72 LIPIDES (fats and RELATED SUBSTANCES) 



The underlined H of the alcohol and HO of the acid become separated 

 from their previous points of attachment and unite to form H2O, while 

 the remaining portions of the acid and alcohol combine to form the 

 ester as indicated. The chemical formula of any ester therefore follows 

 directly from the formulas of the alcohol and acid of which it is composed. 

 The name of any pai'ticular ester is derived similarly. Thus in the above 

 equation the product is called ethyl acetate. An ester prepared from 

 methyl alcohol and lactic acid would be called methyl lactate, and so on. 



Preparation 



The actual preparation of esters in the laboratory is carried out, in 

 general, by warming the chosen alcohol and acid together with a small 

 amount of a strong mineral acid, such as sulfuric or hydrochloric, which 

 serves as a catalyst. The process is called esterification. Since esterifica- 

 tion reactions are, in general, reversible, removal of the water as it is 

 formed often helps to secure a good yield of the desired ester. It is 

 obvious that a very large number of different esters may be prepared from 

 the various alcohols and acids (particularly organic acids) that are 

 known and are available. 



Properties of esters 



Many of the simpler esters are liquids that possess pleasant, fruity- 

 odors and hence are used to some extent as artificial flavoring essences. 

 More complex esters are found very abundantly and widely distributed 

 in nature, e.g., in fats, waxes, and other lipides, as explained below. By 

 far the most important industrial use of synthetic esters is based on their 

 properties as solvents. Automobile lacquers, for example, are prepared 

 by dissolving pyroxylin, a pigment, and certain other ingredients in a 

 suitable ester such as butyl acetate: 



O 



II 

 C4HSOCCH3 



Butyl acetate 



All esters may be broken down into their acid and alcohol components 

 by hydrolysis: 



O 



II II 



C4H9OCCH3 + H2O > CHgOH + HOCCH3 



Butyl acetate Water Butyl alcohol Acetic acid 



It will be noted that this reaction is the reverse of esterification. The 

 hydrolysis may be brought about with the aid of an enzyme, if one is 



