Reaction mass of [[(2-hydroxyethyl)imino]dimethylene]bisphosphonic acid, sodium salt and 4-(Phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxazaphosphorinane, sodium salt

Endpoint summary

Description of key information

HEBMP-xNa is a multi-constituent substance with two constituents that are the linear and cyclised forms of the same basic structure and differing numbers of sodium anions (x = 1-3).

In solution, the linear from, [[(2-hydroxyethyl)imino]bis(methylene)]-bisphosphonic acid (and its anions) (l-HEBMP (CAS 5995-42-6)) undergoes a reversible internal condensation reaction to form a pH-dependent equilibrium mixture with the cyclic form, 4-(phosphonomethyl)-2-hydroxy-2-oxo-1,4,2-oxaza-phosphorinane and its anions (CAS 32422-02-9, c-HEBMP) and water. The precise proportion of the two constituents is dependent on pH, temperature, concentration and time. 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.

Higher amounts of linear form are expected at higher pH.

The two constituents exist in equilibrium. The properties of the whole substance, in which both constituents are present at representative levels, are used in the chemical safety assessment.

The anhydrous form of HEBMP-xNa is a pale yellow, tranlucent powder of variable particle size under ambient conditions, however, commercial samples as supplied in Europe are manufactured in situ as aqueous solutions (liquid). HEBMP-xNa will undergo thermal decomposition when heated from 129°C, the substance has a measured density of 1740 kg/m³ at 21.0 ± 0.5°C, negligible vapour pressure at 25°C, predicted log K_ow values of -4 and -3.4 for the linear and cyclic forms respectively. The substance is very soluble in water and has a water solubility value of 75.7 - 77.2% w/w of solution at 20.0 ± 0.5°C.

l-HEBMP has four P-OH groups and c-HEBMP has three P-OH groups that can be ionised in solution. The ionised species present is dependent on the pH of the solution. The pKa values of both l-HEBMP and c-HEBMP are in the range 1.3 to >8, the results indicate that HEBMP will be ionised at environmenatlly relevant pH values.

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008 based on a preliminary screening study performed according to EU Method A.10. There is no evidence of relative self-ignition observed below 400°C based on EU Method A.16. It is not explosive and not oxidising based on structural examination.