Metolachlor

Herbicide Glasses and Databases. Herbicides can be classified as selective and nonselective. Selective herbicides, like 2,4-D (2,4-dichlorophenoxyacetic acid), metolachlor [51218-45-2] and EPTC [759-94 ] are more effective against some types of plants than others, eg, broadleaved plants vs grasses. Glyphosate [1071 -83-6] is representative of the nonselective herbicides used for total vegetable control. 

Acid amide herbicides are nonionic and moderately retained by soils. The sorption of several acid amide herbicides has been investigated (369). Acetochlor [34256-82-1] is sorbed more than either alachlor or metolachlor, which are similarly sorbed by a variety of soils. Sorption of all the herbicides is well correlated to soil organic matter content. In a field lysimeter study, metolachlor has been found to be more mobile and persistent than alachlor (370) diphenamid [957-51-7] and napropamide [15299-99-2] have been found to be more readily leached (356). 

Health advisories have been issued (269) for diphenamid, metolachlor, pronamide, and propachlor. Other acid amide herbicides include butachlor [23184-66-9] and ethalfluralin [55283-68-6],... 

Alkyl-Hyd.roxyla.tion. This is commonly observed as the initial transformation of alkyl-substituted aromatic pesticides such as alachlor [15972-60-8] and metolachlor [51218-45-2] (eq. 2) (2) (16). These reactions are typically catalyzed by relatively nonspecific oxidases found in fungi and actinomycetes. 

Hydrodechlorination is a common reaction of chlorinated pesticides such as atrazine (eq. 15), alachlor, and metolachlor (2) (eq. 16). These reactions are catalyzed primarily by transition metals or by soil surfaces (clays or humic substances). 

Studies have appeared where photolysis in natural bodies of water under normal sunlight conditions has been examined. For example, metolachlor was slowly photodegraded by sunlight in lake water, with a half-life of 22 days in summer and 205 days in winter (28). Addition of a 5% solution of dissolved organic matter to the water extended the half-Hves two to three times longer, depending on the season (see PHOTOCHEMICAL TECHNOLOGY, photocatalysis). ... 

The documented occurrence of pesticides in surface water is indicative that mnoff is an important pathway for transport of pesticide away from the site of appHcation. An estimated 160 t of atra2ine, 71 t of sima2ine, 56 t of metolachlor, and 18 t of alachlor enter the Gulf of Mexico from the Mississippi River annually as the result of mnoff (47). Field appHcation of pesticides inevitably leads to pesticide contamination of surface mnoff water unless mnoff does not occur while pesticide residues remain on the surface of the soil. The amount of pesticides transported in a field in mnoff varies from site to site. It is controUed by the timing of mnoff events, pesticide formulation, physical—chemical properties of the pesticide, and properties of the soil surface (48). Under worst-case conditions, 10% or more of the appHed pesticide can leave the edge of the field where it was appHed. 

It appears that pesticides with solubiHties greater than 10 mg/L are mainly transported in the aqueous phase (48) as a result of the interaction of solution/sediment ratio in the mnoff and the pesticide sorption coefficient. For instance, on a silt loam soil with a steep slope (>12%), >80% of atra2ine transport occurs in the aqueous phase (49). In contrast, it has been found that total metolachlor losses in mnoff from plots with medium ground slopes (2—9%) were <1% of appHed chemical (50). Of the metolachlor in the mnoff, sediment carried 20 to 46% of the total transported pesticide over the monitoring period. 

Conservation tillage increased atra2ine and metolachlor surface mnoff by 42% and decreased tile discharge by 15% compared with conventional tillage, but total field mnoff was the same from all treatments (53). Runoff events shordy after herbicide appHcation produced the greatest herbicide concentrations and losses in both surface mnoff and subsurface drainage. 

Methyl-3-heptanone Methylhydrazine Metolachlor Methyl mercaptan Methyl parathion Methyl phenol N-Methyl-2-pyrrolidinone Methyl tert-butyl ether Mevinphos ... 

BHP (Broken Hill Proprietary Company) Ltd., See BHP Billiton Ltd. Australia and United Kingdom, 141 BHP Billiton Ltd., 141 BHP Billiton Pic, 207 BHP Minerals Ltd., 142 BHP Petroleum Ltd., 142 BICEP , atrazine metolachlor, 25 BIDRIN , dicrotophos, 25... 

Methyl silicate, 93 a-Methylstyrene, 93 Methyl-tert-butyl ether, 90 Methyl thiocyanate, 93 Methylthiouracil, 93 Methyltrichlorosilane, 94 Methyl vinyl ketone, 94 Methylal, 89 Metolachlor, 94 Metolcarb, 94 Metorex (Pty) Ltd., 199 Metribuzin, 94 Metronidazole, 94 Mevinphos, 94 Mexacarbate, 94... 

Liu S-Y, Z Zheng, R Zhang, J-M Bollag (1989) Sorption and metabolism of metolachlor by a bacterial community. Appl Environ Microbiol 55 733-740. 

Reaction between glutathione and reactive chloro compounds such as l-chloro-2,4-dinitrobenzene (Niimi et al. 1989), or the chloroacetamide group in demethylated metolachlor (Cruz et al. 1993). 

Krause A, WG Lfancock, RD Minard, AJ Freyer, RC Lfoneycutt, HM LeBaron, DL Paulson, SY Liu, JM Bollag (1985) Microbial transformation of the herbicide metolachlor by a soil actinomycete. J Agric Food Chem 33 584-589. 

An even more impressive example of catalytic efficiency has recently been disclosed by Novartis (Bader and Bla.ser, 1997). The key step in a proce.ss for the synthesis of the optically active herbicide, (S)-metolachlor involves asymmetric hydrogenation of a prochiral imine catalysed by an iridium-ferrocenyldipho-sphine complex (see Fig. 2.36). 

The substrate/catalyst ratio is 75,000, and one million turnovers are achieved in six hours, giving a product with an ee of 80%. A higher ee can be obtained, at lower substrate/catalyst ratios, but are not actually necessary for this product. This process will be used to produce several thousands tons per annum of (S)-metolachlor, to replace the previously marketed racemic metolaclor. 

Optically active drugs now occupy centre stage status and some agrochemicals like (S)-metolachlor, have also been introduced as optically pure isomers, so that the ballast of the unwanted isomer is avoided. Asymmetric synthesis is a topic of great interest in current research, and there is a steady flow of articles, reviews and books on almost every aspect of this subject. Table 4.8 lists examples of industrially important asymmetric synthesis. 

Dupont s DuPhOS catalyst A.symmetric hydrogenation for making S-metolachlor Blaser and Spindler... 

A fascinating example of enantioselective catalysis for agrochemicals is the production of a well-known herbicide of Novartis (formerly Ciba Geigy), metolachlor (Trade name Dual... 

Chloroacetanilides are soil-applied herbicides used for pre- and early post-emergence control of annual grasses and broadleaf weeds in crops. Representative chloroacetanilide compounds, alachlor, acetochlor, and metolachlor, are extensively used worldwide. Other chloroacetanilides with limited usages include propachlor, bu-tachlor, metazachlor, pretilachlor, and thenylchlor. Public environmental concerns and government regulatory requirements continue to prompt the need for reliable methods to determine residues of these herbicides. There now exist a variety of analytical methods to determine residues of these compounds in crops, animal products, soil, and water. The chemical structures and major crops in which these compounds are used are summarized in Table 1. 

The focus of this article is to describe the residue methodologies for alachlor, acetochlor, metolachlor, and propachlor. Four residue analytical methods are discussed ... 

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