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Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From Apr. 10, 2002 to June 27, 2002
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose for cross-reference:
reference to other study
Qualifier:
according to guideline
Guideline:
OECD Guideline 112 (Dissociation Constants in Water)
Deviations:
no
GLP compliance:
yes
Remarks:
According to OECD GLP
Dissociating properties:
yes
No.:
#1
pKa:
4.05
Remarks on result:
other: Temperature during the measurements varied between 25 and 26.9 °C.
No.:
#2
pKa:
4.09
Remarks on result:
other: Temperature during the measurements varied between 25 and 26.9 °C.
No.:
#3
pKa:
3.88
Remarks on result:
other: Temperature during the measurements varied between 25 and 26.9 °C.

Results: The pKa value was determined from the linear portion of the titration curve, which was roughly between 3.5 and 4.5. The equivalence point of test material was determined by plotting the absolute values of (dpH1 - dpH2) against the pH. The maximum of this plot indicates the location of the equivalence point.

The dissociation constant value for the control solution imidazole was 7.04.

Test temperature: The temperature was measured at the start and end of titrations and varied between 25 and 26.9 °C during all measurements.

Conclusions:
The dissociation constant (pKa) of C12/14 alkyl dimethyl amine oxide was 4.01 ± 0.1 (n = 3) at temperatures varying between 25 and 26.9 °C
Executive summary:

The dissociation constant (pKa) of C12/14 alkyl dimethyl amine oxide was determined following OECD 112 (Dissociation constants in water).

Test solutions (100 mL of approx. 0.01 mol/L) were titrated semi-automatically with 0.1 mol/L hydrochloric acid (HCI) (titrant). Imidazole (0.01 mol/L) served as the control. The titration was continued until after the last equivalence point of the test substance had been reached. The measurement was done in triplicate, and the temperature varied between 25 and 26.9 °C (measured at the start and end of titrations).

The dissociation constant (pKa) of C12/14 alkyl dimethyl amine oxide was 4.01±0.1 (n = 3).

This dissociation constant test is classified as acceptable, and satisfies the guideline requirements for the OECD 112.

Description of key information

The dissociation constant (pKa) of the substance was 4.01 ± 0.1 at temperatures varying between 25 and 26.9 °C. This value is read across from measured data on the C12-14 amine oxide.

Key value for chemical safety assessment

pKa at 20°C:
4.01

Additional information

The dissociation constant (pKa) of C12 -14 amine oxide was determined in a GLP study according to OECD TG 112 [Van Assche, 2002]. Measurements were performed in triplicate and the temperature varied between 25 and 26.9 °C. Dissociation constant is not expected to be affected to any great extent by the alkyl chain length and hence it is justified to read this value across to the C10 amine oxide.

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