CHEMICAL PROPERTIES OF FATTY ACIDS AND RELATED COMPOUNDS 133 



(c) Hydrocarbons. On complete reduction of the carboxyl group of the 

 fatty acids to a CH3 group, a hydrocarbon results. Although this is not a 

 general biological reaction, the presence of hydrocarbons, particulai'ly cyclic 

 ones, in animal and plant products, would seem to indicate that such com- 

 pounds can be formed by living tissue. Hydrocarbons are discussed in 

 Chapter IV. 



(d) Acid Anhydrides. The acid anhydrides are compounds which are 

 very closely related to the fatty acids. The lower members are liquids 

 which quickly revert to the acids when dissolved in water. On the other 

 hand, the anhydrides of the longer chain fatty acids are solids which are 

 quite stable and, in some cases, hydrolyze only with difficulty. Since 

 each anhydride is made up of two fatty acid molecules, there are two pos- 

 sible types of compound, i.e., the simple or symmetrical anhydride, in which 

 the two components are identical, and the mixed or unsymmetrical anhy- 

 dride in which the fragments represent two different fatty acids. In 

 general, the anhydrides of the shorter chain acids melt at lower tempera- 

 tures than do the corresponding fatty acids, while the longer chain com- 

 pounds have melting points somewhat higher than those of their parent 

 fatty acids. 



a'. Methods of Preparation of Acid Anhydrides: The principal method 

 for the preparation of the symmetrical anliydrides is by treatment of the 

 fatty acids with a suitable dehydrating agent. The preparation of a 

 typical anhydride such as capryl anhydride by this method is as follows : 



^0 -HjO /) 0^ 



2CH3(CH2)eC-0H ^CHjlCHjJsC-O-ClCHjjgCHj 



Capric acid Capryl anhydride 



Albitskii'"'^^ first suggested the use of acetic anhydride as a dehydrating 

 agent with the fatty acids heated in a glass tube at 150-1G0°C. under 

 pressure. The procedure apparently has wide application with unsatu- 

 rated as well as with saturated acids. ^^^'^^* Linoleyl anhydride has been 

 obtained in a yield of 73%,^" and erucyl anliydride to the extent^^^ of 

 84.5%. As high a recovery of oleyl anhydride as 94% of the theoretical 

 was reported, when the acetic anhydride was used as the dehydration 

 agent. ^'* In the case of the higher fatty acids, it is only necessary to reflux 



«2 A. All)it.skii, ./. Russ. Phys. Ckem. Soc, 31, 103-106 (1899); cited by A. W. Ralston, 

 Fatly Acids atui Their Derivatives, Wiley, New York, 1948, p. 794. 



•>" D. Hokle and H. Smelkus, Ber., B53, 1889-1897 (1920). 



*'•' D. Ilolde and I. Tacke, Ber., B53, 1898-1907 (1920). 



''•'" A. Grlin and H. Schonfcld, Z. angcio. Chcm., 20, 37-39, 46-48 (1916). 



"«D. Holde and I. Tacke, Chem.-Ztg., 45, 949-950 (1921); Chem. Abst, 16, 56-57 

 (1922). 



