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Investigations on the oxidation of the carbamate pesticide aminocarb
Abstract
The electron transfer stoichiometry and principal oxidation products of the carbamate pesticide Aminocarb (3-methyl-4-dimethylaminophenyl N-methylcarbamate) were investigated in methanol + water and acetonitrile + water media, using flow injection coulometry,1H and 13C nuclear magnetic resonance spectrometry, and mass spectrometry. The four-electron oxidation was found to occur at aliphatic as opposed to aromatic sites, involving oxidation and nucleophilic attack at an N-methyl group to yield the hydroxy/methoxy analogs in water + methanol media, and yielding ultimately an aldehyde. The pathway in water + acetonitrile, as expected, was found to yield only the hydroxy analogs and the aldehyde.
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A packed graphite bed electrode has been used for separation and recovery of copper from dilute solutions containing nickel. The cell has been operated under low flow conditions and in plane parallel position. Well defined limiting current plateaus have been observed for copper deposition and the deposition proceeds with almost 100% recovery. Anodic stripping efficiency of deposited copper decreases with increase in the extent of loading and is practically independent of flow rate. Copper concentration of a typical solution containing 1 multiplied by 10** minus **3 M copper, 1 multiplied by 10** minus **2 M nickel and 0. 5 M H//2SO//4 has been reduced to less than 1 multiplied by 10** minus **6 M in a single pass.
Anodic oxidation of several N-hydroxycarbamates is studied by cyclic voltammetry and controlled potential electrolysis in acetonitrile with or without amines at a glassycarbon electrode. In the presence of excess amine, the corresponding N, O-dialkoxycarbonyl-and O-alkoxycarbonyl-N-hydroxycarbamates, alcohols and N-alkylacetamides, are produced from ethyl and benzyl N-hydroxycarbamates. N-Methylation of the compound markedly decreases the yields of the corresponding alcohol and N-alkylacetamide, whereas it increases O-alkoxycarbonylation of the starting compound and the demethylated product. O-Alkylated N-hydroxycarbamates yield N, N'-dialkoxycarbonyl-N, N'-dialkoxyhydrazines quantitatively. Plausible oxidation processes for these compounds are proposed.
In the section entitled 'flow-through electrodes,' the following topics are discussed: cell dispositions, factors affecting reaction rates (hydrodynamics and electrochemistry), the theory of porous flow electrodes, flow-by porous electrodes, flow-through porous electrodes, a comparison of flow-through and flow-by porous electrodes, applications, trickle-bed reactors, and fluidized-bed electrodes. In the section entitled 'three-phase electrodes,' the following topics are discussed: Soviet studies of three-phase electrodes and Western work.
The electrochemical activity of 13 carbamate pesticides has been investigated in the potential range of a glassy carbon electrode, over a pH range from 2.5 and 10. Four compounds, pirimicarb, methiocarb, aminocarb and zectran, give oxidation waves; however, only those for aminocarb and zectran are suitable for analytical electrochemical detection in association with high-pressure liquid chromatography. The oxidation reaction has an ECE mechanism, proposed to involve formation of a carbamate cation radical. This hydrolyses to form a phenol which is in turn oxidized, the end product being a substituted dimethylamino-benzoquinoneimine.
A theoretical model is described for coulometry employing a flow electrolytic cell with a porous electrode working under condition of a limiting current. The model allows the “cell factor” of a flow electrolytic cell to be calculated. The possibility of eliminating secondary electrochemical reactions in the flow coulometric determination is discussed. A relation is derived for the upper limit of the chemical rate constant in an e.c.e. mechanism, so that the second electron transfer will not be observed in the flow coulometric determination.
A new cell design for detection in flowing streams incorporating a reticulated vitreous carbon (RVC) working electrode has been investigated. The principal feature is geometrical symmetry in the radial direction between the working electrode and counterelectrode. This arrangement produced well-defined hydrodynamic voltammograms. The reticulated structure of the working electrode provides a large surface-area-to-volume ratio which alows rapid coulometric conversion without significant band broadening when the detector is used for flow injection analysis (FIA) or high-performance liquid chromatography (HPLC).
The electrolyses at constant current intensity of α-methoxy-p-xylene, p-methylbenzaldehyde dimethyl acetal and p-methoxymethylbenzaldehyde dimethyl acetal are carried out in methanol—sodium methoxide and graphite paste anode. High yields in side-chain methoxylated products are obtained. In spite of stabilization of the carbocations due to the methoxyl groups, in two cases methoxylations occurs in the carbon atom which support a lower number of methoxyl groups.
