Registration Dossier
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EC number: 200-655-4 | CAS number: 67-48-1
Dissociation constant
Administrative data
Link to relevant study record(s)
- Endpoint:
- dissociation constant
- Data waiving:
- study scientifically not necessary / other information available
- Justification for data waiving:
- other:
Reference
Description of key information
In accordance with section 1 of REACH Annex XI, the dissociation constant study does not need to be conducted as the substance is a salt. Salts are reaction products of acids and bases that retain their ionic character. So, salts are never undissociated. The dissociation constant is only relevant for substances with an acid or basic character.
Key value for chemical safety assessment
Additional information
First of all, the dissociation constant study does not need to be conducted as the substance is a salt. Salts are reaction products of acids and bases that retain their ionic character. So, salts are never undissociated. The dissociation constant is only relevant for substances with an acid or basic character.
Nevertheless, choline chloride has an ionic substance and one of the ions contains an alcohol group which typically is able to dissociate. To cover this both facts as best approximation for the calculation of the dissociation constant of choline chloride, Choline (CAS 62 -49 -7) was used as input molecule for calculation model because of restrictions for pKa calculation of ionized structures. Using the OASIS Consensus, a pKa value of 10.6 at 25 °C was predicted, indicating dissociating properties.
Supporting information to confirm dissociation properties of choline chloride is given by OECD SIDS Report. Choline chloride is a quaternary amine salt, it can be easily concluded that it dissociates in water into the corresponding positively charged quaternary hydroxyl alkylammonium ion and the negatively charged chloride ion. The data was gained from secondary literature (OECD SIDS, 2004).
This is because typically salts (ionic bonding) are electrovalent substance. Electrovalent substances are made up of ions in the solid state. The oppositely charged ions are held together by strong electrostatic (coulombic) force of attraction. Due to these forces the ions cannot move. When these substances are dissolved in water, the ions free themselves from this binding. Thus the break up of an electrovalent compound into free mobile ions when dissolved in water or when melted, is called electrolytic dissociation. This is a 100 % dissociation. Nevertheless, the quaternary ammonium salt has an alcohol group which is from a chemically point of view able to dissociate. This dissociation from to alcohol into a proton and the hydroxyl-molecule is calculated as mentioned above and can be considered as the dissociation constant beside the electrolytic dissociation.
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