In the previous paper, we reported the optimum conditions for the iodine-sensitized conjugation of methyl linoleate and its reaction mechanism.
This paper discusses isomerization arising from irradiation with a 100W high-pressure mercury lamp using methyl linolenate with a 1, 4, 7-triene structure. Conjugated diene-trienoates and small amounts of conjugated trienoates are formed in this reaction. Slightly milder conditions than in methyl linoleate are suitable for the formation of conjugated diene-trienoates. The reaction conducted at room temperature using a sample with a concentration of 10 to 20% adding approximately 0.1% of iodine to a nonpolar solvent such as petroleum ether by irradiation for 46h is considered optimum. To obtain conjugated trienoates mainly, however, milder conditions such as no more than 0.03% iodine should be used. Under such conditions, the amounts of conjugated compounds were as much as about 70% (conjugated diene-trienoates 5562%; conjugated trienoates 815%) of the reaction products.
This sensitized isomerization proceeds in the same way as indicated in the previous report and double bonds shift only in the direction of the conjugation.