Preparation
In industry, TNT is produced in a three-step process. First, toluene is nitrated with a mixture of sulfuric and nitric acid to produce mono-nitrotoluene or MNT. The MNT is separated and then renitrated to dinitrotoluene or DNT. In the final step, the DNT is nitrated to trinitrotoluene or TNT using an anhydrous mixture of nitric acid and oleum. Nitric acid is consumed by the manufacturing process, but the diluted sulfuric acid can be reconcentrated and reused. Subsequent to nitration, TNT is stabilized by a process called sulphitation, where the crude TNT is treated with aqueous sodium sulfite solution in order to remove less stable isomers of TNT and other undesired reaction products. The rinse water from sulphitation is known as red water and is a significant pollutant and waste product of TNT manufacture.
Control of nitrogen oxides in feed nitric acid is very important because free nitrogen dioxide can result in oxidation of the methyl group of toluene. This reaction is highly exothermic and carries with it the risk of a runaway reaction leading to an explosion.
In the laboratory, 2,4,6-trinitrotoluene is produced by a two step process. A nitrating mixture of concentrated nitric and sulfuric acids is used to nitrate toluene to a mixture of mono- and di-nitrotoluene isomers, with cooling to maintain careful temperature control. The nitrated toluenes are then separated, washed with dilute sodium bicarbonate to remove oxides of nitrogen, and then carefully nitrated with a mixture of fuming nitric acid and sulfuric acid. Towards the end of the nitration, the mixture is heated on a steam bath. The trinitrotoluene is separated, washed with a dilute solution of sodium sulfite and then recrystallized from alcohol.
Read more about this topic: Trinitrotoluene
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