Chlortoluron, chlorotoluron and CTU are the

common names In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often contras ...

for an

organic compound Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...

of the phenylurea class of

herbicide Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

s used to control broadleaf and annual grass weeds in cereal crops.

History

In 1952, chemists at E. I. du Pont de Nemours and Company patented a series of

aryl In organic chemistry, an aryl is any functional group or substituent derived from an aromatic ring, usually an aromatic hydrocarbon, such as phenyl and naphthyl. "Aryl" is used for the sake of abbreviation or generalization, and "Ar" is used ...

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

derivatives as

herbicides Herbicides (, ), also commonly known as weed killers, are substances used to control undesired plants, also known as weeds.EPA. February 201Pesticides Industry. Sales and Usage 2006 and 2007: Market Estimates. Summary in press releasMain page f ...

. Several compounds covered by this patent were commercialized as herbicides: monuron (4-chlorophenyl), diuron (3,4-dichlorophenyl) and chlortoluron, the 3-chloro-4-methylphenyl example. Subsequently, over thirty related urea analogs with the same mechanism of action reached the market worldwide. Chlortoluron entered the British market in 1971, alongside isoproturon. CTU was more effective against black-grass, though suffered greater herbicide resistance, so by the 1980s isoproturon overtook it in popularity. Both saw large use as British agriculture was then moving towards earlier sowing, to reduce damage to soil structure, by sowing at drier times. Chlortoluron and isoproturon were useful to control blackgrass while growing winter wheat.

Synthesis

As described in the du Pont patent, the starting material is a substituted aryl

amine In chemistry, amines (, ) are organic compounds that contain carbon-nitrogen bonds. Amines are formed when one or more hydrogen atoms in ammonia are replaced by alkyl or aryl groups. The nitrogen atom in an amine possesses a lone pair of elec ...

, an

aniline Aniline (From , meaning ' indigo shrub', and ''-ine'' indicating a derived substance) is an organic compound with the formula . Consisting of a phenyl group () attached to an amino group (), aniline is the simplest aromatic amine. It is an in ...

, which is treated with

phosgene Phosgene is an organic chemical compound with the formula . It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. It can be thought of chemically as the double acyl chloride analog of ...

to form its

isocyanate In organic chemistry, isocyanate is the functional group with the formula . Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyan ...

derivative. This is subsequently reacted with

dimethylamine Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to around ...

to give the final product. :Aryl-NH₂ + COCl₂ → Aryl-NCO :Aryl-NCO + NH(CH₃)₂ → Aryl-NHCON(CH₃)₂

Mechanism of action

The phenylurea class of herbicides including chlortoluron are inhibitors of photosynthesis. They block the Q_B

plastoquinone Plastoquinone (PQ) is a terpenoid-quinone ( meroterpenoid) molecule involved in the electron transport chain in the light-dependent reactions of photosynthesis. The most common form of plastoquinone, known as PQ-A or PQ-9, is a 2,3-dimethyl-1,4- ...

binding site of

photosystem II Photosystem II (or water-plastoquinone oxidoreductase) is the first protein complex in the light-dependent reactions of oxygenic photosynthesis. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. Within the photosystem ...

, preventing electron flow from Q_A to Q_B. This interrupts the photosynthetic

electron transport chain An electron transport chain (ETC) is a series of protein complexes and other molecules which transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

and kills the plant. Chlortoluron is in the Group C, (Australia), C2 (global), Group 7, (numeric), herbicide resistance class.

Usage

Chlortoluron was first licensed for use in the European Union in 1994 and this has been extended, currently until October 2021. It is now mainly used in mixture with other herbicides including diflufenican and pendimethalin. It can be used to control broadleaf weeds and grasses including ''

Alopecurus myosuroides ''Alopecurus myosuroides'' is an Annual plant, annual Poaceae, grass, native to Eurasia, found in moist meadows, Deciduous, deciduous forests, and on cultivated and waste land. It is also known as slender meadow foxtail, black-grass, twitch grass ...

'', '' Anthemis arvensis'', '' Atriplex prostrata'', '' Calendula spp.'', '' Convolvulaceae spp.'', '' Galeopsis spp.'', '' Lamium spp.'', ''

Papaver rhoeas ''Papaver rhoeas'', with common names including common poppy, corn poppy, corn rose, field poppy, Flanders poppy, red poppy, and Odai, is an annual herbaceous species of flowering plant in the poppy family Papaveraceae. It is native to north Afr ...

'', ''

Paspalum distichum ''Paspalum distichum'' is a species of Poaceae, grass. Common names include knotgrass, water finger-grass, couch paspalum, eternity grass, gingergrass, and Thompson grass. Its native range is obscure because it has long been present on most conti ...

'', ''

Poa annua ''Poa annua'', or annual meadow grass (known in America more commonly as annual bluegrass or simply poa), is a widespread low-growing turfgrass in temperate climates. Notwithstanding the reference to annual plant in its name, perennial bio-types ...

'', '' Solanaceae spp.'', '' Stellaria media'' and '' Veronica spp.'' It is mainly used in cereal crops including wheat and barley.

United Kingdom

Chlorotoluron was banned in the UK in 2010, but in 2014 was reapproved after new formulations came with lower application rates, 250 g/Ha down from (up to) 3500 g/Ha, though farmers must spray it earlier in weeds' growth cycles. Agform did this at the same time to the previously banned isoproturon; both reregistrations are mixes with diflufenican, chlorotoluron's Tower® also contains pendimethalin.

References

External Links

* {{Phenylurea herbicides Herbicides Ureas Chloroarenes Anilines Group 7 herbicides