Large degree of racemization observed in the amide bond forming reaction on silica gel

A systematic study of racemization from the coupling of DNB-L-Leu and 3-aminopropyl silica gel with several amide coupling reagents was investigated. Significant amounts of racemization were observed from all except one coupling reagent. In comparison, similar reactions completed in homogeneous solution can be accomplished with much lower racemization and in much higher yields.     

Extraction of uranium by amine, amide and benzamide grafted covalently on silica gel

Organic complexing moieties such as amine, 2°-amide and benzamide functional groups were covalently linked to silica gel by performing organomodification on commercially available silica gel. The extraction of uranium as a function of pH, time, concentration of uranium and the effect of ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- on the distribution coefficient of uranium by sorbent was studied. The data was fitted into Langmuir adsorption isotherm. The selectivity of the sorbents towards uranium were found to decrease in the order gel-amine >> gel-benzamide ≅ gel-2°-amide at all pHs. The presence of metal ions such as Fe²⁺, Co²⁺, Ni²⁺ and CO₃ ^2- were found to decrease the distribution coefficients (K _d, ml/g) of uranium and the decrease was very high when Fe²⁺ was present. The performance of the sorbent, gel-amine, under a given column condition was tested by following the breakthrough curve of uranium up to C/C ₀ = 0.025. The sorbent was found to be good for the quantitative pre-concentration of uranium from a large amount of sodium. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synthesis of large-ring lactams by a carbene-anion bond forming reaction

Treatment of large-ring lactams 1 with potassium t-butoxide results in the formation of bicyclic structures 2 . Evidence was obtained to support the formation of 2 through a carbene-anion coupling. The structures of a series of bicyclic lactams 2 have been rigorously defined.     

Oxidative bromination reaction using Cu-perfluorophthalocyanine-immobilized silica gel catalyst under mild reaction conditions

A simplified, facile route has been applied for the grafting of copper(II) perfluorophthalocyanine complex onto functionalized silica gel. The resulting organic-inorganic hybrid material is used as an efficient and recyclable catalyst for the regioselective oxidative bromination of various aromatic substrates using KBr/H₂O₂ as the reagents, affording high yields under mild conditions. High catalytic activity efficiency could be attributed to the heterogenization of soluble metal complexes on the high surface area host.     

Sorption of transition metals by silica gel with fixed amide of maleic acid and polyhexamethyleneguanidine on the surface

The possibility was determined for covalent binding of amide of maleic acid and polyhexamethyleneguanidine to a silica gel surface previously activated with cyanur chloride. Adsorption of Zn(II), Cd(II), Pb(II), Cu(II), Mn(II), Ni(II), Fe(III), and Co(II) cations from aqueous solution with a modified silica obtained was studied. The possibility of subsequent formation on the surface of mixed ligand complexes     

Low-temperature reaction of trialkoxysilanes on silica gel: a mild and controlled method for modifying silica surfaces

The room temperature reaction of 4-(triethoxysilyl)butyronitrile, 4-TBN ((C2H5O)3Si(CH2)3CN), on weakly hydrated silica samples pretreated at 393 K has been studied by desorption experiments and by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy at different aging times under various water partial pressures. The reaction is demonstrated by the decrease of desorption of 4-TBN with time and the simultaneous disappearance of the 2980 and 1394 cm(-1) signals in the DRIFT spectra, assigned to the CH3 moiety of the ethoxy functions. Water partial pressure is shown to have a crucial effect on the rate and efficiency of the process as, after 6 days, for samples kept at room temperature under vacuum, ca. 50% of the silane has reacted, while for those kept in a water-saturated atmosphere the silane reaction reaches 96%. Although the silane appears to be irreversibly bonded to the surface, no definite conclusion may be drawn from these preliminary results as to the nature of the bonding (grafting or coating). These samples are compared to modified silicas prepared according to conventional methods. The same extent of silane reaction (50%) is achieved for preadsorbed samples kept under vacuum and either cured at 473 K for 30 h or kept at room temperature for 6 days. A mild and controlled modification of silica by triethoxysilanes can thus be achieved by first physisorbing known amounts of the modifying silanes from an organic solvent on pretreated silica and then letting the samples mature for a few days at room temperature in a water-saturated atmosphere.     

