Last updated
Preferred IUPAC name
O,O-Diethyl O-(4-nitrophenyl) phosphorothioate
Other names
3D model (JSmol)
ECHA InfoCard 100.000.247 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 200-271-7
PubChem CID
RTECS number
  • TF4550000
UN number 3018 2783
  • InChI=1S/C10H14NO5PS/c1-3-14-17(18,15-4-2)16-10-7-5-9(6-8-10)11(12)13/h5-8H,3-4H2,1-2H3 Yes check.svgY
  • InChI=1/C10H14NO5PS/c1-3-14-17(18,15-4-2)16-10-7-5-9(6-8-10)11(12)13/h5-8H,3-4H2,1-2H3
  • S=P(Oc1ccc(cc1)[N+]([O-])=O)(OCC)OCC
Molar mass 291.26 g·mol−1
AppearanceWhite crystals (pure form)
Melting point 6 °C (43 °F; 279 K)
24 mg/L
Solubility in other solventshigh solubility

in xylene and butanol

GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
H300, H311, H330, H372, H410
P260, P264, P270, P271, P273, P280, P284, P301+P310, P302+P352, P304+P340, P310, P312, P314, P320, P321, P322, P330, P361, P363, P391, P403+P233, P405, P501
NFPA 704 (fire diamond)
Flash point 120 °C (248 °F; 393 K)
Lethal dose or concentration (LD, LC):
5 mg/kg (mouse, oral)
10 mg/kg (rabbit, oral)
3 mg/kg (dog, oral)
0.93 mg/kg (cat, oral)
5 mg/kg (horse, oral)
8 mg/kg (guinea pig, oral)
2 mg/kg (rat, oral) [1]
84 mg/m3 (rat, 4 hr) [1]
50 mg/m3 (rabbit, 2 hr)
14 mg/m3 (guinea pig, 2 hr)
15 mg/m3 (mouse) [1]
NIOSH (US health exposure limits):
PEL (Permissible)
none (methyl parathion), [2] TWA 0.1 mg/m3 [skin] (ethyl parathion) [3]
REL (Recommended)
TWA 0.2 mg/m3 [skin] (methyl parathion) [2] TWA 0.05 mg/m3 [skin] (ethyl parathion) [3]
IDLH (Immediate danger)
N.D. (methyl parathion) [2] 10 mg/m3 (ethyl parathion) [3]
Safety data sheet (SDS)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
X mark.svgN  verify  (what is  Yes check.svgYX mark.svgN ?)

Parathion, also called parathion-ethyl or diethyl parathion and locally[ clarification needed ] known as "Folidol", is an organophosphate insecticide and acaricide. It was originally developed by IG Farben in the 1940s. It is highly toxic to non-target organisms, including humans, so its use has been banned or restricted in most countries. The basic structure is shared by parathion methyl. [5]



Bottle with E605 E605-forte.jpg
Bottle with E605

Parathion was developed by Gerhard Schrader for the German trust IG Farben in the 1940s. After World War II and the collapse of IG Farben due to the war crime trials, the Western allies seized the patent, and parathion was marketed worldwide by different companies and under different brand names. The most common German brand was E605 (banned in Germany after 2002); this was not a food-additive "E number" as used in the EU today. "E" stands for Entwicklungsnummer (German for "development number"). It is an irreversible acetylcholinesterase inhibitor.

Safety concerns have later led to the development of parathion methyl, which is somewhat less toxic.

In the EU, Parathion was banned after 2001. [6] In Switzerland, the substance is no longer approved as a pesticide.

Handling properties

Pure parathion is a white crystalline solid. It is commonly distributed as a brown liquid that smells of rotting eggs or garlic. The insecticide is somewhat stable, although it darkens when exposed to sunlight.

Industrial synthesis

Parathion is synthesized from diethyl dithiophosphoric acid (C2H5O)2PS2H by chlorination to generate diethylthiophosphoryl chloride ((C2H5O)2P(S)Cl), and then the chloride is treated with sodium 4-nitrophenolate (the sodium salt of 4-nitrophenol). [7]

2 (C2H5O)2P(S)SH + 3 Cl2 → 2 (C2H5O)2P(S)Cl + S2Cl2 + 2 HCl
(C2H5O)2P(S)Cl + NaOC6H4NO2 → (C2H5O)2P(S)OC6H4NO2 + NaCl


As a pesticide, parathion is generally applied by spraying. It is often applied to cotton, rice and fruit trees. The usual concentrations of ready-to-use solutions are 0.05 to 0.1%. The chemical is banned for use on many food crops.

