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EC number: 211-522-5 | CAS number: 657-84-1
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
The HYDROTOPES Category comprises the following 6 substances:
STS - Sodium toluene 4-sulphonate (CAS 657-84-1, EC 211-522-5)
SXS - Sodium (xylenes and 4-ethylbenzene) sulphonate (EC 701-037-1)
NH4XS - Ammonium (xylenes and 4-ethylbenzene) sulphonate (EC 943-024-5)
SCS - Sodium p-cumenesulphonate (CAS 15763-76-5, EC 239-854-6)
KCS - Potassium p-cumenesulphonate (CAS 164524-02-1, EC 629-764-9)
NH4CS - Ammonium p-cumenesulphonate (CAS 680972-33-2, EC 811-484-5)
All the category members except STS were tested and the pKa values are:
SXS: pKa = 7.10
NH4XS pKa = 7.78
SCS: pKa < 2 (The dissociation constant was estimated on the free non-neutralised cumenesulfonic acid. The degree of dissociation at relevant pH values (5-9) is equal or larger than 99.9 %.)
KCS: pka < 2 (The dissociation constant was estimated on the free non-neutralised cumenesulfonic acid. The degree of dissociation at relevant pH values (5-9) is equal or larger than 99.9 %.)
NH4CS: pKa = 6.59
All the category members are sodium, potassium and ammoniun salt. When dissolved in water, hydrotropes are completely ionised.
Key value for chemical safety assessment
- pKa at 20°C:
- 6.59
Additional information
The lowest value of the dissociation constant of Hydrotropes was selected for the risk assessment.
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