Acylation by acetyl trifluoracetate and trifluoroacetic anhydride

Abstract

The reaction of acetic anhydride with trifluoroacetic anhydride in carbon tetrachloride has been studied kinetically and it was found that under anhydrous conditions no reaction occurred, but when small quantities of either acetic or trifluoroacetic acid were present there was conversion of the symmetric anhydrides to acetyltrifluoroacetate. The mechanism of this acid catalysis was discussed.The acylation of phenols in carbon tetrachloride by acetic anhydride, trifluoroacetic anhydride and acetyl trifluoroacetate was investigated in the presence and absence of pyridine. In the case of the symmetric anhydrides the presence of pyridine caused a considerable increase in the rate of the reaction and with acetyl trifluoroacetate there was a change from acetate to trifluoroacetate formation.Pyridine had little or no effect on the rate or product of the reaction of alcohols with any of the anhydrides.The mechanism of the effect of pyridine on the reactions between hydroxy compounds and the anhydrides mentioned above is discussed and an attempt to decide whether the catalysis is due to hydrogen bonding between the pyridine and the hydroxy compound or to reaction of the pyridine with the anhydride is made.