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Description of key information

Hydrolysis (HEBMP-H): the substance is not susceptible to hydrolytic degradation.

HEBMP-H is not susceptible to hydrolytic degradation.

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 ≥50% w/w.                                               

The registration substance HEBMP-xNa theoretically covers all possible values of x and therefore it should be noted that at high pH values the non-cyclic constituent ([[(2-hydroxyethyl) imino]bis(methylene)]-bisphosphonic acid (CAS 5995-42-6)) predominates. At present, the forms of the sodium salt supplied in EU are acidic / neutral only, and in the environment the prevailing neutral conditions will dominate, regardless of the ionisation state of the substance initially released.

Spectroscopic evidence from 31P-NMR analysis suggests that in the pH range ca. 1 – 7 a high proportion (typically 50%, range 50-75% w/w) is present as the cyclised constituent. The two constituents exist in equilibrium therefore it is extremely difficult to separate and purify both constituents.