Experimental Investigation Of Conjugation Reaction Of Linoleic Acid

Conjugated linoleic acid (CLA), which is naturally and minimally existed in multipleanimal fats and vegetable oils, is a group of positional and geometrical isomers of conjugatedoctadecadienoic acid. The main isomers of CLA are―c9, t11‖and―t10, c12‖, which havebeneficial physiological functions. As is shown to inhibit carcinogenesis and atherosclerosis,lower cholesterol levels, participate in fat metabolism and enhance immune function, CLA hasbeen widely applied in food, pharmaceutical, health care, cosmetics and many other fields.Therefore, the synthesis of CLA has attracted more and more attention nowadays. To prepareCLA from natural unsaturated fatty acids have been the main methods, including dehydrationof ricinoleic acid in castor oil, alkali or metal-catalyzed isomerization of linoleic acid (LA),enzymatic-catalyzed transformation and microbial fermentation. But all of these methodshave some shortcomings, such as too many synthesis steps, the expensive price of regents,poor selectivity and low yield. However, alkali isomerization is the most impressing methodbecause of its simple synthesis process, low-cost regents and high yield.In traditional alkali isomerization method, LA would combine with alkali and transforminto fatty acid soap, which would expend lots of alkali, and enhance the saponification. Andthe dosages of solvent were also need to increase to insure the mass-transfer of the system.The process of acidification after isomerization as well needed more acid. This paper wasstarting from this point. Some methods to prepare CLA were compared with each other fromnatural safflower seed oil which enriched LA, such as traditional one-pot method, methanolpre-esterification method, glycol pre-esterification method and improved esterification-isomerization step by step in one-pot synthesis. It hopes to control the synthesis reaction ofCLA and reduce the dosages of alkali and solvent, which expected to obtain a simple andeconomic method to prepare CLA.On the other hand, the acid isomerization of LA to prepare CLA was also a focus in thispaper, which could solve the saponification from the source. And the investigation ofconjugation of double bones in LA would be studied in little or no solvent, which would bepractical of the synthesis process from natural LA modified prepare CLA.In this paper, the main results and conlusions are as follows:(1) High content LA was prepared through saponified from natural safflower seed oil toremove unsaponifiable matters, and enriched by urea adducted fractionation with m(mixedfatty acids): m(urea): V(solvent)=1:2.5:8. The content of LA, which resulted in98.2%, wasfurther obtained through GC.(2) The alkali isomerization of CLA was prepared by LA with NaOH as alkali andethylene glycol (EG) as solvent. The products of these methods were characterized by IR andGC for qualitative and quantitative analysis. The results showed that improved esterification-isomerization step by step in one-pot synthesis was an economic and suitable route for alkaliisomerization to prepare CLA. Compared with traditional one-pot methods, it could reducethe dosages of alkali and solvent. Compared with methanol pre-esterification method, it didn’tbring in new materials and decreased the process of esterification. Compared with glycol pre-esterification method, it could not only simplified the esterification, but also furtherreduce the dosages of alkali and solvent. The optimal condition of esterification was n(LA):n(EG)=1:1.5with NaOH as catalyst, which quality dosage was0.5%of LA, at170oC for4h. The conversion of LA was91.2%. And under the isomerization condition: m(NaOH):m(LA): V(EG)=1:5:7.5,170oC,4h, the yield of CLA was90.0%and the ratio of twobeneficial physiological isomers of CLA was82.4%.(3) Compared with alkali isomerization, acid isomerization could be taken underfree-solvent system, which could not only save production cost, but also simplified theproduction process since it skipped the step of acidification. The acid isomerization of CLAwas prepared by LA with different acid catalysts. The feasibility of acid isomerization wouldbe explored and the products were characterized by UV for qualitative and quantitativeanalysis. The results showed that through the perpendicular experiment, the optimal conditionof acid isomerization was H3PO4as catalyst, which quality dosage was15%of LA, at150oCfor2h. The verify experiment showed the content of CLA in product was42.9%.