Synthesis and physical properties of some 2,3- and 2,2′-epithio C 18 fatty acid derivatives

Abstract

Methyl oleate, linoleate, ricinoleate and derivatives of ricinoleate were converted to the corresponding 2,3-epoxy fatty esters and subsequently transformed to their 2,3-epithio derivatives by treatment with dimethylthioformamide. 2,2′-Epoxy fatty esters gave 2,2′-epithio derivatives by similar reation. All epithio derivatives were readily purified by silica chromatography, but most decomposed during GLC analysis and were found to polymerise even when stored at 0°C under nitrogen. In the 1H-NMR spectral analysis, the chemical shift signal for the protons of the 2,3-epithio system appeared at 2.8–3.2δ (multiplet) and for the 2,2′-epithio system at 2.32δ (singlet). The 13C-NMR results of these derivatives were much more informative. The methine carbon nuclei of the 2,3-epithio system were shifted to 41.88 ppm, and in the 2,2′-epithio derivatives the methylene and quarternary carbon nuclei of the three-membered sulfur ring system appeared at 33.64 and 50.38 ppm, respectivelty. Neighbouring group effects on the chemical shifts of carbon nuclei of the epithio system by other functional groups were significant. During the chemical transformation of methyl 9,10-epoxy-12-oxostearate to 9,10-epithio-12-oxostearate, two heteroaromatic by-products (viz. C 18 furanoid and thiopene fatty esters) were also obtained