Acidity Scale in 1,2-Difluorobenzene

Equilibrium Brønsted acidity measurements have been established in 1,2-difluorobenzene (1,2-DFB), both in terms of acid pKa values measured using UV–vis spectrophotometry and unified pH (pHabs) values measured using differential potentiometry. The pKa values of 137 acids were obtained in 1,2-DFB, of which 33 have been directly measured, spanning 15 orders of magnitude of acidity. The rest have been estimated using pKa values in other solvents (acetonitrile, 1,2-dichloroethane). The pKa values have been anchored to the computational pKa values of 9 compounds. An experimental pHabs scale spanning more than 10 orders of magnitude has been established and aligned with the aqueous pH scale, resulting in a pHabsH2O range from −0.6 to 10.0. The potentiometrically measured pHabsH2O values and pHabsH2O values calculated independently from the experimental pKa values anchored to computational reference values agree well, which demonstrates the solid foundation of the underlying theory. These results open the possibility of quantitatively describing and measuring acid–base processes in 1,2-DFB, including potentiometric and UV–vis spectrophotometric pHabsH2O measurement.