Curie-point pyrolysis of sodium salts of functionalized fatty acids

Abstract

Selected sodium salts of functionalized fatty acids were subjected to Curie-point pyrolysis and their pyrolysis products subsequently analyzed by gas chromatography/mass spectrometry in order to study the thermal dissociation mechanisms of lipid moieties in bio- and geomacromolecules. Pyrolysis of the sodium salts of hydroxy and keto acids yields in each case a methylketone as the major product, which is generated via a concerted, six-membered ring rearrangement triggered by the functionality in the alkyl chain. The thermal dissociation of alkylbenzene and alkylthiophene moieties proceeds mainly via hydrogen abstraction at the - and -carbon atoms, followed by -scission. The ratios of the main product pairs, i.e. styrene/toluene and vinylthiophene/2-methylthiophene, are largely controlled by radical mobility during pyrolysis. The major fragmentation pathway of monounsaturated alkyl chains is -cleavage adjacent to the double bond. The identification of both Z and E isomers of alkenes in the pyrolysates demonstrates that the initial stereospecifity of the double bond is not retained during pyrolysis. The formation of linear alkylbenzenes from non-phenylic precursor moieties (e.g. diunsaturated fatty acids) shows that specific alkylbenzenes in Curie-point pyrolysates are not always derived from monoaromatic precursors. The addition of organic or mineral matter suppresses these secondary processes. The extension of the model compound results to the recognition of specific types of pyrolysis products and their relevance to the reconstruction of structures of lipid moieties in natural biomacromolecules in kerogens and coals are discussed.