C 18 ‐saturated cyclic acids from linseed oil: A structural study

The preparation of C 18 ‐saturated cyclic acids from linseed oil by heat treatment in the presence of alkali, followed by hydrogenation and subsequent isolation of the cyclic fraction, gives rise to a series of at least 11 isomers as evidenced by GLC. Eight of these isomers have now been shown to be geometric pairs of positional isomers with the following general formula: {fx244–1} An unequivocal synthesis of isomers (x=0,1,2 and 3) indicates that the principal positional isomer (ca. 55%) of HCal is 9‐(2′‐ n ‐propylcyclohexyl)‐nonanoic acid. This isomer undoubtedly results from the cyclization of 10,12,14‐octadecatrienoic acid present in the isomerized mixture. The predominance of this isomer is further substantiated by mass spectral analysis. The four positional isomers prepared constitute about 80% of the mixture as determined by gas‐liquid chromatography. The four synthetic aromatic positional isomers show single peaks whereas their hydrogenated counterparts show two peaks. Thus each of the positional isomers of saturated cyclic acids is composed of two geometric isomers.