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A series of hydrophilic N,N-dimethylpyrrolidinium- and N,N-dimethylpiperidinium-based ionic liquids (ILs) have been prepared and applied as reaction media in the Wacker oxidation of styrene by hydrogen peroxide using PdCl2as the catalyst. The efficiency of these ILs was compared with hydrophilic and hydrophobic imidazolium systems (including those with nitrile functionalities). The nature of the ionic liquid strongly influences the product distribution. In particular, in hydrophobic ILs, relevant amounts of 1,3-diphenyl-1-butene arising from styrene dimerization were detected, in addition to the expected phenylmethylketone. The formation of 1,3-diphenyl-1-butene may be attributed to the formation of Pd(0) species from “ClPdOH” (probably formed during the Wacker process) in a side-reaction. Consequently, the ability of the IL to favor or disfavor the reoxidation of “ClPdOH” to “ClPdOOH” by hydrogen peroxide, giving an homogeneous phase or a biphasic system, appears to be the main factor affecting selectivity. [ABSTRACT FROM AUTHOR]

A series of task-specific ionic liquids (TSILs) based on glycerylimidazolium cations have been prepared by reaction of 1-chloropropanediol, a compound obtainable from glycerol (a widely available and in-expensive waste product), with the appropriate base (1-H-imidazole, 1,2-dimethylimidazole and 1-methyl-1-H-imidazole). The reaction of 3-(1H-imidazol-1-yl)propane-1,2-diol with chloroalkanes, bromoalkanes and alkyl mesylates gave the corresponding salts which were characterized. The possibility to use these ILs in palladium catalyzed reactions was evaluated, evidencing good catalyst stability and a high recyclability. [ABSTRACT FROM AUTHOR]

To reduce the emission of NO from fossil fuel combustion and the energy consumption associated with NH3 production, the development of simple and efficient methods to transform NO into high-value-added NH3 is essential. Here, we report the efficient catalytic hydrogenation of NO to NH3 under mild reaction conditions by the synergistic catalysis of functionalized ionic liquids (FILs) and Pd catalysts. In this system, an FIL [TEPA][Im] acted as both an absorbent and a catalyst. The presence of [TEPA][Im] enhanced the catalytic performance by changing the coordination and electronic environment of Pd on the Pd/C catalyst. First, NO was absorbed by [TEPA][Im]; then, the hydrogenation of absorbed NO to NH3 was performed at a low temperature via the synergistic catalyzation of [TEPA][Im] and Pd/C. The effects of various factors on NO hydrogenation to NH3 were also investigated. Remarkably, Pd/C exhibited outstanding properties in the formation of NH3 with a high yield of 67% in the FIL [TEPA][Im] under the conditions of 100 °C and an H2 pressure of 0.5 MPa. [TEPA][Im] could be reused multiple times and the product NH3 could be recovered by flashing. [ABSTRACT FROM AUTHOR]

novel ionic liquid functionalized magnetic nanoparticle was prepared by anchoring an imidazolium ionic liquid bearing triethylene glycol moieties on the surface of silica-coated iron oxide nanoparticles. The material proved to be an effective host for the immobilization of a Pd catalyst through a subsequent simple ion-exchange process giving a highly water dispersible, active and yet magnetically recoverable Pd catalyst (Mag-IL-Pd) in the Suzuki-Miyaura coupling reaction in water. The as-prepared catalyst displayed remarkable activity toward challenging substrates such as heteroaryl halides and ortho-substituted aryl halides as well as aryl chlorides using very low Pd loading in excellent yields and demonstrating high TONs. Since the catalyst exhibited extremely low solubility in organic solvent, the recovered aqueous phase containing the catalyst can be simply and efficiently used in ten consecutive runs without significant decrease in activity and at the end of the process can be easily separated from the aqueous phase by applying an external magnetic field. This novel double-separation strategy with negligible leaching makes Mag-IL-Pd an eco-friendly and economical catalyst to perform this transformation. [ABSTRACT FROM AUTHOR]

The asymmetric carbonyl-ene reaction of trifluoropyruvate with five alkenes catalysed by [Pd{(R)-BINAP}](SbF6)2 were carried out in good yields and enantioselectivities (up to 96% yield and 96% ee) in low antimicrobial toxicity C2-substituted imidazolium ionic liquids (ILs). Toxicity data was included in the selection criteria for reaction optimisation after a preliminary IL screen. The Pd(ii) catalyst immobilised in an IL was recycled and reused up to 7 times without decrease of either yield or ee. One IL prepared, which was determined to be of high antimicrobial toxicity was assigned a low priority for future applications. [ABSTRACT FROM AUTHOR]

Silica and polyaniline supported palladium catalysts prepared by different techniques (incipient-wetness impregnation, deposition precipitation) using Pd(OAc)2or H2PdCl4as precursors were studied in the liquid-phase hydrogenation of citral under addition of several ionic liquids ([BMIM][NTf2], [BMIM][PF6], [BMPL][NTf2], [BMIM][DCA], [BMPL][DCA], [B3MPYR][DCA]) either as catalyst coating or as additive. By an incipient-wetness technique, the catalysts were coated with a mixture of IL in acetone. The catalysts were characterized by nitrogen physisorption, whereby a decrease of surface area and pore volume was detected by the IL coated catalysts. Furthermore, ICP-OES, TEM and IR spectroscopy were performed to analyze metal content, particle size and coverage of the catalyst with ionic liquid. Citral hydrogenation was performed at 323 K and under 2.0 MPa H2in an autoclave with off-line GC analysis of the product mixtures. Beside stirrer speed, catalyst mass and citral concentration, the type and quantity of ionic liquid were also varied to elucidate their influence on activity and selectivity of the Pd/SiO2catalysed citral hydrogenation. The results show that treatment of the catalyst with ionic liquids—independent of catalyst coating or additive—leads to a selectivity enhancement of the desired product, citronellal. With [PF6]−or [NTf2]−as the IL anion, maximum selectivities were (60 ± 2)% at 70% conversion. In particular, dicyanamide (DCA) containing ionic liquids allow, under optimised conditions, the quantitative one-pot synthesis of citronellal, at least if the Pd/SiO2catalyst was coated with 29 wt% [B3MPYR][DCA]. By using polyaniline supported Pd catalysts and [BMIM][DCA] as additive, the consecutive hydrogenation towards dihydrocitronellal was less pronounced and the influence of metal precursor, support material and preparation technique of the catalyst could be excluded. Hydrogenation of pure citral on [BMIM][DCA] coated palladium catalysts offers a solvent-free, green route to citronellal in reasonable selectivities (S= 86%). [ABSTRACT FROM AUTHOR]