Fast derivatization and GC analysis of phenolic acids

Summary

Phenolic acids, i.e. benzoic, phenylacetic, phenylpropenoic (cinnamic), phenylglycolic (mandelic), phenylpropionic and their variously substituted forms can be converted almost instantly to derivatives amenable to GC by treatment with methyl or ethyl chloroformate. The reaction, catalyzed by pyridine, proceeds even in the presence of water. The carboxylic group is esterified to the corresponding alkyl ester but even the alkoxycarbonyl ester (mixed anhydride) can be produced by altering the reaction conditions. Hydroxyl groups on the benzene ring or adjacent to the carboxylic group are converted to the alkoxycarbonyl ethers. Benzoic acid and some of its substitutents, unlike the other aromatic acids, shows a tendency to mixed anhydride formation even under conditions used for alkyl esters. A well deactivated capillary column with a thin film of stationary phase of low polarity enables even the mixed anhydrides to be analyzed successfully.