Brønsted Acid Catalysis in the Oxidation of Purine Based Alkaloids by Mn(VII) in Aqueous Acetonitrile and Sodium Fluoride Medium: A Kinetic Approach

Brønsted acid (HClO4, H2SO4) catalyzed Mn(VII) oxidation of purine alkaloids such as caffeine, theophylline and theobromine in aqueous acetonitrile and sodium fluoride medium revealed first order kinetics in both [(Mn(VII)] and [Alkaloid] at constant acidity and temperature. Sodium fluoride was added to the reaction mixture in order to avoid/suppress auto catalytic reaction due to the generation of Mn(III) and Mn(IV) species during the course of Mn(VII) oxidations in acidic solutions. An increase in the Brønsted acids (HClO4, H2SO4) concentration accelerated the rate of oxidation. Rate enhancements observed here in are analyzed by Zucker-Hammett, Bunnett and Bunnett-Olsen criteria of acidity functions. On the basis of observed Bunnett-Olsen criteria of acidity functions, the most plausible mechanism has been proposed with the involvement of water molecule in the slow step (as proton transferring agent).

Anion Exchange Behaviour of Zr, Hf, Nb, Ta and Pa as Homologues of Rf and Db in Fluoride Medium

Studies of the chemical property of transactinide elements are very difficult due to their short half-lives and extremely small production yields. However it is still possible to obtain considerable information about their chemical properties, such as the most stable oxidation states in aqueous solution, complexing ability, etc., comparing their behaviour with their lighter homologous in the periodic table. In order to obtain a better knowledge of the behavior of rutherfordium, Rf (element 104), dubnium, Db (element 105) in HF medium, the sorption properties of Zr, Hf, Nb, Ta and Pa, homologues of Rf and Db, were studied in NH4F/HClO4 medium in this work. Stability constants of the fluoride complexes of these elements were experimentally obtained from Kd obtained at different F- and H+ concentrations. The anionic complexes: [Zr(Hf)F5]-, [Zr(Hf)F6]2-, [Zr(Hf)F7]3-, [Ta(Pa)F6]-, [Ta(Pa)F7]2-, [Ta(Pa)F8]3-, [NbOF4]- and [NbOF5]2- are present as predominant species in the HF range over investigation.

Synthesis and characterization of Cr-ZSM-5 composite in fluoride medium and its performance in oxidation reaction of 2-mercaptobenzotiazole

Purpose The purpose of this paper is to synthesize Cr-ZSM-5 using hydrothermal synthesis in acidic fluoride medium and the investigation of its catalytic performance in heterogeneous oxidation of 2-mercaptobenzothiazole in the presence of H2O2. Design/methodology/approach The framework was characterized by chemical composition, FT-IR, UV-visible spectroscopy, N2 adsorption (BET), and diffraction x-ray (DRX). FT-IR spectroscopy shows the characteristic band of Si-O-Cr linkage around 960-990 cm−1 and bands around 688-690 and 627 cm−1, indicating the presence of extraframework chromium oxide. UV spectra show a shoulder around 244-257 and bands around 360-380 nm, assigning the tetrahedral coordinated environment in (O2−=Cr6+) − (Cr5+-O−1), charge transfer transition state (CT) of isolated Cr (VI) inside the structure of Cr-ZSM-5. Findings The catalytic degradation of 2-mercaptobenzothiazole by H2O2 heterogenous oxidation using catalyst Cr-ZSM-5 showed the formation of bis (benzothiazoyl) disulfide with 95 percent yield. Originality/value The application of this process in the environment (catalysis, adsorption, and degradation of organic compounds).

A non-chemically selective top-down approach towards the preparation of hierarchical TS-1 zeolites with improved oxidative desulfurization catalytic performance

Hierarchical TS-1 zeolites with enhanced performance in oxidative desulfurization of bulky molecules are prepared by treatment in fluoride medium.