An acid-functionalized ionic liquid was entrapped within a silica gel to yield a recyclable liquid phase catalyst for the dehydration of rac-1-phenyl ethanol. Hot filtration tests showed that the activity was within the gel. Comparison with an analogous SILP system revealed fundamental differences in the properties and behavior of the materials.The discovery of facile ionic-liquid silica gel formation, 1,2 enabled the introduction of the first ionic liquid mediated sol-gel methods for the preparation of solid catalysts. [3][4][5] There followed a period of relatively few publications, during which ionic liquid gels were seldom investigated as catalysts. Currently, in parallel with the development of new classes of ionic liquid, and an increase in interest in softmatter, the area of ionic liquid gel catalysts has come back into focus, and new methods are emerging. This catalyst preparation methodology involves the entrapment of an ionic liquid within an inorganic oxide matrix by a gel method. At the same time a catalyst is co-entrapped, 3,[5][6][7] or, alternatively the catalytic center can be associated with the ionic liquid. 4 The worked-up material is then used as a heterogeneous catalyst. Materials consisting of an ionic liquid within a porous oxide are often referred to as ionogels. 8 These catalysts are a sub-set of the sol-gel prepared entrapped catalysts pioneered by Blum and Avnir. 9,10 In contrast to the gel-based catalysts, the related SILP catalysts, in which a heterogeneous catalyst is prepared by layering an ionic liquid on a pre-existing oxide matrix, have elicited an explosion of interest in the last ten years. Several reviews and concept articles have been published covering the method. [11][12][13][14][15][16][17] Exemplars have been demonstrated in the gaseous phase, 18 and using supercritical fluids, [19][20][21] and the application of SILP technology is at an advanced stage. The simplicity of the system enables a wide variety of matrices, ionic liquids and dopants to be screened easily. In liquid phase reactions the ease of addition and removal of the ionic liquid is potentially detrimental, and leaching can be facile.The development of supported nanoparticles catalysts by ionic-liquid assisted gel methods 3 has been recently developed further by Han and co-workers. 22 Catalysts with hierarchical pores were achievable by employing a metal salt (e.g. CaCl 2 ) initiated gelation. Doping with gold afforded a catalyst for esterification, and ruthenium catalyzed hydrogenation.The introduction of functionalized ionic liquids that are 'task specific' 23-26 opens up many new possibilities for the application of ionic liquids to liquid phase reactions, not least the incorporation of Brønsted-Lowry Acidic/Basic sites. Acid functionalized ionic liquids have been demonstrated as robust catalysts for continuous esterification in a miniplant. 27 In order to improve separation and prevent corrosion caused by liquid phase acids, it would be fortuitous to develop a heterogenised system. The combinat...
Molecular hydrogenation catalysts have been co-entrapped with the ionic liquid [Bmim]NTf(2) inside a silica matrix by a sol-gel method. These catalytic ionogels have been compared to simple catalyst-doped glasses, the parent homogeneous catalysts, commercial heterogeneous catalysts, and Rh-doped mesoporous silica. The most active ionogel has been characterised by transmission electron microscopy, X-ray photoelectron spectroscopy, and solid state NMR before and after catalysis. The ionogel catalysts were found to be remarkably active, recyclable and resistant to chemical change.
The application of basic ionic liquid gels (BILGs) as recyclable promoters of hydrogen borrowing chemistry was investigated. The hydrogen transfer initiated dehydration of 1,3-propanediol to propanal was catalysed by a [Cp*IrCl2(NHC)] complex promoted by BILGs containing [P6,6,6,14][OH]. Gels comprising a mixture of basic and hydrophobic ionic liquids gave the best results. The reaction proceeded in the ionic liquid [C2mmim][NTf2] enabling the continuous removal of propanal under reduced pressure. Tuning of the composition of the BILG led to a catalytic system that exhibited excellent conversion, selectivity and good recyclability.
Abstract.Combining whole cell biocatalysis and chemocatalysis in a single reaction sequence avoids unnecessary separations, and the associated waste and energy consumption. Bacterial fermentation has been employed to convert waste glycerol from biodiesel production into 1,3-propanediol. This 1,3-propanediol can be extracted selectively from the aqueous fermentation broth using ionic liquids. 1,3-propanediol in ionic liquid solution was converted to propionaldehyde by hydrogen transfer initiated dehydration (HTID) catalysed by a Cp*IrCl 2 (NHC) (Cp* = pentamethylcyclopentadienyl; NHC = carbene ligand) complex. The use of an ionic liquid solvent enabled the reaction to be performed under reduced pressure, facilitating the isolation of the product, and improving the reaction selectivity. The Ir(III) catalyst in ionic liquid was found to be highly recyclable.Introduction.
The water-soluble Rh(I)-THP complexes: RhCl(1,5-cod)(THP) (), [Rh(1,5-cod)(THP)(2)]Cl (), RhCl(THP)(4) (), and trans-RhCl(CO)(THP)(2) () have been synthesized and characterized, where THP = P(CH(2)OH)(3); - are the first potentially useful entries into Rh(I)-THP chemistry, while and are the first structurally characterized Rh(I)-THP complexes.
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