Tetrasodium (1-hydroxyethylidene)bisphosphonate

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Dissociating properties:

yes

pKa:

2.18

Temp.:

200 °C

Conclusions:

The test item HEDP #13082 Nachsubstanz has a Dissoziation constant of pKa = 2.18.

Description of key information

Dissociation constant: 2.18 at 20 °C 

Key value for chemical safety assessment

pKa at 20°C:

2.18

Additional information

An experimental test shows a dissociation constant in water of 2.18 at 20°C.

Dissociation constant values of 1.7, 2.47 , 7.28, 11.41 are reported at 25 °C in a handbook which has been subject to peer-review and in which the original data sources are traceable. The result (Martell 1968) is considered to be reliable and selected for key study.

Dissociation constant values of 1.35, 2.87, 7.03, 11.3 are reported in other secondary literature (Lacour 1999). They are considered as supporting studies.

In general, commercial formulations vary in concentration between suppliers and formulation types. The pH value of solutions at around 1% in water are shown in the table below.

CAS	Product at typically 1%
2809-21-4	pH <2	Acid
3794-83-0	pH 11-12	Salt