1-[bis[3-(dimethylamino)propyl]amino]propan-2-ol

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-05-09 to 2012-05-10

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 112 (Dissociation Constants in Water)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch number of test material: PFW100207
- Purity: contains 0.03% water
- Physical state: Liquid

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: in cool, well-ventilated area

Dissociating properties:

yes

No.:

#1

pKa:

9.6

Temp.:

20 °C

Remarks on result:

other: No details on temperature are provided, however ambient temperature is anticipated

No.:

#2

pKa:

8.9

Temp.:

20 °C

Remarks on result:

other: No details on temperature are provided, however ambient temperature is anticipated

Estimation of pKa of the test substance:

The point of inflection of the reaction of the test substance with the titrant was determined from the ratio of change in pH of the solution to change in volume after each addition of the acid; versus mean volume of the acid applied. From the point of inflection curve, two points at 30 mL and 48 mL were obtained as volumes of the titrant consumed.The volumes were divided by 2 to obtain the mid-point of the neutralisation points.

The mid-point of the point of the neutralisation points was therefore obtained at the stage of the titration when 15mL and 24 mL of the titrant had been added to the test solution. The pKa of the test substance was estimated as 9.54 (the pH when 16 mL of titrant had been added to test solution) and 8.88 (i.e. pH at addition of 24 mL of titrant).

Formal Determination of pKa
The titration was repeated as in the pKa estimation stage by adding 4.0 mL of the titrant at a time until 12.0 mL of the acid had been added to the test solution. This was followed by 1.0 mL additions to 16.0 mL and then 4.0 mL added up to 20 mL. 1.0 mL additions were made thereafter until 26.0 mL of acid had been added (Table 20.2). The pH of test solution observed at the points where the volume of titrant added was 15.0 mL and 24.0 mL was then determined as the pKa of the sample.

In the formal determination, performed comparable to the estimation phase, the pKa of the test substance was determined as 9.6± 0.5 and 8.9±0.5.

Conclusions:

The dissociation constants of the substance were determined to be 9.6 and 8.9 at ambient temperature.

Description of key information

The dissociation constants of the test substance were determined to be 9.6 and 8.9 at ambient temperature following a GLP-compliant study conducted in accordance with guideline OECD 112 using the titration method (Younis S, 2012). The strongest pKa was selected as key value. 

Key value for chemical safety assessment

pKa at 20°C:

9.6

Additional information

pKa1: 9.6 at 20°C

pKa2: 8.9 at 20°C