Hydrolysis carbamate pesticides

Faust SD, Gomaa HM. 1972. Chemical hydrolysis of some organic phosphorus and carbamate pesticides in aquatic environments. Environ Lett 3 171 -201. 

Attempts have been made to apply the structure-activity concept (Hansch and Leo 1995) to environmental problems, and this has been successfully applied to the rates of hydrolysis of carbamate pesticides (Wolfe et al. 1978), and of esters of chlorinated carboxylic acids (Paris et al. 1984). This has been extended to correlating rates of biotransformation with the structure of the substrates and has been illustrated with a number of single-stage reactions. Clearly, this approach can be refined with the increased understanding of the structure and function of the relevant degradative enzymes. Some examples illustrate the application of this procedure ... 

Absorbance- and reflectance-based measurements are widespread, as there are many enzymatic reaction products or intermediates that are colored or if not, can react with the appropriate indicator. Sensors using acetylcholinesterase for carbamate pesticides detection are an example of indirect optical fiber biosensors. This enzyme catalyses the hydrolysis of acetylcholine with concomitant decrease in pH41 ... 

Organophosphate and carbamate pesticides are potent inhibitors of the enzyme cholinesterase. The inhibition of cholinesterase activity by the pesticide leads to the formation of stable covalent intermediates such as phosphoryl-enzyme complexes, which makes the hydrolysis of the substrate very slow. Both organophosphorus and carbamate pesticides can react with AChE in the same manner because the acetylation of the serine residue at the catalytic center is analogous to phosphorylation and carbamylation. Carbamated enzyme can restore its catalytic activity more rapidly than phosphorylated enzyme [17,42], Kok and Hasirci [43] reported that the total anti-cholinesterase activity of binary pesticide mixtures was lower than the sum of the individual inhibition values. 

Meier, E.R, M.C. Warner, W.H. Dennis, W.F. Randall, and T.A. Miller. 1976. Chemical Degradation of Military Standard Formulations of Organophosphate and Carbamate Pesticides. I. Chemical Hydrolysis of Diazinon. U.S. Army Med. Bioengin. Res. Dev. Lab., Fort Detrick, Frederick, MD. Tech. Rep. 7611. 32 pp. 

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. 

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

The hydrolysis data collected for this group of carbamate pesticides have significance for several reasons. The kgijg values are expected to correlate directly with batch and column RIEX data such as those reported In this paper (vide Infra). ... 

Table VI. Base Hydrolysis Rate Constants of Carbamate Pesticides and Metabolites at 15°C...

The pesticides methyl and ethyl parathion were determined in run-off water er preconcentration on XAD-2. This allowed analyses of these compounds at the parts per billion level (497). Parathion and paraoxon obtained from leaf extracts and orchard soil have also been determined (492). The separation of 30 carbamate pesticides by RPC has been described (493). Various modes of postcolumn fluorometric detection of carbamate insecticides have been reported including post-colun)n reaction between o-phthalaldehyde and methylamine, a carbamate hydrolysis... 

A photometric flow-through sensor for the determination of carbamate pesticides (carbofuran, propoxur and carbaryl) based on similar principles as regards the detector and sensor used (a diode array spectrophotometer and a flow-cell packed with C,g resin, respectively) was employed to monitor the formation of the products resulting from hydrolysis of the analytes and online coupling of the respective phenols with diazotized sulphanilic acid. This... 

RJ Argauer. Determination of residues of band and other carbamate pesticides after hydrolysis and chloroacetylation. J Agric Food Chem 17 888-892, 1969. 

The use of NBD-Cl for the fluorescence analysis of alkylamine-generating pesticides has been investigated [173]. A two-phase reaction system is employed for the hydrolysis and labeling of N-methyl- and N,N-dimethyl-carbamate pesticides. The residue is hydrolyzed in 0.1 M sodium carbonate and the liberated amine is treated with NBD-Cl in an organic phase (IBMK, isobutyl methyl ketone) above the aqueous layer. An aliquot portion of the organic layer is used for chromatography. The reactions involved are shown in Fig. 4.65. 

Carbamate pesticides are best analyzed by HPLC using postcolumn deriva-tization technique. Some common carbamate pesticides are listed in Table 2.19.1. Compounds are separated on a C-18 analytical column and then hydrolyzed with 0.05 N sodium hydroxide. Hydrolysis converts the carbamates to their methyl amines which are then reacted with o-phthalaldehyde and 2-mercaptoethanol to form highly fluorescent derivatives. The derivatives are detected by a fluorescence detector. o-Phthaladehyde reaction solution is prepared by mixing a 10-mL aliquot of 1% o-phalaldehyde solution in methanol to 10 mL of acetonitrile containing 100 pL of 2-mercaptoethanol and then diluting to 1 L with 0.05 N sodium borate solution. 

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. 

The effect of irreversible inhibition of acetylcholinesterase has been used in dendrimer-based electrochemical biosensors for environmental applications. Acetylcholinesterase is a very efficient protein catalyst for the hydrolysis of its physiological substrate acetylcholine. Organophosphorus and carbamic pesticides, heavy metals and detergents exert strong specific... 

Many pesticides are esters or amides that can be activated or inactivated by hydrolysis. The enzymes that catalyze the hydrolysis of pesticides that are esters or amides are esterases and amidases. These enzymes have the amino acid serine or cysteine in the active site. The catalytic process involves a transient acylation of the OH or SH group in serin or cystein. The organo-phosphorus and carbamate insecticides acylate OH groups irreversibly and thus inhibit a number of hydrolases, although many phosphorylated or carbamoylated esterases are deacylated very quickly, and so serve as hydrolytic enzymes for these compounds. An enzyme called arylesterase splits paraoxon into 4-nitrophenol and diethyl-phosphate. This enzyme has cysteine in the active site and is inhibited by mercury(ll) salts. Arylesterase is present in human plasma and is important to reduce the toxicity of paraoxon that nevertheless is very toxic. A paraoxon-splitting enzyme is also abundant in earthworms and probably contributes to paraoxon s low earthworm toxicity. Malathion has low mammalian toxicity because a carboxyl esterase that can use malathion as a substrate is abundant in the mammalian liver. It is not present in insects, and this is the reason for the favorable selectivity index of this pesticide. 

The U.S.A., through the National Pesticide Survey, " which was organized by the Environmental Protection Agency (US-EPA), established a fist of compounds based on the amount used (>7000 Tons), water solubility (>30 mg/1), and hydrolysis half-life (>25 weeks). The list includes some carbamate pesticides (e.g., aldicarb, propoxur, carbaryl, carbofuran, methiocarb, methomyl, oxamyl, cycloate, butylate, propham, and swep) and various derivatives (e.g., aldicarb sulphone, aldicarb sulphoxide, and 3-hidroxycarbofiiran). In Europe, a list of priority pollutants including pesticides was established in order to protect the environment from the adverse ecological impact of these compounds. ... 

The insecticide carbaryl (1-naphthyl-A-methylcarbamate, Figure 7.4) has been measured on filter paper exposed during aerial spraying using an ODS-modified silica column and ED (GCE, +0.75 V vs Ag/AgCl) after pre-column alkaline hydrolysis to 1-naphthol. The eluent was acetonitrile-acetic acid-aq. potassium chloride (0.5 mol L ) (50 + 1 + 49). 2-Naphthol was the internal standard. Postcolumn hydrolysis with sodium hydroxide of carbaryl and some other A -methyl-carbamate pesticides has also been employed in measuring crop residues of these compounds. The analytical column used was octyl-modified silica. Elution was... 

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