Solvent effects on protonation of crotonic acid in different aqueous solutions of ethanol

The protonation constants of crotonic acid has been determined in different aqueous solutions of ethanol (0 – 40 % v/v) at 25 °C and constant ionic strength (0.1 mol dm3 sodium chloride), using a potentiometric technique. The determined protonation constant values were analyzed in term of Kamelt-Tafts parameters. Single parameter correlation of the values versus α (hydrogen-bond donor acidity), β (hydrogen bond accepter basicity), and π* (the polarity/polarizibility) are poor in all solutions but multi–parameter correlation represents significant improvement with regards to the single–parameter models. Also, a linear relationship is observed when the experimental values of the logarithm of protonation constants is plotted versus the calculated ones, while all the Kamlet and Taft's parameters are considered. Finally, the results are discussed in terms of the effect of solvent on protonation of crotonic acid.

Keywords:

Solvent effect , crotonic acid , protonation constant , potentiometic method