Silica gel silanation

TLC was carried out on various types of plates silica gel, silanized silica gel, cellulose and alumina, as well as in several different solvent systems benzene, chloroform, cyclohexane, benzene/acetone (90 10), cyclohexane/ethyl acetate (95 5), cyclo-hexane/acetone/triethylamine (70 25 5), hexane/benzene (60 40) and hexane/ether (80 20). Spots were either visualized by ultraviolet or developed by pulverization of a 1% blue B salt aqueous solution. 

Fig. 3. DRIFT-spectrum of silica gel silanized by I-oc(enyl-8-dimethylethoxysilane...

The latter possibility was employed by Wawrzynow-icz and Waksmundzka-Hajnos for micropreparative TLC isolation of furano-coumarins tom Archangelica, Pastinaca, and Heracleum fruits on silica gel, silanized gel, and florisil. 

Phenolic acids. Table 11 lists the Rf values for a number of phenolic acids and certain of their relatives on silica gel, silanized silica gel, cellulose, and polyamide layers. Silica gel (Silica Rapid Platten Woelm F-254) was used with solvents I [dichloromethane-toluene-formic acid (50 40 10)] and II [dichloromethane-acetic acid-water (100 50 50, lower phase)], followed by UV examination of the plates and subsequent spraying with 1 % methanolic ferric chloride. HPTLC precoated plates with silica gel 60 F-254, RP-8, and Wang polyamide were used with solvents 111 [benzene-ethyl acetate-formic acid (40 10 5)], IV [ethanol-water (55 45)], and IX [benzene-ethyl methyl ketone-methanol (60 26 14)], respectively. The upper part of Table 11 lists the Revalues of hydroxybenzoic acids and the lower part those for hydroxycinnamic acids. For columns V, VI, VII, and VIII, the solvents used were 2% formic acid (V), 20% potassium chloride solution (VI), isopropanol- ammonium hydroxide-water (8 1 1) (VII), and 10% acetic acid (VIII). For each layer the relative trends of the Revalues follow the polarity of the compounds listed. Table 12 gives the Revalues for certain phenolic acids on silver oxide-impregnated silica gel G by two-dimensional development on cellulose (107). 

Figure 3 C-NMR CP-MAS of the aliphatic region of silica gel silanized with 3-chloropropyl silane with hydration, (A) and without hydration, (B) showing the methoxyl peak intensity.

A solution of 3 mmol of trifluoro(3-mcthyl-2-butenyl)silane, 2 mmol of hydroxypropanone and 3 mmol of Ft jN in 5 ml, of THF is heated under reflux for 20 h. Chromatography of the mixture on silica gel gave the product yield 71 %. 

These poly(2-alkyl-2-oxazoline) silane coupling agents were copolycondensed with tetraethoxysilane by acid-catalyst to produce poly(2-alkyl-2-oxazoline)-modified silica gel. The composite gel from 2-ethyl-2-oxazoline was also homogeneous and transparent glass. Poly(2-alkyl-2-oxazoline)-modified silica gels, especially gels based on poly(2-ethyl-2-oxazoline) absorbed water and also organic solvents such as DMF or alcohols as shown in Table 7. This result means that the obtained composite gel shows the amphiphilic adsorption property. 

Analysis of neutral product for active species. The di- and poly sulfonates present in AOS have been isolated from monosulfonates by column chromatography using silanized silica gel by Puschmann [109]. The content of mono-and disulfonates in the fractions obtained were determined gravimetrically. 

New silica gels obtained by sol-gel polycondensation of tetra-ethylorthosilicate (TEOS) or related silanes offer largely superior performance in liquid chromatography (LC) separation of organic compounds, a task for which several thousands tons of silica are employed worldwide by industry. LC devices now rank third behind analytical balances and pH meters in number of installed analytical instruments.1... 

In a typical reaction, the macrocycle is treated with a 2-3 M excess of (3-isocyanatopropyl)triethoxysilane in dry DMF. The derivative is then added to a dry DMF slurry of silica gel ( 2 g of functionalized selector to 4 g of silica gel). The solution is stirred, allowed to react for 20 h at 107°C, and then cooled, filtered, and washed with methanol, 50% aqueous methanol, and methanol again, and finally dried. Surface coverage data are reported only in the case of the commercially available vancomycin CSP (see Table 2.2), immobilized by joining on average three linkers per vancomycin molecule, probably via a 3-isocyanatopropyl-silane [48]. 

Wirth, M.J. and Fatunmbi, H.O., Horizontal polymerization of mixed trifunctional silanes on silica. 2. Application to chromatographic silica-gel. Anal. Chem., 65, 822, 1993. 

The surface chemistry of SAMs of silanes on planar substrates such as oxidized silicon wafers is comparable to the chemistry of silica gel, with the absence of a porous structure [47]. 

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