Prepare 4-bromoaniline from aniline | p-bromoaniline synthesis

4-bromoaniline can be prepared by aniline easily. Aniline is an ortho para activator. In 4-bromoaniline bromine atom exist in para position related to the amine group.

With liquid bromine

But reaction of aniline and bromine liquid will give 2,4,6-tribromoaniline. Therefore we have to control the reaction if we need to prepare 4-bromoaniline.

Question: Derive 4-bromoaniline from benzene

4-bromoaniline / p-bromoaniline

4-bromoaniline , p-bromoaniline

Solution

Aniline is a ortho para activator. When liquid bromine (Br2(l)) is added to the aniline, it gives 2,4,6-bromoaniline.

aniline and liquid bromine reaction

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 Br2(l) to the newly formed compound.



Aniline and ethanoyl chloride reaction

Aniline is a strong ortho para activator. Aniline and ethanoyl chloride react to give N-phenylethanamide which is a ortho para Moderate activator. This product is an amide compound.

-NH-CO-CH3 group results a steric impediment around that group. Therefore, substitutions to ortho places is more difficult than para places.

Aniline and ethanoyl chloride reaction

N-phenylethanamide and liquid bromine reaction

Two products are given. Due to steric impediment, bromine is substituted more to para position. Therefore major product is para substituted compound.

N-phenylethanamide and liquid Br2 reaction


Conversion of benzene to 4-bromoaniline

benzene to 4-bromoaniline

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.



Prepare 2,4,6-tribromoaniline from aniline

Reaction between aniline and liquid bromium will give 2,4,6-tribromoaniline. 2,4,6-tribromoaniline is a white precipitate.

Prepare 2,4,6-tribromoaniline


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.