scholarly journals Kinetics and Mechanism of the Oxidation of α-Hydroxy Carboxylic Acids by Bromine

1973 ◽  
Vol 28 (7-8) ◽  
pp. 450-453 ◽  
Author(s):  
Kalyan K. Banerji
Keyword(s):  
Isotope Effect ◽  
Hydroxy Acid ◽  
Kinetic Isotope Effect ◽  
Activation Parameters ◽  
Probable Mechanism ◽  
Molecular Bromine ◽  
Solvent Isotope Effect ◽  
First Order ◽  
Kinetic Isotope ◽  
Solvent Isotope

The oxidation of glycollic, lactic, u-hydroxybutyric, and 2-phenyllactic acids by aqueous bromine has been studied. The reaction is of first order with respect to the oxidant and the anion of the hydroxy acid respectively. The active oxidising species is molecular bromine. The oxidation of α,α-dideuterioglycollic acid indicated a kinetic isotope effect, kH/kD=4.62 at 25°C. The reaction does not show any appreciable solvent isotope effect. The activation parameters arc evaluated. A probable mechanism has been suggested.

Kinetics and Mechanism of the Oxidation of Some α-Hydroxyacids by Morpholinium Chlorochromate

2008 ◽  
Vol 33 (4) ◽  
pp. 393-405
Author(s):  
Neha Malani ◽  
Manju Baghmar ◽  
Preeti Swami ◽  
Pradeep Kumar Sharma
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Ion Transfer ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
First Order ◽  
Hydride Ion ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Hydride Ion Transfer

The oxidation of glycollic, lactic, malic and a few substituted mandelic acids by morpholinium chlorochromate (MCC) in dimethylsulfoxide (DMSO) leads to the corresponding oxoacids. The reaction is first order each in MCC and hydroxyacid. The reaction failed to induce the polymerisation of acrylonitrile. The oxidation of α–deuteriomandelic acid shows a primary kinetic isotope effect ( kH/ kD = 5.63 at 298 K) but does not exhibit a solvent isotope effect. The reaction is catalysed by hydrogen ions according to: kobs = a + b[H+]. The oxidation of p-methyl mandelic acid has been studied in 19 different organic solvents and the solvent effect analysed using Kamlet's and Swain's multiparametric equations. A mechanism involving a hydride ion transfer via a chromate ester is proposed.

Kinetics and mechanisms of the oxidation of methyl aryl ketones by acid permanganate

1976 ◽  
Vol 29 (9) ◽  
pp. 1939 ◽  
Author(s):  
MP Nath ◽  
KK Banerji
Keyword(s):  
Isotope Effect ◽  
Reaction Rate ◽  
Activation Parameters ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
Fluoride Ions ◽  
First Order ◽  
Kinetic Isotope ◽  
Aryl Ketones ◽  
Solvent Isotope

The oxidation of six methyl aryl ketones by acid permanganate has been studied, in the presence of fluoride ions. The products of the oxidation are formaldehyde and the corresponding benzoic acids.The oxidation is first order with respect to each the ketone, the oxidant and hydrogen ions. The reaction rate increases sharply with the increase in the amount of acetic acid in the solvent. The oxidation of acetophenone exhibits the kinetic isotope effect, kH/kD = 4.60 at 30�C. The solvent isotope effect is given by k(D2O)/k(H2O) = 5.03. The acid-catalysed enolization rate of the ketones has been measured by the bromination method. The activation parameters for both the oxidationand enolization reactions have been evaluated. The oxidation is slower than the acid-catalysed enolization. The relative rates of the oxidation are proportional to the relative rates of enolization.These results coupled with the magnitude of the solvent isotope effect suggest that the enol form of the ketone is involved in the oxidation process. A possible mechanism has been suggested.

scholarly journals A solvent-isotope-effect study of proton transfer during catalysis by Escherichia coli (lacZ) β-galactosidase

1990 ◽  
Vol 268 (2) ◽  
pp. 317-323 ◽  
Author(s):  
T Selwood ◽  
M L Sinnott
Keyword(s):  
Escherichia Coli ◽  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Isotope Effects ◽  
Effect Study ◽  
Solvent Isotope Effect ◽  
Kinetic Isotope ◽  
Solvent Isotope ◽  
Paper Abstract ◽  
Hydrolysis Of

1. Michaelis-Menten parameters for the hydrolysis of 4-nitrophenyl β-D-galactopyranoside and 3,4-dinitrophenyl β-D-galactopyranoside Escherichia coli (lacZ) β-galactosidase were measured as a function of pH or pD (pL) in both 1H2O and 2H2O. 2. For hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-free enzyme, V is pL-independent below pL 9, but the V/Km-pL profile is sigmoid, the pK values shifting from 7.6 +/- 0.1 in 1H2O to 8.2 +/- 0.1 in 2H2O, and solvent kinetic isotope effects are negligible, in accord with the proposal [Sinnott, Withers & Viratelle (1978) Biochem. J. 175, 539-546] that glycone-aglycone fission without acid catalysis governs both V and V/Km. 3. V for hydrolysis of 4-nitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme varies sigmoidally with pL, the pK value shifting from 9.19 +/- 0.09 to 9.70 +/- 0.07; V/Km shows both a low-pL fall, probably due to competition between Mg2+ and protons [Tenu, Viratelle, Garnier & Yon (1971) Eur. J. Biochem. 20, 363-370], and a high-pL fall, governed by a pK that shifts from 8.33 +/- 0.08 to 8.83 +/- 0.08. There is a negligible solvent kinetic isotope effect on V/Km, but one of 1.7 on V, which a linear proton inventory shows to arise from one transferred proton. 4. The variation of V and V/Km with pL is sigmoid for hydrolysis of 3,4-dinitrophenyl β-D-galactopyranoside by Mg2(+)-enzyme, with pK values showing small shifts, from 8.78 +/- 0.09 to 8.65 +/- 0.08 and from 8.7 +/- 0.1 to 8.9 +/- 0.1 respectively. There is no solvent isotope effect on V or V/Km for 3,4-dinitrophenyl β-D-galactopyranoside, despite hydrolysis of the galactosyl-enzyme intermediate governing V. 5. Identification of the ‘conformation change’ in the hydrolysis of aryl galactosides proposed by Sinnott & Souchard [(1973) Biochem. J. 133, 89-98] with the protolysis of the magnesium phenoxide arising from the action of enzyme-bound Mg2+ as an electrophilic catalyst rationalizes these data and also resolves the conflict between the proposals and the 18O kinetic-isotope-effect data reported by Rosenberg & Kirsch [(1981) Biochemistry 20, 3189-3196]. It should be noted that the actual Km values were determined to higher precision than can be estimated from the Figures in this paper.(ABSTRACT TRUNCATED AT 400 WORDS)

