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  • Stereoselective synthesis of 9-b-D-arabianofuranosyl guanine and 2-amino-9-(b-D-arabianofuranosyl)purine
  • 更新时间:2014-04-06;信息类型:SCI论文
  • 9-beta-D-Arabianofuranosyl guanine (6) and 2-amino-9-(beta-D-arabianofuranosyl)purine (8) were prepared from 2-amino-6-chloro-9-(2,3,5-triphenylmethoxyl-p-D-arabianofuranosyl)purine (4), a key intermediate which was stereoselectively prepared from 2,3,5-triphenylmethoxyl-D-arabianofuranose and 2-amino-6-chloro-purine. The yield of the intermediate was obviously improved and only P-isomer was formed by using the activated molecular sieve as environmental friendly catalyst, overcoming the defect that a 1: 1 mixture of alpha- and beta-isomers was formed, which was difficult to separate, when toxic mercury cyanide was previously used as catalyst.
  • 链接地址:http://www.ionicliquid.org/download/article/2014-04-06/46.html
  • Silica Gel Confined Ionic Liquid-Metal Complexes for Oxygen-Free Carbonylation of Amines and Nitrobenzene to Ureas
  • 更新时间:2014-04-06;信息类型:SCI论文
  • A new kind of silica gel confined ionic liquid containing a metal complex as heterogenized catalysts was prepared for the carbonylation of amines and nitrobenzene without molecular oxygen to afford the corresponding ureas with greatly enhanced catalytic activity (TOF exceeded 11000mol.mol(-1). h(-1)), with a much lower amount of ionic liquids being needed, with easy catalyst separation and possible reusability, and avoidance of the using of explosive CO + O-2 gas mixtures. Such an enhancement in catalytic activity may be derived from the effect of a high concentration of ionic liquid containing a metal complex due to the confinement into the nanopores or cavities of the silica gel matrix.
  • 链接地址:http://www.ionicliquid.org/download/article/2014-04-06/45.html
  • Pechmann Reaction in Non-Chloroaluminate Acidic Ionic Liquids under Solvent-Free Conditions
  • 更新时间:2014-04-06;信息类型:SCI论文
  • Four non-chloroaluminate acidic ionic liquids have been used as catalysts for Pechmann condensations of phenols under solvent-free conditions. SO3H-functionalized trifluoromethanesulfonate imidazolium ionic liquid has proved to be the most active catalyst. Ionic liquid loads as low as 5 mol % can be used leading to high yields with activated phenols at an oil bath temperature of 80 degrees C. The acidities of the four ionic liquids have also been tested using the Hammett method in dichloromethane. The results are consistent with their catalytic activities as observed in the Pechmann reaction of resorcinol. This methodology offers significant improvements for the synthesis of coumarins with regard to yield of products, simplicity in operation, and green aspects by avoiding toxic catalysts and solvents.
  • 链接地址:http://www.ionicliquid.org/download/article/2014-04-06/42.html
  • Silica-Gel-Confined Ionic Liquids: A New Attempt for the Development of Supported Nanoliquid Catalysis
  • 更新时间:2014-04-06;信息类型:SCI论文
  • A new concept of designing and synthesizing highly dispersed ionic-liquid catalysts was developed through physical confinement or encapsulation of ionic liquids (with or without metal complex) in a silica-gel matrix through a sol-gel process. We studied ionic liquids such as EMImBF4, BuMImBF4, DMImBF4, CMImBF4, BuMImPF6, either with or without [Pd(PPh3)2Cl2] and [Rh(PPh3)3Cl], in a silica-gel matrix (E=ethyl, Bu=butyl M=methyl, D=decyl, C=cetyl and Im=imidazolium). The contents of ionic liquids and loadings of Pd or Rh were 8-53 wt % and 0.10.15 wt %, respectively. Analyses of FT-Raman spectra showed that abnormal Raman spectra of the confined ionic liquids were observed in comparison with the bulk and pure ionic liquids. EMImBF4 and BuMImBF4 ionic liquids could be completely washed out from the silica-gel matrix under vigorous reflux conditions, but ionic liquids with larger molecular size, for example, DMImBF4 or CMImBF4, could be confined into the silica-gel nanopores relatively firmly. These results suggested that the ionic liquids were physically confined or encapsulated into the silica gel. The N2 adsorption measurements indicated that the silica-gel skeleton was mesoporous with 50-110 ? pore size after the BuMImBF4 ionic liquid was removed completely. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analysis showed that the silica-gel matrix was amorphous and non-uniformly mesoporous. Carbonylation of aniline and nitrobenzene for synthesis of diphenyl urea, carbonylation of aniline for synthesis of carbamates, and oxime transformation between cyclohexanone oxime and acetone were used as test reactions for these catalysts. Catalytic activities were remarkably enhanced with much lower amounts of ionic liquids needed with respect to bulk ionic-liquid catalysts or silica-supported ionic-liquid catalysts prepared with simple impregnation, in which the ionic liquid may be deposited as a thin layer on the support. Such unusual enhancement in catalytic activities may be attributed to the formation of nanoscale and high-concentration ionic liquids due to the confinement of the ionic liquid in silica gel; this results in unusual changes in the symmetry and coordination geometry of the ionic liquids.
  • 链接地址:http://www.ionicliquid.org/download/article/2014-04-06/38.html
  • Abnormal FT-IR and FTRaman spectra of ionic liquids confined in nano-porous silica gel
  • 更新时间:2014-04-06;信息类型:SCI论文
  • A new concept of designing and synthesizing highly dispersed ionic liquids was developed through physical confinement or encapsulation of them into silica gel matrix with sol–gel process. A series of silica gel confined ionic liquids were synthesized through this process and characterized by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS) and FTRaman analysis, and abnormal FT-IR and FTRaman spectra were observed. The silica gel matrixes confined ionic liquid BMImBF4 were further characterized by BET analysis after the ionic liquid was almost completely washed out by acetone under refluxing conditions and meso-porous silica gel matrixes were obtained according to the N2 adsorption measurements, which suggested that the particle-size of the dispersed ionic liquids was in nano-scale. In consideration of the results obtained together, it could be found that the abnormal FT-IR and FTRaman spectra were changed with the poresize of the silica gel matrix. For example, obvious abnormal FT-IR and FTRaman spectra appeared when the particle-size of ionic liquid BMImBF4 is smaller than 11 nm while they disappeared again if the corresponding particle-size >11 nm. These results indicated that nano-effect, or restriction effect, produced from the nano-pores of silica gel was the reason for the abnormal FT-IR and FTRaman spectra.
  • 链接地址:http://www.ionicliquid.org/download/article/2014-04-06/36.html