Amines

(i) Aromatic amines react with nitrous acid (prepared in situ from NaNO₂and a mineral acid such as HCl) at 273 - 278 K to form stable aromatic diazonium salts e., NaCl and water.

(ii) Aliphatic primary amines react with nitrous acid (prepared in situ from NaNO₂and a mineral acid such as HCl) to form unstable aliphatic diazonium salts, which further producealcohola and acid called as hydrochloric acid and evolution of nitrogen

(iii) Aliphatic amines are stronger bases than aromatic amines due to following reasons:

(a) The lone pair of electrons of the nitrogen atom of aromatic amines is involved in

conjugation with the π−bond pairs of the ring as follows

(b) Anilinium ion obtained by accepting a proton is less stabilized by resonance. Due to the −R effect of the benzene ring, the electrons on the N- atom are less available in the case of aromatic amines. Therefore, the electrons on the N-atom in aromatic amines cannot be donated

So, aniline is a weaker base than alkyl amines, in which +1 effect increases the electron density on the nitrogen atom.

1- C₆H₅NH₂ + CHCl₃ + KOH

It is a carbylamine reaction in which a isocyanide compound is formed along with side products of potassium chloride.Basically the name of reaction is given is due to formation of a foul smelling compound called as isocyanide.

2- C₆H₅N₂Cl + H₃PO₂ + H₂O

Benzenediazonium chloride is a very reactive compound which oxidises hypophosphorous acid to hypophosphoric acid and the reactant is reduced to benzene.

3- C₆H₅NH₂ + H₂SO₄ (conc.)

Aniline undergoes sulphonation to anillium hydrogensulphate.

4- C₆H₅N₂Cl + C₂H₅OH

Aniline is very activating group which undergoes reaction to give ortho and para product. But in acidic medium aniline accquires positive charge on N atom which is metadirecting group and hence the product.

5- C₆H₅NH₂ + Br₂ (aq)

It is clubbing reaction of a very reactive compound undergoing addition to give benzene.

6- C₆H₅NH₂ + (CH₃CO)₂O

As mentioned aniline is avery activating group, so to reduce its activity it is reacted with anhydride to give n-phenylethanamine.

7- C₆H₅N₂Cl

Hydrofluroburic acid reacts qith benzenediazonium chloride along with sodium nitrite to give a reduced product as Nitrobenzene.

(i) Ethyl iodide reacts with NaCN gives a substitution reactions to give propanitrile upon partial hydrolysis gives B, upon reaction with sodium hydroxide gives C.

(ii) Benzenediazoniumchloride gives nucleophilic substitution reactions gives A, upon hydrolysis the CN ion is replaced by OH ion which is less better leaving group gives B upon heating with ammonia gives C.

(iii) Ethylbromide gives nucleophilic substitution reactions gives B, upon reduction gives B followed by reacting with nitrous acid, i.e oxidation gives propanol.

(iv) Nitrobenzene upon reduction with iron/acid gives A, reacting with sodium nitrite gives benzenediazonium chloride, followed by complete Hydrolysis gives phenol.

(v) Acetic acid upon heating with ammmonia gives A, which is an amide. This amide reacts with NaOBr which extracts the carbonyl carbon giving B, followed by reacting with sodium nitrite gives methanol.

(vi) Nitrobenzene upon reduction with iron/acid mixture gives A, followed by oxidation with nitrous acid gives B and reacting with phenol undergoes addition reaction to give C.

(i) Carbylamine reaction

Carbylamine reaction is used as a test for the identification of primary amines. When aliphatic and aromatic primary amines are heated with chloroform and ethanolic potassium hydroxide, carbylamines (or isocyanides) are formed. These carbylamines have very unpleasant odours. Secondary and tertiary amines do not respond to this test.

For example,

(ii) Diazotisation

Aromatic primary amines react with nitrous acid (prepared in situ from NaNO2 and a mineral acid such as HCl) at low temperatures (273-278 K) to form diazonium salts. This conversion of aromatic primary amines into diazonium salts is known as diazotization.

For example, on treatment with NaNO₂ and HCl at 273?278 K, aniline produces

benzenediazonium chloride, with NaCl and H₂O as by-products.

(iii) Hoffmann bromamide reaction

When an amide is treated with bromine in an aqueous or ethanolic solution of sodium hydroxide, a primary amine with one carbon atom less than the original amide is produced. This degradation reaction is known as Hoffmann bromamide reaction. This reaction involves the migration of an alkyl or aryl group from the carbonyl carbon atom of the amide to the nitrogen atom.

For example,

(iv) Coupling reaction

The reaction of joining two aromatic rings through the? N=N? bond is known as coupling reaction. Arenediazonium salts such as benzene diazonium salts react with phenol or aromatic amines to form coloured azo compounds.

It can be observed that, the para-positions of phenol and aniline are coupled with the diazonium salt. This reaction proceeds through electrophilic substitution.

(v)  Ammonolysis

When an alkyl or benzyl halide is allowed to react with an ethanolic solution of ammonia, it undergoes nucleophilic substitution reaction in which the halogen atom is replaced by an amino (? NH2) group. This process of cleavage of the carbon-halogen bond is known as ammonolysis.

When this substituted ammonium salt is treated with a strong base such as sodium hydroxide, amine is obtained.

Though primary amine is produced as the major product, this process produces a mixture of primary, secondary and tertiary amines, and also a quaternary ammonium salt as shown.

(vi) Acetylation

Acetylation (or ethanoylation) is the process of introducing an acetyl group into a molecule. Aliphatic and aromatic primary and secondary amines undergo acetylation reaction by nucleophilic substitution when treated with acid chlorides, anhydrides or esters. This reaction involves the replacement of the hydrogen atom of? NH2 or > NH group by the acetyl group, which in turn leads to the production of amides. To shift the equilibrium to the right hand side, the HCl formed during the reaction is removed as soon as it is formed. This reaction is carried out in the presence of a base (such as pyridine) which is stronger than the amine.

When amines react with benzoyl chloride, the reaction is also known as benzoylation. For example,

(vii) Gabriel phthalimide synthesis

Gabriel phthalimide synthesis is a very useful method for the preparation of aliphatic primary amines. It involves the treatment of phthalimide with ethanolic potassium hydroxide to form

potassium salt of phthalimide. This salt is further heated with alkyl halide, followed by alkaline hydrolysis to yield the corresponding primary amine.