Dipotassium 3,4,5,6-tetrabromophthalate

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Guideline study demonstrating high level of water solublity for the potassium salt

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

GLP compliance:

no

Type of method:

flask method

Specific details on test material used for the study:

Sample name: Dipotassium 3,4,5,6-tetrabromophthalate
Batch: 18112019
Sample description: White Powder

Water solubility:

> 200 g/L

Conc. based on:

test mat.

Loading of aqueous phase:

200 g/L

Temp.:

19.5 °C

pH:

ca. 9.9

Details on results:

The pH was measured at 200 g/l

Although the results are based on 200g/l being miscible in water, further evaluation showed it ws possible to dissolve even more material but above 200 g/l, the results became less reliable.

Conclusions:

The potassium salt is highly water soluble under neutral-alkaline conditions
However, it is expected that at lower pH, with formation of the aicd form, water solublity will be greatly reduced.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Justification for type of information:

Performed by Lead Registrant in-house using calibrated equipment.
Information was generated to help support observations from environmental testing and to confirm suspected solublity under environmental and biological conditions.

Qualifier:

no guideline available

Principles of method if other than guideline:

The substance was disolved in two types of commercially available bottled water of known hardness, pH and analysis and concentrations up to 100 mg/l.
The substance was dissolved in molar HCl (ca pH1) at up to 100 mg/l
Precipitation of insoluble salts/acid was determined by use of a calibrated turbidity meter

GLP compliance:

no

Other quality assurance:

other: Use of calibrated instrumentation

Type of method:

flask method

Water solubility:

< 5 mg/L

Conc. based on:

other: estimation in considering presence of undisolved material

Loading of aqueous phase:

100 mg/L

Incubation duration:

ca. 1 h

Temp.:

20 °C

pH:

> 6.7 - < 7.4

Water solubility:

< 5 mg/L

Conc. based on:

other: estimation in considering presence of undisolved material

Loading of aqueous phase:

100 mg/L

Incubation duration:

ca. 1 h

Temp.:

20 °C

pH:

ca. 1

Details on results:

The measured pH for the mineral water was based on analysis provided by the suppliers.
The test substance did not impact on the pH.
The figure of 5 mg/l cited for solublity is based on report solublity for the acid form. Turbity was considered hardly detectable at < 10 mg/l

Conclusions:

The substance showed low solubiilty when diluted to below 100 mg/l in water typically used for ecotoxocity testing
The substance showed low solublity when diluted at pH 1 to mimic possible effects if ingested.
Acutal solubility was not possible to establish since it was in equilibrium

Executive summary:

Standard testing to EC A6 method demonstrated very high water solubility / miscibility with a slightly alkaline pH 9.9.

 

However, under dilute conditions in 'natural' water (as required for environmental toxicity testing), the substance proved to be poorly soluble with the apparent formation of calcium and other salts from the hardened test water. The apparent solubility decreased as concentrations were reduced. A solubility limit of ca 5 mg/l is reported in environmental toxicity testing for tetrabromophthalate salts.

 

It is likely that under these dilute conditions, the salt will exist in equilibrium and apparent solubility will depend greatly on actual hardness of the water and also the pH

 

Further work (Report, Dixon Chew, 19 March 2020) demonstrated precipitation under diluted conditions at pH 1 or in natural water (assessed by turbidity), thus confirming dissociation with formation of insoluble salts (natural water) and also formation of the poorly soluble acid form (pH 1, molar HCl). Although this work was non-quantitative in terms of determining actual solubility under these conditions, the observations demonstrated that the potassium salt will behave in the same way as the acid form under environmental and biological conditions.

 

These conclusions need to also be considered in the light of the well established observations that the anhydride quickly hydrates to the acid form under similar environmental conditions. Likewise, research has shown that the alkyl esters also hydrolyse to the acid form under environmental conditions. 

 

It must also be noted that the functionality of these substances is to provide the same propertied to different fabrics for fire retardant properties. The purpose of creating alkyl esters, or water soluble potassium salts is to allow use in different textile treatment media, but the functionality come from the C-O and C=O bonds of the phthalate to adhere to proteins and other charged groups in wool and other fibres. 

Description of key information

Susbtance is miscible at high concentrations in water

However, when diluted to < 100 mg/l in environmentally relevant water or in biological conditions, poor solubility is noted.

The solubility of the acid form is used for the CSR (ca 5mg/l) as this is more relevant for risk assessment.

Key value for chemical safety assessment

Water solubility:

5 mg/L

at the temperature of:

20 °C