ESTERS. 



Alcohols are like the bases NaOH, KOH in containing an OH 

 group. The bases combine with acids to form salts. Alcohols com* 

 bine with acids to form esters. 



An enormous number of esters is possible since any alcohol can be 

 combined with any acid, inorganic or organic. The organic acids may 

 be grouped into three classes : (a) those insoluble or very insoluble in 

 water ; () those soluble in water, but volatile with steam ; (c) those 

 soluble in water, but not volatile with steam. 



Preparation. 



There are several methods of preparing esters : 



(1) By the action of the acid upon the- alcohol in the presence of a 

 dehydrating agent, or catalyst. 



(2) By the action of concentrated sulphuric acid upon the sodium 

 salt of the acid and the alcohol. 



(3) By the action of the acid chloride, or anhydride, upon the 

 alcohol. 



(4) By the action of the alkyl halide upon the silver salt. 



ESTERS OF INORGANIC ACIDS. 



Halogen Acids. 



These compounds are the same as the monosubstituted halogen 

 derivatives of the hydrocarbons (p. 57) : 



C 2 H 5 OH + HC1 = C 2 H 5 C1 + H 2 0. 



Amyl Nitrite. 



The calculated quantity of concentrated sulphuric acid is allowed to drop 

 slowly upon the calculated quantity of sodium nitrite mixed with the calcu- 

 lated quantity of amyl alcohol contained in a flask cooled by a freezing 

 mixture. Amyl nitrite floats to the surface as an oil. It is separated, washed 

 with water, dried with calcium chloride and distilled. 



Ethyl Sulphuric Acid. Barium and Potassium Ethyl Sulphate. 



10 c.c. of concentrated sulphuric acid are poured carefully into 

 and mixed with 20 c.c. of ethyl alcohol ; the mixture becomes hot. It 

 is heated on a water-bath under a reflux condenser for |-i hour. On 

 cooling it is poured into about 200 c.c. of cold water. The acid 

 solution is neutralised to litmus by stirring it up with calcium or 



71 



