:Chlortoluron

In 1952, chemists at E. I. du Pont de Nemours and Company patented a series of aryl urea derivatives as herbicides. 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.{{cite patent |country=US |number=2655445 |status=patent |gdate=1953-10-13 |fdate=1952-02-14 |pridate=1949-12-06 |invent1 =Todd C.W. |title=3-(Halophenyl)-1-methyl-1-(methyl or ethyl) ureas and herbicidal compositions and methods employing same |assign1=E. I. du Pont de Nemours & Co.}}{{cite book |doi=10.1016/B978-0-12-374367-1.00080-X |chapter=Phenylurea Herbicides |title=Hayes' Handbook of Pesticide Toxicology |year=2010 |last1=Liu |first1=Jing |pages=1725–1731 |isbn=9780123743671 }} Subsequently, over thirty related urea analogs with the same mechanism of action reached the market worldwide.{{cite web |url=http://www.alanwood.net/pesticides/class_herbicides.html#urea_herbicides |title=Urea herbicides |website=alanwood.net|access-date=2021-03-26}}

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.{{cite web |title=Isoproturon – the great soil improver {{!}} NIAB |url=https://www.niab.com/news-views/blogs/isoproturon--the-great-soil-improver |website=www.niab.com |date=18 Nov 2016}}

As described in the du Pont patent, the starting material is a substituted aryl amine, an aniline, which is treated with phosgene to form its isocyanate derivative. This is subsequently reacted with dimethylamine to give the final product.

:Aryl-NH₂ + COCl₂ → Aryl-NCO

:Aryl-NCO + NH(CH₃)₂ → Aryl-NHCON(CH₃)₂

The phenylurea class of herbicides including chlortoluron are inhibitors of photosynthesis. They block the Q_B plastoquinone binding site of photosystem II, preventing electron flow from Q_A to Q_B.{{cite journal |doi=10.1074/jbc.M110.215970 |doi-access=free |title=Structural Basis of Cyanobacterial Photosystem II Inhibition by the Herbicide Terbutryn |year=2011 |last1=Broser |first1=Matthias |last2=Glöckner |first2=Carina |last3=Gabdulkhakov |first3=Azat |last4=Guskov |first4=Albert |last5=Buchta |first5=Joachim |last6=Kern |first6=Jan |last7=Müh |first7=Frank |last8=Dau |first8=Holger |last9=Saenger |first9=Wolfram |last10=Zouni |first10=Athina |journal=Journal of Biological Chemistry |volume=286 |issue=18 |pages=15964–15972 |pmid=21367867 |pmc=3091205 }} This interrupts the photosynthetic electron transport chain and kills the plant.{{cite book |doi=10.1016/B978-0-444-89440-3.50018-7 |chapter=Herbicides of photosystem II |title=The Photosystems |year=1992 |last1=Oettmeier |first1=Walter |pages=349–408 |isbn=9780444894403 }}

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

Chlortoluron was first licensed for use in the European Union in 1994{{cite web|url=http://sitem.herts.ac.uk/aeru/ppdb/en/Reports/151.htm |title=Chlorotoluron |publisher=University of Hertfordshire |author=Pesticide Properties Database |access-date=2021-03-27}} and this has been extended, currently until October 2021.{{cite web |url=https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:32020R1511

|title=Commission implementing regulation (EU) 2020/1511 |date=2020-10-16 |access-date=2021-03-27}} It is now mainly used in mixture with other herbicides including diflufenican and pendimethalin.{{cite web |url=https://www.pcs.agriculture.gov.ie/media/pesticides/content/products/labels/05425%20-%20Tower%20-%202017%20to%20date.pdf |website=pcs.agriculture.gov.ie |author=Adama |date=2017 |access-date=2021-03-27 |title=Tower |archive-date=2021-11-14 |archive-url=https://web.archive.org/web/20211114092425/https://www.pcs.agriculture.gov.ie/media/pesticides/content/products/labels/05425%20-%20Tower%20-%202017%20to%20date.pdf |url-status=dead }}

It can be used to control broadleaf weeds and grasses including Alopecurus myosuroides, Anthemis arvensis, Atriplex prostrata, Calendula spp., Convolvulaceae spp., Galeopsis spp., Lamium spp., Papaver rhoeas, Paspalum distichum, Poa annua, Solanaceae spp., Stellaria media and Veronica spp. It is mainly used in cereal crops including wheat and barley.

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.{{cite news |title=How agchem firms are breathing new life into old pesticide actives |url=https://www.fwi.co.uk/arable/agchem-firms-breathing-new-life-old-pesticide-actives |work=Farmers Weekly |date=15 September 2015}}

{{reflist}}

• {{PPDB|151}}

{{Herbicides}}

{{Phenylurea herbicides}}

Category:Herbicides

Category:Ureas

Category:Chloroarenes

Category:Anilines

Category:Group 7 herbicides