Styphnic acid (from Greek stryphnos "astringent"^[1]), or 2,4,6-trinitro-1,3-benzenediol, is a yellow astringent acid that forms hexagonal crystals. It is used in the manufacture of dyes, pigments, inks, medicines, and explosives such as lead styphnate. It is itself a low-sensitivity explosive, similar to picric acid, but explodes upon rapid heating.^[2]

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Styphnic acid

Names
Preferred IUPAC name 2,4,6-Trinitrobenzene-1,3-diol
Identifiers
CAS Number	82-71-3 Y
3D model (JSmol)	Interactive image
ChemSpider	6465 Y
ECHA InfoCard	100.001.306
PubChem CID	6721
UNII	R4TJB1U00D Y
UN number	0219 – Dry or wetted with < 20% water/alcohol 0394 – Wetted with >= 20% water/alcohol
CompTox Dashboard (EPA)	DTXSID7058880
InChI InChI=1S/C6H3N3O8/c10-5-2(7(12)13)1-3(8(14)15)6(11)4(5)9(16)17/h1,10-11H Y Key: IXHMHWIBCIYOAZ-UHFFFAOYSA-N Y InChI=1/C6H3N3O8/c10-5-2(7(12)13)1-3(8(14)15)6(11)4(5)9(16)17/h1,10-11H Key: IXHMHWIBCIYOAZ-UHFFFAOYAQ
SMILES c1c(c(c(c(c1[N+](=O)[O-])O)[N+](=O)[O-])O)[N+](=O)[O-]
Properties
Chemical formula	C6H3N3O8
Molar mass	245.11 g/mol
Density	1.829 g/cm3
Melting point	180 °C (356 °F; 453 K)
Boiling point	decomposes
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is YN ?) Infobox references

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It may be prepared by the nitration of resorcinol with a mixture of nitric and sulfuric acid.^[3]

This compound is an example of a trinitrophenol.

Like picric acid, it is a moderately strong acid, capable of displacing carbon dioxide from solutions of sodium carbonate, for example.

It may be reacted with weakly basic oxides, such as those of lead and silver, to form the corresponding salts.

The solubility of picric acid and styphnic acid in water is less than their corresponding mono- and di-nitro compounds, and far less than their non-nitrated precursor phenols, so they may be purified by fractional crystallisation.