The branched-chain fatty acids of butterfat. I. The isolation from butterfat of branched-chain fatty acids with special reference to the C17 acids.

Although branched-chain saturated fatty acids have been found in the lipids of certain bacteria as well as in wool wax, they have not hitherto been reported as existing in natural glycerides, with the solitary exception of i8ovaleric acid found by Chevreul in 1817 (cf. Hilditch, 1947) in the head and jaw oil of the dolphin. Recently, Hansen & Shorland (1950) observed that the methyl ester concentrates of C18 unsaturated acids of butterfat when oxidized with finely ground potassium permanganate in acetone solution (Armstrong & Hilditch, 1925) yielded a residual neutral saturated product which was liquid at room temperature. Concentrates of other Cl. unsaturated acids, such as those from pig fat, had been found to yield a solid neutral product corresponding to methyl stearate. Further purification of this liquid neutral product from butterfat was effected by recrystallization from acetone at 300 followed by fractionation in an electrically heated column packed with glass helices (cf. Longenecker, 1937). A combustion analysis of one of the fractions suggested the presence of a C19 branched-chain acid contaminated with traces of oxygenated acids (cf. Hansen & Shorland, 1950). Subsequent to this preliminary investigation it was found that the suspected branched-chain constituents could be separated by hydrogenation of the methyl esters of the unsaturated acids and subsequent crystallization from acetone at 300, under which conditions the methyl esters of the branchedchain acids remained in solution. The purpose of this paper is, first, to describe the general technique employed in the isolation from butterfat of two isomeric C17 branched-chain fatty acids; and, secondly, to record their properties.