Phenylcarbamate herbicide

Phenylcarbamates. Phenylcarbamate herbicides represent one of two subgroups of carbamate herbicides, the phenylcarbamates and the thiocarbamates (299). Both groups are prone to volatilization losses the thiocarbamates are particularly susceptible and should be sod-incorporated immediately after apphcation (2). The carbamate herbicides are used, in general, for the selective pre-emergence control of grass and broadleaved weeds (299). Exceptions would include barban, desmedipham, and phenmedipham which are appHed post-emergence. 

Phenylcarbamate herbicides, 13 320 N-Phenylcarbamate herbicides, 13 303 Phenyl chloroformate... 

Interference by certain phenylurea and tf-phenylcarbamate herbicides with the photochemical reactions of isolated chloroplasts was first reported in 1956 (2). Over the next few years, inhibition by the s-triazines, uracils, benzimidazoles, and ben-zonitriles was reported 3, 6). ... 

Leroux and Gredt (46) described the enhanced sensitivity of benzimidazole-resistant biotypes of Penicillium expansum and Botrytis cinerea to several N-phenylcarbamate herbicides. Following this lead, methyl 3,5-dichlorophenylcarbamate and isopropyl... 

Chlorinated anilines are common metabolites of the microbial degradation of various phenylurea, acylanilide and phenylcarbamates herbicides (Figure 13). Basicity and oxidabiUty are the features of tiiese compoxmds. They can react with oxygen and ozone present in air, with soil components [235-237], with lignin of plants [238], and with the microbial enzymatic systems. 

Both 5.8 X 4.6 mm Cig and 10 x 2 mm PRP-1 precolumns were used to extract six phenylcarbamate herbicides in surface and drinking waters. The elution solvent, a water-acetonitrile-methanol solution, was the mobile phase used in gradient mode for the subsequent LC fractionation [73]. A multiresidue analysis of 16 herbicides and fungicides was performed by injecting only 25 jjlL of water from different somces in online SPE-LC-MS apparatus [74]. Using a 1 x 10 mm Cis extraction colimm and a solution of acetonitrile-water acidified as elution system, recoveries ranged between 91% and 113% with limits of detection (LODs) between 41 and 957 ng/L. A volume of 1-3 mL was extracted... 

Hidalgo, C. et al.. Automated determination of phenylcarbamate herbicides in environmental waters by online trace enrichment and reversed-phase liquid chromatography-diode array detection, /. Chromatogr. A, 823,121, 1998. 

Potential Uses of These Polymers. We have studied the phenyl isocyanate modification of poly(vinyl alcohol) as a model system. Many uses exist for carbamates as medicines, pesticides and herbicides (67,68). For example, ethyl carbamate has been used to treat leukemia and multiple myeloma. Ethyl carbamate has also been used as an antidote for central nervous system poisoning by strychnine. The tranquilizer Meprobamate is a carbamate derivitive. Numerous pesticides and herbicides, such as Sevin and Propham, are also carbamate derivatives. Propham is isopropyl N-phenylcarbamate which bears a strong resemblence to the polymers of Equation 21, and this compound is used as a preemergence herbicide. Numerous other close analogs could be cited also. We might note also that the N-phenyl carbamoyl unit bears... 

Carbamates and ureas constitute important groups of pesticides that are used as herbicides (phenylureas, sulfonylureas, phenylcarbamates, and alkylthiocarbamates), insecticides (ben-zoylureas, methylcarbamates, and oximemethylcarbamates), or fungicides (dithiocarbamates, alkylenebisdithiocarbamates, and benzimidazolecarbamates) in different crops to control various weeds, pests, and diseases. 

Carbamates are substituted esters of carbamic acid (NH2COOH) with aliphatic or aromatic substituents on the oxygen and nitrogen atoms. Carbamate insecticides have an aryl or oxime N-methylcarbamate structure, and their mode of action is based on the inhibition of the enzyme acethylcholine esterase (1). However, this inhibition is reversible, and recovery from sublethal doses occurs rapidly. Some carbamate fungicides have a dithio, bisdithio, or benzimidazole carbamate basic structure, and dithiocarbamate fungicides inhibit the enzyme aldehyde deshydro-genase (2). The herbicides have an /V-alkylthiocarbamate or A-phenylcarbamate structure and interfere with photosynthetic activity or affect meristematic activity or lipid metabolism (3). Representative structures of carbamate pesticides are shown in Fig. 1. 

