Formamidine sulfides

Amidinothioureas N-Thioureidoamidines 25 N-Thioureidoformamidines 15 Formamidine sulfides Hydrazonyl sulfides Thiocarbohydrazones... 

Formamidines s. Chloro-formamidine-N-carbonyl chlorides, 3-Isoxazolyl-formamidines, N-Sulfonyl formamidines —, trisubst. 19, 494 Formamidine sulfides... 

On treatment of 5-amino- and 5-alkylamino-thiatriazoles with concentrated hydrochloric acid, formamidine disulfide dihydrochlorides (54) are formed, along with 50% hydrolysis leading to hydrazoic acid, carbon dioxide and hydrogen sulfide. It is postulated that hydrazoic acid reduces the positive ion presumably formed by ring cleavage of the thiatriazole in the presence of the strong acid (equation 26) (64AHC(3)263). 

The use of carbonyl chloride in the conversion of thioureas to chloro-formamidines offers the advantage of gaseous by-product. Phosphorus pentachloride can be used equally well, but complete separation from the liquid trichlorophosphorus sulfide is sometimes more difficult to accomplish. In one instance, chlorine has been used to convert a pseudothiourea derivative to the corresponding chloroformamidine hydrochloride. Thus, addition of chlorine to a solution of the pseudothiourea derivative XIII in carbon tetrachloride afforded a quantitative yield of trimethylchloro-formamidine hydrochloride (XIV) C ). 

The Sandmeyer diphenylurea isatin synthesis uses symmetrical diphenylthiourea 1 as a substrate for generation of cyanoformamidine 2, via treatment of 1 with potassium cyanide in the presence of lead carbonate. Reaction of formamidine 2 with ammonium sulfide leads to thioamide 3, which can undergo acid-induced cyclization and hydrolysis to produce isatin (4). Examples of the diphenylurea isatin synthesis in the literature are scarce. This is due to Sandmeyer developing the more practical isonitrosoacetanilide isatin synthesis 16 years later. 

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