Aromatic Amines

• Aromatic amines are organic compounds derived from ammonia (NH₃) where one or more hydrogen atoms are replaced by an aromatic ring, such as benzene or naphthalene.

• The general formula is Ar-NH₂, where Ar represents an aromatic group.

Types and Classification of Aromatic Amines

Based on the Number of Aromatic Groups:

• Primary Aromatic Amines: One aromatic group attached to nitrogen (e.g., aniline, naphthylamine).

• Secondary Aromatic Amines: Two aromatic groups attached to nitrogen (e.g., diphenylamine, N-phenylnaphthylamine).

• Tertiary Aromatic Amines: Three aromatic groups attached to nitrogen (e.g., triphenylamine, N,N-diphenylaniline).

Based on Substituents on the Aromatic Ring:

• Mono-substituted: One substituent on the ring (e.g., 2-methylaniline, 4-chloroaniline).

• Di-substituted: Two substituents on the ring (e.g., 2,4-dimethylaniline, 3,5-dichloroaniline).

• Poly-substituted: Multiple substituents on the ring (e.g., 2,4,6-trimethylaniline).

Applications

• Dye Manufacturing: Intermediates in azo dye production.

• Pharmaceuticals: Used in the synthesis of drugs like analgesics and antihistamines.

• Pesticides: Intermediates for pesticide production.

• Polyurethane Production: Chain extenders in foams and coatings.

• Rubber Antioxidants: Used as stabilizers in the rubber industry.

Examples of Aromatic Amines

1. Aniline (C₆H₅NH₂): Intermediate in dye, pharmaceutical, and pesticide production.

2. 4-Nitroaniline (C₆H₄(NH₂)NO₂): Used as a dye intermediate.

General Methods of Preparation

Reduction of Nitro Compounds:

• Reduction of aromatic nitro compounds to amines using agents like hydrogen gas, tin, or iron.

• Example: Nitrobenzene to aniline:

• C6​H5​NO2​ + 3H2 ​→ C6​H5​NH2 ​+ 2H2​O

Amination of Aryl Halides (Buchwald-Hartwig Amination):

• Reaction of aryl halides with ammonia or amines in the presence of a palladium catalyst.

• Example: Bromobenzene to aniline:

• C6​H5​Br + NH3 ​→ C6​H5​NH2 ​+ HBr

Hofmann Rearrangement:

• Conversion of primary amides to amines using halogen and a strong base.

• Example: p-Toluamide to p-Toluidine:

• C6​H4​(CH3​)CONH2​ + Br2 ​+ 4NaOH → C6​H4​(CH3​)NH2 ​+ 2NaBr + Na2​CO3 ​+ 3H2​ 

Important Reactions

Acylation:

• Aromatic amines react with acid chlorides or anhydrides to form amides.

• Example: Acylation of aniline with acetyl chloride:

• C6​H5​NH2​ + CH3​COCl → C6​H5​NHCOCH3 ​+ HCl

Diazotization:

• Primary aromatic amines react with nitrous acid to form diazonium salts.

• Example: Diazotization of aniline:

• C6​H5​NH2​ + HNO2 ​→ C6​H5​N2 + ​Cl− + 2H2​O

Coupling Reactions:

• Diazotized aromatic amines react with activated aromatic compounds to form azo compounds, used in dye synthesis.

• Example: Coupling of benzenediazonium chloride with phenol:

• C6​H5​N2 + ​Cl− + C6​H5​OH → C6​H5​N=N-C6​H4​OH + HCl