Registration Dossier
Registration Dossier
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EC number: 237-066-7 | CAS number: 13598-36-2
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
Phosphonic acid has dissociation constants of 1.80 and 6.20.
Key value for chemical safety assessment
- pKa at 20°C:
- 6.2
Additional information
The dissociation constants of hydrochloric, orthophosphoric, phosphorous, methylphosphonic, dimethylphosphonic, ethylphosphonic,
phenylphosphonic, diphenylphosphonic, phenylphosphourous acids in methyl, ethyl, n-propyl, n-butyl, and isopropyl alcohols have been determined from potentiometric titration curves. For Phosphonic acid this has resulted in dissociation constants in methyl- (5,86), ethyl- (7,13), n-propyl- 7,49), n-butyl- 7,75), and isopropyl- (7,44) alcohols. Dissociation constants for phosphonic acid in water have been reported in literature 1,80 and 6,20.
As the dielectric constant and the basicity of the solvent decrease, the acid strength falls but differentiating power of the solvent with the respect to the acid becomes enhanced, which makes possible differential titration of mixtures of acids which cannot be titrated differentially in aqueous solutions.
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