CHEMICAL PROPERTIES OF FATTY ACIDS AND RELATED COMPOUNDS 157 



OHO ^^0 



CHjICHjIC-CICHzItCOOH ^CHjlCHjlyC-H+HOCHjtCHaJjCOOH 



9-Keto-10-h.\droxy- Nonanal 9-Hydroxy- 



octadecanoic acid pelargonic acid 



The reactions between air and the unsaturated acids are of considerable 

 importance because they form the basis for several interesting properties of 

 the fats. In the first place, rancidity results from the development of this 

 reaction. Before rancidity can be detected by odor or taste, the forma- 

 tion of peroxides occurs; this corresponds to the so-called induction period. 

 The presence of these peroxides can be quantitatively determined by 

 organoleptic tests which depend upon the liberation of iodine from hydro- 

 gen iodide. ^'"'^"^ An extensive discussion of rancidity, as well as of condi- 

 tions which promote or retard it, is included in Chapter III. 



The production of a hard film of paint likewise depends on the oxidation 

 of the double bonds. Thus, trilinolenin is most suitable as a component of 

 drying oils, while the triglyceride of the monoethenoid acid, oleic, is useless 

 for this purpose. Elaeostearic acid is even more efficient as a constituent 

 in a drying oil than is the corresponding non-conjugated triethenoid acid, 

 linolenic, because of the conjugated position of the double bonds. 



(c) Oxidation vnth Various Oxidizing Agents. There are a number of 

 different oxidizing agents which can be used for oxidation of the unsaturated 

 acids. The end products vary with the reagent employed. Although 

 concentrated nitric acid was formerly the most common oxidizing agent, 

 it has been used but little in recent years. 



The results of chromic acid, when used with the unsaturated acids, dif- 

 fer according to the conditions of the oxidation. When the reaction is 

 carefully controlled, hydroxy- and keto-acids result. With more strenuous 

 oxidation procedures, the end products of oleic acid may be the monobasic 

 saturated acids from pelargonic to acetic, and the dicarboxylic acids^'^^ 

 from C9 to C2. However, when oleic acid was refluxed with 2% potassium 

 dichromate acidified wdth sulfuric acid, no reaction occurred for 4 days, but 

 after 10 days, pelargonic (nonanoic) and azelaic acids were produced.®''^ 

 Silver chromate is an excellent oxidizing agent which decomposes fatty 

 acids completely to carbon dioxide."^ Chromic anhydride, on the other 

 hand, does not effect as complete a destruction as the silver salt, since the 

 extent of breakdown depends upon the molecular configuration. Simon ®^^ 

 calculated the oxidation deficiency by a formula employing the data ob- 

 tained by oxidation with both silver chromate and chromic anhydride 



6™ A. Taffel and C. Revis, /. Soc. Chem. Ind., 60, 87-91T (1931). 

 6" C. H. Lea, Proc. Roy. Soc. London, B108, 175-189 (1931). 

 672 F. G. Ehmed, /. Chem. Soc, 73, 627-634 (1898). 



•^'L. G. Simon, Comvt. rend., 174, 1706-1708 (1922); 175, 1070-1072 (1922); 179, 

 975-977 (1924); 180, 673-675, 833-836, 1405-1407 (1925). 