The behaviour of ece reactions in flow electrolysis in porous electrodes (epf) is discussed theoretically. An equation for the selectivity of the primary electrode reaction product is derived as a function of the limiting degree of conversion of substrate and of the kinetic parameter expressing the ratio of the intervening homogenous reaction rate constant and of the rate constant of electrolysis. Based on the assumption of a negligible amount of the intervening reaction in the diffusion layer an equation is given for the yield of the final product in an ece reaction, expressed in terms of the limiting degree of conversion of substrate and of the kinetic parameter. A condition of validity of the above assumption is formulated based on the calculation of the thickness of the diffusion layer and of the time of traversing the diffusion layer by molecules which have reacted at the electrode interface. A discussion is presented concerning the application of epf with a limiting current for determination of the number of electrones transferred per molecule in an ece reaction.
The design and characteristics of a porous tubular electrode in which effective mass transport is ensured by a stirrer rotating inside the tube are described. The electrode provides high analytical currents owing to the combination of the high surface area with high mass-transport rates. The dependence of the limiting current and the degree of conversion on stirring rate, flow rate, and electrode length are described. The completeness of the electrolytic process is as high as 100%. A new hydrodynamic modulation mode, based on measuring the current difference while switching the stirring on and off, is used to correct background contributions. Analytical utility of the cell is demonstrated by application to flow injection and continuous flow analyses. Caffeic acid, p-acetylaminophenol, dopamine, and hexacyanoferrate(II) were used as test systems to give detection limits at the nanomolar concentration level.
An amperometric detector was used to determine some carbamate pesticides after a reversed-phase high-performace liquid chromatographic separation. Detection limits were determined which compared favorably with those obtained with other detectors. Dual detection, where the amperometric detector was in series with an ultraviolet detector, was employed to quantifiy pesticides that were not resolved on the chromatographic column.
Each of the 33 methyl- and dimethylcarbamate insecticide chemicals and related compounds studied is metabolized by the rat liver microsome-reduced nicotinamide-adenine dinucleotide phosphate (NADPH2) system, producing one or more carbamate metabolites in each case. In this system, NADPH2 is required for each of the following types of enzymatic reactions, as demonstrated with the listed carbamates: N-demethylation (dimetilan, Matacil, Zectran, and 1-naphthyl dimethylcarbamate); conversion of N-methyl to N-formamide (Zectran) and to N-hydroxymethyl groups (Banol, Baygon, carbaryl, HRS-1422, Matacil, UC 10854, and Zectran); aromatic ring hydroxylation (Baygon and carbaryl) or formation of a dihydrodihydroxy derivative (carbaryl); O-dealkylation (Baygon); alkyl hydroxylation of an aralkyl substituent (UC 10854); sulfoxidation (Mesurol and Temik). Carbaryl is produced on N-demethylation of 1-naphthyl dimethylcarbamate by the microsome-NADPH2 system, and on spontaneous or enzymatic hydrolysis of 1-naphthyl N-acetyl-N-methylcarbamate. The microsome-NADPH2 system usually forms one or more anticholinesterase metabolites from methyl-and dimethylcarbamate insecticide chemicals, and certain of these metabolites are more potent inhibitors than the carbamate from which they are derived. Although hydrolysis of the carbamate ester group is not a major reaction in this enzyme system, certain of the products formed in its presence are hydrolyzed, spontaneously or by enzymatic action. Carbamoylation of microsomal proteins probably occurs with certain of the methylcarbamates, their carbamate metabolites, and metabolites of the dimethylcarbamates.
The anodic oxidation of methyl N,N-dialkylcarbamate (4) in methanol yielded three types of products, that is, α-methoxylated compound (5), enamine-type product (6) and dealkylated carbamate (7). Inter- and intramolecular isotope effects were measured to be 1.5-1.6 and 1.8-1.9, respectively. The reaction mechanism was discussed on the bases of product study, oxidation potential of carbamate, current-potential relationship, and isotope effect, and the electron transfer from the carbamate to anode was suggested as the initiation process.
