II. CHEMISTRY 



275 



ondary products. The general mechanism of oxidation is given on the 

 following page. 



For a more detailed discussion of autoxidation of the essential fatty acids, 

 the reader is referred to a recent review.-^ 



Oxidative rancidity of edible oils is due largely to the oxidation of the 

 essential acids contained in them. The products of oxidation of these 

 acids, at least in large quantities, are probably harmful, for rancid fats are 

 toxic. 



50 



100 



Hours 



Fig. 2. Rates of oxidation of ethyl oleate (1), ethyl linoleate (2), ethyl linole- 

 nate (3), and method arachidonate.^^ (4) 



F. PHYSICAL PROPERTIES 



The essential fatty acids are colorless oils at room temperature. Their 

 light absorption in the ultraviolet region is negligible but increases with 

 decrease in wavelength. ^^ These acids do exhibit strong maxima in the 

 vacuum ultraviolet, or Schumann region.-^ 



The acids themselves boil under high vacuum with some decomposition, 

 but their esters can conveniently be distilled at pressures of 2 to 4 mm. Hg. 

 They have negligible solubility in water, but are highly soluble in organic 

 solvents such as ether, ethanol, acetone, and chloroform. They form col- 

 loidal soap solutions above pH 9. By virtue of their high unsaturation, 

 these compounds have high refractive indexes, and the refractive index 



27 S. Borgstrom, and R. T. Holman, Advances in Enzymol. 8, 425 (1948). 



28 I. I. Rusoff, R. T. Holman, and G. O. Burr, Oil & Soap 22, 290 (1945). 



29 I. I. Rusoff, J. R. Piatt, H. B. Klevens, and G. O. Burr, /. Am. Chem. Soc. 67, 

 673 (1945). 



