N-(3-aminopropyl)-N-dodecylpropane-1,3-diamine

Dissociation constant

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2006

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Reason / purpose for cross-reference:

reference to other study

Principles of method if other than guideline:

Method: Titration with 0.1M HCl in distilled water.

GLP compliance:

no

Dissociating properties:

yes

No.:

#1

pKa:

ca. 6.9

Remarks on result:

other: Tertiary amine

No.:

#2

pKa:

ca. 9

Remarks on result:

other: Primary amines

The test substance resulted in 2 pKa values, one at 9, which was attributed to the two primary amino groups and one at 6.9 attributed to the tertiary amine group. The three amino groups in the test substance will affect each other as a result of the short distance between them and it is expected that the central ammonium group will become the least acidic due to the two electron withdrawing terminal ammonium groups, both situated three carbon atoms away.

Further, the trend of decreasing pKa with increasing number of neighbouring ammonium groups was clearly seen from other literature evidence (Burns et al., 1996). For example, pKa of N-dodecylammonium chloride is 10.63 while for N-dodecyl-N-(aminopropyl) ammonium chloride pKa1 is 10.62 and pKa2 is 8.64. The pH dependence of the derivatives of the test substance will depend on the type of substituents attached to the primary amino groups.

Conclusions:

Under the study conditions, the dissociation constant (pKa) of the test substance was determined to be approx 9 for the two primary amine groups and approx 6.9 for the tertiary amine group.

Executive summary:

A study was conducted to determine the dissociation constant (pKa) of the test substance by titration with 0.1M HCl in distilled water. Under the study conditions, the pKa of the test substance was determined to be approximately 9 for the two primary amine groups and approximately 6.9 for the tertiary amine group (Oskarsson, 2006).

Reference 2

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

January 11, 2000

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 830.7370 (Dissociation constants in water)

Dissociating properties:

yes

No.:

#1

pKa:

9.3

Temp.:

20 °C

No.:

#2

pKa:

7.15

Temp.:

20 °C

Preliminary test:

During the preliminary test, there was no difference between the titration curves of CO2 free reagent water and the test wabstance solution when titrated with 0.09999N NaOH. Maxima also did not exist in the plot of the derivative of the titratin curve. Therefore, the test substance could not have a pKa greater than approximately 11. Two pKa values were identified from the titration curve at ca. 9.6 and 14.0 mL of added titrant. The preliminary pKa values were estimated to be 9.27 and 7.2 based on the pH at approximately half neutralisation of each acidic group.

Main test:

In the definitive test, the pKa values of the test substance were determined by titration at 20°C. Each test was performed in triplicate.

Replicate	Ka 1	Ka2
1	6.37E-10±6.27E-11	8.14E-8 ±5.52E-9
2	4.09E-10±1.38E-10	6.46E-8±1.73E-9
3	4.59E-10±1.33E-10	6.82E-8±2.33E-9
pKa	9.30±0.104	7.15±0.054

All solution concentrations were calculated as 100 %, thus the actual amount of pure test substance in the solutions would be slightly lower. The pKa value was therefore slightly biased.

Conclusions:

Under the study conditions, the pKa values for the test substance were determined to be 9.30±0.104 and 7.15±0.054 at 20°C.

Executive summary:

A study was conducted to determine a dissociation constant (pKa) in water for the test substance according to EPA OPPTS 830.7370. A potentiometric titration test was conducted to examine the presence of any ionizable groups. The study was performed in two tests, each with three replicates, and the measurements were taken at 20°C. All solution concentrations were calculated as 100 %, thus the actual oncentrations of the test substance were slightly lower. Under the study conditions, the pKa values for the test substance were determined to be 9.30±0.104 and 7.15±0.054 at 20°C (Flack, 2000).

Description of key information

Determination of the dissociation constant by:

- Titration with 0.1 M HCl in distilled water (Oskarsson, 2006)

- Potentiometric titration according to EPA OPPTS 830.7370 (Flack, 2000)

Key value for chemical safety assessment

pKa at 20°C:

6.9

Additional information

- Approximately 9 for the two primary amine groups and approximately 6.9 for the tertiary amine group (Oskarsson, 2006)

- 9.30±0.104 and 7.15 ± 0.054 at 20°C (Flack, 2000)