Seema Kothari

Kinetics and mechanism of the oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide

The oxidation of substituted benzyl alcohols by sodium N-bromobenzenesulfonamide (BAB) in acid solution results in the formation of the corresponding benzaldehydes. The reaction is first order with respect to BAB, the alcohol, and hydrogen ions. The reaction exhibits a primary kinetic isotope effect (kH/kD = 5.26). The value of the solvent isotope effect, k(H2O)/k(D2O), equals 0.43 at 298 K. Addition of benzenesulfonamide has no effect on the rate. Increase in amount of acetic acid in the solvent increases the rate. The reaction rate has been determined at five different temperatures and the activation parameters have been calculated. (PhSO2NH2Br)+ has been postulated as the reactive oxidizing species. The rates of oxidation of substituted benzyl alcohols correlate very well with Browns σ+ constants. The value of the reaction constant is −2.84 at 298 K. A hydride transfer from the alcohol to the oxidant, in the rate-determining step, has been proposed.

Correlation analysis of reactivity in the addition of substituted benzylamines to benzylidenemalononitrile

The kinetics of addition of a number of ortho-, meta-, and para-substituted benzylamines to benzylidenemalononitrile (BMN) in acetonitrile have been studied. The reaction is first-order with respect to BMN. The order with respect to the amine is more than one. It has been shown that the reaction followed two mechanistic pathways, uncatalyzed and catalyzed by the amine. The enthalpy of activation for the catalyzed path is negative indicating the presence of a preequilibrium (k1, k−1) leading to the formation of a zwitterion. The values of rate constant, k1, for the nucleophilic attack have been determined for twenty-eight benzylamines. The rate constant, k1 was subjected to correlation analyses using various single- and multi-parametric equations. The best correlation is obtained in terms of Chartons LDR and LDRS equations. The polar regression coefficients are negative indicating the formation of a cationic species in the transition state. The reaction is subject to steric hindrance by ortho-substituents.

Correlation analysis of reactivity in the addition of substituted benzylamines to ethyl ?-cyanocinnamate

The kinetics of addition of a number of ortho-, meta-, and para-substituted benzylamines to ethyl α-cyanocinnamate (ECC) in acetonitrile have been studied. The reaction is first-order with respect to the amine and ECC. The rates of reaction of meta- and para-substituted benzylamines showed excellent correlations with Tafts σ1 and σR0, and with σ1 and σRBA values, respectively. The reaction of the ortho-compounds showed a very good correlation with Chartons triparametric equation. The reaction is subject to steric hindrance by the ortho-substituents. A mechanism involving formation of a zwitterionic intermediate in a slow step followed by a fast proton transfer has been proposed.

Kinetics and mechanism of the oxidation of lower oxyacids of phosphorus by hexamethylenetetramine bromine

The oxidation of lower oxyacids of phosphorus by hexamethylenetetramine bromine (HABR) in glacial acetic acid resulted in the formation of corresponding oxyacids with phosphorus in a higher oxidation state. The reaction exhibited 2:1 stoichiometry. The reaction is first order with respect to HABR. Michaelis–Menten-type kinetics were observed with respect to the acids. The formation constant of the phenylphosphinic acid–HABR complex also has been determined spectrophotometrically. The thermodynamic parameters for the complex formation and the activation parameters for their decomposition were calculated. The reaction showed the presence of a substantial kinetic isotope effect. It is proposed that the HABR itself is the reactive oxidizing species. It has been shown that the pentacoordinated tautomer of the phosphorus oxyacid is the reactive reductant. A suitable mechanism has been proposed.

KINETICS AND MECHANISM OF THE OXIDATION OF DIOLS BY PYRIDINIUM BROMOCHROMATE

The kinetics of oxidation of four vicinal diols, four nonvicinal diols, and one of their monoethers by pyridinium bromochromate (PBC) have been studied in dimethyl sulfoxide. The main product of oxidation is the corresponding hydroxyaldehyde. The reaction is first-order with respect to each the diol and PBC. The reaction is acid-catalyzed and the acid dependence has the form: kobs=a+b[H+]. The oxidation of [1,1,2,2-2H4]ethanediol exhibited a primary kinetic isotope effect (kH/kD=6.70 at 298 K). The reaction has been studied in 19 organic solvents including dimethyl sulfoxide and the solvent effect has been analyzed using multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical transition state in the rate-determining step. A suitable mechanism has been proposed.

Kinetics and mechanism of the oxidation of DL-methionine bybis(2,2′-bipyridyl)copper(II) permanganate

SummaryThe oxidation ofDL-methionine (MT) bybis(2,2′-bipyridyl)copper(II) permanganate (BBCP) to the corresponding sulphoxide is first order in BBCP. Michaelis-Menten-type kinetics were observed with respect to MT. The formation constant of the intermediate complex and the rate constant for its decomposition were evaluated. The thermodynamic and activation parameters were also evaluated. The reaction is catalysed by H+ but 2,2′-bipyridine does not affect the reaction rate. A mechanism is proposed.

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

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 mechanism of the oxidative regeneration of carbonyl compounds from oximes by cetyltrimethylammonium permanganate

The oxidative deoximination of several aldo- and keto-oximes by cetyltrimethylammonium permanganate (CTAP), in dichloromethane, proceeding through the formation of a cyclic intermediate, in the rate-determining step, has been proposed.

Correlation analysis of structure and reactivity in the oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate

The oxidation of substituted benzyl alcohols by bis(2,2′-bipyridyl) copper(II) permanganate (BBCP), leading to the corresponding benzaldehydes is first-order with respect to BBCP. Michaelis-Menten type kinetics were observed with respect to the alcohols. The oxidation of a,a-dideuteriobenzyl alcohol indicated the presence of a substantial kinetic isotope effect. The rates of oxidation of meta- and para-substituted benzyl alcohols were correlated in terms of Chartons triparametric LDR equation whereas ortho- substituted benzyl alcohols were correlated with a four parametric LDRS equation. The results of correlation analyses point to an electron-deficient reaction center in the transition state.

KINETICS AND MECHANISM OF THE OXIDATION OF SOME THIOACIDS BY BENZYLTRIMETHYLAMMONIUM DICHLOROIODATE

The oxidation of thioglycolic, thiolactic, and thiomalic acids by benzyltrimethylammonium dichloroiodate (BTMAIC) to the corresponding disulfide dimer, is first-order with respect to each the thioacid and BTMAIC. The rates of oxidation were determined at different temperatures and the activation parameters were evaluated. The reaction failed to induce polymerization of acrylonitrile. The reaction rate increases with the increase in the concentration of zinc chloride. Addition of benzyltrimethylammonium chloride enhances the reaction rate. Suitable mechanism has been proposed.