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Electrophilic Substitution and the Nitration of Benzene

This page gives you the facts and a simple, uncluttered mechanism for the electrophilic substitution reaction between benzene and a mixture of concentrated nitric acid and concentrated sulfuric acid. If you want the nitration mechanism explained to you in detail, there is a link at the bottom of the page.

The Electrophilic Substitution Reaction Between Benzene and Nitric acid

The Facts

Benzene is treated with a mixture of concentrated nitric acid and concentrated sulfuric acid at a temperature not exceeding 50°C. As temperature increases there is a greater chance of getting more than one nitro group, -NO2, substituted onto the ring.

Nitrobenzene is formed.

\text{C}_6\text{H}_6 + \text{HNO}_3 \longrightarrow \text{C}_6\text{H}_5\text{NO}_2 + \text{H}_2\text{O}

or:

The concentrated sulfuric acid is acting as a catalyst.

The Formation of the Electrophile

The electrophile is the "nitronium ion" or the "nitryl cation", NO2+. This is formed by reaction between the nitric acid and the sulfuric acid.

\text{HNO}_3 + 2\text{H}_2\text{SO}_4 \longrightarrow {\text{NO}_2}^+ + 2{\text{HSO}_4}^- + \text{H}_3\text{O}^+

The Electrophilic Substitution Mechanism

Stage one

Stage two