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Diquat dibromide
Skeletal formula of diquat
Ball-and-stick model of the component ions of diquat
IUPAC name
6,7-Dihydrodipyrido[1,2-a:2′,1′-c]pyrazinediium dibromide
Other names
1,1′-Ethylene-2,2′-bipyridyldiylium dibromide
3D model (JSmol)
ECHA InfoCard 100.001.436
Molar mass 344.050 g·mol−1
Appearance Yellow crystals[1]
Density 1.22–1.27 g/cm3
Melting point 335 °C (635 °F; 608 K)
Boiling point Decomposes[1]
70% (20 °C)[1]
Vapor pressure <0.00001 mmHg (20 °C)[1]
US health exposure limits (NIOSH):
PEL (Permissible)
REL (Recommended)
TWA 0.5 mg/m3[1]
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Diquat is a contact herbicide that produces desiccation and defoliation most often available as the dibromide, diquat dibromide.[2] Brand names for this formulation include Aquacide, Dextrone, Preeglone, Deiquat, Spectracide, Detrone, Reglone, Reglon, Reglox, Tribune, Ortho-Diquat, Weedtrine-D,[3] Weedol 2, and in combination with glyphosate, Resolva.[4]

Diquat is a nonselective herbicide that acts quickly to damage only those parts of the plant to which it is applied.[5] It has been used in pre-harvest crop desiccation.[6] It 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 concentrations typically observed in agricultural soils.[5]

Diquat dibromide is moderately toxic. It may be fatal to humans if swallowed, inhaled, or absorbed through the skin in large quantities.[5]


Pyridine is oxidatively coupled to 2,2′-bipyridine over a heated Raney nickel catalyst. The ethylene bridge is formed by the reaction with 1,2-dibromoethane:[7][8]

Diquat Synthesis V1.svg

See also[edit]


  1. ^ a b c d e f g NIOSH Pocket Guide to Chemical Hazards. "#0243". National Institute for Occupational Safety and Health (NIOSH).
  2. ^ Merck Index, 11th Edition, 3359.
  3. ^ PubChem listing for diquat dibromide
  4. ^ Weedkillers for Home Gardeners. RHS Advisory Service, Royal Horticultural Society, February 2013. Accessed May 2013.
  5. ^ a b c EXTOXNET, Pesticide Information Project
  6. ^ "The agronomic benefits of glyphosate in Europe" (PDF). Monsanto Europe SA. February 2010. Archived from the original (PDF) on January 17, 2012. Retrieved June 2, 2013.
  7. ^ "Paraquat and Diquat". IPCS INCHEM.
  8. ^ Diquat was first synthesized by the British chemist Richard Fielden of the Dyestuffs Division of the Imperial Chemical Industries, Blackley, England. See:
    • Fielden, R. J. ; Homer, R. F. ; Jones, R. L., British Patent Specification no. 785,732 (1957).
    • Fielden, Richard J. ; Homer, Ronald Frederick ; Jones, Richard Lewis. "New quaternary salts" U.S. Patent no. 2,823,987 (issued: 18 February 1958).
    • Brian, R.C.; Homer, R. F.; Stubbs, J.; Jones, R. L. (15 February 1958). "A new herbicide: 1:1'-ethylene-2:2'-dipyridylium dibromide". Nature. 181 (4607): 446–447.