Chemical hydrolysis carbamates

Carboxyhc acid ester, carbamate, organophosphate, and urea hydrolysis are important acid/base-catalyzed reactions. Typically, pesticides that are susceptible to chemical hydrolysis are also susceptible to biological hydrolysis the products of chemical vs biological hydrolysis are generally identical (see eqs. 8, 11, 13, and 14). Consequentiy, the two types of reactions can only be distinguished based on sterile controls or kinetic studies. As a general rule, carboxyhc acid esters, carbamates, and organophosphates are more susceptible to alkaline hydrolysis (24), whereas sulfonylureas are more susceptible to acid hydrolysis (25). 

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

Carbamates are subject to chemical hydrolysis, which takes place relatively slowly under neutral or acid conditions, but more rapidly under alkaline conditions. 

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. 

Thus, there will be a major difference in the design of carbamate prodrugs of phenols and alcohols, as illustrated below. In the case of alcohols, both W-monosubstituted and AOV-disubstituted carbamates will a priori be stable. For phenols, AUV-disubslilulcd carbamates are also stable toward chemical hydrolysis, whereas the /V-monosubsti luted carbamates are, as a rule, more labile toward chemical hydrolysis. However, some notable exceptions are discussed below. In addition, many other factors beside chem-... 

The investigated carbamate insecticides were susceptible to chemical hydrolysis in alkaline media. The hydrolysis rates of the monomethyl-carbamates, Sevin and baygon, were much higher than those of the dimethylcarbamates, pyrolan and dimetilan. The pseudo-first order rate constants for hydrolyzing Sevin and baygon increased with the rise of the pH of the medium. 

Thus, the persistence of the carbamate insecticides, Sevin and baygon, in natural water is affected by the different environmental conditions. The two compounds are readily hydrolyzed in slightly alkaline waters they are also slightly adsorbed on mineral particulate matter common in streams and are slowly decomposed by solar ultraviolet radiation. Also, these compounds and their hydrolysis products are readily used by the microbial flora present in natural waters. Pyrolan and dimetilan, however, are expected to persist for long periods of time in natural waters these compounds are resistant to chemical hydrolysis under normal pH conditions of stream waters and are not readily used by the aquatic microorganisms. Still, pyrolan is partially removed by adsorption on mineral suspended solids of a high montmorillonite content. 

Phosphoryloxymethyl carbamates (114, X = NH) and carbonates (114, X = O) have also been evaluated as linkers to make phosphate derivatives of drugs containing amines and hindered alcohols, respectively. The carbonates were too unstable towards chemical hydrolysis, whereas the carbamates were more stable and should release the amine (for example, benzocaine) in vivo in the presence of phosphatase [126]. 

The first synthetic pyrogaHol plant using hydrolysis of chlorinated cyclohexanol (2,2,6,6-tetrachlorocyclohexanone) was built by BFC Chemicals, Inc. (Muskegon, Michigan) and has been producing pyrogaHol for the carbamate insecticide Beniocarb since 1982 (8,19). SocifitH Fransaise Hoechst offers pyrogaHol for sale in the United States (American Hoechst Corp.), and Japan is also a source of this chemical. 

Enzymatic Method. L-Amino acids can be produced by the enzymatic hydrolysis of chemically synthesized DL-amino acids or derivatives such as esters, hydantoins, carbamates, amides, and acylates (24). The enzyme which hydrolyzes the L-isomer specifically has been found in microbial sources. The resulting L-amino acid is isolated through routine chemical or physical processes. The D-isomer which remains unchanged is racemized chemically or enzymatically and the process is recycled. Conversely, enzymes which act specifically on D-isomers have been found. Thus various D-amino acids have been... 

FIGURE 5.46 Interaction of the serine hydroxyl residue in the catalytically active site of acetylcholinesterase enzyme with esters of organophosphates or carbamates. The interaction leads to binding of the chemical with the enzyme, inhibition of the enzyme, inhibition of acetylcholine hydrolysis, and thus accumulation of acetylcholine in the synapses. 

Oxime carbamates have high polarity and solubility in water and are relatively chemically and thermally unstable. They are relatively stable in weakly acidic to neutral media (pH 4-6) but unstable in strongly acidic and basic media. Rapid hydrolysis occurs in strongly basic aqueous solutions (pH > 9) to form the parent oxime/alcohol and methylamine, which is enhanced at elevated temperature. Additionally, oxime carbamates are, generally, stable in most organic solvents and readily soluble in acetone, methanol, acetonitrile, and ethyl acetate, with the exception of aliphatic hydrocarbons. Furthermore, most oxime carbamates contain an active -alkyl (methyl) moiety that can be easily oxidized to form the corresponding sulfoxide or sulfone metabolites. 

Oxime carbamates are generally stable in aqueous solutions at pH 4-6. Their chemical degradation (hydrolysis) in water depends strongly on pH. Strongly basic conditions... 

Although geneologically related to indoles, the dihydroindoles behave chemically rather like alkyl anilines. When diphenylamine reacts with chloro-propionyl chloride, amide 40 results this in turn readily cyclizes to oxindole 41. Sodium hydride followed by 2-chloroethyldimethylamine alkylates the 3-position (possibly through an intermediate aziridinium ion) partial demethylation is accomplished by refluxing with ethylchiorocarbonate, followed by hydrolysis of the intermediate carbamate to give indolinone 42, the antidepressant amedalin Repetition of this sequence on the chloropropyl homologue, followed by reduction of the appropriate indolinone produces dihydroindole 43, daledalin, which also has antidepressant activity. ... 

Enzymes can be used not only for the determination of substrates but also for the analysis of enzyme inhibitors. In this type of sensors the response of the detectable species will decrease in the presence of the analyte. The inhibitor may affect the vmax or KM values. Competitive inhibitors, which bind to the same active site than the substrate, will increase the KM value, reflected by a change on the slope of the Lineweaver-Burke plot but will not change vmax. Non-competitive inhibitors, i.e. those that bind to another site of the protein, do not affect KM but produce a decrease in vmax. For instance, the acetylcholinesterase enzyme is inhibited by carbamate and organophosphate pesticides and has been widely used for the development of optical fiber sensors for these compounds based on different chemical transduction schemes (hydrolysis of a colored substrate, pH changes). 

For N-methyl-p-toluyl carbamate, a chemical susceptible to neutral and base-promoted decomposition, the rates of hydrolysis on Na-montmorillonite and kaolinite were slower than in aqueous solution of the same bulk pH. A possible explanation is the lower pH at the clay surface (74). The following hydrolysis mechanism in aqueous solution was proposed ... 

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]. 

Fig. 8.19. Sequential activation of acetoxymethyl carbamate derivatives of secondary amines, as exemplified with a model amine. The sequence is initiated by chemical and enzymatic hydrolysis of the terminal ester group [209][210]. 

Chemical degradation has been investigated by Shlh and Dal Porto Q) and by Lande ( ) under EPA auspices as an alternative approach (to landfill disposal) for the removal of pesticide residues. Among candidate reactions for the safe detoxification of pesticides, only alkaline hydrolysis was recommended. Several organophosphates and carbamates were identified as amenable to a degradation procedure using strong base/aqueous alcohol. The... 

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