Yinyin Yu

Imidazolium Polyoxometalate: An Ionic Liquid Catalyst for Esterification and Oxidative Esterification

A new family of polyoxometalate‐based ionic liquids (POM‐IL) is synthesized, characterized, and employed as catalysts in the esterification of various alcohols with acetic acid. The ionic liquid catalyst shows high activity and gives excellent yields of esters. An emulsion forms between the IL catalyst and substrates during the reaction and promotes the catalytic process. After reaction, the emulsion can conveniently be broken by the addition of a weakly polar organic solvent to facilitate the separation of the catalyst. On the basis of the above results, a direct transformation of benzaldehyde to methyl ester under relatively mild conditions is also developed in the absence of any cocatalyst. Finally, the scope of the substrates and recyclability of the catalyst are also investigated.

Cooperative effects in catalytic hydrogenation regulated by both the cation and anion of an ionic liquid.

The use of transition-metal nanoparticles/ionic liquid (IL) as a thermoregulated and recyclable catalytic system for hydrogenation has been investigated under mild conditions. The functionalized ionic liquid was composed of poly(ethylene glycol)-functionalized alkylimidazolium as the cation and tris(meta-sulfonatophenyl)phosphine ([P(C(6)H(4)-m-SO(3))(3)](3-)) as the anion. Ethyl acetate was chosen as the thermomorphic solvent to avoid the use of toxic organic solvents. Due to a cooperative effect regulated by both the cation and anion of the ionic liquid, the nanocatalysts displayed distinguished temperature-dependent phase behavior and excellent catalytic activity and selectivity, coupled with high stability. In the hydrogenation of α,β-unsaturated aldehydes, the ionic-liquid-stabilized palladium and rhodium nanoparticles exhibited higher selectivity for the hydrogenation of the C=C bonds than commercially available catalysts (Pd/C and Rh/C). We believe that the anion of the ionic liquid, [P(C(6)H(4)-m-SO(3))(3)](3-), plays a role in changing the surrounding electronic characteristics of the nanoparticles through its coordination capacity, whereas the poly(ethylene glycol)-functionalized alkylimidazolium cation is responsible for the thermomorphic properties of the nanocatalyst in ethyl acetate. The present catalytic systems can be employed for the hydrogenation of a wide range of substrates bearing different functional groups. The catalysts could be easily separated from the products by thermoregulated phase separation and efficiently recycled ten times without significant changes in their catalytic activity.

Ionic Liquid Immobilized Nickel(0) Nanoparticles as Stable and Highly Efficient Catalysts for Selective Hydrogenation in the Aqueous Phase

Nickel nanoparticles (NPs) well-dispersed in the aqueous phase were conveniently prepared by reducing nickel(II) salt with hydrazine in the presence of the functionalized ionic liquid 1-(3-aminopropyl)-2,3-dimethylimidazolium bromide. UV/Vis spectroscopy, elemental analysis, thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS) show the presence of a weak interaction of the functionalized ionic liquid with Ni(II) and Ni(0) complexes. The face-centered cubic structure of the Ni(0) NPs was confirmed by X-ray diffraction (XRD) characterization. Transmission electron microscopy (TEM) images reveal that smaller Ni(0) particles of approximately 6-7 nm average diameter assemble to give larger, blackberry-shaped particles with an average diameter of around 35 nm. The Ni NPs were employed as highly efficient catalysts for the selective hydrogenation of C=C double bonds in the aqueous phase under mild reaction conditions (40-90 degrees C at 1.0-3.0 MPa), and the Ni(0) nanocatalysts in the aqueous phase are stable enough to be reused at least seven times without significant loss of catalytic activity during subsequent reuse cycles.

