Preparation of Activated Magnesium

Renaud first reported that improved yields to Grignard reagents, as well as organolithiums and aluminiums, could be obtained by sonolysis of the reagents in undried diethyl ether (960 kHz, 2 W cm ). These results were first published in 1950 but did not kindle further interest in the use of ultrasound to accelerate chemical reactions [64]. 

The overall process is rapid and avoids the need to use the high boiling solvents recommended by Rieke [69a], or naphthalene, which may prove difficult to remove. p-Bromoethylbenzene reacts with magnesium prepared in this way at 0 °C and hydrolysis of the Grignard reagent gives the reduced product in over 90 % yield. These results are comparable with those of Riecke. 

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Arnoid, R. T., Kuienovic, S. T. Activated metais. A procedure for the preparation of activated magnesium and zinc. Synth. Common. 1977,... 

In general it can be stated that modern developments in the preparation of active magnesium have been extremely helpful to overcome starting problems of reactions of organo halides with this metal. 

Typical Procedures for Preparation of Active Magnesium and Typical Grignard Reactions as Well as 1,3-Diene Chemistry... 

Chemistry of (2-Butene-1,4-diyl)magnesium Preparation of Activated Magnesium (Mg )... 

Different syntheses of y-amino-/3-ketoeter derivatives from iV-protected L-aminoacids by Al,Al -carbonyldiimidazole activation and treatment with the magnesium enolate of hydrogen ethyl malonate are described. These compounds are useful intermediates in the preparation of active amino acid analogues, as illustrated and summarized in equation 103. 

Figure 8 The cell and the procedure for the in situ preparation of active metal electrodes such as Li and magnesium. The metal rod is pressed through the C.E. into the W.E. and a SS wire is wrapped around it. The three parts are placed in the polyethylene bath, which is filled with solution. Once in solution the SS wire is pulled to cut the rod and prepare fresh surfaces in solution. The last stage includes rearrangement of the electrodes in the bath [17]. (Reprinted with copyright from Elsevier Science Ltd.)...

Freshly distilled THF (10 ml) is added to the active magnesium (black powder), followed by the appropriate substrate. This is the current method of choice for the preparation of Rieke magnesium [54]. 

The mixture of active magnesium metal and potassium salts as prepared before is allowed to cool to room temperature, after which 1.25 g (0.00958 mol) of 1-chloronorborane is injected with a syringe through the septum into the flask. 

Fig. 21. Preparation and reaction of activated magnesium via the Mg.BTHF complex (anthracene).

Dialkylaminoethyl acryhc esters are readily prepared by transesterification of the corresponding dialkylaminoethanol (102,103). Catalysts include strong acids and tetraalkyl titanates for higher alkyl esters and titanates, sodium phenoxides, magnesium alkoxides, and dialkyitin oxides, as well as titanium and zirconium chelates, for the preparation of functional esters. Because of loss of catalyst activity during the reaction, incremental or continuous additions may be required to maintain an adequate reaction rate. 

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