(8α,9R,8'''α,9'''R)-1,1'-[(2,3,5,6-tetrafluoro-1,4-phenylene)bis(methylene)]bis(6'-methoxycinchonan-1-ium-9-ol) dibromide

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)

Version / remarks:

1981

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Dissociating properties:

yes

No.:

#1

pKa:

4

Temp.:

20 °C

Remarks on result:

other: Constant for the first quinoline functional group

No.:

#2

pKa:

3.4

Temp.:

20 °C

Remarks on result:

other: Constant for the second quinoline functional group

No.:

#3

pKa:

11.4

Temp.:

20 °C

Remarks on result:

other: Constant for the first alcohol functional group

The dissociation constant of the second alcohol functional group exceeded the working range of the methodology used and was therefore concluded to exceed the environmentally relevant range of 2 to 12.

Due to the limited aqueous solubility of the test item at the pH ranges required for the determinations, the water solubility at pH 5 and pH 9 were both <1.0 g/L (<1 E-3 M), it was not possible to titrate samples as simple aqueous solutions. However, by titrating a series of test item solutions with differing water to methanol compositional ratios, it was possible to obtain values for the dissociation constants of the relevant functional groups in pure water for this substance by a Yasuda-Shedlovsky extrapolation method.

Conclusions:

The substance has several functional groups that potentially dissociate in water. The two quinoline functional groups will be present mainly in the ionised form under acetic pH conditions with dissociation constant (pKa) values of 4.0 and 3.4 for the first and second quinoline functional group at 20 °C. The dissociation constant for the first alcohol functional group was estimated to be 11.4 at 20 °C, i.e. the ionised form will dominate at pH values above 11.4. The dissociation constant of the second alcohol functional group exceeded the working range of the test method and therefore is anticipated to exceed the environmentally relevant range of 2 to 12.

Executive summary:

The dissociation constant of the test substance in water was tested under GLP to OECD TG 112. Due to the limited aqueous solubility of the test item at the pH ranges required for the determinations, the water solubility at pH 5 and pH 9 were both <1.0 g/L (<1 E-3 M), it was not possible to titrate samples as simple aqueous solutions. However, by titrating a series of test item solutions with differing water to methanol compositional ratios, it was possible to obtain values for the dissociation constants of the relevant functional groups in pure water for this substance by a Yasuda-Shedlovsky extrapolation method. The substance has several functional groups that potentially dissociate in water. The dissociation constant of the first quinoline functional group was determined to be 4.0 at 20 °C, and the ionised form will dominate at pH values below 4.0. The dissociation constant of the second quinoline functional group was determined to be 3.4 at 20 °C, i.e. the ionised form will dominated at pH values below 3.4. The dissociation constant of the first alcohol functional group was estimated to be 11.4 at 20 °C. Due to exerimental constraints resulting from the limited solubility of the test item in aqueous media, this dissociation constant being at the very extreme of the method domain and the second overlapping alcohol dissociation constant exceeding the domain of the methodology, this dissociation constant could only be estimated. The ionised form will dominated at pH values exceeding 11.4. The dissociation constant of the second alcohol functional group exceeded the working range of the applied test method and is anticipated to exceed the environmentally relevant range of 2 to 12.

Description of key information

pKa 1 = 4.0 at 20 °C for first quinoline functional group

pKa 2 = 3.4 at 20 °C for second quinoline functional group

pKa 3 = 11.4 at 20 °C for first alcohol functional group

pKa for second alcohol functional group expected to exceed the environmentally relevant range of 2 to 12

(GLP, OECD TG 112)