II. Oleic Series:—

Acid. Formula. Melting Point, °C. Found in
Tiglic C4H7COOH 64.5 Croton oil.
Moringic C14H27COOH 0 Ben oil.
Physetoleic C15H29COOH 30 Sperm oil.
Hypogæic C15H29COOH 33 Arachis and maize oils.
Oleic C17H33COOH 14 Most oils and fats.
Rapic C17H33COOH ... Rape oil.
Doeglic C18H35COOH ... Bottle-nose oil.
Erucic C21H41COOH34Mustard oils, marine animal oils, rape oil.

The unsaturated nature of these acids renders their behaviour with various reagents entirely different from that of the preceding series. Thus, they readily combine with bromine or iodine to form addition compounds, and the lower members of the series are at once reduced, on treatment with sodium amalgam in alkaline solution, to the corresponding saturated acids of Series I. Unfortunately, this reaction does not apply to the higher acids such as oleic acid, but as the conversion of the latter into solid acids is a matter of some technical importance from the point of view of the candle-maker, a number of attempts have been made to effect this by other methods.

De Wilde and Reychler have shown that by heating oleic acid with 1 per cent. of iodine in autoclaves up to 270°-280° C., about 70 per cent. is converted into stearic acid, and Zürer has devised (German Patent 62,407) a process whereby the oleic acid is first converted by the action of chlorine into the dichloride, which is then reduced with nascent hydrogen. More recently Norman has secured a patent (English Patent 1,515, 1903) for the conversion of unsaturated fatty acids of Series II. into the saturated compounds of Series I., by reduction with hydrogen or water-gas in the presence of finely divided nickel, cobalt or iron. It is claimed that by this method oleic acid is completely transformed into stearic acid, and that the melting point of tallow fatty acids is raised thereby about 12° C.

Another method which has been proposed is to run the liquid olein over a series of electrically charged plates, which effects its reduction to stearin.

Stearic acid is also formed by treating oleic acid with fuming hydriodic acid in the presence of phosphorus, while other solid acids are obtained by the action of sulphuric acid or zinc chloride on oleic acid.

Acids of Series II. may also be converted into saturated acids by heating to 300°C. with solid caustic potash, which decomposes them into acids of the stearic series with liberation of hydrogen. This reaction, with oleic acid, for example, is generally represented by the equation—

C18H34O2 + 2KOH = KC2H3O2 + KC16H31O2 + H2,

though it must be really more complex than this indicates, for, as Edmed has pointed out, oxalic acid is also formed in considerable quantity. The process on a commercial scale has now been abandoned.

One of the most important properties of this group of acids is the formation of isomeric acids of higher melting point on treatment with nitrous acid, generally termed the elaidin reaction. Oleic acid, for example, acted upon by nitrous acid, yields elaidic acid, melting at 45°, and erucic acid gives brassic acid, melting at 60°C. This reaction also occurs with the neutral glycerides of these acids, olein being converted into elaidin, which melts at 32°C.