Silica solid support

M. Pawlowska, Enantiomer separations by normal HPLC systems with permethylated /3-cyclodextrin dynamically coated on silica solid supports, J. Liquid Chromatogr., 14 2213 (1991). 

Stationary Phase—The immobile phase responsible for retaining the sample component in the column. In RPLC, this is typically the layer of hydrophobic groups bonded on silica solid support materials. 

The mciY)-functionalized acid 12 and its -functionalized analogue 13 were attached to aminopropyl silica gel u.sing an amide-coupling reagent (BOP). Tliis produced two new silica solid supports, both of which contain amidocalix[4J-pyrrole recognition groups, gel M (me.vo-hook) and gel B ( -hook) (Scheme 1). 

For convenience, the partition coefficients P s nd P s are usually treated by considering the entire volume of the silica support particles. One should keep in mind, however, that only the surface bonded layer is actually involved in the partitioning equilibria. The calculation of P s from eq. 5.1 r uires knowledge of Vs, which cannot be determined easily. Usually, the difference between the empty column volume and Ihe packed colunrn void volume is taken as Vs, which gives an overestimation of this volume since it includes the entire volume occupied by the silica solid support particles, rather than just the true stationary phase. Although the use of such a value will result in accurate values for P m, the values obtained for P s and Pms will be expected to be significantly in error, with underestimated partition coefficients. An approach that completely excludes any volume associated with the base silica material should thus be used. 

Transition metals absorbed onto a solid support metal Pd,Pt, Ni, Rh support Carbon, alumina, silica solvent EtOH, EtOAc, Et20, hexanes, etc. 

Flash chromatography is widely employed for the purification of crude products obtained by synthesis at a research laboratory scale (several grams) or isolated as extracts from natural products or fermentations. The solid support is based on silica gel, and the mobile phase is usually a mixture of a hydrocarbon, such as hexane or heptane, with an organic modifier, e.g. ethyl acetate, driven by low pressure air. (Recently the comparison of flash chromatography with countercurrent chromatography (CCC), a technique particularly adapted to preparative purposes, has been studied for the separation of nonchiral compounds [90].)... 

As a unichiral template which is used as a stationary phase itself, or which is bonded to a solid support (silica particles or fused silica capillaries). 

The allcylation of a number of aromatic compounds through the use of a chloroa-luminate(III) ionic liquid on a solid support has been investigated by Holderich and co-workers [87, 88]. Here the allcylation of aromatic compounds such as benzene, toluene, naphthalene, and phenol with dodecene was performed using the ionic liquid [BMIM]C1/A1C13 supported on silica, alumina, and zirconia. With benzene, monoalkylated dodecylbenzenes were obtained (Scheme 5.1-56). 

The synthesis of imidazoles is another reaction where the assistance of microwaves has been intensely investigated. Apart from the first synthesis described since 1995 [40-42], recently a combinatorial synthesis of 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles has been described on inorganic solid support imder solvent-free conditions [43]. Different aldehydes and 1,2 dicarbonyl compounds 42 (mainly benzil and analogues) were reacted in the presence of ammonium acetate to give the trisubstituted ring 43. When a primary amine was added to the mixture, the tetrasubstituted imidazoles were obtained (Scheme 13). The reaction was done by adsorption of the reagent on a solid support, such as silica gel, alumina, montmorillonite KIO, bentonite or alumina followed by microwave irradiation for 20 min in an open vial (multimode reactor). The authors observed that when a non-acid support was used, addition of acetic acid was necessary to obtain good yields of the products. 

The problems of stationary phase erosion can be largely overcome by solvent-generated LLC, where the stationary liquid phase is generated dynamically by the mobile phase, in this approach, one of the phases of an equilibrated liquid-liquid system is applied as a mobile phase to a solid support which is better wetted by the other phase of the liquid-liquid system. The support is usually silica when the stationary phase is aqueous or a polar solvent and a reversed-phase chemically bonded support when the stationary phase is a nonpolar solvent. Under these Conditions a multimolecular layer is formed on the surface of the solid support which has the properties of the liquid phase in... 

Silica is the most commonly used solid support. Treatment with complexes bearing alkoxy- or chlorosilane functional groups is a common way to generate supported complexes on silica or any inorganic oxide containing surface silanol (Si-OH) groups (Scheme 7.2).23,24... 

Adsorption of carotenoids on activated silica-alumina results in their chemical oxidation and carotenoid radical formation. Tumbling of carotenoid molecules adsorbed on solid support is restricted, but the methyl groups can rotate. This rotation is the only type of dynamic processes which is evident in the CW ENDOR spectrum. 

Jeevarajan, A. S., L. D. Kispert et al. (1993b). An ENDOR study of carotenoid cation radicals on silica-alumina solid support. Chem. Phys. Lett. 209 269-274. 

Fused silica capillary columns of various internal bores and of lengths in the range 25 to 50 m are mainly employed for analytical separations. A variety of polar and non-polar column types are available including those open tubular types with simple wall coatings (WCOT), those with coatings dispersed on porous solid-supports to increase adsorbent surface area (SCOT) and porous layer open tubular (PLOT) columns. Important stationary phases include polyethylene glycol, dimethylpolysiloxane and different siloxane copolymers. Various sample introduction procedures are employed including ... 

Even when the trifluoroaeetyl-(+)-camphor ligand is linked to a solid support (Hypersil silica 205d), if retains its activity both in terms of yield and optical induction. 

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