Carbamate agrochemicals

The oxidative carbonylation of amines to give ureas is at present one of the most attractive ways for synthesizing this very important class of carbonyl compounds via a phosgene-free approach. Ureas find extensive application as agrochemicals, dyes, antioxidants, resin precursors, synthetic intermediates (also for the production of carbamates and isocyanates), and HIV-inhibitors. Many transition metals (incuding Au [244], Co [248,253-255], Cu [242], Mn [249,256-258], Ni [259], Rh [246,247,260-262], Ru [224,260,263] and especially Pd [219,225,226,264-276], and, more recently, W [277-283]) as well as main-group elements (such as sulfur [284-286] and selenium [287— 292]) have been reported to promote the oxidative carbonylation of amines, usually under catalytic conditions. In some cases, carbamates and/or oxamides are formed as byproducts, thus lowering the selectivity of the process. 

Huang, C. H., Hydrolysis of Amide, Carbamate, Hydrazide, and Sulfonylurea Agrochemicals, Ph.D. thesis, Johns Hopkins University, Baltimore, MD, 1997. 

This dimer reacts as two molecules of free 5- alkyli-soxazolyl-3-isocyanate with secondary amines or with alcohols to give the corresponding ureas or carbamates useful as agrochemicals or fine chemicals intermediates. For example, 3-amino-5-tert-butyl isoxazole is a key intermediate for 3- 5-tert-butylisoxazolyl)-1,1-dimethyl urea (common name Isouron) which is useful as a herbicide for sugar cane and other crops (Ref. 180) [Scheme 127]. 

Typically, insecticides represent about 30% of the market in agrochemicals. Activity depends on the ability to penetrate insects rapidly and reach sites of action in membranes of nerve cells. Insecticides are more soluble in fats than in water. The aryl amine insecticides include carbamic esters, such as pirimicarb (104), a diazine derivative (Scheme 23). It is of short-to-moderate persistence, but more selective than organophosphorus compounds. Acylation of A-methyl-l-naphthylamine, or reacting the chloroacetamido derivative with potassium fluoride in glycerol, affords the insecticide and acaricide known as nissol (105). 

The term pesticide includes chemicals used to eradicate rodents (rodenticides), fungi (fungicides), weeds (herbicides) and insects (insecticides). These agrochemicals may be used directly on the medicinal plant crop itself, they may be used on crops growing adjacent to the herbs or they may occur as general environmental pollutants in soil, air or water. The presence of insecticide residues is of particular concern because those of the organochlorine type (DDT etc.) have been shown to cause cancers in animals and those of the organophosphate and carbamate types are potent cholinesterase inhibitors. 

In the late 1960s, specific requirements of these fine chemicals became the impetus for industry growth. Examples of products in this time period were intermediates for pharmaceuticals and agrochemicals such as side chain modifications of penicillins and carbamates for fungicides. Very specific fine chemicals for specific products were developed. 

Carbamic acid esters (methanes) and their derivatives are important precursors to agrochemicals (herbicides, fungicides, and pesticides) as well as to pharmaceuticals. Also, they can be transformed to isocyanates, which are major building blocks for polyurethanes, widely used in construction, transportation, and several other fields. Presently, the main technical process for the manufacture of isocyanates is phosgena-tion of the corresponding amines. Since the global consumption of polyurethane raw... 

Insecticides accounted for 74% of the total agrochemical market value. Within this sector, organophosphates have 41% of the market by value, pyretliroids 20%, organochlorines 6% and carbamates 5%. Tlie remainder of the agrochemical market was represented by herbicides 14%, fungicides 9%, acaricides 2% and fumigants 1 %. 

The environmental significance of organic sulfoxides results primarily from their importance as agrochemicals specifically, the organophosphorus and carbamate insecticides containing sulfoxide moieties. Studies suggest that reduction of these chemicals can be the primary pathway for their transformation in anoxic sediments. For example, reduction of phorate sulfoxide to phorate in anoxic pond sediments occurred with half-lives ranging from 2 to 41 days (Equation 3.38) (Tratnyek and Wolfe, 1988). 

The foregoing examples of phosgene-free methods for synthesis of carbamates, isocyanates, ureas, polycarbonates, dyes, polymers, and other pharmaceutical or agrochemical intermediates and products all illustrate ways that green chemistry reduces the environmental impact... 

The formation of carbamates RR N-COOR" has been discussed in Chap. 4. There are several applications in the pharmaceutical, agrochemical, materials, and polymer industries. Dicarbamates are of particular interest as they are used as monomers for polymers. Among dicarbamates, those derived from primary amines are of great industrial interest as they can easily lose alcohol and produce isocyanates (6.22). 

Nanita et al. (2009) developed a FI approach for high-throughput pesticide residue quantitation without chromatographic separation prior to MS/MS. The method allowed the fast quantitation of agrochemicals (sulfonylureas and carbamates) in food and water samples. Samples were injected directly into a triple quadrupole instrument and data were obtained at the rate of 15 s/injection, allowing sample injection every 65 s, representing a significant improvement from the 15 - 30 min needed in typical HPLC-MS/MS methods, with accuracy limit of 0.01 ng mL in food samples and 0.1 ng mL of water samples with LODs of 0.003 mg mL" for food and 0.03 ng mL" for water samples. 

Carbamates are not common natural biological constituents, but carbamates of various types find use as agrochemicals. Biological systems do, however, widely use amide and ester materials. Both amide and ester functions are found in the carbamate molecule. 

The oxygen atoms of the carbamate can be replaced by sulfur atoms to give important agrochemicals. 

This is a broad grouping of many different types of agrochemicals (see Table 29.13). The classes of agrochemicals previously discussed often include heterocyclic types. There are heterocyclic acid types such as picloram, heterocyclic phosphates such as diazinon, heterocyclic carbamates such as benomyl, and heterocyclic ureas such as tebuthiuron. 

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