Tetraethyl pyrophosphate

TEPP is an insecticide to aphids, mites, spiders, mealybugs, leafhoppers, lygus bugs, thrips, leafminers, and many other pests.{{cite journal|doi=10.1093/jee/48.2.157|title=Tests with Acaricides against the Brown Wheat Mite12|year=1955|last1=Henderson|first1=Chas. F.|last2=Tilton|first2=Elvin. W.|journal=Journal of Economic Entomology|volume=48|issue=2|pages=157–161}} TEPP and other organophosphates are the most widely used pesticides in the U.S. due to their effectiveness and relative small impact on the environment because this organophosphate breaks down so easily.{{cn|date=January 2025}}

TEPP has been used for treatment for myasthenia gravis, an autoimmune disease. The treatment would deliver an increase in strength.{{Cite journal |last=Marr |first=W.G. |last2=Grob |first2=David |date=1950-06-20 |title=Some Ocular Effects of a new Anticholinesterase Agent* |url=https://doi.org/10.1016/0002-9394(50)91606-0 |journal=American Journal of Ophthalmology|volume=33 |issue=6 |pages=904–908 |doi=10.1016/0002-9394(50)91606-0 |issn=0002-9394}}

The synthesis by De Clermont and Moschnin was based on the earlier work by Alexander Williamson (who is well known for the Williamson ether synthesis). Their synthesis made use of ethyl iodide and silver salts to form esters in combination with pyrophosphate.{{cite journal | year = 2015 | title = History of organophosphorus cholinesterase inhibitors & reactivators | journal = Military Medical Science Letters | volume = 84 | issue = 4| pages = 182–185 | doi = 10.31482/mmsl.2015.023 | last1 = Petroianu | first1 = Georg | doi-access = free }}

:{{chem2|Ag4P2O7 + 4EtI → [(EtO)2P(O)]2O + 4AgI}}

Commercial routes to TEPP often use methods developed by Schrader, Woodstock, and Toy. Triethyl phosphate reacts with phosphorus oxychloride (Schrader's method) or phosphorus pentoxide (Woodstock's method).{{cite book |url=https://books.google.com/books?id=icnYBAAAQBAJ |title=Thin-Layer and Liquid Chromatography and Pesticides of International Importance: Analytical Methods for Pesticides and Plant Growth Regulators |last1=Sherma |first1=Joseph |last2=Zweig |first2=Gunter |date=1973 |publisher=Academic Press |isbn=978-1-4832-2084-0 |volume=7 |pages=471–477 |language=en}}{{cite book |url=https://books.google.com/books?id=s2QrAAAAYAAJ |title=Report on "no Residue" and "zero Tolerance". |author=National Research Council (U S. ) Pesticide Residues Committee |date=1965 |publisher=National Academies |pages=3–4 |language=en}} Alternatively, controlled hydrolysis of diethyl phosphorochloridate delivers the compound:{{cite journal|title=Reactions of Dialkyl Phosphites. Synthesis of Dialkyl Chlorophosphates, Tetraalkyl Pyrophosphates, and Mixed Orthophosphate Esters|author=Steinberg, Geo. M.|journal=Journal of Organic Chemistry|year=1950|volume=15|issue=3|pages=637–47|doi=10.1021/jo01149a031}}

:{{chem2|2(EtO)2P(O)Cl + H2O → [(EtO)2P(O)]2O + 2HCl}}

The related tetrabenzylpyrophosphate is prepared by dehydration of dibenzylphosphoric acid:{{cite journal|title=Tetrabenzyl Pyrophosphate|author=Todd D. Nelson |author2=Jonathan D. Rosen |author3=M. Bhupathy |author4=James McNamara |author5=Michael J. Sowa |author6=Chad Rush |author7=Louis S. Crocker |journal=Organic Syntheses|year=2003|volume=80|page= 219|doi=10.15227/orgsyn.080.0219}}

:{{chem2|2(RO)2P(O)OH → [(EtO)2P(O)]2O + H2O}}

TEPP and most of the other organophosphates are susceptible to hydrolysis.{{Cite journal|last1=Sogorb|first1=Miguel A|last2=Vilanova|first2=Eugenio|date=2002-03-10|title=Enzymes involved in the detoxification of organophosphorus, carbamate and pyrethroid insecticides through hydrolysis|journal=Toxicology Letters|volume=128|issue=1–3|pages=215–228|doi=10.1016/S0378-4274(01)00543-4|pmid=11869832}} The product is diethyl phosphate.{{Cite journal|last=Jokanović|first=Milan|date=2001-09-25|title=Biotransformation of organophosphorus compounds|journal=Toxicology|volume=166|issue=3|pages=139–160|doi=10.1016/S0300-483X(01)00463-2|pmid=11543910}}

TEPP is bioactive as an acetylcholinesterase inhibitor. It reacts with the serine hydroxyl group at the active site, preventing this enzyme from acting on its normal substrate, the neurotransmitter acetyl choline.{{cn|date=January 2025}}

TEPP is highly toxic for all warm-blooded animals, including humans.{{cite web |url=http://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+407 |title=Benfluralin - National Library of Medicine HSDB Database |website=toxnet.nlm.nih.gov |access-date=2016-03-08}} There are three types of effects on these animals that have come forward during laboratory studies.

