DİQUAT

Diquat is a non-selective, contact herbicide belonging to the bipyridylium family of herbicides. 
Diquat is primarily used for the rapid control of unwanted vegetation and aquatic weeds. 
Diquat acts mainly on the plant tissues that Diquat directly contacts and is generally characterized by relatively rapid herbicidal activity.

CAS No.85-00-7
Chemical Name:Diquat dibromide
CBNumber:CB4384274
Molecular Formula:C12H12Br2N2
Molecular Weight:344.05
MDL Number:MFCD01074187
MOL File:85-00-7.mol

Synonyms: DIQUAT DIBROMIDE D4,pp100,Dquat,reglon,Reward,Reglox,KIAA0571,preeglone,weedtrine-d,ortho-diquat

Chemical & Physical Properties
Formula (Diquat ion): C₁₂H₁₂N₂²⁺
Molecular Weight: 184.24 g/mol (ion); 344.05 g/mol (dibromide salt)
Appearance: Typically handled as a yellowish or brownish aqueous solution.
Mechanism of Action: Works via free radical generation, disrupting cell membranes during photosynthesis.

Description
Diquat (DQ) is a bipyridyl herbicide that has been in use since the 1950s. 
Diquat is employed as a general use herbicide that is fast acting and nonselective. Additionally, on average, 90% of DQ consumption is reported in North America, Europe, Australia, and Japan.

Diquat is a non-selective, contact herbicide that acts primarily on the plant tissues directly exposed to the application. 
Diquat is a quaternary bipyridyl compound and functions through redox reactions that generate reactive oxygen species in plant cells. 
These reactions cause rapid damage to cell membranes, resulting in tissue desiccation and plant death.

Diquat is the ISO common name 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.

Diquat is a fast-acting, contact bipyridylium herbicide and plant desiccant. 
Its primary chemical profile, often referenced on the Diquat Dibromide on ChemicalBook database, lists Diquat under CAS Registry Number 85-00-7 for the dibromide salt.

Diquat is a fast-acting, non-selective contact herbicide belonging to the bipyridylium class of herbicides. 
Diquat is widely used for the control of a broad range of annual and perennial weeds and for vegetation management.

Chemical Properties
Pale yellow crystals; forms monohydrate; mp320°C (608 °F) (decomposes); readily solublein water, insoluble in organic solvents; stablein acids or neutral solution.

Chemical Properties
Diquat is a quaternary ammonium compound containing two pyridinium rings connected by an ethylene bridge. 
The commercial active ingredient is commonly supplied as diquat dibromide, in which the positively charged diquat cation is associated with bromide ions.
Diquat is highly water-soluble and has a strong ionic character. 
Its herbicidal activity is associated with its ability to participate in electron-transfer reactions within plant cells, resulting in the formation of reactive oxygen species.

Uses
Nonselective contact herbicide used to control broad-leaved weeds in fruit and vegetable crops.
DQ is used in a manner similar to paraquat. 
Diquat is found predominantly as a mixture with paraquat, sold as Weedol and Pathclear. 
The most widely used formulation of DQ alone, Reglone, is an aqueous solution containing 200 g l-1 DQ dibromide. 
Besides the use as a general weed control agent on noncrop land, DQ is used as a preharvest desiccant on crops such as cotton, flax, and alfalfa. 
Additionally, almost one-third of all DQ sold is used to control emergent and subemergent aquatic weeds.
Diquat Dibromide is a herbicidal desiccant.

Advantages
Diquat is known for its rapid contact action and can provide visible effects relatively soon after application. 
Because Diquat primarily damages plant tissues that are directly contacted, Diquat is useful where rapid vegetation suppression or desiccation is required.

Production Methods
The commercial production of diquat dibromide involves a multi-step process. 
Diquat begins with the quaternisation of 2,2'-bipyridine with 1,2-dibromoethane in a polar solvent, such as acetonitrile, under controlled temperature and pressure to form the cyclic ethylene-bridged bipyridylium structure. 
The reaction mixture is then treated with bromide salts to ensure the dibromide form.

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.
Diquat was active on test plants at application rates as low as 0.1 lb/acre. 
Diquat 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. 
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. 
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 Diquat was introduced commercially for potato haulm desiccation in 1961. 
In the mid 1960s, diquat's use was extended to the pre-harvest desiccation of oilseed crops such as sunflower, linseed, cotton and soya. 
The patent to the active ingredient has now expired in all countries.

