Chlortoluron or chlorotoluron 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 contra ...

for an

organic compound In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen or carbon-carbon bonds. Due to carbon's ability to catenate (form chains with other carbon atoms), millions of organic compounds are known. The ...

of the phenylurea class of

herbicide Herbicides (, ), also commonly known as weedkillers, 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 fo ...

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 DuPont de Nemours, Inc., commonly shortened to DuPont, is an American multinational chemical company first formed in 1802 by French-American chemist and industrialist Éleuthère Irénée du Pont de Nemours. The company played a major role in ...

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 as ...

urea Urea, also known as carbamide, is an organic compound with chemical formula . This amide has two amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest amide of carbamic acid. Urea serves an important r ...

derivatives as

herbicides Herbicides (, ), also commonly known as weedkillers, 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 fo ...

. Several compounds covered by this patent were commercialized as herbicides: monuron (4-chlorophenyl),

diuron DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is an algicide and herbicide of the arylurea class that inhibits photosynthesis. It was introduced by Bayer in 1954 under the trade name of Diuron. History In 1952, chemists at E. I. du Pont de Nemo ...

(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.

Synthesis

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

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituen ...

, an

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...

, which is treated with

phosgene Phosgene is the organic chemical compound with the formula COCl2. It is a toxic, colorless gas; in low concentrations, its musty odor resembles that of freshly cut hay or grass. Phosgene is a valued and important industrial building block, espe ...

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 aroun ...

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 an isoprenoid quinone 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-benzoquinone m ...

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 that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples th ...

and kills the plant.

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 Pendimethalin is an herbicide of the dinitroaniline class p.328 used in premergence and postemergence applications to control annual grasses and certain broadleaf weeds. It inhibits cell division and cell elongation. Pendimethalin is listed in the ...

. It can be used to control broadleaf weeds and grasses including ''

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

'', ''

Anthemis arvensis ''Anthemis arvensis'', also known as corn chamomile, mayweed, scentless chamomile, or field chamomile is a species of flowering plant in the genus ''Anthemis'', in the aster family. It is used as an ornamental plant. Distribution ;Native :;P ...

'', ''

Atriplex prostrata ''Atriplex prostrata'', called the spear-leaved orache, hastate orache, thin-leaf orache, triangle orache, and fat hen, is a widespread species of flowering plant in the saltbush genus ''Atriplex ''Atriplex'' () is a plant genus of about 250 ...

'', '' 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, and red poppy, is an annual herbaceous species of flowering plant in the poppy family Papaveraceae. It is a temperate native with ...

'', ''

Paspalum distichum ''Paspalum distichum'' is a species of 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 continents, an ...

'', ''

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.

References

{{Herbicides Herbicides Ureas Chloroarenes Anilines