Herbicides carbamates

N-methylcarbamate and N,N -dimethylcarbamates were determined in water samples by hydrolyses with sodium bicarbonate and ttie resulting amines reacted with 4-chloro-7-nitrobenzo-2,l,3-oxadiazole in isobutyl methyl ketone solution to produce fluorescent derivatives [21]. These derivatives were separated to thin layer chromatography on silica gel G or alumina with tetrahydrofuran-chloroform (1 49) as solvent. The fluorescence is then measured in situ (excitation at436nm, emission at 528 and 537nm for the derivatives of methylamine and dimettiylamine, respectively). The method was applied to non saline water samples containing parts per 10 levels of carbamate. The disadvantage of ttie mettiod is its inabihty to differentiate between carbamates of any one class. 

Ceirbofuran and its degradation products carbofuranphenol, 3-keto-carbofuran, 3-hydroxycarbofuranphenol, N-hydroxymethylcarbofuran and 3-hydroxycarbofuran, have been determined in water samples by thin layer chromatography of ether extracts of ttie sample [23]. 

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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. 

Brilliant green neutral esters of phosphoric acid [125], carbamate herbicides [34]... 

Chlorinated anilines are produced by the hydrolysis of a range of acetanilide, urea, and carbamate herbicides, and are therefore widely distributed in agricultural soils. Mechanisms for their loss... 

Carbamate herbicides, 13 320 Carbamates, 13 108 amine, 16 359 Carbamic acid nitrile, 3 158 Carbamide derivatives, as cellulose solvents, 11 272 Carbamodiimide, 8 158 Carbamoylated gelatin, 12 444 Carbamoyl-methylphosphoryl family, extractants of, 10 789 Carbamyl chlorides, 12 180 Carbanion coordination, 13 656—657 Carbanions, 21 101... 

Kaufman, D.D. Degradation of carbamate herbicides in soil, J. Agric. Food Chem., 15 (4) 582-591, 1967. 

Danielson LL, Gentner WA. 1970. Effect of solvent composition on inactivation of several phenyl and thio carbamate herbicides in soil. Proceedings of the Northeastern Weed Control Conference 24 308-312. 

Cohen and Wheals [185] used a gas chromatograph equipped with an electron capture detector to determine 10 substituted urea and carbamate herbicides in river water, soil and plant materials in amounts down to 0.001-0.05ppm. The methods are applicable to those urea and carbamate herbicides that can be hydrolysed to yield an aromatic amine. A solution of the herbicide is first spotted on to a silica gel G plate together with herbicide standards (5-10pg) and developed with chloroform or hexane-acetone (5 1). The plate containing the separated herbicide or the free amines is sprayed with 1-fluoro-1,4-dinitrobenzene (4% in acetone) and heated at 190°C for 40min to produce the 2,4-dinitrophenyl derivative of the herbicide amine moiety. Acetone extracts of the areas of interest are subjected to gas chromatography on a column of 1% of XE-60 and 0.1% of Epikote 1001 on Chromosorb C (AE-DCMS) (60-80 mesh) at 215°C. 

Several of the older and more common herbicides have been shown to interfere with one or more steps of photosynthesis. A number of these are powerful inhibitors at or near photosystem II (PS II) ( 1). Beginning in 1981, J. N. Phillips and J. L. Huppatz and their group at CSIRO (Australia) have shown that a series of cyanoacrylate (vinylogous carbamate) herbicides are potent inhibitors of PS II (2-6). 

Isocyanates can be reacted with poly(vinyl alcohol) In homogeneous solutions In dlmethylsulf-oxlde to produce modified polymers that contain between 10 and 100 S of the hydroxyl groups replaced by the appropriate carbamate group. In this study, modified polymers were prepared using phenyl, 3-chlorophenyl and 4-chlorophenyl Isocyanates and these polymers bear a strong structural similarity to known carbamate herbicides. 

Figure 1. Structural relationships between the modified polymers and some carbamate herbicides.

Dichloroacetic acid has no herbicidal activity, but the N,N-diallylamide of dichloroacetic acid is an important commercial product as the antidote of thiol carbamate herbicides (see Swtion 6.10). 

An interesting side-effect is its increasing selectivity of thiol carbamate herbicides in maize. 

The carbamate herbicides discussed in the foregoing diifer considerably from one another, with respect to both the skeleton of the molecule and the substituent groups. 

Almost all of the carbamate herbicides inhibit photosynthesis, as has been shown by the investigations of Moreland and Hill (1959). Asulam and terbutol do not inhibit photosynthetic electron transport in vitro, while the other carbamates do only in high concentrations not occurring in vivo. The conclusion of Corbett (1974), that the inhibition of photosynthesis is only a side-effect of these compounds, therefore seems justified. 

The general and primary action of carbamate herbicides is their inhibiting effect on mitosis, as has been shown by several workers in hundreds of experiments. Of the biochemical reactions of plant cells, carbamate herbicides inhibit oxidative phosphorylation and the synthesis of ATP, RNA and protein. As a result of these processes abnormal cells with anomalous nucleotides are formed in sensitive plants, which finally leads to the destruction of the plant. 

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