The polarity of ionic liquids (ILs), usually denoted as ET(30) by the solvatochromic probe Reichardt’s dye, is one of the most fundamental properties that remarkably affect the solvation and chemical reaction in ILs. It was generally accepted that the ET(30) of ILs was dominated by the nature of the cation. However, in this work, it was found that the common ammonium-based ILs showed strongly anion-dependent ET(30). For example, the ET(30) value for [N1124][DCA] and [N1124][NTf2] is 49.0 and 59.0 kcal mol 1, respectively, while the corresponding imidazolium ILs bearing the same anions possess nearly identical ET(30), the ET(30) value for [BMIm][DCA] and [BMIm][NTf2] is 51.4 and 51.6 kcal mol 1, respectively. Moreover, introduction of an ether group was found to increase the ET(30) of imidazolium ILs while having no obvious effect on that of ammonium-based ILs. The Kamlet–Taft parameters and density functional theory (DFT) calculations indicated that the distinct result is related to different stabilization of the ground state of Reichardt’s dye 30. In imidazolium ILs, the main interactions between ILs and zwitterionic dye involve both coulombic interaction (between the cation and the phenolate oxygen atom) and H-bonding interaction (between the acidic hydrogen on imidazolium ring and the phenolate oxygen atom). However, with the ammonium ILs lack of active hydrogen, the dye is only stabilized by the coulombic interaction between the cation and the phenolate oxygen atom. Interestingly, in both imidazolium and ammonium-based ILs, the spiropyran–merocyanine equilibrium exhibit obvious anion-dependent photochromism, solvatochromism, and thermal relaxation.

★★★☆☆ Zhang SG,Chen ZJ,Qi XJ,et al. Distinct Influence Of The Anion And Ether Group On The Polarity Of Ammonium And Imidazolium Ionic Liquids[J]. New J. Chem.,2012,36:1043-1050.

A series of silica, glass and molecular sieves supported chloroaluminate ionic liquids (ILs) were prepared and their catalytic performance on the trimerization of isobutene based on C4 mixture was investigated. Interestingly, it was found that the carrier played a key role in the reaction route. Among these supported catalysts, silica supported chloroaluminate ionic liquid was highly efficient for the trimerization of isobutene. X-ray photoelectron spectroscopy (XPS) and differential scanning calorimetry (DSC) characterizations suggested that the synergy between Al2Cl7− anion and silica induced the catalytic activity for isobutene oligomerization due to the strong interaction between ILs and silanol group. The reaction conditions including loading amount, temperature, reactant concentration, and space velocity for the isobutene oligomerization were optimized. Ultimately, complete conversion of isobutene and 91.4% selectivity of trimers were obtained over the IL/silica (30 wt.%) catalyst at mild conditions. Moreover, catalyst stability and deactivation were preliminarily studied.

Keywords: Ionic liquid; Silica supported; Isobutene; Trimerization; C4 feed

★★★☆☆ Liu SM,Shang JP,Zhang SG,et al. Highly Efficient Trimerization Of Isobutene Over Silica Supported Chloroaluminate Ionic Liquid Using C4 Feed[J]. Catalysis Today,2012,200:41-48.

Catalytic syntheses of cyclohexyl carbamates via alcoholysis of dicyclohexyl urea (DCU), which can be synthesized from CO2 and amines, were first investigated with low-molecular-weight alcohols, i.e., methanol, ethanol, butan-1-ol. TiO2/SiO2 catalyst was prepared by wet impregnation method using tetrabutyl titanate as titanium source. The catalyst was characterized by inductively coupled plasma/atomic emission spectroscopy (ICP/AES), N-2 adsorption, X-ray diffraction (XRD), field emission/scanning electron microscopy (FE/SEM), transmission electron microscopy TEM), and NH3/temperature-programmed desorption (TPD) in detail. TiO2/SiO2 with 5 wt % loadings and calcination at 600 degrees C exhibited better catalytic activity, and excellent yields of > 95 % with 98 % selectivities for desired carbamates were achieved. Accordingly, the strong acidity was considered to be responsible for its superior activity. Moreover, the catalytic activity can essentially be preserved during the recycling tests. The scope was also expanded to synthesize other alkyl or aryl carbamates via alcoholysis of the corresponding disubstituted ureas, and 94 % yields with 96 % selectivities can be achieved. It provided a good candidate for the organic carbamates syntheses via a phosgene/halogen-free and effective route.

Keywords: alcoholysis;  disubstituted ureas;  N-substituted carbamates;  TiO2/SiO2;  phosgenefree

★★★☆☆ Wang LG,Shang JP,Liu SM,et al. Environmentally Benign And Effective Syntheses Of N-substituted Carbamates Via Alcoholysis Of Disubstituted Ureas Over Tio2/sio2 Catalyst[J]. Pure And Applied Chemistry,2012,84:461-471.

