Hydrolysis, highly soluble cationic

Table 10.2 summarizes some examples of zeolites based on their classification by chemical composition. Low-silica zeolites (Si/Al < 5) are synthesized in basic conditions (pH >13) using a silicon source, an aluminum source, and alkali hydroxides at moderate temperatures, typically less than 120°C. The identity of the alkaU species used is a determining factor in which phase is obtained from synthesis, as the relative rates of (alumino)silicate hydrolysis and condensation reactions are dependent on the identity of the alkali cation. It is also believed that hydrated alkali cations effectively direct the assembly of (alumino)silicate precursors into fuUy connected three-dimensional structures. Sodium and potassium hydroxide have been used most frequently in low-silica zeolite syntheses due to their low cost and high solubility in... 

Based on the excellent solubility and reducing properties of amine boranes, they are often used for the stabilization and purification of industrial materials. Further, they are applied as additives in hydrocarbon fuels and in lubricating oils, as polymerization catalysts, as ingredients in photographic processing and in the electroplating industry.169 High stability towards hydrolysis and oxidation makes cationic boron chelates useful as water-soluble dyes.170... 

Biphasic conditions also circumvent the salt solubility problem but classic phase transfer conditions using aqueous sodium hydroxide suffer from competing hydrolysis of the phosphorus(III) esters. However, Kem and co-workers found that butyl esters (their substrate was dibutyl phosphonate) are sufficiently stable to provide Michaelis-Becker products in high yields dialkylphosphine oxides were also suitable substrates.67 Salvatore and co-workers have recently developed an efficient biphasic solid-liquid procedure utilising the cesium cation effect Protocol 7. 

The pH-dependence of the solubility of sulfide minerals is of considerable interest in relation to their interaction with successions of microorganism populations which are themselves pH-dependent. In pure water, the solubility of the majority of sulfide minerals is extremely low (pKjp ZnS, 24 PbS, 27 HgS, 53) (Sillen and Martel, 1964), but the potential remains of reaction with water to yield hydrated metal cations and sulfide ions. The latter are strong bases and further hydrolysis can yield HS ions or even H S. The equilibrium concentration of S " ions in solution and consequently the solubility of the metal sulfide in water is highly pH-dependent. 

In this respect the solution chemistry of common anions is very different. For example with phosphate (Fig. 4.4), HP04 and H2P04 are the dominating solution species over the typically studied pH range, and fully dissociated anions occur only at extremely high pH values, which are of limited interest in adsorption studies, e.g. many common adsorbents are unstable at such a high pH (dissolution). On the other hand, the final products of hydrolysis on anions, i.e. fully protonated acid molecules are usually water soluble, thus, the applicability of surface complexation model is not limited by surface precipitation as it was discussed above for metal cations. 

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