Picric acid

Picric acid[10] was probably first mentioned in the alchemical writings of Johann Rudolf Glauber in 1742. Initially, it was made by nitrating substances such as animal horn, silk, indigo, and natural resin. Its synthesis from phenol, and the correct determination of its formula, were successfully accomplished in 1841. Not until 1830 did chemists think to use picric acid as an explosive. Before then, chemists assumed that only the salts of picric acid were explosive, not the acid itself. In 1873 Hermann Sprengel proved it could be detonated and by 1894 the Russian workers had worked out a method of manufacture for artillery shells. Soon after, most military powers used picric acid as their primary high explosive material. However, shells filled with picric acid become highly unstable as the compound corrodes bomb casings to form metal picrates which are more sensitive than the parent phenol. The sensitivity of picric acid was demonstrated in the Halifax Explosion. Picric was used in World War I, but the 20th century saw picric acid largely replaced by TNT and cordite. Picric acid is also used in the analytical chemistry of metals, ores, and minerals.
In 1885, based on research of Hermann Sprengel, French chemist Eugene Turpin patented the use of pressed and cast picric acid in blasting charges and artillery shells. In 1887 the French government adopted it under the name melinite, with addition of gun cotton. Since 1888, Britain started manufacturing a very similar mixture in Lydd, Kent, under the name lyddite. Japan followed with an improved formula known as schimose. In 1889, a similar material, a mixture of ammonium cresylate with trinitrocresol, or an ammonium salt of trinitrocresol, started to be manufactured under the name ecrasite.

IUPAC NAME: 2,4,6-trinitrophenol
OTHER NAME: Carbazotic Acid; phenol trinitrate; picronitric acid; trinitrophenol; 2,4,6-trinitro-1-phenol; 2-hydroxy-1,3,5-trinitrobenzene; TNP

The aromatic ring of phenol is highly activated towards electrophilic reactions, and attempted nitration of phenol, even with dilute nitric acid, results in the formation of high molecular weight tars. In order to minimize these side reactions, anhydrous phenol is sulphonated with oleum, and the resulting p-phenolsulfonic acid is then nitrated with concentrated nitric acid. During this reaction, nitro groups are introduced, and sulfonic acid groups are displaced. The reaction is highly exothermic, and careful temperature control is required.

C6H5OH(s) + H2SO6 → (HO.C6H4.SO3H + H2O) + HNO3(aq) → C6H3N3O7

Picric acid is toxic, soluble in hot water, and readily soluble in alcohol, ether, benzene, and acetone. The explosive power of picric acid is somewhat superior to that of TNT, both as regards the strength and the detonation velocity. Picric acid is prepared by dissolving phenol in sulfuric acid and subsequent nitration of the resulting phenoldisulfonic acid with nitric acid or by further nitration of dinitrophenol (prepared from dinitrochlorobenzene). The crude product is purified by washing in water.
Picric acid was used as a grenade and mine filling. It needs a high pouring temperature, which is undesirable. However, the solidification point can be depressed by the addition of nitronaphthalene, dinitrobenzene or trinitrocresol.
Picric Acid is used in electric batteries, leather industry, dies, pigments, inks, paints, manufacture of colored glass, textile mordants, as a laboratory reagent, in matches and explosives.

Picric Acid can be used alone or in the synthesis of picrate salts.

A picrate is a salt or an ester of picric acid. But it could also be an additional compound which picric acid forms with many aromatic hydrocarbons, aromatic amines, aliphatic amines, alkalines, and other compounds. These additional compounds are also called picrates even that they are not a salt of picric acid.
The picrate ion has yellow color. Many picrates are explosives, for example ammonium picrate (known as Dunnite). Some are used as primary explosives, namely lead picrate or potassium picrate which find their use as primers for cartridge ammunition. Ferrous picrate is used in some applications as a diesel fuel additive to achieve better mileage.
Picrates of some metals tend to be significantly more sensitive to impact and friction than picric acid itself (therefore storage of picric acid and mixtures containing it in containers made of these metals is strongly discouraged).

Potassium Picrate
Lead Picrate
Ammonium Picrate