Aniline properties, preparing, reactions, physical properties

Aniline is an aromatic primary amine compound. Aniline belongs to Nitrogen substituted organic compounds. In this tutorial, you can learn aniline preparing, reactions and characteristics of aniline. Aniline has some different characteristics than other primary amines.

aniline molecule
Fig 01: Aniline molecule

In this tutorial, we study about followings.

  1. Physical properties of aniline
  2. Preparation of aniline
  3. Aniline reactions
  4. Questions

Physical properties of aniline

  • A light brown solution
  • Aniline has a characteristic odour
  • Aniline is a polar compound. Due to exist of hydrogen bonds, melting and boiling points are high. But H bonds of aniline is weaker than hydrogen bonds of phenol.
  • Aniline can make hydrogen bonds with water. But due to large phenyl group solubility of aniline is low.
  • Aniline is less basic than ammonia. But amides are less basic than aniline.

Preparation of aniline

Preparation of aniline from benzene is explained below.

Preparation of aniline from benzene

There are two steps to prepare aniline from benzene.

Benzene to nitrobenzene

Benzene reacts with concentrated sulfuric acid and concentrated nitric acid on heating about 400C and give nitrobenzene. A -NO2 group is substituted to the benzene ring.

Nitrobenzene to aniline

Aniline is prepared by the reaction of nitrobenzene and Sn / concentrated HCl / excess NaOH with nitrobenzene. In this reaction, nitrobenzene is reduced to aniline salt by Sn / concentrated HCl. Then aniline is recovered by adding NaOH.

aniline from benzene and nitrobenzene

Aniline reactions

Aniline is an activataor and it is also an ortho para director. We study following aniline reactions. Electrons density of benzene ring in aniline is much higher than benzene.

  1. Aniline and alkyl halide reaction
  2. Aniline and halogen reaction
  3. Aniline and nitrous acid reaction
  4. Aniline and dilute acids reaction

Aniline and alkyl halide reaction

Secondary amines or tertiary amines or quaternary ammonium salts can be given from reaction of aniline and alkyl halides. The product depends on the amount of aniline and alkyl halide.

Aniline and less alkyl halide

Secondary amines are given.

Aniline and less alkyl halide

Aniline and excess alkyl halide

Tertiary amines are given by the reaction of aniline and excess alkyl halide. If there are more alkyl halides, quaternary ammonium salts are given.

Aniline and excess alkyl halide

Aniline and halogen reaction

Aniline and liquid bromine reaction

Aniline reacts with liquid bromine to give 2-4-6-tribromoaniline.

aniline and liquid bromine reaction

Aniline and liquid chlorine reaction

Aniline reacts with liquid chlorine to give 2-4-6-trichloroaniline.

aniline and liquid chlorine reaction

Aniline and nitrous acid reaction | Aniline + HNO2

This reaction is used to prepare phenol or benzene diazonium chloride. Sodium nitrite and dilute hydrochloric acid ( NaNO2 and HCl ) are mixed to prepare nitrous acid (HNO2). According to the temperature, phenol or benzene diazonium chloride is given.

Preparing Nitrous acid

Nitrous acid is prepared by mixing sodium nitrite and dilute hydrochloric acid. ( NaNO2 / HCl ). Aniline reacts with nitrous acid in two ways.

Aniline and nitrous acid under cold conditions

When reaction occurs below 50C, benzene diazonium chloride is given as the product.

aniline and nitrous gives benzene diazonium chloride

Aniline and nitrous acid in room temperature

In room temperature or above 100C, phenol is given as the product of aniline and nitrous acid reaction.

aniline and nitrous gives phenol

Aniline and HCl reaction

Aniline has weak basic characteristics. HCl is a strong acid. Aniline reacts with HCl and forms Aniline hydrochloride which has weak acidic characteristics.

Aniline hydrochloride - C6H5NH3+Cl-

Aniline reactions summary

aniline reactions summary

Questions of Aniline

Are aniline reactions are different from other primary aliphatic amines?

Aniline is a primary amine. But some of aniline reactions differ from other primary amine reactions. As an example aniline gives benzene diazonium salt with nitrous acid below 50C. But other primary aliphatic amines give primary alcohols with nitrous acid below 50C.

How many steps are required to preparation of aniline from benzene.

It takes only two steps. First benzene is converted into nitrobenzene. Then nitrobenzene is converted to aniline.

How reactions of aniline are different from reactions of phenol?

We know, aniline is basic and phenol is acidic. So aniline can react with acids and phenol reacts with bases.

  • Aniline reacts with dilute HCl.
  • Phenol reacts with Na and NaOH.

  • What are the chemical properties of aniline?

    Electrons density of benzene ring in aniline is higher than benzene. Therefore electrophilic substitution reactions are occurred easily than benzene.

    Example: Aniline reacts with bromine liquid to give 2,3,4-dibromoaniine. But benzene does not give products with Br2(l). Benzene requires a lewis acid catalyst to give products with Br2(l)

    What is the reaction of HCl and aniline.

    Aniline is a weak base. It reacts with HCl and forms a weak acid (phenylammonium chloride).

    Lewis structures

    P2O5 lewis structure OH- lewis structure Ammonium ion (NH4+) lewis structure H2CO3 lewis structure