ABSTRACT

Oleic acid (cis-9-octadecenoic acid) was converted to monocarboxylic acids and γ- and δ-lactones by heating at 200°C under free oxygen. The monocarboxylic acids showed a C₉ acid predominance in the presence of Na-montmorillonite in contrast to a C₈ acid predominance in the absence of the clay. The γ-lactones showed a C₆ lactone predominance in the former case and C₄ and C₈ lactone predominances in the latter case. Accordingly, it was postulated that the catalytic cracking of oleic acid in the presence of the clay produced mainly the C₉ acid that, in turn, generated the C₆ lactone by thermal oxidation. The molecular distribution patterns of the monocarboxylic acids and the γ-lactones in the range of C₄ to C₁₂ produced by the heating in the presence of the clay resemble those found in the Neogene Shinjo sediments. Therefore, unsaturated monocarboxylic acids with a C-C double bond at C₉ were probably important precursors of the monocarboxylic acids and the γ-lactones found in the sediments.