Four non-chloroaluminate acidic ionic liquids have been used as catalysts for Pechmann condensations of phenols under solvent-free conditions. SO3H-functionalized trifluoromethanesulfonate imidazolium ionic liquid has proved to be the most active catalyst. Ionic liquid loads as low as 5 mol % can be used leading to high yields with activated phenols at an oil bath temperature of 80 degrees C. The acidities of the four ionic liquids have also been tested using the Hammett method in dichloromethane. The results are consistent with their catalytic activities as observed in the Pechmann reaction of resorcinol. This methodology offers significant improvements for the synthesis of coumarins with regard to yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents.

★★★☆☆ Keywords: acid catalysis; coumarins; determination of acidity; ionic liquids; Pechmann condensation

★★★☆☆ Adv. Synth. Catal. 2005, 347, 512– 516.

The reactions of propargylic alcohols, aliphatic primary amines, and CO2 were conducted in CuCl/[BMIm]BF4 system to produce the corresponding 5-methylene-1,3-oxazolidin-2-ones under relatively mild conditions. The products could be conveniently isolated by means of liquid-liquid extraction. The solvent ionic liquid as well as CuCl catalyst can be recovered and reused three times without appreciable loss of activity. By this green approach, several new 5-methylene-1,3-oxazolidin-2-ones were prepared in excellent yields and purity and were well-characterized.

★★★★☆ J. Org. Chem. 2005, 70, 7376-7380.

Reactions of propargylic alcohols with CO2 in a [BMIm][PhSO3]/CuCl catalytic system to produce the corresponding R-methylene cyclic carbonates were conducted with high yields. Mild reaction conditions, enhanced rates, improved yields, and recyclable ionic liquid catalyst systems are the remarkable features exhibited in this process. Furthermore, the use of large amounts of tertiary amines as well as nitrogen-containing organic solvent as employed in previously studies was avoided.

★★★★☆ Yanlong Gu, Feng Shi, and Youquan Deng. J. Org. Chem. 2004, 69, 391-394.

The solubilities of taurine (2-aminoethanesulfonic acid (H2NCH2CH2SO3H)) and sodium sulfate in a series of room temperature ionic liquids were examined, and a novel and greener separation method combined with chlorinated dialkylimidazolium ionic liquid as leaching reagent and organic solvent as precipitating reagent was developed. Using such process, selective separation of taurine from solid mixture containing large amount of sodium sulfate could be realized with 67–98.5% of single separation yield. The recycling of ionic liquid and organic solvent used in this separation process is possible.

★★★☆☆ Keywords: Ionic liquid; Leaching separation; Taurine; Solubility; Sodium sulfate

★★★☆☆ Y. Gu et al. / Separation and Purification Technology 35 (2004) 153–159.

Addition reactions of aliphatic acids with olefins to give corresponding esters have been investigated using SO3H-functionalized ionic liquids as dual catalyst–solvent. The isolation of the desired products could be achieved via simple decantation and ionic liquids could be reused continuously after dried in vacuum (5–12 mmHg) at ca. 80 ◦C.

★★★☆☆ Y. Gu et al. / Journal of Molecular Catalysis A: Chemical 212 (2004) 71–75.

SO3H-functionalized ionic liquids have been employed as an alternative reaction medium to conventional acid catalysts for oligomerization of various olefins, to produce branched olefin derivatives in high conversions and excellent selectivity. The ionic liquid plays a dual role as both catalyst and solvent, providing an efficient and reusable acidic catalyst system for the oligomerization of olefins.

★★★☆☆ Y. Gu et al. / Catalysis Communications 4 (2003) 597–601.