Reductions of Amines with Nitric(III) Acid

• All amines react with nitric(III) acid

• As nitric(III) acid is a weak and unstable acid, it is prepared by treating NaNO₂ with an aqueous solution of a strong acid

NaNO₂(aq) + HCl(aq) ®¾ HNO₂(aq) + NaCl(aq)

2NaNO₂(aq) + H₂SO₄(aq) ®¾ 2HNO₂(aq) + Na₂SO₄(aq)

 

Reductions of Primary Amines with Nitric(III) Acid

Reaction of Primary Aliphatic Amines with Nitric(III) Acid

• 1° aliphatic amines react with HNO₂ to yield aliphatic diazonium salts

• Diazonium salts, even at low temperatures, are highly unstable, they decompose spontaneously by losing nitrogen to form carbocations

Example:

 

Reaction of Primary Aromatic Amines with Nitric(III) Acid

• 1° aromatic amines react with HNO₂ to yield benzenediazonium salts

• Benzenediazonium salts are unstable, but they do not decompose when the temperature of the reaction mixture is kept below 5°C

• The greater stability of benzenediazonium salts is due to the delocalization of the positive charge of the diazonium group

+

(–N º N) over the benzene ring

Reductions of Secondary Amines with Nitric(III) Acid

• 2° aliphatic and aromatic amines react with HNO₂ to yield

N-nitrosoamines

Examples:

Reductions of Tertiary Amines with Nitric(III) Acid

• 3° aliphatic amines don’t react with HNO₂

Example:

 

6. Arendiazonium Salts

Primary arylamines react with nitrous acid, HNO₂, to yield stable arenediazonium salt

• Arendiazonium salts are extremely useful in synthesis because the diasonio group (N₂⁺) can be replaced by nucleophiles in asubstitution reaction

 

Preparation of Substituted Aromatic Compounds by Diazonio Replacement Reactions

Replacement of the Diazonium Group by –Cl, –Br or –CN (The Sandermeyer Reaction)

The diazonium group of benzenediazonium ions can be replaced by –Cl, –Br and –CN by treating with CuCl, CuBr and CuCN respectively

,

 

Replacement of the Diazonium Group by –NO₂

The diazonium group of benzenediazonium ions can be replaced by –NO₂ by treating with NaNO₂ in the presence of catalysts such as CuNO₂

Replacement of the Diazonium Group by –SO₂Cl

The diazonium group of benzenediazonium ions can be replaced by –SO₂Cl on reacting with SO₂ in the presence of catalysts such as CuCl

 

Replacement of the Diazonium Group by –I

The diazonium group of benzenediazonium ions can be replaced by –I on reacting with KI

Replacement of the Diazonium Group by –F

The diazonium group of benzenediazonium ions can be replaced by –F on reacting with KBF₄