Aluminum hydroxides metal chlorides, hydrolysis

The isolation and structural characterization of aluminum hydroxides with terminal OH groups is a s)mthetic challenge, and efforts were made to prepare well-defined analogues of methylalumoxane (MAO). The strategy of hydrolysis of metal chlorides in the presence of a base to quench the hydrogen chloride generated during the reaction was adopted. This synthesis can be performed in two different ways (i) hydrolysis of a metal halide in a two-phase liquid NHs-toluene system in the presence of KOH and KH and (ii) hydrolysis of a metal halide in the presence of a stoichiometric amount of N-heterocyclic carbene. Both routes are reliable, but the latter one may prove to offer more versatility and be relatively easier to conceive. 

Actually, the drop of pH is related to more complex reactions and species. Thus, in more sophisticated models, several hydrolysis reactions and metal chloride formation are taken into account but the selection of species and reactions is somewhat different from model to model. Oldfield and Sutton [94] and Watson and Postlethwaite [2] considered only hydroxides as the product of cation hydrolysis. Sharland [96] introduced simple metallic chlorides. The most complete set of species and reactions has been used by Bernhardsson et al. [4], which made available the thermodynamic data of a large number of species, including several iron, nickel, chromium, and molybdenum polycations as well as metal chlorides and hydroxychlorides. Gartland [19] used a more limited set of species (Table 10.3) selected among the Bernhardsson data. According to their experimental results, Hebert and Alkire [95] included Al(OH) " as the hydrolysis product in their model of the crevice corrosion of aluminum alloys. 

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