Alkoxides, alkali metal aluminum

From Metals and Alcohol. Alkali metals, alkaline earth metals, and aluminum react with alcohols to give metal alkoxides (2,3,65) ... 

Modified MPV-type reductions carried out with chiral magnesium alkoxides and with chiral Grignard reagents have been discussed in detail (1). These reagents differ from the aluminum alkoxides since the Grignard reaction is essentially irreversible. Chiral alkali metal alkoxides have also been used to effect asymmetric reductions (1). 

Again several alkyls add—molybdenum, chromium, iron, cobalt, nickel, the alkali metal alkyls and aluminum alkyls react. A tin alkoxide has recently been studied by Russian workers and found to add to acetylenes. Mercury chloride, of course, adds and two cobalt—cobalt bonded compounds add to acetylene. The second is questionable because it dissociates in solution and the reaction may be a radical reaction, one cobalt adding to each end of the triple bond. 

Cobalt hydrocarbonyl, diborane, and aluminum hydrides add, I think, to all of these carbonyl compounds. Of course, there is the well known Grignard reagent and the alkyllithium additions to carbonyl compounds. Aluminum alkyls add, and we could have listed all the other alkali metal alkyls. Recent work has shown that the tin alkoxides add readily to all these derivatives, and similarly, a tin amide adds to most of these carbonyl compounds. 

Synthetic routes include anionic, cationic, zwitterionic, and coordination polymerization. A wide range of organometallic compounds has been proven as effective initiators/catalysts for ROP of lactones Lewis acids (e.g., A1C13, BF3, and ZnCl2) [150], alkali metal compounds [160], organozinc compounds [161], tin compounds of which stannous octoate [also referred to as stannous-2-ethylhexanoate or tin(II) octoate] is the most well known [162-164], organo-acid rare earth compounds such as lanthanide complexes [165-168], and aluminum alkoxides [169]. Stannous-2-ethylhexanoate is one of the most extensively used initiators for the coordination polymerization of biomaterials, thanks to the ease of polymerization and because it has been approved by the FDA [170]. 

The Henry reaction is routinely performed in the presence of only catalytic quantities of a base. Several base catalysts including alkali metal hydroxides, carbonates, bicarbonates, alkoxides, calcium and barium hydroxides and magnesium and aluminum ethoxides have been used. Anion-exchange resins and, among organic bases, primary and tertiary amines and ammonium acetate and fluoride have proven to be... 

Alkali metal hydroxides, dissolution rate effect, 521-523f Alkoxides, formation of uniform precipitates, 451-464 Aluminum, silicic acid effect on adsorption in food, 612/ 613 Aluminum in biological systems, 604, 605f, 606 Aluminum-modified silica sol, formation, 62, 63/ Aluminum-silicon interactions in biology,... 

Chirally modified lanthanide alkoxides [prepared in situ from Ln(0-/-Bu)3 and chiral ligands] give higher asymmetric induction in the reduction of acetophenone (for La. 32%ee) than the normally used aluminum or alkali metal alkoxides208. However, the decrease of ee values with increasing reaction time shows that kinetic control is not maintained with 2-propanol as the reducing agent. 

Metal alkoxides, also known as alcoholates, constitute a class of compounds in which the metal atom is attached to one or more alkyl groups by an oxygen atom. These substances have the general formula, M—O—R, where M is the metal atom and R, an alkyl group. Many metals in the Periodic Table are known to form alkoxides. However, only a few of them have commercial applications. These include the alkali and alkaline-earth metals, aluminum, titanium, and zirconium. Metal alkoxides have found applications as catalysts, additives for paints and adhesives, and hardening agents for synthetic products. They are also used in organic synthesis. 

A stereospecific anionic polymerization of acetaldehyde was originally reported in 1960 [343, 344]. Two alkali metal compounds [341] and an organozinc [342] one were used as the initiators. Trialkylaluminum and triarylaluminum in heptane also yield crystalline, isotactic polymers from acetaldehyde, heptaldehyde, and propionaldehyde at -80°C [343]. Aluminum oxide, activated by diethylzinc, yields stereoblock crystalline polymers from various aldehydes [342, 344], Lithium alkoxide formed polyacetaldehyde is insoluble in common solvents. It melts at 165°C [341],... 

The strategy of metal alkoxides synthesis is entirely related to the electronegativity of the element concerned. Some electropositive metals, such as alkali metals, alkaline earth metals, and lanthanides, react directly with alcohols. But some less electropositive metals such as magnesium and aluminum require a catalyst (I or HgCy for successful reaction with alcohols. Use of electrochemical synthesis by anodic dissolution of some metals or metalloids (Sc, Y, Ti, Zr, Nb, Ta, Fe, Co, Ni, Cu, Pb, Si, Ge, etc.) in dry alcohol performs a promising procedure because it does not produce any by-products except hydrogen gas. Another applicable method for the synthesis of some alkoxides (B, Si, Ti, Zr, Hf, Nb, Ta, Fe, etc.) is the reaction of their chlorides with alcohols which require a base such as... 

Alkali metal alkoxides have also been examined in some detail. The addition of bulky lithium alkoxides to alkyllithium initiators retards the rate of intramolecular cyclization, thus allowing the polymerization temperature to be raised. LiCl has been used to similar effect, allowing the preparation of monodisperse PMMA (Af /Mn = 1.2) at -20 Sterically bulky lithium aluminum alkyls have been used to similar effect, with good chain length control retained even at ambient temperature. However, these approaches have not yet been successfully applied to stereoselective polymerizations. 

As already highlighted in the partial list of Scheme 20, various groups of compounds may act as precursors alkali metals alkali metal hydrides, oxides, hydroxides, alkoxides, halides, carbonates alkali metal salts of organic acids alkyl aluminums alkali aluminum hydrides and their alkoxides quaternary ammonium salts guanidium salts of lactams, etc. 

The reaction is facile at room temperature and in the absence of catalysts only for alkali metals (M = Li, Na, K) and barium [59]. To obtain the derivatives of alkaline earth metals with aliphatic alcohols, it is necessary to apply heat (reflux) and add a catalyst, usually elementary iodine, to clean the surface of the metal applied [110]. The same is true for aluminum alkoxides that can be produced in high yields by reaction of aluminum metal with dry alcohols on addition of l2(s) [2]. For drying the alcohols, one can apply aluminum alkoxides produced even from household aluminum foil, but it is necessary to remember that the latter is doped by some few percent of iron and is not a suitable material for the synthesis of aluminum alkoxides for preparation of high-purity ceramics. 

The classic study of Al(OR)3 was carried out by Tishchenko [1585] at the end of nineteenth century. His dissertation, entitled On the Action of Amalgamated Aluminum on Alcohols (Aluminum Alkoxides, Their Properties and Reactions), became a great resonance for the chemistry of alkoxides (see also Chapter 1). The synthetic approaches, that he developed are still in use the purity of the samples obtained by Tishchenko, taking into account the data he reported, was definitely not worse than that of those described at present. In 1929 Meerwein and Bersin [1101], performing the acidimetric titration of Al(OR)3 solutions by solutions of alkali alkoxides, discovered the existence of bimetallic alkoxides (Meerwein salts), which play an important role in the modern chemistry of metal alkoxides. 

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