Identification and origins of isopropylmethylphenols in crude oils

Crude oils have been analysed for isopropylmethylphenols using GC-FID, GC-MS and GC-FTIR techniques. Six of the 10 isomeric isopropylmethylphenols have been identified in crude oils by comparison of their chromatographic behaviour and infrared and mass spectral properties with authentic standards. The relative abundances of isomers vary among the samples, however three different types of isomer distribution patterns have been recognized. The relative abundances of isomers in the first type are at or near equilibrium values. In the second type, isomers with isopropyl groups in the ortho and para positions are abundant and may represent the products from isopropylation of cresols. A third type of crude oils has high relative concentrations of the natural products carvacrol and thymol. Because these compounds occur widely in extant conifers and angiosperms, their presence in crude oils whose source rocks were deposited when these plant types were widespread suggests that they also originate from these plants.