Hydrolysis aldicarb

Given, C.J. andDierberg, F.E. Effect of pH on the rate of aldicarb hydrolysis. Bull Environ. Contam. Toxicol, 34(5) 627-633, 1985. 

Transformation of aldicarb and its derivatives was also studied in three experiments in unsterilized Palymra soil (Experiments 7 9) to determine the biological component of each transformation process. The value of kx in unsterilized soil ranged from 0.009-0.010 hr-1, compared to 0.009 hr 1 in the sterilized soil of experiment 2. This result implies that aldicarb hydrolysis is primarily a chemical process. The value of kx was approximately four times the value in unsterilized soil (0.015-0.018 hr 1) than in sterilized soil (0.004... 

Carbamate hydrolysis is frequendy observed as the initial reaction for pesticides having carbamate bonds, such as aldicarb, carbofuran, carbaryl, and benomyl (eq. 12) (19). Numerous genera of carbamate-hydroly2ing bacteria have been identified, including Pseudomonas, Jhihrobacter, Bacillus, Nocardia, Achromobacter, Flavobacterium, Streptomyces, Alcaligenes, A spirillum, Micrococcus, and Bhodococcus. 

With aldicarb, primary metabolic attack is again by oxidation and hydrolysis. Hydrolytic cleavage yields an oxime and represents a detoxication. Oxidation to aldicarb sulfoxide and sulfone, however, yields products that are active anticholinesterases. Carbofuran is detoxified by both hydrolytic and oxidative attack. 

Aldicarb undergoes simple hydrolysis at pH values above 7, whereas at pH values <5 an elimination reaction intervenes (Figure 1.20) (Bank and Tyrrell 1984). 

Bank S, RJ Tyrrrell (1984) Kinetics and mechanism of alkaline and acidic hydrolysis of aldicarb. JAgric Food Chem 32 1223-1232. 

Oxime carbamates are not directly amenable to gas chromatography (GC) because of their high thermal instability, which often leads to their breakdown at the injection port or in the column during analysis. Analysis of oxime carbamates by GC with sulfur detection or flame photometric detection involves oxidation of the intact insecticides or alkaline hydrolysis to form the more volatile but stable oxime compound. Enzymatic techniques have been reported for the analysis of these compounds. Enzyme-linked immunosorbent assay (ELISA) has been used to determine aldicarb and its sulfone and sulfoxide metabolites and methomyl in water, soil, and sediment samples. 

Phenylcarbamates, or carbanilates, generally exhibit low water solubilities, and thus they are almost immobile in soil systems. Chlorpropham and Propham are readily volatilized from soil systems, but Terbutol and Carbaryl (Fig. 10, Table 3) are not. Ester- and amide-hydrolysis, N-dealkylation and hydroxylation are among the chemical reactions that carbamates undergo. The N-methylcar-bamate insecticides (Fig. 10, Table 3) commonly used in soils are Carbaryl, Methiocarb,Aldicarb,and Carbofuran [74,173]. 

Hansen, J.L. and Spiegel, M.H. Hydrolysis studies of aldicarb, aldicarb sulfoxide and aldicarb sulfone. Environ. Toxicol. Chem., 2(2) 147-153, 1983. 

Base hydrolysis kinetic data are reported for ppb solutions of carbofuran,3-OH carbofuran, methomyl and oxamyl. The results are compared with those reported previously for aldicarb, aldlcarb sulfoxide, and aldicarb sulfone. Second order reaction rate constants, k, have been calculated and range from 169 liter mln mole for oxamyl to 1.15 liter mln mole for aldicarb. The order for rate of base hydrolysis is as follows oxamyl >3-hydroxycarbofuran >aldicarb sulfone v- carbofuran >aldicarb sulfoxide > methomyl -v aldicarb. The activation energy for the base hydrolysis of carbofuran was measured to be 15.1 +0.1 kcal mole , and is similar to the value previously reported for aldicarb sulfone. Rapid detoxification of aldicarb, a representative oxime carbamate pesticide, by in situ hydrolysis on reactive ion exchange beds is reported. 

Nucleophilic cleavage, acid catalyzed hydrolysis, and oxidation of aldicarb in dilute solution were achieved in batch and/or column experiments using macroporous reactive ion exchange resins. As in solution, nucleophilic cleavage proceeds faster than acid catalyzed hydrolysis. The basis for pursuing study of the latter mechanism is discussed. 

Investigation of the kinetics of hydrolysis of aldicarb and other carbamate pesticides under a variety of conditions in solution. 

