Magnesium hydrogen phosphate

Dimagnesium phosphate is a compound with formula MgHPO₄. It is a Mg²⁺ salt of monohydrogen phosphate. The trihydrate is well known, occurring as a mineral.

It can be formed by reaction of stoichiometric quantities of magnesium oxide with phosphoric acid.

MgO + H₃PO₄ → MgHPO₄ + H₂O

Dissolving monomagnesium phosphate in water, forms phosphoric acid and depositing a solid precipitate of dimagnesium phosphate trihydrate:

Mg(H₂PO₄)₂ + 3 H₂O → Mg(HPO₄)^.3H₂O + H₃PO₄

The compound is used as a nutritional supplement, especially for infants and athletes. Its E number is E343.