Diquat

Last updated
Diquat dibromide
Diquat Structural Formula V1.svg
Diquat dibromide 3D ball.png
Names
IUPAC name
6,7-dihydrodipyrido[1,2-a:2′,1′-c]pyrazine-5,8-diium dibromide
Other names
1,1′-Ethylene-2,2′-bipyridyldiylium dibromide
Identifiers
  • Compounds
  • Dibromide: Diquat dibromide
  • Dichloride: Diquat dichloride
  • Dication: Diquat dication
3D model (JSmol)
ChEMBL
ChemSpider
ECHA InfoCard 100.001.436 OOjs UI icon edit-ltr-progressive.svg
KEGG
PubChem CID
UNII
  • InChI=1S/C12H12N2.2BrH/c1-3-7-13-9-10-14-8-4-2-6-12(14)11(13)5-1;;/h1-8H,9-10H2;2*1H/q+2;;/p-2 Yes check.svgY
    Key: ODPOAESBSUKMHD-UHFFFAOYSA-L Yes check.svgY
  • Dichloride:InChI=1S/C12H12N2.2ClH/c1-3-7-13-9-10-14-8-4-2-6-12(14)11(13)5-1;;/h1-8H,9-10H2;2*1H/q+2;;/p-2
    Key: SKYNPRKUXHXZFJ-UHFFFAOYSA-L
  • Dication:InChI=1S/C12H12N2/c1-3-7-13-9-10-14-8-4-2-6-12(14)11(13)5-1/h1-8H,9-10H2/q+2
    Key: SYJFEGQWDCRVNX-UHFFFAOYSA-N
  • Dibromide:C1[n+]2ccccc2-c3cccc[n+]3C1.[Br-].[Br-]
Properties [1]
C12H12Br2N2
Molar mass 344.050 g·mol−1
AppearanceWhite/yellow crystals
Density 1.61 g/cm3
Melting point Decomposes
71.8% (20 °C)
log P -4.6
Vapor pressure 0.01 mPa (20 °C)
Hazards [2]
GHS labelling:
GHS-pictogram-skull.svg GHS-pictogram-exclam.svg GHS-pictogram-silhouette.svg GHS-pictogram-pollu.svg
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 0: Will not burn. E.g. waterInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
4
0
0
NIOSH (US health exposure limits):
REL (Recommended)
TWA 0.5 mg/m3 [3]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Diquat is the ISO common name [4] for an organic dication that, as a salt with counterions such as bromide or chloride is used as a contact herbicide that produces desiccation and defoliation. Diquat is no longer approved for use in the European Union, although its registration in many other countries including the USA is still valid.

Contents

Synthesis

Pyridine is oxidatively coupled to form 2,2′-bipyridine over a heated Raney nickel catalyst. The ethylene bridge is formed by the reaction with 1,2-dibromoethane [5]

Diquat Synthesis V1.svg

History

Diquat's herbicidal properties were recognized in 1955 in the Imperial Chemical Industries (ICI) laboratories at Jealott's Hill, following its first synthesis at ICI's Dyestuffs Division in Blackley, England. [5] [6] [7] It was active on test plants at application rates as low as 0.1 lb/acre. It was found that only those quaternary salts which were capable of being converted by reducing agents to radical cations had herbicidal activity and another of these was paraquat, which was more effective as a non-selective herbicide than diquat. [8] Initial attempts to commercialize diquat focused on its ability to control broadleaved annual weeds while damage to cereal crops was, by comparison, minor. However, the auxin herbicides including ICI's MCPA were more selective and hence this use of diquat was unattractive. [6] Instead, diquat was combined with the use of specialised mechanised equipment which by the late 1950s was becoming common in the harvesting of crops such as potatoes. A concern in that use was the possibility that the compound could cause stem-end rot, but protocols were developed that overcame this problem and it was introduced commercially for potato haulm desiccation in 1961. [9] [10] In the mid 1960s, diquat's use was extended to the pre-harvest desiccation of oilseed crops such as sunflower, linseed, cotton and soya. [6] The patent to the active ingredient has now expired in all countries.

