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Participation of singlet oxygen in photosensitized oxidation of 1,4‐dienoic systems and photooxidation of soybean oil
Author(s) -
Clements A. H.,
Van Den Engh R. H.,
Frost D. J.,
Hoogenhout K.,
Nooi J. R.
Publication year - 1973
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02641366
Subject(s) - autoxidation , singlet oxygen , chemistry , photochemistry , isomerization , singlet state , oxygen , soybean oil , diene , organic chemistry , catalysis , excited state , physics , nuclear physics , natural rubber , food science
Sensitized photooxidation of a model 1,4‐diene, 4 cis , 7 cis ‐undecadiene, was shown to yield 4‐hydroperoxy‐5 trans ,7 cis ‐undecadiene and 5‐hydroperoxy‐3 trans ,7 cis ‐undecadiene as initial products. Further irradiation (in the presence of the sensitizer) caused the isomerization of 4‐hydroperoxy‐5 trans ,7 cis ‐undecadiene to 4‐hydroperoxy‐5 trans ,7 trans ‐undecadiene. Oxidation of 4 cis ,7 cis ‐undecadiene with chemically formed singlet oxygen gave the same initial products as the photosensitized oxidation. 5‐Hydroperoxy‐3 trans ,7 cis ‐undecadiene is, however, not formed in the radical autoxidation of the diene. It is concluded that singlet oxygen is the reactive intermediate in the photooxidation. Comparison with this model reaction suggests that the photooxidation of refined soybean oil in propanol also proceeds via singlet oxygen: the photooxidations of both 4,7‐undecadiene and soybean oil are inhibited by β‐carotene and by triethylamine, but unlike radical chain autoxidation, they are not inhibited by 2,6‐di‐ t ‐butyl‐4‐methylphenol. Also soybean oil can act as a sensitizer for the photooxidation of 4,7‐undecadiene. Chlorophyl‐like sensitizers are probably unimportant in the well refined soybean oil used in this work. The observed photooxidation of the skipped dienoic components of soybean oil, which is probably due to some other, unidentified sensitizer(s), absorbing below 500 nm, can be avoided by using a yellow filter.