CONVERSION OF OLEIC-ACID TO MONOCARBOXYLIC ACIDS AND GAMMA-LACTONES BY LABORATORY HEATING EXPERIMENTS IN RELATION TO ORGANIC DIAGENESIS

Oleic acid (cis-9-octadecenoic acid) was converted to monocarboxylic a cids and gamma- and delta-lactones by heating at 200 degrees C under f ree oxygen. The monocarboxylic acids showed a C-9 acid predominance in the presence of Na-montmorillonite in contrast to a C-8 acid predomin ance in the absence of the clay. The gamma-lactones showed a C-6 lacto ne predominance in the former case and C-4 and C-8 lactone predominanc es in the latter case. Accordingly, it was postulated that the catalyt ic cracking of oleic acid in the presence of the clay produced mainly the C-9 acid that, in turn, generated the C-6 lactone by thermal oxida tion. The molecular distribution patterns of the monocarboxylic acids and the gamma-lactones in the range of C-4 to C-12 produced by the hea ting in the presence of the clay resemble those found in the Neogene S hinjo sediments. Therefore, unsaturated monocarboxylic acids with a C- C double bond at C-9 were probably important precursors of the monocar boxylic acids and the gamma-lactones found in the sediments.