From Haloformamidines or Carbonimidoyl Dihalides

The phosgenation of N,N -dialkyl- and N-alkyl-N -arylureas at 110-120 °C in chlorobenzene, followed by reaction with amines affords N,N, N -trisubstituted guanidines via the intermediate chloroformamidines.  

Heating of chloroformamidines 118 causes isomerization to give carbodiimides 119.  

N-Chloroamidines, upon reaction with silver oxide, also give carbodiimides.  

N -dicyclohexylcarbodiimide is also obtained in good yield in the bromination of N,N -dicyclohexylfomiamidine with N-bromosuccinimide, in the presence of pyridine or with bromine in the presence of NaOH. The bromoformamidine is an intermediate in this conversion. 

Heating of carbonimidoyl dihalides with amines or amine hydochlorides affords carbodi-imides. For example, heating of trifluoromethylcarbonimidoyl difluoride 120 with amines produces the corresponding trifluoromethyl substituted carbodiimides 121.  

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