A new method of detection based on constant potential coulometry for liquid chromatography has been developed. This paper presents an improvement of the electrolytic flow cell for the detection of sample constituents in the column effluent. The new cell had a response time of within 1 second and could be used in the flow rate of effluent as large as 6 ml/min with the electrolytic efficiency of more than 99.5%. Primary, secondary, and indirect coulometry were applied to the detection of the materials such as metal ions, inorganic anions, organic acids, phenols, and sugars. The method was applied to the detection of 5 × 10 -7 to 5 × 10 -10 mole of these substances separated by ion-exchange chromatography with good results.
A reverse-phase liquid Chromatographie method with electrochemical detection Is described for the trace determination In water of selected examples of the Important and ubiquitously applied carbamate class of agricultural pesticides. The thinlayer, Kel-F-graphHe electrochemical detector Is operated In the oxldatlve, constant-potential amperometrlc mode at +1.1 V vs. Ag|AgCl|3.5 M KCl. Calibration curves are linear over a wide range of sample concentration - typically at least 3 orders of magnitude - with relative standard deviations for repetitive determinations of 1-2% through most of the range. Detection limits In the range of 40-150 pg (signal/noise ratio 2:1) have been obtained for test carbamates, corresponding to sample concentrations of 2-7 ppb, using simple and Inexpensive equipment. Detection limits are controlled by "pump" noise resulting from fluctuations in background water oxidation current.
A flow-through electrolytic cell which contains a working electrode composed of a variable number of Reticulated Vitreous Carbon (RVC) disks is described. Well defined current-potential curves are reported for various numbers of disks. The dependence of the limiting current and the limiting degree of conversion on the flow rate and on the number of disks employed has been Investigated. The completeness of the electrolytic process is as high as 92%. The Imiting current is linear with respect to the concentration of electroactive material. Stopped-flow voltammetry at a RVC electrode permits discrimination against nonconvective background currents, and allows a limit of detection around 1 nM ferro-cyanlde.
Flow-through electrodes have been fabricated from Reticulated Vitreous Carbon (RVC). This material has low electrical resistance, large surface area, and a physically continuous structure. The resistance to solution flow is low and flow rates up to 25 mL/min were easily attained. Solutions in the concentration range 1 to 1000 μM produced currents from about 1 to 1000 μA, respectively, using flow rates from 0.5 to 25 mL/min. Current-voltage curves were generated using these electrodes. At constant potential, the analyte solution was pumped through the electrode at a constant rate, thereby generating a steady-state current. The linearity and slope of calibration curves (steady-state current vs. concentration) were found to depend on flow rate. Higher sensitivities were obtained at higher flow rates and coulometric conversions occurred at the lowest flow rates. Ferricyanide ion and ascorbic acid were used as test systems, and ascorbic acid in vitamin C tablets was determined with results that were in excellent agreement with a titrimetric check method.
The properties and advantages of microarray electrodes are discussed relative to solid electrodes as flow detectors. Amperometric response for a series of Kelgraf microarray electrodes of varying percent graphite is in agreement with theoretical predictions. The Kelgraf electrodes effectively discriminates between oxidation reactions limited by the rate of mass transport and reactions (including solvent oxidation) limited by the rate of electron transfer or other surface processes, affording improved detection limits for measurement of carbamate pesticides spiked into a river water matrix, using liquid chromatography with electrochemical detection.
A coulometric detector made of crushed reticulated vitreous carbon was used to determine the purity of reference standards by counting the number of coulombs generated as each compound eluted from a high-performance liquid Chromatographic column. The purity of acetaminophen, L-dopa, ascorbic acid, hydroquinone, and 2,5-dihydroxybenzoic acid could be determined with a relative accuracy and precision of 0.5% or better by using reversed-phase columns with flow rates of less than 3 mL/min and injecting the optimum range of 100-400 nmol of sample. The coulometric yield was monitored with a downstream amperometric detector.
The present review discusses the physical, chemical and electrochemical characteristics of Reticulated Vitreous Carbon. A survey is given of the electrochemical applications of this relatively new electrode material, together with trends towards possible future applications.
A tubular platinum electrode packed with small chips of platinum is described which was shown to function with 100% electrolytic efficiency. Application of the electrode is described for the coulometric determination of electroactive species in the effluent from a liquid chromatograph. Cu and Fe were determined in a series of standards. An average relative deviation of less than 2 ppt was obtained for analysis of samples containing 5 mug of Cu(II) and 5 mug of Fe(III).
