Analysis of long side chain alkylaromatics in crude oil for evaluation of their fate in the environment

It has long been believed that the n-hexane fraction of crude oil only cont ains saturates. However, we found that one-third of its content was aromati cs with long alkyl side chains and that these aromatics could be separated from the saturates by preparative thin-layer chromatography. The separated alkylaromatic fraction was characterized by UV-visible, NMR and mass spectr ometries. A gas chromatographic-mass spectrometric-analysis showed the pres ence of a homologous series of long-side-chain n-alkylaromatics, namely mon o-, di-, and tri-n-alkylbenzenes in the C-7-C-27 range (the subscript to C indicates the total number of carbon atoms in the alkyl side chain) and di- and tri-n-alkylbenzothiophenes in the C-3-C-22 range. The biodegradation o f these crude oil components by a natural bacterial population in seawater and their photooxidation by artificial sunlight were investigated. The n-al kylbenzenes were found to be quite susceptible to biodegradation but resist ant to photooxidation, whereas the n-alkylbenzothiophenes were almost compl etely photooxidized and substantially biodegraded.