The Kinetics of the Oxidation of Acetaldehyde by Acid Permanganate

1972 ◽  
Vol 27 (7) ◽  
pp. 772-774 ◽  
Author(s):  
K. K. Banerji
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Activation Parameters ◽  
Hydrogen Ion ◽  
First Order ◽  
Hydride Ion ◽  
Kinetic Isotope ◽  
Kinetics Of

The kinetics of the oxidation of aceltaldehyde by acid permanganate has been studied. The reaction is of first order with respect to the aldehyde, the oxidant and hydrogen ion individually. The oxidation does not induce polymerisation of acrylonitrile and show a kinetic isotope effect (kH/kD= 6.1). The activation parameters for the oxidation and enolisation reactions have been evaluated. The rate of enolisation, under similar conditions, is less than that of oxidation. A mechanism involving the transfer of a hydride ion from the aldehyde hydrate to the oxidant has been suggested.

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

1985 ◽  
Vol 63 (10) ◽  
pp. 2726-2729 ◽  
Author(s):  
Seema Kothari ◽  
Kalyan Kumar Banerji
Keyword(s):  
Isotope Effect ◽  
Activation Parameters ◽  
Hydrogen Ions ◽  
Solvent Isotope Effect ◽  
Benzyl Alcohols ◽  
Rate Determining Step ◽  
Kinetic Isotope ◽  
Reaction Constant ◽  
Different Temperatures ◽  
Solvent Isotope

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 Brown's 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.

ORTHO PARTICIPATION IN THE CONVERSION OF syn-BENZALDOXIME ESTERS TO NITRILES

1965 ◽  
Vol 43 (12) ◽  
pp. 3178-3187 ◽  
Author(s):  
Robert J. Crawford ◽  
Charles Woo
Keyword(s):  
Isotope Effect ◽  
Kinetic Isotope Effect ◽  
Alcoholic Solution ◽  
First Order ◽  
Rate Determining Step ◽  
First Order Kinetics ◽  
Kinetic Isotope ◽  
Marked Enhancement

Substituted syn-benzaldoxime esters are transformed, in an alcoholic solution, to the corresponding nitriles according to first-order kinetics. All ortho substituents were observed to accelerate the rate of nitrile formation relative to the corresponding para derivative. While the ko/kp ratios for the bromo, chloro, fluoro, methoxy, and methyl substituents fall within the range of 2 to 9, the iodo and methylthio substituents are 119 and 11 000 respectively. Isotopic replacement of the aldoximino hydrogen by deuterium gives rise to a kinetic isotope effect, kH/kD being 5.21 for syn-o-chlorobenzaldoxime p-toluenesulfonate, 1.22 for syn-o-iodobenzaldoxime p-toluenesulfonate, and 1.23 for syn-o-methylthiobenzaldoxime o-iodobenzoate. The marked enhancement of rate and the absence of an appreciable isotope effect are considered to be associated with sulfur and iodine participation in the rate-determining step. A mechanism which is capable of explaining the results observed is suggested.

scholarly journals Kinetics and Mechanism of the Decarboxylation of Pyrrole-2-carboxylic Acid in Aqueous Solution

1971 ◽  
Vol 49 (7) ◽  
pp. 1032-1035 ◽  
Author(s):  
G. E. Dunn ◽  
Gordon K. J . Lee
Keyword(s):  
Aqueous Solution ◽  
Ionic Strength ◽  
Carboxylic Acid ◽  
Isotope Effect ◽  
Anthranilic Acid ◽  
Kinetic Isotope Effect ◽  
Pyrrole Ring ◽  
First Order ◽  
Kinetic Isotope ◽  
Ph Range

The decarboxylation of pyrrole-2-carboxylic acid in aqueous buffers at 50° and ionic strength 1.0 has been found to be first order with respect to substrate at a fixed pH. As the pH is decreased, the rate constant increases slightly in the pH range 3–1, then rises rapidly from pH 1 to 10 M HCl. The 13C-carboxyl kinetic isotope effect is 2.8% in 4 M HClO4 and negligible at pH ~ 3. These observations can be accounted for by a mechanism, previously proposed for the decarboxylation of anthranilic acid, in which the species undergoing decarboxylation is the carboxylate ion protonated at the 2-position of the pyrrole ring. This intermediate can be formed both by ring-protonation of the carboxylate anion and by ionization of the ring-protonated acid. At low acidities ring-protonation is rate determining, but at higher acidities the rate of protonation exceeds that of decarboxylation.

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