Halogenation of Ureas

The reaction of substituted ureas with carbonyl chloride provides another useful method of synthesis of chloroformamidines However, oxygen is not as nucleophilic as sulfur and consequently attack on nitrogen often occurs. In the case of 1,3-dialkylureas good yields of 

Similarly, N,N-dimethylurea reacts with carbonyl chloride via N-attack ( ). 

N Dicyclohexylchloroformamidine hydrochloride ( ). To a solution of 60.4 g (0.27 mole) of 1,3-dicyclohexylurea in 400 ml of ethylene dichloride a solution of 27.4 g (0.28 mole) of phosgene in 200 ml of ethylene dichloride is added dropwise and with stirring and ice-cooling. After stirring for one hour at room temperature and purgation with nitrogen the solvent is removed under reduced pressure. Trituration of the residue with diethyl ether precipitates 58.6 g (77.8 %) of N,N -dicyclohexylchloroformamidine hydrochloride, m.p. 143-144°C. 

However, the reaction of tri- and tetrasubstituted ureas with carbonyl chloride affords high yields of the chloroformamidine hydrochlorides ( ). 

Instead of carbonyl chloride, phosphorus pentachloride can be used to prepare chloroformamidines (8 2o,s5j hydrochlorides (6o.63.66j 

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