Petroleum singlet oxygen

Photooxidafions are also iudustriaHy significant. A widely used treatment for removal of thiols from petroleum distillates is air iu the presence of sulfonated phthalocyanines (cobalt or vanadium complexes). Studies of this photoreaction (53) with the analogous ziuc phthalocyanine show a facile photooxidation of thiols, and the rate is enhanced further by cationic surfactants. For the perfume iudustry, rose oxide is produced iu low toimage quantifies by singlet oxygen oxidation of citroneUol (54). Rose bengal is the photosensitizer. 

Petroleum-derived fuels can be autooxidized in a similar fashion. Since some refined fractions, such as No. 2 fuel oil, are often rich in two- and three-ring condensed aromatic compounds that strongly absorb light, the possibility of sensitized processes involving singlet oxygen or electron transfer intermediates is quite likely in these materials (Larson et al. 1977, 1979 Lichtenthaler et al., 1989). In addition, readily oxidized compounds such as tetrahydronaphthalenes and indans... 

The mechanism of photooxidation of petroleum probably includes significant contributions from both radical and singlet oxygen pathways. Petroleum contains polycyclic aromatic hydrocarbons and other compounds with known photosensitizing activity Lichtenthaler et al. (1989) demonstrated quantum yields for O2 formation ranging from 0.5 to 0.8 for a number of crude oils. The photooxidation of a 2 fuel oil was inhibited by /3-carotene, an excellent quencher of O2 and free radicals, at concentrations > lO" M (Larson and Hunt, 1978). A mechanism incorporating... 

Figure 6.9. Proposed mechanism, incorporating singlet oxygen and radical steps, for the photodecomposition of a refined petroleum containing alkylbenzenes, indenes, and tetrahydronaphthalenes. From Larson et al. (1979). Reprinted by permission. Copyright 1979 American Chemical Society.

Larson, R. A. and L. L. Hunt. 1978. Photooxidation of a refined petroleum oil inhibition by 8-carotene and role of singlet oxygen. Photochem. Photobiol. 28, 553-555. 

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