Ureas Aminos

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Chiral amines and diamines are readily available substrates for the synthesis of ligands for transition metal-catalysed reactions since they can easily be transformed into chiral ureas and thioureas. Therefore, several groups have prepared chiral symmetrical ureas and thioureas, dissymmetrical ureas and thioureas, amino-urea and thiourea derivatives. Finally polyureas and non-soluble polythioureas were also prepared and tested as ligands for asymmetric catalysis. 

Moreau and co-workers have also prepared (ll ,2K)-l,2-diaminocyclo-hexane amino-urea and thiourea derivatives [43]. Diphenylethylenediamine-substituted monothioureas are more stable than the cyclohexyldiamine counterpart, but they can also rearrange to guanidine derivatives, especially at high temperature or in the presence of metal [43]. Under the same conditions, thioureas also rearrange to guanidines in the presence of amines. Selective formation of substituted guanidines from thiourea derivatives of diaminocy-clohexane or diphenylethylenediamine were also reported in a recent paper from Ishikawa [44]. 

SYNS AMIDOUREA HYDROCHLORIDE AMINO-UREA HYDROCHLORIDE O CARBAMYLHYDRAZINE HYDROCHLORIDE CH HYDRAZINECARBOX-A.MIDE MONOHYDROCHLORIDE... 

Semi-carbazid is an important reagent forming derivatives with aldehydes and ketones. Its name indicates that it is a hydrazine derivative of carbonic acid or of carbamic acid. It is also amino urea. 

Mao, L.-J., and Chen, R.-Y., Highly selective Arbuzov reaction of a-chlorocarbonyl compounds with PfOEtfj and substituted amino urea. Phosphorus, Sulfur Silicon Relat. Elem., Ill, 167, 1996. 

There are two basic types of aminos urea formaldehydes (UF) and melamine formaldehydes (MF). These thermosets are hard, rigid plastics with good abrasion resistance. Their mechanical properties are sufficiently good for continuous use at moderate temperatures, up to 100°C (212°F). UF is relatively inexpensive, but its propensity for moisture absorption can result in poor dimensional stability. It is generally used for bottle caps, electrical switches, plugs, utensil handles, and trays. MF has lower water absorption and improved temperature and chemical resistance. It is used for tableware, laminated worktops, and electrical fittings. See the melamine and urea sections that follow in this chapter for more details. 

Bied, C., J. J. E. Moreau, and M. Chi Man Wong, 2001. Chiral amino-urea derivatives of (lR,2R)-l,2-diaminocyclohexaneas hgands in the ruthenium catalyzed asymmetric reduction of aromatic ketones by hydride transfer. Tetrahedron Asymmetry 12 329-36. 

Bis[[[3-hydroxy-5-hydroxymethyl-2-methyl-4-pyridyl]methylene]amino]urea, see B-00375... 

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