Aluminum alkoxide basic

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). 

Irrespective of the solvent the aldehyde, acid or ester 1 is first transformed into the aluminum alkoxide 5. Transfer of hydride to the C-C double bond to give 6 occurs only when electron density is delivered to aluminum by a solvent with Lewis base character. Only in solvents of strong Lewis basicity (tetrahydrofuran, 1,2-dimethoxyethane) is the carbanionic character of the C-Al bond (e.g. 7) sufficient to induce intramolecular substitution to give phenylcyclo-propane 4. " 3-Phenylpropanols 3 are byproducts in the synthesis of 4, if insufficient reflux time is applied before acidic workup. ... 

The basic behavior of carbonyl compounds such as aldehydes is illustrated by their condensation reactions in the presence of aluminum alkoxides (acids). 

Alkoxides like Al(OR)3 will behave as fairly strong acid catalysts, owing to the tendency of the aluminum atom in these compounds to accept a share in a pair of electrons. In view of this fact it is to be expected that aluminum alkoxides will cause the amphoteric aldehydes to behave as bases, so that a simple ester results. As this behavior involves only the basic characteristics of the carbonyl group itself it makes little difference whether we have one, two, or no a-hydrogen atoms in the aldehyde an ester is the result. The first step is a typical acid-base neutralization reaction with the formation of a coordinate covalent bond ... 

In the sol-gel process, ceramic polymer precursors are formed in solution at ambient temperature shaped by casting, film formation, or fiber drawing and then consolidated to furnish dense glasses or polycrystalline ceramics. The most common sol-gel procedures involve alkoxides of silicon, boron, titanium, and aluminum. In alcohol water solution, the alkoxide groups are removed stepwise by hydrolysis under acidic or basic catalysis and... 

When aldehydes, with or without a hydrogen, are treated with aluminum ethoxide, one molecule is oxidized and another reduced, as in 9-69, but here they are found as the ester. The process is called the Tishchenko reaction. Crossed Tishchenko reactions are also possible. With more strongly basic alkoxides, such as magnesium or sodium alkoxides, aldehydes with an a hydrogen give the aldol reaction. Like 9-69, this reaction has a mechanism that involves hydride transfer.751 The Tishchenko reaction can also be catalyzed752 by ruthenium complexes.753 by boric acid,754 and, for aromatic aldehydes, by disodium tetracarbonylferrate Na2Fe(CO)4,755 OS I, 104. 

Silicon alkoxides exhibit very slow hydrolysis and condensation reactions compared with other alkoxides of aluminum, titanium or zirconium generally used for membrane preparation. Accordingly, acid or basic catalysts are used in the case of silicon alkoxides while methods for the control of hydrolysis are advisable with transition metal alkoxides [36,37]. 

Although the traditional Oppenauer conditions utilized aluminum catalysts, alternative metal alkoxides, for example, chloromagnesium alkoxides, are competent in the transformation.3 In 1945, Woodward devised a new system, which involved the use of potassium r-butoxide, and benzophenone for the oxidation of quinine (29) to quinone (30).13 This was termed the modified Oppenauer oxidation. The traditional aluminum catalytic system failed in this case due to the complexation of the Lewis-basic nitrogen to the aluminum centre. The synthetic flexibility of this procedure was extended by the use of more potent hydride acceptors.46... 

Now, unlike the dianion in Figure 17.50, a molecule of aluminum oxide can be lost to generate the aldehyde (Fig. 17.53). Because the LiAlH4 can continue to provide hydride (some experiments show 3.8 equivalents of hydride come from LiAlH4), the newly formed aldehyde cannot survive for long (p. 801). Another addition of hydride gives the alkoxide.The alkoxide is stable in the basic environment and subsequent addition of water forms the primary alcohol. 

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. 

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