Mode of action

When acting as a herbicide, diquat inhibits photosynthesis. In light-exposed plants, it accepts an electron from photosystem I (more specifically ferredoxin), to form its green radical cation:

[diquat]2+ + e− [diquat]+•

The electron is then transferred to molecular oxygen, producing destructive reactive oxygen species. In forming these, the diquat dication is regenerated and is again available to shunt electrons from photosystem I to restart the cycle. [11]

Formulation

Diquat is made available to end users only in formulated products. Since it has extremely high solubility in water, modern formulations contain up to 40% of the active dibromide salt. [12]

Usage

All pesticides are required to seek registration from appropriate authorities in the country in which they will be used. [13] In the United States, the Environmental Protection Agency (EPA) is responsible for regulating pesticides under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Food Quality Protection Act (FQPA). [14] A pesticide can only be used legally according to the directions on the label that is included at the time of the sale of the pesticide. The purpose of the label is "to provide clear directions for effective product performance while minimizing risks to human health and the environment". A label is a legally binding document that mandates how the pesticide can and must be used and failure to follow the label as written when using the pesticide is a federal offense. [15] Within the European Union, a 2-tiered approach is used for the approval and authorisation of pesticides. Firstly, before a formulated product can be developed for market, the active substance must be approved for the European Union. After this has been achieved, authorisation for the specific product must be sought from every Member State that the applicant wants to sell it to. Afterwards, there is a monitoring programme to make sure the pesticide residues in food are below the limits set by the European Food Safety Authority. Although diquat was used in many European countries from the 1960s, an EU directive has removed its approval for any use, effective from 12 October 2018. [16]

Diquat use in USA to 2018 (estimated by USGS) Diquat use in USA.png
Diquat use in USA to 2018 (estimated by USGS)

Diquat is an unusual herbicide because it is often not used for weed control but is instead applied directly on mature crops. This causes desiccation, making the crop easier to harvest, particularly with mechanised equipment. The advantage to the farmer can be to advance the harvesting date, reduce the time taken to harvest and, in the case of seed crops, reduce the moisture content of the seed and increase its useful yield. [6] Farmers can act in their best economic interest: the value of these benefits can be estimated and the total cost of using the herbicide, including the cost, for example of aerial spraying, informs the decision to purchase. This cost-benefit analysis by the end user sets a maximum price which the supplier can demand. When used as a conventional herbicide for weed control, diquat must be applied after the weeds have emerged since it is only effective on contact with green tissue. In this use it is fast-acting in sunlight and more effective on broadleaved weeds than grasses. [17] [18] Mixing of diquat with other herbicides is also feasible. [12] The estimated annual use of diquat in US agriculture is mapped by the US Geological Survey. [19] This shows that use is fairly stable and in 2018, the latest date for which figures are available, was about 300,000 pounds (140,000 kg) annually, almost exclusively in fruit and vegetable crops.

Beyond agriculture, diquat is also used to control invasive species such as submerged aquatic vegetation in the California Delta. [20] Because California public drinking water is drawn through the delta as part of the California State Water Project, trace amounts of this pesticide are in much of the state's water supply.

Human safety

Diquat dibromide is moderately toxic. It may be harmful to humans if swallowed, inhaled, or absorbed through the skin in large quantities. [1] [17] Swallowed doses of 10ml and above are often lethal. [21] Its chronic neurotoxic effects have been investigated. [22] First aid measures are included with the label information. [12]

The World Health Organization (WHO) and Food and Agriculture Organization (FAO) joint meeting on pesticide residues has determined that the acceptable daily intake for diquat (as its ion) is 0-0.006 mg/kg bodyweight per day, [23] with an acute reference dose of 0.8 mg/kg bodyweight. [24] The Codex Alimentarius database maintained by the FAO lists the maximum residue limits for diquat in various food products. [25]

Effects on the environment

Diquat bonds strongly to mineral and organic particles in soil and water, where it remains without significant degradation for years. However, bound to clays, diquat is biologically inactive at the concentrations typically observed in agricultural soils. [26] [27]

