Simple Metal Alkoxides

The chemistry of metal alkoxides is considerably different from that of silica acid esters also called silicon alkoxides. Metal alkoxides are salts of alcohols as 

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 

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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. 

The mass spectra do not give any conclusive evidence in the gas phase probably due to the breakdown of the heterometallic alkoxides into simple metal alkoxides, and finally decomposes into simple metal oxides under the high vacuum pressure used in mass speedometer. 

The choice of commercially available simple metal alkoxides is actually a bit larger, incorporating diluted solutions of alkali and some alkaline earth metal alkoxides in parent alcohols as welL The latter are very sensitive to moisture and oxygen on storage. In feet, they can be produced by customary synthesis in situ. 

Much work has been done on the structure of the metal alkoxides (49). The simple alkaU alkoxides have an ionic lattice and a layer stmcture, but alkaline earth alkoxides show more covalent character. The aluminum alkoxides have been thoroughly studied and there is no doubt as to their covalent nature the lower alkoxides are associated, even in solution and in the vapor phase. The degree of association depends on the bulkiness of the alkoxy group and can range from 2 to 4, eg, the freshly distilled isopropylate is trimeric (4) ... 

The ease of hydrolysis of metal alkoxides makes metal analysis a comparatively simple task. In many cases, the metal may be estimated by hydrolysis of a sample in a cmcible, and ignition to the metal oxide. Alternatively, the metal ion may be brought into solution by hydrolysis of a sample with dilute acid, followed by a standard analytical procedure for a solution of that particular metal. If the alcohol Hberated during the hydrolysis is likely to cause interference, it may be distilled from the solution by boiling. 

Various inorganic esters have been claimed as coupling agents for reinforced plastics, including aminobenzyl phosphonates, dicetylisopropylborate, alkoxy compounds of aluminum, zirconium and titanium, zircoaluminates, and numerous substituted titanates [1]. These metal alkoxides could function in a similar manner to the orthosilicates by reacting with hydroxylated substrates. Like the simple orthosilicates such as tetraethyl orthosilicate (TEOS), it is less evident how an-... 

HYDROLYSIS OF METAL ALKOXIDES AND SYNTHESIS OF SIMPLE OXIDES BY THE SOL-GEL METHOD... 

Chapter 9. Hydrolysis of metal alkoxides and synthesis of simple oxides... 

Now for some of the reactions you have seen in the last few chapters. Starting with carbonyl substitution reactions, the first example is the conversion of acid chlorides into esters. The simplest mechanism to understand is that involved when the anion of an alcohol (a metal alkoxide RO ) reacts with an acid chloride. The kinetics are bimolecular rate = fc[MeCOCl] [RO ]. The mechanism is the simple addition elimination process with a tetrahedral intermediate. 

Simple (RO)4Si compounds may readily be prepared by the reaction between a chlorosilane and an alcohol (or phenol) (Scheme 41). A problem in this type of reaction is that the HCl formed may canse unwanted side reactions. This may be minimized by blowing dry N2 gas throngh the reaction mixture or heating the reaction so that HCl is driven olf as it is formed, or a tertiary amine snch as pyridine may be added to the reaction, which forms an amine hydrochloride salt that precipitates to remove the HCl. Sihcon alkoxides may also be made by reaction of a sihcon halide and an aUcah metal alkoxide (Scheme 41). ... 

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