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Diss Factsheets

Physical & Chemical properties

Dissociation constant

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Description of key information

Dissociation constants of 4 thiol groups at 20°C:

Calculation with SPARC software, Dr. Knoell Consult GmbH (2009)

Key value for chemical safety assessment

Additional information

Four pKa values correspond to the dissociation of consecutive thiol groups. The dissociation of one thiol group is predicted in the environmentally relevant pH (pKa1=8.75).Therefore further validation of the predicted value was done. The dissociation constant of thiol groups appears at pH~10. pKa for the ethanethiol was calculated with SPARC (pKa of thiol group is 10.03 at 20°C and 9.94 at 25°C) and experimental value is 10.6 (Serjeant, E.P. & Dempsey, B. (1979) in SRC PhysProp database). The experimental and predicted by SPARC values differ by 0.66pKa with SPARC predictions lower than experimental values, which can lead to the conclusion that pentaerythritol tetrakis(3-mercaptopropionate) exists in non-ionised form in the whole range of the environmentally relevant pH. Calculations performed by SPARC online calculator are considered to be reliable and valid.