Question

Tetrachloroethylenedoes not add chlorine quantitatively under ordinary conditions. However, when the same reaction is carried out in presence of aluminium chloride, addition occurs easily. The role of $AlC{l}_3$ is

• A. to decrease the activation energy of the reaction
  
  
• B. to enhance the formation of chloronium ion
  
• C. to accelerate the reaction by removing impurity in the alkene
  
• D. to stabilize the dichloride formed by coordination

Answer 1

The correct option is B

to enhance the formation of chloronium ion

Four chlorine decreases electron density around C = C double bond which can not polarise $C{l}_2$ to form $C{l}^{+}.$ Addition of $AlC{l}_3$ produces $C{l}^{+}$ in the following way.

$AlC{l}_3+C{l}_2\to AlC{l}_4^{-}+C{l}^{+}$