Model experiments about the formation of volatile carbonyl compounds

Autoxidation of linoleic acid, 9-hydroperoxy-10, 12-octadecadienoic acid (9-HPOD), 13-hydroperoxy-9, 11-octadecadienoic acid (13-HPOD), 2-octenal and 2,4-decadienal at 38 C were investigated with respect to the formation of volatile carbonyl compounds. The 13-HPOD and all compounds having a double bond in ω-6-position produce hexanal. After initiating by small amounts of alkoxy radicals, both hexanal and 2,4-decadienal autoxideize further. While, individually, hexanal reacts somewhat faster than 2,4-decadienal, forming the corresponding acid, in a mixture of the two aldehydes, hexanal is protected to a certain extent by the unsaturated aldehyde against autoxidation. This explains the predominance of hexanal among the volatile carbonyl compounds resulting from linoleic acid autoxidation. Small amounts of 2-octenal originate from both the 9-HPOD and the 2,4-decadienal as a result of oxidation of the ω-8-double bond of these compounds. Aside from its acid as main autoxidation product, 2-octenal yields heptanal and hexanal as volatile compounds.