18855-84-0Relevant articles and documents
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.
An Open Transition State in Carbonyl Acyl Group Transfer in Aqueous Solution
Ba-Saif, Salem A.,Colthurst, Matthew,Waring, Mark A.,Williams, Andrew
, p. 1901 - 1908 (2007/10/02)
The second-order rate constants have been measured for the reaction of substituted phenolate ions with 2,4-dinitrophenyl acetate, 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate and acetic anhydride in aqueous solution at 25 deg C.The data are over a wide range of phenolate ion basicity and obey good Broensted equations which have βnuc values of, respectively, 0.57 +/- 0.03, 0.15 +/- 0.07 and 0.59 +/- 0.05.The principal conclusion of this work is that the identity reaction of 2,4-dinitrophenolate ion with 2,4-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate has anopen transition state, namely one with very weak bonds to entering and departing ligands.The transition state possesses a Kreevoy tightness parameter (τ) of 0.18.The open transition state arises from the stabilising effect of the acyl group substituents on the benzoylium ion and their destabilising effect on the putative tetrahedral intermediate as well as the weak basicities of the nucleophile and nucleofuge.This is the first example of an open transition state in an acyl group transfer which does not require the assistance of a negatively charged internal nucleophile.The data for 2,4-dinitrophenyl acetate may be employed to calculate an identity rate constant (kii) for the reaction of 2,4-dinitrophenolate ion with the ester.This data may be fitted to a theoretical Lewis-Kreevoy plot (log kii vs. pKi) possessing both positive and negative values of βii (slope of the line).Microscopic medium effects place a limit to the accuracy of predictions of rate constants, including kii, from linear free energy relationships.
