Chemistry:Chloropicrin

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Chloropicrin, also known as PS (from Port Sunlight[1]) and nitrochloroform, is a chemical compound currently used as a broad-spectrum antimicrobial, fungicide, herbicide, insecticide, and nematicide.[2] It was used as a poison gas in World War I and the Russian military has been accused of using it in the Russo-Ukrainian War.[3][4][5] Its chemical structural formula is Cl
3C–NO
2.

Synthesis

Chloropicrin was discovered in 1848 by Scottish chemist John Stenhouse. He prepared it by the reaction of sodium hypochlorite with picric acid:

HOC
6H
2(NO
2)
3 + 11 NaOCl → 3 Cl
3CNO
2 + 3 Na
2CO
3 + 3 NaOH + 2 NaCl

Because of the precursor used, Stenhouse named the compound chloropicrin, although the two compounds are structurally dissimilar.

Today, chloropicrin is manufactured by the reaction of nitromethane with sodium hypochlorite:[6]

H
3CNO
2 + 3 NaOCl → Cl
3CNO
2 + 3 NaOH

Reaction of chloroform and nitric acid also yields chloropicrin:[7]

Cl
3CH + HONO
2 → Cl
3CNO
2 + H
2O

Properties

Chloropicrin's chemical formula is CCl
3NO
2 and its molecular weight is 164.38 grams/mole.[8] Pure chloropicrin is a colorless liquid, with a boiling point of 112 °C.[8] Chloropicrin is sparingly soluble in water with solubility of 2 g/L at 25 °C.[8] It is volatile, with a vapor pressure of 23.2 millimeters of mercury (mmHg) at 25 °C; the corresponding Henry's law constant is 0.00251 atmosphere-cubic meter per mole.[8] The octanol-water partition coefficient (Kow) of chloropicrin is estimated to be 269.[8] Its soil adsorption coefficient (Koc; normalized to soil organic matter content) is 25 cm3/g.[8]

Uses

Poison

Chloropicrin was manufactured for use as poison gas in World War I.[9] In World War I, German forces used concentrated chloropicrin against Allied forces as a tear gas. While not as lethal as other chemical weapons, it induced vomiting and forced Allied soldiers to remove their masks to vomit, exposing them to more toxic gases used as weapons during the war.[10] It was also used by the Imperial Russian Army in hand grenades as 50% solution in sulfuryl chloride.[11]

In February 2024, Ukrainian General Oleksandr Tarnavskyi accused the Russian Armed Forces of using chloropicrin munitions.[12] In May 2024, the United States Department of State also alleged use of chloropicrin by Russian forces in Ukraine, and imposed sanctions against Russian individuals and entities as a response.[13] Dutch and German intelligence agencies found chloropicrin use to be "commonplace" by July 2025.[14]

Agriculture

In agriculture, chloropicrin is injected into soil prior to planting a crop to fumigate soil. Chloropicrin affects a broad spectrum of fungi, microbes and insects.[15] It is commonly used as a stand-alone treatment or in combination / co-formulation with methyl bromide and 1,3-dichloropropene.[15][16] Chloropicrin is used as an indicator and repellent when fumigating residences for insects with sulfuryl fluoride which is an odorless gas.[citation needed] Chloropicrin's mode of action is unknown[17] (IRAC MoA 8B).[18] Chloropicrin may stimulate weed germination, which can be useful when quickly followed by a more effective herbicide.[19]

Chloropicrin was first registered in 1975 in the US. After a 2008 re-approval, the EPA[20] stated that chloropicrin "means more fresh fruits and vegetables can be cheaply produced domestically year-round because several severe pest problems can be efficiently controlled."[21][22] To ensure chloropicrin is used safely, the EPA requires a strict set of protections for handlers, workers, and persons living and working in and around farmland during treatments.[23][22] EPA protections were increased in both 2011 and 2012, reducing fumigant exposures and significantly improving safety.[24] Protections include the training of certified applicators supervising pesticide application, the use of buffer zones, posting before and during pesticide application, fumigant management plans, and compliance assistance and assurance measures.[citation needed]

Used as a preplant soil treatment measure, chloropicrin suppresses soilborne pathogenic fungi and some nematodes and insects. According to chloropicrin manufacturers, with a half-life of hours to days, it is completely digested by soil organisms before the crop is planted, making it safe and efficient.[citation needed] Contrary to popular belief, chloropicrin does not sterilize soil and does not deplete the ozone layer, as the compound is destroyed by sunlight. Additionally, chloropicrin has never been found in groundwater, due to its low solubility.[25]