Brands

By international convention and in many countries the law, pesticide labels are required to include the common name of the active ingredients. These names are not the exclusive property of the holder of any patent or trademark and as such they are the easiest way for non-experts to refer to individual chemicals. Companies selling pesticides normally do so using a brand name or wordmark which allows them to distinguish their product from competitor products having the same active ingredient. In many cases, this branding is country and formulation-specific so after several years of sales there can be multiple brand names for a given active ingredient. The situation is made even more complicated when companies license their ingredients to others, as is often done. The licensee will normally wish to create their own set of trademarks for use in advertising and to promote to their customers. In addition, they may intend to mix the licensed product with their own proprietary materials and would certainly create a new brand for these mixtures. It is therefore difficult to provide a comprehensive list of brand names for products containing diquat in its many salt and ester forms. The original ICI brand was Reglone and this name is still used by Syngenta. Other names include Aquacide, Dextrone, Preeglone, Deiquat, Spectracide, Detrone, Tribune and Weedtrine-D. [2]

See also

Related Research Articles

<span class="mw-page-title-main">Pesticide</span> Substance used to destroy pests

Pesticides are substances that are meant to control pests. This includes herbicide, insecticide, nematicide, molluscicide, piscicide, avicide, rodenticide, bactericide, insect repellent, animal repellent, microbicide, fungicide, and lampricide. The most common of these are herbicides, which account for approximately 50% of all pesticide use globally. Most pesticides are intended to serve as plant protection products, which in general, protect plants from weeds, fungi, or insects. As an example, the fungus Alternaria solani is used to combat the aquatic weed Salvinia.

<span class="mw-page-title-main">Herbicide</span> Chemical used to kill unwanted plants

Herbicides, also commonly known as weed killers, are substances used to control undesired plants, also known as weeds. Selective herbicides control specific weed species while leaving the desired crop relatively unharmed, while non-selective herbicides can be used to clear waste ground, industrial and construction sites, railways and railway embankments as they kill all plant material with which they come into contact. Apart from selective/non-selective, other important distinctions include persistence, means of uptake, and mechanism of action. Historically, products such as common salt and other metal salts were used as herbicides, however, these have gradually fallen out of favor, and in some countries, a number of these are banned due to their persistence in soil, and toxicity and groundwater contamination concerns. Herbicides have also been used in warfare and conflict.

Roundup is the brand name of a systemic, broad-spectrum glyphosate-based herbicide originally produced by Monsanto, which Bayer acquired in 2018. Glyphosate is the most widely used herbicide in the United States. As of 2009, sales of Roundup herbicides still represented about 10 percent of Monsanto's revenue despite competition from Chinese producers of other glyphosate-based herbicides. The overall Roundup line of products, which includes genetically modified seeds, represented about half of Monsanto's yearly revenue. The product is marketed to consumers by Scotts Miracle-Gro Company.

<span class="mw-page-title-main">Glyphosate</span> Systemic herbicide and crop desiccant

Glyphosate is a broad-spectrum systemic herbicide and crop desiccant. It is an organophosphorus compound, specifically a phosphonate, which acts by inhibiting the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSP). It is used to kill weeds, especially annual broadleaf weeds and grasses that compete with crops. Its herbicidal effectiveness was discovered by Monsanto chemist John E. Franz in 1970. Monsanto brought it to market for agricultural use in 1974 under the trade name Roundup. Monsanto's last commercially relevant United States patent expired in 2000.

<span class="mw-page-title-main">Paraquat</span> Chemical compound used as an herbicide

Paraquat (trivial name; ), or N,N′-dimethyl-4,4′-bipyridinium dichloride (systematic name), also known as methyl viologen, is an organic compound with the chemical formula [(C6H7N)2]Cl2. It is classified as a viologen, a family of redox-active heterocycles of similar structure. This salt is one of the most widely used herbicides. It is quick-acting and non-selective, killing green plant tissue on contact. It is also toxic (lethal) to human beings and animals due to its redox activity, which produces superoxide anions. It has been linked to the development of Parkinson's disease and is banned in several countries.

