Origin of long-chain alkylcyclohexanes and alkylbenzenes in a coal-bed wax

Details Origin of long-chain alkylcyclohexanes and alkylbenzenes in a coal-bed wax Origin of long-chain alkylcyclohexanes and alkylbenzenes in a coal-bed wax

Feb 1993

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57..837d&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 57, Issue 4, pp.837-849

Mathematics

Logic

2

Scientific paper

A coal-bed wax was fractionated and analyzed using capillary column GC and combined GC/MS. It was found that the major components in the wax were n -alkanes (55.6%), cyclic/branched alkanes (26.0%), and several homologous series of alkylbenzenes (5.7%). All alkylbenzene isomers (except 6- n -alkyl- m -xylene) were positively identified by comparison with the retention times and mass spectra of newly synthesized authentic standards. 5- n -Alkyl- m -xylene, 2- n -alkyl- p -xylene, 4- n -alkyl- m -xylene, 4- n -alkyl- o -xylene, 2- n -alkyl- m -xylene, and 3- n -alkyl- o -xylene were identified for the first time from geological sources. All of these long-chain alkyl compounds (e.g., n -alkylcyclohexanes, n -alkylbenzenes, n -alkyl- o -toluenes, n -alkyl- p -toluenes, and 5- n -alkyl- m -xylenes) have similar total carbon number distributions and maxima with a slight even over odd carbon number preference between C 28 -C 30 . Moreover, the carbon number distributions of these compounds resembled those of the n -alkanes found in the same wax with slight odd over even carbon preference between C 27 -C 21 . This indicates that the alkylcyclohexanes and alkylbenzenes may have the same fatty acid precursors as the n -alkanes. The alkylcyclohexanes and alkylbenzenes could have been formed by direct cyclization and aromatization, while the n -alkanes could have been formed by decarboxylation of the straight chain fatty acids. This explanation is further supported by the identification of homologous series of tetramethyl- n -alkylbenzenes and pentamethyl- n -alkylbenzenes with relatively high abundances at C 15 , C 16 , and C 18 , and a fatty acid distribution with maxima at C 16 and C 18 . Based on these findings, mechanisms for the conversion of fatty acids or alcohols to alkylcyclohexanes and alkylbenzenes are proposed.

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