Synthetic silica gel

FCC. (1) Abbreviation for Food Chemicals Codex, a publication giving specifications and test methods for chemicals used in foods. (2) Abbreviation for fluid-cracking catalyst as used in the petroleum refining industry. Examples are powdered silica alumina, in which alumina is impregnated with dry synthetic silica gel, and various natural clays impregnated with alumina. 

Microporous particles 3-10 pm particles used as a solid stationary phase or as the inert support for bonded stationary phases in HPLC, usually made from synthetic silica gel by a proprietary process involving the hydrolysis of SiCl4 to form particles with a controlled pore size ca 5-50 nm). 

The aim of this chapter is more limited the emphasis is to provide an overview of the uses of synthetic silica gels and precipitated silicas that are of significant commercial importance. Excluded from this discussion are naturally occurring silicas, including products such as diatomaceous earth and so-called amorphous silica minerals (which are actually microcrystalline). Also excluded are fumed and arc silicas, forms of synthetic silica made at high temperature (in contrast to silica gels and precipitated silicas, which are generally made in aqueous solution and... 

Synthetic silica gel, Si02(H20)x, is a solid, amorphous form of hydrated silicon dioxide distinguished by its microporosity and hydroxylated surface [61]. It is produced according to the following reaction [34] ... 

Symmetry Shield and XTerra show, as expected, comparable selectivity behavior because of the shielding effect of the carbamate group. The difference in the matrix, synthetic silica gel in the case of Symmetry as opposed to hybrid material in the case of XTerra, shows an effect for polar pairs of analytes, as expected. XTerra is indeed a low covered material, but the activity of this matrix towards bases is low (see Fig. 26). 

The protecting groups are also used to solubilize synthetic intermediates in organic solvents, e.g. methylene chloride. Chromatography is then possible on a larger scale, since silica gel can be used as adsorbent. Six synthetic strategies have been developed (H. Kdster, 1979) ... 

Cellulose acetate Silica gel Scoured wool Sawdust Rayon waste Fluorspar Tapioca Breakfast food Asbestos fiber Cotton linters Rayon staple Starch Aluminum hydrate Kaolin Cryolite Lead arsenate Cornstarch Cellulose acetate Dye intermediates Calcium carbonate White lead Lithopone Titanium dioxide Magnesium carbonate Aluminum stearate Zinc stearate Lithopone Zinc yellow Calcium carbonate Magnesium carbonate Soap flakes Soda ash Cornstarch Synthetic rubber... 

Adsorbents are natural or synthetic materials of amorphous or microcrystalhne structure. Those used on a large scale, in order of sales volume, are activated carbon, molecular sieves, silica gel, and activated alumina [Keller et al., gen. refs.]. 

Florisil is a registered trademark of the Floridin Company, Warren, Pa., for a synthetic magnesia-silica gel. 

Likewise, synthetic 2//-azepines isomerize to 3//-azepines in refluxing chloroform (2-3 h) or in tert-butyl methyl ether at room temperature.291 The isomers can be readily separated by chromatography on silica gel, as the more basic 2//-azepines30 have lower Rf values. In contrast, 7-butyl-2//-azepin-2-acetic acid (11), obtained by heating the tert-butyl ester 10 with iodotrimethylsilane, is stabilized by intramolecular hydrogen bonding and shows no tendency to rearrange to the 3//-isomer.291... 

Synthetic Method 1 6-(dimethylamino)-3-(N-acetyl-N-methylamino)-10-acetylphenothiazine 8a (procedure from US. Patent 4,652,643).5 A mixture of 9.0g of 6-(dimethylamino)-3-(methylamino)phenothiazin-5-ium chloride (Azure B), 150.0ml of acetic anhydride, and lO.Og of zinc dust was maintained at reflux temperature for approximately 4 hs. After the reaction mixture was cooled to ambient temperature, it was poured into ice water with stirring and 300ml of toluene was added. After stirring for approximately 30 min the toluene layer was separated and washed twice, once with tap water and once with saturated aqueous sodium chloride solution. The toluene was then distilled off at reduced pressure. The residue which remained was dissolved in ethyl acetate and separated into various components by subjecting the solution to column chromatography using silica gel as substrate. Elution with ethyl acetate yielded a white-colored solid. 

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