<span class="mw-page-title-main">Glufosinate</span> Broad-spectrum herbicide

Glufosinate is a naturally occurring broad-spectrum herbicide produced by several species of Streptomyces soil bacteria. Glufosinate is a non-selective, contact herbicide, with some systemic action. Plants may also metabolize bialaphos and phosalacine, other naturally occurring herbicides, directly into glufosinate. The compound irreversibly inhibits glutamine synthetase, an enzyme necessary for the production of glutamine and for ammonia detoxification, giving it antibacterial, antifungal and herbicidal properties. Application of glufosinate to plants leads to reduced glutamine and elevated ammonia levels in tissues, halting photosynthesis and resulting in plant death.

<span class="mw-page-title-main">Dicamba</span> Chemical compound used as herbicide

Dicamba is a broad-spectrum herbicide first registered in 1967. Brand names for formulations of this herbicide include Dianat, Banvel, Diablo, Oracle and Vanquish. This chemical compound is a chlorinated derivative of o-anisic acid.

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

Azoxystrobin is a broad spectrum systemic fungicide widely used in agriculture to protect crops from fungal diseases. It was first marketed in 1996 using the brand name Amistar and by 1999 it had been registered in 48 countries on more than 50 crops. In the year 2000 it was announced that it had been granted UK Millennium product status.

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

Sulfentrazone is the ISO common name for an organic compound used as a broad-spectrum herbicide. It acts by inhibiting the enzyme protoporphyrinogen oxidase. It was first marketed in the US in 1997 by FMC Corporation with the brand name Authority.

<span class="mw-page-title-main">Cyhalothrin</span> Synthetic pyrethroid used as insecticide

Cyhalothrin is the ISO common name for an organic compound that, in specific isomeric forms, is used as a pesticide. It is a pyrethroid, a class of synthetic insecticides that mimic the structure and properties of the naturally occurring insecticide pyrethrin which is present in the flowers of Chrysanthemum cinerariifolium. Pyrethroids such as cyhalothrin are often preferred as an active ingredient in agricultural insecticides because they are more cost-effective and longer acting than natural pyrethrins. λ-and γ-cyhalothrin are now used to control insects and spider mites in crops including cotton, cereals, potatoes and vegetables.

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

Monolinuron is a pesticide, more specifically a selective systemic herbicide and an algaecide. As an herbicide, it is used to control broad-leaved weeds and annual grasses in vegetable crops such as leeks, potatoes, and dwarf French beans. Monolinuron affects the photosynthesis in weeds. Following uptake of monolinuron through roots and leaves of weeds, monolinuron causes early symptoms of yellowing and die-back of the leaves, eventually resulting in weed death. In fishkeeping, it is used to control blanket weed and hair algae.

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

Saflufenacil is the ISO common name for an organic compound of the pyrimidinedione chemical class used as an herbicide. It acts by inhibiting the enzyme protoporphyrinogen oxidase to control broadleaf weeds in crops including soybeans and corn.

<span class="mw-page-title-main">Mesotrione</span> Chemical compound used as an herbicide

Mesotrione is the ISO common name for an organic compound that is used as a selective herbicide, especially in maize. A synthetic inspired by the natural substance leptospermone, it inhibits the enzyme 4-hydroxyphenylpyruvate dioxygenase (HPPD) and is sold under brand names including Callisto and Tenacity. It was first marketed by Syngenta in 2001.

<span class="mw-page-title-main">2,4-Dichlorophenoxyacetic acid</span> Herbicide

2,4-Dichlorophenoxyacetic acid is an organic compound with the chemical formula C8H6Cl2O3 which is usually referred to by its ISO common name 2,4-D. It is a systemic herbicide which kills most broadleaf weeds by causing uncontrolled growth in them but most grasses such as cereals, lawn turf, and grassland are relatively unaffected.

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

Acifluorfen is the ISO common name for an organic compound used as an herbicide. It acts by inhibiting the enzyme protoporphyrinogen oxidase which is necessary for chlorophyll synthesis. Soybeans naturally have a high tolerance to acifluorfen and its salts, via metabolic disposal by glutathione S-transferase. It is effective against broadleaf weeds and grasses and is used agriculturally on fields growing soybeans, peanuts, peas, and rice.

