CYCLOHEXYLBENZENES IN CRUDE OILS

A number of alkyl cyclohexylbenzenes have been identified in crude oil s 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 fo r methyl and dimethyl cyclohexylbenzenes and for the structurally rela ted alkyl biphenyls. In general, crude oils with abundant methyl and d imethyl cyclohexylbenzenes also have abundant alkyl biphenyls. The abu ndances of cyclohexylbenzenes and biphenyls were highest in samples wi th inferred oxic depositional conditions and from oxygen-rich source m aterials and were lowest in samples where depositional conditions were more reducing and the organic source materials rich in hydrogen. A me chanism of formation involving coupling of sedimentary phenols, follow ed by defunctionalisation and hydrogenation/dehydrogenation has been s uggested to account for the corresponding amounts of structurally rela ted biphenyls and cyclohexylbenzenes.