Reaction mass of [[(2-hydroxyethyl)imino]bis(methylene)]bisphosphonic acid and Phosphonic acid, P-[(tetrahydro-2-hydroxy-2-oxido-4H-1,4,2-oxazaphosphorin-4-yl)methyl]-

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Experimental Starting Date: 08 June 2012; Experimental Completion Date: 21 August 2012

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

other: visual assessment, using a procedure based on the flask method

Key result

Water solubility:

>= 75.7 - <= 77.2 other: % w/w of solution

Temp.:

20 °C

pH:

> 4.2 - < 4.3

Results

Preliminary Test:

The sample concentrations, observations and solution pH are shown in the following table:

 

Sample	Concentration (% w/w)	Observations	Solution pH
1	50.0	Clear, straw coloured, non-viscous liquid, containing no undissolved test item.	4.0
2	59.9	Clear, straw coloured, slightly viscous liquid, containing no undissolved test item.	4.1
3	69.9	Clear, straw coloured, viscous liquid, containing no undissolved test item.	4.2
4	79.9	Clear, straw coloured, highly viscous liquid, containing a small amount of excess, undissolved test item.	n/a
5	89.9	Translucent, off-white, viscous paste.	n/a

Preliminary result:         In the range 69.9 to 79.9 % w/w at 20.0 ± 0.5°C.

Definitive Test

The sample concentrations, observations and solution pH are shown in the following table:

 

Sample	Concentration (% w/w)	Observations	Solution pH
1	75.7	Clear, straw coloured, viscous liquid, containing no undissolved test item.	4.2
2	77.2	Clear, straw coloured, viscous liquid, containing a small amount of excess, undissolved test item	4.3
3	79.7	Clear, straw coloured, viscous liquid, containing a small amount of excess, undissolved test item	4.2
4	80.9	Clear, straw coloured, viscous liquid, containing a small amount of excess, undissolved test item.	4.2

 

The samples increased in viscosity as the concentration increased.

 

Overall result:             In the range 75.7 to 77.2 % w/w at 20.0 ± 0.5°C.

Conclusions:

The water solubility of the test item has been determined to be in the range 75.7 to 77.2 % w/w of solution at 20.0 ± 0.5 °C. The result is considered to be reliable.

Executive summary:

Method

The determination was carried out by visual assessment, using a procedure based on the flask method, designed to be compatible with Method A6 Water Solubility of Commission Regulation (EC) No 440/2008 of 30 May 2008 and Method 105 of the OECD Guidelines for Testing of Chemicals, 27 July 1995.

Conclusion

The water solubility of the test item has been determined to be in the range 75.7 to 77.2 % w/w of solution at 20.0 ± 0.5°C.

Description of key information

Water solubility (HEBMP-H): 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 (approximately 750 g/L at 20°C) (OECD 105)

Key value for chemical safety assessment

Water solubility:

750 g/L

at the temperature of:

20 °C

Additional information

A measured water solubility of 75.7 - 77.2% w/w of solution at 20.0 ± 0.5°C (approximately 750 g/L) was determined for HEBMP-xNa in accordance with OECD Test Guideline 105 and in compliance with GLP. Due to the high saturation levels produced by the test substance, the study was performed using visual assessment based on the flask method. The result was considered to be reliable and is selected as key study. The measured water solubility is read across to the parent acid.

This value is supported by water solubilities in the range 450 - 820 g/L for HEBMP-H and HEBMP-xNa in secondary sources to which reliability could not be assigned. Aqueous solutions at 50-60% w/w are typical for HEBMP commercial products as supplied. The supporting studies are in agreement with the key study that the substance is highly soluble in water.

The aqueous forms as supplied in EU are miscible in water.

In solution, l-HEBMP (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, 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. A higher proportion of the linear form is expected at high pH values.

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.