<span class="mw-page-title-main">Crop desiccation</span>

Pre-harvest crop desiccation refers to the application of an agent to a crop just before harvest to kill the leaves and/or plants so that the crop dries out from environmental conditions, or "dry-down", more quickly and evenly. In agriculture, the term desiccant is applied to an agent that promotes dry down, thus the agents used are not chemical desiccants, rather they are herbicides and/or defoliants used to artificially accelerate the drying of plant tissues. Desiccation of crops through the use of herbicides is practiced worldwide on a variety of food and non-food crops.

Glyphosate-based herbicides are usually made of a glyphosate salt that is combined with other ingredients that are needed to stabilize the herbicide formula and allow penetration into plants. The glyphosate-based herbicide Roundup was first developed by Monsanto in the 1970s. It is used most heavily on corn, soy, and cotton crops that have been genetically modified to be resistant to the herbicide. Some products include two active ingredients, such as Enlist Duo which includes 2,4-D as well as glyphosate. As of 2010, more than 750 glyphosate products were on the market. The names of inert ingredients used in glyphosate formulations are usually not listed on the product labels.

<span class="mw-page-title-main">Fomesafen</span> PPOi herbicide

Fomesafen is the ISO common name for an organic compound used as an herbicide. It acts by inhibiting the enzyme protoporphyrinogen oxidase (PPO) which is necessary for chlorophyll synthesis. Soybeans naturally have a high tolerance to fomesafen, via metabolic disposal by glutathione S-transferase. As a result, soy is the most common crop treated with fomesafen, followed by other beans and a few other crop types. It is not safe for maize/corn or other Poaceae.

<span class="mw-page-title-main">Fluazifop</span> ACCase herbicide, fop, anti-grass

Fluazifop is the common name used by the ISO for an organic compound that is used as a selective herbicide. The active ingredient is the 2R enantiomer at its chiral centre and this material is known as fluazifop-P when used in that form. More commonly, it is sold as its butyl ester, fluazifop-P butyl with the brand name Fusilade.

<span class="mw-page-title-main">Indaziflam</span> Preemergent herbicide discovered in 2009

Indaziflam is a preemergent herbicide especially for grass control in tree and bush crops.

