Conversion of oleic acid to monocarboxylic acids and y-lactones by laboratory heating experiments in relation to organic diagenesis

Abstract

Oleic acid (cis-9-octadecenoic acid) was converted to monocarboxylic acids and y- and S-lactones by heating at 200°C under free oxygen. The monocarboxylic acids showed a C9acid predominance in the presence of Na-montmorillonite in contrast to a C8acid predominance in the absence of the clay. The y-lactones showed a C6 lactone predominance in the former case and C4 and C8lactone 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 C8 lactone by thermal oxidation. The molecular distribution patterns of the monocarboxylic acids and the y-Iactones in the range of C4to C12produced by the heating in the presence of the clay resemble those found in the Neogene Shin jo sediments. Therefore, unsaturated monocarboxylic acids with a C-C double bond at C9 were probably important precursors of the monocarboxylic acids and the y-lactones found in the sediments. © 1993, GEOCHEMICAL SOCIETY OF JAPAN. All rights reserved.