Picric acid
Encyclopedia
Picric acid is the chemical compound
formally called 2,4,6-trinitrophenol (TNP). This yellow crystalline solid is one of the most acid
ic phenols
. Like other highly nitrate
d compounds such as TNT, picric acid is an explosive
. Its name comes from Greek πικρος (pik' ros), meaning "bitter", reflecting the bitter taste of picric acid.
in 1742. Initially, it was made by nitrating substances such as animal horn, silk
, indigo
, and natural resin
, the synthesis from indigo first being performed by Peter Woulfe
in 1779. 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 picrate
s which are more sensitive than the parent phenol. The sensitivity of picric acid was demonstrated in the Halifax Explosion
. Picric acid was used in the Second Boer War
and World War I
, but the 20th century saw picric acid largely replaced by TNT and RDX
. 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
.
is highly activated towards electrophilic substitution 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 sulfonated with fuming sulfuric acid, and the resulting p-phenolsulfonic acid is then nitrated with concentrated nitric acid
. During this reaction, nitro groups are introduced, and the sulfonic acid group is displaced. The reaction is highly exothermic, and careful temperature control is required. Picric acid has a characteristic acrid odor.
and explosives.
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.
In metallurgy a picric acid etch has been commonly used in optical metallography to reveal prior austenite grain boundaries in ferritic steels. The hazards associated with picric acid has meant it has largely been replaced with other chemical etchants.
Bouin solution
is a common picric acid-containing fixative
solution used for histology
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 burn
s, malaria
, herpes, and smallpox
. It was most notably used for the treatment of burns suffered by victims of the Hindenburg
disaster
in 1937.
Picric acid emits a high-pitched whine during combustion in air and this has led to its widespread use in fireworks.
Picric acid has been used for many years by fly tyers to dye moleskins, feathers, etc… dark olive green. Its popularity has been tempered by its toxic nature.
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.
Bomb disposal
units are often called to dispose of picric acid if it has dried out.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
formally called 2,4,6-trinitrophenol (TNP). This yellow crystalline solid is one of the most acid
Acid
An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...
ic phenols
Phenols
In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of a hydroxyl group bonded directly to an aromatic hydrocarbon group...
. Like other highly nitrate
Nitrate
The nitrate ion is a polyatomic ion with the molecular formula NO and a molecular mass of 62.0049 g/mol. It is the conjugate base of nitric acid, consisting of one central nitrogen atom surrounded by three identically-bonded oxygen atoms in a trigonal planar arrangement. The nitrate ion carries a...
d compounds such as TNT, picric acid is an explosive
Explosive material
An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure...
. Its name comes from Greek πικρος (pik' ros), meaning "bitter", reflecting the bitter taste of picric acid.
History
Picric acid was probably first mentioned in the alchemical writings of Johann Rudolf GlauberJohann Rudolf Glauber
Johann Rudolf Glauber was a German-Dutch alchemist and chemist. Some historians of science have described him as one of the first chemical engineers...
in 1742. Initially, it was made by nitrating substances such as animal horn, silk
Silk
Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity...
, indigo
Indigo
Indigo is a color named after the purple dye derived from the plant Indigofera tinctoria and related species. The color is placed on the electromagnetic spectrum between about 420 and 450 nm in wavelength, placing it between blue and violet...
, and natural resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
, the synthesis from indigo first being performed by Peter Woulfe
Peter Woulfe
Peter Woulfe was an Irish chemist and mineralogist. He first had the idea that wolframite might contain a previously undiscovered element .In 1779, Woulfe reported the formation of a yellow dye when indigo was treated with nitric acid...
in 1779. Its synthesis from phenol
Phenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
, 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
Explosive material
An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure...
. Before then, chemists assumed that only the salts of picric acid were explosive, not the acid itself. In 1873 Hermann Sprengel
Hermann Sprengel
Hermann Sprengel FRS was a German chemist who discovered the explosive nature of picric acid in 1873. He also invented a generic class of materials called Sprengel explosives...
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
Military
A military is an organization authorized by its greater society to use lethal force, usually including use of weapons, in defending its country by combating actual or perceived threats. The military may have additional functions of use to its greater society, such as advancing a political agenda e.g...
powers used picric acid as their primary high explosive material
Explosive material
An explosive material, also called an explosive, is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure...
. However, shells filled with picric acid become highly unstable as the compound corrodes bomb casings to form metal picrate
Picrate
A picrate is a salt or an ester of picric acid . But it could also be an additional compound which picric acid forms with many aromatic hydrocarbons, aromatic amines, aliphatic amines, alkalines, and other compounds. These additional compounds are also called picrates even though they are not a...
s which are more sensitive than the parent phenol. The sensitivity of picric acid was demonstrated in the Halifax Explosion
Halifax Explosion
The Halifax Explosion occurred on Thursday, December 6, 1917, when the city of Halifax, Nova Scotia, Canada, was devastated by the huge detonation of the SS Mont-Blanc, a French cargo ship, fully loaded with wartime explosives, which accidentally collided with the Norwegian SS Imo in "The Narrows"...
. Picric acid was used in the Second Boer War
Second Boer War
The Second Boer War was fought from 11 October 1899 until 31 May 1902 between the British Empire and the Afrikaans-speaking Dutch settlers of two independent Boer republics, the South African Republic and the Orange Free State...
and World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...
