Solid–liquid phase equilibria of (Mg(H2PO2)2 + H2O), (Mg(H2PO2)2 + NaH2PO2 + H2O) and (Mg(H2PO2)2 + MgCl2 + H2O) systems

Abstract

Magnesium hypophosphite Mg(H2PO2)2 is an important hypophosphite, and used as an drugs for the treatment of rheumatoid arthritis, plastic stabilizer, flameresistant material, fertilizer additive and the amendment of the soil, which can be synthesized via neutralization reaction and double decomposition reactions. In this work, the (solid + liquid) phase diagrams of (Mg(H2PO2)2 + H2O) binary systems, and (Mg(H2PO2)2 + NaH2PO2 + H2O), (Mg(H2PO2)2 + MgCl2 + H2O) ternary systems at 298.15 K were experimentally determined via the classical isothermal solubility equilibrium method. It was found that (1) two solid salts of Mg(H2PO2)2·6H2O and Mg(H2PO2)2 with transition temperature 325.15 K occur in the (Mg(H2PO2)2 + H2O) binary system, (2) three solid salts of Mg(H2PO2)2·6H2O, NaH2PO2·H2O and one incompatible double salt [NaMg(H2PO2)3] exist in (Mg(H2PO2)2 + NaH2PO2 + H2O) system, (3) Mg(H2PO2)2·6H2O, MgCl2·6H2O and one unknown double salt exist in (Mg(H2PO2)2 + MgCl2 + H2O) system, the unknown double was identified to be an incompatible double salt [Mg2(H2PO2)2Cl2·6H2O].