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Acetyl trifluoroacetate reacts with phenols in carbon tetrachloride to give exclusively the phenyl acetates. The reaction does not appear to proceed through acetylium ions even when catalysed by trifluoroacetic acid. The rate constants for different phenols satisfy the Hammett equation with a p value of -0.82.Very rapid and exclusive formation of the phenyl trifluoroacetates occurs when the solutions of acetyl trifluoroacetate (in large excess) and the phenol are mixed and immediately treated with saturated potassium hydrogen carbonate solution.

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The change in product from phenyl acetate to phenyl trifluoroacetate which occurs when solutions of a phenol and acetyl trifluoroacetate in carbon tetrachloride are brought into contact with saturated aqueous potassium hydrogen carbonate solution appears to be dependent upon the conversion of the phenol into its anion. It can be interpreted as a shift in the relative importance of bond formation and bond fission in the acylation reaction.PHENOLS react with acetyl trifluoroacetate in carbon acetyl trifluoroacetate in large excess (10 : 1) over tetrachloride to form phenyl acetates almost exclu-9-chlorophenol, immediate treatment with the aqueous sively.192 The formation of the trifluoroacetate, how-solution gives over 90% yield of 9-chlorophenyl triever, can supersede completely the acetate reaction fluoroacetate. Lower concentrations of the anhydride if the solution of the reactants is shaken with aqueous reduce the yield of trifluoroacetate but without producing saturated potassium hydrogen carbonate.1 The reaction any detectable amount of acetate ester. A detailed study in the two-phase system is extremely fast and, with has been made of the effect of the pH of the aqueous 1

Acetylation of phenols by acetyl trifluoroacetate is superseded by more rapid trifluoroacetylation in the presence of low concentrations of pyridine bases.