Composition of castor oil by optical activity

Summary The optical activity of castor oil and its derivatives has been studied. Pure methyl ricinoleate and methyl acetyl ricinoleate were prepared. The mixed methyl esters and acetylated methyl esters of castor oil were also prepared. By the determination of specific rotation of the pure and technical esters, the percentage of ricinoleate fraction can be deduced. This was calculated to be 93% and 90%, respectively. The esters of castor oil were calculated to contain 91.6% ricinoleate from the chemical hydroxyl value. This was about the average of the two values obtained optically and is believed close to the actual value. A number of castor oils were analyzed by both optical and chemical methods and found to be of nearly constant ricinoleic content. Dehydrated castor oil was found to have a comparative high specific rotation. This was believed due to its estolide content formed during dehydration.