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      Volume 131, Issue 1

      January 2019

    • General editorial on publication ethics

      S Natarajan

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    • Table of Contents

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    • Effect of phenyl moiety on the formation of radicals and radical cations of thioamides in n-butyl chloride: a pulse radiolysis study

      G R DEY

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      The formation of radical cations and radicals of thioamides (R)(NH2)CS, where R represents CH3 in thioacetamide (TA) and C6H5 in thiobenzamide (TBA) in n-butyl chloride has been studied using pulse radiolysis technique. The radical cations of TA and TBA are observed in n-butyl chloride, and on their subsequentdeprotonation, respective radicals are generated. In this study on thioamide solutions in n-butyl chloride, the transient species formed at 1.2 μs after the electron pulse exhibiting absorption maxima in 400 nm region are attributed to their radical cations. In the presence of 0.1 M ethanol (C2H5OH), a radical cation scavenger, the absorbance values at corresponding peaks are reduced substantially, revealing the formation of their respective radical cations. Moreover, at a later time, the generation of radical species takes place through deprotonation of radical cations and also through direct reactions during electron pulse irradiation. The mechanisms for the formation of radical cations and radicals of these two thioamides under pulse radiolysis have been revisited inbutyl chloride medium wherein the charge transfer reactions are more prominent. Results of quantum chemical calculation support the mechanistic explanation and provide information on the reactivity of parent molecules, and the charge distribution on radical cations and radicals species of thioamides.

    • Nano-sized Silicalite-1: novel route of synthesis, metal impregnation and its application in selective oxidation of toluene


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      The novel route of synthesis and catalytic performance of nano-sized Silicalite-1 are presented. Nano-sized Silicalite-1 was initially obtained from a clear solution using sodium silicate as silica source and tetrapropylamonium hydroxide as a template. The effects of silica source on the product yield, purity, crystallization rate and crystallinity were investigated. Effect of seeds in the synthesis was also studied. Nucleation time decreased to6hfrom24husing 4% seed, with yield and crystallinity 70% and 90%, respectively. The catalyst was characterized by XRD, FE-SEM, TG, FITR and N2 adsorption–desorption techniques. Transition metals like Fe, Cu and Mo were impregnated by wet impregnation method. Cu-impregnated nanosized Silicalite-1 was found to be highly active for the oxidation of toluene with H2O2.

    • Stabilizing influence of silicon substitution on dibenzene and its isomers


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      The stabilizing effect of silicon substitution on sixteen different isomers of dibenzene (C12H12) has been investigated using second-order Møller-Plesset perturbation (MP2) theory and the cc-pVDZ basis set. While the most stable isomers of Si12H12 have only Si–Si bonds, some of the stable isomers have isolated Si=Si bonds and may be amenable to experimental observation. Vibrational frequencies were calculated for the optimized geometries at the Hartree-Fock level of theory to ensure that they corresponded to true minima on the potential energy landscape. Natural bonding orbital analysis confirms the existence of isolated Si= Si double bonds in some of the isomers. Dipole moment values were determined to check for the presence of centre of symmetry in certain geometries.

    • Hybrid composite of CuO with g-C3N4 as a photoactive catalyst: an efficient approach for the oxidation of alcohols


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      An eco-friendly method for the oxidative transformation of alcohols to their corresponding carbonyl compounds by using g-C3N4@CuO as a photoactive heterogeneous catalyst has been developed. The catalyst was characterized by SEM-EDX, TEM, BET surface area measurements, powder XRD, FTIR, photoluminescence and UV-Vis spectroscopy. It was found to be very effective for the conversion of both primary and secondary alcohols into aldehydes and ketones with excellent yields using tert-butyl hydrogen peroxide (TBHP) as oxidant at room temperature in the presence of visible light in aqueous medium. The catalyst can be separated from the reaction mixture by simple centrifugation and reused up to five cycles without significant loss in activity.

