Synthesis Of Magnesium Alcoholates

The study of the chemistry of metal alkoxides,which began more than 100 years ago,is now experiencing a renaissance connected with the broad application of these compounds as molecular precursors in the synthesis of materials of modern technology based on simple and complex oxides.The solution of this problem is occupying a wide circle of inorganic chemists,technologists specializing in fine synthesis in nonaqueous media,and those working on the production of film and coatings.The application of metal alkoxides in the first step of sol-gel technology can benefit from this monograph covering the modern literature devoted to all the steps of this process.Magnesium alcoholates Mg(OR)₂,R=alkyl,are solids sensitive to hydrolysis which can be used in organic synthesis as selective bases and as constituents of ploymerising catalysts.Due to the ability of the bivalent magnesium cation to form stable chelate complexes with carbonyl compounds,magnesium methylate for example is used as a selective carbonyl condensing agent.Three synthesis routes was proposed based on literatures and comprehensive comparison with other ways.First,Magnesium methylate is prepared by reacting magnesium metal with dry methanol.The magnesium salts of higher"primary alcohols,i.e.alcohols with ≥ 2 carbon atoms,do not react directly with pure alcohols under normal conditions.In fact catalysts are required to set the reaction in motion and the preparation is performed under pressure at the higher temperatures.Second,the sterically demanding substituted magnesium alcoholates can be prepared from dialkylmagnesiums R₂Mg and alcohol.The main disadvantage of this synthesis route lies in the fact that relative expensive dialkyl magnesium compounds,such as Et₂Mg for example,have to be used as starting materials.For this problem,a convenient preparation route of pure dialkylmagnesium from a Grignard reagent.To the clear solution of the Grignard reagent, 1.5mol equivalent ofMe(OCH₂CH₂)₂OMe as tetrahydrofuran solution was added drowise at about 0—10℃ during 30 min.,and the mixture was stirred for 3h.The solution was filtered with glass filter and the filtrate of dialkylmagnesium.The key of this reaction is that the yield of dialkylmagnesium is only 88%,even 1.5mol equivalent of Me(OCH₂CH₂)₂OMe was added,and this is the important research aspect for the furure.Third, most magnesium alcoholates are prepared by alcoholysis.The process is based on the exchange of alkoxide groups of a metal alcoholate in the presence of an alcohol other than the alcohol corresponding to the original alkoxide,i.e.on the alcoholysis of a metal alkoxide with a different alcohol. Primary alcoholates can be prepared by this process,such as magnesium di-n-propanolate,magnesium di-n-butanolate,magnesium di-isobutanolate.But the purity and yield of magnesium di-tert-butanolate is only 80% by alcoholysis.In addition,adding toluene to tert-butanol can also increase the he purity of production,and the purity of the product is 88%.To settle this problem,we replaced tert-butanol by tert-butyl acetate,and got the magnesium di-tert-butanolate with the purity of 95.6%.Mostly magnesium alcoholates can be prepared by those synthesis routes. Magnesium methylate can be prepared by reacting magnesium with dry methanol; Primary alcoholates can be prepared by alcoholysis; the sterically demanding substituted magnesium alcoholates can be prepared by ester exchange or from dialkylmagnesiums.