Active silica gels

Isononane [34464-40-9] M 128.3, b 142"/760mm. Passed through columns of activated silica gel and basic alumina (activity 1). Distd under high vacuum from Na/K alloy. 

Methylpentane (mixture of isomers). Passage through a long column of activated silica gel (or alumina) gave material transparent down to 200nm by UV. 

Paraffin (oil) [8012-95-1 ] d 0.880, n 1.482. Treated with fuming H2SO4, then washed with water and dilute aqueous NaOH, then percolated through activated silica gel. 

Sodium dodecyl sulfate was separated from sodium dodecylbenzenesulfonate and sodium dodecanesulfonate by TLC on activated silica gel G. The spots were located by charring at 250°C for 15 min [281,282]. 

Silica gel [11] or alumina [11a, 12] alone, or silica and alumina together modified by Lewis-acid treatment [13] and zeolites [14], have been widely used as catalysts in Diels-Alder reactions, and these solids have also been tested as catalysts in asymmetric Diels-Alder reactions [12,13b,14]. Activated silica gel and alumina at 140 °C were used [15] to catalyze the asymmetric cycloaddition of (-)-menthyl-N-acetyl-a, S-dehydroalaninate (3) (R = NHCOMe) with cyclopentadiene in the key step for synthesizing optically active cycloaliphatic a-amino acids. When the reactions were carried out in the absence of solvent, a higher conversion was obtained. Some results are reported in Table 4.5 and compared with those obtained by using silica and alumina modified by treatment with Lewis acids. Silica gel gives a reasonable percentage of conversion after 24 h with complete diastereofacial selectivity in exo addition. 

Treatment of sugar-derived carbodiimides with dry hydrogen sulfide (H2S) in the presence of activated silica gel affords the sugar-derived thioureas (Scheme 46).127... 

The choice of stationary phase and its degree of activity is determined by the nature of the sample. If sample components are adsorbed too strongly, they may be difficult to elute or chemical changes may occur. Weakly polar solutes should be separated on highly active adsorbents otherwise they may elute rapidly with little or no resolution. Strongly polar solutes are better separated on adsorbents of low activity. Silica gel can be prepared with a... 

Carbon dioxide obtained from a cylinder of the compressed gas was passed through a tube packed with calcium chloride and either activated silica gel or Drierite (containing an indicator) to remove water. 

TLC Analysis. For experiment 2, thin layer chromatographic analysis was carried out by reducing solvent volumes to less than 250 pi under a nitrogen stream, spotting on activated silica gel plates, and developing in chloroform acetone (20 1, v v). Autoradiographs of these plates were prepared by exposing them to X-ray film for 3 or 4 days at -20 C. 

LiP catalyzes the oxidation of a low-molecular-weight redox mediator, veratryl alcohol, which in mrn mediates one-electron oxidation of lignin to generate aryl cation radicals [100]. The radicals facilitate a wide variety of reactions such as carbon-carbon cleavage, hydroxylation, demethylation, and so on. Dezotti et al. [101] reported enzymatic removal of color from extraction stage effluents using lignin and horseradish peroxidases immobilized on an activated silica gel support. 

Films to be studied chronogravimetrically for moisture desorption and absorption were cast on wafers with a 2kS thick oxide substrate film. These substrates were dried at 205° for two hours, cooled in a desiccator with activated silica gel and... 

A common industrial method of a-terpineol synthesis consists of the hydration of a-pinene or turpentine oil with aqueous mineral acids to give crystalline cis-terpin hydrate mp 117°C), followed by partial dehydration to a-terpineol. Suitable catalysts are weak acids or acid-activated silica gel [83]. 

TLC behavior of these samples observed with various single solvents on highly activated silica gel thin-layer are summarized in Table 6. From the table it is seen that carbon tetrachloride can distinguish chromatographically the 3,4-vinyl sample from either the cis-1,4 or the tram-1,4 sample. For separating the cis-1,4 sample from the tram-1,4 and 3,4-vinyl sample, binaries of (carbon tetrachloride + p-xylene) and (cyclohexane + p-xylene) were found to be effective. When the composition of these binaries was adequately adjusted, the cis-1,4 sample remained on the starting... 

The checkers, apparently using a higher activity silica gel (BDH 60-120 mesh), found product retention and degradation on columns to be a problem. We have also used Florisil (Matheson, Coleman and Bell) for an even lower activity solid phase. Improved yields were also observed when chromatography was carried out under N2 with dried and distilled solvents. 

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