Silica gel, support

Amorphous silica is used as a pigment and filler in paints and coatings. It also is used as an abrasive, absorbent and catalyst support. Silica gel is a common desiccant and adsorbent. It is used in analytical chemistry as a packing material in chromatography columns and in clean-up of organic extracts to remove interference in trace analysis of organic pollutants. 

Notes. (1) Solvents were distilled prior to use. Thin-layer chromatograms were run on glass supported silica gel 60 plates (0.25-mm layer) (E. Mark No. 5765). 

Benzoin 23 could be used instead of benzil 22, provided that the microwave-assisted cyclocondensation is performed on inorganic support (silica gel or alumina) under solvent-free conditions [40]. A related diversity-oriented approach towards imidazoles utilized the cyclocondensation of unsymmetrical keto-oximes with aldehydes in the presence of NH4OAc [41] (Scheme 16). Hydroxyimidazoles 24 were formed in the cyclization step and... 

Isonicotinic acid hydrazide (isoniazid 275), a drug used in treating tuberculosis269, has been 1 -labelled264 by introduction of a [nC]cyano group at the 2-position of the pyridine ring of l-methoxy-4-methoxcarbonyl pyridinium methyl sulphate and subsequent treatment of the 1 -labelled methyl ester 276 with hydrazine hydrate. The reaction has been carried out on a solid support (silica gel) to yield methyl 2[11C]cyano-isonicotinate in 32.4+12% (EOB) yield. 275 was obtained in 10% (EOB), radiochemical... 

Figure 1 Macrocycle host attached to a solid support (silica gel) using a connector arm...

In the present paper, we will focus in a first step, on the results obtained using the same parent support (silica gel) modified by alkyl-dimethyl chlorosilanes of various alkyl chain length 1, 4, 8 and 18 carbon atoms. This material presents a disordered mesoporous texture [8]. 

A similar, physically bound CuBr catalyst on a silica gel support (L-29) was also employed for MMA polymerization.149 The polymers had narrow MWDs (MJMn 1.3), but the molecular weights were higher than the calculated values. The recycled catalysts have a lower activity but lead to better control of molecular weights i.e., the Mn agreed well with the calculated values, and the MWDs were narrower MJ Mn 1.2). The physically supported catalysts were further employed for the synthesis of end-functionalized polymers.150 When physically supported silica gel catalysts are packed into a continuous column reactor, a controlled polymerization is possible.151... 

Silica gel has been used as reagent and absorbent as well as catalyst for many nucleophilic processes. Kotsuki and Shimanouchi have demonstrated an elegant epoxide ring opening using LiX supported silica gel (Scheme 5.35) in the absence of any solvent. 

Support = silica gel MP = methyl propionate MeOH = methanol Conv. = conversion of HCHO Select = selectivity to methyl methacrylate on HCHO basis Yield = single-pass yield of methyl methacrylate on HCHO basis. 

The reaction was performed on four different solid supports (silica gel, acidic alumina, montmorUlonite K-10, and zeolite HY). The best results were obtained by use of silica gel. 

The reaction was conducted under solvent-free conditions in a domestic MW oven using four different kinds of solid support (silica gel, acidic alumina, mont-morillonite K-10, and zeolite HY). The best results (77-94%) were obtained with silica gel and an optimized irradiation time of 2 min. In the absence of a solid support, under neat conditions, the products were obtained in low yields and the results were not reproducible. 

Figure 7. EDX line scan analysis of a metallocene/MAO-supported silica gel regarding the silicon and aluminum distribution in the volume.

Figure 8. (top) HRTEM micrograph of a metallocene/ MAO-supported silica gel. The EDX point analysis of the marked areas (a—b) are given in EDX spectra (bottom). 

Figure 9. (a) TEM micrograph of a supported metallocene/ MAO catalyst particle prepared by gas-phase Impregnation with TMA/H2O. (b) EDX line scan analysis of the metal-locene/MAO-supported silica gel regarding the silicon and aluminum distribution in the volume. Under this condition, the active sites are formed on the outer surface of the particle. The mean particle size shifted from 50 /rm for the silica support to 70 /nm for the catalyst. 

Support Silica gel Functional Group 5-methyl-8-hydroxy-quinoline Method/Coupling Agent Organic functional silane derivatives in solutions and surface Metal Ions Pb(ll), Cu(ll), Ni(ll), Cd(ll)... 

Dipolar cycloaddition of N-methyl-C-phenyl nitrone to methyl acrylate to yield isooxazolidines has been studied in the presence of several inorganic solid supports (silica gel, alumina) using microwave irradiation (Scheme 66). ... 

The analysis consisted of three stages, beginning with SPE of the dyes from pills, using a polyamide solid phase. Thin-layer chromatography was utiliz to screen the dyes via two solvent systems and solid supports (silica gel and cellulose), followed by confirmation by CE coupled to a diode array detector. The authors reported that the 14 dyes could be unambiguously identified with these parameters. 

An unusual new technique for the synthesis of alkyl iodides from chlorides or bromides involves passing the latter in the gas phase over a heated catalytic column of a solid support (silica gel), KI, and a PT catalyst (phosphonium salt) that can be free or immobilized on the silica matrix." The eluate vapours contain the product iodide. 

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