Phenyl chloroformate, from phosgene

Examples of such materials include Af,N -diphenylurea (R = H, R = Ph), lV,/V -diethyl-/V,N -diphenylurea (also known as diethyl centralite, centralite I, or carbamite R = Et, R = Ph), N,fV -dimethyl-fV,lV -diphenylurea (also known as centralite II R = Me, R = Ph), and N,, lV, Af -tetraphenylurea (R = R = Ph) [718a]. Stabilizers derived from urethanes are also employed in the explosives industry [718a]. These materials are prepared either from the corresponding carbamoyl chloride or chloroformate, both of which are derived from phosgene. Examples include methyl phenyl urethane EtO(CO)NMePh ethyl phenyl urethane EtO(CO)NEtPh and diphenyl urethane EtO(CO)NPh j. ... 

The methods described in equations 2-5 are useful in situations where the sulfonylisocyanate is not available. All of these require using a carbamate which can be prepared from the sulfonamide or heterocyclic amine with the appropriate chloroformate. In addition to the added step of chlorformate formation from phosgene and an alcohol, special care is required to prepare some of the carbamates. Although the phenyl carbamates of heterocyclic amines react, as desired, with a broad range of sulfonamides the reaction of phenyl carbamates of sulfonamides is restricted due to the failure of these interme tes to react with triazine amines. 

The product obtained from phenylthiosemicarbazide (92 R = H) and phosgene, described as 2-amino-4-phenyl-l,3,4-thiadiazolin-5-one (93 R = H), is in fact a mixture. Conditions have now been specified for the successful preparation of this compound (93 R = H) by this route. Oxidation of thiosemicarbazones. The oxidative cyclization of benzalthio-semicarbazones and of acetone thiocarbohydrazone is a well-known route to the 1,3,4-thiadiazole ring system. 4-Arylthiosemicarbazones of ketones (99) have now been shown to cyclize in this manner on being stirred in benzene in contact with suspended manganese dioxide, giving satisfactory yields of 5-imino-A -l,3,4-thiadiazolines (101). Ring-closure over alumina in chloroform slowly yields the isomeric l,2,4-triazoline-5-thiones (100). Bicyclo[3,3,l]non-2-en-9-one 4-phenylthiosemicarbazone... 

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