Liquid chromatography with electrochemical detection has been applied for the determination of selected urea pesticides, using a Kelgraf composite electrode. Detection limits of 62-410 ..mu..g/L (1-8 ng) were obtained in a water matrix without sample pretreatment. A flow injection coulometric system based on a reticulated vitreous carbon working electrode was applied for the evaluation of electron transfer stoichiometry (n values) for oxidation of carbamate and urea pesticides. Excellent precision was obtained with relative standard deviations of less than 1% for coulometric n values of nanomole pesticide quantities over a wide range of operating conditions.
Comparative in vitro metabolic activity of human and rat liver fractions toward 5 ring-substituted methylcarbamates are reported. Human liver appeared to be less metabolically active than rat liver toward 4-dimethylamino-3,5-xylyl methylcarbamate (Zectran), 4-dimethylamino-3-cresyl methylcarbamate (Matacil), 4-methylthio-3,5-xylyl methylcarbamate (Mesurol), and 1-naphthyl methylcarbamate (carbaryl). In these studies the human liver metabolized 2-chloro-4,5-xylyl methylcarbamate (Banol) as well as did the rat. Both species produced esssentially the same major metabolites from the carbamates although quantitative differences were observed. Ring hydroxylation and N-dealkylation are the main oxidative metabolic pathways of carbamate metabolism studied in both the human and rat. The human liver produced a few metabolites not seen with the rat liver. The human liver had more difficulty oxidizing the N-methylcarbamate side chain to form the N-hydroxymethylcarbamate derivative of all the carbamates except Mesurol. In both species the major metabolic products from the carbamates retained the OC(O)NC group necessary for acetylcholinesterase inhibition.
An ion-pairing chromatographic method which uses a controlled potential coulometric detector is described. Two coulometric detectors with different electrolytic cell designs have been investigated. The resulting sensitivity can be comparable to the conventional amperometric detector. This technique has been applied to the analysis of catecholamines.
Spectrometric Identification of Organic Compounds Protein and Carbon-13 NMR Spectroscopy
- R E Sioda
- Electrochim
- N A Acta
- A J S Hampson
- D Mcneil
- C Calasanno
- S Sorana
- R Zamponi
- R J Marasst
- P Abraham
- Loftus
R.E. Sioda, Electrochim. Acta, 20 (1975) 457. 16 N.A. Hampson and A.J.S. McNeil, Electrochemistry, 9 (1984) 1. 17 J. Wang, Electrochim. Acta, 26 (1981) 1721. 18 D.J. Curran and T.P. Tougas, Anal. Chem., 56 (1984) 672. 19 D. Calasanno, C. Sorana, S. Zamponi and R. Marasst, Ann. Chim. (Rome), 73 (1983) 167. 20 B.A. Freiha and J. Wang, Anal. Chim. Acta. 151 (1983) 109. 21 W.J. Blaedel and J. Wang, Anal. Chem.. 51 (1979) 799. 22 C.W. Anderson and K.R. Lung, J. Electrochem. Sot.. 129 (1982) 2525. 23 A.N. StrohI and D.J. Curran, Anal Chem., 51 (1979) 353. 24 G.E. Batley and B.K. Afghan, J. Electroanal. Chem.. 125 (1981) 437. 25 T. Shono. H. Hamaguchi and Y. Matsumura, J. Am. Chem. Sot., 97 (1975) 4264. 26 D.A. Memsma and P.T. Kissinger, Curr. Sep., Bioanal. Syst.. 6 (1985) 42. 27 J.E. Richards and D.H. Evans, Anal. Chem., 47 (1975) 964. 28 G.W. Schieffer, Anal. Chem.. 57 (1985) 968. 29 R.M. Silverstein, G.C. Bassler and T.C. Mornll, Spectrometric Identification of Organic Compounds, 4th ed.. Wiley New York, 1981. 30 R.J. Abraham and P. Loftus, Protein and Carbon-13 NMR Spectroscopy, Heyden, London, 1979. 31 G. Levy, J. Lichter and M. Nelson. Carbon-13 NMR Spectroscopy, Wiley, New York, 1980. 32 S. Ozakr and M. Masui, Chem. Pharm. Bull., 27 (1979) 357. 33 A. Strother, Toxicol. Appl. Pharmacol.. 21 (1972) 112. 34 ES. Oonnithan and J.E. Casida. J. Agnc. Food Chem.. 16 (1968) 28. 35 F. Barba, A. Guirado and I. Barba, Electrochim. Acta. 29 (1984) 1639.