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Description of key information

Hydrolysis (HEBMP-H): not hydrolytically unstable

Key value for chemical safety assessment

Additional information

The requirement to test the substance for hydrolysis was waived as the substance is not susceptible to hydrolytic degradation.

In solution, HEBMP-H (CAS 5995-42-6) undergoes a reversible internal condensation reaction to form a pH-dependent equilibrium mixture with the cyclised structure 4-(Phosphonomethyl) -2-hydroxy-2-oxo-1,4,2-oxaza-phosphorinane (CAS 32422-02-9, c-HEBMP) and water. The precise proportion of the two constituents is dependent on pH, temperature, and time, and under acidic or neutral conditions, the proportion of c-HEBMP in the multi-constituent substance may reach proportions as high as 60% w/w.                                               

The acid and sodium salts in the HEBMP category are freely soluble in water and, therefore, the HEBMP anion is fully dissociated from its potassium cations when in solution. Under any given conditions, the degree of ionisation of the HEBMP species is determined by the pH of the solution. At a specific pH, the degree of ionisation is the same regardless of whether the starting material was HEBMP-H, HEBMP-1Na, HEBMP-3Na or another salt of HEBMP.

Therefore, when a salt of HEBMP is introduced into test media or the environment, the following is present (separately):

  1. HEBMP is present as HEBMP-H or one of its ionised forms. The degree of ionisation depends upon the pH in vivo and not whether HEBMP-xNa salt, HEBMP-H (acid form) or another salt was used for dosing
  2. Disassociated sodium cations. The amount of sodium present depends on which salt was dosed.
  3. It should also be noted that divalent and trivalent cations would preferentially replace the potassium ions. These would include calcium (Ca2+), magnesium (Mg2+) and iron (Fe3+).