• Seema Kothari

      Articles written in Journal of Chemical Sciences

    • Kinetic study of oxidation of some thioacids bybis(2,2′-bipyridyl) copper(II) permanganate

      Seema Kothari

      More Details Abstract Fulltext PDF

      Oxidation of thioglycollic, thiolactic and thiomalic acids, to the corresponding disulphide dimers, bybis(2,2′-bipyridyl) copper(II) permanganate (BBCP) is first order with respect to BBCP and exhibits Michaelis-Menten type kinetics with respect to the thioacid. The reaction is catalysed by hydrogen ions. The rate decreases with an increase in the amount of acetic acid in the solvent. There is no effect of added bipyridine and acrylonitrile. A mechanism involving formation of a sulphenium cation in the rate-determining step has been proposed.

    • Kinetic study of the oxidation of aliphatic aldehydes bybis(2,2′-bipyridyl) copper(II) permanganate

      Seema Kothari Vinita Sharma Pradeep K Sharma Kalyan K Banerji

      More Details Abstract Fulltext PDF

      Kinetics of oxidation of aliphatic aldehydes, to the corresponding carboxylic acids, by bis(2,2′-bipyridyl)copper(II) permanganate (BBCP) has been studied. The reaction is first order with respect toBBCP. Michaelis-Menten type kinetics were observed with respect to the aldehyde. The formation constants for the aldehyde-BBCP complexes and the rates of their decomposition, at different temperatures, have been evaluated. Thermodynamic parameters for the complex formation and the activation parameters for their decomposition have also been determined. The reaction is catalysed by hydrogen ions; the acid-dependence being of the form:kobs = a +b [H+]. The oxidation of MeCDO exhibited a substantial kinetic isotope effect (kH/kD = 4.33 at 303 K). The role of aldehyde hydrate in the oxidation process has been discussed. A mechanism involving formation of permanganate ester and its slow decomposition has been proposed.

    • Kinetics and mechanism of the oxidation of primary aliphatic alcohols by pyridinium bromochromate

      P Aparna Seema Kothari Kalyan K Banerji

      More Details Abstract Fulltext PDF

      Oxidation of nine primary aliphatic alcohols by pyridinium bromochromate (PBC) leads to the formation of corresponding aldehydes. The reaction is of overall second order, and of first order with respect to the each reactant. The reaction is promoted by hydrogen ions; the hydrogen-ion dependence has the formkobs=c+d[H+]. The oxidation of [1, 1-2H2] ethanol (MeCD2OH) exhibited a substantial primary kinetic isotope effect. The reaction was studied in nineteen organic solvents and the effect of solvent was analysed using Taft's and Swein's multiparametric equations. The oxidation is susceptible to both the polar and steric effects of the substituents. A suitable mechanism has been proposed.

    • Kinetics and mechanism of the oxidation of formic acid bybis-(2,2′-bipyridyl) copper(II) permanganate

      Baljeet Kaur Satsangi Seema Kothari Kalyan K Banerji

      More Details Abstract Fulltext PDF

      The oxidation of formic acid bybis-(2,2′-bipyridyl)copper(II) permanganate (BBCP) is first order with respect to BBCP. The order with respect to formic acid is less than one in the absence of perchloric acid whereas in the presence of perchloric acid, it is more than one but less than two. Thus in both the cases Michaelis-Menten type kinetics were observed with respect to formic acid. The overall formation constants for the formic acid-BBCP complexes and their rates of decomposition have been evaluated. Thermodynamic parameters for complex formation and the activation parameters for their decomposition have also been calculated. The hydrogen-ion dependence has the formkobs=a+b[H+]+c[H+]2. The oxidation of deuterioformic acid showed the presence of a primary kinetic isotope effect (kH/kD≈4). An increase in the amount of acetic acid in the solvent mixture, acetic acid and water, increases the rate. The addition of 2,2′-bipyridine and acrylonitrile has no effect on the rate. Suitable mechanisms have been proposed.

    • Kinetics and mechanism of the oxidation of phosphinic, phenylphosphinic and phosphorous acids by benzyltrimethylammonium dichloroiodate

      Deepa Suri Seema Kothari Kalyan K Banerji

      More Details Abstract Fulltext PDF

      Oxidation of lower phosphorus oxyacids by benzyltrimethylammonium dichloroiodate (BTACI), in the presence of zinc chloride, resulted in the formation of the corresponding oxyacids with phosphorus in a higher oxidation state. The reaction is first order with respect to the concentration of BTACI, oxyacid and zinc chloride. The reaction exhibited the presence of a substantial kinetic isotope effect. Addition of benzyltrimethylammonium chloride enhances the reaction rate. It is proposed that the reactive oxidizing species is [PhCH2Me3N]+ [Zn2Cl6]−2I+. It has been shown that the pentacoordinated tautomer of the phosphorus oxyacid is the reactive reductant. A mechanism involving a hydride-ion transfer from the P-H bond to the oxidant in the rate-determining step has been postulated.

