4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole

{{Chembox

|ImageFile = Thiourea2D.svg

|PIN = 4-Amino-5-hydrazinyl-2,4-dihydro-3H-1,2,4-triazole-3-thione

|OtherNames = Purpald; AHMT; 1,2,4-Triazolidin-3-one, 4-amino-5-thioxo-, hydrazone (9CI); 4H-1,2,4-Triazole-3-thiol, 4-amino-5-hydrazino- (6CI,7CI)

|Section1={{Chembox Identifiers

|CASNo = 1750-12-5

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = L49PBF7WZF

|PubChem = 2723946

|ChemSpiderID = 2006123

|SMILES = c1(=S)[nH]nc(n1N)NN

|StdInChI = 1S/C2H6N6S/c3-5-1-6-7-2(9)8(1)4/h3-4H2,(H,5,6)(H,7,9)

|StdInChIKey = RDIMQHBOTMWMJA-UHFFFAOYSA-N

}}

|Section2={{Chembox Properties

|C=2 | H=6 | N=6 | S=1

|MolarMass = 146.17

|Appearance = white solid

|Density = 1.69 g/cm³

|MeltingPtC = 228

}}

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4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole is an organic compound with the formula SC₂N₃H(NH₂)(N₂H₃). The compound consists of a 1,2,4-triazole heterocycle with three functional groups: amine, thioamide and hydrazyl. X-ray crystallography shows that this molecule is polar but with a C=S double bond. It is prepared by the reaction of hydrazine with thiourea:N. W. Isaacs and C. H. L. Kennard "Crystal structure of 4-amino-3-hydrazino-5-mercapto-1,2,4-triazole" J. Chem. Soc. B, 1971, 1270-1273. {{doi|10.1039/J29710001270}}

:2 SC(NH₂)₂ + 3 N₂H₄ → SC₂N₃H(NH₂)(N₂H₃) + 4 NH₃ + H₂S

The compound has been used as a reagent for the colorimetric detection of aldehydes.Hopps, Harvey B. "Purpald: a Reagent that Turns Aldehydes Purple!" Aldrichimica Acta 2000, volume 33, pp. 28-30.