The Hammett acidity functions (H0) of mixtures of 1-butyl-3-methylimidazolium
hydrogensulfate with sulfuric acid, and 1-butylimidazolium hydrogensulfate with
sulfuric acid, were measured using UV dyes. A linear correlation between H0 value
and the concentration of sulfuric acid was observed for both mixtures. H0 values
of the mixtures were also measured using an NMR probe, mesityl oxide. The
H0 values calculated from the mesityl oxide experiments agreed well with the H0
values calculated from the UV dye data. 1-Butyl-3-methylimidazolium hydrogensulfate,
1-butylimidazolium hydrogensulfate, 1-butyl-3-methylimidazolium chloride,
1-butylimidazolium chloride, 1-butylimidazolium dihydrogenphosphate and 1-butyl-
3-ethylimidazolium acetate were examined as both solvent and nucleophile in nucleophilic
substitution reactions with 4-methylbenzyl alcohol. Only 1-butyl-3-ethylimidazolium
acetate failed to react. The mechanism of the nucleophilic substitution
reactions of 1-butylimidazolium hydrogensulfate and 1-butyl-3-methylimidazolium
chloride were investigated using Hammett plots. All benzyl alcohols substituted
via the SN2 mechanism in 1-butyl-3-methylimidazolium chloride, however both the
SN2 and SN1 mechanisms were seen in 1-butylimidazolium hydrogensulfate. Finally,
the structures of hydrogendichloride ionic liquids ([HCl2]−) were investigated using
infrared spectroscopy.