The trifluoroacetates of various phenol, thiophenol and N-hydroxyimide derivatives, which are known as hydroxylic partners of various active carboxylic acid ester, have been synthesized, and it has been found that they are good reagents for the preparation of the respective active esters of acylamino acids by the ester-exchange reaction in pyridine. The new method is especially effective in the preparation of p-nitrophenyl, 2, 4, 5- ...