CHEMICAL PROPERTIES OF FATTY ACIDS AND RELATED COMPOUNDS 109 



nionstrated l)y Dunstan and co-workers ^•'^■^^^•"•^ that the curves of the 

 logarithms of the viscosities and molecular weights are approximately 

 linear for the normal fatty acids and for certain of the alkyl esters, includ- 

 ing the methyl and ethyl esters. The values for formic and acetic acids, 

 however, are atypical. The temperature-viscosity relationships are 

 plotted in Figure 23. 



e. Boiling Points of Fatty Acids. The analysis of mixtures of fatty 

 acids by fractional distillation is only possible because of differences in 

 vapor pressure and boiling point. Pool and Ralston^^^ have determined 

 the boiling points of the saturated fatty acids from Ce to Ci8 over a wide 

 range of barometric pressures from 1 to 760 mm. The vapor pressure- 

 temperature curves are given in Figure 2. Table 40, on page 110, gives the 

 boiling points of the saturated fatty acids at varying pressures. 



The boiling point of the saturated fatty acids increases with greater 

 chain length. The increment declines slightly as the number of carbon 

 atoms is increased. Boiling point is a non-alternating property in con- 

 tradistinction to the alternation observed in the melting points. The 

 higher members of the series decompose on boiling at ordinary pressures, 

 but can be distilled at reduced pressures without destruction. Oleic acid 

 has been observed to boil at the following temperatures (°C.): 1.2 mm., 

 200°; 5.0,215°; 10,225°; 15, 234°3"; 29.5,250°; and 49, 264°. "* The 

 following are the boiling points (°C.) reported'* for some other unsaturated 

 acids: 9-decenoic, 142° (4 mm.); erucic, 281° (30 mm.); chaulmoogric, 

 248° (20 mm.); and elaeostearic, 235° (12 mm.). 



The methyl esters of the fatty acids are also readily distillable. In 

 general, they boil at a considerably lower temperature than do the cor- 

 responding acids. Table 41 gives data on the boiling points of methyl es- 

 ters of both saturated and unsaturated acids. 



4. Chemical Properties of Fatty Acids and Related Compounds 



The fatty acids are not the inactive compounds that they were formerly 

 supposed to be, but undergo many reactions of considerable importance 

 commercially. IMany of these reactions involve the carboxyl group. 

 They maj^ be either ionic in nature or they may be concerned with ester 

 formation. Any one of several types of interesterification also falls into 

 the latter category. Other reactions of the carboxyl group result in the 

 synthesis of various derivatives such as aldehydes, alcohols, amides, 

 nitriles, amines, and acid chlorides. 



3'i A. E. Dunstan, T. P. Hilditeh, and F. B. Thole, /. Chem. Soc, 103, 133-144 (1913) 

 5'2 A. E. Dunstan, F. B. Thole, and P. Benson, J. Chem. Soc, 105, 782-795 (1914). 

 "3 J. B. Brown and G. Y. Shinowara, J. Am. Chem. Soc., 59, 6-8 (1937). 

 '•'" E. L. Lederer, Seifensieder-Zt^j., 57, 67-71 (1930); cited by K. S. Markley, Fatly 

 Acids, Interscience, New York, 1947, p. 172. 



