Nitration

Nitration is a type of chemical reaction that adds a nitro group to a chemical compound. The term is also sometimes used to refer to nitrooxylation, a reaction that makes nitrate esters from alcohols. This second use is not formally correct: the two reactions are different.

A common use for nitration is the preparation of nitrobenzene from benzene. This compound is used to make many other aromatic nitrogen compounds, like aniline.

Reaction

Nitration is a type of substitution reaction.

The main reactant in nitration reactions is nitronium. Nitronium is a polyatomic ion with the formula NO+2. Nitronium is normally made by reaction of nitric acid and a stronger acid like sulfuric acid:

HNO₃ + H₂SO₄ ⇌ NO+2 + HSO−4 + H₂O

The nitronium ion is a strong electrophile. It is attracted to organic nucleophiles. It forms a coordination complex and then a chemical bond with the nucleophile, which then releases a hydrogen ion:

C₆H₆ + NO+2 → C₆H₅NO₂ + H⁺

This image shows the full nitration process for benzene.

Difference from nitrooxylation

When nitric acid reacts with an alcohol, it makes a special kind of chemical called a nitrate ester. This process is really called nitrooxylation or nitrate esterification. People sometimes call it nitration, but that name is not fully correct.

A good example is how the explosives nitroglycerin and nitrocellulose are made. Even though their names sound like they are nitro compounds, they are actually nitrate esters.

In this reaction, a particle called nitronium reacts with an alcohol instead of an aromatic ring. This makes a new chemical bond between nitrogen and oxygen, which behaves differently from a bond between nitrogen and carbon.