Insecticidal activity

Parathion acts on the enzyme acetylcholinesterase indirectly. After an insect (or a human) ingests parathion, an oxidase replaces the double bonded sulfur with oxygen to give paraoxon. [8]

(C2H5O)2P(S)OC6H4NO2 + 1/2 O2 → (C2H5O)2P(O)OC6H4NO2 + S

The phosphate ester is more reactive in organisms than the phosphorothiolate ester, as the phosphorus atoms become much more electropositive. [8]

Parathion resistance is a special case of acetylcholinesterase inhibitor resistance.


Degradation of parathion leads to more water-soluble products. Hydrolysis, which deactivates the molecule, occurs at the aryl ester bond resulting in diethyl thiophosphate and 4-nitrophenol. [8]

(C2H5O)2P(S)OC6H4NO2 + H2O → HOC6H4NO2 + (C2H5O)2P(S)OH

Degradation proceeds differently under anaerobic conditions: the nitro group on parathion is reduced to the amine.

(C2H5O)2P(S)OC6H4NO2 + 6 H → (C2H5O)2P(S)OC6H4NH2 + 2 H2O


Parathion is a cholinesterase inhibitor. It generally disrupts the nervous system by inhibiting acetylcholinesterase. It is absorbed via skin, mucous membranes, and orally. Absorbed parathion is rapidly metabolized to paraoxon, as described in Insecticidal activity. Paraoxon exposure can result in headaches, convulsions, poor vision, vomiting, abdominal pain, severe diarrhea, unconsciousness, tremor, dyspnea, and finally pulmonary edema as well as respiratory arrest. Symptoms of poisoning are known to last for extended periods, sometimes months. The most common and very specific antidote is atropine, in doses of up to 100 mg daily. Because atropine may also be toxic, it is recommended that small frequently repeated doses be used in treatment. If human poisoning is detected early and the treatment is prompt (atropine and artificial respiration), fatalities are infrequent. Insufficient oxygen will lead to cerebral hypoxia and permanent brain damage. Peripheral neuropathy including paralysis is noticed as late sequelae after recovery from acute intoxication. Parathion and related organophosphorus pesticides are used in hundreds of thousands of poisonings annually, especially suicides. [9] It is known as Schwiegermuttergift (mother-in-law poison) in Germany. For this reason, most formulations contain a blue dye providing warning.

Parathion was used as a chemical warfare agent, most notably by an element of the British South Africa Police (BSAP) attached to the Selous Scouts during the Rhodesian Bush War. They used it to poison clothing that was then supplied to anti-government guerrillas. When the enemy soldiers put on the clothes, they were poisoned by absorption through the skin. [10] [11] [12]

Based on animal studies, parathion is considered by the U.S. Environmental Protection Agency to be a possible human carcinogen. [13] Studies show that parathion is toxic to fetuses, but does not cause birth defects. [14]

It is classified by the United Nations Environment Programme (UNEP) as a persistent organic pollutant [ citation needed ] and by the World Health Organization (WHO) as Toxicity Class Ia (extremely hazardous).[ citation needed ]

Parathion is toxic to bees, fish, birds, and other forms of wildlife. [14]

Protection against poisoning

To provide the end user with a minimum standard of protection, suitable protective gloves, clothing, and a respirator with organic-vapour cartridges is normally worn. Industrial safety during the production process requires special ventilation and continuous measurement of air contamination in order not to exceed PEL levels, as well as careful attention to personal hygiene. Frequent analysis of workers' serum acetylcholinesterase activity is also helpful with regards to occupational safety, because the action of parathion is cumulative. Also, atropine has been used as a specific antidote.

Use in suicides

A chemist swallowed .00424 ounces of parathion to find the most lethal means of exposure to humans, intending to take an antidote afterwards, but was paralyzed and so died before he could reach it. [15]

Parathion was commonly used for suicides in the 1950s and 1960s. [15]

See also

Related Research Articles

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Bromomethane, commonly known as methyl bromide, is an organobromine compound with formula CH3Br. This colorless, odorless, nonflammable gas is produced both industrially and biologically. It has a tetrahedral shape and it is a recognized ozone-depleting chemical. It was used extensively as a pesticide until being phased out by most countries in the early 2000s.

