Ionic liquid with acidic properties is an important branch in the wide ionic liquid field and the aim of this article is to cover all aspects of these acidic ionic liquids, especially focusing on the developments in the last four years. The structural diversity and synthesis of acidic ionic liquids are discussed in the introduction sections of this review. In addition, an unambiguous classification system for various types of acidic ionic liquids is presented in the introduction. The physical properties including acidity, thermo-physical properties, ionic conductivity, spectroscopy, and computational studies on acidic ionic liquids are covered in the next sections. The final section provides a comprehensive review on applications of acidic ionic liquids in a wide array of fields including catalysis, CO2 fixation, ionogel, electrolyte, fuel-cell, membrane, biomass processing, biodiesel synthesis, desulfurization of gasoline/diesel, metal processing, and metal electrodeposition.

Acidic Ionic Liquids.

Brønsted acidic ionic liquids: Green catalysts for essential organic reactions

Accelerating the design of multi-component nanocomposite imprinted membranes by integrating a versatile metal–organic methodology with a mussel-inspired secondary reaction platform

We review activity on the usage of a biphase H2O/CO2 system in organic synthesis as a reaction medium of green chemistry. The formation of self-neutralizing carbonic acid in such a system eliminates the problem of salt disposal, typical for acid-catalyzed reactions with the usual mineral and organic acids. A large variety of different reactions to be performed in the biphase H2O/CO2 system are discussed in detail, including cyclization/cycloaddition, hydroformylation, hydrogenation, reduction, coupling, rearrangement, substitution, addition, halogenation, hydrolysis, oxidation and others. These reactions cover a significant part of modern organic synthesis. The main physical properties of carbonic acid being formed in the biphase H2O/CO2 system and their dependence on the temperature and pressure of saturating CO2 are analyzed. The problem with the search for the most optimal reaction conditions from the viewpoint of selection of appropriate pressure and temperature regions for the best yields and selectivity achievable is addressed in general. Comparison with formation and utilization of peroxycarbonic acids, alkylcarbonic acids and carbamic acids by means of saturation with pressurized CO2 of some other biphase systems is discussed in relationship to organic synthesis as well. The influence of a CO2 admixture on the unique properties of high temperature water, another promising green solvent, is also considered.

A biphase H2O/CO2 system as a versatile reaction medium for organic synthesis

Application of ionic liquids as recyclable green catalysts for selective alkylation of phenol

Several SO3H-functionalized ionic liquids were used as the acid catalyst for the isopropylation of m-cresol with isopropyl alcohol. The results indicated that the sequence of the catalytic activity was in good agreement with the acidity order. A 77.7% conversion of m-cresol and 48.7% selectivity for 2-isopropyl-5-methylphenol were observed in the presence of [TMBSA][HSO4] (TMBSA = N,N,N-trimethyl ammonium-N-butanesulfonic acid). The catalysts could be recovered by extraction and reused, and after eight times of recycling, a loss of catalytic activity was not evident.

Isopropylation of m-Cresol Catalyzed by Recoverable Acidic Ionic Liquids

The Bamberger rearrangement of N-aryllhydroxylamine was first realized in a CO2–H2O system. The yield of p-aminophenol was 80% when N-phenylhydroxylamine was heated at 100 °C for 1 h under 4 MPa CO2. The process fully avoids the need of inorganic strong acid and is environmentally benign.

Bamberger Rearrangement of N-Arylhydroxylamine to p-Aminophenol in a CO2–H2O System

The invention discloses a method for preparing paraaminophenol from N-phenylhydroxylamine in a pressurized CO2/H2O system, belonging to the technical field of fine chemical engineering. The method is characterized by comprising the step of reacting an N-phenylhydroxylamine water solution with concentration of 1*10 -4*10 mol.L for 0.25-12h by stirring under the conditions that the CO2 pressure is 0.5-14MPa and the reaction temperature is 40-140 DEG C to generate p-aminophenol. The invention has the advantages that carbonic acid formed by water and pressurized CO2 is used as an accelerating agent in a reaction system, thus permanent acid is avoided for using, CO2 is released after reaction, and neutralization can be realized by the reaction system.

Shijuan Liu

Papers

Isopropylation of m-Cresol Catalyzed by Recoverable Acidic Ionic Liquids

Bamberger Rearrangement of N-Arylhydroxylamine to p-Aminophenol in a CO2–H2O System

Method for preparing paraaminophenol from N-phenylhydroxylamine in pressurized CO2/H2O system