What is aniline used for? Preparation, Properties, and Tests

Aniline Preparation

Laboratory method: from tin and HCl reduction of nitrobenzene: in the laboratory, aniline is made by the reduction of nitrobenzene by tin and HCl.

Sn + 4HCl → SnCl4 + 4H

C6H5NO2 + 6H → C6H5NH2 + 2H2O

Industrial manufacturing: from ioran and HCl reduction of nitrobenzene: Anealin is made by reduction of nitrobenzene by moist iron shavings and HCl in commercial quantities.

Fe + 3HCl → FeCl3 + 3H

C6H5NO2 + 6H → C6H5NH2 + 2H2O

Chlorobenzene: Chlorobenzene gets aniline at high pressure with ammonia in the presence of Cu2O and when heated to about 250°C.

C6H5Cl + NH3 → C6H5NH2 + HCl

Phenol: phenol gives aniline at high pressure and heated to 300°C with ammonia in the presence of anhydrous ZnCl2.

C6H5OH + NH3 → C6H5NH2 + H2O

Benzamide: The amide (-CONH2) group is modified into the amines (-NH2) group upon heating amides with bromine and caustic potash. This reaction is called the Huffman bromide reaction. This reaction is used to make aniline from benzamide.

C6H5CONH2 + Br2 + 4KOH → C6H5NH2 + K2CO3 + 2KBr + 2H2O

Aniline Physical Properties

In pure state, aniline is a colorless liquid. Its boiling point is 184°C. When exposed to air, it gets oxidized in small amounts and due to this its color becomes light brown. It is less soluble in water but more soluble in ether, alcohol and chloroform. Its relative density is 1.02. It has a distinct smell. It is a toxic substance.

Basic character: Similar to aliphatic amines, aniline also reacts with acids to form salts.

Example:

C6H5NH2 + HCl → C6H5NH3+Cl–

This is a weaker base than ammonia and aliphatic amines. The reason for this is that the amines group in aniline is linked to the phenol group and the phenol group is negative. The availability of a lone electron pair on nitrogen is reduced due to the -I effect of phenol group and the + M effect of amines group.

Hence aniline is a weaker base than ammonia and aliphatic amines such as CH3NH2 and C2H5NH2. In benzene ring, its basic increases in presence of positive electric group. On this basis, ortho meta and para Toluidine have a stronger base than aniline.

Alkylation: This secondary amin reacts with alkyl halides to form tertiary amine and quaternary ammonium compound.

C6H5NH2 + CH3Cl → C6H5NHCH3 + HCl

C6H5NHCH3 + CH3Cl → C6H5N(CH3)2 + HCl

C6H5N(CH3)2 + CH3Cl → [C6H5N(CH3)3]+Cl–

Acetylation: The reaction of aniline with acetyl chloride or acetic anhydride results in acetylation. In this reaction, a hydrogen atom of the amines group of aniline is displaced by an acetyl (CH3CO-) group.

C6H5NH2 + CH3COCl → C6H5NHCOCH3 + HCl

C6H5NH2 + (CH3CO)2O → C6H5NHCOCH3 + CH3COOH

Reaction of aniline with benzoil chloride (C6H5COCl) results in its benzoylation, similar to acetylation, and benzanilide(C6H5NHCOC6H5) is obtained.

Carbylamine Reaction: Like alifatic amines, aniline also exhibits a carbylamine reaction. On heating it with chloroform and NaOH, a highly deodorant phenyl iso cyanide(C6H5NC) is formed.

C6H5NH2 + CHCl3 + 3KOH → C6H5NC + 3KCl + 3H2O

Grignard reagent reaction: It reacts with Grignard reagents to form hydrocarbon.

C6H5NH2 + CH3MgBr → CH4 + C6H5NHMgBr

Reaction with aldehydes: By reacting with aldehydes, this imines form common names, also known as schiff bases.

C6H5NH2 + C6H5CHO → C6H5 — N = CH — C6H5 + H2O

Reaction with nitrous acid: reacts with aniline nitrous acid in the presence of hydrochloric acid to form benzene di azonium chloride. The nitrous acid required for this reaction is obtained by the action of NaNO2 and HCl. This reaction is carried out at low temperature (0–5°C) because the benzene di azonium chloride decomposes at higher temperatures. In this reaction, -NH2 group is converted into -N group. This reaction is called diazotisation.

C6H5NH2 + HNO2 + HCl → C6H5 — N = N — Cl + 2H2O

The benzene diazonium chloride present — N = N — Cl group can be easily converted into other groups. Hence this reaction is used to make many compounds from aniline to benzene, chlorobenzene, phenol etc. benzene diazonium chloride exhibits coupling reaction with beta naphthyl and some other compounds in alkaline solutions.

Dyes are obtained as a result of this reaction. This reaction is used to test aniline and to make pigments.

Aniline uses

Aniline is used as a catalyst in the manufacture of other aromatic compounds, in the manufacture of pigments, in the manufacture of drugs, and in vulcanisation in rubber industry.

Aniline Tests

By mixing chloroform and alcohol KOH solution in aniline, a very deodorant substance is formed upon heating.

Benzene di azonium chloride is formed when aniline combines sodium nitrite and hydrochloric acid at 0–5°C temperature. A bright red color or precipitate is obtained by adding beta naphthol solution made in NaOH to the mixture obtained.

When adding bromine to dilute aqueous solution of aniline, white precipitate is obtained immediately.