Ab initio studies of the effect of the fluorination on deprotonation reaction of the benzene sulfonic acid.

We carried out quantum chemical calculations to analyze the effects of fluorination on the activation energy (Ea) of sulfonic group deprotonation by water molecules. The model molecule was 2,3,4,5,6-pentafluorobenzenesulfonic acid (5FBSA), which was obtained by substituting all aromatic hydrogen atoms of benzenesulfonic acid (BSA) for fluorine atoms. The target hydration level was three. Our analysis indicated that the Ea of deprotonation in 5FBSA was lower than that of BSA, suggesting that the cation of 5FBSA was stabilized. Previous studies have reported that fluorinated molecules have a lower Ea to deprotonation and a stabilized deprotonated state even at a hydration level of three. This effect is attributed to the strong electron withdrawing ability of fluorine. However, compared with non-aromatic molecules, the Ea of deprotonation of aromatic molecules is slightly higher, and the overall energy change (ΔE) is lower, even if the molecule is fluorinated. [ABSTRACT FROM AUTHOR]