Silica gels as supports

C (associated with various transition metals) Si Si02 (associated with Ti02) Aluminium silicate Silica gel as support or alone 1,2-Ethanediol Various alcohols and acids Various alcohols and acids Various alcohols and acids Terephthalic 129,130) 51,70) 124) 36,131, 134-137, 175)... 

C4C1im][PF6] [Rh(nbd)(PPh3)2][PF6] 2-40 bar, 22-50°C silica gel as support much higher TOF than in normal biphasic system effect of H2-pressure on activity studied no significant loss of activity after 18 cycles leaching below detection limits. [80]... 

The technique and instrumentation for liquid-liquid chromatography are much the same as for adsorption chromatography the main distinction lies in the nature of the stationary phase. In the original development of the method, Martin and Synge effected a separation of acetylated amino acids by using silica gel as support for an aqueous stationary phase. The mobile phase was a mixture of chloroform, butanol, and water. The method was used for analysis of the amino acids of various proteins. ... 

Wu and Siggia described a dynamic coating technique for the application of a liquid stationary phase - Poly G-300 - on a silica gel support. With heptane - ethanol (10 1) saturated with the stationary phase, strychnine and brucine could be separated. Polyethylene glycol coated silica gel as support has, however, been superseded by chemically bonded stationary phases. 

Diplamine was isolated from a Diplosoma sp. tunicate collected in the Fiji Islands. Flash column chromatography of the extract from the tunicate, using silica gel as support and CHCls/MeOH (90 10) as the eluting solvent, yielded 0.08% of diplamine. 

Tundo and Venturello [155,157] proposed a mechanism for a TC system using silica gel as support to account for the active participation of the gel by adsorption of reagents. Telford et al. [158] suggested an alternation shell model that requires periodical changes in the liquid phase filling the pores of the catalyst. Schlunt and Chau [150] from the same research group tried to validate this model using a novel cyclic slurry reactor, and indicated that only the catalyst in a thin shell near the particle surface was utilized. Tomoi and Ford... 

The test is based on chromophore modification resulting from the transformation of a 5,6-epoxide group to 5,8-epoxide in acid medium. This stmctural transformation means the loss of the conjugated double bond at positions 7 and 8 of the central polyene, causing a hypsochromic displacement of the absorption spectmm of 15-20 nm. Chromatographically, the 5,8-epoxide derivatives are more polar, so that chromatographic development by TLC using silica gel as support reveals bands with lower Rf values. 

The reactions of oxiranes with thiocyanate ion or with thiourea are usually done in homogeneous solution in water, alcohols or alcohol-acetic acid. The use of silica gel as a support for potassium thiocyanate in toluene solvent is advantageous for the simple work-up (filtration and evaporation of solvent) (80JOC4254). A crown ether has been used to catalyze reactions of potassium thiocyanate. 

A very interesting approach toward solid-supported synthesis under microwave heating was introduced by Chandrasekhar and coworkers [64], The authors developed a synthesis of N-alkyl imides on a solid phase under solvent-free conditions employing tantalum(V) chloride-doped silica gel as a Lewis acid catalyst (Scheme 7.53). 

Watanabe K, Royer GP. Polyethyleneimine silica-gel as an enzyme support. J Mol Catal 1983 22 145-152. 

Silica gel as a support for Rose Bengal was reported by Tamagaki, Liesner, and Neckers [303], A similar system had been reported previously with the sensitizer methylene blue [304], Rose Bengal immobilized to poly(2-hydroxyethyl methacrylate) has also been reported by Schaap [305],... 

Catalyst supports - [ALUMINUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - ACTIVATED] (Vol 2) - [ALUMINUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - HYDRATED] (Vol 2) - [ALUMINUMCOMPOUNDS - ALUMINIUMOXIDE(ALUMINA) - HYDRATED] (Vol 2) -silica gels as [SILICA - AMORPHOUS SILICA] (Vol 21) -silica sols as [SILICA - INTRODUCTION] (Vol21)... 

In 2003, Balalaie and co-workers published a new paper in the area of imidazole synthesis39. In the above examples reported by Westman, ammonium acetate and primary amines act as the nitrogen source for the imidazole ring. In the Baladie novel one-pot three-component method, ammonium acetate was replaced by benzonitrile derivatives. Thus, benzil, primary amines and benzonitrile derivatives underwent a condensation reaction on acidic silica gel as the solid support, Scheme 5.23. The reaction mixtures were irradiated for 8 min in a domestic oven under solvent-free conditions to give the products in 58-92% yield. 

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