Metal methoxides

The reaction is driven to completion by distilling the lower boiling alcohol. Metal methoxides are frequentiy insoluble and caimot be employed as starting materials in this reaction by the same token, they can be convenientiy prepared from solutions of higher alkoxides by precipitation with methanol. Alcoholysis also gives mixed metal alkoxides ... 

Salt effects on the reaction of 2,4-dinitrochlorobenzene with amines or alkoxides have been investigated.Reinheimer et al. have studied decelerative ion pairing of alkali metal methoxides in reaction with this substrate cations and anions in added salts have specific effects on ion pairing. 

Metal-methoxide reactions of phosphates, phosphorothioates, phosphonates and phosphonothioates. The rate constant data for the (La3 + ( OCH3))2 and 9 Zn2 + ( OCH3)-catalyzed methanolysis of the phosphates and phosphorothioates are given in Tables 9 and 10, respectively, while those for the phosphonates (22a-f)17e and phosphonothioates (23a-e)1 s are given in Tables 11 and 12 along with the corresponding methoxide data. The latter two series data are displayed in... 

Ion-Pairing effects have been recorded occasionally in connection with the use of high alkali metal methoxide concentrations.170... 

To exhibit such an active and selective catalytic effect, the catalyst must be a fairly good hydrogenation catalyst that is able to activate molecular hydrogen. It must also activate carbon monoxide without dissociating it. A nondissociative chemisorption permits the hydrogenation of carbon monoxide to occur on both oxygen and carbon. Considering the formation of surface methoxide in the second mechanism [Eq. (3.43)], a further requirement is that the catalyst not form a too stable metal methoxide. 

The advantages of using lithium salts instead of sodium salts for the preparation of insoluble metal methoxides has been discussed.67 68... 

Alkylation has been carried out with alkyl halides in methanolic alkali metal methoxide,08 103104 112,114 273 in aqueous ethanolic solution of potassium hydroxide and potassium iodide,106 281 and in dimethylforma-mide in the presence of potassium carbonate.114 Alkylation generally led to more than one product. 

Alkylsilyl sulphates were determined180 by potentiometric and conductiometric titration in anhydrous alcohols, ketones, methyl cyanide or nitromethane. Titration curves were the same for all solvents. In potentiometry, titration with sodium, potassium or lithium methoxide gave curves with one step titration with quaternary ammonium compounds gave curves with two steps. In conductiometry, titration with quaternary ammonium compounds gave curves with no inflection, whereas titration with alkali metal methoxides gave curves with a sharp break at the end-point. 

The acidity function H increases as the concentration of alkali metal methoxide in methanol is increased. Introducing the expressions for acidity and autoprotolysis constants into eqn. 3.5.11. we can write it in the form... 

In concentrated solutions the value of H depends on the particular alkali metal methoxide used. For equimolar solutions lithium... 

To reduce the reaction time between diisocyanates and dianhydrides, catalysts such as alkali metal methoxides, or alkali metal fluoride can be optionally combined with a quaternary onium salt. ° However, the addition of catalysts are not advised in the productions of yarns that should exhibit good characteristics. ... 

Most metal chlorides undergo only partial metathetical halide/alkoxide exchange upon reaction with alcohols or no reaction at all even at elevated temperatures. The metal alkoxide chlorides thus obtained, MClx(OR), have not been used in sol-gel processing (see, however. Section 7.10.3.3.2). In order to achieve the preparation of homoleptic metal alkoxides from metal chlorides basic conditions are essential in order to trap the liberated HCl. This can be achieved by reaction of metal chlorides with alcohols in the presence of a base such as ammonia or, less often, trialkylamines or pyridine (Equation (11a)). The base also increases the equilibrium concentration of alkoxide ions, which are a more powerful nucleophile for reaction with the metal chloride than the parent alcohol. For this reason the use of alkali alkoxides (M OR), mostly lithium, sodium, or potassium alkoxides, proves to be more successful (Equation (11b)). The use of LiOR has advantages for the preparation of insoluble metal methoxides because LiCl is soluble in methanol and is thus easily separated from insoluble metal alkoxides. 

The most prevalent known termination process is an intramolecular cychzation (Scheme 23.3) with concomitant formation of an inactive metal methoxide species. This is shown as an anionic process in Scheme 23.3 but may also occur with the metal covalently bonded to the polymer chain end. Cyclization would be expected to occur most readily for sterically unhindered chains, explaining the tendency of poly(acrylate)s such as PMA to be particularly susceptible to this form of... 

Apart from the monomeric methoxides of the metalloids (B, Si, Ge, As, and Te) which are very volatile and soluble in organic solvents, most of the metal methoxides (except niobium and tantalum pentamethoxides and uranium hexamethoxide) are comparatively nonvolatile and insoluble in common organic solvents. Attempts have been made to... 

Table 2.23 Magnetic moment, reflectance spectral data, and proposed stereochemistry of first row transition metal methoxides and ethoxides...

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. 

The rate of polymerization of 4-vinylpyridine in dimethyl sulphoxide initiated by metal methoxides increases with increasing free methanol content and it was concluded" that methanol participates in solvation. The effect of the presence of diphenyl ether upon the addition of 1,1-diphenylethylene to polystyryl-lithium has been examined. Remarkably, neither the kinetics nor the rate was affected even when as much as 0.15M-diphenyl ether was admixed with 10 — 10 M-polystyryl-lithium. 

Accordingly, methanol reacts with the metal acetylide to form metal methoxide and acetylene. The methoxide decomposes to formaldehyde, whieh undergoes a condensation reaction to yield acetaldehyde. Hydrogenation of the acetaldehyde yields ethanol Similar aldol eondensation reaetions occur among the aldehydes with carbon number 1 to yield hi er alcohols. 

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