• DERMAL: LD₅₀ = 2.4 mg/kg (male rat)
• ORAL: LD₅₀ = 1.12 mg/kg (rat)

Death is mostly due to either respiratory failure and in some cases cardiac arrest. The route of absorption might be responsible for the range of effect on certain systems.{{cite book |title=Veterinary Toxicology |last1=Clarke |first1=Myra L. |last2=Harvey |first2=Douglas Graham |last3=Humphreys |first3=David John |publisher=Bailliere Tindal |year=1988 |edition=2 |location=London, England |page=157}}

For cold-blooded animals the effects are slightly different. In a study with frogs, acute exposure caused a depression in the amount of erythrocytes in the blood. There was also a reduction of white bloodcells, especially the neutrophil granulocytes and lymphocytes. There was no visible damage to the bloodvessels to explain the loss of blood cells. Further there were no signs like hypersalivation or tears like in warm-blooded animals, though there was hypotonia leading to paralysis.{{cite journal |last1=Kaplan |first1=Harold M. |last2=Glaczenski |first2=Sheila S. |date=1965-06-01 |title=Hematological effects of organophosphate insecticides in the frog (Rana pipiens) |journal=Life Sciences |volume=4 |issue=12 |pages=1213–1219 |doi=10.1016/0024-3205(65)90335-8|pmid=4284682 }}

It was first synthesized by Wladimir Moschnin in 1854 while working with Adolphe Wurtz. A fellow student Philippe de Clermont is often incorrectly credited as the discoverer of TEPP despite his recognition of the Moschnin primacy in two publications.{{cite book |title=The Chemistry of Organophosphorus Pesticides |publisher=Springer |last1=Fest |first1=Christa |last2=Schmidt |first2=Karl-Julius |doi=10.1007/978-3-642-68441-8|year = 1982|isbn = 978-3-642-68443-2|s2cid=33095322 }}[https://www.ncbi.nlm.nih.gov/pubmed/18468398 The history of cholinesterase inhibitors: who was Moschnin(e)?]

The ignorance about the potential toxicity of TEPP is evidenced by De Clermont himself, who described the taste of TEPP as having a burning taste and a peculiar odor.{{cite journal |last=Petroianu |first=G. A. |date=2009-04-01 |title=The synthesis of phosphor ethers: who was Franz Anton Voegeli? |journal=Die Pharmazie |volume=64 |issue=4 |pages=269–271 |issn=0031-7144 |pmid=19435147 |doi=10.1691/ph.2009.8244}} Even though TEPP has repeatedly been synthesized by other chemists during the years that followed, not until the 1930s had any adverse effects been observed. Furthermore, Philippe de Clermont has never been reported ill by his family up to his passing at the age of 90. In the meantime, organophosphorus chemistry has really started developing with the help of A. W. von Hofmann, Carl Arnold August Michaelis and Aleksandr Arbuzov.{{cite book |chapter-url=https://books.google.com/books?id=Je7rCAAAQBAJ |title=Cholinesterases and Anticholinesterase Agents |date=1963 |publisher=Springer Science & Business Media |isbn=978-3-642-99875-1 |volume=15 |pages=434–437 |language=en |chapter=9: "Structure-Activity Relationships of the Organophosphorus Anticholinesterase Agents, Historical development of organophosphorus cholinesterase inhibitors"|series= Handbook of Experimental Pharmacology}}

It was not until 1932 before the first adverse effects of compounds similar to TEPP had been recognized. Willy Lange and Gerda von Krueger were the first to report such effects, about which the following statement was published in their article (in German):{{cite journal |last=Petroianu |first=G. A. |date=2010-10-01 |title=Toxicity of phosphor esters: Willy Lange (1900-1976) and Gerda von Krueger (1907-after 1970) |journal=Die Pharmazie |volume=65 |issue=10 |pages=776–780 |issn=0031-7144 |pmid=21105582}}

{{blockquote|"Interestingly, we report the strong effect of monofluorophosphate phosphoric acid alkyl esters on the human organism. The vapor of these compounds have a pleasant odor and sharply aromatic. After only a few minutes of inhaling the vapor, there is a strong pressure on the larynx, associated with shortness of breath. Then comes decreased awareness, opacities, and dazzling phenomena causing painful sensitivity of the eye to light. Only after several hours is there relief from these phenomena. They are apparently not caused by acidic decomposition products of the ester, but they are probably due to the Dialkyl monofluorophosphates themselves. The effects are exerted by very small amounts."}}

Starting in 1935 the German government started gathering information about new toxic substances, of which some were to be classified as secret by the German Ministry of Defence. Gerhard Schrader, who has become famous for his studies into organophosphorus insecticides and nerve gases, was one of the chemists who was also studying TEPP. In his studies, in particular his studies into the biological aspects, he noticed that this reagent could possibly be used as an insecticide. This would make the classification of the compound as secret disadvantageous for commercial firms.

Around the beginning of the Second World War, TEPP was discovered to be an inhibitor of cholinesterases. Schrader referred to the studies by Eberhard Gross, who was the first to recognize the mechanism of action for TEPP in 1939. More experiments were conducted including those of Hans Gremels, who confirmed Gross's work. Gremels was also involved in the development of nerve gases at that time. His studies involved several species of animals and human volunteers. Around that same time, atropine was discovered as a possible antidote for the anticholinesterase activity of TEPP.{{cn|date=January 2025}}

After the Second World War, Schrader was among many German scientists who were interrogated by English scientists, among others. During the war, the English had been developing chemical weapons of their own to surprise their enemies. In these interrogations the existence of TEPP and other insecticides were disclosed. The existence of nerve gases, however also being disclosed by Schrader, was kept secret by the military.{{cite journal|year=1948|title=The Preparation of Tetraethyl Pyrophosphate and Other Tetraalkyl Pyrophosphates|journal=Journal of the American Chemical Society| volume=70|issue=11| pages=3882–3886| doi=10.1021/ja01191a104|pmid=18102975| last1=Toy| first1=A. D. F.}}

{{Acetylcholine metabolism and transport modulators}}

Category:Pyrophosphate esters

Category:Ethyl esters

Category:Acetylcholinesterase inhibitors