Recovery of gossypol acetic acid from cottonseed soapstock

Abstract Gossypol is a yellow pigment found in the cotton plant and is of scientific and medical interest because of its anti-tumor, anti-fertility, and anti-viral properties. In order to support additional studies into the medicinal activity of gossypol, methods are needed to isolate large quantities of the compound in high purity. A process is described to recover gossypol from cottonseed soapstock, a low-value co-product of crude oil refining that can contain concentrations of gossypol as high as 8%. Soapstock is refluxed in acidic methyl ethyl ketone (MEK) to hydrolyze covalently bound gossypol. Upon cooling, the mixture separates into organic and aqueous phases with the gossypol distributing between the two phases. The MEK phase is recovered, and the aqueous phase is re-extracted with additional volumes of MEK. After combining and concentrating the MEK extracts, acetic acid is added to induce gossypol crystallization, which precipitates as an equimolar crystalline complex with acetic acid (gossypol acetic acid). From a soapstock sample containing 3.7% gossypol, 63% of the gossypol was recovered as an 87% gossypol acetic acid product. A single re-crystallization of this crude material yielded a 99% gossypol acetic acid product with an overall recovery of 58%. With different soapstock samples, the yield of crude product was positively correlated with the initial gossypol concentration in the soapstock. Recovery, however, was not well correlated with soapstock gossypol concentration, possibly due to the co-extraction of other components that influence the solubility of gossypol in the crystallization solution.