Hydroxy complexes, aluminum

In the equilibrium constant, the superscript asterisk indicates that the dissolution reaction is written in terms of protons. The subscript following K (zero in this case) is the number of hydroxyl ions associated with AF+ in the reaction. According to Nordstrom et al. (1990), Kq = 10. Reactions similar to (7.35) can be written in which kaolinite is dissolved to form each of the aluminum hydroxy complexes listed in mass-balance equation (7.22) for total aluminum. These reactions can be generated by successively adding the cumulative reactions for the Al-hydroxy complexes—Eqs. (7.23) to (7.26)—to Eq. (7.35). For example, adding Eqs. (7.35) and (7.23) and their log values for 25°C, we obtain ... 

Relations Among Equilibrium and Nonequilibrium Aqueous Species of Aluminum Hydroxy Complexes... 

Smith, R.W. 1971. Relations among equilibrium and nonequilibrium aqueous species of aluminum hydroxy complexes, pp. 250-279. 

Aluminum-hydroxy species are known to exhibit different biological activity. For xample, data have shown that some leafy plants are sensitive to Al3+ while others are mown to be sensitive to Al(OH) monomers. It has also been shown that polymeric duminum (more than one A1 atom per molecule) is toxic to some organisms. Alumi-lum is one of the cations most difficult to predict in the soil solution. This is because t has the ability to form complex ions such as sulfate pairs and hydroxy-AI monomers ind polymers. 

Aluminum hydroxy species, 65,69,160 Stability constants, 69 Stability diagrams, 78 pH of minimum solubility, 65, 71, 72 Ammonium, 326, 331 Volatilization, 330 Oxidation, 334-336,472 Nitrate, 334-336,472 Adsorption, 336,465-466 Metal-ammine complexes, 460—461, 465... 

Tanida and coworkers111 and Landor and coworkers112 explain the stereospecificity by a mechanism that initiates in nucleophilic attack of the LAH on the hydroxy group, forming hydrogen and an aluminum-oxime complex (equation 37). 

A solution of 0.001 Af iron(lll) is masked by the addition of 0.05 Af EDTA. (a) Calculate the masking index at pH 2, assuming formation of hydroxy complexes is negligible, (b) Calculate the masking index for aluminum(III) under the same conditions. 

The 1,2-addition of chiral aluminum ate complexes to various aldehydes and ketones has been re-viewed and, generally, this protocol produces very disappointing results with respect to the overall stereospecificity of the process as compared to other organometallics however, the recent extension of this methodology to the preparation of chiral a-hydroxy esters and acids, via 1,2-additions to the pro-chiral ketone moieties of a-keto esters, " has renewed interest in this area. TTie transformation outlined in equation (8) proceeds in excellent overall yield with exclusive selectivity for the ketone functionality unfortunately, the stereospecificity is not as impressive. 

For the formation of hydroxyl and proton complexes, the story is different. Aluminum, for example, may exist in solution dominantly as various hydroxy-complexes such as Al(OH)2 andAl(OH)2+. Obviously, then, the charge on much of the aluminum in solution is less than +3. But the OH- contribution to the charge balance is determined from the p, which reflects only the free OH-, not the complexed OH-. In acid solutions, free OH- are completely insignificant, but the complexed OH- is not. In very alkaline solutions, the story is similar, but it is the role of H+ which becomes important. It is this factor which causes the difference between stoichiometric and speciated charge balances. 

Aluminum is a hard trivalent ion, and is usually found as an aquo- or hydroxy-complex or hydrous oxide solid (Martell and Motekaitis 1989). Aluminum can act as a complexing agent of other metals, or as a metal center to other inorganic and organic ligands (Buffle 1990). As the hexa-coordinated hydrolyzed cation, aluminum is octahedrally coordinated by six waters (Fig. 6), and as such acts as a multiprotic acid (Stumm and Morgan 1981). 

The concentration of aluminum in serum can be determined by adding 2-hydroxy-1-naphthaldehyde p-methoxybenzoyl-hydrazone and measuring the initial rate of the resulting complexation reaction under pseudo-first-order conditions.The rate of reaction is monitored by the fluorescence of the metal-ligand complex. Initial rates, with units of emission intensity per second, were measured for a set of standard solutions, yielding the following results... 

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