<span class="mw-page-title-main">Carbofuran</span> Toxic carbamate pesticide

Carbofuran is a carbamate pesticide, widely used around the world to control insects on a wide variety of field crops, including potatoes, corn and soybeans. It is a systemic insecticide, which means that the plant absorbs it through the roots, and from there the plant distributes it throughout its organs where insecticidal concentrations are attained. Carbofuran also has contact activity against pests. It is one of the most toxic pesticides still in use.

<span class="mw-page-title-main">Carbaryl</span> Chemical compound

Carbaryl is a chemical in the carbamate family used chiefly as an insecticide. It is a white crystalline solid previously sold under the brand name Sevin, which was a trademark of the Bayer Company. The Sevin trademark has since been acquired by GardenTech, which has eliminated carbaryl from most Sevin formulations. Union Carbide discovered carbaryl and introduced it commercially in 1958. Bayer purchased Aventis CropScience in 2002, a company that included Union Carbide pesticide operations. Carbaryl was the third-most-used insecticide in the United States for home gardens, commercial agriculture, and forestry and rangeland protection. As a veterinary drug, it is known as carbaril (INN).

<span class="mw-page-title-main">Malathion</span> Chemical compound

Malathion is an organophosphate insecticide which acts as an acetylcholinesterase inhibitor. In the USSR, it was known as carbophos, in New Zealand and Australia as maldison and in South Africa as mercaptothion.

<span class="mw-page-title-main">Organophosphate</span> Organic compounds with the structure O=P(OR)3

In organic chemistry, organophosphates are a class of organophosphorus compounds with the general structure O=P(OR)3, a central phosphate molecule with alkyl or aromatic substituents. They can be considered as esters of phosphoric acid.

<span class="mw-page-title-main">Diazinon</span> Chemical compound

Diazinon, a colorless to dark brown liquid, is a thiophosphoric acid ester developed in 1952 by Ciba-Geigy, a Swiss chemical company. It is a nonsystemic organophosphate insecticide formerly used to control cockroaches, silverfish, ants, and fleas in residential, non-food buildings. Diazinon was heavily used during the 1970s and early 1980s for general-purpose gardening use and indoor pest control. A bait form was used to control scavenger wasps in the western U.S. Diazinon is used in flea collars for domestic pets in Australia and New Zealand. Residential uses of diazinon were outlawed in the U.S. in 2004 because of human health risks but it is still approved for agricultural uses. An emergency antidote is atropine.

Demeton-S-methyl is an organic compound with the molecular formula C6H15O3PS2. It was used as an organothiophosphate acaricide and organothiophosphate insecticide. It is flammable. With prolonged storage, Demeton-S-methyl becomes more toxic due to formation of a sulfonium derivative which has greater affinity to the human form of the acetylcholinesterase enzyme, and this may present a hazard in agricultural use.

Iodomethane, also called methyl iodide, and commonly abbreviated "MeI", is the chemical compound with the formula CH3I. It is a dense, colorless, volatile liquid. In terms of chemical structure, it is related to methane by replacement of one hydrogen atom by an atom of iodine. It is naturally emitted by rice plantations in small amounts. It is also produced in vast quantities estimated to be greater than 214,000 tons annually by algae and kelp in the world's temperate oceans, and in lesser amounts on land by terrestrial fungi and bacteria. It is used in organic synthesis as a source of methyl groups.

<span class="mw-page-title-main">Azinphos-methyl</span> Chemical compound

Azinphos-methyl (Guthion) is a broad spectrum organophosphate insecticide manufactured by Bayer CropScience, Gowan Co., and Makhteshim Agan. Like other pesticides in this class, it owes its insecticidal properties to the fact that it is an acetylcholinesterase inhibitor. It is classified as an extremely hazardous substance in the United States as defined in Section 302 of the U.S. Emergency Planning and Community Right-to-Know Act, and is subject to strict reporting requirements by facilities which produce, store, or use it in significant quantities.

<span class="mw-page-title-main">Dichlorvos</span> Insect killing chemical, organophosphate

Dichlorvos is an organophosphate widely used as an insecticide to control household pests, in public health, and protecting stored products from insects. The compound has been commercially available since 1961 and has become controversial because of its prevalence in urban waterways and the fact that its toxicity extends well beyond insects. Since 1988, dichlorvos cannot be used as a plant protection product in the EU.

