Barium hypophosphite has the formula, Ba(H2PO2)2,
and the molecular weight of 267.30388 g/mol. This salt
can be prepared by the aqueous reaction of the
carbonate or oxide with H3PO2:
BaO + 2H3PO2 ? Ba(H2PO2)2
The salt is slightly soluble in water (3.62 g/100 ml at
20°C) so that the solution must be evaporated to obtain
crystals. This procedure forms barium hypophosphite
monohydrate, Ba(H2PO2)2·H2O, whose CAS number
is 14871-79-5. Its molecular weight is 285.320 g/mol. It
occurs as monoclinic plates with a density of
2.94 g/cm3. It is soluble in water but insoluble in alcohol.
Therefore, the addition of alcohol during evaporation
serves to hasten the crystallization process from
aqueous solution. Heating to about 110°C causes the
loss of the water of hydration to form the anhydrate.
The anhydrate is soluble in water at about 35 g/100 ml
at 20°C but only 30 g/100 ml at 100°C.
White, crystalline powder; odorless. Soluble in water; insoluble in alcohol.
The major usage of barium hypophosphite has been
as a source of hypophosphorous acid because the addition of H3PO4 to a solution allows the separation
of the very insoluble BaSO4. Although this salt is
mentioned in a few patents concerning metal surface
finishing, electroplating, chemical intermediates and
as a source of hypophosphite anions, it is the calcium
salt that is preferred since it is lower in cost and easier
to use.
