| melting point 80.1 °C |
boiling point ignites at 295 °C |
trinitrotoluene | molecular mass 227.13 g/mol |
density 1.654 g/mL |
| table key | sensitivity very low |
chemical formula C7H5N3O6 |
explosive velocity 7028 m/s |
estimated cost $?.00/g |
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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.
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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