A new method for the preparation of peroxymonophosphoric acid

A new method for the preparation of peroxymonophosphoric acid (H₃PO₅) has been developed. It utilizes a biphasic solution to moderate the vigorous reaction between phosphorous pentoxide (P₂O₅) and hydrogen peroxide (H₂O₂). P₂O₅ is suspended in carbon tetrachloride (CCl₄), and concentrated H₂O₂ is slowly added while being vigorously stirred at low temperature. Careful control of the reaction temperature through the slow addition of H₂O₂ is critical. Using typical preparation conditions (P₂O₅:H₂O₂ = 0.5:1, H₂O₂ 70 wt %, 2°C, 120–180 min), ~70% of the H₂O₂ is effectively converted to H₃PO₅. Increasing the concentration of H₂O₂, as well as the mole ratio of P₂O₅:H₂O₂, leads to an even higher % conversion of H₂O₂ to H₃PO₅. The addition of glacial acetic acid to the P₂O₅:H₂O₂ suspension at the end of the 120–180 min reaction (P₂O₅:H₂O₂:CH₃COOH = 0.5:1:0.3) leads to the formation of peracetic acid in addition to H₃PO₅, and to an overall increase in the conversion ratio of total peroxy acids based on H₂O₂ (>95%).Key words: peroxymonophosphoric acid, synthesis, stability, conversion ratio.