PHYSICAL PROPERTIES OF FATTY ACIDS 63 



similar data for a large numl)er of other soh'ents which were studied ; these 

 include acetone, 2-butanone, and glacial acetic acid.^^" In a later publica- 

 tion,-'-- the results were extended to nitromethane, methanol, trichloro- 

 methane, tetrachloromethane, /i-butanol, butyl acetate, ethyl acetate, 

 nitroethane, and acetonitrile. Most recentl,y, Hoerr, Sedgwick, and 

 Ralston--' have added to their studies results on the solubilities of satu- 

 rated acids in chlorobenzene, 1,2-dichloroethane, 1,4-dioxane, furfural, 

 nitrobenzene, toluene, and o-xylene. The reader is referred to the original 

 papers for the specific data. The comparative solubilities of the acids in 

 all of the different solvents at 20° and 60°C. are summarized in Tables 26 

 and 27. 



The most impressive fact that stands out from an examination of the 

 data in Tables 23 to 28 is the marked increase in solubilities of the satu- 

 rated acids, in all of the solvents studied, with a rise in temperature. 

 The increases are far greater than have been observed with inorganic salts, 

 carbohj^drates, or amino acids in aqueous solutions under similar circum- 

 stances. Infinite solubility for the individual acids is reached at corre- 

 sponding temperatures in all solvents. These temperatures are 20° C. for 

 caprylic (Cg) and pelargonic (Cg), 30°C. for undecanoic (Cn), 40°C. for 

 capric (Cio), 50°C. for lauric (C12) and tridecanoic (C13), and 60°C. for 

 myristic (Ch) and pentadecanoic (C15) acids. Had studies been made at 

 higher temperatures (70°C. or 80°C.), it is probable that infinite solu- 

 bility would have been observed for palmitic (Cie), margaric (Cn), and 

 stearic (Cjg) acids. 



"Whereas the solubility throughout varies inversely with the length of the 

 carbon chain, marked discrepancies are observed between the even- and 

 odd-chain acids. In practically every case the solubility of the odd-chain 

 acid exceeds that of the next lower even-chain acid. This reminds one of 

 the similar discrepancy in relation to melting point. 



There is a considerable difference in the effectiveness of the several sol- 

 vents, but this varies with temperature and also with the acids tested. 

 Thus, in the case of palmitic acid, the three best solvents at 20°C. are tri- 

 chloromethane, isopropanol, and 2-butanol, respectively. At 60°C., 

 methanol is the best solvent for palmitic acid, although at 20°C. it has been 

 found to be one of the poorest. The second and third best at 60°C. for 

 this acid are 99.4% ethanol and cyclohexane, both of which are inferior sol- 

 vents at 20°C. Similar variations are to be noted with stearic acid. 

 The best solvents at 20°C. are trichloromethane, n-butanone, and benzene, 

 while at 60°C., methanol, acetic acid, and benzene are the three solvents in 

 which stearic acid is most readily soluble. Of these, methanol and acetic 



223 C. W. Hoerr, R. S. Sedgwick, and A. W. Ralston, /. Org. Chem., 11, 603-609 

 (1946). 



