CALCIUM PHOSPHITE

Description

Calcium phosphite can have the molecular formula of CaHPO3 or Ca(H2PO3)2. It is the former that appears when a solution of phosphorous acid is reacted with the oxide, hydroxide or carbonate:
CaO +H3PO3 ? CaHPO3·H2O +H2O
The product is a monohydrate. It can also be prepared by the action of ammonium phosphite on calcium chloride:
CaCl2 (aq) +NH4HPO3 (aq) ? CaHPO3·H2O +NH4Cl2 (aq)
A white, crystalline powder is obtained. The solubility of CaHPO3·H2O has apparently not been determined exactly. If heated to about 250°C, the anhydrate results. This is stable when heated further up to about 320°C where it decomposes to form phosphine and hydrogen:
3CaHPO3 + heat ? 2PH3 + 3Ca(PO3)2 +H2

Chemical properties

crystal(s); used in fertilizers and polymerization catalysts [MER06]

Physical properties

Calcium Phosphite is a colorless, monoclinic crystal which loses water at about 150°C and is slightly soluble in water but insoluble in alcohol. The anhydrate, calcium phosphite (CaHPO3), is stable in air even when heated at 95°C for 2 months.

Flammability and Explosibility

Not classified