Analysis of Long-Side-Chain Alkylaromatics in Crude Oil for Evaluation of Their Fate in the Environment

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Abstract
It has long been believed that the n-hexane fraction of crude oil only contains saturates. However, we found that one-third of its content was aromatics 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 spectrometries. A gas chromatographic-mass spectrometric analysis showed the presence of a homologous series of long-side-chain n-alkylaromatics, namely mono-, di-, and tri-n-alkylbenzenes in the C7−C27 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 C3−C22 range. The biodegradation of these crude oil components by a natural bacterial population in seawater and their photooxidation by artificial sunlight were investigated. The n-alkylbenzenes were found to be quite susceptible to biodegradation but resistant to photooxidation, whereas the n-alkylbenzothiophenes were almost completely photooxidized and substantially biodegraded.