824-38-4Relevant articles and documents
Ambident Reactivity of Phenolate Anions Revisited: A Quantitative Approach to Phenolate Reactivities
Mayer, Robert J.,Breugst, Martin,Hampel, Nathalie,Ofial, Armin R.,Mayr, Herbert
, p. 8837 - 8858 (2019/07/08)
Prompted by the observation that the regioselectivities of phenolate reactions (C versus O attack) are opposite to the predictions by the principle of hard and soft acids and bases, we performed a comprehensive experimental and computational investigation of phenolate reactivities. Rate and equilibrium constants for the reactions of various phenolate ions with benzhydrylium ions (Aryl2CH+) and structurally related quinone methides have been determined photometrically in polar aprotic solvents. Quantum chemical calculations at the SMD(MeCN)/M06-2X/6-31+G(d,p) level confirmed that O attack is generally favored under kinetically controlled conditions, whereas C attack is favored under thermodynamically controlled conditions. Exceptions are diffusion-limited reactions with strong electrophiles, which give mixtures of products arising from O and C attack, as well as reactions with metal alkoxides in nonpolar solvents, where oxygen attack is blocked by strong ion pairing. The Lewis basicity (LB) and nucleophilicity (N, sN) parameters of phenolates determined in this work can be used to predict whether their reactions with electrophiles are kinetically or thermodynamically controlled and whether the rates are activation- or diffusion-limited. Comparison of the measured rate constants for the reactions of phenolates with carbocations with the Gibbs energies for single-electron transfer manifests that these reactions proceed via polar mechanisms.
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.
