Parathion

Key takeaways

Parathion belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Parathion to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Parathion from memory before moving on to harder problems.

Reference excerpt

Parathion, also called parathion-ethyl or diethyl parathion, 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. In response to safety concerns, the less toxic but still dangerous analogue parathion methyl was later developed.

History

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. In the EU, Parathion was banned in 2001.

Handling properties 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).

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

Applications 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.

(C2H5O)2P(S)OC6H4NO2 +⁠1/2⁠O2 → (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. Parathion resistance is a special case of acetylcholinesterase inhibitor resistance. Parathion is toxic to most forms of wildlife in addition to insects if not applied at correct concentrations.

Degradation 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:

(C2H5O)2P(S)OC6H4NO2 + H2O → HOC6H4NO2 + (C2H5O)2P(O)SH 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

Illicit uses

As a chemical weapon Parathion was used as a chemical warfare agent, most notably by an element of the British South Africa Police 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.

Use in suicides Parathion was commonly used for suicides in the 1950s and 1960s.

Safety Parathion disrupts the nervous system by inhibiting acetylcholinesterase. It is absorbed via skin, mucous membranes, and orally. Absorbed parathion is rapidly metabolized to 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. Based on animal studies, parathion is considered by the U.S. Environmental Protection Agency to be a possible human carcinogen. Studies show that parathion is toxic to fetuses, but does not cause birth defects. It is classified by the United Nations Environment Programme as a persistent organic pollutant and by the World Health Organization as Toxicity Class Ia (extremely hazardous).

See also Pesticide toxicity to bees Parathion methyl

References

External links Parathion in the Pesticide Properties DataBase (PPDB) ATSDR - Methyl Parathion Expert Panel Report Archived 2019-06-14 at the Wayback Machine U.S. Department of Health and Human Services (public domain) CDC - NIOSH Pocket Guide to Chemical Hazards U.S. Department of Health and Human Services (public domain) Ethyl parathion: International Chemical Safety Card 0006 Methyl parathion: International Chemical Safety Card 0626

Illustrations

Worked examples

Example 1 — a first encounter with Parathion

Start with the simplest possible case. Write down what Parathion claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Parathion before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Parathion ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Parathion

In research: Parathion appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Parathion in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Parathion is common in secondary-school and first-year university syllabi. It links to neighbouring topics 4-Nitrophenyl compounds, Acetylcholinesterase inhibitors, Ethyl esters, so understanding it makes those chapters shorter.
In everyday life: Look for Parathion outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Parathion in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Parathion means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Parathion out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Parathion in simple terms?

Parathion, also called parathion-ethyl or diethyl parathion, is an organophosphate insecticide and acaricide. It was originally developed by IG Farben in the 1940s.

Why does Parathion matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Parathion?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Parathion.