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: Understanding the Question:
The question asks for the product of the sequential reaction of an arene diazonium chloride with fluoroboric acid (\( \text{HBF}_4 \)) followed by heating.
Step 2: Detailed Explanation:
This specific reaction sequence is known as the Balz-Schiemann reaction.
1. Arene diazonium chloride (\( \text{Ar}-\text{N}_2^+\text{Cl}^- \)) reacts with fluoroboric acid (\( \text{HBF}_4 \)) to precipitate arene diazonium fluoroborate (\( \text{Ar}-\text{N}_2^+\text{BF}_4^- \)).
2. Upon heating the dried fluoroborate salt, it decomposes to yield the fluoroarene (\( \text{Ar}-\text{F} \)), nitrogen gas, and boron trifluoride.
\[ \text{Ar}-\text{N}_2^+\text{BF}_4^- \xrightarrow{\Delta} \text{Ar}-\text{F} + \text{N}_{2(\text{g})} + \text{BF}_{3(\text{g})} \]
Step 3: Final Answer:
The resulting product is a fluoroarene (\( \text{Ar} - \text{F} \)).