• N Venkatasubramanian

      Articles written in Journal of Chemical Sciences

    • Kinetics and mechanism of oxidation of aromatic secondary alcohols by Tl(III) acetate

      V S Srinivasan N Venkatasubramanian

      More Details Abstract Fulltext PDF

      The kinetics of oxidation of ortho, meta and para substituted α-phenyl ethyl alcohols by Tl(III) shows that these reactions are susceptible to electronic influences. The negative ρ(−2·11) points to the formation of electron deficient carbon atom. The oxidation of benzhydrol exhibits a kinetic isotope effect 6·4. The Tl(III) oxidation of l-phenyl propyl alcohol, 4-chloro benzhydrol, 1-naphthyl methyl carbinol, 2-naphthyl methyl carbinol and fluorenol has been studied. A mechanism involving the loss of hydrogen atom as a hydride ion is proposed. The thermodynamic parameters of the reaction are also presented.

    • Kinetics of Tl(III) oxidation of hydroxylamine hydrochloride in aqueous sulphuric acid

      Vangalur S Srinivasan N Venkatasubramanian

      More Details Abstract Fulltext PDF

      The kinetics of Tl(III) oxidation of hydroxylamine hydrochloride in 1·0 M H2SO4 at a fixed chloride concentration has been investigated to make a formal comparison of the observed rate with that of hydrazine sulphate. The reaction exhibits total second order kinetics—first order in each reactant. The rate of the reaction depends inversely on the first power of [H+] and [Cl] suggesting the possible reactive species as TlOH2+. To account for the stoichiometry of the reaction [Tl(III)]: [H2NOH·HCl)=1·5∶1 and the products of the reaction, HNO2 and N2O, two reaction schemes have been proposed.

    • Kinetics of chlorination of ketones by 1-chlorobenzotriazole

      P S Jayaraman S Sundaram N Venkatasubramanian

      More Details Abstract Fulltext PDF

      The kinetics of chlorination of aliphatic, aralkyl and alicyclic ketones by 1-chlorobenzotriazole (cbt) have been studied in aqueous acetic acid media. In the presence of a mineral acid (HClO4), the order of the reaction with respect to [ketone] is one and that with respect to [cbt] is zero, suggesting the enolisation of ketone as the slow step, followed by a fast attack of the halogenating species. A primary kinetic isotope effect (kH/kD=6·6) is also noticed, when acetone and acetone-d6 are used as the substrates. Initial addition of chloride ion leads to a first order dependence on [cbt] and a fractional order (0·6) on [acetone]. Thermodynamic parameters for the reaction have also been reported. A negative Hammett reaction constant (ρ=−0·57) has been obtained for the halogenation of substituted acetophenones bycbt.

    • Tl(III) acetate oxidation of cyclanols and bicyclo(2,2,1) heptan-2-ols

      Vangalur S Srinivasan N Venkatasubramanian

      More Details Abstract Fulltext PDF

      Tl(III) acetate oxidation of cyclohexanol, cyclopentanol, cycloheptanol,trans-2-chlorocyclohexanol,cis-4-t-butylcyclohexanol,trans-4-t-butylcyclohexanol, borneol, isoborneol, exo (β) norborneol and endo (α) norborneol has been studied in the presence of 0·90 M H2SO4. The observed reactivity pattern among the cyclanols is cyclopentanol < cyclohexanol > cycloheptanol < cyclooctanol which is the same as the one noted in V(V) oxidation of the substrates under similar conditions—an order contrary to the I-strain concept. In both cases Mn(II) catalysis and acrylonitrile polymerisation have been observed in cyclohexanol oxidation alone. The kinetic isotope effect in the Tl(III) oxidation of cyclohexanol is 2.82 as against a value of 6·4 obtained for Tl (III) oxidation of benzhydrol. The kinetic observations are explained on the basis of a radical mechanism operating in the case of cyclohexanol, as it is a strainless ring system, with the intermediacy of Tl (II).Trans-2-chloro andtrans-2-phenyl groups, due-I effect, retard the rate of the reaction.Cis-4-t-butylcyclohexanol reacts faster than the trans compound due to relief of strain in the transition state. The reactivity pattern among the bicyclo (2,2,1) heptan-2-ols is, isoborneol > borneol > exo (β)-norborneol > cyclopentanol >endo-(α)-norborneol. This is consistent with the relief of strain in the transition state due to the hybridisation change from sp3 to sp2 and lessening of torsional interaction. This can also be due to the formation of less-strained products.

    • Oxidation of phenylmethylcarbinols by bromamine-T

      S Gunasekaran N Venkatasubramanian

      More Details Abstract Fulltext PDF

      The kinetics of oxidation of phenylmethylcarbinol and substituted phenylmethylcarbinols by bromanine-T have been studied in aqueous acetic acid medium in the presence of sulphuric acid. The effects of added toluene-p-sulphonamide and sodium bromide have been investigated. The solvent effect and temperatures effect on these reactions have also been studied. The Hammett correlation gives a π value of-2.5. A suitable mechanism consistent with the experimental observations has been suggested.

    • Alkaline hydrolysis of arylesters of diphenylphosphorodiamidates—evidence consistent with an elimination—addition mechanism

      P Krishnan S Sundaram N Venkatasubramanian

      More Details Abstract Fulltext PDF

      The alkaline hydrolysis of a series of aryl phosphorodiamidates has been studied in aqueous ethanol and aqueous DMSO mixtures. Although the reactions do not show any saturation kinetics with respect to the hydroxide ion, the low solvent isotope effect, the highly negative Bronsted β value, the large Hammett ρ for the leaving aryloxy group and the decrease in rate with increase in the proportion of DMSO in the solvent mixtures indicate that the hydrolysis proceeds by an elimination-addition pathway. Comparison of rate data with other hydrolytic E1CB reactions show that the title reaction belongs to the (E1CB)R category.

  • Journal of Chemical Sciences | News

© 2021-2022 Indian Academy of Sciences, Bengaluru.