The first objective has been accomplished by the development of an HPLC procedure as reported by Spalik et al. ( 5) and GC/NPD procedures developed by Lemley and Zhong ( ). The second and third objectives are being accomplished by fundamental solution studies and reactive ion exchange experiments conducted in parallel. Lemley and Zhong (7) determined recently the solution kinetics data for base hydrolysis of aldicarb and its oxidative metabolites at ppm concentrations and for acid hydrolysis of aldicarb sulfone. They have since ( ) reported similar results for ppb solutions of aldicarb and its metabolites. In addition, the effect on base hydrolysis of temperature and chlorination was studied and the effect of using actual well water as compared to distilled water was determined. Similar base hydrolysis data for carbofuran, methomyl and oxamyl will be presented in this work. 

These data were measured at or extrapolated to ambient temperature and pH values. The data are discussed in the text. NA = not available. b/ Kq = soil water distribution coefficient (K ) divided by the organic carbon content of the soil, cj Whenever possible, half-life for soil dissipation is derived from the field data half-lives described in the text rather than lab data. As such, it may not represent a true first-order process. Value has been estimated from the equation in ref. 20. e/ Hydrolysis of total residues (aldicarb + sulfoxide + sulfone). pK for p -phthalic acid is 3.5. The chlorine atoms of DCPA should lower the pK to about 2. Conditions optimized for soil metabolism. 

One quite prominent example is the Cu2+-catalyzed decomposition of aldicarb, a widely used systematic pesticide (Bank and Tyrell, 1985). In this case the most likely reaction mechanism is not a facilitated hydrolysis but a -elimination (see also Huang, 1997) ... 

Aldicarb, metabolites Hydrolysis, partition, column (silica gel) Sugarbeets GC 14... 

AT Lemley, W-Z Zhong. Hydrolysis of aldicarb, aldicarb sulfoxide, and aldicarb sulfone at parts per billion levels in aqueous mediums. J Agric Food Chem 32 714-719, 1984. 

Lemley, A.T., Zhong, W.Z. (1983) Kinetics of aqueous base and acid hydrolysis of aldicarb, aldicarb sulfoxide and aldicarb sulfone. J. Environ. Sci. Health B18, 189-206. 

Similarly, on-column methylation has been applied to carbamate pesticides containing an active N-H group. Wien and Tanaka (41) showed that N-aryl carbamates are methylated on-column with tri-methylanilinium hydroxide-methanol to give the intact N-methyl and N-aryl derivatives. On the other hand N-methyl, 0-aryl carbamates such as carbaryl or carbofuran yielded only the methyl ethers of their respective phenols. This work has now been extended to sulfur-containing carbamates such as methomyl, methio-carb, aldicarb, etc. (42-43). Here the oxime hydrolysis products of these carbamates are chromatographed as the 0-methyl oximes. 

Carbamates also include pesticides such as Sevin, aldicarb, and carbaryl. They are more degradable than organophosphates and have lower dermal toxicides. Their toxicity is also due to inhibition of acetylcholinesterase but they do not penetrate the central nervous system, so most effects are respiratory in nature. An acetylcholinesterase, which has been carbamylated can undergo spontaneous hydrolysis in vivo, which reactivates the enzyme leading to less severe symptoms or a shorter duration of symptoms. Carbaryl has a low toxicity for mammals however, Perimicarb is highly toxic to mammals, but not readily absorbed through the skin. 

The oxidation of pesticide compounds usually generates products with aqueous mobilities that are either similar to or greater than that of the parent compound. The oxidation of aldicarb, for example, produces aldicarb sulfoxide and aldicarb sulfone, both of which have lower A/qc values than aldicarb (Moye and Miles, 1988). Similarly, because most phototransformations involve either the hydrolysis or oxidation of the parent compound, they yield products that are generally more polar (Mill and Mabey, 1985), and thus more water soluble than the parent compound. Reduction reactions, by contrast, may result in products that are less water soluble than their parent compound. Examples include the reduction of aldicarb sulfoxide to aldicarb (Miles and Delfino, 1985 Lightfoot et al, 1987) and the reduction of phorate sulfoxide to phorate (Coats, 1991). The reactivity of transformation products may be either higher or lower than that of their parent compounds. However, those in the former category (i.e., reactive intermediates) are, of course, much less likely to be detected in the hydrologic system than more stable products. 

Aldicarb (A) is both chemically and biologically oxidized to aldicarb sulfoxide (A-SO), which is then further oxidized by similar processes to aldicarb sulfone (A-S02). These compounds are simultaneously subject to other degradative chemical processes dominated by hydrolysis. These reactions have been successfully described by first-order kinetics (J ), and can be generally summarized as ... 

Experiments 1-2, 3-4, and 5-6 represent paired cases of investigation of A, A-SO and A-S02 in Palmyra soil. Sterilized soil was used in these cases to isolate chemical oxidation and hydrolysis from biological conversion processes, and to determine whether the curve-fitted values of K and k depend on water velocity. The only difference within a pair of experiments was in the flow velocity (v). Between pairs, the difference was the aldicarb metabolite applied. 

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