    • Kinetics of singlet oxygen sensing using 9-substituted anthracene derivatives


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      Singlet oxygen (1O2), the lowest excited-state of molecular oxygen receives great attention in basic research and clinical and industrial settings. Despite several spectroscopic methods available for 1O2 sensing, fluorescence sensing receives great attention, for which many fluorogenic sensors based on substituted anthracene are reported. Nonetheless, the roles of substituents on the sensing efficiency, in terms of detection time, remain largely unknown. In this work, we examine the 1O2 sensing efficiency of a fluorescence sensor based on a coumarin–anthracene conjugate, which is an electron donor-acceptor dyad, and compare the efficiency with that of 9-methylanthracene. Here,1O2 is generated using the standard photosensitizer Rose Bengal, which is followed by estimation of the rate of reaction of 1O2 to the sensor and 9-methylanthracene. The second order reaction rate of the sensor is an order of magnitude less than that of 9-methylanthracene. The lower reactivity of the sensor to 1O2 suggests that the roles of substituents, such as electronic interactions, steric interactions and the reactivity of precursor complexes, on sensing efficiency should be carefully considered during construction of fluorogenic molecular sensors.

    • Uncatalyzed gas phase aziridination of alkenes by organic azides. Part 2. Whole azide reaction with alkene


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      The B3LYP/6-31G(d,p) DFT method was used to study alkene aziridination by azides through uncatalyzed thermal gas phase routes which involve the whole azide reactant molecule without dissociation.Two mechanisms were studied – Route I involving concerted azide addition to alkene with the elimination of N2, and the multi-step Route II involving 1,3-dipolar cycloaddition between azide and alkene. Three azides RN3 (R = H, Me, Ac) are reacted with alkene substrates forming aziridine products. The concerted addition–elimination step of Route I is exothermic with an appreciable barrier, where the facility order Ac > Me > Hpoints to electrophilicity of the azide reactant. The initial 1,3-dipolar cycloaddition step of Route II involves smaller barriers than Route I, while thermal decomposition of the triazoline intermediate to aziridine and N2 involves two more steps with an N-alkylimine intermediate. The very high barrier for N-alkylimine cyclization to aziridine could be offset by the high exothermicity of the previous step. Geometries of the transition states for various reaction steps studied here are described as ‘early’ or ‘late’ in good accordance with the Hammondpostulate. Two other mechanisms (Routes A and B) studied earlier (involving discrete nitrene intermediates) are compared with Routes I and II, where Route II involving 1,3-dipolar cycloaddition is predicted to be energeticallythe most favored of all the four mechanisms for thermal gas-phase aziridination of alkenes by azides.

    • Synthesis and structure of Anderson cluster based organic–inorganic hybrid solid, [{ Cu(2- pzc)(H2O)2}2 {H7AlMo6O24}] · 17H2O and its dye adsorption properties


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      An inorganic–organic hybrid compound, namely [{Cu(2-pzc)(H2O)2}2{H7AlMo6O24}]·17H2O was synthesized based on Anderson–Evans cluster by the normal stirring process at room temperature. Its structure consists of metal coordination polymer covalently linked with Anderson–Evans cluster forming a2D-sheet with void space containing water chains as determined by Single-Crystal X-ray Diffraction technique. This material owing to its void space of approx. 13 Å was utilized for adsorption of organic dyes like MethyleneBlue (MB), Basic Violet 1 (BV1) and shows ultra-high uptake (more than 90%) within 5 min.

    • Cu-doped zeolitic imidazolate framework catalysed highly selective conversion of alkynes to β-keto and vinyl sulfones using sodium sulfinates


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      Cu2+ -doped zeolitic imidazolate framework-8 (ZIF-8)-catalyzed one-pot procedure to synthesize β-keto and vinyl sulfones by the direct oxysulfonylation and hydrosulfonylation of alkynes via radical reaction under mild conditions has been described. The advantages of this protocol included broad substrate scope and excellent β-keto and E-stereoselectivity. The Cu/ZIF-8 catalyst not only exhibited excellent performance but also had a great stability in the reaction, successfully allowing its reuse up to five cycles. This efficient Cu/ZIF-8heterogeneous catalyst is explored for the first time to generate β-keto and vinyl sulfones.

    • Editorial

      S Natarajan

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