CYCLOHEXYLBENZENES IN CRUDE OILS

A number of alkyl cyclohexylbenzenes have been identified in crude oils using authentic standards by comparison of their gas chromatography retention behaviour and their mass spectra. A suite of crude oils with a wide range of locations, source types and ages has been analysed for methyl and dimethyl cyclohexylbenzenes and for the structurally related alkyl biphenyls. In general, crude oils with abundant methyl and dimethyl cyclohexylbenzenes also have abundant alkyl biphenyls. The abundances of cyclohexylbenzenes and biphenyls were highest in samples with inferred oxic depositional conditions and from oxygen-rich source materials and were lowest in samples where depositional conditions were more reducing and the organic source materials rich in hydrogen. A mechanism of formation involving coupling of sedimentary phenols, followed by defunctionalisation and hydrogenation/dehydrogenation has been suggested to account for the corresponding amounts of structurally related biphenyls and cyclohexylbenzenes.