72 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



barium carbonate. Carbon dioxide is evolved and the excess of 

 sulphuric acid is precipitated as insoluble sulphate ; this is filtered off 

 after heating on a water-bath for -J-i hour. The solution contains 

 calcium or barium ethyl sulphate (as shown below under hydrolysis). 



UO\ C 2 H 5 O\ 



C 2 H 5 OH + \S0 2 = \S0 2 + H 2 



HCT HCT 



C 2 H 6 0\ 

 2 \S0 2 



HCT 



The clear filtrate is heated on the water-bath and treated with a strong 

 solution of potassium carbonate (10 gm.) or potassium oxalate until no further 

 precipitate is formed :^ 



/O SO 2 OC 2 H S C 2 H 5 O\ 



Ba/ + K 2 C0 3 = BaC0 3 + 2 \SO r 



\0-S0 2 OC 2 H 5 KCT 



The barium carbonate is filtered off and the filtrate evaporated to a 

 small volume (a drop withdrawn on a glass rod should crystallise on cooling). 

 The crystals which form after standing for several hours are filtered off, 

 washed with dilute alcohol and dried between sheets of filter paper. The 

 mother liquor yields more crystals on further evaporation. The salt is dis- 

 solved in boiling alcohol under a reflux condenser, filtered, using a hot- 

 water funnel, and allowed to crystallise out. 



ESTERS OF ORGANIC ACID. 



Ethyl Acetate. 



Molecular proportions of glacial acetic acid (50 c.c) and absolute 

 alcohol (50 c.c.) are mixed in a distilling flask, and I per cent, by 

 volume of concentrated sulphuric acid (i c.c.) is added. The distilling 

 flask is connected to a condenser and receiver and the mixture is dis- 

 tilled. A yield of 86*5 per cent, of ester is obtained (Senderens, 

 method). Ethyl sulphuric acid appears to be the catalyst : 



C 2 H 5 HS0 4 + C 2 H 5 OH = (C 2 H 5 ) 2 S0 4 + H 2 O 

 (C 2 H 5 ) 2 SO 4 + CH 3 COOH = C 2 H 5 HSO 4 + CH a COOC 2 H 5 . 



The distillate which contains water, alcohol and acetic acid is purified 

 by shaking it in a separating funnel with strong sodium carbonate 

 solution which is added in small quantities until the aqueous por- 

 tion shows an alkaline reaction. The aqueous portion is withdrawn 

 and the ester shaken with saturated salt or strong calcium chloride 

 solution to remove alcohol ; the ester layer is separated and dried by 

 contact with solid calcium chloride. It is then distilled from a dry 

 flask, the portion passing over when the thermometer reads 74-7 8 

 being collected. 



