Aluminium methoxide, preparation

The reaction of magnesium and methanol to form magnesium methoxide and used to prepare dry methanol [1] is very vigorous, but often subject to a lengthy induction period. Sufficient methanol must be present to absorb the violent exotherm which sometimes occurs [2], Mixtures of powdered magnesium (or aluminium) and methanol are capable of detonation and are more powerful than military explosives [3],... 

This method is very useful for the construction of 1-substituted 3,4-dihydroisoquinolines, which if necessary can be oxidized to isoquinolines. A P-phenylethylamine (l-amino-2-phenylethane) is the starting material, and this is usually preformed by reacting an aromatic aldehyde with nitromethane in the presence of sodium methoxide, and allowing the adduct to eliminate methanol and give a P-nitrostyrene (l-nitro-2-phenylethene) (Scheme 3.17). This product is then reduced to the p-phenylethylamine, commonly by the action of lithium aluminium hydride. Once prepared, the p-phenylethylamine is reacted with an acyl chloride and a base to give the corresponding amide (R = H) and then this is cyclized to a 3,4-dihydro-isoquinoline by treatment with either phosphorus pentoxide or phosphorus oxychloride (Scheme 3.18). Finally, aromatization is accomplished by heating the 3,4-dihydroisoquinoline over palladium on charcoal. 

The novel enol sulphonates (331) have been prepared from the 3-oxo-steroids with the appropriate sulphonic anhydride in dimethylformamide. They are stable to aqueous acids and bases, but attacked at sulphur by methoxide ion, regenerating the ketone. Reduction with lithium aluminium hydride afforded mainly the 3)8-alcohol, and no olefin (see p. 400 for rearrangement). 

Sol-gel chemistry offers flexible methods for the preparation of porous metal oxides such as the transition aluminas used as catalyst supports. The physical properties of sol-gel materials depend on the nature of the reactants, the rate of mixing and the conditions of drying. High surface area aluminas have been prepared from various alkoxide and salt solutions and their textures have been examined extensively. The interest in the use of these chemically prepared materials is largely for catalyst and absorbent applications [1]. The first user of alkoxide precursor was Teichner who prepared pure aluminas by the water vapour action on aluminimn methoxide [2] and reported materials with surface area of 200 m /g. Harris and Sing [3] reported gels prepared from aluminium isopropoxide with water and... 

For the preparation of double salts and alkoxides, the most popular method involves dissolving the two alkoxides in a mutual solvent, mixing the solutions, and refluxing at elevated temperatures (eg, refluxing an aluminium sec-butoxide and magnesium methoxide in alcohol at 600 K). One can also prepare a double alkoxide by refluxing the oxide of the first element with the alkoxide of the second element in alcohol. Bradley and co-workers (16) provided an excellent summary of available double alkoxides and techniques used in their synthesis. 

More than two decades after the preparation of a large nnmber of the so-caUed alkoxo salts by Meerwein and Bersin in 1929, U Al(OPr )4 4 was synthesized in 1952 by Albers et al. and evidence for the formation of M U(OEt)6 n (M = Na, Ca, Al) was obtained by Jones et al in 1956. Similarly, formation of a number of anionic methoxide species was indicated in the potentiometric titrations of chlorides of metals (B, Al, Ti, Nb, Ta) with lithium methoxide in methanol by Gut in 1964. Ludman and Waddington studied the conductometric titrations of a wide variety of Lewis acids with basic metal methoxides and reported the formation of alkoxo salts of the type KB(OMe)4 and K3Fe(OMe)e. Schloder and Protzer also synthesized a number of bimetallic alkoxides of aluminium with the formulae, MAl(OMe)4 and M Al(OMe)4 2 where M and M are alkali and alkaline earth metals respectively. 

Preparation by demethylalion of 2,4-dimelhoxy-3,5,6-trifluorobenzophenone (SMI) or of 2-hydroxy-4-methoxy-3,5,6-trifluorobenzophe-none (SM2) with aluminium chloride in methylene chloride at 20° for 6 h (97% and 60% yields, respectively) [570]. SMI was obtained in two steps first, preparation of 4-methoxy-2,3,5,6-tetrafluorobenzophenone by treatment of 2,3,4,5,6-pentaflu-orobenzophenone with sodium methoxide in methanol at 20° for 3 days (91%). Then, this new ketone, by reaction with sodium methoxide in boiling methanol for 15 h gave SMI (82%) [570]. The preparation of SM2 was also described in this book (94%) [570]. 

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