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Nitration

01Nitration

Nitrating mixture

This section covers the importance, reagents, conditions and nitronium-ion formation for nitration of benzene.

Reagents and conditions

Nitration replaces a hydrogen atom on the benzene ring with a nitro group, −NOX2\ce{-NO2}. Nitrating benzene therefore produces nitrobenzene.

Nitration is an important step in organic synthesis, including the manufacture of explosives and synthetic routes that lead to aromatic amines.

Feature Nitration of benzene
Reagents Concentrated nitric acid and concentrated sulfuric acid
Role of HX2SOX4\ce{H2SO4} Catalyst
Electrophile NOX2X+\ce{NO2+}
Reaction type Electrophilic substitution
Conditions Heat under reflux at 2525–60∘C60^\circ\mathrm{C}

Keeping the reaction at no more than about 60∘C60^\circ\mathrm{C} favours formation of the monosubstituted product; at higher temperatures, a further nitro group may be introduced.

Generating the nitronium ion

The species that attacks the aromatic ring is the nitronium ion, NOX2X+\ce{NO2+}. The acid mixture generates this electrophile before it reacts with benzene.

  1. Sulfuric acid transfers HX+\ce{H+} to nitric acid, giving protonated nitric acid together with HSOX4X−\ce{HSO4-}.
  2. Water is then eliminated from the protonated species, producing the NOX2X+\ce{NO2+} ion.
1

Proton transfer

HNOX3+HX2SOX4→HX2NOX3X++HSOX4X−\ce{HNO3 + H2SO4 -> H2NO3+ + HSO4-}
2

Water eliminated

HX2NOX3X+→NOX2X++HX2O\ce{H2NO3+ -> NO2+ + H2O}

Combining these two stages gives:

HNOX3+HX2SOX4→NOX2X++HSOX4X−+HX2O\ce{HNO3 + H2SO4 -> NO2+ + HSO4- + H2O}

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