Question

What type of arenes are obtained when arene diazonium chloride is treated with fluoroboric acid and then heated further?

• A. Ar – NO\(_2\)
• B. Ar – F
• C. Ar – Cl
• D. Ar – H

Hint:

The formation of arene fluorides is a characteristic reaction of arene diazonium salts when treated with fluoroboric acid, which replaces the diazonium ion with a fluoride.

Answer 1

The Correct Option is B

Step 1: Understand the process.
Arene diazonium chloride is an important intermediate in organic chemistry. The general reaction for generating aryldiazonium salts involves the substitution of a hydrogen atom with a diazonium group (\(Ar-N_2^+\)). When treated with fluoroboric acid (\(BF_4\)), it forms arene fluorides via the substitution of the diazonium group by a fluoride ion (\(F^-\)).

Step 2: Reaction mechanism.
In the reaction of an arene diazonium chloride with fluoroboric acid, the diazonium ion (\(Ar-N_2^+\)) reacts with the fluoride ion (\(F^-\)) to form arene fluoride: \[ Ar-N_2^+ + F^- \rightarrow Ar-F + N_2^+ \]

Step 3: Analyze other options.
- \(Ar - NO_2\) is the nitro group, which would be produced if the diazonium ion was treated with an oxidizing agent such as nitric acid (\(HNO_3\)).
- \(Ar - Cl\) is the chloro group, typically produced by reactions involving chlorine gas (\(Cl_2\)) or hydrochloric acid (\(HCl\)).
- \(Ar - H\) represents the removal of the diazonium group by heating, resulting in a simple hydrocarbon (benzene).

Step 4: Identify the correct reaction.
From the given choices, the treatment of the arene diazonium chloride with fluoroboric acid leads to the formation of arene fluorides (\(Ar - F\)).

Step 5: Final Answer.
Thus, the correct product of the reaction is \(Ar – F\), corresponding to option \((2)\).