We are pleased to share our latest open-access article titled “Acidity scale in 1,2-difluorobenzene” by John Paulo Samin, Helerin Roomet, Märt Lõkov, Sofja Tshepelevitsh, Jaan Saame, Agnes Heering, and Ivo Leito, published in ACS Omega (DOI: 10.1021/acsomega.6c02089).

In this work, we established equilibrium Brønsted acidity measurements in 1,2-difluorobenzene (1,2-DFB) in terms of pK_a values measured by UV-vis spectrophotometry and unified pH (pH_abs) values measured by differential potentiometry.

The pK_a scale in 1,2-DFB spans 15 orders of magnitude. The pK_a values were determined for 137 acids, 33 of which were directly measured (see Table 1). The remaining values were estimated using correlation equations relating pK_a values in other solvents (acetonitrile and 1,2-dichloroethane) to those in 1,2-DFB. The pK_a scale was anchored to the computational pK_a values of 9 acid compounds.

Furthermore, an experimental unified pH scale spanning more than 10 orders of magnitude was established. The scale was aligned to the aqueous pH scale, assigning pH_abs(H₂O) values to the buffer solutions of 22 acids ranging from −0.6 to 10.0 (see Table 2). The potentiometrically measured pH_abs(H₂O) values showed good agreement with the values independently calculated from experimental pK_a values anchored to computational reference values, demonstrating the solid foundation of the underlying theory.

These results open the possibilities for quantitatively describing and measuring acid−base processes in 1,2-DFB, including potentiometric and UV−vis spectrophotometric pH_abs(H₂O) measurement.

(This research was supported by grant PRG2557 from the Estonian Research Council and TK210 from the Estonian Ministry of Education and Research.)