Silica gel separation

All materials are to be handled under an inert gas atmosphere in Schlenk-type vessels.811 All solvents must be dry, degassed, and distilled from natrium wire. The preparation of FeCo2(CO)9(PC6H5) requires a medium scale chromatographic separation (silica gel Macherey Nagel 0.06-0.2 mm, dried for... 

Normal-phase adsorption on silica gel with a relatively less polar mobile phase is the most widely used mode in conventional TLC. To improve separations, silica gel may be impregnated with various solvents, buffers, and selective reagents. Other commercial precoated layers include alumina, florisil, polyamide, cellulose, and ion exchangers. 

A solution of (3) (215mg, 0.799mmol) in methanol (10ml) was refluxed for 13 h in the presence of two drops of triethylamine. After column chromatographic separation (silica gel, dichloromethane), crude methyl ester (4) (192 mg, 0.759 mmol) was obtained, m.p. 166-167°C (recrystallization from dichloromethane/carbon tetrachloride/n-hexane and water/methanol). Crude (4) thus obtained was treated with... 

A soln of the crude amino aldehyde was dissolved in 70% EtOH (90 mL) and was treated with semicarbazide hydrochloride (3.3 g, 30 mmol) and NaOAc (2.7 g, 33 mmol) at 80 °C for 5 min. The solvent was removed and the residue was extracted with EtOAc. The EtOAc was washed with H20 and dried (Na2S04) giving a syrup. The syrup was purified by chromatography (silica gel, 120 g, CHC13/ MeOH 100 1) for Z-D-Phe-H and Z-Phe-H. In the case of Z-Trp-H, elution was carried out in CHC13/ MeOH (100 5). Z-Tyr-H was purified by recrystallization (MeOH/CHCl3). The mother liquor left after collection of Z-Tyr-H was concentrated and the residue was chromatographically separated (silica gel, 100 g, EtOAc). 

Bis[(2-phenyl-1,3-dioxolan-2-yl)methyl] Tellurium2 Under an atmosphere of nitrogen 0.30 g (2.3 mmol) finely pulverized tell urium and 0.22 g (9.6 mmol) sodium are s tirred in 15 ml dry dimethylformamide at 110 for 15 min. To the resulting yellowish-white suspension at 20" are added 1.15 g (4.7 mmol) of 2-bromomethyl-2-phenyl-l,3-dioxolane dissolved in 10 ml dry tetrahydrofuran. After 2.5 h at 20° the reaction mixture is poured into water, and the resulting mixture extracted with dichloromethane. Chromatographic separation [silica gel, dichloromethane/petroleum ether (40 60°) (1 1)] from the starting material gives the product yield 60% m.p. 68° (ethanol). 

Thin-layer chromatography (TLC) is mainly applied in micropreparative taxoid separation.Silica gel 6OF254 preparative plates are usually employed for this purpose. The problem of taxoid separation involves not only their similar chemical structure (e.g., paclitaxel vs. cephalomannine) but also the different coextracted compounds usually encountered in crude yew extracts (polar compounds such as phenolics and non-polar ones such as chlorophylls and biflavones) the separation is therefore very difficult. The common band of paclitaxel and cephalomannine was satisfactorily resolved from the extraneous fraction in isocratic elution with ethylacetate as polar modifier " and n-heptane-dichloromethane as solvent mixture, and was of suitable purity for high-performance liquid chromatography (HPLC) quantitative determination. The combination of micropreparative... 

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%). 

An important publication by Kost et al. (63JGU525) on thin-layer chromatography (TLC) of pyrazoles contains a large collection of Rf values for 1 1 mixtures of petroleum ether-chloroform or benzene-chloroform as eluents and alumina as stationary phase. 1,3- and 1,5-disubstituted pyrazoles can be separated and identified by TLC (Rf l,3>i y 1,5). For another publication by the same authors on the chromatographic separation of the aminopyrazoles, see (63JGU2519). A-Unsubstituted pyrazoles move with difficulty and it is necessary to add acetone or methanol to the eluent mixture. Other convenient conditions for AH pyrazoles utilize silica gel and ethyl acetate saturated with water (a pentacyanoamine ferroate ammonium disodium salt solution can be used to visualize the pyrazoles). 

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). 

Distd, then repeatedly fractionally crystd by partial freezing. Immediately before use, the material was passed through a column containing Woelm silica gel (activity I) and Woelm alumina (neutral) in separate layers. 

Carbon soot from resistive heating of a carbon rod in a partial helium atmosphere (0.3bar) under specified conditions is extracted with boiling C H or toluene, filtered and the red-brown soln evapd to give crystalline material in 14% yield which is mainly a mixture of fullerenes C q and C70. Chromatographic filtration of the crude mixture with allows no separation of components, but some separation was observed on silica gel... 

Separated from retinol by column chromatography on water-deactivated alumina with hexane containing a very small percentage of acetone. Also chromatographed on TLC silica gel G, using pet ether/isopropyl ether/acetic acid/water (180 20 2 5) or pet ether/acetonitrile/acetic acid/water (190 10 1 15) to develop the chromatogram. Then recrystd from propylene at low temperature. 

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