Acyl trifluoroacetates. Part IV. Trifluoroacetylation of hydroxy-compounds with trifluoroacetic anhydride

Abstract

Acyl Trifluoroacetates. Part 1V.l Trifluoroacetylation of Hydroxycompounds w i t h Trifluoroacetic Anhydride By T. G. Bonner," P. M. McNamara, and (in part) B. Smethurst, Royal Holloway College, University of Alcohols and phenols are trifluoroacetylated in carbon tetrachloride much more rapidly by trifluoroacetic anhydride than by acetyl trifluoroacetate. Pyridine bases are effective catalysts for the trifluoroacetylation of phenols but not of alcohols or thiophenoi, and this effect is attributed to phenolic compounds showing greater nucleophilicity through hydrogen-bonding with the base.London, Englefield Green, Egham, Surrey THE fact that hydroxy-compounds are more rapidly trifluoroacetylated by trifluoroacetic anhydride than by acetyl trifluoroacetate in carbon tetrachloride must arise, at least partly, because the trifluoroacetate anion is a better leaving-group 2*3 than the acetate ion. The importance of this effect is evident from the very similar rates in carbon tetrachloride at 0" of acetylation of 9-chlorophenol by acetyl trifluoroacetate (1.1 x 10-4 sec.-l) and of trifluoroacetylation of the same substrate by trifluoroacetic anhydride (0.9-1*0 x sec.-l). The rate in both cases appears to depend markedly on the bond-breaking step in the anhydride.The change from predominant acetylation of phenols by acetyl trifluoroacetate to a faster trifluoroacetylation reaction on addition of pyridine bases has been attributed t o an increase in the nucleophilicity of the hydroxy-Part 111, T.

Quantitative Kinetic Measurements of the Esterification of Self-Assembled Monolayers of Mercaptoundecanol by Trifluoroacetic Anhydride Using Friction Force Microscopy

“…25,26 In the bulk phase, the trifluoroacetylation of alcohols with TFAA occurs via a straightforward esterification mechanism in which a tertiary amine base acts as a nucleophilic catalyst. 27,28 The conversion of an alcohol terminus to the corresponding trifluoroester group is desirable, as the functional group yields prominent, readily quantifiable peaks in infrared (IR) or X-ray photoelectron spectroscopy (XPS) spectra. 24,26,29,30 This type of fluorine labeling has been used with great success on polymeric films, [30][31][32] in the study of the composition of mixed monolayers containing alcohol functionalities, 33 and for investigations of the properties of hydroxyl-terminated SAMs including reaction kinetics.…”

“…The attachment of trifluoroacetic anhydride (TFAA) to self-assembled monolayers presenting alcohol termini was selected as the model system for the present study. This reaction is known to proceed quickly both in solution , and in the vapor phase, and it is not thought to be complicated by uncontrollable side processes. , In the bulk phase, the trifluoroacetylation of alcohols with TFAA occurs via a straightforward esterification mechanism in which a tertiary amine base acts as a nucleophilic catalyst. , The conversion of an alcohol terminus to the corresponding trifluoroester group is desirable, as the functional group yields prominent, readily quantifiable peaks in infrared (IR) or X-ray photoelectron spectroscopy (XPS) spectra. ,,, This type of fluorine labeling has been used with great success on polymeric films, − in the study of the composition of mixed monolayers containing alcohol functionalities, and for investigations of the properties of hydroxyl-terminated SAMs including reaction kinetics. , However, the kinetics of the reaction have not previously been established. In terms of reactivity, interfaces often demonstrate unusual behavior that is not observed in the analogous bulk phase reaction.…”