Reactions of Carbonyl Compounds in Basic Solutions. Part 34. The Mechanism of the Base-Catalysed Ring Fission of 2,3-Diphenylcycloprop-2-en-1-one

1999 ◽  
Vol 64 (10) ◽  
pp. 1594-1600 ◽  
Author(s):  
Keith Bowden ◽  
Emma J. Burgess
Keyword(s):  
Carbonyl Compounds ◽  
Activation Parameters ◽  
Rate Coefficients ◽  
Solvent Isotope Effect ◽  
Hydroxide Anion ◽  
Mechanistic Pathway ◽  
Ring Fission ◽  
Reaction Constant ◽  
Basic Solutions ◽  
Solvent Isotope

The rate coefficients for the base-catalysed ring fission of a series of 2-phenyl-3-(2-, 3- or 4-substituted phenyl)cycloprop-2-en-1-ones to give the corresponding (E)-2,3-diphenylacrylic acids have been determined in water at 30.0 °C, as well as for the unsubstituted compound at 40.0, 50.0 and 60.0 °C. The effects of meta- and para-substituents on the rates have been correlated using the Hammett equation to give a reaction constant, ρ, equal to ca 1.2 at 30 °C. For the unsubstituted compound, the activation parameters have been calculated and the kinetic solvent isotope effect has been studied. The effects of ortho-substituents on the rates appear to be mainly polar, rather than steric, in origin. The evidence indicates a mechanistic pathway which proceeds by addition of hydroxide anion to the ketone, which is rate-determining. The adduct suffers ring fission to give the final product via a carbanionic intermediate.

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.

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 for the Hydrolysis of Chlorothionoformate and Chlorodithioformate Esters in Water and Aqueous Acetone

1972 ◽  
Vol 50 (9) ◽  
pp. 1401-1406 ◽  
Author(s):  
D. M. McKinnon ◽  
A. Queen
Keyword(s):  
Isotope Effect ◽  
Structural Changes ◽  
Activation Parameters ◽  
Aqueous Acetone ◽  
Kinetics And Mechanism ◽  
Solvent Isotope Effect ◽  
Hydrocarbon Group ◽  
Solvent Isotope ◽  
Electron Donation ◽  
Hydrolysis Of

The effects of structural changes on the rates of hydrolysis of a series of chlorothionoformate esters and the analogous chlorodithioformate esters have been studied. For both classes of compound, the reactivity is enhanced by increased electron donation by the hydrocarbon group. These results, the activation parameters for the hydrolyses of the methyl compounds, and the solvent isotope effect are shown to be consistent with the operation of the SN1 mechanism.

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.

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