A Ti-substituted polyoxometalate as a heterogeneous catalyst for olefin epoxidation with aqueous hydrogen peroxide

The Ti-substituted polyoxometalates ([C12mim]5PTiW11O40, [CTA]5PTiW11O40 and [TBA]5PTiW11O40) were prepared and characterized by FT-IR, NMR, UV-vis and ICP-AES. Then the polyoxometalates (POM) were used as catalysts for the epoxidation of various olefins. It was found that the organic countercations had a considerable effect on the catalytic performance. In addition, UV-vis and the FT-IR spectroscopy indicated that the peroxo structure regarded as the active site for oxygen transfer was present even after the reaction, which led to the increasing reaction rate in the second run due to the disappearance of the induction period, as compared with that in the first run. A heterogeneous reaction mechanism has been suggested in olefin epoxidation catalyzed by a Ti-substituted polyoxometalate ([C12mim]5PTiW11O40) with aqueous hydrogen peroxide in ethyl acetate. The heterogeneous POM catalyst can be easily separated and recycled eight times without decreasing the catalytic activities.

Ionic liquid-Pluronic P123 mixed micelle stabilized water-soluble Ni nanoparticles for catalytic hydrogenation.

Ionic liquid (1-butyl-2,3-dimethylimidazolium acetate, [BMMIm]OAc)-Pluronic P123 mixed micelle stabilized water-soluble Ni nanoparticles were characterized by UV-vis, XRD, XPS and TEM and then employed for catalytic hydrogenation. It was demonstrated that the mixed-micelle stabilized Ni NPs showed excellent catalytic performance for the selective hydrogenation of CC and nitro compounds in the aqueous phase under very mild reaction conditions, and also the Ni NPs catalysts can be recycled at least for eight times without significant decrease in catalytic activity. The results of characterization revealed that the mixed micelle-stabilized Ni NPs catalysts were highly dispersed in aqueous phases even after five catalytic recycles. In addition, adding ionic liquid ([BMMIm]OAc) can affect the micelle structure of P123 solutions and thus afford an additional steric protection from aggregation of Ni NPs, resulting in enhancing stability and catalytic activity of Ni NPs.

Immobilization of polyoxometalate-based ionic liquid on carboxymethyl cellulose for epoxidation of olefins

A novel ionic liquid consisting of a PEG-functionalized ammonium cation and a lacunary-type phosphotungstate anion was synthesized and characterized structurally. The ionic liquid was then immobilized onto environmentally benign polymer-carboxymethyl cellulose by two different routes: the impregnation method and the co-precipitation method. The immobilized ionic liquid can be used as a catalyst for olefin epoxidation with aqueous hydrogen peroxide in ethyl acetate. It was found that both of the immobilized ionic liquid catalysts showed better catalytic activities and stability than the homogeneous analogue in consecutive runs. In particular, the ionic liquid catalyst immobilized by the co-precipitation method afforded a higher catalytic stability than the catalyst immobilized by the impregnation method. It is suggested that the crucial factor influencing the catalytic performance is the difference in the interactions between the heteropoly anions and the polymer supports.

Ionic Liquid–Catalyzed Internal Redox Esterification Reaction

Abstract The internal redox esterification of α,β-unsaturated aldehydes and alcohols was carried out using different ionic liquids (ILs) as catalysts and reaction solvents. The basic ionic liquid, 1-butyl-3-methylimidazolium acetate ([bmim]OAc), exhibited the best activity for this reaction. The influences of the amount of ionic liquid catalyst and reaction time on yield of saturated ester have been investigated. The results showed that ionic liquid anions have a crucial effect on the redox esterification of α,β-unsaturated aldehydes and alcohols. The nucleophilic carbenes generated in situ from the ionic liquid cation were believed to be actual active species for this reactions. GRAPHICAL ABSTRACT

Polyoxometalate and copolymer-functionalized ionic liquid catalyst for esterification

A new room-temperature ionic liquid (RTIL) consisting of a polyoxometalate (POM) anion and tri-block copolymer (P123)-functionalized imidazolium cation was synthesized and utilized as a halogen-free catalyst for esterification. The catalytic system was a homogeneous solution at the beginning of the reaction, but an emulsion formed during the course of the reaction, and a progressive phase separation of the catalyst occurred at 0 °C over the course of 3 h. Dynamic light scattering (DLS), transmission electron microscopy (TEM), and Fourier transform/infrared spectroscopy (FT/IR) have been used to characterize the properties of the IL during the reaction. The new IL catalyst was found to be highly efficient in the esterification of various alcohols and can be recycled at least seven times.