Consider the following statements about the preparation of haloarenes.
(A) Aryl chlorides and bromides can be prepared by electrophilic substitution of arenes with chlorine and bromine in the presence of Lewis acid catalysts like iron(III) chloride.
(B) The ortho and para isomers formed in the halogenation of an arene can be easily separated due to the large difference in their boiling points.
(C) The reaction of an arene with iodine is reversible and requires the presence of an oxidising agent such as HNO3 or HIO4.
(D) The replacement of the diazonium group of a diazonium salt by iodine requires the presence of a cuprous halide.
Which of the statements given above are incorrect? Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → (B) and (D) only
Haloarenes are made in two main ways: by electrophilic substitution of an arene with a halogen, and from a primary aromatic amine through its diazonium salt.
(A) Aryl chlorides and bromides can be prepared by electrophilic substitution of arenes with chlorine and bromine in the presence of Lewis acid catalysts like iron(III) chloride. — Correct statement. Iron or iron(III) chloride acts as the Lewis acid catalyst.
(B) The ortho and para isomers formed in the halogenation of an arene can be easily separated due to the large difference in their boiling points. — Incorrect statement. The two isomers are separated by the large difference in their melting points. A difference in boiling points is not the basis of this separation.
(C) The reaction of an arene with iodine is reversible and requires the presence of an oxidising agent such as HNO3 or HIO4. — Correct statement. The oxidising agent oxidises the HI formed during iodination, so the reaction can go forward.
(D) The replacement of the diazonium group of a diazonium salt by iodine requires the presence of a cuprous halide. — Incorrect statement. Cuprous chloride or bromide is needed only to bring in –Cl or –Br. For iodine, the diazonium salt is shaken with potassium iodide, and no cuprous halide is needed.
NCERT (2026-27 edition):
6.5 Preparation of Haloarenes – “Aryl chlorides and bromides can be easily prepared by electrophilic substitution of arenes with chlorine and bromine respectively in the presence of Lewis acid catalysts like iron or iron(III) chloride.”
“The ortho and para isomers can be easily separated due to large difference in their melting points. Reactions with iodine are reversible in nature and require the presence of an oxidising agent (HNO3, HIO4) to oxidise the HI formed during iodination.”
“Replacement of the diazonium group by iodine does not require the presence of cuprous halide and is done simply by shaking the diazonium salt with potassium iodide.”