2-(2,6-diethyl-4-methyl-phenyl)propanediamide

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

09 December 2003 to 11 December 2003

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

Qualifier:

according to guideline

Guideline:

EPA OPPTS 830.7370 (Dissociation constants in water)

Deviations:

no

GLP compliance:

yes

Dissociating properties:

yes

pKa:

12.39

Temp.:

20 °C

The estimated pKa value from the calculation with the ACD/pKa software was 6.69 in the range from 0 to 12. However the actual pKa value was expected to be significantly higher.

From the preliminary experiments a pKa value of around 12.4 was anticipated.

The pKa was attributed to two species, the first present at pH <12.4 and the second present at pH > 12.4

Table 1: Summary of the results of the three main experiments

Experiment No.	pKa
1	12.39
2	12.39
3	12.38
Average ± standard deviation	12.39 ± 0.01

Conclusions:

Under the conditions of the test, the test material was determined to have a dissociation constant (pKa) of 12.39 (acidic) at 20 °C. The study is considered to be reliable, relevant and adequate for risk assessment purposes.

Executive summary:

The dissociation constant of the test material was determined in accordance with the standardised guideline OECD 112 using the spectrophotometric titration method. Under the conditions of the test, an initial estimation of the dissociation constant produced at extremely underestimated value for this substance (6.69) whereas the pKa determined from the experimental data was 12.39 (acidic) at 20 °C.

Description of key information

pKa 12.39, 20 °C, OECD TG 112, Martin 2004

Key value for chemical safety assessment

pKa at 20°C:

12.39

Additional information

The dissociation constant of the test material was determined in accordance with the standardised guideline OECD 112 using the spectrophotometric titration method. Under the conditions of the test, an initial estimation of the dissociation constant produced at extremely underestimated value for this substance (6.69) whereas the pKa determined from the experimental data was 12.39 (acidic) at 20 °C. The study was performed in line with GLP and accepted standardised guidelines with a high standard of reporting. The study was assigned a reliability score of Klimisch 1 and considered suitable for assessment as an accurate reflection of the test substance.

The available data are considered to be complete and the result determined, pKa 12.39 at 20 °C was taken forward for risk assessment.