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Q.
Which one of the following is obtained when acetone is treated with bleaching powder?
AMUAMU 2001
Solution:
When acetone is treated with bleaching powder, then chloroform is formed.
Bleaching powder $\left( CaOCl _{2}\right)$ supplies the necessary chlorine and slaked lime (calcium hydroxide) for the reaction.
$\underset {\text{bleaching powder}}{CaOCl _{2}} + H _{2} O \longrightarrow \underset{\text{slaked lime}}{Ca ( OH )_{2}+ Cl _{2}}$
Chlorine so obtained acts as a chlorinating agent. It reacts with acetone and gives trichloroacetone which formed chloroform on hydrolysis.
$\underset{\text{acetone}}{CH _{3} COCH _{3}}+3 Cl _{2} \longrightarrow \underset{\text{trichloroacetone}}{C \cdot Cl _{3} \cdot COCH _{3}}+3 HCl$
$Ca ( OH )_{2}+2 CCl _{3} COCH _{3} \longrightarrow \underset{\text { chloroform }}{2 CHCl _{3}} +\underset{\text{calcium acetate}}{\left( CH _{3} COO \right)_{2} Ca}$
This is the laboratory method of chloroform preparation.
Ethyl alcohol also gives chloroform with bleaching powder. In this reaction bleaching powder functions as oxidising, chlorinating and hydrolysing agent.