• K S Rangappa

      Articles written in Journal of Chemical Sciences

    • Mechanistic investigations of the oxidation of phenethyl alcohols by sodium-N-bromo-benzenesulphonamide in acid medium

      H Ramachandra D S Mahadevappa K S Rangappa

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      The kinetics of oxidation of six substituted phenethyl alcohols (X-C6H4-CH2-CH2-OH where X=-H, -Cl, -Br, -CH3, -OCH3 and -NO2) by sodium-N-bromo-benzenesulphonamide or bromamine-B(BAB) in the presence of HCl at 35°C showed that the rate has first-order dependence on [BAB]0 and [H+] and fractional order on [PEA]0 and [Cl]. Ionic strength variations, addition of reaction product of benzenesulphonamide and variation of dielectric constant of the medium have no effect on the rate. The solvent isotope effectk1(H2O)/k1(D2O)⊇0.82. Proton inventory studies have been made in H2O-D2O mixtures. The Hammett plot is biphasic and the reaction constantρ was −3.2 for electron-releasing substituents and −0.34 for electron-withdrawing groups. The activation parameters ΔH#, ΔS# follow an isokinetic relationship.

    • Oxidation of methylpentoses by sodium N-chlorobenzene sulphonamide in alkaline medium: A kinetic and mechanistic study

      K S Rangappa M P Raghavendra D S Mahadevappa K M L Rai D Channe Gowda

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      Kinetics and mechanism of oxidation of three methylpentoses, namelyD-fucose,L-fucose andL-rhamnose with sodiumN-chlorobenzene-sulphonamide (chloramine-B or CAB) in alkaline medium were studied at 313 K. The rate law, rate =k[CAB][S][HO] was observed. Benzenesulphonamide and chloride ions, the reduced products of the oxidant had no effect on the reaction rate. The rate increased with increase in ionic strength of the medium and the dielectric effect was negative. Proton inventory studies were made in H2O-D2O mixtures. HPLC analysis of products indicated a mixture of aldonic acids in varying proportions. A mechanism involving the furanosidic ringform of methylpentoses which preferentially reacts with CAB in the rate limiting step is suggested.

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