Carbamic acid chlorides Urethans

The acid chloride (chloioformamide [463-72-9 ], "uiea chloride"), NTT. COC1, and its salts have been prepared. Ammonium carbamate [1111-78-0], can be obtained as a white crystalline solid by reaction of dry carbon dioxide and ammonia. It is an impurity in commercial ammonium carbonate [506-87-6] (see Ammonium compounds). Esters of carbamic acid are quite stable. The best known is the ethyl ester usually called urethane [51 -79-6],... 

Carbamic Acids. The esters of carbamic add or substituted carbamic acids (urethans) do not react readily with hydrazine, but the corresponding carbamyl chlorides do. The semicarbazide or substituted semi-carbazides that result yield carbamyl azides with nitrous acid. Most carbamyl azides are prepared more conveniently from the carbamyl chlorides and sodium azide. Monosubstituted carbamyl azides can also be synthesized from isocyanates and hydrazoic acid. -... 

To prevent side reactions, the amino group of alanine must be protected to make it nonnucleophilic. In Section 24-7B, we saw that an amino acid reacts with benzyl chlo-roformate (also called benzyloxycarbonyl chloride) to form a urethane, or carbamate ester, that is easily removed at the end of the synthesis. This protecting group has been used for many years, and it has acquired several names. It is called the benzyloxycarbonyl group, the carbobenzoxy group (Cbz), or simply the Z group (abbreviated Z). 

This urethane forms white crystals, melting at 61° C., which on heating to 200° to 250° C. decompose forming phosgene and diphenyl carbamic chloride. Cold water decomposes it into diphenylamine, hydrochloric acid and carbon dioxide. 

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