Question

Aryl diazonium reacts with fluoroborate to give aryl fluoride:

• A. Balz-Schiemann reaction
• B. Stephen reaction
• C. Gattermann reaction
• D. Gomberg reaction

Hint:

Remember: Balz-Schiemann reaction is the key method to prepare aryl fluorides from aryl diazonium salts — an important named reaction for GPAT organic chemistry.

Answer 1

The Correct Option is A

- The Balz-Schiemann reaction involves the conversion of an aryl diazonium salt into an aryl fluoride by thermal decomposition of the corresponding aryl diazonium tetrafluoroborate salt.
- General reaction: \[ \text{Ar-N}_2^+ BF_4^- \xrightarrow{\Delta} \text{Ar-F} + N_2 + BF_3 \] where Ar = aryl group.
- This reaction is widely used to introduce fluorine atoms into aromatic rings, which is important in the synthesis of fluorinated aromatic compounds.
- Other options: - Stephen reaction reduces nitriles to aldehydes.
- Gattermann reaction introduces formyl groups into aromatic rings.
- Gomberg reaction is related to the formation of triphenylmethyl radicals.
- Therefore, the correct reaction that produces aryl fluoride from aryldiazonium salts using fluoroborate is the Balz-Schiemann reaction.

Answer 2

This question asks which named reaction turns an aryl diazonium salt paired with a fluoroborate counter ion into an aryl fluoride. Let's check what each reaction is actually used for.

1. Balz-Schiemann reaction: An aryl diazonium chloride is first treated with fluoroboric acid or sodium tetrafluoroborate to form the aryl diazonium tetrafluoroborate salt. Gently heating this dry salt causes it to break down, releasing nitrogen gas and boron trifluoride while leaving the fluorine attached to the ring. This is the standard laboratory route to aromatic fluorides.
2. Stephen reaction: This reaction reduces a nitrile group to an aldehyde using stannous chloride and hydrochloric acid, followed by hydrolysis of the resulting imine salt. It has nothing to do with diazonium salts or fluorine.
3. Gattermann reaction: This is a formylation reaction, where an aromatic ring is treated with hydrogen cyanide and hydrogen chloride in the presence of a Lewis acid catalyst to introduce a -CHO group. Again, no diazonium chemistry or fluorine is involved.
4. Gomberg reaction: This reaction couples an aryl diazonium salt with an aromatic compound in the presence of a base to form a biaryl product, through a free radical pathway. It builds a new carbon-carbon bond between two rings rather than installing a fluorine atom.

Only the Balz-Schiemann reaction starts from an aryl diazonium tetrafluoroborate salt and, on heating, delivers the aryl fluoride.

So the correct answer is Balz-Schiemann reaction.