Abstract
A method for determining cis-trans isomers in dimethyl di (9-octadecenyl) ammonium chloride was devised based on NMR spectrometry. Chemical shift of the vinyl carbon of cis-9-octadecenoic acid was noted at around 130 ppm, this being essentially the same as that of trans-9-octadecenoic acid. However, chemical shifts of methylene carbons adjacent to the double bond differed between the two isomers. The ratio of signal intensities of isomers in standard mixtures agreed well with isomer content. The cis-trans ratio of dimethyl di (9-octadecenyl) ammonium chloride was determined by the same procedure. The ratio and degree of unsaturation were determined in the starting oleic acid, the intermediate octadecennitrile, dioctadecenylamine, methyl dioctadecenylamine, and finally obtained quaternary salts. Considerable increase in the trans isomer and decrease in unsaturation were observed during the conversion of the nitrile into dioctadecenylamine. Reductive reaction is thus not completely selective to the nitrile group; that is the double bound of the alkenyl group is partially hydrogenated.
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