Mechanistic Study of Oxidation of Palladium(II) by Cerium(IV) in Aqueous Acid

The kinetics of oxidation of Pd^II by Ce^IV have been studied spectrophotometrically in HClO₄ media at 40 °C. The reaction is first order each in [Ce^IV] and [Pd^II] at constant [H⁺]. Increasing [H⁺] accelerates the reaction rate with fractional order in [H⁺]. The initially added products, palladium(IV) and cerium(III) do not have any significant effect on the reaction rate. At constant acidity, increasing the added chloride concentration enhances the rate of reaction. H₃Ce(SO₄)₄⁻ and PdCl₄²⁻ are the active species of oxidant and reductant respectively. The possible mechanisms are proposed and the reaction constants involved have been determined.     

Mechanistic study on the oxidation of l-phenylalanine by copper(III) in aqueous alkaline medium: a kinetic approach

Abstract  

Oxidation of the amino acid l-phenylalanine by diperiodatocuprate(III) in alkaline medium at constant ionic strength of 0.25 mol dm⁻³ was studied spectrophotometrically at different temperatures (298–313 K). The reaction between diperiodatocuprate(III) and l-phenylalanine in alkaline medium exhibits 1:2 stoichiometry. Intervention of free radicals was observed in the reaction. Based on the observed orders and experimental evidence, a mechanism involving monoperiodatocuprate(III) as the reactive oxidant species has been proposed, proceeding through the formation of a complex and reaction of the intermediate of l-phenylalanine with monoperiodatocuprate(III) to give the products. The products were identified by spot test, infrared (IR), and gas chromatography-mass spectrometry (GC-MS). The reaction constants involved in the different steps of the mechanism were calculated. The activation parameters with respect to the slow step of the mechanism were computed and are discussed. The thermodynamic quantities were determined for different equilibrium steps. The isokinetic temperature was also calculated and found to be 331 K.     

Electrochemical Behavior of Graphene‐Based Sensors on the Redox Mechanism of Aspirin

The electrochemical behavior of aspirin at a graphene modified glassy carbon electrode has been investigated using cyclic and differential pulse voltammetric techniques. The dependence of the current on pH, concentration and scan rate was investigated to optimize the experimental conditions for determination of aspirin. A plausible oxidation mechanism was proposed. Under the optimum conditions, the oxidation peak current was linearly proportional to the concentration of aspirin in the range from 1.00×10^?6 to 2.00×10^?4 M with a detection limit of 20.2 nM. The proposed method was successfully applied to aspirin determination in pharmaceutical and real samples.     

Ruthenium(III) catalysed and uncatalysed oxidative mechanisms of methylxanthine drug theophylline by copper(III) periodate complex in alkali media: a comparative approach

The kinetics of oxidation of methylxanthine drug, theophylline (TP), by diperiodatocuprate(III) (DPC) has been investigated in the absence and presence of ruthenium(III) (Ru(III)) as homogeneous catalyst in alkaline medium at a constant ionic strength of 0.21 mol dm^?3 spectrophotometrically. The reaction exhibits 1:4 stoichiometry ([TP] : [DPC]) in both the cases. The order of the reaction with respect to [DPC] was unity, while the order with respect to [TP] was less than unity over the concentration range studied in both the cases. The rate was increased with an increase in [OH^?] and decreased with an increase in [IO₄^?]. The order with respect to [Ru(III)] was unity. The ionic strength and dielectic constant of the medium did not affect the rate significantly. The main product 1‐methyl‐(3‐N‐formyl)‐2,4‐purinodione was identified by spot tests, Fourier transform infrared spectroscopy and liquid chromatography–mass spectrometry spectral studies. Based on the experimental results, the possible mechanisms were proposed. The reaction constants involved in the different steps of the mechanisms were evaluated. The catalytic constant (K_c) was also calculated for Ru(III) catalysis at different temperatures. The activation parameters with respect to the catalyst and slow step of the mechanisms were computed, and thermodynamic quantities were determined. Kinetic studies suggest that the active species of DPC and Ru(III) are found to be [Cu(H₂IO₆)(H₂O)₂] and [Ru(H₂O)₅OH]²⁺, respectively. Copyright © 2015 John Wiley & Sons, Ltd.     

Voltammetric Determination of Chlorpheniramine Maleate Based on the Enhancement Effect of Sodium‐dodecyl Sulfate at Carbon Paste Electrode

The voltammetric oxidation and determination of chlorpheniramine maleate (CPM) was studied at a carbon paste electrode (CPE) in the presence of sodium‐dodecyl sulfate (SDS) by cyclic and differential pulse voltammetry. The results indicated that the voltammetric response of chlorpheniramine maleate was markedly increased in the low concentration of SDS, suggesting that SDS exhibits observable enhancement effect to the determination of chlorpheniramine maleate. Under the optimal conditions the peak current was proportional to chlorpheniramine maleate concentration in the range of 8.0×10⁻⁶ to 1.0×10⁻⁴ M with detection limit of 1.7×10⁻⁶ M by differential pulse voltammetry. The proposed method was successfully applied to the determination of chlorpheniramine in pharmaceutical and urine samples.     

