Phosgene allophanoyl chloride

The in situ generated disubstituted ureas (26) also react with phosgene to yield thermally unstable allophanoyl chlorides (27) and chloroformamides (28) (75). As shown in Figure 5, the allophanoyl chlorides eliminate hydrogen chloride to form the isocyanate. The chloroformamides, however, yield chloroformamidine-A/-carbonyl chloride (29), which decomposes to yield both carbodiimides (30) and isocyanide dichlorides (31). The carbodiimides simply contribute to yield loss. The isocyanide dichlorides, although present in small amounts, are a contributor to chlorine-containing impurities which detrimentally affect product performance. 

Cyclic carbodiimides also undergo a rapid reaction with phosgene in methylenechloride to form the expected adducts 55, which on hydrolysis give cyclic allophanoyl chlorides 56.22... 

In the case of N,N -dialkyl ureas, phosgene is attacked by both oxygen and nitrogen atoms to give a mixture of chloroformamidinium chlorides (A) (0-acylation of the ureas) and allophanoyl chlorides (B) (N-acylation) as shown in scheme 155 (Ref. 211). 

The preparation of aliphatic diisocyanates, using bisacylazides, has to be conducted with caution because an explosion occurred in the preparation of ethylene diisocyanate by using this method (13). Ethylene diisocyanate is readily obtained by dehydrochlorination of a heterocyclic allophanoyl chloride derivative obtained in the phosgenation of ethyleneurea (14). 

The aliphatic-aromatic isocyanate dimer 5 is obtained in the cyclization of the corresponding allophanoyl chloride in the presence of pyridine as the hydrogen chloride scavenger. Allophanoyl chlorides are readily obtained from aliphatic or aliphatic/aromatic ureas and phosgene. ... 

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