The use of DNS-C1 for the fluorimetric analysis of N-phenylcarbamate and urea herbicides has been examined [175]. The herbicides are hydrolyzed in 2Npotassium hydroxide in... 

Phenylcarbamate, phenylurea and many amide herbicides which yield anilines on hydrolysis can be detected after TLC by spraying with fluorescamine [100]. The limits of detection of a number of anilines separated by TLC and detected with fluorescamine are given in Table 4.16. A number of pesticides which yield anilines on hydrolysis or degradation is listed in Table 4.28. The analysis of anilines by this technique is described in Section 4.2.1.2.3. 

Herbicides that act as inhibitory uncouplers are dinitro-phenols, N-phenylcarbamates, acylanilides, halogenated benzoni-triles, substituted imidazoles, substituted benzimidazoles, bromofenoxim, substituted 2,6-dinitroanilines, pyridinols, and substituted 1,2,4-thiadiazoles (2). 

These herbicides contain nitrogen and respond to both FID and AFID. However, the analysis of these compounds is complicated by their thermal instability. For example, the total ion current trace obtained from the GC-MS ofamethanolic solution of monolinuron shows four peaks (Fig. 9). The formation of these peaks is illustrated in Fig. 10. This thermal decomposition appears to be general for the substituted ureas and reaction of substituted phenyl isocyanates with higher alcohols also occurs. As certain substituted alkyl phenylcarbamates are used as pesticides in their own right, inert solvents such as ethyl acetate or hexane should always be used for injection. The mass spectra of the thermal... 

Aniline is the parent compound of the aromatic amines, which are used in the synthesis of agrochemicals, dyes, and pharmaceuticals. There is a concern that aromatic amines may be released into the environment during production processes or incomplete treatment of industrial waste streams. Additiondly, aromatic amines can enter the environment from the reduction of azo dyes, polynitroaromatic munitions (e.g. TNT), and dinitro herbicides, and from hydrolytic degradation of several classes of pesticides, including the phenylurea, phenylcarbamate, and acylanilide herbicides. 

Adsorption mechanisms for retention of nonionic polar organic molecules, such as phenylcarbamates and substituted ureas used as herbicides, are illustrated in Figure 13. The great importance of hydrogen bonding in retention is suggested. Other adsorption mechanisms include van der Waals... 

Leroux and Gredt reported that benzimidazole-resistant strains of Botrytis cinerea and Penicillium expansum exhibited negatively correlated cross resistance to herbicidal N-phenylcarbamates such as barban, chlorpropham, and chlorbufam (10, 11, 12). Based on their observation, Sumitomo scientists evaluated many examples of N-phenylcarbamates to search for compounds with potent fungitoxicity and no phytotoxicity. This effort was eventually successful, leading to new fungicides such as MDPC ( , 21 ) and diethofencarb (14, 23, 24) (Figure 2). 

Templeman and Sexton (1945,1946) found that N-phenylcarbamates are toxic to monocotyledons but not dicotyledons. Of this group the first herbicide used in agriculture was isopropyl N-phenylcarbamate (IPC, propham, 3). 

George et al. (19S4) studied the effect of the alcohol component (R) of N-phenylcarbamic acid esters on herbicidal activity. 

Proximpham is a selective soil herbicide, but it is absorbed also through the leaves. It is used in beet, onion, vegetables and ornamental plant cultures for the control of Compositae, Labiatae and Cruciferae weeds, which are tolerant to the other phenylcarbamates. 

Hermann and Fischer (1967) described the selective herbicidal activity of a new group of compounds, the substituted phenylcarbamic acid ureidophenylesters. The new group of compounds has the following general formula ... 

Substituted aromatic amines have been widely used in the chemical industry as intermediates in the production of dyes, pesticides, pharmaceuticals, paints, etc. They may be released into the environment directly as a result of industrial discharge form factories or indirectly as a result of degradation of phenylcarbamates, phenylurea and anilide herbicides, and azodyes. Chromatographic separation and quantification of primary amines is hampered by their polarity that can cause tailing and irreversible adsorption. Aromatic primary amines were derivatized to 7/-allyl-7/ -arylthioureaby... 

Phenylcarbamates and Carbanilates. The phenylcarbamate pesticides are much more water soluble than the substituted anilines (Table VIII), but despite the higher solubilities they are also immobile in soil systems. All are herbicides except for carbaryl which is an insecticide. Chlorpropham and terbutol resisted leaching, and propham leached only slightly 137, 143, 144, 343, 344, 345, 346), In herbicide mobility studies in soils, Harris (151) ranked chlorpropham with the substituted anilines as having low movement. 

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