Prepare 4-bromoaniline from aniline | p-bromoaniline synthesis

4-bromoaniline can be prepared by aniline from several steps. Aniline is an ortho para activator compound like phenol. In 4-bromoaniline bromine atom exist in para position related to the amine group (-NH₂ group).

Aniline with liquid bromine reaction

Reaction of aniline and bromine liquid will give 2,4,6-Tribromoaniline. Therefore we have to control the reaction (to stop joining three bromine atoms to benzene ring and stop it by joining only one bromine atom at para position). if we need to prepare 4-Bromoaniline.

Question: Synthesis 4-bromoaniline from benzene. In this reaction you can only use benzene and CH₃COCl as organic compounds.

4-bromoaniline (p-bromoaniline)

Solution - steps of the conversion

Aniline is a ortho para activator. When liquid bromine (Br_2(l)) is added to the aniline, it gives 2,4,6-bromoaniline.

But we need only one bromine atom to connect to the para position of aniline. Therefore we reduce the activity of aniline by the reaction of aniline and ethanoyl chloride (CH₃COCl). Then we add Br_2(l) to the newly formed compound.

Conversion of benzene to 4-bromoaniline

We have already discussed how to prepare p-bromoaniline from aniine. Now, we want to prepare aniline by benzene.

Benzene to aniline

• First, benzene reacts with concentrated HNO₃ and concentrated H₂SO₄ to prepare nitrobenzene (nitration) For this reaction around 55⁰C temperature is required.
• Then, nitrobenzene is reduced to aniline salt by adding Sn and concentrated HCl. To release aniline from aniline salt, aqueous NaOH is added.

Aniline to p-bromoaniline mechanism

We know, electrons density of ortho and para positions are higher than meta positions. So, brominine subsitution should be occurred at ortho or para positions because this reaction is an electrophilic substitution reaction.

Brominum positive +1 ion forms by the reaction of FeBr₃ and Br₂. Br⁺ is an electrophile.

Benzene ring of aniline attacks the brominum ion. But due to steric impediment around ortho positions, Br⁺ cannot reach to the ortho position. Therefore brominium ion goes to the para position.

Questions

transformation of aniline to 2-bromoaniline ?

Aniline cannot be transformed to 2-bromoaniline directly because aniline is a strong activator. So, as preparation of 4-bromoaniline, we first add ethanoyl chloride with aniline. Then add liquid bromine to it. As major product, 4-bromoaniline will be given But as a by-product, 2-bromoaniline is given and it can be separated from a sepation method of chemicals.

How to synthesis o-bromoaniline from aniline

According to the previosly discussed method, o-bromoaniline is prepared as a minor product. So we can distillate mixture of p-bromoaniline and o-bromoaniline to separate both compounds. But receiving o-bromoaniline amount is very low tobecause it is a minor product of the reaction.

m-bromoaniline can be prepared by aniline?

We cannot prepare m-bromoaniline in one step from aniline because aniline is a ortho - para activator. In m-bromoaniline, bromine atom is attached to the meta position of aniline. We have to convert aniline to a deactivater and then attach bromine atom to the meta position.

What are the other names of 4-bromoaniline

p-bromoaniline | para-bromoaniline

How many steps are required to preparation of 4-bromoaniline from aniline?

There are three steps in preparation of 4-bromoaniline from aniline.

1. Reducing activity of aniline
2. Substitution of bromine
3. Recovery of aniline

How is phenyl amine converted into 4-bromoaniline?

Phenyl amine is aniline. The conversion of aniline to 4-bromoaniline is explained above.

How benzene is converted into meta chlorine aniline?

We know, aniline is an ortho para director. Therefore we cannot connect chlorine into the meta position. Then We use nitrobenzene to connect the chlorine atom to the meta position. Finally nitrobenzene is reduced to aniline.