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Physical & Chemical properties

Melting point / freezing point

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Description of key information

Melting point (HEBMP-H): melt with decomposition from 129°C (OECD 102)

Key value for chemical safety assessment

Additional information

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 forms 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. Spectroscopic evidence from 31P-NMR analysis suggests that in the pH range ca. 1 – 7 a high proportion (50-75% w/w) is present as the cyclised form. The two forms exist in equilibrium therefore it is extremely difficult to separate and purify both forms.The properties of the whole substance, in which both forms are present at representative levels, are used in the chemical safety assessment.

A recent, reliable DSC test conducted in accordance with OECD 102, demonstrates that the salt (HEBMP-xNa) melts with decomposition from 129°C. The acid would be expected to melt and decompose. This read-across is supported by secondary sources with data for HEBMP-H, to which no reliability could be assigned. Melting points of < 0°C, and ~-10°C with a decomposition temperature of >200°C after evaporation of water were reported for the aqueous solution of the substance.