    • Kinetics and mechanism of the oxidation of some diols by benzyltrimethylammoniumtribromide

      Garima Goswami Seema Kothari Kalyan K Banerji

      More Details Abstract Fulltext PDF

      The kinetics of oxidation of five vicinal and four non-vicinal diols, and two of their monoethers by benzyltrimethylammonium tribromide (BTMAB) have been studied in 3:7 (v/v) acetic acid-water mixture. The vicinal diols yield the carbonyl compounds arising out of the glycol bond fission while the other diols give the hydroxycarbonyl compounds. The reaction is first-order with respect to BTMAB. Michaelis-Menten type kinetics is observed with respect to diol. Addition of benzyltrimethylammonium chloride does not affect the rate. Tribromide ion is postulated to be the reactive oxidizing species. Oxidation of [1,1,2,2-2H4] ethanediol shows the absence of a kinetic isotope effect. The reaction exhibits substantial solvent isotope effect. A mechanism involving a glycol-bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidized by a hydride ion transfer to the oxidant, as are the monohydric alcohols.

    • Kinetics and mechanism of the oxidation of formic and oxalic acids by benzyltrimethylammonium dichloroiodate

      Poonam Gupta Seema Kothari

      More Details Abstract Fulltext PDF

      The oxidation of formic and oxalic acids by benzyltrimethylammonium dichloroiodate (BTMACI), in the presence of zinc chloride, leads to the formation of carbon dioxide. The reaction is first order with respect to BTMACI, zinc chloride and organic acid. Oxidation of deuteriated formic acid indicates the presence of a kinetic isotope effect. Addition of benzyltrimethylammonium chloride enhances the rate. It is proposed that the reactive oxidizing species is [(PhCH2Me3N)+ (IZn2Cl6)-]. Suitable mechanisms have been proposed.

    • Kinetics and mechanism of the oxidation of some α-hydroxy acids by hexamethylenetetramine-bromine

      Dimple Garg Seema Kothari

      More Details Abstract Fulltext PDF

      The oxidation of lactic acid, mandelic acid and ten monosubstituted mandelic acids by hexamethylenetetramine-bromine (HABR) in glacial acetic acid, leads to the formation of the corresponding oxoacid. The reaction is first order with respect to each of the hydroxy acids and HABR. It is proposed that HABR itself is the reactive oxidizing species. The oxidation of α-deuteriomandelic acid exhibits the presence of a substantial kinetic isotope effect (kH/kD = 5.91 at 298 K). The rates of oxidation of the substituted mandelic acids show excellent correlation with Brown’s σ+ values. The reaction constants are negative. The oxidation exhibits an extensive cross conjugation between the electron-donating substituent and the reaction centre in the transition state. A mechanism involving transfer of a hydride ion from the acid to the oxidant is postulated.

    • Kinetics and correlation analysis of reactivity in the oxidation of organic sulfides by butyltriphenylphosphonium dichromate

      K M Dilsha Seema Kothari

      More Details Abstract Fulltext PDF

      The oxidation of a number of monosubstituted aryl methyl, alkyl phenyl, dialkyl, and diphenyl sulfides by butyltriphenylphosphonium dichromate (BTPPD), to the corresponding sulfoxides, is first order with respect to BTPPD and is second order with respect to sulfide. The reaction is catalysed by hydrogen ions and the dependence is of second order. The oxidation of meta- and para-substituted aryl methyl sulfides correlated best in terms of Hammett equation, the reactions exhibited negative polar reaction constant. The ortho-substituted compounds correlated best in terms of Charton’s triparametric equation with negative polar constant and a small degree of steric hindrance. The oxidation of alkyl phenyl sulfides exhibited a good correlation in terms of Pavelich-Taft equation confirming that the electron-donating power of the alkyl group increases the rate, however, the reactivity is not markedly controlled by the bulkiness of the alkyl group. The rates of oxidation of sulfides were determined in nineteen organic solvents. An analysis of the solvent effect by multi-parametric equations indicated the relatively greater importance of the cation-solvating power of the solvents. A mechanism involving a single-step electrophilic oxygen transfer from BTPPD to the sulfide leading to polar transition state has been proposed.

  • Journal of Chemical Sciences | News

    • Editorial Note on Continuous Article Publication

      Posted on July 25, 2019

      Click here for Editorial Note on CAP Mode

© 2017-2019 Indian Academy of Sciences, Bengaluru.