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Dissociation constant

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Description of key information

The key pKa value of 8.77 is estimated by ARChem's physicochemical calculator (SPARC). The value is supported by the experimental value of 8.76 determined at 24 °C (Golec et al., 1989). 

Key value for chemical safety assessment

pKa at 20°C:

Additional information

The pKA value has been estimated by ARChem's physicochemical calculator (SPARC). The tool uses computational algorithms based on fundamental chemical structure theory to estimate a wide variety of reactivity parameters strictly from molecular structure. For the substance BDEA (CAS 102 -79-4) a pKa of 8.77 has been calculated.

In a supporting study, experimental data have been determined for proton ionization of a series of hydroxyalkylamines and their hydrochloride salts whereby the only result for BDEA is reported in this robust study summary) (Golec et al., 1989). As a result thermodynamic data for amine proton ionization have been obtained. Titration curves for the aqueous solutions оf amines at 2% concentration were recorded at 24, 40 and 55 °С (± 1°C). Inflexion points in the pH versus titrant volume curves were identified graphically and the corresponding pH was taken as the logarithm of the proton ionization constant. The following pKa values were obtained: 8.76 (at 24 °C), 8.59 (at 40 °C) and 8.29 (at 55 °C).

Strong correlations were observed to link the degree of proton ionization and alkyl chain length. A good linear least squares fit of the data is found in most cases and the slopes were used to calculate heats of proton ionization (enthalpy), ΔHPl. Enthalpy of proton ionization (ΔHPl) of 30.0 kJ/mol (at 24 -55 °C) was calculated for BDEA. Additionally, free energy of 50.0 kJ/mol and entropy (ΔSPl) of 67 J/mol x K are also reported. Separate experiments did not indicate concentration dependent pKavalues in water.

At physiological pH values the investigated hydroxyalkylamines occur in cationic form.

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