RAPID PREPARATION OF FATTY-ACID METHYL-ESTERS USING ORGANIC BASE-CATALYZED TRANS-ESTERIFICATION

Methyl esters are still the most popular derivative for the gas chromatography (GC) of fatty acids. When analyzing triglycerides and other liquids for fatty acid composition, methyl esters usually are made by a saponification-acidic methanolysis technique. Transesterification with sodium methoxide also is used often for preparing methyl esters. However, there are some drawbacks to both these procedures, i.e., the saponification-esterification method requires an extraction step which can be troublesome, and the sodium methoxide transesterification technique does not convert any free fatty acids present to esters. A technique was developed which overcomes these disadvantages. Tetramethylammonium hydroxide in methanol (TMAH) is used to catalyze the transesterification of the fat [salad oil, coconut oil, tallow, butter, human ear wax] dissolved in diethyl ether, and methyl esters form almost instantly. Glycerine drops out of solution to form a 2nd layer containing the bulk of any free fatty acids present as their TMAH soaps. GC of the ether layer gives the fatty acid composition of the glycerides. On injecting the lower layer, the TMAH soaps pyrolyze to form methyl esters. If methanol is added to the flask to solubilize the glycerine and excess base neutralized with methanolic HCl, total fatty acid composition can be obtained by chromatographing the resulting solution.