Silica gel dissolution

Purified by Soxhlet extraction with pet ether for 24h, followed by dissolution in acetone MeOH H20 90 5 5(v/v) and recrystn [Politi et al. J Phys Chem%9 2345 1985. Also purified by two recrystns from absolute EtOH, aqueous 95% EtOH, MeOH, isopropanol or a 1 1 mixture of EtOHrisopropanol to remove dodecanol, and dried under vacuum [Ramesh and Labes J Am Chem Soc 109 3228 1987]. Also purified by foaming [see Cockbain and McMullen Trans Faraday 5oc 47 322 1951] or by liquid-liquid extraction [see Harrold J Colloid Sci 15 280 I960]. Dried over silica gel. For DNA work it should be dissolved in excess MeOH passed through an activated charcoal column and evaporated until it crystallises out. 

Silica gel or alumina is usually used as the stationary phase. For these active phases a solvent of weak elution power is recommended for dissolution of the sample. A... 

TLC is used to determine copper in aluminum alloys. The process involves the sampling of the investigated material by anodic dissolution, development of TLC plate with acetone -f HCl -f HjO (70 15 15), and the identification of analyte by 1-(2-pyridylazo)-2-naphthol [70]. A TLC system comprising silica gel as stationary... 

The mechanism of action by which silane and siloxanes reduce expansion has been attributed to water repellence and air entrainment. Phosphate addition or coatings may interfere with the dissolution of silica gel and the formation of gel. It is also possible that phosphate reduces the osmotic potential and the swelling pressure in the gel. The manner in which air entrainment reduced expansion was attributed to the accommodation of alkali-silica gel in the air void system. For example, it was found that air-entrained concrete with 4% air voids could reduce AAR expansion by 40% [23]. 

A vial containing ( )-4-phenyl-3-butyn-2-ol (73.0 mg, 0.5 mmol) and catalyst (3.3 mg, 5.0 pmol) in t-amyl alcohol (1.0 mL) was capped with a septum and sonicated to assist catalyst dissolution. The resulting purple solution was cooled to 0 °C, and Ac20 (35.4 pL, 0.375 mmol) was added via a syringe. After 49 h, the reaction mixture was quenched by the addition of a large excess of MeOH. After concentration in vacuo, the residue was purified by FC on silica gel (EtOAchexanes, 1 9 to 1 1, then EtOAc hexanes EtsN, 9 9 2) to afford the (R)-acetate (68.6% ee by chiral-GC) and the (S)-alcohol (96.0% ee by chiral-GC on the acetate obtained following esterification). The calculated selectivity value at 58.3% conversion was s = 20.2. 

Another method applied to produce porous polymers is based on the addition of an inorganic matrix of well-known porosity, for example, silica gel or aluminum oxide, to the reacting mixture [210-212], Subsequent to the polymerization process, the inorganic pattern is eliminated by dissolution without destruction of the produced polymer [211], These materials develop a complex pore system [211-213],... 

So to develop a separation on a bare silica gel column, the chroma-tographer first would know that the C 8 approach had resulted in excessive retention and or tailing. Next the chromatographer would choose a pH at which the compounds are ionized. Often a pH of 7.8 is used since it is a basic pH within the safe range (i.e., no silica dissolution) and can be... 

When the yellow color of the reaction mixture persists, the introduction of diazomethane is interrupted and the solution is left overnight. After evaporation, the residue is dissolved in diethyl ether and the solution filtered through a small column of silica gel (—150-200 mg). The resulting colorless solution, containing the aromatic carboxylic acid esters, is again evaporated, and the residue, after dissolution in a small amount of dichloromethane, is transferred to a vial equipped with a Teflon-lined screwcap. 

To a magnetically stirred solution of 152 mg (1.0 mmol) of 4-cyclooctene-1-carboxylic acid in 5 mL of CHjdj is added 110 mg (1.1 mmol) of F,t3N and the reaction mixture is kept at r.t. for short period. The solution is then cooled to —78 C and solid 212 mg (I.I mmol) of phenylselenenyl chloride is added in one portion. The reaction mixture is stirred at that temperature until completion which is indicated hy the full dissolution of the red-orange selenenyl chloride. The pale-yellow solution is then allowed to reach r.t., concentrated and chromatographed (silica gel, CH, CI2). Removal of the solvent from the appropriate fractions gives the six-membered lactone 42A as colorless crystals yield 94% mp 67 -69 °C. 

Chemical stability of carbon over the entire pH range has led to considerable interest in the development of carbon-based stationary phases for RPC. Porous graphitised carbon with sufficient hardness, well-defined and stable pore structure without micropores, which ensures sufficient retention and fast mass transfer can be prepared by a complex approach consisting of impregnation of the silica gel with a mixture of phenol and formaldehyde followed by formation of phenol-formaldehyde resin in the pores of the silica gel, then thermal carbonisation and dissolution of the silica gel by hydrofluoric acid or a hot potassium hydroxide. solution [48. The retention and selectivity behaviour of carbon phases significantly differs from that of chemically bonded pha.ses for RPC. Carbon adsorbents have greater affinity for aromatic and polar substances so that compounds can be separated that are too hydrophilic for adequate retention on a Cix column. Fixed adsorption sites make these materials more selective for the separation of geometric isomers [49]. 

Samples dried initially at 60°C over silica gel for 24 hours. Note at 90% relative humidity, sufficient water was absorbed to cause dissolution of the solid. 

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