KETONES 89 



Purification. 



The proper quantity of crude acetone (100 gm. or 125 c.c.) is added to 

 the calculated quantity of sodium bisulphite (70 gm.) in saturated solution 

 (this should smell of sulphur dioxide, if not, SO 2 is passed into it until it 

 smells strongly of the gas), and the mixture is shaken vigorously in a closed 

 vessel. Heat is evolved and a mass of crystals, C 3 H 6 O . NaHSO 3 , separates out. 

 After standing, the crystals are filtered off on a Buchner funnel and well drained. 

 They are placed in a distilling flask and decomposed by adding a solution of 

 sodium carbonate (40 gm.). The solution is distilled, preferably using a frac- 

 tionating column, until the thermometer reaches 60. 



The distillate is dried with calcium chloride and the acetone distilled off. 



Properties. 



Ketones closely resemble aldehydes in most of their properties, but 

 there are several differences. 



Acetone is a colourless, pleasant smelling liquid which boils at 

 56 and has a sp. gr. of 797 at 15. It is very volatile and in- 

 flammable. It mixes with water, alcohol and ether in all proportions. 

 Like alcohol it can be separated from water by saturating the solution 

 with potassium carbonate. 



Polymerisation and Condensation. 



Acetone does not polymerise like aldehyde, but when distilled with 

 moderately concentrated sulphuric acid it is converted into mesitylene 

 (sym. trimethylbenzene). 



Action of Ammonia. 



Acetone does not form simple condensation products with ammonia like 

 aldehyde does, but it reacts forming diacetonamine, C 6 H 13 ON, and triaceton- 

 amine, C 9 H 17 ON. 



Acetone Sodium Bisulphite. 



On shaking together about I c.c. of acetone and 5 c.c. of a cold 

 saturated solution of sodium bisulphite, acetone sodium bisulphite 

 crystallises out : 



CH 3 \ CH 3 \ /OH 



>CO + NaHSO 3 = )C\ 



CH/ CH 3 / >S0 3 Na. 



Acetone Cyanhydrin. 



Acetone combines with hydrogen cyanide forming the addition 



compound, acetone cyanhydrin : 



CH 3V CH 3X /OH 



\CO + HCN = >C 



CH/ 



