Chloroxynil

Chloroxynil is a postemergent^[5] benzonitrile herbicide, used to control broad leaved weeds on cereal crops. It was manufactured by Rhone-Poulenc and May & Baker, and is now considered obsolete, though its usage may continue.^[4]

Chloroxynil

Names
Preferred IUPAC name 3,5-dichloro-4-hydroxybenzonitrile
Identifiers
CAS Number	1891-95-8
3D model (JSmol)	Interactive image
ECHA InfoCard	100.015.976
EC Number	217-572-4
PubChem CID	74685
UNII	GI6X21WSVN
CompTox Dashboard (EPA)	DTXSID8022167
InChI InChI=1S/C7H3Cl2NO/c8-5-1-4(3-10)2-6(9)7(5)11/h1-2,11H Key: YRSSHOVRSMQULE-UHFFFAOYSA-N
SMILES C1=C(C=C(C(=C1Cl)O)Cl)C#N
Properties
Chemical formula	C7H3Cl2NO
Molar mass	188.01 g·mol−1
Appearance	Off-white solid[1]
Melting point	140 °C (284 °F; 413 K)[2]
Solubility in water	Slightly soluble[3]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Toxic, harmful to aquatic life, irritant
GHS labelling:[1]
Pictograms
Signal word	Danger
Hazard statements	H301, H311, H315, H319, H331, H335
Lethal dose or concentration (LD, LC):
LD50 (median dose)	200 mg/kg (oral, rat)[4]
LC50 (median concentration)	21.4-27.5mg/L (96h, Pimephales promelas)[1]
Related compounds
Related compounds	Ioxynil, Bromoxynil, Bromoxynil octanoate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Chloroxynil was developed as a variant of bromoxynil, which is identical except for bromines replacing chloroxynil's chlorines. A 1972 study found chloroxynil less injurious to alfalfa and red clover, but also less potent at controlling broadleaf weeds.^[6]

Chloroxynil's MoA inhibits electron transfer in the photosystem II receptor.^[7] Its HRAC group is Group C, (Australia) C3 (global) or 6 (numeric).^[4]

Genetic engineering

Chloroxynil can greatly improve the speed and efficiency of agrobacterium-mediated transformation of plants. Compared to the control, acetosyringone was 6 times faster, and chloroxynil was 60 times faster. Chloroxynil's related herbicides were also tested: bromoxynil was 18 times faster than control but caused plant damage, and ioxynil showed no significant improvement.^[8]

Soil behaviour

In soil, chloroxynil lasts about a month in aerobic soil (soil with sufficient oxygen to support microbial activity), or about two weeks in anaerobic soil.^[5] Sunlight can photochemically degrade it, by splitting off the chlorine atoms.^[9]

Application

Chloroxynil was used on wheat, barley, oats, lucerne, sorghum and fax, to control pigweed, mayweed, knotweed, shepherd's purse, goosefoot and stinkweed.^[4]