Semicarbazide

semicarbazide [¦sem·i′kär·bə‚zīd]

(organic chemistry)

H₂N‒NHCONH₂A reagent used to produce semicarbazones by reaction with aldehydes or ketones.

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Semicarbazide 

H₂N—NH—CO—NH₂, the hydrazide of carbamic acid. Semicarbazide occurs as colorless crystals; it has a melting point of 96°C (with decomposition) and is soluble in water and alcohol. Semicarbazide possesses chemical properties similar to those of hydrazine and hydrazine’s organic derivatives. Combined with acids, it yields salts, for example, semicarbazide hydrochloride (CH₅N₃O·HCl), with a melting point of 173°C); with aldehydes and ketones, it yields readily crystallizing semicarbazones, as seen in the reaction

R₂C=O + H₂NNHCONH₂

→R₂C=NNHCONH₂ + H₂0

Semicarbazide readily condenses (for example, with β-diketones) to form heterocyclic compounds. It is obtained by, for example, the reaction of hydrazine with potassium cyanate (KOCN). Semicarbazide is used primarily in the identification of aldehydes and ketones.