Formation of Peracetic Acid upon Aging of Perborate in Acetic Acid. Kinetics of the Oxidation of S-Phenylmercaptoacetic Acids

 Upon aging, perborate in glacial acetic acid generates peracetic acid and thus oxidizes S-phenylmercaptoacetic acid rapidly. Perborate dissolved in ethylene glycol, however, does not show the aging effect, and the corresponding oxidation proceeds smoothly. The oxidation is of second order and not acid catalyzed. Boric acid and borate do not influence the oxidation. In the smooth oxidation, is the reactive species. The oxidation of some para-substituted S-phenylmercaptoacetic acids conforms to the Exner relationship, indicating operation of a common mechanism. Also, the oxidation obeys the Hammett equation with a negative reaction constant. However, the oxidation of p-nitro-S-phenylmercaptoacetic acid follows a different kinetic pathway.     

Thickness dependence of the phase transition temperature in Ag2Te thin films

Electrical resistance measurements of Ag₂Te thin films of different thicknesses, vacuum deposited on clean glass substrates held at room temperature in a vacuum of 5 × 10^?5 Torr, have been carried out from about 300 to 450 K. A semiconducting-to-metallic-phase transition, which takes place during heating, is indicated by a sharp change in the slope of the resistance-vs-temperature curve. For films of different thicknesses the phase transition is found to occur at different temperatures. The size-dependent phase transition is explained by taking into account the varying surface and intergrain surface (interface) energy contributions to the total energy of the stable phase as a function of thickness and the difference in specific surface and integrain surface energies of the two phases. An order of magnitude of the difference in the function of specific surface and interfacial energies of the two phases is also made.     

Synthesis of semifluorinated block copolymers by atom transfer radical polymerization

Two sets of styrene‐based semifluorinated block copolymers, one with a perfluoroether pendant group and another with a perfluoroalkyl group, were synthesized by atom transfer radical polymerization. Microphase separation of the block copolymers was established by small‐angle X‐ray scattering and differential scanning calorimetry (DSC). DSC measurements also showed that the perfluoroether‐based polymer had a low glass‐transition temperature (?44 °C). Contact‐angle measurements indicated that the semifluorinated block copolymers had low surface energies (ca. 13 mJ/m²). These materials hold promise as low‐surface‐energy additives or surfactants for supercritical CO₂ applications. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 853–861, 2004     

Acetyl- and O-alkyl- derivatives of β-mangostin from Garcinia mangostana and their anti-inflammatory activities

Pure β-mangostin (1) was isolated from the stem bark of Garcinia mangostana L. One monoacetate (2) and five O-alkylated β-mangostin derivatives (3–7) were synthesised from β-mangostin. The structures of these compounds were elucidated and determined using spectroscopic techniques such as 1D NMR and MS. The cytotoxicities and anti-inflammatory activities of these five compounds against RAW cell 264.7 were tested. The structural-activity relationship studies indicated that β-mangostin showed a significant activity against the LPS-induced RAW cell 264.7, while the acetyl- as well as the O-alkyl- β-mangostin derivatives did not give good activity. Naturally occurring β-mangostin demonstrated comparatively better anti-inflammatory activity than its synthetic counterparts.     

Inhibition of photooxidation of iron(II) by some semiconductors

The photooxidation of iron(II) in aqueous ethanol is less in presence of TiO₂, ZrO₂, V₂O₅, CeO₂, ZnO, Fe₂O₃, CdO, PbO, SnO₂, CdS, ZnS and Al₂O₃ than in their absence. The photogeneration of iron(III) was studied at different [Fe²⁺], amounts of semiconductors suspended, airflow rates, light intensities, solvent compositions and wavelengths of illumination. The catalysts show sustainable photocatalytic activity. The metal oxides and sulfides reduce iron(III), formed by the homogeneous photooxidation of iron(II). TiO₂, CeO₂, ZnO, Fe₂O₃, CdO, PbO, SnO₂ and Al₂O₃ effectively suppress the photooxidation of iron(II); ZrO₂, ZnS and CdS also suppress but not completely. At high catalyst-loading V₂O₅ catalyses the photooxidation of iron(II). The mechanisms of the photocatalytic processes are discussed.     

Molybdenum(VI) catalysis of perborate or hydrogen peroxide oxidation of iodide ion

Summary Perborate in aqueous solution generates H₂O₂; in its presence the molybdenum(VI) catalysed oxidation of iodide ion is first order with respect to the oxidant and catalyst, and is independent of [I^–] and [H⁺]. Kinetic studies point to peroxymolybdenum(VI) species as the oxidizing species.     

Spin-Dependent Electron Tunneling in ZnSe/Zn_(1-x)Mn_xSe Heterostructures with Double δ-Potentials

Using the matrix method, spin-dependent tunneling properties such as barrier transparency, the degree of resonance polarization, and tunneling lifetime of electrons are examined in the non-magnetic/diluted magnetic semiconductor heterostructure. The effects of the double δ-potential and the magnetic field are discussed on the transport properties of the electrons. The introduction of double δ-potential shifts the resonance peak of polarization to the higher energy value. Both height and position of the δ-potential influence the degree of resonance polarization in the considered heterostructure. The increasing magnetic field enhances the spin-polarization.     

Vanadia-catalyzed solar photooxidation of aniline

Vanadia photocatalyzes the oxidation of aniline to azobenzene in ethanol. The reaction was studied using natural sunlight and UV irradiation (365 nm) as a function of [aniline], catalyst loading, airflow rate, solvent composition, etc. The photocatalyst exhibits sustainable catalytic activity. The product formation is greater with illumination at 254 nm than at 365 nm. Electron donors such as triphenylphosphine, diphenylamine, and hydroquinone enhance the photocatalysis. The singlet oxygen quencher azide ion fails to inhibit the catalysis. The photocatalysis takes place in both protic and aprotic solvents. The mechanism of photocatalysis is discussed and the product formation analyzed using a kinetic model.     

Kinetics of perborate oxidation of quinol

The perborate oxidation of quinol in aqueous acetic acid is first order with respect to perborate, zero order with respect to quinol, and first order with respect to H⁺. The oxidation is faster than H₂O₂ oxidation. Breakdown of protonated perboric acid is suggested as the rate-limiting step.

---

, H⁺. . , , , .

     

Ethylene Polymerization Studies with an MAO Synthesized by a Non‐Hydrolytic Synthetic Route

A facile nonaqueous synthetic route to methylaluminoxane (MAO) by heating a mixture of benzophenone and trimethylaluminium (TMA) is described. The MAO prepared such reveals to be an efficient activator of metallocenes and late transition metal complexes for ethylene polymerization. The [TMA]/[benzophenone] ratio used for the preparation of MAO is shown to have a dramatic effect on the catalytic activity as well as the molecular weight distribution of the resulting polyethylenes.