1- Formyl-3-thiosemicarbazide

A. l-Formyl-3-thiosemicarbazide. Four hundred milliliters of 90% formic acid contained in a 2-1. round-bottomed flask is heated on a steam bath for 15 minutes, and then 182 g. (2 moles) of colorless thiosemicarbazide (Note 1) is added. The mixture is swirled until the thiosemicarbazide dissolves. The heating is continued for 30 minutes, during which time crystalline 1-formyl-3-thiosemicarbazide usually separates. Boiling water (600 ml.) is added, and the milky solution that results is filtered through a fluted filter paper. After standing for 1 hour, the filtrate is cooled in an ice bath for 2 hours, and the l-formyl-3-thiosemicarbazide that separates is collected by suction filtration and air-dried overnight. It weighs 170 192 g. (71-81%) and melts at 177-178° with decomposition. 

The thiosemicarbazide must be of good quality or the yield and quality of l-formyl-3-thiosemicarbazide will suffer. The thiosemicarbazide supplied by Olin Mathieson Chemical Corporation, obtained as a colorless free-flowing powder, can be used without purification. 

Triazole-3(5)-thiol has been prepared by heating thio-semicarbazide and formic acid, by heating l-formyl-3-thiosemi-carbazide, and by heating 1,3,5-triazine and thiosemicarbazide. The ring closure of l-formyl-3-thiosemicarbazide using aqueous base was suggested by L. F. Audrieth and F. Hersman. 

Thionyl fluoride, as by-product in sulfur tetrafluoride reactions, 41, 105 toxidty of, 41,105 Thiophene-2-OL, 43, 55 2(5H)-Thiophenone, 43, 55 Thiosemicarbazide, in synthesis of 1,2,4 triazole, 40, 99 reaction with formic acid to yield l-formyl-3-thiosemicarbazide, 40,99... 

On the other hand, refluxing 9 in formic acid for 5 h afforded the N-formyl derivative 11 in high yield. Acetylation of 9 by refluxing in acetic acid, afforded acetic acid N -(2-(7-hydroxy-2-oxo-2H-chromen-4-yl)-acetyl)-hydrazide 12 in good yield. Compound 13 was also obtained by refluxing 9 with 3-(2-bromoacetyl)-4-hydroxy-2H-chromen-2-one in ethanol. Reaction of compound 9 with phenyl isothiocyanate in ethanol at room temperature gave 4-phenyl-1 - (7-hydroxy-2-oxo-2 H-chromen-4-acetyl- )thiosemicarbazide 14. 

Preparation. Thiosemicarbazide is condensed with formic acid to produce l-formyl-3-thiosemicarbazide (1) this is cyclized with alkali to produce 1,2,4-... 

The 4-formyl and 4-acyl-3-pyrazolin-5-ones react like normal carbonyl compounds with active methylene groups,898-1190 amines,107,1190 hydroxylamine,196 hydrazines196-201 and semicarba-zide,201 although some fail to react with thiosemicarbazide.799 They... 

Condensation reactions can be grouped into two categories. The first category involves pyrazol-3-ones with formyl, acyl, nitroso, a,jS-unsaturated oxo, 3-oxo-2-azobutyric acid ethyl ester or acetonitrile substituents at position 4 or formyl substituents at position 5 and their reaction with carbanions, heterocyclic methylcarbenium salts, primary and secondary amines, diamines, heterocyclic perchlorates, hydroxylamine, hydrazines, urea or thiosemicarbazide. The second category involves pyrazol-3-ones with amino, hydrazino, heteroaromatic amino, acetyl or acetonitiilo groups at position 4 and their reaction with aryl or heteroaromatic aldehydes or cyclic ketones. 

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