Zinc Nitrite, Zn(NO₂)₂

Colourless prismatic crystals of Zn(NO₂)₂.2H₂O.C₆H₁₂N₄ are obtained by adding sodium nitrite to the solution of a zinc salt containing hexamethylenetetramine. Zinc nitrite also occurs in the hygroscopic yellow crystalline double salt, 3KNO₂.Zn(NO₂)₂.3H₂O, obtained by acting with nitrous acid on zinc hydroxide suspended in potassium nitrite solution, and in the similar salt, 2KNO₂.Zn(NO₂ )₂.H₂O, prepared by mixing solutions of potassium nitrite and zinc acetate or nitrate. According to Ray, zinc nitrite can only exist pure and uncombined in dilute solutions. This solution is acid, and the nitrous acid set free by hydrolysis decomposes on concentration -

3HNO₂ = HNO₃+2NO+2H₂O.

Zinc nitrate is thus continuously formed, and the residue from evaporation, even when conducted in vacuo, is a basic nitrate.

A dilute solution of zinc nitrite may be prepared by interaction between solutions of zinc sulphate and barium nitrite, but, though the trihydrate, Zn(NO₂)₂.3H₂O, is said to have been obtained from such a solution, only basic or very impure zinc nitrites have usually been obtained.

The monohydrate, Zn(NO₂)₂.H₂O, was said to be obtained in fine needles by treating a mixture of sodium nitrite and magnesium sulphate with alcohol, filtering, and evaporating in vacuo. The dry salt, its aqueous solution, and (more gradually) its alcoholic solution, give off nitrogen oxides and leave a mixture of zinc nitrate and hydroxide. Vogel could not in this way obtain a salt with a higher ratio for NO₂:Zn than 1.76:1.