Alkoxides aluminum hydroxides, preparation

The class of compounds identified as basic aluminum chlorides [1327-41 -9] is used primarily ia deoderant, antiperspirant, and fungicidal preparations. They have the formula Al2(OH)g where x = 1 5, and are prepared by the reaction of an excess of aluminum with 5—15% hydrochloric acid at a temperature of 67—97°C (18). The same compounds are obtained by hydro1y2ing aluminum alkoxides with hydrochloric acid (19,20) (see Alkoxides, METAl). Basic aluminum chloride has also been prepared by the reaction of an equivalent or less of hydrochloric acid with aluminum hydroxide at 117—980 kPa (17—143 psi) (20). 

The reaction of complex hydrides with carbonyl compounds can be exemplified by the reduction of an aldehyde with lithium aluminum hydride. The reduction is assumed to involve a hydride transfer from a nucleophile -tetrahydroaluminate ion onto the carbonyl carbon as a place of the lowest electron density. The alkoxide ion thus generated complexes the remaining aluminum hydride and forms an alkoxytrihydroaluminate ion. This intermediate reacts with a second molecule of the aldehyde and forms a dialkoxy-dihydroaluminate ion which reacts with the third molecule of the aldehyde and forms a trialkoxyhydroaluminate ion. Finally the fourth molecule of the aldehyde converts the aluminate to the ultimate stage of tetraalkoxyaluminate ion that on contact with water liberates four molecules of an alcohol, aluminum hydroxide and lithium hydroxide. Four molecules of water are needed to hydrolyze the tetraalkoxyaluminate. The individual intermediates really exist and can also be prepared by a reaction of lithium aluminum hydride... 

The mesoporous aluminas synthesized using a nonionic templating method are thermally stable not only to template removal, but also to prolonged heating at elevated temperature. Therefore, these aluminas would be able to maintain their unique structural features in fairly demanding catalyst preparations and catalytic applications. Unlike sol-gel-derived aluminas, the synthesis temperature used for the hydrolysis and condensation of the aluminum alkoxide did not affect the resulting thermal evolution from the aluminum hydroxide to transitional alumina and the subsequent thermal stability of the transitional alumina. The only observed effect of synthesis temperature was the impact on median pore diameter and pore volume.[231]... 

Hydrolyses of alkoxides that give preparations free of electrolytes (see aluminum hydroxide gel p. 1652). 

Aluminum oxide (alumina or AI2O3) occurs in various crystallographic modifications. Completely anhydrous aluminum oxide is a-Al203 (corrundum), which is the most stable. It has a structure of hexagonal closest packing of oxide ion, with Al ion occupying two-thirds of the octahedral sites, a-Alumina is prepared by heat treatment above ca. 1470 K of aluminum hydroxides, oxyhydroxides, or alumina hydrates, which are obtained by neutralization of solution of aluminum salts or hydrolysis of aluminum alkoxides. Heat treatments at lower temperatures form various kinds of transi-... 

Gawel et al. present a scheme for sol-gel alumina monolith preparation starting with aluminiun alkoxides, aluminum salts, or aliuninum oxide hydroxide [8]. In the case of aliuninimi salts, they hydrolyze and condensate it into aliuninimi oxide hydroxide gels imder basic conditions [44,45]. However, since aqueous aluminum salt solutions are acidic, this requires a gradual process of increasing pH. 

In preparing the membrane, a clear sol was obtained by the addition of acid into the aluminum sec-butoxide sol to peptise the sol and obtain a stable colloid solution. Aluminum monohydroxides formed by the hydrolysis of aluminum alkoxides, which are peptisable to a clear sol. Peptisation was performed by the addition of acid and heat treatment for a sufficient time. It was found that stable sols cannot be obtained when the concentration of the peptisation acid is too low. The critical range for inorganic acids such as nitric, hydrochloric and perchloric acids is 0.03-0.1 mole/mole of hydroxide. In this study, nitric acid was used as the peptising agent. The resulting sols are poured into Petri dishes and dried in an oven at a controlled drying rate to obtain a gel layer. The molar ratio of zirconia salt... 

Considerable effort has been carried out by different groups in the preparation of amphiphihc block copolymers based on polyfethylene oxide) PEO and an ahphatic polyester. A common approach relies upon the use of preformed co- hydroxy PEO as macroinitiator precursors [51, 70]. Actually, the anionic ROP of ethylene oxide is readily initiated by alcohol molecules activated by potassium hydroxide in catalytic amounts. The equimolar reaction of the PEO hydroxy end group (s) with triethyl aluminum yields a macroinitiator that, according to the coordination-insertion mechanism previously discussed (see Sect. 2.1), is highly active in the eCL and LA polymerization. This strategy allows one to prepare di- or triblock copolymers depending on the functionality of the PEO macroinitiator (Scheme 13a,b). Diblock copolymers have also been successfully prepared by sequential addition of the cyclic ether (EO) and lactone monomers using tetraphenylporphynato aluminum alkoxides or chloride as the initiator [69]. 

Hydroxide suspensions of mullite with partially stabilized zirconia were prepared from metal alkoxide starting materials. Zirconium isoamyloxide and yttrium isopropoxide were mixed in the proper proportions for the partially stabilized zirconia. Aluminum isopropoxide and silicon ethoxide were added in the proper proportions for mullite. These solutions were refluxed for 4 to 8 h and then hydrolyzed to a pH of 0.5 using HNO3. The solutions were then neutralized to a pH of 8 using NH4OH. The resulting suspensions then contained the proper amount of each component as a hydroxide to form the mullite partially-stabilized zirconia matrix materials. With MgO as a stabilizer, procedures were identical to the above, except that MgO ethoxide was used instead of yttrium isopropoxide. Batch sizes were 25 to 100 g of final material. 

Earlier in this chapter we discussed the sol-gel processing of aqueous silicates and mentioned the preparation of Si02 gels from fine particles made by flame oxidation (2)-(4). The preparation of alumina sols from alkoxides has been characterized by Yoldas (45). Aluminum alkoxides such as aluminum sec-butoxide and aluminum isopropoxide are readily hydrolyzed by water to form hydroxides. Which hydroxide is formed depends on the conditions used in the hydrolysis. The initial hydrolysis reaction of aluminum alkoxides can be written... 

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