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Physical & Chemical properties

Dissociation constant

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Description of key information

QSAR calculations on the dissociation constants of the five main constituents revealed pKa values in the range of 9.9-10.9.

Key value for chemical safety assessment

pKa at 20°C:
9.9

Additional information

"Should read: 9.9 -10.9 at 25 °C"

Discussion

For the UVCB substance a defined dissociation constant may not be determined. Furthermore, OECD test method 112 on "Dissociation Constants in Water" was developed for mono substances and not for complex mixtures. Thus, from a scientific point of view conducting a study to fulfil the REACH data requirement "dissociation constant" of Annex IX is not justified and should be understood as technically not possible which would allow waiving based on Annex XI, section 2. However, there are five main constituents which were quantified with >= 10% (w/w):

  • 2,2-bis(4-hydroxyphenyl)propane,
  • 2-[2-(4-hydroxyphenyl)propan-2-yl]phenol,
  • 3-(4-hydroxyphenyl)-1,1,3-trimethylindan-5-ol,
  • 4-(2,2,4-trimethyl-3,4-dihydro-2H-chromen-4-yl)phenol
  • Phenol

While determination of the dissociation constant of this UVCB substance is technically not possible QSAR was used to calculate pKa of the four main constituents listed above. With pKa values between 9.9 and 10.9 the main constituents can be expected to be available as undissociated molecules at environmentally relevant pH ranges of 5-9. The main constituents are considered as representative for the complete UVCB substance.