Molecule of the Day - Trinitrotoluene (TNT)
Trinitrotoluene (C7H5N3O6), better known as TNT, is probably one of the most well-known molecules due to its heavy usage as an explosive since the early 20th century. Under regular conditions, it is a yellow solid that is poorly soluble in water.
Upon detonation, TNT decomposes according to the following equation:
2 C7H5N3O6 → 3 N2 + 5 H2O + 7 CO + 7 C
As seen above, 15 moles of gases are produced for every 2 moles of solid TNT. The large amount of gases produced means that TNT is a powerful explosive. Additionally, the formation of the thermodynamically stable N2 gas makes the reaction extremely favourable.
TNT was first synthesised in the mid-19th century, and was used as a yellow dye. Its potential as an explosive went unnoticed due to its high activation energy. This meant that TNT was not easily detonated and was relatively stable under regular conditions. Consequently, other explosives such as picric acid and nitroglycerine were more frequently used. However, these other explosives were often too flammable or explosive; in fact, the first shipment of nitroglycerine exploded en route to a construction site and killed 15 people.
On the other hand, TNT was relatively safer to handle, and could be easily melted and moulded to form certain shapes and sizes, depending on the application. This is because TNT has a melting point of 80 degrees Celsius, which is below its decomposition temperature of 240 degrees Celsius (see below for a melted sample of TNT).
Additionally, TNT has a high detonation velocity of 6,640 m/s, as well as a energy density of 4.6 megajoules per kilogram, which is still used as a reference figure for bombs.
While TNT has been used for war, we shouldn’t forget that it has also been used to improve human lives - it was used as an explosive to construct tunnels through mountains in the United States, allowing different regions to be connected by trains. Even now, TNT is still sometimes used in the demolition of old buildings to clear old infrastructure for repurposing of the land.
TNT is a suspected carcinogen, and has been linked to anaemia and liver problems. It also irritates skin, causing yellow or orange discolourations.
TNT can be produced by the exhaustive nitration of toluene using a mixture of concentrated nitric and sulfuric acids, resulting in three successive nitrations of the toluene molecule.