Registration Dossier
Registration Dossier
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EC number: 946-260-7 | CAS number: -
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
The pKa for the protonation of the alkylamine group is 10.67 ± 0.10 at 25°C.
The pKa for the protonation of the acetate group is 4.76 at 25°C.
Key value for chemical safety assessment
- pKa at 20°C:
- 10.67
Additional information
An experimental determination of the pKa value is not possible due to the interaction between amine and acetate groups.
The pKa for the protonation of the alkylamine group of the major components (C16 and C18 alkyl) is 10.67 ± 0.10 at 25°C (calculated).
The pKa for the protonation of the acetate group is 4.76 at 25°C (literature).
N-Primary alkyl amines are strong bases with a pKa of around 10.6 which protolyze with water to their corresponding ammonium salt. The pH in the environment e.g. 4-9 (OECD Guideline 111) influences how much of the unprotonated amine is available when compared with their corresponding ammonium salts. The fraction of base Xb at a given pH can be calculated with the following algorithm
Xb= Ka / (Ka+ CH+) with Ka the acid constant and CH+ the proton concentration
The fraction of acid (ammonium salt) Xs is calculated from XB as Xx= 1-XB (Becke- Goehring, 1968). The following table summarizes the fractions of acid and base at pH 4 to 9.
Acid base fractions of n-Primary alkyl amines as function of pH
| pH | Acid fraction Xs | Base fraction Xb |
| 9 | 97.50% | 2.500000% |
| 7 | 99.975% | 0.025000% |
| 4 | 99.99997% | 0.00003% |
This means that already at the high pH 9 only 2.5% of unprotonated amine exists aside 97.5 % of the corresponding protonated ammonium salt. At pH 4 the percentage of unprotonated amine is extremely low.
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