Aluminum hydroxy species

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... 

As shown in Fig. 10, the PZR 1 of a cordierite suspension is consistent with the lEP of a fumed silica (Aerosil 200 Degussa Co., Belgium) suspension. This indicates that the interfacial properties of an aqueous cordierite suspension in an acid region are governed by the surface silanol sites ( SiOH) and therefore suggests that the PZR 1 corresponds to the inherent lEP of an aqueous cordierite suspension. The anomalous increase in the potential above pH 3.5 leads to a second potential reversal (PZR 2) at a higher pH value. This was attributed to the readsorption of dissolved aluminum hydroxy species via the surface-induced hydrolysis [44], for example. 

When a salt is introduced to water (e.g., A1C13s), the charged metal (Al3+) has a strong tendency to react with H20 or OH" and forms various Al-hydroxy species. Metal-hydroxide reactions in solution exert two types of influences on metal-hydroxide solubility, depending on the quantity of hydroxyl supplied. They either decrease or increase metal solubility. The solubility of a particular metal-hydroxide mineral depends on its Ksp, quantity of available hydroxyl, and solution pH of zero net charge. For example, aluminum (Al3+) forms a number of hydroxy species in water as shown below ... 

One may plot Equations 2.69, 2.71, and 2.73 as pAlhydroxy species versus pH. This will produce three linear plots with different slopes. Equation 2.69 will produce a plot with slope 3, whereas Equations 2.71 and 2.73 will produce plots with slopes 2 and -1, respectively. The sum of all three aluminum species as a function of pH would give total dissolved aluminum. This is demonstrated in Figure 2.12, which describes the pH behavior of eight Al-hydroxy species. The following three points can be made based on Figure 2.12 (1) aluminum-hydroxide solubility exhibits a U-shaped behavior, (2) aluminum in solution never becomes zero, and (3) different aluminum species Predominate at different pH values. 

Some soils produce conductimetric titration lines that parallel the x axis they represent adsorbed Al3+. When the slopes of the titration lines become positive, they represent surface-adsorbed Al-hydroxy species (Kissel and Thomas, 1969, Kissel et al., 1971, and Rich, 1970). For example, at all three initial pH values, the Nicholson soil (Fig. 3.35) exhibits titration lines that nearly parallel the x axis. On the other hand, the Eden soil exhibits a line nearly parallel to the x axis only for the sample with an initial pH of 5.78. One expects this behavior to be exhibited by the sample with initial pH of 4.3. For the samples with initial pH 4.3 or 7.3 the titration lines exhibit positive slopes, suggesting neutralization of surface-adsorbed Al-hydroxy species. The overall data in Figure 3.35 show that most surface acidity of the soils is dominated by aluminum under various degrees of hydroxylation. 

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. 

A series of crystalline aluminum hydroxy fluorides in cubic pyrochlore structure AlFx(OH)(3 x)-H20 with variable F-content x were investigated by solid-state NMR by applying different magnetic fields up to 21.1 T. Distinguishable octahedral species AlFx(OH)(e x) (x=l—6) were identified in the crystalline aluminum hydroxy fluorides. Both Al and F solid-state NMR experiments were carried out. °" ... 

Conversion to the Aldehyde. This transformation is accomplished through a two-step procedure. One such variant requires reduction to the alcohol (e.g. LiAllTt, H2O) and subsequent oxidation (e.g. Swem conditions). Alternatively, Wein-reb transamination " followed by Diisobutylaluminum Hydride or conversion to the thioester (see below) and subsequent Triethylsilane reduction, afford the desired aldehyde in excellent yields. Weinreb transamination proceeds with minimal endocyclic cleavage when there is a p-hydroxy moiety free for internal direction of the aluminum species. 

Once they have reached higher pH, reducing conditions of the intestinal tract (Davis et al, 1992), sulhdes should be more stable, and may actually precipitate if reduced sulfur is present. Other solids, such as hydroxides or hydroxy-sulfates of aluminum, and possibly iron, may also precipitate. The increased pH should also lead to the increased sorption onto particulates of various metals and metalloids such as lead and copper (Smith, 1999). However, in vitro tests (Ruby et al, 1993) indicate that the increased complexing with unprotonated organic acids and enzymes helps offset the pH-driven precipitation and sorption of the base metals that were dominantly chloride-complexed in the stomach fluids. Arsenic and other oxyanionic species are likely to be sorbed as the stomach acids are neutralized, but may be partially desorbed once higher pH values are reached in the intestine (Ruby et al, 1996). 

Several less important mechanisms, with varying timescales, also contribute to acid neutralization. (i) In soils rich in iron and aluminum secondary phases, excess SO4 from the atmosphere may be reversibly adsorbed or desorbed, thereby retarding acidification and recovery from acidification, respectively (David et al., 1991a,b). Such soils are common in unglaciated areas, (ii) As pH declines, dissociated inorganic carbon species protonate toward H2CO3 and aqueous CO2. (iii) Protonation, condensation, and precipitation of organic acids increases, (iv) Hydroxy- 2+ lated aluminum species shift toward Ar. The... 

The occurrence of coordination numbers greater than four for the aluminum is another feature of the phosphate-based solids in comparison with the zeolites. For example, in some phases aluminum adopts five-fold (trigonal bipyramidal) or sixfold (octahedral) coordination. In these cases, anionic species such as hydroxy or... 

Further studies indicated that aluminum alkyls are capable of capturing an oxo-nium intermediate generated from the corresponding acetal (Scheme 6.155) [199]. The substrate 160, in which a hydroxy group was substituted by acetal, was amenable to this type of rearrangement and subsequent alkylation by alkylaluminum species. Again the dual function of organoaluminum as a Lewis acid and a base were demonstrated. 

The supported chromium oxide catalysts can be prepared by impregnating a silica-alumina support with a solution of chromium ions or by coprecipitating the oxides. The preferred impregnating solutions contain dissolved Cr(N03)s.9H20 or CrOs in nitric acid because catalysts made from chromium chlorides or sulfates retain some of the anions after calcination. The solid mixture of chromium-silicon-aluminum compounds is calcined in dry air at 400-700° C or higher to obtain the desired oxide. This probably results in the reaction of surface hydroxy groups in the support material with CrOs to form chromate (IV) and dichromate (V) species ... 

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