Preparation of pure fatty acid methyl esters by countercurrent distribution

Summary Acetonitrile‐pentane‐hexane makes a desirable solvent system for preparation of pure methyl esters because of its immiscibility, selectivity toward unsaturation, low boiling point, stability, and ease of recovery. Since separated esters are removed from the apparatus dissolved in the pentane‐hexane layer, successive batches may be fractionated without removing the acetonitrile layer from the instrument. Applications have been illustrated for the preparation of methyl linolenate from an 85% linolenate concentrate, methyl linoleate from safflower esters, and methyl arachidonate from pig liver lipids. This procedure provides a source of “natural” fatty acids with the double bond configuration unchanged, in contrast to those from the conventional bromination‐debromination process. Automation of the process is completed by use of a recording refractometer which monitors concentration of solutions issuing from the extractor. Resolutions to be anticipated with lesser numbers of extraction tubes than 200 are calculated for an equal mixture of linoleate and linolenate.