Abstract
Conjugated methyl cis, trans-and trans, trans-octadecadienoates were autoxidized in the conditions free from natural antioxidants and metals. The autoxidation of conjugated cis, trans-and trans, trans-isomers gave the induction period of 17 and 27h, and showed the oxidative weight increase rate 0.661 and 0.615mg/h at the autoxidation level after the induction period (specified as the time required to gain 10mg by weight). In comparison with methyl linoleate, the autoxidation of conjugated isomers gave the shorter induction period, but showed the lower oxidative weight increase rate. Results from analyses of the various autoxidation products from the conjugated isomers showed that the products from cis, trans-isomer were formed in a shorter interval of autoxidation in comparison with those from trans, trans-isomer, but the amount of products from the former was almost the same to that from the latter if the products were compared at the same autoxidation level (oxidative weight gains). Differences on the autoxidation products from conjugated isomers, such as conjugated dienes, radicals, isolated trans double bonds and etc, showed that the large parts of the conjugated isomers were autoxidized by the addition of oxygen molecules to olefinic double donbs. It was concluded that the different rates of the autoxidation between conjugated cis, trans-and trans, trans-isomers resulted from the geometric isomeric effect of olefinic double bonds upon the addition of oxygen molecules.
