What Is Picric Acid?
Picric acid, known as 2,4,6-trinitrophenol, is a nitro compound of phenol derivatives. It is a pale yellow crystal at room temperature, with a CAS number of 88-89-1, a melting point of 252.5°F, a density of 1.76 g/cm3, and an ignition point of 611.6°F. Picric acid is soluble in water and polar organic solvents but insoluble in non-polar solvents.
Properties of Picric Acid
Picric acid is a strong acid due to the electron-withdrawing effect of its three nitro groups, with a pKa of 0.38 compared to phenol’s 9.95. It is toxic, causing diarrhea and vomiting if ingested, and is explosive under heat or impact. Picric acid forms explosive salts with various metals and reacts with organic compounds to form picrates. Unlike typical phenols, picric acid does not react with iron(III) chloride due to reduced electron density in its benzene ring.
Uses of Picric Acid
Historically used as a military explosive, picric acid’s sensitivity to impact and friction and its tendency to form explosive salts with metals have reduced its use in explosives, replaced by TNT. Today, picric acid is used as an analytical reagent in biological tissue specimen preparation, acid-base indicator, and in fireworks, agrochemicals, dyes, and gas desulfurization catalysts.
Other Information on Picric Acid
Picric acid is synthesized by nitrating phenol, typically using the sulfophenol method to avoid oxidation. It can also be synthesized by hydrolyzing chlorodinitrobenzene. Picric acid is toxic and irritant; it must be handled with care, stored securely, and disposed of by licensed waste disposal companies.