This acid combines with two atoms of bromine or iodine, and is converted by nitrous acid into the isomeric ricinelaidic acid, which melts at 52°-53° C. Pure ricinoleic acid, obtained from castor oil, is optically active, its rotation being αd +6° 25'.
Hydrolysis or Saponification of Oils and Fats.—The decomposition of a triglyceride, brought about by caustic alkalies in the formation of soap, though generally represented by the equation already given (pp. 6 and 7)—
C3H5(OR) + 3NaOH = C3H5(OH)3 + 3RONa,
is not by any means such a simple reaction.
In the first place, though in this equation no water appears, the presence of the latter is found to be indispensable for saponification to take place; in fact, the water must be regarded as actually decomposing the oil or fat, caustic soda or potash merely acting as a catalytic agent. Further, since in the glycerides there are three acid radicles to be separated from glycerol, their saponification can be supposed to take place in three successive stages, which are the converse of the formation of mono- and diglycerides in the synthesis of triglycerides from fatty acids and glycerine. Thus, the above equation may be regarded as a summary of the following three:—
| { | OR | { | OH | ||
| (i.) | C3H5 | { | OR + NaOH = C3H5 | { | OR + RONa |
| { | OR | { | OR |
| { | OH | { | OH | ||
| (ii.) | C3H5 | { | OR + NaOH = C3H5 | { | OR + RONa |
| { | OR | { | OH |
| { | OH | { | OH | ||
| (iii.) | C3H5 | { | OR + NaOH = C3H5 | { | OH + RONa |
| { | OH | { | OH |
Geitel and Lewkowitsch, who have studied this question from the physical and chemical point of view respectively, are of opinion that when an oil or fat is saponified, these three reactions do actually occur side by side, the soap-pan containing at the same time unsaponified triglyceride, diglyceride, monoglyceride, glycerol and soap.
This theory is not accepted, however, by all investigators. Balbiano and Marcusson doubt the validity of Lewkowitsch's conclusions, and Fanto, experimenting on the saponification of olive oil with caustic potash, is unable to detect the intermediate formation of any mono- or diglyceride, and concludes that in homogeneous solution the saponification is practically quadrimolecular. Kreeman, on the other hand, from physico-chemical data, supports the view of Geitel and Lewkowitsch that saponification is bimolecular, and though the evidence seems to favour this theory, the matter cannot be regarded as yet definitely settled.