Picric acid
- "TNP" redirects here. For the airport with the IATA airport code TNP, see Twentynine Palms Airport.
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| Names | |||
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| IUPAC name
2,4,6-Trinitrophenol
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| Other names
Carbazotic Acid; phenol trinitrate; picronitric acid; trinitrophenol; 2,4,6-trinitro-1-phenol; 2-hydroxy-1,3,5-trinitrobenzene; TNP
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| Identifiers | |||
3D model (JSmol)
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| ECHA InfoCard | 100.001.696 | ||
| RTECS number |
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CompTox Dashboard (EPA)
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| Properties | |||
| C6H3N3O7 | |||
| Molar mass | 229.10 g/mol | ||
| Appearance | Colorless to yellow solid | ||
| Density | 1.763 g/cm³, solid | ||
| Melting point | 122.5 °C | ||
| Boiling point | > 300 °C | ||
| 1.40 g/100 mL | |||
| Acidity (pKa) | 0.38 | ||
| Hazards | |||
| NFPA 704 (fire diamond) | |||
| Explosive data | |||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Picric acid is the chemical compound more formally called 2,4,6-trinitrophenol (TNP). This, a 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—"bitter", reflecting the bitter taste of picric acid.
History
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. 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 was used in World War I,[1] but the 20th century saw picric acid largely replaced by TNT and cordite. 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.
Synthesis
The aromatic ring of phenol is highly activated towards electrophilic reactions, and attempted nitration of phenol, even with dilute nitric acid, results in the formation of high molecular weight tars. In order to minimize these side reactions, anhydrous phenol is sulphonated with oleum, and the resulting p-phenolsulfonic acid is then nitrated with concentrated nitric acid. During this reaction, nitro groups are introduced, and sulfonic acid groups are displaced. The reaction is highly exothermic, and careful temperature control is required.
Uses
By far the largest use has been in munitions and explosives, as discussed above.
In microscopy, picric acid is a reagent for staining samples, e.g., Gram staining. It has found some use in organic chemistry for the preparation of crystalline salts of organic bases (picrates) for the purpose of identification and characterization.
Bouin's picro-formol is a preservative solution used for biological specimens.
Workplace drug testing utilizes picric acid for the Jaffe Reaction to test for creatinine. It forms a colored complex that can be measured using spectroscopy.
Much less commonly, wet picric acid has been used as a skin dye or temporary branding agent. It reacts with proteins in the skin to give a dark brown color that may last as long as a month.
In the early 20th century, picric acid was stocked in pharmacies as an antiseptic and as a treatment for burns, malaria, herpes, and smallpox.
Safety
Modern safety precautions recommend storing picric acid wet. Dry picric acid 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 easily form metal picrate salts that are even more sensitive and hazardous than the acid itself. Industrially, picric acid is especially hazardous because it is volatile and slowly sublimes even at room temperature. Over time, the buildup of picrates on exposed metal surfaces can constitute a grave hazard.
There have been at least three separate instances when Winnipeg bomb squad have been called in to the University of Manitoba to deal with picric acid related incidents, including in 2000 when a completely dehydrated sample was detonated. [2]
In 2007, a bomb squad removed a World War I-era bottle containing two ounces of picric acid in Columbus, Wisconsin.[3] That same year, the Alameda County bomb squad detonated two samples, one in Fremont, California[4] and one in Hayward, California.[5]
In 2008, bomb disposal experts removed and later detonated a 200 g (7 oz) sample found at the Marling School (Stroud, Gloucestershire) science department.[6][7] In the same year, a 1-lb. bottle of the acid was removed from an old pharmacy in Jerseyville, Illinois, and was later detonated by a bomb squad.[8] In the summer of 2008, German police blasted at least 50 picric acid bottles they had found in schools (34 bottles), pharmacies and industry. [9] The official justification given in news media was that the dry picric acid would be too dangerous to handle in order to add water for desensitization, and the picric acid might detonate when the bottles were opened. In October 2008, more than 100 staff and students were evacuated from the University of Queensland Centre for Clinical Research and surrounding buildings after a routine audit found a quantity of old picric acid in an unstable state. (actual number many hundreds more as 100 were from that building alone but adjacent buildings were also evacuted including a 14 story administration block). [10]
On Nov. 13, 2008, at St. Clare's Mercy Hospital in the city of St. John's, Newfoundland and Labrador, Canada, hospital workers discovered a 500 ml bottle of crystalized picric acid in a lab undergoing renovations. Police disposed of the container after the hospital was partially evacuated.[11]
References
- ^ Marc Ferro. The Great War. London and New York: Routeladge Classics, p. 98.
- ^ "University of Manitoba Environmental Health and Safety Office Newsletter General Safety Edition" (PDF). November 2004.
- ^ "Old Sample of Acid Detonated in Wis" (reprint). Associated Press. 16 April 2007.
- ^ "Explosion from chemical disposal shocks students" (PDF). Ohlone College. 6 February 2007.
- ^ "Bomb Squad Detonates Acid At Hayward Lab". KTVU. 22 August 2007.
- ^ "School evacuated after chemical found". Stroud News and Journal. 23 April 2008.
- ^ "'Unsafe chemical' found in school". Press Association. 23 April 2008.
- ^ "'Bomb Squad Removes Explosive: Container of Acid Found in Old Drugstore". The Alton Telegraph. 8 May 2008.
- ^ [www.wdr.de/themen/kurzmeldungen/2008/08/13/pikrinsaeure-alarm_lka_rueckt_24_mal_aus.jhtml "Pikrinsäure-Alarm an immer mehr Schulen in NRW"] (reprint). WDR. 16 August 2008.
{{cite news}}: Check|url=value (help) - ^ "Chemical find forces evacuation at Royal Brisbane Hospital". The Courier Mail. 24 October 2008.
- ^ http://www.cbc.ca/canada/newfoundland-labrador/story/2008/11/14/st-clares-picric.html
- Cooper, Paul W., Explosives Engineering, New York: Wiley-VCH, 1996. ISBN 0-471-18636-8