Pradeep K. Sharma

Kinetics and mechanism of oxidation of aliphatic alcohols by tetrabutylammonium tribromide

Oxidation of nine primary aliphatic alcohols by tetrabutylammonium tribromide (TBATB) in aqueous acetic acid leads to the formation of the corresponding aldehydes. The reaction is first order with respect to TBATB. Michaelis-Menten type kinetics is observed with respect to alcohols. The reaction failed to induce the polymerization of acrylonitrile. Tetrabutylammonium chloride has no effect on the reaction rate. The proposed reactive oxidizing species is the tribromide ion. The oxidation of [1,1-2H2]ethanol exhibits a substantial kinetic isotope effect. The effect of solvent composition indicates that the rate increases with increase in the polarity of the solvent. The reaction is susceptible to both polar and steric effects of substituents. A mechanism involving transfer of a hydride ion in the rate-determining step has been proposed.

Kinetics and mechanism of the oxidation of organic sulphides by 2,2 ' '-bipyridinium chlorochromate

The oxidation of 34 organic sulphides hy 2,2′-hipyridinium chlorochromate (BPCC) resulted in the formation of the corresponding sulphoxides. The reaction is first order with respect to both BPCC and the sulphide, and is catalysed by hydrogen ions. The hydrogen-ion dependence has the form:kobs = a+b[H+]. The oxidation was studied in 19 different organic solvents. An analysis of the solvent effect by Swain’s equation showed that the both cation-and anion-solvating powers of the solvents play important roles. The rates of oxidation meta- andp-substituted phenyl methyl sulphides were correlated with Charton’s LDR equation. The rates of theo-compounds showed excellent correlation with the LDRS equation. Oxidation of thep-compounds is more susceptible to the delocalizationeffect. Oxidation of themcompounds exhibited a greater dependence on the field effect. In the oxidation of theo-compounds, the contribution of delocalized effect is slightly more than that of the field effect. The oxidation of alkyl phenyl sulphides is subject to both polar and steric effects of the alkyl groups. Polar reaction constants are negative, indicating an electron-deficient sulphur centre in the rate-determining step. A mechanism involving formation of a sulphurane intermediate in the slow step has been proposed.

Biobutanol from Renewable Agricultural and Lignocellulose Resources and Its Perspectives as Alternative of Liquid Fuels

Biobutanol (n-C4H9OH, available as fermentation product of various carbohydrate derivatives obtained from different resources of agricultural production such as crops and wastes) is one of the most promising biofuels in the near future. It can be produced by the so-called ABE (acetone-butanol-ethanol) type anaerobic fermentation discovered by Pasteur [1, 2] and industrialized by Weizmann [3]. Main problems associated with industrial production of biobutanol include high energy demand for processing of dilute ferment liquors and high volume of wastewater. A bioreactor with a volume of 100 m3 produces at 90% filling ratio 1053 kg of butanol, 526 kg of acetone and 175 kg of ethanol together with 2900 kg of carbon dioxide, 117 kg of hydrogen and 84150 kg of wastewater. Efforts to increase productivity and decrease production costs resulted in many new methods. This chapter summarizes some selected results on methods of biobutanol production.

Kinetics and mechanism of the oxidation of formic and oxalic acids by quinolinium fluorochromate

Kinetics and mechanism of oxidation of formic and oxalic acids by quinolinium fluorochromate (QFC) have been studied in dimethylsulphoxide. The main product of oxidation is carbon dioxide. The reaction is first-order with respect to QFC. Michaelis-Menten type of kinetics were observed with respect to the reductants. The reaction is acid-catalysed and the acid dependence has the form: kobs =a +b[H+]. The oxidation of α-deuterioformic acid exhibits a substantial primary kinetic isotope effect (kH/kD = 6.01 at 303 K). The reaction has been studied in nineteen different organic solvents and the solvent effect has been analysed using Taft’s and Swain’s multiparametric equations. The temperature dependence of the kinetic isotope effect indicates the presence of a symmetrical cyclic transition state in the rate-determining step. Suitable mechanisms have been proposed.

Kinetics and mechanism of the oxidation of substituted benzaldehydes by hexamethylenetetramine‐bromine

The oxidation of thirty-six monosubstituted benzaldehydes by hexa-methylenetetramine-bromine (HABR), in aqueous acetic acid solution, leads to the formation of the corresponding benzoic acids. The reaction is first order with respect to HABR. Michaelis-Menten–type kinetics were observed with respect to aldehyde. The reaction failed to induce the polymerization of acrylonitrile. There is no effect of hexamethylenetetramine on the reaction rate. The oxidation of [2H]benzaldehyde (PhCDO) indicated the presence of a substantial kinetic isotope effect. The effect of solvent composition indicated that the reaction rate increases with an increase in the polarity of the solvent. The rates of oxidation of meta- and para-substituted benzaldehydes showed excellent correlations in terms of Chartons triparametric LDR equation, whereas the oxidation of ortho-substituted benzaldehydes correlated well with tetraparametric LDRS equation. The oxidation of para-substituted benzaldehydes is more susceptible to the delocalization effect but the oxidation of ortho- and meta-substituted compounds displayed a greater dependence on the field effect. The positive value of γ suggests the presence of an electron-deficient reaction center in the rate-determining step. The reaction is subjected to steric acceleration when ortho-substituents are present.

Kinetics and Mechanism of the Oxidation of Some Thioacids by Hexamethylenetetramine-Bromine

Oxidation of thioacids by hexamethylenetetramine-bromine proceeds through an intermediate complex in the pre-equilibrium and its subsequent decomposition in the slow step.

Kinetics and mechanism of oxidation of aliphatic aldehydes by quinolinium fluorochromate

Oxidation of aliphatic aldehydes by quinolinium fluorochromate (QFC) proceeds by a mechanism involving transfer of a hydride ion from the aldehyde to the oxidantvia an intermediate complex.

Kinetics and mechanism of the oxidation of diols by bromine in acid solution

Kinetics of oxidation of five vicinal diols, four non-vicinal diols, and two of their monoethers by bromine in strong acid solutions have been studied. The vicinal diols yielded the products arising out of glycol bond fission while the other diols yielded the hydroxycarbonyl compounds. The reaction is first order with respect to both bromine and the diol. The rate decreases with an increase in the acidity. The oxidation of [1,1,2,2-2H4] ethanediol showed the absence of a primary kinetic isotope effect. The value of solvent isotope effect, k(H2O)/k(D2O), at 303 K for the oxidation of ethanediol, propane-1,3-diol and 3-methoxybutane-1-ol are 4.71, 1.04 and 1.07 respectively. A mechanism involving a glycol bond fission has been proposed for the oxidation of the vicinal diols. The other diols are oxidised by a hydride-transfer mechanism as are monohydric alcohols.

Kinetics and mechanism of the oxidation of organic sulfides by quinolinium fluorochromate

The oxidation of organic sulfides to corresponding sulfoxides by quinolinium fluorochromate proceeds through a sulfurane intermediate.

KINETICS AND MECHANISM OF OXIDATION OF DIOLS BY HEXAMETHYLENETETRAMINE-BROMINE

The oxidation of vicinal diols by hexamethylenetetramine–bromine (HABR) proceeds by a glycol-bond fission via an intermediate complex whereas non-vicinal diols behave like monohydric alcohols towards HABR.