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Physical & Chemical properties

Dissociation constant

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Reference
Endpoint:
dissociation constant
Type of information:
(Q)SAR
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
Please refer to attached justification documents
Principles of method if other than guideline:
Structure-based QSAR property prediction by means of linear free energy relationships and molecular orbital properties.
GLP compliance:
no
Dissociating properties:
yes
No.:
#1
pKa:
15.76
Temp.:
25 °C
Remarks on result:
other: This predicted value is relevant for ambient temperatures.

The value of pKa indicates that in the range of pH usually considered relevant to the human body and environment, i.e. pH 2-9, the substance will be non-ionised.

Conclusions:
A dissociation constant value of 15.76 was obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

The pKa of docosan-1-ol is predicted to be 15.8 using a reliable freely-available method.

Key value for chemical safety assessment

pKa at 20°C:
15.8

Additional information

No measured data for dissociation constant of 1 -docosanol were available. The pKa value (normal conditions) was predicted using SPARC.

While the hydroxyl group is ionisable, aliphatic alcohols are extremely weak acids and only dissociate under strongly basic conditions. In the range of pH usually considered relevant to the human body and environment, i.e. pH 2-9, docosan-1-ol will be non-ionised. There is no need to conduct further testing.

Discussion of trends in the Category of C6-24 linear and essentially-linear aliphatic alcohols:

Measured data have not been collated. However, in general, long chain aliphatic alcohols are extremely weak acids and only dissociate under strongly basic conditions (pKa= 15.8). In the range of pH usually considered relevant to the human body and environment, i.e. pH 2-9, the substances of this Category will be non-ionised.