68 



II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



Although data are not available for the solubility of linoleic acid at a 

 temperature above — 50°C,, or for oleic acid above — 30°C., it is evident 

 that these acids are rapidly approaching infinite solubility. The solubility 

 of the common fatty acids is thus shown to be influenced first by the de- 

 gree of unsaturation, while the length of the carbon chain plays a secondary 

 role. This finding is in line with the corresponding effects on the melting 

 point. With monoethenoid acids the solubility is inversely proportional 



+ 10 -10 -20 -30 -40 -50 -60 "70 

 TEMPERATURE 'C 



Fig. 9. Solubilities of fatty acids in acetone. 22* 



to the chain length, as illustrated by the progressively lower rate of solu- 

 bility of oleic (Cis), eicosenoic (C20), and erucic (C22) acids in methanol 

 (Figure 8). 



d. Effect of Substitution on the Solubility of Fatty Acids, (a) Soluhilihj 

 of Hydroxy- Acids. In the case of the fatty acids, the solubility may be 

 markedly altered by the introduction of hydroxyl groups into the mole- 

 cule. Such hydroxy-acids dissolve in water to a greater degree than do 

 the unsubstituted acids. On the other hand, they may become entirely 

 insoluble in petroleum ether; in fact, their solubility may even be de- 

 pressed in such an excellent solvent as ethanol. Octahydroxyarachidic 

 acid is readily soluble in water, hexahydroxystearic acid somewhat less so, 

 while tetrahydroxystearic acid dissolves only to the extent of 50 milligram 

 per cent in boiling water. ^® 



(6) Solubility of Bromo-Acids. Since bromine dissolved in chloroform 

 or diethyl ether adds itself to most of the unsaturated fatty acids, even in 

 the cold state, one has an excellent method for the characterization of un- 



