1523-08-6Relevant academic research and scientific papers
Effective charge development in the transfer of the acetyl group between nucleophiles in acetonitrile solution: Acetolysis and butylaminolysis of substituted phenyl esters
Maude, Antony B.,Williams, Andrew
, p. 179 - 183 (2007/10/03)
Equilibrium and rate constants have been measured for the phenolyses of acetic anhydride in acetonitrile solution. Acetolysis of substituted phenyl acetates by acetate ion possesses a Bronsted βlg value of -1.50 which, together with a βeq value of 2.86, indicates substantial fission of the C-OAr bond in the transition structure. The value of βeq is employed to identify the rate-limiting steps in aminolyses in acetonitrile. Butylaminolysis of substituted phenyl acetates in acetonitrile solution yields amide and substituted phenolate anion and the kinetics obey the general rate law: Rate = k1[ester][amine] + k2[ester][amine]2 + k3[ester][amine][18-crown-6] Free energy plots of log k1 and log k2 exhibit breaks near pKaArOH values of 9 and 8, respectively, and these can be interpreted by a mechanism which involves a common zwitterionic adduct T±, which partitions to give the product by two routes: A involving direct expulsion of the phenolate ion leaving group (k1 parameter) and B involving proton transfer prior to phenolate ion expulsion (k2 parameter). The formation of T± is rate-limiting for the A path and C-OAr bond fission is rate-limiting for the B mechanism.
Kinetics and Equilibria of Reactions between Acetic Anhydride and Substituted Phenolate Ions in Aqueous and Chlorobenzene Solutions
Ba-Saif, Salem A.,Maude, Antony B.,Williams, Andrew
, p. 2395 - 2400 (2007/10/02)
Potassium acetate, solubilised in chlorobenzene by 18-crown-6, displaces the phenolate ion from substituted phenyl acetates by a second-order (kCl-2) process.Potassium phenolate ions, under similar conditions, react with acetic anhydride via a second order (kCl2) to yield the phenyl acetate.The concentration of the crown does not affect the reactivity unless it is not sufficient to solubilise the reactants.The rate constants correlate with the ionisation of the substituted phenols in water: log kCl2=1.60+/-0.23pKArOH(aq)a - 9.06+/-1.4 log kCl-2=-0.97+/-0.12pKArOH(aq)a + 4.78+/-0.78.The equilibrium constant for transfer of the acetyl group between phenolate ions and acetic anhydride in chlorobenzene has a Broensted βCleq of 2.6 measured against pKArOH(aq)a.The second-order rate constants (k2aq) have been measured for the reaction of substituted phenolate ions with acetic anhydride in water and they obey the Broensted equation: log (k2aq) = 0.56 +/- 0.06 pKArOH(aq)a - 2.52 +/- 0.51 Comparison of the value of the Broensted exponent for the equilibrium constant in chlorobenzene (β = 2.6) compared with that for aqueous solution (β = 1.7) indicates a greater development of effective charge consistent with the weaker solvating power of chlorobenzene.The reaction of substituted phenoxide ion with acetic anhydride has a Leffler α value of 0.33 and 0.62 for aqueous and chlorobenzene solutions, respectively, indicating a more advanced bond formation in the transition state of the reaction in the latter solvent even though the reactions in chlorobenzene are faster than in water.
