Silica gel acids

In column chromatography, the adsorbant is usually alumina but can be silica gel. Except that alumina tends to be basic and silica gel, acidic, I don t know why the former is used more often. Remember, if you try out an eluent (solvent) on silica gel plates, the results on an alumina column may be different. 

A S332 Phosphine 0.4 HgCN coated silica gel Acidic permanganate Color. 0.195-0.877... 

Incinerator stack emission air from contaminated building (CDDs) Addition of 13C-labeled TCDD to collection tube followed by collection of sample addition of internal standards Soxhlet extraction clean-up and sequential fractionation on acidic silica/potassium, silicate/silica gel, acidic alumina, carbon, neutral alumina columns volume HRGC/HRMS (MIM) 1 pg/m3 No data Smith et al. 1986b... 

The sample was denatured with formic acid and extracted with cyclohexane. The organic extracts were purified 130 on a Power Prep automated sample cleanup system with acidic silica gel, acid/base/neutral silica, and a carbon column. PCBs were eluted using dichloromethane and cyclohexane. The eluates were concentrated using a nitrogen evaporator for analysis by GC-HRMS... 

Reaction of anthranilic acid derivatives with formamide on silica gel, acidic alumina, or montmorillonite KIO under the action of MW irradiation generates quina-zolines in good yields [181]. Another one-step MW method for preparation of sub-... 

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. 

Silica gel Acid-catalyzed sol-gel method Photocatalytic degradation acid orange 7 [554]... 

The adsorption and the isolation technique is an efficient method in environmental problems, the toxic materials in sorts of industrial waste-water and exhaust ffimes can be absorbed by using various adsorbents, so that the ffimes and the liquid are up to standard of environmental protection. The key problem of the adsorption and the isolation technique lies in the adsorbents the commonly used adsorbents are activated carbon, silica gel, acid terra alba and zeolite molecular sieve, etc. [20-22]. But, not only the adsorption characterization of these materials but also the operating characterization and the reproducing ability of these materials are all very weak. So searching for a high quality adsorption material has become a subject concerned by experts all over the world. 

Silicon tetrafluoride is a colourless gas, b.p. 203 K, the molecule having, like the tetrahalides of carbon, a tetrahedral covalent structure. It reacts with water to form hydrated silica (silica gel, see p. 186) and hexafluorosilicic acid, the latter product being obtained by a reaction between the hydrogen fluoride produced and excess silicon tetrafluoride ... 

Silica gel is again obtained but silicon does not form the corresponding hexachlorosilicic acid since the small silicon atom is unable to coordinate six chlorine atoms. 

The beat method of drying, if time permits, is to place the crystals in a desiccator containing an appropriate substance (usually anhydrous calcium chloride, silica gel, or concentrated sulphuric acid) to absorb the solvent. More eflicient and more rapid drying is obtained with the aid of a vacuum desiccator (see Section 11,38 and Fig. 77, 38, 1). 

The o,p-dinitrostyrene (1 mmol) and ammonium formate (10 mmol) W ere dissolved in methanol and 10% Pd/ C (5% by wt) was added. The mixture was refluxed under nitrogen for 1 h. Formic acid (0.44 ml) w as added and reflux was continued for 0.5-1 h until the completion of the reaction (tic). The solution was filtered through Celite, evaporated in vacuo and eluted through silica gel with CH2CI2. 

A solution of 2,3-dimethylindole (145 g, 1 mol) in dry dioxan containing hydroquinone (100 mg) was treated with JV,JV,JV-trimethylbenzylammonium ethoxide (5 ml of a 40% solution in MeOH) and warmed to 35 C. Freshly distilled acrylonitrile (150 ml, 2.5 mol) was added at a rate such that the temperature did not rise above 40°C. The solution was then stirred overnight and diluted with 10% aq. acetic acid (11). The solution was extracted with CH Clj and the extract was washed with water and dried (MgS04). extract was then mixed with silica gel (800 g) and the solvent removed in vacuo. The silica was placed in a Soxhlet extractor and extracted with cyclohexane. The extract deposited the product as colourless needles (125 g, 63% yield). 

A solution of 6-bromoindole (O.lOmol) in toluene (200 ml) was treated with Pd(PPh3)4 (5mol%) and stirred for 30 min. A solution of 4-fluorophenyl-boronic acid (0.25 M, 0.15 mol) in abs. EtOH was added, followed immediately by sal aq. NaHCOj (10 eq.). The biphasic mixture was refluxed for several hours and then cooled to room temperature. The reaction mixture was poured into sat. aq. NaCl (200 ml) and the layers separated. The aq. layer was extracted with additional EtOAc (200 ml) and the combined organic layers dried (Na2S04), filtered and concentrated in vacuo. The solution was filtered through silica gel using hexane-CHjCl -hexanc for elution and evaporated. Final purification by recrystallization gave the product (19 g, 90%). 

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. 

In the course of mixture separation, the composition and properties of both mobile phase (MP) and stationary phase (SP) are purposefully altered by means of introduction of some active components into the MP, which are absorbed by it and then sorbed by the SP (e.g. on a silica gel layer). This procedure enables a new principle of control over chromatographic process to be implemented, which enhances the selectivity of separation. As a possible way of controlling the chromatographic system s properties in TLC, the pH of the mobile phase and sorbent surface may be changed by means of partial air replacement by ammonia (a basic gaseous component) or carbon dioxide (an acidic one). 

In the present work, the technique of XO and MTB immobilization onto silica gel in the form of its complexes with Fe(III) and Bi(III) respectively were found. The acid - base and chemical-analytical characteristics of solid-phase reagents were examined. The optimal conditions of quantitative recovery of Pb(II) and Zn(II) from diluted solutions, such as acidity of aqueous phase, the mass of the sorbents, the volume of solutions and the time of equilibrium reaching, were found. The methods of and F" detenuination were based on a competitive reactions of Zr(IV) with immobilized MTB and or F". Optimal conditions of 0,0 and F" determination in solution using SG, modified ion associates QAS-MTB (pH = 1,5, = 5-10 mol/1). 

R SiBr, trace MeOH. Methoxymethyl ethers are stable to these cleavage conditions. Methoxymethyl esters are unstable to silica gel chromatography, but are stable to mild acid (0.01 N HCl, EtOAc, MeOH, 25°, 16 h)." ... 

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