<span class="mw-page-title-main">Organophosphate poisoning</span> Medical condition

Organophosphate poisoning is poisoning due to organophosphates (OPs). Organophosphates are used as insecticides, medications, and nerve agents. Symptoms include increased saliva and tear production, diarrhea, vomiting, small pupils, sweating, muscle tremors, and confusion. While onset of symptoms is often within minutes to hours, some symptoms can take weeks to appear. Symptoms can last for days to weeks.

<span class="mw-page-title-main">Chlorethoxyfos</span> Chemical compound

Chlorethoxyfos is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is registered for the control of corn rootworms, wireworms, cutworms, seed corn maggot, white grubs and symphylans on corn. The insecticide is sold under the trade name Fortress by E.I. du Pont de Nemours & Company.

<span class="mw-page-title-main">Disulfoton</span> Chemical compound

Disulfoton is an organophosphate acetylcholinesterase inhibitor used as an insecticide. It is manufactured under the name Di-Syston by Bayer CropScience. Disulfoton in its pure form is a colorless oil but the technical product used in vegetable fields is dark and yellowish with a sulfur odor. Disulfoton is processed as a liquid into carrier granules, these granules are mixed with fertilizer and clay to be made into a spike, designed to be driven into the ground. The pesticide is absorbed over time by the roots and translocated to all parts of the plant. The pesticide acts as a cholinesterase inhibitor and gives long lasting control.

<span class="mw-page-title-main">Demeton</span> Chemical compound

Demeton, sold as an amber oily liquid with a sulphur like odour under the name Systox™, is an organophosphate derivative causing irritability and shortness of breath to individuals repeatedly exposed. It was used as a phosphorothioate insecticide and acaricide and has the chemical formula C8H19O3PS2. Although it was previously used as an insecticide, it is now largely obsolete due to its relatively high toxicity to humans. Demeton consists of two components, demeton-S and demeton-O in a ratio of approximately 2:1 respectively. The chemical structure of demeton is closely related to military nerve agents such as VX and a derivative with one of the ethoxy groups replaced by methyl was investigated by both the US and Soviet chemical-weapons programs under the names V.sub.X and GD-7.

<span class="mw-page-title-main">Tetraethyl pyrophosphate</span> Chemical compound

Tetraethyl pyrophosphate, abbreviated TEPP, is an organophosphate compound with the formula [(C2H5O)2P(O)]2O. It is the tetraethyl derivative of pyrophosphate (P2O74-). It is a colorless oil that solidifies near room temperature. It is used as an insecticide. The compound hydrolyzes rapidly.

<span class="mw-page-title-main">Sulfotep</span> Chemical compound

Sulfotep (also known as tetraethyldithiopyrophosphate and TEDP) is a pesticide commonly used in greenhouses as a fumigant. The substance is also known as Dithione, Dithiophos, and many other names. Sulfotep has the molecular formula C8H20O5P2S2 and belongs to the organophosphate class of chemicals. It has a cholinergic effect, involving depression of the cholinesterase activity of the peripheral and central nervous system of insects. The transduction of signals is disturbed at the synapses that make use of acetylcholine. Sulfotep is a mobile oil that is pale yellow-colored and smells like garlic. It is primarily used as an insecticide.

<span class="mw-page-title-main">Terbufos</span> Chemical compound

Terbufos is a chemical compound used in insecticides and nematicides. Terbufos is part of the chemical family of organophosphates. It is a clear, colourless to pale yellow or reddish-brown liquid and sold commercially as granulate.

<span class="mw-page-title-main">EPN (insecticide)</span> Chemical compound

EPN is an insecticide of the phosphonothioate class. It is used against pests such as European corn borer, rice stem borer, bollworm, tobacco budworm, and boll weevil.

<span class="mw-page-title-main">Parathion methyl</span> Chemical compound

Parathion methyl, or methyl parathion, is an organophosphate insecticide, possessing an organothiophosphate group. It is structurally very similar to parathion-ethyl. It is not allowed for sale and import in nearly all countries around the world, while a few allow it under subject to specified conditions only.


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  4. "Hazard Rating Information for NFPA Fire Diamonds". Archived from the original on 2015-02-17. Retrieved 2015-03-13.
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  6. Non-inclusion of parathion in Annex I to Council Directive 91/414/EEC
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  14. 1 2 "Pesticide Information Profiles - Parathion". Extension Toxicology Network. Oregon State University. September 1993.
  15. 1 2 Carson, Rachel (1962). Silent Spring. ISBN   978-0-547-52762-8. OCLC   1346358856.