Trans-9,cis-11-octadecadienoic acid is produced by forming a urea inclusion complex with cis-linoleic acid, treating the complex with a catalytic amount of a base, and recovering the trans-9,cis-11 octadecadienoic acid. Tans-10,cis-12-octadecadienoic acid is produced by iodinating cis-linoleic acid at temperatures of about −5–20° C. A mixture of trans-9,cis-11 octadecadienoic acid and trans-10,cis-12-octadecadienoic acid comprising is produced by iodinating cis-linoleic acid at temperatures ranging from about 50 to about 90° C.