Metal alkoxides commercial production

Pyrrohdinone forms alkaU metal salts by direct reaction with alkaU metals or their alkoxides or with their hydroxides under conditions in which the water of reaction is removed. The potassium salt prepared in situ serves as the catalyst for the vinylation of 2-pyrrohdinone in the commercial production of A/-vinylpyrrohdinone. The mercury salt has also been described, as have the N-bromo and N-chloro derivatives (61,62). 

While high polymers of /3-lactones can also be formed by cationic polymerization, most of the commercial production seems to be by the anionic route. Carboxylate salts such as sodium acetate or benzoate are commonly the initiators, but other nucleophiles, such as triethylamine, betaine, potassium f-butoxide, aluminum and zinc alkoxides, various metal oxides and tris(dimethylamino)benzylphosphonium chloride (the anion of which is the initiator), are of value. Addition of crown ethers to complex the counter cation increases the rate of reaction. When the reaction is carried out in inert but somewhat polar organic solvents, such as THF or ethyk acetate, or without solvent, chain propagation is very fast and proceeds without transfer reactions. 

An important advantage of the electrochemical technique lies in its simplicity because metals are much easier to handle than metal halides and are always commercially available the consumption of the solvents is also much smaller than for conventional techniques [1639, 1612]. The electrochemical method allows the creation of a highly efficient, low-waste continuous process for commercial production of metal alkoxides [948]. 

Both reactions are used for the commercial production of alkaline and alkaline-earth alkoxides from very cheap raw materials. As far as the metal alkoxides thus formed are soluble in alcohols, both reactions are reversible. Thus, application of these methods is expedient in the case of alcohols with the boiling temperature higher than 100°C (water is distilled off). When low-boiling alcohols are used the reaction time increases greatly, water is eliminat-... 

Few data are available on the hydrolysis of simple metal alkoxides of these elements. Alkoxides of alkaline and alkaline earth metals are mostly used as precursors for the preparation of complex oxides or solid oxide solutions. Commercial production of pure magnesium oxide by hydrolysis of Mg(OMe)2 with formation of transparent gel has been described [715], as well as hydrolysis of Mg(OC5H11i)2 with the following thermal treatment to produce a fine MgO powderthat sinters at low temperatures [1766]. Solutions prepared by dissolving magnesium in methoxyethanol are by far the most convenient precursors for preparation of magnesium oxide films. 

In this case, the silylation of the metal alkoxide initially formed represents the key step of the overall process which releases the chromium salt from the organic product. The other crucial parameter is the use of the stoichiometric reducing agent for the regeneration of the active Cr" species. Commercial Mn turned out to be particularly well suited, as it is very cheap, its salts are essentially non-toxic and rather weak Lewis acids, and the electrochemical data suggest that it will form an efficient redox couple with Cr . Moreover, the very low propensity of commercial Mn to insert on its own into organic halides guarantees that the system does not deviate from the desired chemo- and diastereoselective chromium path. Thus, a mixture of CrX ( = 2, 3) cat., TMSCl and Mn accounts for the first Nozaki reactions catalytic in chromium [13]. 

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. 

These were developed to impart some of the properties of tung oil to the non-conjugated oils, such as linseed or soybean oil. The processes involved treatment of those latter oils with catalysts such as nickel, alkali or alkali metal alkoxides to conjugate the double bonds. Products with up to 50% diene and 15% triene conjugation could be obtained. They resembled dehydrated castor oil more than tung oil in properties. None is used commercially to any extent at the present time. 

The reaction described by Eq. (5.9) forms the most useful procedure for the preparation of many alkoxides (including Zr, Hf, Si, Ti, Fe, Nb, Ge, V, Ta, Th, Sb, U, and Pu) and is used widely for commercial production. The reaction between anhydrous metal chlorides and sodium alkoxide in the presence of excess alcohol and an inert solvent such as benzene or toluene is also a usefiil method ... 

In addition to the nse of specific Lewis bases to influence the vinyl content of products formed via anionic polymerizations, the use of alkali metal alkoxide salts in lithinm polymerizations can also affect the ratio of vinyl enchainment (338). Salts of lithinm have little to no effect on microstructure at typical molecular weights and commercial polymerization temperatures, while those of sodium, potassium, and rubidinm increase the vinyl content significantly. The addition of... 

The electrochemical technique appears to have been successfully employed in Russia for the commercial production of alkoxides of Y, Ti, Zr, Nb, Ta, Mo, W, Cu, Ge, Sn, and other metals. 

Despite the lack of selectivity, some structured Upid-hke products have been synthesized by chemicals methods. The catalyst most often used for chemical interesterification of triacylglycerols or for alcoholysis between triacylglycerols and fatty acids is sodium methoxide, which is more active than other base, metal or acid catalysts. In general, sodium alkoxides are easy to use as catalysts. They are inexpensive, active at relatively low temperatures (50-90 ), and are effective at low concentrations. Although no regioselectivity or fatty acid selectivity occurs, the chemically synthesized commercial products listed in Table 2 contain sTAG with the desired nutritional function. 

It is to be noted that alkoxides of more electropositive metals - alkaline, alkaline earth, rare earth (RE), and Zr(IV), Hf(IV), and Sn(IV) - often form quite stable complexes with protic ligands, which are also Lewis bases (alcohok, amines). Their formation is supported by both complexation of the metal atom with this additional Lewis base function, which is apparently weaker than the alkoxide one, and formation of the hydrogen bonds with active hydrogen atoms of the additional ligands [61]. No stable complexes are formed with stronger but aprotic nucleophiles such as trialkylamines, R3N [62]. Very often, the alcohol solvates have a bit lower solubility, but are easily purified by recrystallization, which makes them attractive as commercial products. When the pure alkoxides are highly... 

A large number of metal alkoxides are available commercially (see Table 6.2). These are mostly the derivatives of main group or early transition elements M (III), M(rv), and M(V). The availability is dictated by request Thus, the derivatives of Al, Ti, and Zr are large-scale products offered by multiple producers. The alkoxides of rare earth elements became broadly available in the 1990s in connection with the studies of high-temperature superconductor materials, produced then in particular by sol-gel synthesis. Their accessibility strongly declined since then as they are used at the moment mostly as additives to luminescent materials and the desired quantities have apparently decreased. 

Titanium alkoxides are also effective and sought-after initiators for the ROP of lactides due to a low toxicity, which minimizes the problems linked to the presence of catalyst residues in commercial PLA products [18, 19]. Despite impressive advancements in the use of Lewis acidic metal initiators in the preparation of PLAs, surprisingly little attention has been paid to the group 4 metal (Ti, Zr, Hf) initiators, probably due to the highly oxophilic nature of M(1V) which has a natural tendency to form aUcoxy-bridged multinuclear complexes. Verkade and coworkers previously demonstrated a series of titanium aUcoxide complexes 118-122 (Fig. 17) that function as moderately efficient initiators in bulk homopolymeization of L-lactide and rac-lactide, some of these initiators displaying a well-controlled polymerization behavior [119]. 

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