Picric acid
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| Picric acid | |
|---|---|
| |
| General | |
| Systematic name | 2,4,6-trinitrophenol |
| Other names | Carbazotic Acid phenol trinitrate picronitric acid trinitrophenol 2-hydroxy-1,3,5-trinitrobenzene |
| Molecular formula | (NO2)3C6H2OH |
| SMILES | Oc1c(N(=O)=O)cc (N(=O)=O)cc1N(=O)=O |
| Molar mass | 229.1056 g/mol |
| Appearance | Colorless-yellow solid. |
| CAS number | |
| Properties | |
| Density and phase | 1.763 g/cm3, solid. |
| Solubility in water | 1.40 g/100 ml (?°C) |
| Melting point | 122.5°C (395.65 K) |
| Boiling point | Explodes > 300°C (573.15 K) |
| Acidity (pKa) | 0.38 |
| Structure | |
| Molecular shape | Planar. |
| Crystal structure | ? |
| Dipole moment | ? D |
| Hazards | |
| MSDS | External MSDS |
| Main hazards | Explosive, flammable, irritant, toxic. |
| NFPA 704 | |
| Flash point | 150°C |
| R/S statement | R: R1, R10, R36, R37, R38. S: S28, S35, S37, S45. |
| RTECS number | TJ7875000 |
| Supplementary data page | |
| Structure and properties | n, εr, etc. |
| Thermodynamic data | Phase behaviour Solid, liquid, gas |
| Spectral data | UV, IR, NMR, MS |
| Related compounds | |
| Related Phenols | ? |
| Related compounds | ? |
| Except where noted otherwise, data are given for materials in their standard state (at 25°C, 100 kPa) [Chemical infoboxInfobox disclaimer and references] | |
Picric acid is the common term for the chemical compound 2,4,6-trinitrophenol, also known as TNP; the material is a yellow crystalline solid. Like other highly nitrated compounds (e.g. trinitrotoluene), picric acid is an explosive.
Modern safety precautions recommend storing picric acid wet. When picric acid is dry, it is relatively sensitive to shock and friction, so laboratories that use it store it in bottles under a layer of water, rendering it safe. Glass or plastic bottles are required, as picric acid can form metal picrate salts that are even more sensitive and hazardous than the acid.
Modern safety precautions for plain picric acid are moderately overstated, as it was used successfully as an explosive filler for most artillery shells and bombs in the First World War. Those applications necessarily subject it to shock and friction during firing of the shells.
Properties
- Velocity of detonation: 7,350 m/s at density 1.70
- Autoignition temperature: Explodes over 300 °C
History
Picric acid was first mentioned in the alchemical writings of 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 Russians had worked out a method of manufacture for artillery shells. Soon after, every military power used picric acid as their primary high explosive material. The 20th century saw the decline of picric acid, the replacement being TNT. Shells filled with picric acid become highly unstable as the compound reacts with the metal bomb shell, forming extremely sensitive metal picrates, making them unusable. Today picric acid is more suited to detonators or booster charges. It is also used in the analytical chemistry of metals, ores, and minerals.
Picric acid was one of the main compenents in the Halifax explosion.
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.
Uses
By far the largest use has been in munitions and explosives; it was known in World War I as Lyddite (from Lydd, Kent, where the British undertook work to develop it as a shell filling) or Melinite.
The principal laboratory use of picric acid is in microscopy, where it is used as a reagent for staining samples, e.g. Gram staining.
Bouin's picro-formol is a preservative solution used for biological specimens.
Much less commonly, wet picric acid has been used as a skin dye or temporary branding agent. It is not acidic enough to cause chemical burns, and reacts with proteins in the skin to give a dark brown color that may last as long as a month.
Other
Picric acid is well known as another easy 'homemade explosive,' since its synthesis requires chemicals that can be bought at the store. Many people have injured or killed themselves during the synthesis of picric acid, since its synthesis with acetylsalicylic acid produces the deadly nitrogen dioxide gas.
See also
External links
- For a full list of external links to MSDSs, spectroscopic data, commercial chemicals suppliers etc. for this compound, see [Chemical sources].
References
- Cooper, Paul W., Explosives Engineering, New York: Wiley-VCH, 1996. ISBN 0-471-18636-8
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