The geometric isomers of conjugated octadecadienoates from dehydrated methyl ricinoleate

The dehydration of methyl ricinoleate by heating in vacuo in the presence of KHSO 4 resulted in the formation of the following conjugated octadecadienoates expressed as a percentage of the final product: cis, trans (trans, cis) , 14.3; cis, cis, 11.2; trans, trans, 7.3. The isomers contained the double bonds predominantly in the 9,11 position but the possible presence of traces of 8,10 and other conjugated isomers is not excluded. Using urea 舠inclusion舡 fractionation and low temp crystallization from acetone methyl, cis ‐9, cis ‐11‐octadecadienoate was isolated. The methyl esters of commercially dehydrated castor oil fatty acids on the other hand, contained the following percentages of conjugated octadecadienoate isomers: cis, trans (trans, cis), 20.3; cis, cis, 8.0; trans, trans, 5.4. From these mixtures conc of cis, trans (trans, cis) ‐ and trans, trans ‐octadecadienoates were prepared by fractional distillation and low temp crystallization. It was found that the conjugated octadecadienoates consisted of mixtures of positional isomers with double bonds mainly in the 8,10 and 9,11 positions with lesser amounts in the 7,9 and 10,12 positions.