Guoying Zhao

Mannich reaction using acidic ionic liquids as catalysts and solvents

Several Bronsted acidic ionic liquids were synthesized and successfully used as solvents and catalysts of three-component Mannich reactions of aldehdyes, amines, and ketones at 25 °C. The used Bronsted acidic ionic liquids include l-butyl-3-methylimidazolium hydrogen sulfate ([Bmim]+[HSO4]−), l-butyl-3-methylimidazolium dihydrogen phosphate ([Bmim]+[H2PO4]−), 1-methylimidazolium p-toluenesulfonic acid ([Hmim]+Tsa−) and 1-methylimidazolium trifluoroacetic acid ([Hmim]+Tfa−). Higher yields were obtained in the presence of [Hmim]+Tfa− in comparison with other Bronsted acidic ionic liquids. The [Hmim]+Tfa− was reused four times without considerable loss of activity.

Efficient production of 5-hydroxymethylfurfural and alkyl levulinate from biomass carbohydrate using ionic liquid-based polyoxometalate salts

Direct conversion of fructose into 5-hydroxymethylfurfural (HMF) and alkyl levulinate is achieved by making use of ionic liquid-based polyoxometalate salts (IL-POMs) as solid acid catalysts. Among these solid acids, phosphotungstic acid-derived IL-POM shows the highest catalytic performance in both the HMF and ethyl levulinate (EL) formation. A study for optimizing the reaction conditions such as the reaction time and the temperature has been performed. High HMF and EL yields of up to 99% and 82%, respectively, are obtained from fructose under the investigated conditions. Moreover, the generality of the catalyst is further demonstrated by processing representative di- and polysaccharides such as sucrose and inulin with good yields to HMF (76% from inulin and 48% from sucrose) and EL (67% from inulin and 45% from sucrose), again under mild conditions, thereby eliminating the separate hydrolysis step before the dehydration reaction. The catalyst recycling experiment indicates that the adsorption and accumulation of oligomeric products on the catalyst surface results in a partial deactivation of catalyst. The mechanism research reveals that a major pathway for EL formation involves a fructose-to-HMF transformation followed by HMF etherification and rehydration of HMF-ether to give EL. The research highlights an efficient, environment-friendly and recyclable solid acid for biomass valorization.

Selective hydrogenation of phenol and derivatives over an ionic liquid-like copolymer stabilized palladium catalyst in aqueous media

A combination of “water soluble” palladium nanoparticles stabilized by an ionic liquid-like copolymer and phosphotungstic acid synergistically promotes selective hydrogenation of phenol to cyclohexanone. The nanocatalyst preparation and selective phenol hydrogenation are successfully combined into a one-pot process in this research. Conversion exceeding 99% was achieved with >99% selectivity under an atmospheric pressure of hydrogen in aqueous media. Moreover, even at room temperature, >99% conversion and >99% selectivity could still be obtained. The generality of the catalyst system for this reaction was demonstrated by selective hydrogenation of other hydroxylated aromatic compounds with similar performance.

Mid-infrared spectroscopic properties and energy transfer of Er3+/Yb3+ co-doped bismuth germanate glass.

An Er3+/Yb3+ co-doped bismuth germanate glass is synthesized and analyzed. The radiative characteristics and mid-infrared spectroscopic properties are investigated under excitation of a conventional 980 nm laser diode. The prepared glass possesses higher spontaneous transition probability (68.82 s(-1)) and larger calculated emission cross-section (7.73×10(-21) cm2) corresponding to the 4I11/2→4I13/2 transition. The calculated energy migration coefficient (CDD) among Yb3+ ions is larger than the energy transfer coefficient (CDA) from Yb3+ to Er3+, indicating the energy transfer process assisted with energy migration. The excellent spectroscopic properties along with the outstanding thermal stability suggest that this glass may become an attractive host for developing solid state lasers operating in the mid-infrared range.

Isobutane/butene alkylation catalyzed by ionic liquids: a more sustainable process for clean oil production

The alkylation of isobutane with butene is an important refining process for the production of a complex mixture of branched alkanes, which is an ideal blending component for gasoline. The current catalysts used in industrial processes are concentrated H2SO4 and HF, which have problems including serious environmental pollution, equipment corrosion, potential safety hazard, high energy consumption in waste acid recycling, etc. Solid catalysts are another type of catalyst for this alkylation; however, they suffer from problems related to rapid deactivation. Ionic liquids (ILs) can be considered as catalysts of the third generation to replace traditional catalysts in isobutane/butene alkylation to produce clean oil. In this review, alkylation catalyzed by various kinds of acidic ILs, including Lewis acidic ILs (such as chloroaluminate ones) and ILs containing Bronsted acidic functional groups (e.g., –SO3H, [HSO4]−), is reviewed. The currently reported ILs used in the catalysis of isobutane alkylation and their corresponding catalytic activity are summarized and compared. This will help the readers to know what kinds of ILs are effective for the alkylation of isobutane with butene and to understand which factors affect the catalytic performance. The advantages of the catalysis of isobutane/butene alkylation by ILs include tunable acidity of the catalyst by varying the ion structure, limited solubility of the products in the IL phase and therefore easy separation of the alkylate from the catalyst, environmental friendliness, less corrosion of equipment, etc., thus making catalysis by ILs greener. The mechanism and kinetics of the alkylation catalyzed by ILs are discussed. Finally, perspectives and challenges of the isobutane/butene alkylation catalyzed by ILs are given.

