Kinetics and mechanism of oxidation of some para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B(CAB)

The kinetics of oxidation of ethyl S-phenylmercapto acetate and several para-, meta-, and ortho-substituted ethyl S-phenylmercaptoacetates by chloramine-B have been studied in 50% (V/V) aqueous ethanol medium containing phosphate buffer. This oxidation is of first order with respect to substrate and zero order with respect to oxidant. A catalytic effect of mercury is observed and the order with respect to mercury is fractional (0.74). The increase in pH decreases the rate of oxidation and the order with respect to H⁺ is 0.05. In general electron-releasing substituents accelerate the rate while electron-attracting groups retard the rate. A good correlation is found to exist between log k ₁ and Hammett constants. Susceptibility of the reaction to the steric effect of ortho-substituents has been analyzed in the light of application of Taft's steric energy parameters. © John Wiley & Sons, Inc.     

Influence of surface morphology on the oxidation of metal electrodes studied by in-situ grazing incidence x-ray diffractometry

The successful application of in-situ grazing incidence x-ray diffractometry (GIXD) for the investigation of oxidation processes at copper electrodes in pH 12 electrolytes is demonstrated. A penetration/escape depth of about 1 μm could be detected for a smooth polycrystalline copper foil and an x-ray incidence angle of 1.7°. Oxide layers generated at overpotentials less than about 0.5 V in respect to the equilibrium formation potentials of Cu₂O or CuO, respectively, showed a dependence of the crystalline oxide formation on the defect density of the copper substrate. Highly disordered ground or polished specimens exhibited an order of magnitude higher GIXD reflexes from crystalline Cu₂O than electrodeposited copper. Beyond overpotentials of 0.5 V, this epitaxial information for the Cu₂O crystal growth became irrelevant. Further, GIXD turned out to be an appropriate tool to monitor atmospheric corrosion processes under thin humidity films with oxygen access. When oxygen diffusion through the polymer window membrane is allowed, oxygen reduction led to the concurrent formation of a crystalline CuO phase coexisting with amorphous Cu(OH)₂ and Cu₂O, though the potential was kept in the region of Cu₂O. Received: 30 July 1997 / Revised: 28 May 1998 / Accepted: 13 July 1998     

Synthesis of oxalate doped polyaniline and its corrosion protection performance

It is known that dopants present in polyaniline (PANI) play an important role in corrosion protection of mild steel since the dopant ions form a secondary layer with iron. Since oxalate ions form a stable iron oxalate layer on mild steel, a study has been made on the corrosion protection performance of steel by vinyl coating containing oxalate doped PANI in acid and neutral media. Electrochemical impedance spectroscopy (EIS) studies have shown that the oxalate doped PANI is able to protect mild steel in sodium chloride solution since the impedance values are maintained at 10¹⁰ Ω cm² even after 100 days of exposure.     

Kinetics and mechanism of oxidation of S-phenylthioacetic acids by Ce(IV)

The kinetics of oxidation of several S-phenylthioacetic acids by ceric ammonium nitrate (CAN) in presence of perchloric acid has been studied spectrophoto- metrically in 50 %(v/v) aqueous acetic acid. The order with respect to Ce(IV) is one and the order with respect to S-phenylthioacetic acid is found to be 0.8. A linear plot of k_obs⁻¹ vs [substrate]⁻¹ with an intercept on the rate of axis suggests the formation of an equilibrium complex between the reactants prior to the rate determining step. The added acrylonitrile retards the reaction rate considerably suggesting that the oxidation process may involve a free radical mechanism. Electron-releasing substituents generally accelerate the rate, while electron-withdrawing groups retard the rate. A good correlation is found to exist between log k_1.8 and Hammett σ constants.     

Inhibition of iron corrosion in 0.5 M sulphuric acid by metal cations

Corrosion inhibitors are widely used in acid solutions during pickling and descaling. Mostly organic compounds containing N, O, and S groups are employed as inhibitors. In this study, the inhibition performance of metal cations such as Zn²⁺, Mn²⁺ and Ce⁴⁺ ions in the concentration range 1-10 × 10⁻³ M has been found out. The corrosion behaviour of iron in 0.5 M H₂SO₄ in the presence of metal cations is studied using polarization and impedance methods. It is found that the addition of these metal cations inhibits the corrosion markedly. The inhibition effect is in the following order Ce⁴⁺ ? Mn²⁺ > Zn²⁺.     

Efficient iodine catalyzed three components domino reaction for the synthesis of 1-((phenylthio)(phenyl)methyl)pyrrolidin-2-one derivatives possessing anticancer activities

A simple and efficient three components domino reaction of γ-butyrolactam (2-pyrrolidinone), aromatic aldehyde and substituted thiophenol catalyzed by elemental iodine resulted in the formation of 1-((phenylthio)(phenyl)methyl)pyrrolidin-2-one derivatives. The stability of the synthesized analogues was evaluated in stimulated gastric fluid (SGF) and bovine serum albumin (BSA). In vitro anticancer activity was investigated in the low micromolar range and a few analogues were found to possess good activity. This current protocol provides several advantages like shorter reaction time, excellent yield and convenient work-up.     

The ArNe-N2O van der Waals trimer: a high resolution spectroscopic study of its rotational spectrum,structure and dynamics

A new ternary van der Waals complex of the type rare gas-rare gas'-linear molecule, ArNe-N₂O, was investigated using a pulsed molecular beam cavity Fourier transform microwave spectrometer. The rotational spectra of six isotopomers of the trimer were studied in detail. These include Ar²⁰Ne-¹⁴N¹⁴NO, Ar²²Ne-¹⁴N¹⁴NO, Ar²⁰Ne-15N¹⁴NO, Ar²²Ne-¹⁵N¹⁴N0, Ar²⁰Ne-¹⁴N¹⁵NO and Ar²²Ne-¹⁴N¹⁵NO. Nuclear quadrupole hyperfine structures of the rotational transitions that are due to the one or two ¹⁴N nuclei were resolved and analysed. The resulting spectroscopic constants were used to provide structural and dynamical information about the trimer. Based on the quartic centrifugal distortion constants, a harmonic force field analysis was performed to estimate the frequencies of the van der Waals vibrational modes. A perturbation of the electronic charge distribution at the site of the central ¹⁴N nucleus of N²0 upon complex formation was detected and discussed. Differences of structural parameters of the trimer as compared to those of the respective dimer units are indicative of the presence of significant three-body non-additive contributions to the interaction energy.     

Ab-initio calculations of interactions between Cu adatoms on Cu(1 1 0): Sensitivity of strong multi-site interactions to adatom relaxations

We have parameterized the various interactions between Cu adatoms on Cu(1 1 0) using density-functional theory based ab-initio calculations. Our results indicate that in addition to pair interactions, 3-adatom and 4-adatom interactions of significant strengths are present in this system. This further stresses the importance of multi-site interactions in constructing a complete lattice–gas picture. Even though adding these multi-site interactions leads to good convergence in interaction energies, we find that some multi-site interactions are very sensitive to adatom relaxations. This makes the application of a simple lattice–gas picture inadequate for such surfaces. We also parameterize adatom interactions on this surface using the recently developed connector model. The connector model parameterization is as efficient as the parameterization using lattice–gas model. Further, we present diffusion barriers for nearest-neighbor (NN) and next-nearest-neighbor (NNN) hops on this surface.     

A Validated,Stability-Indicating HPTLC Method for Analysis of Doxofylline

JPC – Journal of Planar Chromatography – Modern TLC - A simple, sensitive, selective, precise, and stability-indicating high-performance thin-layer chromatographic method for analysis...