氯化钙在粗孔硅胶上的单层分散研究

由于氨合成反应平衡的限制,使得冷冻分离氨的能量消耗较大[1].开发一种对氨比对H2、N2具有更高吸附能力和很强选择性的吸附剂,实现一次循环即获得纯氨产品,由此达到节能降耗的目的.     

Influence of reaction parameters on the structure of in situ rubber/silica compounds synthesized via sol–gel reaction

In situ silica was synthesized in three non‐vulcanized rubber matrices, namely natural rubber, styrene‐butadiene rubber, and EPDM (ethylene‐propylene diene ter‐polymer), using the sol–gel method with tetra‐ethoxysilane (TEOS) as silica precursor and hexylamine as catalyst. The effect of the reaction parameters such as the amount of TEOS, the reaction time (15–120 min), and the type of rubber was explored. Transmission electron microscopy was used to study the gradient in silica content and particle size over the sample thickness. The diffusion gradient of TEOS and catalyst solution in the rubber matrix responsible for the gradient was studied with Fick's law. An excellent dispersion of silica was obtained for all rubbers, even for the very non‐polar EPDM, without the use of any additives to improve the dispersion. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 967–978     

多孔活性硅胶的制备及吸附性能的研究

以硅酸钠和氯化铵为原料,通过添加表面活性剂制备高吸附活性的多孔硅胶.采用SEM,IR和XRI)等手段对硅胶样品的结构和形貌进行表征,并利用紫外分光光度法研究硅胶样品对垃圾渗滤液中有机污染物的吸附性能.结果表明,合成的硅胶样品是由纳米量级的无定形二氧化硅颗粒组成的多孔性、疏松状物质,对垃圾渗滤液中的有机物分子具有较强的吸...     

Phosphine-free perfluoro-tagged palladium nanoparticles supported on fluorous silica gel: application to the Heck reaction

The immobilization of phosphine-free perfluoro-tagged palladium nanoparticles Pd-1 on fluorous silica gel (FSG) and their utilization in the Heck reaction have been investigated. High yields of vinylic substitution products have been obtained. Recycling studies have shown that the solid-supported palladium catalyst can be readily recovered and reused several times without significant loss of activity. Reactions and recovery of the solid-supported palladium catalyst system can be carried out in the presence of air, without any particular precaution.     

Solvent-free cyclopalladation on silica gel

Tertiary, secondary and primary benzylamines, as well as structurally different oxazolines readily reacted with Pd(OAc)₂ on silica gel to form cyclopalladated complexes containing a five or six-membered palladacycle with a (sp²)C-Pd or (sp³)C-Pd bond. The complexes were obtained in 45-98% yield, which is comparable with or exceeds the yields reported for preparation of the same compounds in solution. Aliphatic (sp³)C-H bond activation took place in the cyclopalladation of (S)-2-tert-butyl-4-phenyl-2-oxazoline on SiO₂ leading to the exclusive formation of the corresponding endo palladacycle, whereas two products were reported for the same reaction performed in AcOH.     

HPLC on pentalfuoroanilinopropyl silica gel

Summary The preparation of a new pentafluoroanilino-phase for HPLC is described. The retention times (t_r) of about twenty aromatic hydrocarbons have been determinated. It has been shown that the aromatics were eluted according to the number of rings. The influence of water content in the mobile phase is commented.     

Diastereoselective construction of azetidin-2-ones by electrochemical intramolecular C-C bond forming reaction

A convenient method for synthesis of optically active azetidin-2-ones using electrochemical oxidation has been exploited. The method consists of a diastereoselective intramolecular C-C bond forming reaction between active methylene and methyne groups through an electrochemical system in which positive iodine species acted as mediators under mild conditions.