Picric acid

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122.5 °C

> 300 °C (Explodes)

Picric acid is the chemical compound formally called 2,4,6-trinitrophenol (TNP). This yellow crystalline solid is one of the most acidic phenols. Like other highly nitrated compounds such as TNT, picric acid is an explosive. Its name comes from Greek πικρος (pik' ros), meaning "bitter", reflecting the bitter taste of picric acid.



Picric acid 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, the synthesis from indigo first being performed by Peter Woulfe in 1779. 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 acid was used in the Second Boer War[1] and World War I,[2] but the 20th century saw picric acid largely replaced by TNT and RDX. Picric acid is also used in the analytical chemistry of metals, ores, and minerals.

In 1885, based on research of Hermann Sprengel, French chemist Eugène 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.

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