5-Aminotetrazole
5-Aminotetrazole is an organic compound with the formula HNCNH. It is a white solid that can be obtained both in anhydrous and hydrated forms. The molecule is planar. The hydrogen bonding pattern in the hydrate supports the assignment of NH being adjacent to carbon in the ring. Preparation. A synthesis of 5-aminotetrazole through the action of nitrous acid on aminoguanidine was reported by Johannes Thiele in 1892. The exact structure of the compound was not known at the time, although it was known to crystallize as a monohydrate when prepared in aqueous solution. The correct structural  formula was published in 1901 by Arthur Hantzsch, who obtained it from the reaction between cyanamide and hydrazoic acid. To avoid direct handling of the problematic hydrazoic acid, a mixture of sodium azide and hydrochloric acid has been used and gave the monohydrate at 73% yield. In a much more efficient and controllable one-pot synthesis, cyanamide is reacted with hydrazine hydrochloride to give aminoguanidine hydrochloride, which is then diazotized as in Thiele's original process. Addition of ammonia or sodium hydroxide to decrease the acidity followed by heat-induced cyclization gives the anhydrous product in 74% yield. Uses. 5 -Aminotetrazole has found applications in heterocyclic chemistry, particularly as a synthon for numerous multicomponent reactions. The compound has a particularly high nitrogen content of 80%. Partly for this reason, the compound is prone to decomposition to nitrogen gas (N). It has been widely investigated for gas-generating systems, such as airbags and blowing agents.