Urea material selection

Sulfur-coated urea (SCU) is a controlled-release material developed by TVA during the 1960s and 1970s.53 Sulfur was selected as the coating material on the basis of economy and efficiency after many coating materials were tried. Urea was selected as the material to be coated because of its high nitrogen content, low cost, and commercial availability. 

Many large chemical companies produce amino resins and the raw materials needed, ie, formaldehyde, urea, and melamine. Some companies may buy raw materials to produce amino resins for use in their own products, such as plywood, chipboard, paper, textiles, or paints, and may also find it profitable to market these resins to smaller companies. The technology is highly developed and sales must be supported by adequate technical service to select the correct resin and see that it is appHed under the best conditions. 

Scotts technology (17) uses fluid-bed (Wurster column) technology to apply polymeric coatings to a number of fertilizer substrates including urea, potassium nitrate, potassium sulfate, and monoammonium phosphate (MAP). The coating material is appHed as a water-borne latex onto the fluidized substrate. As the substrate is fluidized with warm air (40—50°C), water is driven off and the latex coalesces into a continuous film around the fertilizer particle. The particular latex compositions used have selected glass-transition and blocking temperatures, which enable quick removal of the water before the soluble fertilizer core dissolves. This obviates the need to use precoats prior to the latex appHcation. 

Oxidative carbonylation generates a number of important compounds and materials such as ureas, carbamates, 2-oxazolidinones, and aromatic polycarbonates. The [CuX(IPr)] complexes 38-X (X = Cl, Br, I) were tested as catalysts for the oxidative carbonylation of amino alcohols by Xia and co-workers [43]. Complex 38-1 is the first catalyst to selectively prepare ureas, carbamates, and 2-oxazolidinones without any additives. The important findings were the identity of the counterion and that the presence of the NHC ligand influenced the conversions. 2-Oxazohdinones were formed from primary amino alcohols in 86-96% yield. Complex 38-1 also catalysed the oxidative carbonylation of primary amines to ureas and carbamates. n-Propylamine, n-butylamine, and t-butylamine were transformed into the... 

During this investigation, however, conditions were found under which urea, or carbon dioxide and ammonia, could be made to aminate either ethylene glycol or ethanolamine to produce satisfactory yields of ethyleneurea. This work represents an extension of urea chemistry and is reported here in detail. Patents have been granted which pertain to certain aspects of the problem.3 Of the reactants cited above, urea and ethylene glycol were selected for most thorough study because these raw materials were readily available at low cost and could be made to react at atmospheric pressure. 

Other considerations can influence the selection of the highest dose level. Rats and mice are relatively insensitive to sulfo-ureas used for the treatment of diabetes. Rats counteract the hypoglycaemic effect of these drags by secretion of glucagon and 25-hydroxy-cortisol and no hypoglycaemia occurs at the maximum dose level (> 5 000 mg/kg). In one case of a novel antidiabetic sulfonylurea it was demonstrated that absorption becomes saturated at relatively low oral dose (ca. 1000 mg/kg). This observation convinced the FDA that testing of the maximum tolerated dose (probably not determinable) is not necessary. By that the demand of test material could be reduced at least by a factor of 5. 

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