Preparation, Reactions, Physical Properties of Aniline (C6H5NH2)
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.
Fig 01: Aniline molecule
Content
- Physical properties of aniline
- Preparation of aniline from benzene
- Preparation of aniline
- Reactions of aniline
- Aniline and alkyl halide reaction
- Aniline and halogen reaction
- Aniline and nitrous acid reaction
- Aniline and dilute acids reaction
- 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 and they are explained in detail.
- 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 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.
Reactions of aniline
Aniline is an activatator and it is also an ortho-para director. We study following reactions of aniline. Electrons' density of benzene ring in aniline is much higher than benzene and that is the reason why aniline shows different reactions than benzene..
- Aniline and alkyl halide reaction
- Aniline and halogen reaction
- Aniline and nitrous acid reaction
- 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 available aniline and alkyl halide.
Aniline and less alkyl halide
Secondary amines are given as the major product.
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 halogen reaction
Aniline and liquid bromine reaction
Aniline reacts with liquid bromine to give 2,4,6-tribromoaniline which is a white powder. Though aniline reacts with liquid bromine, benzene does not. This reaction proves that aniline has a higher electron density in the benzene ring than the benzene ring in benzene.
Aniline and liquid chlorine reaction
Aniline reacts with liquid chlorine to give 2,4,6-trichloroaniline. As with liquid bromine, 2,4,6-trichloroaniline is a white powder.
Aniline and nitrous acid reaction | Aniline + HNO2
This reaction is used to prepare phenol or benzene diazonium chloride according to the temperature. Because, Nitrous acid is not a stable acid and readily decomposes, Nitrous acid has to be prepared when it is required. Sodium nitrite and dilute hydrochloric acid (NaNO2 and HCl) are mixed at low temperature to prepare nitrous acid (HNO2).
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 chloridee is given as the product.
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 HCl acid reaction
Aniline has weak basic characteristics and HCl is a strong acid. Aniline reacts with HCl acid and forms Aniline hydrochloride (C6H5NH3+Cl-) which has weak acidic characteristics.
Aniline reactions summary
Have Questions?
Are aniline reactions are different from other primary aliphatic amines?
Aniline is a primary aromatic amine compound. But some of aniline reactions differ from other primary amine reactions because aniline has a benzene ring. 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 Sodium and aqueous 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).