78 GENERAL BIOCHEMISTRY 



Unsaturated fatty acids react quantitatively with hydrogen to pro- 

 duce the corresponding saturated analogs. Thus I mole of oleic, 

 linolic, and linolenic acid react with 1, 2, and 3 moles of hydrogen, 

 respectively, to form stearic acid. By a similar reaction, these same 

 unsaturated acids react with a halogen, such as bromine, to produce 

 di-, tetra-, and hexabromostearic acids. Considerable use has been 

 made of these bromo derivatives in the separation and identification 

 of mixtures of the unsaturated acids. The free acids can be regen- 

 erated from the bromo derivatives by the action of zinc. 



Under more stringent conditions of temperature and pressure and 

 in the presence of a catalyst, the carboxyl group of any fatty acid 

 may be reduced to yield an alcohol. This reaction has proved to be 

 of great commercial significance in the preparation of a large number 

 of soap substitutes called detergents. The alcohol formed by the 

 reduction of a higher-molecular-weight fatty acid is treated with 

 sulfuric acid to form the sulfuric acid ester, which is then converted 

 to the sodium salt, as shown in the following equations: 



CH3(CH2)ioCH20H + H2SO4 -^ CH3(GH2)ioGH20S03H + H2O 



lauryl alcohol lauryl sulfate 



CH3(CH2)ioCH20S03H + NaOH -^ CH3(CH2)ioCH20S03Na -f H2O 



lauryl sulfate sodium lauryl sulfate 



The final product is a water-soluble substance with all the desirable 

 characteristics of a soap. These sulfated alcohols are especially desir- 

 able in hard-water areas because their calcium and magnesium salts 

 are water soluble, thus eliminating the bothersome precipitation 

 of the insoluble salts formed when true soaps are used. 



Fatty acids form salts with inorganic bases in a typical neutralization 

 reaction, as shown by the following equation: 



CH3(CH2)i4COOH + NaOH -^ CH3(CH2)i4COONa + H2O 



palmitic acid sodium palmitate 



Needless to say, a large variety of bases and fatty acids can be used 

 to produce a myriad of soaps with different properties and applica- 

 tions. Some of these will be considered in a later section of this 

 chapter. 



By far the most important reaction of fatty acids from a biological 

 standpoint is that of ester formation. In living tissues fatty acid 

 derivatives can and do react with a variety of alcohols to form 

 biologically important esters. Thus, a fatty acid might react with 

 a high-molecular-weight monohydric alcohol, such as cetyl alcohol 

 [CH3 (CHo)iiCH20H], to form a wax. On the other hand, a fatty 



