Ionic Liquids in Selective Oxidation: Catalysts and Solvents

Selective
oxidation has an important role in environmental and green chemistry
(e.g., oxidative desulfurization of fuels and oxidative removal of
mercury) as well as chemicals and intermediates chemistry to obtain
high-value-added special products (e.g., organic sulfoxides and sulfones,
aldehydes, ketones, carboxylic acids, epoxides, esters, and lactones).
Due to their unique physical properties such as the nonvolatility,
thermal stability, nonexplosion, high polarity, and temperature-dependent
miscibility with water, ionic liquids (ILs) have attracted considerable
attention as reaction solvents and media for selective oxidations
and are considered as green alternatives to volatile organic solvents.
Moreover, for easy separation and recyclable utilization, IL catalysts
have attracted unprecedented attention as “biphasic catalyst”
or “immobilized catalyst” by immobilizing metal- or
nonmetal-containing ILs onto mineral or polymer supports to combine
the unique properties of ILs (chemical and thermal stability, capacity
for extraction of polar substrates and reaction products) with the
extended surface of the supports. This review highlights the most
recent outcomes on ILs in several important typical oxidation reactions.
The contents are arranged in the series of oxidation of sulfides,
oxidation of alcohols, epoxidation of alkenes, Baeyer–Villiger
oxidation reaction, oxidation of alkanes, and oxidation of other compounds
step by step involving ILs as solvents, catalysts, reagents, or their
combinations.