Picric acid, also known as 2, 4, 6-trinitrophenol, has a formula of C6H3N3O7 and forms a pale yellow odorless Crystal. It was first obtained in 1771 by Peter Woulfe by treating indigo with nitric acid. Much like TNT, it is a highly nitrated compound giving it explosive capabilities. It is synthesized from a combination of ethanol, phenol, sulphuric acid, nitric acid, and distilled water. This is not a synthesis that is made in nature; it is a man made compound. Picric acid has many uses, its main use is in ammunition and explosives but it is also used in drug testing for creatinine, a skin dye or temporary branding, fireworks (it produces a high pitched whine during combustion), a yellow dye for silk, antiseptics, and burn ointments. Also picric acid gets its name from the Greek pikros, “bitter” because of its bitter taste.
In the time of the Russo-Japanese war, Picric acid was the most widely used military explosive. A disadvantage of using picric acid in ammunition was that it would react with the metal casing of the ammunition, sometimes causing premature detonation. In 1902 TNT began replacing picric acid in ammunition because it was safer to manufacture and store. Eventually TNT replaced picric acid for most military uses. Ammonium picrate, a salt formed from picric acid, is still used today in armor piercing ammunition.
The Molecule looks as follows:
The center of the molecule is made up of a ring of carbons with three double bonds (represented by the two wooden dowels). Coming out of the carbons are three NO2's (nitrogen dioxide) that have double bonds between one oxygen and the nitrogen, one OH (hydroxide), and two H's (hydrogen). |
Lewis Structure
(with arrows of polarity)
VESPR Form- Cyclic, it is a cyclic molecule because of the ring that the six carbons form
London Dispersion, Dipole-Dipole, Hydrogen Bonding
There are london dispersion forces between any two molecules, therefore you know that there this force must be acting between the two molecules. Dipole-dipole forces occur when both of the molecules are polar covalent molecules, which means the molecule has both a positive and negative pole formed from an unequal sharing of electrons. Because the molecule is polar you know that dipole-dipole forces are acting between them. Hydrogen bonding occurs between hydrogen on one molecule and a fluorine, nitrogen, or oxygen on another molecule. Both molecules contain hydrogen, oxygen and nitrogen therefore it is evident that hydrogen boding will occur between the two molecules.
Precautions
The fact that picric acid is explosive means that it needs to be handled with extreme care. It is relatively sensitive to friction, heat, and shock when dry so it is often stored in water to desensitize it. It must be contained in glass or plastic because picric acid will form picrate salts that can be even more sensitive than the acid itself. Picrate salts can form when picric acid reacts win any of the following: metals, metal salts, bases, ammonia and concrete. It is a toxic compound and will produce toxic products on decompositions. Picric acid can also be an allergen and skin irritant. Picric acid should never be allowed to dry out especially on metal or concrete surfaces. Dry picric acid is disposed of by the bomb squad.
Conclusion
Picric acid no longer has a huge impact on the world like it once did when it was a widespread military explosive. Today it is mainly used in fireworks antiseptics, and some medicines for burn treatment. It is considered very dangerous because of its explosive abilities and its ability to react with metals and concrete forming salts that are even more sensitive than the acid itself. One salt that still has practical use is ammonium picrate. Formed from a reaction between picric acid and ammonia, it is still used today in armor piercing ammunition. Although picric acid is no longer very important in modern times it is still a dangerous compound that should not be played around with.
