Overview of the Nitration Mechanism

Nitration is the general term used for the chemical process in which a nitro group (NO2) is introduced into an organic chemical compound.

Introduction

Nitration reactions are one of the most studied organic reactions. Aromatic and aliphatic compounds can both be nitrated by various methods such as heterolytic and radical nitrations. Aromatic nitration is most frequently electrophilic, whereas aliphatic nitration is free radical.

Nitration of Benzene

Nitrobenzene is formed when benzene interacts slowly with heated concentrated nitric acid. The reaction proceeds more quicker if benzene is heated with a combination of concentrated nitric acid and concentrated sulfuric acid, increasing the concentration of the electrophile- the nitronium ion (NO2)

Nitration Reaction

The nitration reaction of Nitration Benzene can be written as:

HNO3 + 2H2SO4     NO2+  + 2HSO4–  + H3O+

The above is an Electrophilic Aromatic Substitution Nitration Reaction

Summary of the Nitration Reaction:

• Overall transformation: Ar-H to Ar-NO2

• Reagent: for benzene, HNO3 in H2SO4 / heat

• Electrophilic species: the nitronium ion (i.e., NO2+) formed by the loss of water from the nitric acid.

Nitration of Benzene Mechanism

The nitration of Benzene Mechanism can be explained in the following way:

When the NO2+ ion approaches the benzene’s delocalised electrons, these electrons are strongly attracted to the positive charge. The delocalised system’s two electrons are subsequently utilised to create a new connection with the NO2+. Because the delocalisation is partially disrupted, the two electrons are no longer a member of the delocalised system, causing the ring to obtain a positive charge. The second stage involves the production of a hydrogen sulphate ion, HSO4–, at the same time as the NO2+ ion. This results in the removal of a hydrogen from the ring, resulting in the formation of sulphuric acid and the regeneration of the catalyst. The electrons that initially connected the hydrogen to the ring are now utilised to re-establish the delocalised system.

The nitration of Benzene Mechanism can also be explained as a 4-step nitration reaction process, which is as follows:

Step 1.

The first step is an acid/base reaction. The hydroxyl group of nitric acid is protonated. This results in a better departing group.

Step 2.

The electrophile that is reactive. The nitronium ion is produced by the loss of the leaving group, which is a water molecule.

Step 3.

The aromaticity of the arene is destroyed in this step, which determines the rate. The electrophilic nitronium ion combines with the arene’s nucleophilic C=C.

Step 4.

Water acts as a base in this phase, removing the proton from the sp3 C carrying the nitro group and reuniting the C=C and aromatic system.

Conclusion

Nitration reactions are one of the most studied organic reactions. Aromatic and aliphatic compounds can both be nitrated by various methods such as heterolytic and radical nitrations. Aromatic nitration is most frequently electrophilic, whereas aliphatic nitration is free radical.

The nitration reaction of Nitration Benzene can be written as:

HNO3 + 2H2SO4   NO2+  + 2HSO4–  + H3O+

The above is an Electrophilic Aromatic Substitution Nitration Reaction.

Nitrobenzene is formed when benzene interacts slowly with heated concentrated nitric acid. The reaction proceeds more quicker if benzene is heated with a combination of concentrated nitric acid and concentrated sulphuric acid, increasing the concentration of the electrophile- the nitronium ion (NO2)