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Question

Given below are two reactions :
(i) C6H6+IClAnhyd.AlCl3−−−−−−−−→iodobenzene
(ii) C6H6+I2Anhyd.AlCl3−−−−−−−−→iodobenzene

A
Reaction (i) is more favored for preparation of iodobenzene as compared to reaction (ii)
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B
Reaction (ii) is more favored for preparation of iodobenzene as compared to reaction (i)
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C
Both are equally favored for preparation of iodobenzene.
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D
Chlorobenzene is formed in reaction (i) instead of iodobenzene.
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Solution

The correct option is A Reaction (i) is more favored for preparation of iodobenzene as compared to reaction (ii)
Since iodine is less electronegative than chlorine, AlCl3 reacts with ICl to form iodonium ion (I+) as an electrophile. Hence iodobenzene is formed in reaction (i).

Iodination of benzene is done with ICl+AlCl3 because if we take
I2+AlCl3 then HI will be formed as byproduct. HI being a strong reducing agent will reduce the iodobenzene making the reaction reversible.
So to prevent the reversibility of reaction we use ICl with lewis acid.
So, reaction (i) is more favored for preparation of iodobenzene as compared to reaction (ii)

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