Question

Which diazonium salt is water insoluble and stable at room temperature? 

Hint:

Most diazonium salts decompose rapidly in water, but \( C_6H_5N_2BF_4 \) is water-insoluble and stable due to the strong tetrafluoroborate ion \( BF_4^- \) interaction.

Answer 1

Step 1: Understanding Stability of Diazonium Salts 
- Diazonium salts have the general formula \( ArN_2^+X^- \),
where:
- \( Ar \) represents an aromatic group.
- \( X^- \) represents the anion, such as \( Cl^-, Br^-, SO_4^{2-}, BF_4^- \), etc.
- Most diazonium salts are water-soluble and unstable at room temperature, decomposing rapidly to release nitrogen gas. 
Step 2: Properties of \( C_6H_5N_2BF_4 \) 
- Benzenediazonium tetrafluoroborate \( (C_6H_5N_2BF_4) \) is an exception.
- The tetrafluoroborate ion \( BF_4^- \) stabilizes the diazonium cation, making it:
- Insoluble in water (hence it precipitates).
- Stable at room temperature without decomposing. 
Step 3: Conclusion 
Among diazonium salts, benzenediazonium tetrafluoroborate \( C_6H_5N_2BF_4 \) is the most stable and water-insoluble at room temperature.