Urea 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. 

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]. 

Linuron Methoxydiuron Arresin Afalon. A residual urea herbicide for the control of weeds in field crops including potatoes and carrots. Crystals mp = 93-94° soluble in H2O, acetone, alcohol, benzene, toluene, xylene LDso (rat orl) = 1500 mg/kg. Agan Chemical Manufacturers Ashlade Formulations Ltd. Adas Interlates Ltd DuPont UK Farm Protection Ltd. Hoechst UK Ltd. ICI Chem. Polymers Ltd. MTM AgroChemicals Ltd. 

Since most of the commercially produced urea for fertilizer applications is prilled by the tower melt solidification process and urea is one of the most important nitrogen providing fertilizers, farmers and suppliers often wrongly name all spheroidal agrochemicals prills even if they were produced by true agglomeration processes, for instance on discs or in drums (see also Section 7.4.1). 

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... 

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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