13780-06-8

white or yellowish deliquescent, hexagonal crystal(s); prepared from nitric oxide and a mixture consisting of calcium ferrate and calcium nitrate; used to inhibit corrosion in lubricants and concrete [MER06]

Corrosion inhibitor in lubricants, concrete.

Calcium nitrite has the formula of Ca(NO2)2 and the molecular weight of 132.0894 g/mol. It can be made by the usual double decomposition reaction of sodium nitrite and CaCl2. It forms a tetrahydrate that is isomorphous with the strontium and barium salts:
2Na2NO2 (aq) + CaCl2 ? Ca(NO2)2 (aq) + 4NaCl (aq)

Calcium nitrite, Ca(NO2)2, has the CAS number of 13780-06-8 and occurs as yellow-white crystals. It is very hygroscopic. Its density is 2.23 g/cm³ and it decomposes at 392°C to form nitrogen oxides and CaO. It is slightly soluble in alcohol. Ca(NO2)2·4H2O loses two waters of hydration at about 80°C and one at 105°C to form the monohydrate. It loses the other at about 155°C. The anhydrate, if further heated, is unstable and oxidizes to the nitrate in air above 220°C:
Ca(NO2)2 + O2 + heat?Ca(NO3)2

Industrially, calcium nitrite is manufactured by reacting “NOX” gas with “lime”:
Ca(OH)2 + NO +NO2?Ca(NO2)2 +H2O
By carefully controlling calciumnitrite conditions, the selectivity on converted lime, on a molar basis, is over 95% pure. It is soluble in water (98.2 g/100 ml at 20 °C) and the solution must be evaporated at low temperature to obtain the tetrahydrate. If heated with NO2 gas, it also form the nitrate:
Ca(NO2)2 + NO2?Ca(NO3)2 + NO
Anhydrous calcium nitrite is unstable and slowly oxidizes in air to form the nitrate. It is also soluble in alcohol at 0.97 g/100 ml at 20 °C.

Crystallise it from hot water (1.4mL/g) by adding ethanol and cooling to give the hydrate. It is deliquescent. [Ray & Ogg J Am Chem Soc 79 265 1957.]

Notclassified