Metolachlor content

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). 

Metolachlor is the active ingredient of Dual, one of the most important grass herbicides for use in maize and a number of other crops. In 1996, after years of intensive research, Dual Magnum with a content of approximately 90% (S)-diaste-... 

Zimdahl and Clark (1982) reported half-lives of 15-38 and 33-100 d for the herbicide in clay loam soil, and sandy loam soil, respectively. They also reported that soil moisture increased the dissipation rate. At 20 °C, the dissipation rates of metolachlor in the clay loam and sandy loam soils at 20, 50, and 80% soil moisture contents were 0.028, 0.053, 0.062, and 0.016, 0.028, and 0.037/day, respectively. The half-lives of metolachlor in soil maintained at temperatures of 30 and 40 °C were approximately 3.85 and 2.75 wk, respectively (Bravermann et al., 1986). The reported half-lives of metolachlor in soil is approximately 6 d (Worthing and Hance, 1991) and 3-4 wk (Bowman, 1988). 

Metolachlor is the active ingredient of Dual , one of the most important grass herbicides for use in maize and a number of other crops. In 1997, after years of intensive research. Dual Magnum, with a content of approximately 90% (I S)-diastereomers and with the same biological effect at about 65% of the use rate, was introduced into the market. This chiral switch was made possible by the new technical process that is briefly described below. The key step of this new synthesis is the enantioselective hydrogenation of the isolated MEA imine, as depicted in Figure 1.3. 

Zhang, X.C., L.D. Norton, and M. Hickman (1997). Rain pattern and soil moisture content effects on atrazine and metolachlor losses in runoff. J. Environ. Qual., 26 1539-1547. 

The chiral switch of the metolachlor was achieved in 1997. It was put on the market with a content of approximately 90% of the Sc active diastereomers. The key step of the large-scale enantioselective synthesis is the catalytic hydrogenation of the MEA imine shown in Figure 17. A mixture of [IrCl(l,5-cyclooctadiene)]2, the chiral diphosphine (i ,5)-xylyphos, iodide (as tetrabutylammonium or sodium salts) and acetic (30%) or sulfuric (at low... 

The dissipation of metolachlor in the soil is three times slower than that of alachlor. Gerber et al. (1974) found, at 22°C and a 50% soil moisture content in sandy loam of 3.8% organic content, a 50% dissipation time of 26 days. Under identical laboratory conditions this value was 60 days for atrazine, 100 days for trifluralin and 80 days for diuron. Under field conditions, metolachlor is completely degraded in a growing season, and thus does not interfere, with crop rotation. 

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