Thermodynamics of ester and orthoester formation from trifluoroacetic acid

Abstract

J. PETER GUT^-IRIE. Can. J. Chenl. 54, 202 (1976). The equilibrium constant for the addition of sodiunl methoxide to methyl trifluoroacetate, in methanol as solvent, has been measured by 1" nnnlr, and is 7 M-1. From this was calculated an equilibrium constant, 2 X 10-"-1, for addition of methanol to the ester. The equilibrium constant for formation of methyl trilluoroacetate in aqueous sol~~tions is 0.06 M-1. These results, with literature data, permit calc~~lation of the free energies of formation in aqueous solution of orthotrit~uoroacetic acid and its n~ono-, di-, and trimethyl esters. These in t~~r n permit calculation of the standard free energy changes for addition of water and methanol to trifluoroacetic acid and its methyl ester. These combined with the analogous values for formic and acetic acids permit evaluation of p'3' values for these addition reactions. Linear plots are obtained if correction is made for steric effects, and the p:"alues are somewhat larger, 2.1-2.9, than was observed for the analogo~~s carbonyl addition reactions.

Hydrolysis of esters of oxy acids: pKa values for strong acids; Brønsted relationship for attack of water at methyl; free energies of hydrolysis of esters of oxy acids; and a linear relationship between free energy of hydrolysis and pKa holding over a range of 20 pK units

“…variations in solvation effects is considerable; in particular, the balance between ionization and dissociation constants is likely to be quite different and thus the meaning of the global ionization constant will not be the same for different structural types; (c) it has not been demonstrated as far as one can tell that HCI in trifluoroacetic acid is actually HCI and has not to some considerable extent undergone covalent addition to the acid. HCI has a significant tendency to add to carbonyl groups as shown by chloroalkyl ether formation (36), when the equilibrium is not shifted by dissociation into Hf and Cl-, and trifluoroacetic acid is far more prone to undergo nucleophilic addition than are less electron deficient carboxylic acids (37).…”

An investigation of the biphasic kinetics observed during the hydroxide ion-catalyzed hydrolysis of alkyl dithioesters

“…of such intermediates can also be inferred from the existence of stable salts formed by the addition of sodium methoxide to ethyl trifluoroacetate in di-n-butyl ether (24) and to methyl trifluoroacetate in methanol (25).…”

Concertedness and E2 elimination reactions: prediction of transition state position and reaction rates using two-dimensional reaction surfaces based on quadratic and quartic approximations

“…The change in pKa from water to methanol for a series of OH acids was 4.9 2 0.2 (48). The change in pK, from water to ethanol is 5.7 k 0.5 based on the data in Table S3.…”