NITRATION OF TOLUENE

Nitration of toluene is the only important reaction that involves the aromatic ring rather than the aliphatic methyl group. The nitration reaction occurs with an electrophilic substitution by the nitronium ion. The reaction conditions are milder than those for benzene due to the activation of the ring by the methyl substituent. A mixture of nitrotoluenes results. The two important monosubstituted nitrotoluenes are o- and p-nitrotoluenes:

Mononitrotoluenes are usually reduced to corresponding toluidines, which make dyes and rubber chemicals:

Dinitrotoluenes are produced by nitration of toluene with a mixture of concentrated nitric and sulfuric acid at approximately 80°C. The main products are 2,4- and 2,6-dinitrotoluenes:

The dinitrotoluenes are important precursors for toluene diisocyanates (TDI), monomers used to produce polyurethanes. The TDI mixture is synthesized from dinitrotoluenes by a first-step hydrogenation to the corresponding diamines. The diamines are then treated with phosgene to form TDI. The yield from toluene is approximately 85%:

An alternative route for TDI is through a liquid-phase carbonylation of dinitrotoluene in presence of PdCl₂ catalyst at approximately 250°C and 200 atmospheres:

Trinitrotoluene TNT is a well-known explosive obtained by further nitration of the dinitrotoluenes.