QS Study

Preparation of chloroform from acetone:

A mixture of acetone, bleaching powder and water, when heated produce chloroform. The reaction occurs in 3 steps.

Step-1: Water and bleaching powder react to form lime and chlorine

Ca(OCl)Cl (bleaching powder) + H2O → Ca(OH)2 Cl2

Step-2: Then the chlorine reacts with the acetone and by its chlorination 1, 1, 1-tri-chloroacetone is formed.

CH3-CO-CH3 (acetone) + Cl2 → Cl3C-CO-CH3 (1, 1, 1-trichloro acetone) + HCl

Step-3: The produced trichloro acetone reacts with lime forming chloroform.

Cl3C-CO-CH3 + Ca(OH)2 → CHC13 (chloroform) + (CH3COO)2Ca

Procedure: The preparation is ranted out in the following manner.

A paste of bleaching powder made with a little water is taken in a round-bottomed flask fitted with a Liebig condenser by means of a delivery tube. There is a receiver at the other end of the condenser. Alcohol is added slowly into the flask. The mouth of the flask is then closed and the flask is heated on a sand bath. The cold water circulating through the jacket of the condenser tube cools the heavy vapour of the chloroform which is collected as a liquid in the receiver, some water also condensed with chloroform.

Purification: The chloroform thus obtained contains unreached alcohol, hydrochloric acid etc. as impurities. The distillate from the receiver is taken in a separating funnel. Chloroform being heavier than water forms the lower layer which is separated by a separating funnel. It is then washed with dilute NaOH solution to remove alcohol and HCl and then with water. The chloroform thus freed from HCl and alcohol is dried over fused CaCl2 redistillated (bp. 620C) when pure chloroform is obtained as distillate.