1-Butyl-3-methylimidazolium Tetrafluoroborate as a Green Reaction Medium

Biographical Sketches

Yogesh R. Jorapur was born in Dombivli, Thane, Maharashtra, India in 1976. He received a B.Sc. (Chemistry) degree in 1998 from Mumbai University and M.Sc. (Organic Chemistry) degree in 2000 from Pune University. He is currently in the 2^nd year of his Ph.D. under the tutelage of Prof. Dae Yoon Chi, Inha University, Inchon, S. Korea. His research interest is mainly focused on the applications of ionic liquids as reaction media.

Introduction

Ionic liquids [1] as green high tech reaction media of the ­future are considered as environmentally friendly sub­stitutes for volatile organic solvents, because of their low vapor pressures and their ability to act as catalysts. They also possess several other attractive properties, [2-4] including chemical and thermal stability, non-flammability, high ionic conductivity, a wide electrochemical potential window, and are 100% recyclable solvent media for synthesis and catalytic processes.

Ionic liquids first described in 1914, [5] consist of inorganic anions and nitrogen containing organic cations whose chemical and physical properties can be finely tuned for a range of applications by varying the cations or anions.⁴

Ionic liquid, [bmim][BF₄], can be easily prepared [6] from N-methylimidazole. The crude 1 obtained was purified by filtering through silica gel followed by washing with ­saturated Na₂CO₃ to give pure 1 (Scheme 1), which is now commercially [7] available. It showed enhanced reactivity and selectivity in reactions like hydrogenation, [8] coupling, [9] carbonylation, [10] and cycloaddition [11] in comparision with several other ionic liquids.

The toxicological and/or eco-toxicological effects [12] of 1 in comparision with volatile organic solvents is uncertain.

Abstracts

(A) Dupont and co-workers [8] carried out ruthenium-catalyzed enantioselective hydrogenations in ionic liquids. The chiral [RuCl2(S)-BINAP]2NEt3 complex was shown to catalyze the asymmetric hydrogenation of 2-(6-methoxy-2-naphthyl)acrylic acid in 1 and i-PrOH, which afforded the anti-inflammatory drug, (S)-naproxen in 80% ee.
(B) To overcome the drawbacks such as incorporation of the catalyst, and/or poor reagent solubility, Welton and co-workers [9] carried out Suzuki cross-coupling in 1, which showed significant increase in catalyst reactivity without loss of yield or degradation of catalyst.
(C) Enhancement in the solubility and nucleophilicity of KF was achieved in 1. Kim and co-workers [13] reported nucleophilic substitution reactions such as halogenations, acetoxylation, nitrilation, and alkoxylation of mesyloxyalkane in 1; significant reactivity and improved selectivity were observed.
(D) Monteiro and co-workers [10] reported palladium-catalyzed alkoxycarbonylation of styrene in 1/cyclohexane. Using (+)-neomenthyl diphenylphosphine [(+)-NMDPP] as a ligand, the product was obtained in 89% yield and 99.5% regioselectivity.
(E) As an environmentally friendly alternative, 1 was used as reaction media for butylbutyrate synthesis [14] catalyzed by free Candida antartica lipase (CAL) B with 2% water content at 50 °C and showed enhanced synthetic activity.
(F) Several two-phase bio-catalytic transformations have been ­reported in ionic liquids. The epoxidation [15] of cyclohexene by peroxyoctanoic acid, generated in situ by Novozyme 435-catalyzed reaction of octanoic acid with 60% aqueous H2O2, proceeded smoothly in 1.
(G) The cycloaddition [11] of propylene oxide and carbon dioxide (2.5 MPa) has been conducted in ionic liquids. Optimal results were obtained with 1 as catalyst.

References

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