Usage
All pesticides are required to seek registration from appropriate authorities in the country in which they will be used. 
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).
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.
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 Diquat 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.

Diquat use in USA to 2018 (estimated by USGS)
Diquat is an unusual herbicide because Diquat 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. 
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 Diquat is only effective on contact with green tissue. 
In this use Diquat is fast-acting in sunlight and more effective on broadleaved weeds than grasses.
Mixing of diquat with other herbicides is also feasible. 
The estimated annual use of diquat in US agriculture is mapped by the US Geological Survey.
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.
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.

Health Hazard
The acute toxicity of diquat dibromide ismoderate to high in most species. 
In domes-tic animals, its toxicity is greater than thatin small laboratory animals. 
The oral LD50value in cows, dogs, rabbits, and mice is30, 187, 188, and 233 mg/kg, respectively.
The symptoms of acute toxicity are somnolence, lethargy, pupillary dilation, and respiratory distress. 
Prolonged exposure to thiscompound produced cataracts in experimental animals. 
Intratracheal administration ofdiquat dibromide in rats showed toxic effectsin the lung and caused lung damage (Manabeand Ogata 1986). 
But when administered byoral or intravenous routes, there was no toxiceffect on the lung.

Flammability and Explosibility
Not classified

Mechanism of action
Non-selective, contact absorbed through foliage, some desiccant action. 
Photosystem I (electron transport) inhibitor.

Safety Profile
Poison by ingestion, subcutaneous, intravenous, and intraperitoneal routes. 
Experimental teratogenic and reproductive effects. A skin and eye irritant. 
Human mutation data reported. 
When heated to decomposition it emits very toxic fumes of NOx, and Br-. 
See also PARAQUAT

Environmental Fate
Biological. 
Under aerobic and anaerobic conditions, the rate of diquat mineralization in eutrophic water and sediments was very low. 
After 65 days, only 0.88 and 0.21% of the applied amount (5 μg/mL) evolved as carbon dioxide (Simsiman and Chesters, 1976). 
Diquat is readily mineralized to carbon dioxide in nutrient solutions containing microorganisms. 
The addition of montmorillonite clay in an amount equal to adsorb one-half of the diquat decreased the amount of carbon dioxide by 50%. 
Additions of kaolinite clay had no effect on the amount of diquat degraded by microorganisms (Weber and Coble, 1968).
Photolytic. 
Diquat has an absorption maximum of 310 nm (Slade and Smith, 1967). 
The sunlight irradiation of a diquat solution (0.4 mg/100 mL) yielded 1,2,3,4-tetrahydro1-oxopyrido[1,2-a]-5-pyrazinium chloride (TOPPS) as the principal metabolite.
Chemical/Physical. 
Decomposes at 320°C (Windholz et al., 1983) emitting toxic fumes of bromides and nitrogen oxides (Lewis, 1990). 
Diquat absorbs water forming welldened, pale yellow crystalline hydrate (Calderbank and Slade, 1976).
In aqueous alkaline solutions, diquat decomposes forming complex colored products including small amounts of dipyridone (Calderbank and Slade, 1976).

Toxicity evaluation
DQ is a dipyridyl compound that is capable of redox cycling. 
DQ can become reduced to produce a free radical. 
Diquat can then transfer this electron to molecular oxygen to yield superoxide anion. 
This redox cycling mechanism allows DQ to generate reactive oxygen species (ROS) resulting in oxidative stress, damage to cellular macromolecules and even cell death. 
Due to its standard redox potential (E0), DQ is more likely to accept an electron compared to paraquat. 
Because of this property, DQ is expected to generate greater amounts of ROS compared to paraquat at equivalent concentrations. 
In vitro studies have shown that DQ is dependent on mitochondrial complex I and III in isolated mitochondria and primarily complex III in midbrain neuronal cultures for ROS production. 
DQ treatment can lead to NADPH depletion, lipid peroxidation, alteration in intracellular redox status, and liberation of ferritin-bound iron stores.

Uses & Safety
Applications: Used for aquatic weed control, pre-harvest crop desiccation, and broadleaf weed elimination.
Toxicity: Acts as a toxic convulsant upon acute ingestion or high-level occupational exposure. 
Proper safety gear is required.