Abstract
It was known that unsaturated fatty acids were very sensitive to oxygen, but little studies on the thermal isomerization were made. We investigated the effect of thermal change of methyl-linoleate.
The isomerization was conducted by passing nitrogen containing 1, 5 and 10 vol% of oxygen into pure cis methyl-linoleate at the rate of 3l/hr at 100 and 200°C. The obtained results are summarized as follows :
1) In the presence of oxygen, cis methyl-linoleate isomerizes rapidly, even at low temperature, to trans-trans conjugated or trans non-conjugated one.
2) The increase of oxygen content is only effective to increase the speed of isomerization.
3) At the first stage of isomerization, the yield of trans-trans conjugated isomer is almost independent of the oxygen content. This can be explained by the assumption that oxygen is consumed by the polymerization or oxidation reactions (such as to -OH, -OOH or = CO).
4) The formation of trans-trans conjugated isomer reaches to the equilibrium concentration of about 12%. This may due to either the polymerization of the resulting conjugated isomer, or its isomerization to the thermal stable trans non-conjugated isomer.
5) Although Lundberg reported the formation of cis-trans conjugated isomer in the oxidation of methyl-linoleate, only trans-trans isomer was found in our experiment.
