The
acidity ladder scale in [BMPY][NTf2] was successfully
expanded toward the weak acidity region for about five more pK units compared to the previously established one. This
allows the acidities of a series of 13 aliphatic and aromatic nitroalkanes
to be determined accurately by the UV–vis spectroscopic method.
The acidity of nitroalkane in [BMPY][NTf2] covers ∼8
pK units and is significantly weaker than those in
DMSO and water. The Hammett plot for 4-substituted phenylnitromethanes
shows an excellent linearity with a slope of 2.06, which is rather
close to that in DMSO but significantly larger than that in water
(0.80). The regression analyses reveal that the solvation behavior
of [BMPY][NTf2] on the acidic dissociations of C–H
acids is similar to that of DMSO.