ignites at 295 °C
2,4,6-trinitrotoluene, or just TNT, is the oft used military and industrial explosive that may be the among the best recognized explosive around. Other names for TNT include: trinitrotoluol; sym-trinitrotoluene; a-trinitrotoluol; 2-methyl-1,3,5-trinitrobenzene; entsufon; 1-methyl-2,4,6-trinitrobenzene; methyltrinitrobenzene; tolite; trilit; s-trinitrotoluene; s-trinitrotoluol; trotyl; sym-trinitrotoluol; alpha-trinitrotoluol; tolite; triton; tritol; trilite; tri; tutol; trinol; füllpulver 1902; Fp02; tritolo; trillit; tolita; tol; and trotil. TNT was first synthesized in 1863 by a scientist named Wilbrand who treated toluene with sulfuric and nitric acid at near boiling temperatures. Although there are several isomers of trinitrotoluene, only the 2,4,6- isomer is of importance. Pure TNT is in the form of small columns or needles and is insoluble in water. It is quite stable, being meltable ,or able to act like a plastic at around 50 °C. TNT can even be boiled although the experiments did this under reduced pressure (50mm Hg) to lower the boiling point to around 245 °C. The normal detonation temperature is 333 °C, the calculated boiling point at normal atmospheric pressure is 345 °C, so don't do it. Some experiments have determined that the presence of foreign material like 1.9% of Fe2O3 will lower the amount of time it takes for TNT to explode once it reaches its critical temperature, or 295 °C, the temperature at which decomposition begins. Also, mixing pure sulfur with TNT will lower the initiation temperature and increase the explosive power. For example, pure TNT explodes at 333 °C, 5% sulfur explodes at 304 °C, 10% sulfur at 294 °C, 20% sulfur at 284 °C, and 30% sulfur at 275 °C. The increase in explosive power is gained through the addition of 5-10% sulfur. Because the stability of TNT is so great, it is harder to detonate it, the sensitivity increases somewhat above 80º C, but is still rather low even when molten. A powerful blasting cap, or booster charge, will be needed to detonate TNT. This lab is carried out in three separate operations, forming mononitrotoluene, then dinitrotoluene, and finally trinitrotoluene.
|ethyl alcohol||100/500/600-mL beaker|
|nitric acid||Buchner funnel|
|sodium bisulfite||graduated cylinder|
Prepare a nitrating solution of 160 mL of 95% sulfuric acid and 105 mL of 75% nitric acid in a 500-mL beaker set in a salt-ice bath. Mix the acids very slowly to avoid the generation of too much heat. Allow the mixture to cool to room temperature. The acid mixture is slowly added dropwise, with a pipet or buret, to 115 mL of toluene in a 600-mL beaker while stirring rapidly. Maintain the temperature of the beaker during the addition at 30-40 °C by using either a cold water or salt-ice bath. The addition should require 60-90 minutes. After the addition, continue stirring for 30 minutes without any cooling, then let the mixture stand for 8-12 hours in a separatory funnel. The lower layer will be spent acid and the upper layer should be mononitrotoluene, drain the lower layer and keep the upper layer.
Dissolve one-half of the previously prepared mononitrotoluene and 60 mL of 95% sulfuric acid in a 500-mL beaker set in a cold water bath. Prepare a nitrating solution of 30 mL of 95% sulfuric acid and 36.5 mL of 95% nitric acid in a 100-mL beaker. Preheat the beaker of mononitrotoluene to 50 &Deg;C. Very slowly add the nitrating acid to the beaker of mononitrotoluene, with a pipet or buret, drop by drop while stirring rapidly. Regulate the rate of addition to keep the temperature of the reaction between 90-100 °C. The addition will require about 1 hour. After the addition, continue stirring and maintaining the temperature at 90-100 °C for 2 hours. If the beaker is allowed to stand, a layer of dinitrotoluene will separate, it is not necessary to separate the dinitrotoluene from the acid in this step.
While stirring the beaker of dinitrotoluene, heated to 90 °C, slowly add 80 mL of 100% fuming sulfuric acid, containing about 15% SO3, by pouring from a beaker. Prepare a nitrating solution of 40 mL of 100% sulfuric acid, with 15% SO3, and 50 mL of 99% nitric acid. Very slowly add the nitrating acid to the beaker of dinitrotoluene, with a pipet or buret, drop by drop while stirring rapidly. Regulate the rate of addition to keep the temperature of the reaction between 100-115 °C. It may become necessary to heat the beaker after three-quarters of the acid has been added in order to sustain the 100-115 °C temperature. The addition will require about 90-120 minutes. Maintain the stirring and temperature at 100-115 °C for 2 hours after the addition is complete. Allow the beaker to sit undisturbed for 8-12 hours, it should form a solid mass of trinitrotoluene crystals. Pour the contents of the beaker over a Buchner funnel without any filter paper to collect the bulk of the crystals, save the acidic filtrate as well. Break up the collected crystals and wash them with water to remove any excess acid. Add the collected acid and wash filtrates to a large volume of water, this will cause any remaining trinitrotoluene to precipitate. Decant off as much of the water as possible and combine these crystals with the previous ones on the funnel. Drown the crystals in a large volume of water, filter to collect them, and wash several times with water. Wash the crystals by adding them to a beaker of water, heat the water enough to melt the crystals while stirring rapidly. Repeat the melting and stirring with a fresh batch of water three or four times to wash thoroughly. After the last washing, the trinitrotoluene is granulated by allowing it to cool slowly under hot water while the stirring is continued. Filter to collect the crystals and allow to dry. The TNT can be further purified by recrystallizing from ethyl alcohol, dissolve the crystals in 60 °C and allow the solution to cool slowly. A second method of purification is to digest the TNT in 5 times its weight of 5% sodium bisulfite solution heated to 90 °C while stirring rapidly for 30 minutes. Wash the crystals with hot water until the washings are colorless, then allow the crystals to granulate as before. You will need a graduated cylinder for measuring liquids, a stirring rod or magnetic stirrer for mixing, and a thermometer to monitor the temperature.
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