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Aryl chlorides and bromides can be easil...

Aryl chlorides and bromides can be easily prepared by electropilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts. But why does preparation of aryl iodides requires presence of an oxidising agent?

Text Solution

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Iodination of hydrocarbon (RH or ArH) is a reversible reaction. To shift the equilibrium to the forward direction, HI formed during the reaction should be removed by using an oxidising agent, e.g., `HNO_(3) or HIO_(3)`

`2HI+2HNO_(3) = I_(2)+2NO_(2)+2H_(2)O`
`5HI+HIO_(3)=3I_(2)+3H_(2)O`
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Knowledge Check

  • Assertion (A) : Arly iodides can be prepared by reaction of arenes with iodine in the presence of an oxidising agent. Reason (R) : Oxidising agent oxidises I_(2) into HI.

    A
    (A) and (R) both are correct statement and (R) is correct explanation for (A)
    B
    (A) and (R) both are correct statement but (R) is not correct explanation for (A)
    C
    (A) is correct statement but (R) is wrong statement.
    D
    (A) and (R) both are incorrect statement.

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    An alkane A on ozobolysis yields acetone and an aldeyde. The aldehyde is easily oxidised to an acid B. When B is treated with bromine in presence of yields a compound C which on hydrolysis gives a hydroxyle acid D. This acid can also be obatined from acetone by the reaction with hydrogen cyanide followed by hydrolysis. Identify the compounds A, B C and D.

    (a) Name the starting material used in the industrial preparation of phenol. (b) Write complete reaction for the bromination of phenol in aqueous and non-aqueous medium. (c) Explain why Lewis acid is not required in bromination of phenol ?

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