Electro‐oxidation and Determination of Tripelennamine Hydrochloride at MWCNT‐CTAB Modified Glassy Carbon Electrode

An electrochemical method for the determination of tripelennamine hydrochloride (TPA) using cetyltrimethylammoniumbromide‐multiwalled carbon nanotubes modified glassy carbon electrode (MWCNT‐CTAB/GCE) was developed. Because of good electrical conductivity of MWCNT and catalytic behavior of CTAB, new electrode significantly enhances the sensitivity for the detection of TPA. Parameters such as amount of modifier suspension, scan rate, pH of measure solution, heterogeneous rate constant were investigated. The electrode exhibits a linear potential response in the range of 1.0×10^?8 M to 3.0×10^?6 M with a detection limit of 2.38× 10^?9 M. The modified electrode was successfully applied to the determination of TPA in pharmaceutical and real samples.     

Kinetics and Mechanism of the Oxidation of 1,10-Phenanthroline by Diperiodatonickelate(IV)in Aqueous Alkaline Medium

Summary.  The title reaction was investigated in aqueous alkaline medium. A first order dependence on both [diperiodatonickelate(IV)] and [OH⁻] and an apparent fractional order in [1,10-Phenanthroline] was obtained. Addition of the reaction product has no effect on the reaction. The effects of dielectric constant, ionic strength, and temperature on the rate of the reaction were studied. A mechanism based on the experimental results is proposed, and the constants involved in the mechanism were evaluated. A good agreement between the observed and calculated rate constants at varying experimental conditions was obtained. Received May 26, 2000. Accepted (revised) July 27, 2000     

A kinetic and mechanistic study of thallium(I) oxidation by quinolinium dichromate (QDC), a new oxidant

Quinolinium dichromate (QDC) oxidation of Tl^I in aqueous AcOH containing large concentrations of HCl is considerably accelerated both by H⁺ and Cl^– ions as well as by increasing the AcOH concentration in the medium; oxidation is made possible by altering the redox potentials. The reaction is first order in oxidant and in reductant but apparently less than unit order in [Cl^–] and nearly second order in [H⁺]. The active species of QDC and Tl^I are ClCrO₃ ^– and TlCl₂ ^– respectively. A possible mechanism is proposed and verified, and the reaction constants involved have been evaluated.     

Mechanistic and Spectral Studies of the Ruthenium(III) Catalysed Oxidation of Sulfanilic Acid by Alkaline Hexacyanoferrate(III)

Summary. The kinetics of ruthenium(III) catalysed oxidation of sulfanilic acid (p-aminobenzenesulfonic acid) by hexacyanoferrate(III) in alkaline medium at a constant ionic strength of 2.5mol·dm^–3 has been studied spectrophotometrically using a rapid kinetic accessory. The reaction exhibits 2:8 stoichiometry (SNA:HCF(III)). The reaction showed first order kinetics in [hexacyanoferrate(III)] and [ruthenium(III)] and apparent less than unit order in both sulfanilic acid and alkali concentrations. The reaction rate increases with increasing ionic strength but the relative permittivity (_T) of the medium has a negligible effect on the rate of the reaction. Initial addition of reaction products did not affect the rate significantly. A mechanism involving the formation of a complex between sulfanilic acid and hydroxylated species of ruthenium(III) has been proposed. The active species of HCF(III) and ruthenium(III) are understood as [Fe(CN)₆^3–] and [Ru(H₂O)₅OH]²⁺, respectively. The main products were identified by IR, NMR, and mass spectral studies. The reaction constants involved in the different steps of mechanism are calculated. The activation parameters with respect to the slow step of the mechanism are computed and discussed and thermodynamic quantities are also calculated.     

Kinetics of oxidative degradation of pantothenic acid by cerium(IV) in aqueous perchloric acid

The kinetics of oxidation of pantothenic acid (PA), Me₂C(CH₂OH)CH(OH)C(O)NHCH₂CH₂CO₂H, by cerium(IV) in aqueous HClO₄ medium at constant ionic strength, 2.0 mol dm^–3, has been studied spectrophotometrically. The reaction showed first-order kinetics in Ce^IV concentration, an apparent less than unit order dependence in [PA] and an inverse fractional order in [H⁺]. Initial addition of products had no significant effect on the rate of the reaction. A possible mechanism is proposed, and the reaction constants involved in the mechanism have been computed. There is good agreement between the observed and calculated rate constants under different experimental conditions. The activation parameters were calculated with respect to the slow step of the proposed mechanism.     

Osmium(VIII)/palladium(II) catalysis of cerium(IV) oxidation of allyl alcohol in aqueous acid

Summary Catalysis of the Ce^IV-allyl alcohol (AA) reaction in acid solution depends both on the of rate enhancement and product distribution on the catalyst used: Os^VIII results mainly in acrolein, whereas Pd^II gives acrylic acid. The rate laws in the two cases also differ:viz., Equations 1 and 2K₁ is the equilibrium constant of formation of the Os^VIII-allyl alcohol complex and k₁ is the rate constant of its oxidation by Ce^IV; K₂ is the equilibrium constant for the formation of the Ce^IV-Pd^II-allyl alcohol complex and k₂ is its rate constant of decomposition. Rate = K₁k₁[Ce^IV][AA][Os^VIII]/(1+K₁[AA]) (1) Rate = K₁k₁[Ce^IV][Pd^II]/(1+K₂[Ce^IV]) (2)While Os^VIII is effective in H₂SO₄ solution, aqueous HClO₄ is needed for Pd^II. Both reactions proceed through formation of catalyst-allyl alcohol complexes with participation of free radicals. The details of these observations are discussed.     

Thermodynamic quantities for the oxidation of ranitidine by diperiodatocuprate(III) in aqueous alkaline medium

The kinetics of oxidation of the anti-ulcer drug, ranitidine hydrochloride (RNH) by diperiodatocuprate(III) (DPC) in alkaline medium was studied spectrophotometrically. The reaction exhibits 1:2 stoichiometry (ranitidine:DPC). The reaction is of first order in [DPC] and has less than unit order in [RNH] and negative fractional order in [alkali]. The involvement of free radicals was observed in the reaction. The oxidation has been found to proceed via a DPC-ranitidine complex, which decomposes slowly in a rate-determining step followed by other fast steps to give the products, which were identified as ranitidine sulfoxide by spot test and spectroscopic studies. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Osmium(VIII) oxidation of arsenic(III) in aqueous sulphuric acid

The oxidation of As^III by Os^VIII or Os^VI in aqueous H₂SO₄ follows the rate law: