Hydrazinium

Hydrazinium is the cation with the formula N₂H+
5. In some cases, "hydrazine" implies N₂H+
5, e.g. the salt hydrazinium sulfate. Hydrazinium is derived from hydrazine by protonation (treatment with a strong acid). Salts of hydrazinium are common reagents in chemistry and are often used in certain industrial processes. Both are water-soluble, colorless salts. Hydrazinium is a weak acid with pK_a = 8.1.

One of the most unusual (and more unstable) salts of hydrazinium is the azide. Hydrazine azide (N₅H₅), the salt of hydrazine and hydrazoic acid, is of scientific interest, because of its high nitrogen content and explosive properties. Structurally, it is [N
2H
5]+
[N
3]−
. It decomposes explosively into hydrazine, ammonia, and nitrogen gas:

Hydrazinium may be protonated to give a dication known as hydrazinediium or hydrazinium(2+); with the formula N₂H2+
6. Reaction of hydrazinium azide with sulfuric acid gives quantitative yields of pure hydrazinediium sulfate and hydrazoic acid:

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