Determination of acidic constants of tetrafluoro-p-hydroquinone

Fluorine substituent has significant effect on acidity of hydroquinones. The acidic constants of tetrafluoro-p-hydroquinone, H2TFQ, have been determined experimentally and theoretically by means of reliable electrochemical, spectroscopic and ab initio calculations. While first acidic constant, pKa1, has been successfully determined by means of cyclic voltammetry, determination of the second acidic constant, pKa2, was not feasible by this technique. Instead, UV-vis spectroscopy with the application of chemometrics method of rank annihilation factor analysis has been employed to determine the second acidic constant. Standard ab initio quantum chemistry calculations have been also carried out to determine both pKa1 and pKa2. The theoretical values for acidic constants (pKa1 = 6.7 and pKa2 = 9.4) are in good agreement with the experiments (pKa1 = 6.4 and pKa2 = 10.0), which were obtained using UV-vis spectroscopy. This work is in line with our previous research that addressed the electrochemical behavior of H2TFQ [J. Fluorine Chem. 129 (2008), 222-225].