California

In California, experience with acute effects of chloropicrin when used as a soil fumigant for strawberries and other crops led to the release of regulations in January 2015 creating buffer zones and other precautions to minimize exposure to farm workers, neighbors, and passersby.[26][27]

Safety

At a national level, chloropicrin is regulated in the United States by the United States Environmental Protection Agency as a restricted use pesticide.[28] Because of its toxicity, distribution and use of chloropicrin is available only to licensed professionals and specially certified growers who are trained in its proper and safe use.[28] In the US, occupational exposure limits have been set at 0.1 ppm over an eight-hour time-weighted average.[29]

High concentrations

Gas identification art for chloropicrin

Chloropicrin is harmful to humans. It can be absorbed systemically through inhalation, ingestion, and the skin. At high concentrations, it is severely irritating to the lungs, eyes, and skin.[30]

Damage to protective gear

See also

References

  1. ↑ Foulkes, C. H. (31 January 2012). "GAS!" – The Story of the Special Brigade. Andrews UK Limited. p. 193. 
  2. ↑ "RED Fact Sheet: Chloropicrin". US Environmental Protection Agency. 10 July 2008. p. 2. http://www.epa.gov/oppsrrd1/REDs/factsheets/chloropicrin-fs.pdf. 
  3. ↑ Office of the Spokesperson (1 May 2024). "Imposing New Measures on Russia for its Full-Scale War and Use of Chemical Weapons Against Ukraine". https://www.state.gov/imposing-new-measures-on-russia-for-its-full-scale-war-and-use-of-chemical-weapons-against-ukraine-2/#:~:text=The%20Department%20of%20State%20has,Chemical%20Weapons%20Convention%20(CWC).. 
  4. ↑ "A top Russian general is killed in a Moscow bombing claimed by Ukraine". 2024-12-17. https://apnews.com/article/russia-explosion-head-of-nuclear-defense-forces-killed-9656bce946a9f552454df9debe5fbd18?utm_source=firefox-newtab-en-us. 
  5. ↑ Quell, Molly (2025-07-04). "Dutch intelligence services say Russia has stepped up use of banned chemical weapons in Ukraine". Reuters. https://apnews.com/article/ukraine-russia-chemical-weapons-netherlands-26a1bea82a7d1a57b581c60683628712. 
  6. ↑ Markofsky, Sheldon B. (2005). "Nitro Compounds, Aliphatic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. 
  7. ↑ Jackson, Kirby E. (1934). "Chloropicrin". Chemical Reviews 14 (2): 251–286. doi:10.1021/cr60048a003. https://doi.org/10.1021/cr60048a003. 
  8. ↑ 8.0 8.1 8.2 8.3 8.4 8.5 "Executive Summary - Evaluation of Chloropicrin As A Toxic Air Contaminant". Department of Pesticide Regulation - California Environmental Protection Agency. February 2010. p. iv. http://www.cdpr.ca.gov/docs/emon/pubs/tac/exec_sum_0210.pdf. 
  9. ↑ Ayres, Leonard P. (1919). The War with Germany (2nd ed.). Washington, DC: United States Government Printing Office. p. 80. https://archive.org/details/warwithgermanya02ayregoog. 
  10. ↑ Heller, Charles E. (September 1984). "Chemical Warfare in World War I: The American Experience, 1917–1918". Leavenworth Papers (10): 23. https://www.armyupress.army.mil/Portals/7/combat-studies-institute/csi-books/leavenworth-papers-10-chemical-warfare-in-world-war-i-the-american-experience-1917-1918.pdf. 
  11. ↑ Sartori, Mario (1939). The War Gases. D. Van Nostrand. pp. 165. 
  12. ↑ "Ukraine accuses Russia of intensifying chemical attacks on the battlefield". 9 February 2024. https://www.reuters.com/world/europe/ukraine-accuses-russia-intensifying-chemical-attacks-battlefield-2024-02-09/. 
  13. ↑ "Imposing New Measures on Russia for its Full-Scale War and Use of Chemical Weapons Against Ukraine". United States Department of State. https://www.state.gov/imposing-new-measures-on-russia-for-its-full-scale-war-and-use-of-chemical-weapons-against-ukraine-2/. 
  14. ↑ Quell, Molly (2025-07-04). "Dutch intelligence services say Russia has stepped up use of banned chemical weapons in Ukraine". Reuters. https://apnews.com/article/ukraine-russia-chemical-weapons-netherlands-26a1bea82a7d1a57b581c60683628712. 
