The Handbook of Soap Manufacture | Page 8

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--
C{18}H{34}O{2} + 2KOH = KC{2}H{3}O{2} + KC{16}H{31}O{2} + H{2},
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.
The lead salts of the acids of this series are much more soluble in ether, and the lithium salts more soluble in alcohol than those of the stearic series, upon both of which properties processes have been based for the separation of the solid from the liquid fatty acids.
III. Linolic Series:--
-------------------------------------------------------------------------- Acid. | Formula. | Melting | Found in | | Point, | | | °C. | -------------------------------------------------------------------------- El?omargaric | C{16}H{29}COOH | ... | Chinese-wood oil. -------------------------------------------------------------------------- El?ostearic | C{16}H{29}COOH | 71 | Chinese-wood oil. -------------------------------------------------------------------------- Linolic | C{17}H{31}COOH | Fluid | Linseed, cotton-seed and | | | maize oils. -------------------------------------------------------------------------- Tariric | C{17}H{31}COOH | 50.5 | Tariri-seed oil. -------------------------------------------------------------------------- Telfairic | C{17}H{31}COOH | Fluid | Telfairia oil. --------------------------------------------------------------------------
These acids readily combine with bromine, iodine, or oxygen. They are unaffected by nitrous acid, and their lead salts are soluble in ether.
IV. Linolenic Series:--
-------------------------------------------------------------------- Acid. | Formula. | Found in -------------------------------------------------------------------- Linolenic | C{17}H{29}COOH | Linseed oil. -------------------------------------------------------------------- Isolinolenic | C{17}H{29}COOH | Linseed oil. -------------------------------------------------------------------- Jecoric | C{17}H{29}COOH | Cod-liver and marine animal oils. --------------------------------------------------------------------
These acids are similar in properties to those of Class III., but combine with six atoms of bromine or iodine, whereas the latter combine with only four atoms.
V. Ricinoleic Series:--
----------------------------------------------------------- | | | | | | Acid. | Formula. | Melting | Found in | | | | Point, | | | | | °C. | | |------------|----------------------|---------|-------------| | | | | | | Ricinoleic | C{17}H{22}(OH)COOH | 4-5 | Castor oil. | -----------------------------------------------------------
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 [alpha]{d} +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)--
C{3}H{5}(OR) + 3NaOH = C{3}H{5}(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.) C{3}H{5} | OR + NaOH = C{3}H{5} | OR + RONa |OR |OR | OH | OH (ii.) C{3}H{5} | OR + NaOH = C{3}H{5} | OR + RONa |OR |OH | OH | OH (iii.) C{3}H{5} | OR + NaOH = C{3}H{5} | 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