ESTERS 75 



Ethyl Benzoate. 



The hydrolysis is effected as described above for ethyl acetate. 



The insoluble acid is more readily prepared by hydrolysing with 

 alcoholic soda and then identified : 



5-10 gm. of the ester are placed in a flask and boiled under 

 a reflux condenser with excess of caustic soda (1-2 gm.), dissolved 

 in 10 c.c. water and 100 c.c. of alcohol, for 10-15 minutes. The 

 saponification is continued until a few drops poured into water show 

 no oily drops of unchanged ester. 



If any insoluble sodium benzoate separates out, it is dissolved by 

 adding a little water through the condenser. 



The solution is poured into an evaporating basin, water added and 

 the alcohol evaporated off on the water-bath. On cooling and after 

 adding about 25-50 c.c. of water the solution is acidified with dilute 

 mineral acid. Benzoic acid is precipitated. It is washed with water, 

 recrystallised from hot water, and identified (p. 256). 



Ethyl Oxalate. 



10-20 gm. of ethyl oxalate are hydrolysed with caustic soda 

 solution containing sufficient alkali (6-12 gm.) as described undei 

 -ethyl acetate and the alcohol is distill *d off. 



The acid contained in the solution on acidifying with mineral acid 

 is not precipitated nor is it volatile with steam. The acid solution 

 may be extracted several times with ether, the ethereal solution dis- 

 tilled to remove the ether, and the acid which is left identified. 



Oxalic acid is more easily separated as its calcium salt. The acid 

 liquid is carefully neutralised with soda and calcium oxalate is precipi- 

 tated by adding calcium chloride. The acid is obtained as described 

 under oxalic acid (p. 108). 



