exhibits 1:3 stoichiometry. The main products were identified by spot test, IR, 1H NMR, and GC–MS studies. The reaction is first order in cerium(IV) and manganese(II) and has less than unit order in thiamine hydrochloride. As the acid concentration increases the rate of reaction decreases. The added product cerium(III) retards the rate of reaction. The active catalyst and oxidant species were identified as [Mn(H2O)4]2+ and [Ce(OH)]3+, respectively. A probable mechanism involving free radicals and the formation of a complex between substrate and catalyst is proposed. The reaction constants, activation parameters, and thermodynamic quantities are calculated and discussed.

Kinetics and Mechanism of Aquachlororuthenium (III) Catalyzed Oxidation of Tartaric Acid by Acid Bromate

The kinetics of the oxidation of Ru (III) catalyzed oxidation of tartaric acid by potassium bromate in aqueous perchloric acid medium at constant ionic strength was investigated in the temperature range 303- 318 K. The reactions exhibit first order kinetics at low concentration of bromate, tending to zero order at high concentration. Zero order kinetics with respect to (tartaric acid) and first order kinetics in (Ru (III)) were observed in the oxidation of tartaric acid. A positive effect on the rate of reaction has been found on the successive addition of (H + ) and (Cl - ). Variation in mercuric acetate concentration, (Hg(OAc)2) and ionic strength of the medium did not bring any significant change on the rate of reaction. The first order rate constant increases with decrease in the dielectric constant of the medium. The values of rate constants observed at four different temperatures were utilized to calculate the activation parameters. Formic acid and carbon dioxide have been identified as main oxidation products of the reaction. A plausible mechanism from the results of kinetic studies, reaction stoichiometry and product analysis has been proposed.

Kinetic and mechanistic investigations of chlorocomplex of Ru(III) and Ir(III) catalyzed oxidation of d-fructose by N-bromophthalimide in acidic medium

The kinetic and mechanistic studies of Ru(III) and Ir(III) homogeneously catalyzed oxidation of d-fructose (d-fru) by N-bromophthalimide (NBP) in the presence of aqueous perchloric acid medium have been made at 303K using mercuric acetate as Br− ion scavenger. The stoichiometry and the oxidation products in both catalysts were found to be the same. The determined stoichiometric ratio was found to be 1:2 ([d-fru]:[NBP]). Arabinonic and formic acids were obtained as the major oxidized products of both the reactions. The kinetics of the reaction were studied as a function of temperature, ionic strength, concentration of the salt, concentration of the added reaction product, and the dielectric constant of the medium to learn the mechanistic aspects of the reaction. Possible mechanisms are proposed, which are consistent with the kinetics, stoichiometry and products of the reaction.

Kinetics and Mechanism of the Autocatalyzed Oxidation of Theophylline by Permanganate in Aqueous Perchloric Acid Medium

The reaction kinetics for the oxidation of theophylline by permanganate ions have been investigated in perchloric acid medium using spectrophotometric techniques at 25 ∘C, and at constant ionic strength 1.60 mol⋅dm−3, under pseudo first order conditions. An autocatalyzed reaction is observed due to one of the products formed is Mn(II). The orders with respect to theophylline and Mn(VII) were both found to be unity, whereas fractional order is observed with respect to the autocatalyst, Mn(II). The rate of the reaction increases as the concentration of acid increases, but the order with respect to acid concentration is less than unity. The influence of temperature on the rate of reaction was studied. Based on the experimental results a suitable mechanism is proposed. The activation and thermodynamic parameters were determined with respect to slow reaction step.

Kinetics and Mechanistic Investigation of Decarboxylation for the Oxidation of Levofloxacin by Chloroamine-T in Acidic Medium

The mechanistic investigation of oxidation of levofloxacin (LF) has been studied by chloramine-T(CAT) in aqueous perchloric acid medium at 25 °C. The reaction followed first-order kinetics with respect to [CAT], [LF], and [H+] in their lower concentrations range, tending to zero-order at their higher concentrations. First-order kinetics with respect to [CAT] was observed for the oxidation of levofloxacin. An increase in perchloric acid concentration increased the rate of reaction. The effect of added products, ionic strength, and dielectric constant of the medium was studied on the rate of reaction. The main products were identified by spot test, FT-IR, and NMR. A mechanism was proposed on the basis of experimental results. The activation parameters with respect to the slow step of the mechanism was evaluated, and the thermodynamic parameters were also determined and discussed.

Kinetics and Mechanism of Permanganate Oxidation of Clopidogrel Hydrogen Sulfate: An Antiplatelet Drug in Acid Perchlorate Solutions

The oxidation of clopidogrel hydrogen sulfate, commercially known as Plavix, by permanganate ion in aqueous perchloric acid medium at a constant ionic strength (I = 0.06 mol dm–3) has been investig...

Kinetics and Mechanism of Deamination and Decarboxylation of 2-Aminopentanedioic Acid by Quinolinium Dichromate (QDC) in Aqueous Perchloric Acid Medium

Kinetic data for the oxidation of 2-aminopentanedioic acid/l-glutamic acid (Glu-e) by quinolinium dichromate (QDC) in perchloric acid medium are reported. The results of the reactions studied spectrophotometrically over a wide range of experimental conditions show that the rate of the reaction is increased by increases in perchloric acid, the ionic strength, and the concentration of Glu-e. The reactions are first order with respect to both QDC and Glu-e. Added products are found to have an insignificant effect on the reaction rate. The activation parameters and thermodynamics have been evaluated and lend further support to the proposed mechanism.

A UV study of the behavior of some benzaldehyde hydrazones in acid medium

The spectral behavior of some benzaldehyde hydrazones was examined via the UV spectroscopic technique at room temperature and in the pH region between 1 and 7 in aqueous perchloric acid medium. The acid-base equilibrium was characterized qualitatively and quantitatively. It was found that the protonation reaction took place. The spectra of the solution of benzaldehyde hydrazones at different pHs were studied and utilized for the determination of ionization constants of the protonated forms of hydrazones (pKBH+). The pKBH+ values were determined numerically and graphically from the absorbance values of the experimental and reconstructed spectra by characteristic vector analysis. In order to obtain thermodynamic pKBH+ values, measurements were performed at ionic strengths of 0.1, 0.25 and 0.5 M (NaClO4). There was a good agreement between the obtained pKBH+ values of the investigated hydrazones and those of similar classes of compounds. The site of protonation of the investigated hydrazones was also studied, too. The proton affinities for the different nitrogen atoms of the hydrazone molecule were calculated using AM1 and PM3 semiempirical methods. It was demonstrated that the protonation occurred at the imino nitrogen atom of hydrazone molecule. The effect of the chemical structure on the ionization constants was also examined.