Diarylureas, formation

The diarylurea is very sparingly water-soluble and is therefore easily separated from the monoarylurea which is readily soluble. Diarylurea formation is less extensive when ring-substituted anilines are used. 

It is an excellent reagent for the preparation of )V,)V -diarylureas. Reaction of a carboxylic acid, primary amine, and (15) in acetonitrile leads to the disubstituted urea (16) (eq 10). There is an additional competing reaction to the formation of the diarylurea formation of phenyl Al-phenylphosphorodiamidates, involving nucleophilic attack of the carboxylate ion and the aLkylamine on the phosphorus atom of phenyl -phenylphosphoramidoazidate. This work has been fully reviewed. ... 

No such delay, however, is observed in formation of diarylurea. While no direct measurement is yet available, it is taken that "gel profile" measures association of the polyureas into domains. In "HR" foams this domain formation is delayed, permitting larger, more completely aligned polyurea domains and accounting for the principal property characteristics which distinguish high resiliency foam 3). 

Compounds of type (P) have also initially received a lot of attention, partly because they have been among the first to be structurally characterised [237] and because they can be obtained in several different ways [231], including carbonylation of derivatives of type (N) [234]. This kind of complex (R = Ar) affords diarylurea when heated to 120-130 °C in diglyme [238] or when treated with LiAUTi [239]. We have previously discussed a similar reaction of a rhodium complex (paragraph 6.5.3.). The formation of diarylureas via... 

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