★★★☆☆ Zhang SG,Liu SM,Zhang Y,et al. Photoinduced Isothermal Phase Transition Of Ionic Liquid Crystals[J]. Chemistry – An Asian Journal,2012,7(9):2004-2007.

Hydrotalcite-supported nano-gold (Au/HT) was found to be a highly efficient heterogeneous catalyst for the dehydrogenative synthesis of amide from alcohol and amine. Amines and alcohols with different structures could be converted into the amides under mild reaction conditions with up to 98% isolated yields. Mechanism exploration suggested that ester might be the reaction intermediate.

Keywords: Amides; Gold; Heterogeneous catalysis; Amines; Alcohols

★★★★☆ Jiangling Zhu,Yan Zhang,Feng Shi,et al. Dehydrogenative Amide Synthesis From Alcohol And Amine Catalyzed By Hydrotalcite-supported Gold Nanoparticles[J]. Tetrahedron Letters,2012,53:3178-3180.

A Pd–Au/SiO2 catalyst was prepared for the oxidative imination of toluenes with up to 99% yields in the absence of dehydrating agents under mild conditions. Nanoparticles with a PdO layer and PdO–Au core may be the active structure for the reaction.

★★★★☆ Cui XJ,Shi F,Deng YQ. Oxidative Imination Of Toluenes Catalyzed By Pd–au/silica Gel Under Mild Reaction Conditions[J]. Chem. Commun.,2012,48:7586-7588.

★★★★★ Zhang Y,Cui XJ,Shi F,et al. Nano-gold Catalysis In Fine Chemical Synthesis[J]. Chem. Rev.,2012,112:2467-2505.

Gas-phase structure, hydrogen bonding, and cation–anion interactions of a series of 1-(2-hydroxyethyl)-3- methylimidazolium ([HOEMIm]+)-based ionic liquids (hereafter called hydroxyl ILs) with different anions (X=[NTf2]–, [PF6]–, [ClO4]–, [BF4]–, [DCA]–, [NO3]–, [AC]– and [Cl]–), as well as 1-ethyl-3-methylimizolium ([EMIm]+)-based ionic liquids (hereafter called nonhydroxyl ILs), were investigated by density functional theory calculations and experiments. Electrostatic potential surfaces and optimized structures of isolated ions, and ion pairs of all ILs have been obtained through calculations at the Becke, three-parameter, Lee–Yang–Parr/6-31+G(d,p) level and their hydrogen bonding behavior was further studied by the polarity and Kamlet–Taft Parameters, and 1H-NMR analysis. In [EMIm]+-based nonhydroxyl ILs, hydrogen bonding preferred to be formed between anions and C2–H on the imidazolium ring, while in [HOEMIm]+-based hydroxyl ILs, it was replaced by a much stronger one that preferably formed between anions and OH. The O–H___X hydrogen bonding is much more anion-dependent than the C2–H___X, and it is weakened when the anion is changed from [AC]– to [NTf2]–. The different interaction between [HOEMIm]+ and variable anion involving O–H___X hydrogen bonding resulted in significant effect on their bulk phase properties such as 1H-NMR shift, polarity and hydrogen-bond donor ability (acidity, a).

Keywords: calculation; cation–anion interaction; hydrogen bonding; hydroxyl; ionic liquids; polarity

★★★☆☆  Zhang SG,Qi XJ,Ma XY,et al. Investigation Of Cation–anion Interaction In 1-(2-hydroxyethyl)-3-methylimidazolium-based Ion Pairs By Density Functional Theory Calculations And Experiments[J]. J. Phys. Org. Chem.,2011,25(3):248-257.

A new class of azobenzene-based photoresponsive ionic liquids was prepared and showed reversible modulation of ionic conductivity in specific solvents under alternative UV/visible light irradiation.

★★★★☆ Zhang SG,Liu SM,Zhang QH,et al. Solvent-dependent Photoresponsive Conductivity Of Azobenzene-appended Ionic Liquids[J]. Chem. Commun.,2011,47:6641-6643.

Due to their unique properties, ionic liquids have offered great potential for developing clean catalytic technologies. After a short introduction of their advantages in green catalysis, recent advances in ionic liquid catalysis are reviewed with emphasis on four hot fields, viz. biomass conversion in ionic liquids, catalytic production of fine chemicals in ionic liquids, supported ionic liquid phase catalysis, as well as Friedel–Crafts reactions in ionic liquids. In particular, through selected samples, we show here the advantages and potential of ionic liquids in exploring cleaner catalytic technologies, as compared to traditional catalytic processes. Finally, further development of ILs in catalysis is briefly prospected.

★★★★☆ Green Chem., 2011, 13, 2619–2637