The Function of Sulfuric Acid in Nitration

Nitration is a part of the organic reaction known as electrophilic aromatic substitution. This is the reaction in which there is a substitution of an atom attached to an aromatic system with an electrophile.

In a more simple definition, nitration is the process of adding a nitro group to an aromatic ring. To understand this process better, let’s learn about this bit by bit.

  • Electrophilic

To make the reaction happens, we need two things: an electrophile and a nucleophile. Both acts as consecutively as the electron acceptor and the electron donor.

In the process of Electrophilic Aromatic Substitution (EAS), the aromatic ring acts as the electron donor while the nitro group acts as the electron acceptor.

  • Aromatic

The description above mentioned that the electron donor is the aromatic ring itself. Specifically, there are pi electrons inside the aromatic ring. These electrons act as the nucleophile or the electron donor.

  • Substitution

The substitution in the EAS is held between a hydrogen atom on the aromatic ring with the nitro group. The nitro group will replace one of the hydrogen atoms.

One of the chemicals that has a role in nitration is sulfuric acid. What is the role of sulfuric acid in nitration? Let’s find out!

Related: Uses of Sulfur in daily life

The Function Of Sulfuric Acid In Nitration 

We need an electrophile as the electron acceptor in the nitration. In this case, we need the nitro group to play this role.

There are two ingredients that we need to generate a nitrogen electrophile, they are nitric acid and sulfuric acid. The making of electrophile happens when both chemicals are mixed together. This is the step-by-step explanation of generating electrophile:

  1. There is a group of hydroxyl (OH) in the molecule of nitric acid, while the sulfuric acid provides with a hydrogen ion. The OH is protonated by the hydrogen ion.
  2. A water molecule is the result of protonation. Water, as a good leaving group (a molecular fragment which is stable by itself), falls off. This process creates nitronium ion, which in this case we call a nitro group. This nitro group is ready to react with the aromatic ring.

The Process Of Nitration

Now we have the nitronium ion we need in nitration. The next step is when the pi electrons inside the aromatic ring bond with the nitro group. Because of its character, nitrogen cannot have more than 4 bonds so the first thing to do is breaking the existing bond between the nitrogen and the oxygen.

Water is involved in this step. Water, as a base, pulls off the hydrogen atom. This process has two things as results.

The first one is the regeneration of aromaticity in the ring system. Aromaticity is the characteristic of an organic molecule in the shape of a cyclic and flat structure with a ring that functions as a stabilizer.  The second result if this is the final nitrated product.


The Use Of Nitro Compound

There are many nitro compounds used commercially wide as explosives. They also function as solvents or chemical intermediates.


One of the popular use of the nitro compound as explosive is TNT. The process of making TNT or trinitrotoluene is by nitration. We just need an aromatic hydrocarbon called Toluene and nitrate it three times. The nitration process is exactly the same as the description above.

Nitro compounds contain one or more nitro functional group which commonly used in pharmaceuticals. In spite of this, the nitro group is often connected to issues such as mutagenicity and genotoxicity. Because of its association with changing and damaging the genetic material and information, the nitro group is considered as a burden in the process of drugs discovery.

Now we have learned that without sulfuric acid, the nitration cannot happen. We also learned about the uses of the nitration result which is most beneficial for making explosives.