Occluded Alkali

Alkali metal ion-exchanged zeolites and occluded alkali metal oxide zeolites have been investigated extensively and applied as basic catalysts for a variety of organic transformations (1,41,221,222). Zeolites modified with alkaline earth compounds have been applied much less frequently as base catalysts for organic reactions. 

Alkenes may also be used as reagents in side-chain alkylation. Zeolites with occluded alkali metal and alkali metal oxide clusters were tested in alkylation of toluene with ethylene439 440 Alkali metal clusters created by decomposing Na or... 

A further possibility for side-chain alkylation of toluene is oxidative methylation with methane. Catalysts with occluded alkali metal oxides, prepared by impregnating zeolites with alkali metal hydroxides followed by calcination, usually exhibit better performance.441 Further enhancement was achieved by impregnating ion-exchanged zeolites 442 Significant improvements in stability and the yields of Cg hydrocarbons were also observed when NaX was impregnated with 13% MgO which was found to increase the amounts of active sites.443... 

Solid basic catalysts such as K-X zeolite and Cs-loaded K-X zeolite have been studied by CO2 adsorption microcalorimetry [138]. Carbon dioxide adsorbed on K-X with a Affads of about 70 kj mol up to a loading of about 80 xmolg The addition of cesium to K-X zeolite increased both the heat of adsorption (to more than 100 kJ mor ) and the maximum CO2 uptake. Nonetheless, the heats of carbon dioxide adsorption on Cs/K-X zeolites remained 50 kJ mol lower than on, for example, MgO or CS/AI2O3. The stronger basicity of Cs/K-X compared to K-X can be attributed to the occluded alkali metal oxide species, which may be either cesium or potassium oxide. The values of AHads on Cs/K-X samples were similar to those reported previously for Cs-loaded into Cs-X using analogous synthesis procedures [139]. 

The perspectives of the use of basic zeolites as catalysts has been reviewed recently by Davis [287], Extraframework material free, alkali exchanged zeolites are used as quite mild basic catalysts. As seen earlier, light alkali-metal zeolites, such as Na-X and Na-Y, have a mild Lewis acid behavior and do not appear to have strong basic character [245], However, heavy-alkali metal zeolites like Cs-Y act actually as basic catalysts, or better as acid-base catalysts, for example, for toluene side chain alkylation. Stronger basic character arises from impregnation of alkah-zeolites with alkali salts, later decomposed to occluded alkali oxide, as evidenced by CO2 adsorption microcalorimetry. The characterization of such materials is still quite poor. 

On standing, gelatinous aluminium hydroxide, which may initially have even more water occluded than indicated above, is converted into a form insoluble in both acids and alkalis, which is probably a hydrated form of the oxide AI2O3. Both forms, however, have strong adsorptive power and will adsorb dyes, a property long used by the textile trade to dye rayon. The cloth is first impregnated with an aluminium salt (for example sulphate or acetate) when addition of a little alkali, such as sodium carbonate, causes aluminium hydroxide to deposit in the pores of the material. The presence of this aluminium hydroxide in the cloth helps the dye to bite by ad sorbing it—hence the name mordant (Latin mordere = to bite) dye process. 

When these benzoyl compounds separate in the course of the Schotten-Baumann reaction, they frequently occlude traces of unchanged benzoyl chloride, which thus escapes hydrolysis by the alkali it is advantageous there fore to recrystallise the benzoyl compounds whenever possible from ethanol or methylated spirit, since these solvents will esterify the unchanged chloride and so remove the latter from the recrystallised material. 

The precipitated metallic hydroxides or hydrated oxides are gelatinous in character, and they tend to be contaminated with anions by adsorption and occlusion, and sometimes with basic salts. The values presented in Table 11.2 suggest that many separations should be possible by fractional precipitation of the hydroxides, but such separations are not always practical owing to high local concentrations of base when the solution is treated with alkali. Such unequal concentrations of base result in regions of high local pH and lead to the precipitation of more soluble hydroxides, which may be occluded in the desired precipitate. Slow, or preferably homogeneous, precipitation overcomes this difficulty, and much sharper separations may be achieved. 

C6H2 (supermesityl, mes ) into the ligand such substituents sterically occlude vacant metal coordination sites and greatly increase the solubility of the complexes in common organic solvents. The subtle variations possible within P- and As-donor ligand complexes of the alkali metals lead to an almost bewildering array of structural types, many of which are not observed in other areas of alkali metal chemistry, and to wide variations in reactivity between complexes. 

Ruthenium(III) hydroxide is formed by the action of alkali on a solution of ruthenium(III) chloride. It is easily oxidized by air to the tetravalent state, The dioxide, R11O2, forms when the metal is heated in air. Hydrous ruthenium(IV) oxide can be precipitated by adding alcohol to a less than 3-M NaOH solution of ruthenium(VIII) oxide, followed by boiling. Above 3-complete reduction is not obtained. The hydrous oxide that is soluble in concentrated HQ tends to occlude impurities. 

Therefore, an alternative test method, such as heating at 80 °C for 2 h, an alkali modified Coomassie-dye assay (e.g. Boyes et al. 1997), or the more recently available reagent based test kits such as Proteotest or Prostab, could present an opportunity to decrease bentonite dose and reduce volume of wine occluded in bentonite lees if confirmed to predict more accurately haze formation in wine. If these alternative test methods could replace the current heat test method of 80 °C for 6 h, this would also reduce the amount of time and/or effort presently required by a winery s laboratory to conduct heat stability testing. 

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