  15. ↑ 15.0 15.1 "Factsheet: Chloropicrin". New South Wales: WorkCover. http://www.workcover.nsw.gov.au/Documents/Publications/AlertsGuidesHazards/DangerousGoodsExplosivesFireworksPyrotechnics/chloropicrin_fact_sheet_1371.pdf. 
  16. ↑ Fries, Amos Alfred; West, Clarence Jay (1921). Chemical warfare. McGraw-Hill. p. 144. https://archive.org/details/chemicalwarfare00westgoog. 
  17. ↑ Chloropicrin in the Pesticide Properties DataBase (PPDB), University of Hertfordshire, accessed 2021-03-10.
  18. ↑ "IRAC Mode of Action Classification Scheme Version 9.4". March 2020. http://irac-online.org/documents/moa-classification/. 
  19. ↑ Martin, Frank N. (2003). "Development of Alternative Strategies for Management of Soilborne Pathogens Currently Controlled with Methyl Bromide". Annual Review of Phytopathology (Annual Reviews) 41 (1): 325–350. doi:10.1146/annurev.phyto.41.052002.095514. ISSN 0066-4286. PMID 14527332. Bibcode: 2003AnRvP..41..325M. 
  20. ↑ "RED Fact Sheet: Chloropicrin". US Environmental Protection Agency. 10 July 2008. p. 2. https://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P1010HX8.txt. 
  21. ↑ "Amended Reregistration Eligibility Decision (RED) for Chloropicrin". United States Environmental Protection Agency. May 2009. http://www.epa.gov/oppsrrd1/REDs/chloropicrin-red-amended.pdf. 
  22. ↑ 22.0 22.1 "Chloropicrin Mitigation Proposal". Department of Pesticide Regulation – California Environmental Protection Agency. 15 May 2013. p. 2. http://www.cdpr.ca.gov/docs/whs/pdf/dpr_chloropicrin_mitigation_proposal_and_app_1-3.pdf. 
  23. ↑ "Chloropicrin – Background". http://www.chloropicrinfacts.org/background.html. 
  24. ↑ "Chloropicrin Mitigation Proposal". Department of Pesticide Regulation – California Environmental Protection Agency. 15 May 2013. p. 2. http://www.cdpr.ca.gov/docs/whs/pdf/dpr_chloropicrin_mitigation_proposal_and_app_1-3.pdf. "The Amended RED incorporated final new safety measures to increase protections for agricultural workers and bystanders. These measures establish a baseline for safe use of the soil fumigants throughout the United States, reducing fumigant exposures and significantly improving safety." 
  25. ↑ "Chloropicrin Soil Fumigation in Potato Production Systems". Plant Management Network. American Phytopathological Society. https://www.plantmanagementnetwork.org/edcenter/seminars/potato/Chloropicrin/. 
  26. ↑ "Control Measures for Chloropicrin". California Department of Pesticide Regulation. January 6, 2015. http://www.cdpr.ca.gov/docs/whs/pdf/control_measures_chloropicrin_summary.pdf. "added controls for chloropicrin when it is used as a soil fumigant. The controls are intended to reduce risk from acute (short-term) exposures that might occur near fields fumigated with products containing chloropicrin." 
  27. ↑ "Chloropicrin Mitigation Proposal". Department of Pesticide Regulation – California Environmental Protection Agency. 15 May 2013. p. 2. http://www.cdpr.ca.gov/docs/whs/pdf/dpr_chloropicrin_mitigation_proposal_and_app_1-3.pdf. "The new measures appearing on soil fumigant Phase 2 labels include buffer zones and posting, emergency preparedness and response measures, training for certified applicators supervising applications, Fumigant Management Plans, and notice to State Lead Agencies who wish to be informed of applications in their states." 
  28. ↑ 28.0 28.1 "Chloropicrin Mitigation Proposal". Department of Pesticide Regulation – California Environmental Protection Agency. 15 May 2013. p. 1. http://www.cdpr.ca.gov/docs/whs/pdf/dpr_chloropicrin_mitigation_proposal_and_app_1-3.pdf. 
  29. ↑ "NIOSH Pocket Guide to Chemical Hazards". Centers for Disease Control and Prevention. https://www.cdc.gov/niosh/npg/npgd0132.html. 
  30. ↑ "Chloropicrin (PS): Lung Damaging Agent". Emergency Response Safety and Health Database. National Institute for Occupational Safety and Health. August 22, 2008. https://www.cdc.gov/niosh/ershdb/EmergencyResponseCard_29750034.html. 



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