56 ORGANIC AGRICULTURAL CHEMISTRY 



ESTERS OR ETHEREAL SALTS 



Simple Esters 



The acids, with the exception of formic acid, do not usually 

 occur free in nature, but are present in combination as a par- 

 ticular kind of salt known as an ester or ethereal salt. When an 

 acid is neutralized by a base, a salt is formed by the hydroxyl 

 hydrogen of the acid being replaced by the metal of the base, 

 as follows : 



CH3 - COO(H + HO)K -> CH3 - COOK + H2O 



Acetic acid Potassium acetate 



Now alcohols, which in general are neutral substances, when 

 brought in contact with acids act like bases and neutralize the 

 acid. The hydroxyl hydrogen of the acid is replaced by the 

 radical of the alcohol and the resulting compound is termed an 

 ester or ethereal salt. 



CH3 - COO(H + HO)C2H5 -> CH3 - COOC2H5 + H2O 



Acetic acid Ethyl Ethyl acetate 



alcohol 



These esters are exactly analogous to the metallic salts, the 

 organic radical taking the place of the metal. They are named 

 like the metallic salts, viz. the radical name joined to that of 

 the acid with the termination ic changed to ate. Ethyl ace- 

 tate is the ethereal salt of the ethyl radical and acetic acid 

 made by neutralizing acetic acid with ethyl alcohol. Similarly 

 methyl formate is the methyl salt of formic acid, amyl valerate 

 is the amyl salt of valeric acid, etc. The importance of esters is 

 in the fact that they occur very widely distributed in nature in 

 plants, fruits and flowers, and as oils, fats and waxes. Esters 

 of the lower acids and lower alcohols are pleasant-smelling, 

 volatile liquids (hence the name ethereal salts). They are not 

 usually miscible with water, though often slightly soluble in it. 

 The higher members are crystalline solids. 



Fruit Flavors. — While it is probably a fact that the odor of 

 fruits is due to the presence of esters, it is not fully established, 



