Silicagel

The opportunity of application of filters, solid sorbents and absorbing solutions has been investigated for synthetic pyrethroids concentrating from air. Silicagel KSK and polysorb are provided quantitative sorbption and desorbption pyrethroids. In case of aerosol formulations application of paper filters is possible. 

Ingress of moisture through the seals, although Silicagel is provided beneath the arrester sealing to absorb the moisture. 

Capsilgels are transparent hard capsules containing silicagel. The capsule is made from hard gelatine. It consists of two cylindrical parts, a body with a hemispherical... 

Androst-4-ene-3,17,19-trione (0.23g) is added to a precooled solution of 0.23 g of potassium hydroxide in a mixture of 1 ml of water and 5 ml of methanol. The reaction mixture is stirred at 5-10° under nitrogen for 3 hr, diluted with benzene (30 ml) and washed with water (2 x 10 ml). The aqueous layer is reextracted with benzene and the benzene solution dried and evaporated. The crude crystalline product is filtered through 8 g of Merck silicagel and eluted with benzene-ethyl acetate (9 1) to yield 0.19 g of 19-norandrostenedione (88%) mp 169-171° 141° (CHCI3). 

Bei der Reduktion von Oximen mit Natrium-trithio-dihydrido-borat werden meist Gemische von Hydroxylamin und prim. Amin gebildet3. Natriumboranat/Silicagel reduziert Oxime in Benzol-Lo-sungzu Hydroxylamin - Boranen, die durch Salzsiiure in die N-Alky] - hydroxylamin-Hydrochloride iibergefiihrt werden4. 

Mother liquors from the production of bromocriptine 2 were dried by evaporation under vacuum. The dry residue (82.2 g) was applied on chromatographic column (I.D. = 3 cm, lenght = 20 cm) packed with silicagel 60, granulation 0.063 - 0.040 mm and eluted by flash - chromatography with pure dichloromethane. Two separate fractions were obtained and crystallized from dichloromethane (- 15°C). 

Bromocriptine 2 (0.65 g, 1 mmol) was dissolved in 100 ml of dry ethanol and 60 ml of tetrafluoroboric acid / diethylether complex (85 %) was added while stirring. After standing overnight at RT the solvent was evaporated and the raw product isolated by extraction in the system dichloromethane 12% ammonia in water and evaporated to the dry residue. This residue was applied to the chromatographic column (I.D. = 2 cm, lenght = 20 cm) packed with silicagel and eluted with dichloromethane / ethylacetate =1 1. The fractions containing 2 were evaporated to the dry residue and crystallized from alcohol. 

The complex 65 was synthesized by reaction of the imidazolinium salt with the precursor ruthenium complex 67 (catalytically inactive) in the presence of silver carbonate (Scheme 42). The complex being air-stable and stable on silicagel was isolated in 52% yield after chromatography. The diastereomeric and enantiomeric purity of 65 was determined by HPLC analysis and found to be above 98% (de and ee). The molecular structure was determined by X-ray analysis and showed the unusual twist geometry of this complex. 

Silicagel. Silicagel is usually prepared from sodium silicates, which are produced as glasses with a stoichiometry of Si02/Na20 = 0.6-0.25. At the right pH they arc soluble in water and the solution contains mixtures of silicate anions monomeric, dimeric, trimeric species, etc. (Fig. 3.13). 

It is important to have a suitable substrate on which sensibilizer is applied to provide photosensibilization-induced formation of 02. Obviously, the geometric structure of substrate (the pore size, the specific surface value) would affect the amount of collisions of 02 molecules with substrate during transport of these particles from pores into the volume of the vial. Therefore, several features (for instance the dependence on pressure) of the emission of singlet oxygen into gaseous phase for dyes applied to silicagel differ from those of dyes applied to smooth quartz. 

The most common classes of solid adsorbents are Zeolites and Silicagels. The main difference between the two is the way they are built. Zeolites have a crystalline structure and therefore a certain pore size. Silicagel have a pore... 

Figure 237 shows the pore size distribution of narrow pore (A) and wide pore Silicagel (B). 

Silicagel is built of 99% SiC>2, while the rest are OH groups together with changing amounts of integrated water. The properties of Silicagel are shown in Table 31. 

Concerning the application of these adsorbents as thermal energy storages the amount of water, which can be adsorbed is the most important property. Figure 238 shows the maximum water uptake of some commercially available adsorbents. Zeolite A can reach 25% and Zeolite 13X up to 32% of its dry weight. Narrow pore Silicagel can adsorb 38% water. Two special adsorbents Sizeo, which is a mixture of Zeolite and Silicagel, and SWS, which is a wide... 

Figure 241. Thermal breakthrough curves (adsorption) for Zeolite and Silicagel...

Figure 241 shows the shape of two thermal breakthrough curves for Zeolite and Silicagel in adsorption. The adsorption is following a desorption using 130 °C and the inlet air is saturated with water vapor at 25 °C. 

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