[Structural identification of carboxylic esters by pyrolysis gas chromatography]

A pyrolysis gas chromatographic method has been investigated for structural identification of carboxylic esters. The method can be applied to identify not only pure components, but also those separated by thin layer chromatography and scraped from the TLC plate without removing the adsorbent. The samples were pyrolyzed in tube furnace pyrolyzer at 500 degrees C (conventional pyrolysis) or were pyrolyzed at 550 degrees C after mixing with soda-lime powder (pyrolysis with soda-lime). Some esters such as iso-octyl palmitate, glycerol monostearate and diethyl phthalate were pyrolyzed. The pyrolysis products were identified by comparing with the known. The parent alcohols of monohydric and polyhydric alcohol esters can be determined respectively according to alcohols, alkenes produced on pyrolysis and dehydrated products of polyhydric alcohol at high temperature. The parent acids of monocarboxylic esters can be determined according to carboxylic acid produced on conventional pyrolysis or corresponding alkane formed from decarboxylation of parent acids on pyrolysis with soda-lime. For esters formed from dicarboxylic acids that can be dehydrated to produce five-, six-membered cyclic ketones or can be dehydrated and decarboxylated simultaneously to produce five-, six-membered cyclic acid anhydrides, parent acids can be determined according to corresponding cyclic ketones or cyclic acid anhydrides. This method is useful for identification of common carboxylic esters. When the compound or the component of the mixture was confirmed to contain ester-group by infra-red spectroscopy, PGC or TLC-PGC can be employed to make further identification.