150 II. CHEMISTRY OF FATTY ACIDS AND GLYCEROL 



chain mono- and dicarboxylic acids, including some keto-acids.^^^ Alka- 

 line permanganate attacks hydroxy-acids.^^° For example, 2-hydroxy- 

 stearic acid is converted to its next lower homolog, margaric acid (C17H34O2), 

 by alkaline permanganate^^ ^; this seems to be a fairly general reaction for 

 the a-hydroxy acids. Fichter and Lapin^^^ have reported that the satu- 

 rated aliphatic acids are decomposed by potassium percarbonate or potas- 

 sium persulfate. 



(6) Oxidation of Unsaturated Acids. In the case of the unsaturated acids, 

 oxidation occurs preferentially at the double bond. On further treatment 

 with the oxidation medium, the acid is split at the double bond to a mixture 

 of mono- and dicarboxylic acids. ^ The recognition of the nature of the re- 

 sulting acids has long been accepted as a satisfactory method for the deter- 

 mination of the position of the double bond. 



Unsaturated acids are readily oxidized by air. Susceptibility to oxida- 

 tion becomes greater with an increase in the number of double bonds.^^* 

 Linoleic acid is oxidized more easily than is oleic acid, while linolenic 

 acid is more readily attacked than is either of these acids. ^^''•^^^ The 

 position of the double bond is also a factor in controlling the rate of 

 oxidation; thus, acids with conjugated double bonds are more active than 

 are the corresponding non-conjugated compounds. ^^^^®^^ 



The reactions which occur between air and the unsaturated acids are be- 

 lieved to take place in two stages. In the first reaction, peroxides are 

 formed. The second phase of the breakdown results in a cleavage of the 

 peroxide to a hydroxy-keto-acid which, on further standing, changes to an 

 aldehyde and an co-hydroxy-acid. The reactions of oleic acid are pictured 

 below : 



0—0 



CH3(CH2)7CH:CH(CHe)7C00H — * CHjlCHzJyCHCHteHjTCGOH > 



Oleic acid Oleic acid peroxide 



«s9 E. S. Przheval'skii, J. Russ. Phys. Chem. Soc, 43, 1000-1006 (1911). Cited by A. W, 

 Ralston, Fatty Acids and Their Derivatives, Wiley, New York, 1948, p. 413; Chem. Abst., 

 6, 481-482 (1912). 



««° S. Skraup and E. Schwamberger, Ann., 462, 135-158 (1928). 



«si P. A. Levene and C. J. West, /. Biol. Chem., 16, 475-478 (1914). 



««2 F. Fichter and H. Lapin, Helv. Chim. Acta, 12, 993-1002 (1929). 



«" G. E. Holm, G. R. Greenbank, and E. F. Deysher, Ind. Eng. Chem., 19, 156-158 

 (1927). 



6" R. Kuhn and K. Meyer, Z. physiol. Chem., 185, 193-216 (1929). 



««5 C. R. Barnicoat, J. Soc. Chem. Ind., 50, 361-365T (1931). 



666 F. C. Vibrans, Oil & Soap, 18, 109-112 (1941). 



667 E. S. Miller, W. R. Brown, and G. O. Burr, Oil & Soap 15, 62-65 (1938). 



668 J. p. Kass and G. O. Burr, /. Am. Chem. Soc, 61, 3292-3294 (1939). 



669 C. H. Lea, "Rancidity in Edible Fats," Dept. Sci. Ind. Research Food Invest., Special 

 Rept., No. 46 (1939), p. 86. 