, but the 20th century saw picric acid largely replaced by TNT and RDX
RDX
RDX, an initialism for Research Department Explosive, is an explosive nitroamine widely used in military and industrial applications. It was developed as an explosive which was more powerful than TNT, and it saw wide use in WWII. RDX is also known as cyclonite, hexogen , and T4...
. 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
Eugene Turpin
François Eugène Turpin was a French chemist involved in research of explosive materials. He lived in Colombes.-Biography:...
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
Nitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...
. Since 1888, Britain started manufacturing a very similar mixture in Lydd
Lydd
Lydd is a town in Kent, England, lying on the Romney Marsh. It is one of the larger towns on the Marsh, and the most southerly town in Kent. Actually located on Denge Marsh, Lydd was one of the first sandy islands to form as the bay evolved into what is now called the Romney Marsh...
, 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
Ecrasite
Ecrasite is an explosive material which is unaffected by moisture, shock or fire. It is a mixture of ammonium cresylate with picric acid. It was invented in 1888-1889 by Siersch and Kubin, and used in Austria to load artillery shells....
.
Synthesis
The aromatic ring of phenolPhenol
Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...
is highly activated towards electrophilic substitution 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 sulfonated with fuming sulfuric acid, and the resulting p-phenolsulfonic acid is then nitrated with concentrated nitric acid
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
. During this reaction, nitro groups are introduced, and the sulfonic acid group is displaced. The reaction is highly exothermic, and careful temperature control is required. Picric acid has a characteristic acrid odor.
Uses
By far the largest use has been in munitionsAmmunition
Ammunition is a generic term derived from the French language la munition which embraced all material used for war , but which in time came to refer specifically to gunpowder and artillery. The collective term for all types of ammunition is munitions...
and explosives.
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.
In metallurgy a picric acid etch has been commonly used in optical metallography to reveal prior austenite grain boundaries in ferritic steels. The hazards associated with picric acid has meant it has largely been replaced with other chemical etchants.
Bouin solution
Bouin Solution
Bouin solution is a compound fixative used in histology. It is composed of picric acid, acetic acid and formaldehyde in an aqueous solution. It is especially good for gastrointestinal tract biopsies because this fixative allows crisper and better nuclear staining than 10% neutral-buffered formalin...
is a common picric acid-containing fixative
Fixation (histology)
In the fields of histology, pathology, and cell biology, fixation is a chemical process by which biological tissues are preserved from decay, thereby preventing autolysis or putrefaction...
solution used for histology
Histology
Histology is the study of the microscopic anatomy of cells and tissues of plants and animals. It is performed by examining cells and tissues commonly by sectioning and staining; followed by examination under a light microscope or electron microscope...
specimens.
Workplace drug testing utilizes picric acid for the Jaffe Reaction to test for creatinine
Creatinine
Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body...
. 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
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction...
and as a treatment for burn
Burn
A burn is an injury to flesh caused by heat, electricity, chemicals, light, radiation, or friction.Burn may also refer to:*Combustion*Burn , type of watercourses so named in Scotland and north-eastern England...
s, malaria
Malaria
Malaria is a mosquito-borne infectious disease of humans and other animals caused by eukaryotic protists of the genus Plasmodium. The disease results from the multiplication of Plasmodium parasites within red blood cells, causing symptoms that typically include fever and headache, in severe cases...
, herpes, and smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
. It was most notably used for the treatment of burns suffered by victims of the Hindenburg
LZ 129 Hindenburg
LZ 129 Hindenburg was a large German commercial passenger-carrying rigid airship, the lead ship of the Hindenburg class, the longest class of flying machine and the largest airship by envelope volume...
disaster
Hindenburg disaster
The Hindenburg disaster took place on Thursday, May 6, 1937, as the German passenger airship LZ 129 Hindenburg caught fire and was destroyed during its attempt to dock with its mooring mast at the Lakehurst Naval Air Station, which is located adjacent to the borough of Lakehurst, New Jersey...
in 1937.
Picric acid emits a high-pitched whine during combustion in air and this has led to its widespread use in fireworks.
Picric acid has been used for many years by fly tyers to dye moleskins, feathers, etc… dark olive green. Its popularity has been tempered by its toxic nature.
Safety
Modern safety precautions recommend storing picric acid wet. Dry picric acid is relatively sensitive to shockShock (mechanics)
A mechanical or physical shock is a sudden acceleration or deceleration caused, for example, by impact, drop, kick, earthquake, or explosion. Shock is a transient physical excitation....
and friction
Friction
Friction is the force resisting the relative motion of solid surfaces, fluid layers, and/or material elements sliding against each other. There are several types of 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
Picrate
A picrate is a salt or an ester of picric acid . But it could also be an additional compound which picric acid forms with many aromatic hydrocarbons, aromatic amines, aliphatic amines, alkalines, and other compounds. These additional compounds are also called picrates even though they are not a...
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.
Bomb disposal
Bomb disposal
Bomb disposal is the process by which hazardous explosive devices are rendered safe. Bomb disposal is an all encompassing term to describe the separate, but interrelated functions in the following fields:*Military:...
units are often called to dispose of picric acid if it has dried out.