References

  1. 1 2 Pesticide Properties Database. "Diquat dibromide". University of Hertfordshire. Archived from the original on 2020-08-08. Retrieved 2020-02-11.
  2. 1 2 Pubchem. "Diquat dibromide". U.S. National Library of Medicine. Archived from the original on 2019-12-17. Retrieved 2020-02-02.
  3. ↑ NIOSH Pocket Guide to Chemical Hazards. "#0243". National Institute for Occupational Safety and Health (NIOSH).
  4. ↑ "Compendium of Pesticide Common Names: diquat". BCPC. Archived from the original on 2022-01-24. Retrieved 2022-01-24.
  5. 1 2 USpatent 2823987,Fielden, Richard J.; Homer, Ronald Frederick& Jones, Richard Lewis,"New quaternary salts",issued 1957-11-06, assigned to ICI plc
  6. 1 2 3 4 Calderbank, A.; et al. (1978). "Chapter 9: Bipyridylium herbicides". In Peacock, F.C. (ed.). Jealott's Hill: Fifty years of Agricultural Research 1928-1978. Imperial Chemical Industries Ltd. pp. 67–86. ISBN   0901747017.
  7. ↑ Brian, R. C.; Homer, R. F.; Stubbs, J.; Jones, R. L. (1958). "A New Herbicide: 1: 1′-Ethylene-2: 2′-Dipyridylium Dibromide". Nature. 181 (4607): 446–447. Bibcode:1958Natur.181..446B. doi:10.1038/181446a0. S2CID   4242162.
  8. ↑ Homer, R. F.; Mees, G. C.; Tomlinson, T. E. (1960). "Mode of action of dipyridyl quaternary salts as herbicides". Journal of the Science of Food and Agriculture. 11 (6): 309–315. doi:10.1002/jsfa.2740110604.
  9. ↑ Brian, R. C. (1966). "The Bipyridylium Quaternary Salts". Weed Research. 6 (4): 292–303. doi:10.1111/j.1365-3180.1966.tb00895.x.
  10. ↑ Headford, D. W. R.; Douglas, G. (1967). "Tuber Necrosis Following the Desiccation of Potato Foliage with Diquat". Weed Research. 7 (2): 131–144. doi:10.1111/j.1365-3180.1967.tb01361.x.
  11. ↑ Summers, Lindsay Anderson (1980). The Bipyridinium Herbicides. ISBN   9780126764505.
  12. 1 2 3 Syngenta US. "Reglone desiccant". Archived from the original on 2020-02-18. Retrieved 2020-02-11.
  13. ↑ Willson HR (1996). "Pesticide Regulations". In Radcliffe EB, Hutchison WD, Cancelado RE (eds.). Radcliffe's IPM World Textbook. St. Paul: University of Minnesota. Archived from the original on July 13, 2017.
  14. ↑ "Pesticides and Public Health". Pesticides: Health and Safety. US EPA. 2015-08-20. Archived from the original on January 14, 2014. Retrieved 2020-02-04.
  15. ↑ EPA (27 February 2013). "The Pesticide Label". Archived from the original on 2020-02-03. Retrieved 2020-02-04.
  16. ↑ "Non-renewal of approval of diquat". EUR-Lex. Archived from the original on 2021-01-23. Retrieved 2020-02-02.
  17. 1 2 Pesticide Management Information Program. "diquat dibromide". Archived from the original on 2016-08-25. Retrieved 2020-02-02.
  18. ↑ Clayton, John; Matheson, Fleur (2010). "Optimising diquat use for submerged aquatic weed management". Hydrobiologia. 656: 159–165. doi:10.1007/s10750-010-0423-4. S2CID   23209598.
  19. ↑ US Geological Survey (2021-10-12). "Estimated Agricultural Use for diquat in the USA, 2018". Archived from the original on 2022-01-18. Retrieved 2022-01-17.
  20. ↑ "2020 Submersed Aquatic Vegetation Control Program" (PDF). Archived (PDF) from the original on 2020-06-27. Retrieved 2020-06-27.
  21. ↑ Magalhães, N; Carvalho, F; Dinis-Oliveira, Rj (November 2018). "Human and experimental toxicology of diquat poisoning: Toxicokinetics, mechanisms of toxicity, clinical features, and treatment". Human & Experimental Toxicology. 37 (11): 1131–1160. doi:10.1177/0960327118765330. ISSN   0960-3271. PMID   29569487.
  22. ↑ Karuppagounder, Senthilkumar S.; Ahuja, Manuj; Buabeid, Manal; Parameshwaran, Koodeswaran; Abdel-Rehman, Engy; Suppiramaniam, Vishnu; Dhanasekaran, Muralikrishanan (2012). "Investigate the Chronic Neurotoxic Effects of Diquat". Neurochemical Research. 37 (5): 1102–1111. doi:10.1007/s11064-012-0715-3. PMID   22331545. S2CID   6863674.
  23. ↑ Organization, Food Agriculture (2013). Pesticide Residues in Food 2013 (pdf). pp. 155–170. ISBN   9789251080436. ISSN   0259-2517.{{cite book}}: |journal= ignored (help)
  24. ↑ Shah, P.V.; Tasheva, Maria (2013). "Diquat (addendum)" (pdf). WHO.
  25. ↑ FAO / WHO. "Diquat". Archived from the original on 2021-02-17. Retrieved 2020-03-31.
  26. ↑ Calderbank, Alan (1989). "The Occurrence and Significance of Bound Pesticide Residues in Soil". Reviews of Environmental Contamination and Toxicology. Vol. 108. pp. 71–103. doi:10.1007/978-1-4613-8850-0_2. ISBN   978-1-4613-8852-4.
  27. ↑ "Paraquat and Diquat". IPCS INCHEM. Archived from the original on 2018-10-06. Retrieved 2020-02-02.

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