β‐Diketiminate Stabilized Magnesium Hydroxide,Heterobimetallic, and Halide Complexes: Synthesis and X‐ray Structural Studies

The controlled hydrolysis of heteroleptic magnesium amide, LMgN(SiMe₃)₂ (L = CH[C(Me)N(2,6‐iPr₂C₆H₃)]₂) with water afforded the corresponding hydroxide [LMg(OH)·THF]₂ as air and moisture sensitive compound. The presence of a sterically bulky β‐diketiminate ligand prevents the self‐condensation reaction of this hydroxide complex. Single crystal X‐ray analysis shows that the hydroxide is dimeric in the solid state. Reaction of the magnesium amide or LMg(Me)·OEt₂ with LAlMe(OH) generates the heterobimetallic species containing the Mg–O–Al moiety. Additionally, the reaction of methylmagnesiumchloride with the free ligand leads to complex L′MgCl (L′ = CH[Et₂NCH₂CH₂N(CMe)]₂). As revealed by the crystal structure, L′MgCl is a solvent free monomeric magnesium chloride complex that is analogues to the Grignard reagent.     

Kinetics and mechanism of uncatalysed and ruthenium(III)-catalysed oxidation of <Emphasis Type="SmallCaps">d</Emphasis>-panthenol by alkaline permanganate

The oxidation of d-panthenol by MnO₄ ⁻ was studied in the absence and in the presence of ruthenium(III) catalyst in alkaline medium at 298 K and at constant ionic strength of 0.50 mol dm⁻³ by spectrophotometry. The stoichiometry in both the cases was [panthenol]: [MnO₄ ⁻] = 1:4. The oxidation products were identified by IR and GC–MS. The reaction was first-order with respect to both MnO₄ ⁻ and ruthenium(III), while the orders with respect to both panthenol and alkali varied from first order to zero order as the concentrations increased. The effects of added products, ionic strength and dielectric constant were studied. The reaction constants, activation parameters and thermodynamic quantities were calculated for both the uncatalysed and catalysed reactions.     

Synthesis of Novel 4‐Substituted Coumarins,Docking Studies,and DHODH Inhibitory Activity

Coumarins are the important class of naturally occurring heterocyclic compounds. Activities like antioxidant, antibacterial, anti‐inflammatory, and anticancer have been reported for coumarin derivatives. Present work details the synthesis of substituted coumarin‐4‐pyrrolones as well as coumarin‐4‐acetyl amino acids and their DHODH inhibitory activity, which is a dual target for malaria and cancer. Coumarin‐4‐acetic acids ( 2a – c ) were coupled with different methyl esters of α‐amino acids ( 3 ) giving rise to corresponding coumarin‐4‐acetyl amino acid methyl esters ( 4a – o ), which on hydrolysis under basic condition underwent cyclization forming substituted dihydropyrrole‐2‐ones ( 5a – i ), dihydroindolizine‐3‐ones ( 5j – l ), and dihydropyrrolizin‐3‐one ( 5m – o ). Acidic hydrolysis of the compounds ( 4a – o ) yielded corresponding coumarin‐4‐acetyl amino acids ( 6a – f ). The docking study was performed with the protein 4IGH (obtained from PDB) using Surflex–Dock module. The newly synthesized compounds were tested for DHODH inhibitory activity using Brequinar as the standard. Compound 6b showed remarkable inhibition compared with the standard, and the other compounds with terminal COOH showed moderate inhibition.     

Kinetic and Mechanistic Study of the Oxidative Deamination and Decarboxylation of L-Valine by Alkaline Permanganate

Summary.  The kinetics of the oxidation of L-valine, (L-Val) by permanganate in aqueous alkaline medium at a constant ionic strength of 0.50 molċdm⁻³ was studied spectrophotometrically. The reaction is of first order in [permanganate ion] and of fractional order in both [L-Val] and [alkali]. Addition of products has no significant effect on the reaction rate. However, increasing ionic strength and decreasing dielectric constant of the medium increase the rate. The oxidation process in alkaline medium has been shown to proceed via two paths, one involving the interaction of L-valine with permanganate ion in a slow step to yield the products, and the other path the interaction of alkali with permanganate ion to give manganate. Some reaction constants involved in the mechanism were determined; calculated and observed rate constants agree excellently. The activation parameters were computed with respect to the slow step of the mechanism. Received December 30, 1999. Accepted (revised) March 6, 2000