Process for the activation of carboxylic acids

A process for the activation of carboxylic acids, useful for the subsequent conversion of said carboxylic acids into their corresponding esters or amides, comprising the steps of

• (a) reacting one equivalent of a 2-oxazolidinone of the general formula ##STR10## wherein R.sub.1 and R.sub.2 are selected from a group consisting of hydrogen and alkyl groups having from one to four carbon atoms, with a solvent with at least one half equivalent of phosphorus pentachloride at temperatures from -15.degree. C. to +100.degree. C. to yield P-trichlorinated N,N'-bis-3(oxazolydinyl-2-one) phosphoranes of the formula ##STR11## where R.sub.1 and R.sub.2 are likewise selected from a group consisting of hydrogen and alkyl groups having from one to four carbon atoms;
• (b) then adding a salt of the carboxylic acid to be activated, to obtain an activation reaction mixture;
• and
• (c) treating the resulting activation reaction mixture with one of a compound of the group comprising the compounds having an amine function and the compounds having a hydroxyl function to yield, respectively, an amide or an ester.