Analysis of Long-Side-Chain.pdf

Analysis of Long-Side-Chain Alkylaromatics in Crude Oil for Evaluation of Their Fate in the Environment T A P A N K . D U T T A A N D S H I G E A K I H A R A Y A M A * Marine Biotechnology Institute, 3-75-1 Heita, Kamaishi, Iwate 026-0001, Japan 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. Introduction A vast amount of mineral oil is being released into the ocean. Upon its release, the petroleum components undergo various modifications, with biodegradation and photooxidation being considered to be the two major factors contributing to the removal of hydrocarbon molecules from the environment. A homologous series of long-side-chain alkylaromatics, including sulfur-containing compounds, comprise a signifi- cant portion of petroleum and have served as markers to identify the source of oil pollution (1-11). Although the decomposition of C10-C14 phenylalkanes (the subscript to C indicates the number of carbon atoms in the alkyl side chain