Picric acid
Picric acid is the common term for the chemical compound 2,4,6-trinitrophenol; the material is a yellow crystalline solid. Like other highly nitrated compounds (eg. trinitrotoluene), picric acid is an explosive. When picric acid is dry, it is extremely sensitive to shock and friction, so laboratories that use it store it in bottles under a layer of water, rendering it safe. Glass bottles are required, as picric acid can form metal picrate salts that are even more sensitive and hazardous than the acid.
Chemistry
- IUPAC name: 2,4,6-trinitrophenol
- Chemical formula: C6H3N3O7
- Boiling point: Explodes over 300 °C
- CAS number: 88-89-1
Picric acid can be made from phenol, benzene, or acetylsalicylic acid (aspirin). The most common route is through aspirin, since it is much easier to synthesize picric acid from aspirin.
History
Picric acid was first mentioned in the alchemical writings of Glauber in 1742. The old timers made it from nitrating animal horn, silk, indigo, natural resin, and the like. Its synthesis from phenol, and the correct determination of its formula, was in 1841. It was not until 1830 did anybody think to use picric acid as an explosive. Before then it was assumed that only the salts of picric acid were explosive, not the acid itself. In 1873 H. Sprengel proved it could be detonated and by 1894 the Russians had worked out a method of manufacture for artillery shells. Soon after, every military power used picric acid as their primary high explosive material. The 20th century saw the decline of picric acid, the replacement being TNT. The downfall was partially due to the acidic nature and the sensitivity of picric acid. Today picric acid is more suited to detonators or booster charges.
Uses
By far the largest use has been in munitions and explosives; it was known in World War I as Lyddite or Melinite.
The principal laboratory use is in microscopy, where it is used as a reagent for staining samples, e.g. Gram staining.
Bouin's picro-formol is a preservative solution used for biological specimens.
Picric acid was one of the agents in the Halifax explosion.
Other
Picric acid is well known as another easy 'homemade explosive,' since it's synthesis requires chemicals that can be bought at the store. Many people have injured or killed themselves during the synthesis of picric acid, since it's synthesis with acetylsalicylic acid produces the deadly nitrogen dioxide gas.