Alachlor structure

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. 

Structurally related compounds may cross-react with the antibody, yielding inaccurate results. In screening for the herbicide alachlor in well water by immunoassay, a number of false positives were reported when compared with gas chromatography (GC) analysis. A metabolite of alachlor was found to be present in the samples and it was subsequently determined that the cross-reactivity by this metabolite accounted for the false-positive results. On the other hand, cross-reactivity by certain structural analogs may not be an issue. For example, in an assay for the herbicide atrazine, cross-reactivity by propazine is 196% because of atrazine and propazine field use... 

Our previous work showed that alachlor, a compound that is structurally similar to metolachlor, could be separated from its acidic metabolites using a C-18 SPE cartridge (12). However, this procedure does not allow the separation of the OXA and the ESA. Thus, different adsorption mechanisms and solvent systems will be explored to separate the analytes into three fractions metolachlor, OXA, and ESA. This procedure is depicted in Figure 4 [not included in excerpt]. The SPE procedure will be necessary to avoid overlapping of the eight isomers of each compound in the chiral chromatographic analysis. 

Figure 16.7 Structural formulas of Alachlor, pentachlorophenol, and microcidal hexachlorophene and triclosan.

Logusch and co-workers105 further explored the capabilities of 3 mm NMR probe technology in a study of the enzymatic synthesis of a rodent metabolite the preemergence herbicide alachlor. Lipopolysaccharides from Chlamydia trachomatis serotype L2 were the subject of a study using a 2.5 mm Bruker micro-NMR probe reported by Rundt et al.106 This work represents the first complete structural characterization of a lipopolysaccharide from a Chlamydial sp. 

However, a 6-month dog study showed liver toxicity at all doses above 5 mg kg May and a 1-year study established that above lmgkg day alachlor causes effects in the liver, spleen, and kidney. In 2-year rat studies, doses above 2.5 mg kg day caused irreversible degeneration of the iris and related eye structures. 

Cross-Reactivitv of Antibodies. Alachlor belongs to a family of structurally similar chloroacetanilide herbicides. Specificity of the antibodies for alachlor was therefore crucial for the successful application of this assay to environmental samples. The strategy we employed for covalently linking alachlor to proteins through the chloroacetamide group was expected to assure a high degree of specificity for the substitution pattern found in alachlor. To test this assumption, we conducted extensive studies to determine the specificity of the antibodies for alachlor. The alachlor reactivity was defined as 100.0%. As... 

Our cross-reactivity studies demonstrated that the antibodies were sensitive to modifications in the methoxymethyl side chain of alachlor, and were able to distinguish alachlor from structurally similar chloroacetanilide herbicides. Minor modifications in the N-methoxymethyl side chain of alachlor... 

Another concept to consider in reversed-phase elution is selective elution. Selective elution consists of using sequential elution solvents to selectively remove several classes of solutes, or using wash solvents to remove impurities that will interfere with the analysis. An example of selective elution is the separation and isolation of herbicides and their metabolites by a reversed-phase C-18 mechanism. Figure 3.5 shows the separation of alachlor, a herbicide, and its sulfonic-acid metabolite. In this method, both compounds are sorbed to the C-18 resin by a reversed-phase mechanism. Even the ionic sulfonic acid is bound to the C-18 bonded phase. The metabolite, whose structure is shown in Figure 3.5, is a surface-active compound and is bound by reversed phase with its ionic functional group solvated by the aqueous phase. The parent compound is eluted with ethyl acetate while the ionic metabolite stays bound to the C-18 resin. Apparently the solubility of the ionic metabolite in ethyl acetate is too low for dissolution. When methanol is applied to the column, the sulfonic acid metabolite elutes from the column. Thus, a fractionation is obtained by selective elution (Aga et al., 1994). 

Inhibition of the incorporation of uridine into RNA is caused by the herbicides referred to as the chloroacetanilides (e.g., acetochlor, alachlor, butachlor, and several others) and a group of fungicides referred to as phe-nylamides (metalaxyl, ofurace, and oxadixyl). They have similar structure and mode of action ... 

Fig. 2 Structures of parent herbicides and transformation products under investigation. Structures I-X represent alachlor and its transformation products structures XI-XIX represent metolachlor and its transformation products structures XX-XXIV represent acetochlor and its transformation products structures XXV-XXVIII are those transformation products that can result from either metolachlor or acetochlor structures XXIX-XXX represent dimethenamid and its transformation product and structures XXXI-XXXV are triazine herbicides and their transformation products. Reprinted with permission from [50]...

Only hydroxyatrazine deviates from this pattern in cross reactivity. Because it has the same alkyl structure as atrazine, one would predict a cross reactivity similar to ametryn (about 0.6 ug/L as atrazine). However, hydroxyatrazine gave a response of less than 0.1 ug/L as atrazine. A possible explanation is that the hydroxyl group decreases the binding energy at the specific antibody recognition site. The didealkylatrazine was nonreactive (fig. 2). Neither alachlor nor metolachlor cross reacted with atrazine, which is consistent with results of a previous study (12). 

Figure 1. Chemical structures of (a) alachlor, (b) acetochlor, and (c) metolachlor.

Figure 2. Chemical structures of selected alachlor metabolites, (a) ESA metabolite of alachlor, (b) OAA metabolite of alachlor, (c) 2,6-diethylaniline and (d) 2,6-diethylacetanilide.

Al ough alachlor is no longer used in the U.S., the three chemical compounds have very similar structural (Figure 1) and chemical properties. Alachlor degradataion data may be useful as a model for this chemical class. Caution must be used in interpolating these data however since the ESA metabolite of metolachlor is formed more slowly and at lower concentrations in soil (18). The objective of this study was to compare atrazine and alachlor sorption, mineralization, and degradation potential, processes that are major contributors to the environmental fate of pesticides, from surface soil to aquifer sediments in laboratoiy studies. In addition, ctegradation of alachlor was compared under aerobic and anaerobic conditions. 

Fig. 4.4 LC-TOF MS spectra and accurate measurements for the secondary amides of alachlor (a) and acetochlor (b) sulfonic acid in a groundwater sample. The correct elemental composition for both analytes ranks at the second score position. The physico-chemical properties and the chromatographic retention times were predicted from the molecular structure (Ferrer and Thurman 2003, Fig. 4.3, with permission)...

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