Investigations on a series of novel ionic liquids containing the [closo-B12Cl12](2-) dianion

A series of novel imidazolium, ammonium, phosphonium and pyridinium based salts with the [closo-B12Cl12]2− dianion were synthesized by straight forward metathetic reactions and characterized by physical methods. The melting point of each salt with [closo-B12Cl12]2− dianion was measured to investigate if it can be classified in the field of ionic liquids. Thermodynamic results showed observed higher melting points, which can be illustrated both from the higher symmetry of the dianion and the enhanced electrostatic forces of the salts synthesized. Given the above mentioned reasons, the [closo-B12Cl12]2− dianion containing ionic liquids can be designed either by optimizing the structure of cation, especially of the alkylation pattern which naturally affected the cations packing efficiency, or by shielding the cation–dianion interactions with appropriate hydrogen bond (H-bond) donors to form ‘quasi-eutectic ILs’. This can be rationalized by the increased interionic separation and the consequent weakening of the electrostatic forces. Additionally, influence of H-bond interactions on the phase transition temperatures of [closo-B12Cl12]2− dianion containing salts was also investigated and related changes were explained by ab initio calculations, illustrating weak H-bond interactions between the hydroxy protons and the chlorine atoms which showed modest effects on the melting points of the salts with [closo-B12Cl12]2− dianion.

Transesterification between isoamyl acetate and ethanol in supercritical CO2, ionic liquid, and their mixture

Abstract The transesterification between isoamyl acetate and ethanol in supercritical (SC) CO 2 , 1- n -butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF 6 ], a room temperature ionic liquid), and in CO 2 +[bmim][PF 6 ] mixed solvent was studied at 65.0xa0°C and different pressures. p -Xylenesulfonic acid (p-TSA) was used as the catalyst. Results showed that the phase behavior of the reaction system affects the equilibrium conversion of the reaction in SC CO 2 and CO 2 +[bmim][PF 6 ] considerably. The mixtures of SC CO 2 and ionic liquids, which are environmental benign solvents, may have potential applications in tuning the equilibrium conversions.

Tautomeric equilibrium of ethyl acetoacetate in compressed CO2+ethanol and CO2+methanol mixtures

Tautomerism equilibrium of ethyl acetoacetate (EAA) in compressed CO2 + methanol and CO2 + ethanol mixtures was studied by UV-Vis spectroscopy at 308.15 K and different pressures. The volume expansion coefficient (alpha) of the solvents at different pressures was also determined. The relative permittivity (epsilon) of CO2 + methanol and CO2 + ethanol mixtures at different conditions was calculated using the Kc and Onsager solvent parameter. The equilibrium constant (Kc) of EAA in the binary mixtures increases considerably with increasing pressure or volume expansion coefficient. The relative permittivity or the polarity of the binary mixtures decreases sharply with increasing volume expansion coefficient in the range of 0 < alpha < 1.5. However, as the volume expansion coefficient exceeds 1.5, the relative permittivity decreases slowly. In other words, the dissolution of CO2 in the polar solvents can reduce the polarity of the solvents significantly in the low volume expansion coefficient range, and the polarity of the solution is not sensitive to the volume expansion coefficient as its value is large enough. The difference in polarity of the two solvents reduces with increasing pressure and becomes negligible after volume expansion coefficient exceeds about 2.5.

Size effects of alkylimidazolium cations on the interfacial properties and CO2 uptake capacity in layered organic–inorganic imidazolium–TiO2 hybrids

Layered inorganic–organic TiO2–ILs hybrids with tunable basal spacing were fabricated through electrostatic interaction between 2D inorganic nanosheets and organic imidazolium-based ILs. Imidazolium cations with various sizes were intercalated into lamellar titanate nanosheets, forming layered structures with slabs turbostratic restacking. The effects of cation sizes on the interfacial properties of hybrids were comprehensively investigated by XRD, SEM, TEM, AFM, FT-IR, Raman and TG techniques. The results confirmed that the ratio of interlayer imidazolium cations declined with increasing carbon chain length. A CO2 absorption experiment was conducted and TiO2–ILs compounds displayed enhanced CO2 absorption capacity with the increase of alkyl chain length, which could be attributed to the synergistic interfacial effects induced by diverse interactions between ILs and inorganic nanosheets. An absorption mechanism was proposed on account of ion-exchangeable characteristic of these layered hybrids and the intercalated H2O molecules were found to play a crucial role in CO2 uptake.

Tetracarboxyl-Functionalized Ionic Liquid: Synthesis and Catalytic Properties

Novel tetracarboxyl-functionalized 2,2-biimidazolium-based ionic liquids (ILs) with different anions were synthesized in two steps from readily available and sustainable starting materials including ammonium acetate, glyoxal, and halogenated propionic acid. The functionalized IL exhibited higher catalytic activity towards the cycloaddition of CO2 to terminal epoxides. With propylene oxide as a substrate, the optimum yield of propylene carbonate reached 82.7% at an initial CO2 pressure of 2.0 MPa for 4 h at 140 degrees C. Moreover, the functionalized IL catalyst displayed a high stability and can be reused for at least five cycles without obvious loss of catalytic activity. The results provide a simple and economical way to synthesize multi-functionalized imidazolium-based ILs with versatile potential applications.