CHEMICAL PROPERTIES OF FATTY ACIDS AND RELATED COMPOUNDS 113 



Certain soaps are also important as catalysts in the manufacture of 

 mono- and digtycerides. They are likewise used to accelerate interesteri- 

 fication reactions. Lead and chromium soaps serve as catalysts in the re- 

 duction of the fatty acids to alcohol. Sodium soaps have been used as 

 emulsifiers in the manufacture of synthetic rubber. Stearate and oleate 

 have been widely employed in the manufacture of pharmaceutical prepara- 

 tions for the skin, in which they act as antiseptics and astringents. 



b. Reactions Involving Esterification. Esters are compounds which 

 yield an alcohol and an acid on hydrolysis. The esters of chief importance 

 to the fat chemist are those in which the acid component is an organic 

 acid. The principal organic acids involved in the animal kingdom are the 

 fatty acids. Conversely, the fatty acids occur in nature almost exclusively 

 in the form of esters. 



Until recently esters have been regarded as compounds analogous to 

 soaps, where the hydrogen of the carboxyl is replaced by an alkyl group 

 instead of by a metal. On this basis they have frequently been referred to 

 as alkyl salts of the fatty acids. However, the newer views of esterification 

 have postulated that the esters are formed by replacement of the hydroxyl 

 radical of the carboxyl by an alkoxy group of the alcohol. 



(ft) Classification of Esters. There are a large number of theoretically 

 possible esters, but the types of compounds fall into relatively few groups. 

 All of the n-fatty acid series, the unsaturated acids, and the substituted 

 fatty acids are usually found in nature in the form of esters. The more 

 useful classification of these compounds is based upon their alcohol 

 component. Thus, the following types of alcohols are present in ester 

 combination: 



1. Monohydric or Monatomic alcohols, which have an alkyl chain and a hydroxyl group. 

 Since the aldehydes can be formed from the fatty acids in the animal body, it is probable 

 that the corresponding alcohols may also originate here. It is not surprising that counter- 

 parts of most of the fatty acids are represented in the biologically distributed alcohols. 

 The monohj'dric alcohols may he furthei' subdivided : {1) Primary alcohols (RCH2OH ), 

 in which the hydioxvl grou{) is attached to the terminal carbon. (S) Secondary alcohols 



■'X \ . ' . 



,CHOH 1, in which the carbon to which the hj'droxyl is attached is joined to two 

 R"/ / 



f"' \ \ 



other carbon atoms. (5) Tertiary alcohols I R" — ^COH I, in which the carbon to 



\R"'/ / 



which the hydroxyl is attached is joined to three other carbon atoms. 



2. Folyhydrir alcohols having two or more alcohol grou{)s in the chain: (1) Esters of 

 the dihydric alcohol, glycol (CHiOH-CHjOH) and its homologiies. Such esters would 

 contain two fatty acid residues. (^) Esters of the trihydric alcohol, glycerol (CHaOH-- 

 CHOHCH2OH). Such esters normally contain three fatty acid residues, but mono- 

 glycerides (with one acid) and diglycerides (with two acids) are well known and are 

 produced m large amounts commercially. The fatty acids in nature are largely found 

 in the form of triglycerides (see Chapter III). (5) Esters of the tetrahydric alcohol, eryth- 



