Homolytic Decomposition of Linoleic Acid Hydroperoxide: Identification of Fatty Acid Products1

An isomeric mixture of linoleic acid hydro peroxides, 13-hydroperoxy-cis9 trans-II-octadecadienoic acid (79%) a~d 9-hydroperoxy-eis-12,trans-IO-octadecadienoic acid (21 %), was decomposed homolytically by Fe(I!) in an ethanolwater solution. In one series of experiments, the hydroperoxides were decomposed by catalytic concentrations of Fe (II). The 10.5 M Fe(III) used to initiate the decomposition was kept reduced as Fe(I!) by a high concentration of cysteine added to the reaction in molar excess of the hydroperoxides. Nine different monomeric (no detectable dimeric) fatty acids were identified from the reaction. Analyses of these fatty acids revealed that they were mixtures of positional isomers identified as follows: (1) 13-oxo-trans,trans(and cis,trans-) 9,1 I-octadecadienoic and 9-oxo-trans,trans(and cis,trans-) 10,12octadecadienoic acids; (II) 13-oxo-trans9,10-epoxy-trans-ll-octadecenoic and 9-oxo-trans12, 13 -epoxy -trans -1 O-octadecenoic acids; (III) 13-oxo-cis-9,10epoxy-trans-Il-octadecenoic and 9-oxocis-l 2,1 3-epoxy-trans-IO-octadecenoic acids; (IV) 13-hydroxy-9,11-octadecadienoic and 9-hydroxy-1 0, 12-octadecadienoic acids; (V) ll-hydroxy-trans12,13-epoxy-cis-9-octadecenoic and 1 l-hydroxy-trans-9, 10-epoxY-cis-12-octadecenoic acids; (VI) ll-hydroxy-trans12,1 3-e p 0 xy-trans-9-octadecenoic and II-hydroxy-trans-9,10-epoxy-trans-12octadecenoic acids; (VII) 13-oxo-9-hydroxy-trans-IO-octadecenoic and 9-oxo13-hydroxy-trans-II-octadecenoic acids; (VIII) isomeric mixtures of 9,12, 13-dihyd roxyethoxy-trans-l o-octadecenoic and 9,10,1 3-dihydroxyethoxy-trans-Il-octadecenoic acids; and (IX) 9,12,13-trihydroxy-trans-IO-octadecenoic and 9 ,1 0, 13-trihydroxy-trans-II-octadecenoic acids. In another experiment, equimolar amounts of Fe(II) and hydroperoxide 1Presented in part at the American Chemical Society Meeting, Los Angeles, March 1974. 2ARS, USDA. were reacted in the absence of cysteine. A large proportion of dimeric fatty acids and a smaller amount of monomeric fatty acids resulted. The monomeric fatty acids were examined by gas liquid chromatography-mass spectroscopy. Spectra indicated that the monomers were largely similar to those produced by the Fe(III)cysteine reaction.