Picrate

Chemical structure of the picrate anion

A picrate is a salt containing the anion (O₂N)₃C₆H₂O⁻ or an ester derivative of the picrate anion. These salts are often produced by reactions of picric acid (2,4,6-trinitrophenol).^[1][2] The picrate ion is intensely yellow, although many of its salts are brown or orange-red.

Explosives

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. Picrates of some metals tend to be significantly more sensitive to impact, friction and shock than picric acid itself. As a result, storage of picric acid (or mixtures containing it) in metal containers is strongly discouraged due to the high risk of accidental explosion.

Other uses

Ferrous picrate is used in some applications as a diesel fuel additive to achieve better mileage.^[3]

Sodium picrate is used as an etchant in metallography to differ preeutectoid ferrite in hypoeutectoid steel from preeutectoid cementite in hypereutectoid steel by etching cementite to a dark colour, whereas not attacking ferrite and thus it remains reflective.

Ethers and esters of picric acid are also called picrates. The ether methyl picrate (CAS# 606-35-9) has the formula (O₂N)₃C₆H₂OCH₃.

References

1. Olsher, Uriel; Feinberg, Hadar; Frolow, Felix; Shoham, Gil (1996). "The picrate anion as a versatile chelating counterion for the complexation of alkali and alkaline earth metal cations with ionophores: 'the picrate effect'". Pure and Applied Chemistry. 68 (6): 1195–1199. doi:10.1351/pac199668061195. S2CID 96529554.
2. Smith, M. B.; March, J. (2007). March's Advanced Organic Chemistry (6th ed.). John Wiley & Sons. p. 118. ISBN 978-0-471-72091-1.
3. Zhu, Mingming; Ma, Yu; Zhang, Dongke (2012). "Effect of a homogeneous combustion catalyst on the combustion characteristics and fuel efficiency in a diesel engine". Applied Energy. 91: 166–172. doi:10.1016/j.apenergy.2011.09.007.