Metolachlor
Encyclopedia
Metolachlor is an organic compound
that is widely used as an herbicide
. It is a derivative of aniline
and is a member of the chloroacetanilide herbicides. It is highly effective toward grasses but its application is also controversial.
of elongases and of the geranylgeranyl pyrophosphate
(GGPP) cyclases, which are part of the gibberellin
pathway. It is used for grass and broadleaf weed control in corn, soybean, peanuts, sorghum, and cotton. It is also used in combination with other herbicides.
Metolachlor is a popular herbicide in the United States. Metolachlor is becoming less and less common. As originally formulated metolachlor was applied as a racemate, a 1:1 mixture of the (S)- and (R)-stereoisomers. The (R)-enantiomer is inactive, and modern production methods afford only (S)-metolachlor, thus current application rates are far lower than original formulations.
. The resulting imine
is hydrogenated
to give primarily the S-stereoisomeric amine. This secondary amine is acetylated with chloroacetylchloride. Because of the steric effects of the 2,6-disubstituted aniline, rotation about the aryl-C to N bond is restricted. Thus, for both the (R)- and the (S)-enantiomers exist as atropisomer
s. Both atropisomers of (S)-metolachlor exhibit the same biological activity.
(US EPA) which indicates limited evidence of carcinogenicity. Evidence of the bioaccumulation of metolachlor in edible species of fish as well as its adverse effect on the growth and development raise concerns on its effects on human health. There is no set maximum concentration (maximum contaminant level
, MCL) for metolachlor that is allowed in drinking water, the US EPA does have a health advisory level (HAL) of 0.525 mg/L.
Metolachlor induces cytotoxic and genotoxic
effects in human lymphocytes. Genotoxic effects have also been observed in tadpoles exposed to metolachlor. Evidence also reveals that metolachlor affects cell growth. Cell division in yeast was reduced, and chicken embryos exposed to metolchlor showed a significant decrease in the average body mass compared to the control.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
that is widely used as an herbicide
Herbicide
Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...
. It is a derivative of aniline
Aniline
Aniline, phenylamine or aminobenzene is an organic compound with the formula C6H5NH2. Consisting of a phenyl group attached to an amino group, aniline is the prototypical aromatic amine. Being a precursor to many industrial chemicals, its main use is in the manufacture of precursors to polyurethane...
and is a member of the chloroacetanilide herbicides. It is highly effective toward grasses but its application is also controversial.
Agricultural use
Metolachlor was developed by Ciba-Geigy. Its acts by inhibitionEnzyme inhibitor
An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme's activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides...
of elongases and of the geranylgeranyl pyrophosphate
Geranylgeranyl pyrophosphate
Geranylgeranyl pyrophosphate is an intermediate in the HMG-CoA reductase pathway used by organisms in the biosynthesis of terpenes and terpenoids. In plants it is also the precursor to carotenoids, gibberellins, tocopherols, and chlorophylls....
(GGPP) cyclases, which are part of the gibberellin
Gibberellin
Gibberellins are plant hormones that regulate growth and influence various developmental processes, including stem elongation, germination, dormancy, flowering, sex expression, enzyme induction, and leaf and fruit senescence....
pathway. It is used for grass and broadleaf weed control in corn, soybean, peanuts, sorghum, and cotton. It is also used in combination with other herbicides.
Metolachlor is a popular herbicide in the United States. Metolachlor is becoming less and less common. As originally formulated metolachlor was applied as a racemate, a 1:1 mixture of the (S)- and (R)-stereoisomers. The (R)-enantiomer is inactive, and modern production methods afford only (S)-metolachlor, thus current application rates are far lower than original formulations.
Production and basic structure
Metolachlor is produced from 2-ethyl-6-methylaniline (MEA) via condensation with methoxyacetoneAcetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
. The resulting imine
Imine
An imine is a functional group or chemical compound containing a carbon–nitrogen double bond, with the nitrogen attached to a hydrogen atom or an organic group. If this group is not a hydrogen atom, then the compound is known as a Schiff base...
is hydrogenated
Hydrogenation
Hydrogenation, to treat with hydrogen, also a form of chemical reduction, is a chemical reaction between molecular hydrogen and another compound or element, usually in the presence of a catalyst. The process is commonly employed to reduce or saturate organic compounds. Hydrogenation typically...
to give primarily the S-stereoisomeric amine. This secondary amine is acetylated with chloroacetylchloride. Because of the steric effects of the 2,6-disubstituted aniline, rotation about the aryl-C to N bond is restricted. Thus, for both the (R)- and the (S)-enantiomers exist as atropisomer
Atropisomer
Atropisomers are stereoisomers resulting from hindered rotation about single bonds where the steric strain barrier to rotation is high enough to allow for the isolation of the conformers. The word atropisomer is derived from the Greek a, meaning not, and tropos, meaning turn...
s. Both atropisomers of (S)-metolachlor exhibit the same biological activity.
Safety and ecological effects
Metolachlor has been detected in ground and surface waters and concentrations ranging from 0.08 to 4.5 parts per billion (ppb) throughout the U.S. It is classified as a Category C pesticide by the United States Environmental Protection AgencyUnited States Environmental Protection Agency
The U.S. Environmental Protection Agency is an agency of the federal government of the United States charged with protecting human health and the environment, by writing and enforcing regulations based on laws passed by Congress...
(US EPA) which indicates limited evidence of carcinogenicity. Evidence of the bioaccumulation of metolachlor in edible species of fish as well as its adverse effect on the growth and development raise concerns on its effects on human health. There is no set maximum concentration (maximum contaminant level
Maximum Contaminant Level
Maximum Contaminant Levels are standards that are set by the United States Environmental Protection Agency for drinking water quality. An MCL is the legal threshold limit on the amount of a substance that is allowed in public water systems under the Safe Drinking Water Act...
, MCL) for metolachlor that is allowed in drinking water, the US EPA does have a health advisory level (HAL) of 0.525 mg/L.
Metolachlor induces cytotoxic and genotoxic
Genotoxic
In genetics, genotoxicity describes a deleterious action on a cell's genetic material affecting its integrity. This includes both certain chemical compounds and certain types of radiation....
effects in human lymphocytes. Genotoxic effects have also been observed in tadpoles exposed to metolachlor. Evidence also reveals that metolachlor affects cell growth. Cell division in yeast was reduced, and chicken embryos exposed to metolchlor showed a significant decrease in the average body mass compared to the control.