Abstract

ZABIHI, Fatemeh et al. Solvent Effects on Protonation Constants of Betanin in Different Aqueous Solutions of Methanol at T = 25 ºC. J. Mex. Chem. Soc [online]. 2019, vol.63, n.2, pp.94-102.  Epub Apr 20, 2020. ISSN 1870-249X.  https://doi.org/10.29356/jmcs.v63i2.789.

The protonation constants of the betanin (pKa1, pKa2, and pKa3) were determined in mixed solvent of water and methanol containing 0, 10, 20, 30, 40, 50, 60, 70, and 80 % (v/v) methanol, using a combination of the spectrophotometric and potentiometric methods at T = 25 ºC and constant ionic strength (0.1 mol.dm-3 NaClO4). The obtained protonation constants were analyzed using Kamlet, Abboud, and Taft parameters. KAT parameters are α (hydrogen-bond donor acidity), β (hydrogen-bond acceptor basicity), and π* (dipolarity/polarizability). In this study, a good linear relationship was obtained between protonation constants (on the logarithmic scale) and dielectric constant (ɛ) of the water-methanol mixed solvents. It was found that the dual-parameter correlation between log10K,s and π*, β give us the best result in various volume fractions of methanol for water-methanol mixed solvent. Finally, the results are discussed in terms of the effect of the solvent on the protonation constants.

Keywords : Protonation Constants; Methanol; Spectrophotometric; Potentiometric; Solvent.

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