Thiosemicarbazides, reaction with nitrous acid

Thiophene-carbo lic acids, 239, 240 Thiopyrimidines, dialkyl-, 24 Thiosemicarbazides, reaction with nitrous acid, 263... 

By reaction of thiosemicarbazide or its 4-alkyl derivatives with nitrous acid Freund and co-workers in 1896 prepared compounds which were formulated as amino or alkylamino derivatives of the ring system 1,2,3,4-thiatriazole (1). Oliveri-Mandala, however, argued that these compounds are actually thioazides (2), and this view seems to have been generally accepted (e.g. in Beilstein s Handbuch) until... 

It appears quite probable that this reaction occurs by the same mechanism as the reaction of nitrous acid with thiosemicarbazides and of sodium azide with isothiocyanates. The primary reaction product is a thiocarbamoyl azide (CCXIII) to which, however, the cyclic structure of a 5-amino-l,2,3,4-thiatriazole (CCXIV) is attributed. In alkaline medium these compounds rearrange to the corresponding 1 -substituted-Zla-tetrazoline-5-thiones (CCXII) 236, 237). A survey of these compounds, prepared from the dithiocarbamic acid esters, is given in Table 33. 

Another interesting reaction (b + g) was studied by Freund and Schander [27]. Thiosemicarbazide was reacted with nitrous acid to yield 5-aminothiatri-azole which was then saponified to yield sodium azide ... 

Thiatriazoles.—5-Arylamino-l,2,3,4-thiatriazoles (270 R = NHAr) have been prepared by allowing the corresponding thiosemicarbazides RNHC(S)NHNH2 to react with nitrous acid, " and the reaction between PhSC(S)Cl and potassium thiotosylate gives PhSC(S)S—STos, which reacts with sodium azide to give (270 R = PhS). ... 

An alternative method for the preparation of 5-aminothiatriazoles by way of an aza transfer reaction has been reported (780PP59). Benzenediazonium tetrafluoroborate or diazotized sulfanilic acid react rapidly at room temperature with thiosemicarbazides to give substituted aminothiatriazoles (equation 42). The procedure may be of importance with sensitive substrates since nitrous acid is avoided and the reaction proceeds under almost neutral conditions. 

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