Propanil is a widely used contact

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 ...

. With an estimated use of about 8 million pounds in 2001, it is one of the more widely used herbicides in the United States. Propanil is said to be in use in approximately 400,000 acres of rice production each year.

Mode of action

The principal mode of propanil's herbicidal action against weeds is inhibition of their photosynthesis and CO₂ fixation. Plants photosynthesize in two stages. In stage I photosynthetic reactions capture sunlight energy and yield molecules with high energy content. In stage II these molecules react to capture CO₂, yielding carbohydrate precursors. In the stage I reaction a chlorophyll molecule absorbs one photon (light) and loses one electron, starting an electron transport chain reaction leading to the stage II reactions. Propanil inhibits the electron transport chain reaction and its conversion of CO₂ to carbohydrate precursors. That inhibits further development of the weed. Rice is relatively immune to propanil but most weeds are susceptible to it. The reason for the selectivity is that rice contains a high level of the enzyme aryl acylamidase (AAA), which rapidly metabolizes propanil to relatively nontoxic 3,4-dichloroaniline. Susceptible weeds lack the

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...

(s) coding for the AAA enzyme and thus succumb to propanil. However, intensive use of propanil and

natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...

have caused some weeds to become resistant to propanil.

Synthesis

Propanil is made industrially by

nitration In organic chemistry, nitration is a general class of chemical processes for the introduction of a nitro group into an organic compound. The term also is applied incorrectly to the different process of forming nitrate esters between alcohols and ...

of 1,2-dichlorobenzene (1) to give 1,2-dichloro-4-nitrobenzene (2), followed by

hydrogenation Hydrogenation is a chemical reaction between molecular hydrogen (H2) and another compound or element, usually in the presence of a Catalysis, catalyst such as nickel, palladium or platinum. The process is commonly employed to redox, reduce or S ...

of the

nitro group In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nitr ...

with Raney nickel to give 3,4-dichloroaniline (3).

Acylation In chemistry, acylation (or alkanoylation) is the chemical reaction in which an acyl group () is added to a compound. The compound providing the acyl group is called the acylating agent. Because they form a strong electrophile when treated with ...

of the

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 ...

with propanoyl chloride yields propanil (4). The resulting product is white or brown crystals. Propanil synthesis

Patent litigation

Propanil was the subject of several patent infringement suits. In one, '' Monsanto Co. v. Rohm and Haas Co.'', the

United States Court of Appeals for the Third Circuit The United States Court of Appeals for the Third Circuit (in case citations, 3d Cir.) is a federal court with appellate jurisdiction over the district courts for the following districts: * District of Delaware * District of New Jersey * Ea ...

held that Monsanto committed fraud on the Patent Office in procuring its patent on propanil. Compound 3,4-DCPA claimed in US Pat No

Monsanto obtained the patent by providing data to the Patent Office showing that propanil "had "unusual and valuable herbicidal activity" and that its activity was "surprising" because "related compounds possess little or no herbicidal efficiency." Monsanto had conducted a number of tests and submitted test data to the Patent Office that indicated that propanil was superior to other similar chemicals, including one chemical that differed from propanil only in eliminating the CH₂ group to the left of the CH₃ group at the far right of the diagram shown at above right. (The two chemicals are so-called adjacent homologues.) But Monsanto had withheld data on those tests that showed that other similar compounds also had herbicidal activity similar to that of propanil. The court said that this amounted to a misrepresentation and Monsanto was not entitled to a patent, so that the patent was invalid or unenforceable. In an earlier case, however, a judge had accepted Monsanto's argument that Monsanto "did nothing more than put their best foot forward" with the Patent Office.See 456 F.2d at 597 n.4.

References

External links

* {{herbicides Herbicides Chlorobenzenes Anilides