On methylation of unsaturated acids using boron trihalide–methanol reagents

Methanolysis of unsaturated fatty acids and triglycerides was carried out with boron trihalide-methanol reagents of various ages. Boron trichloride-methanol produced esters apparently free from contaminants; boron trifluoride caused some loss of highly unsaturated esters after 90 min at 100 or 120 degrees C in Teflon-lined screw-cap vials and at 120 degrees C in ampoules. The losses were more marked when the reactions were carried out in vinyl-lined screw-cap vials. Noticeable losses did not occur with any of the vessel types when BCl(3)-CH(3)OH was the methylating agent. Long-term studies at 80 degrees C further demonstrated that BCl(3)-CH(3)OH caused less loss of unsaturated acid than did BF(3)-CH(3)OH.