- Active Magnesium from Catalytically Prepared Magnesium Hydride or from Magnesium Anthracene and its Uses in the Synthesis
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Highly reactive, pyrophoric forms of magnesium with specific surface areas of 20-109 m2/g (Mg*) can be generated by the dehydrogenation of catalytically prepared magnesium hydride (MgH2*) or by decomposition of magnesium anthracene * 3 THF (4).The decomposition of 4, with recovery of anthracene and THF, may be accomplished both thermally and by ultrasound in an organic solvent (toluene, n-heptane) or thermally in the solid state in vacuo.Mg* obtained by the latter method exhibits only weak reflections in the X-ray powder diagram and has, in comparison to other mentioned Mg* species, the highest reactivity toward hydrogen.Diverse Grignard compounds can be prepared under mild conditions (* from MgH2* or 4.The cleavage of THF with formation of 1-oxa-2-magnesiacyclohexane (2) is possible by employing Mg* from NgH2* or 4.
- Bartmann, Ekkehard,Bogdanovic, Borislav,Janke, Nikolaus,Liao, Shijan,Schlichte, Klaus,et al.
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p. 1517 - 1528
(2007/10/02)
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- Use of Magnesium Anthracene * 3 THF in Synthesis: Generation of Grignard Compounds and Other Reactions with Organic Halides
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The course (a), (b), (c) (Scheme 1) of the reaction of magnesium anthracene * 3 THF (1) with organic halides (RX) is dependent on the nature of RX.With alkyl halides in THF 1 reacts as a nucleophile, whereby primary as well as secondary alkyl halides produce dialkyldihydroanthracenes (4-4'') and tertiary alkyl halides yield primarily monoalkyl-substituted dihydroanthracenes (2, 2').With bromo- and iodobenzene in THF 1 reacts predominantly as a radical with H atom abstraction from the solvent affording benzene and 9.The formation of Grignard compounds (5) and anthracene (6), originating from primary and secondary alkyl and aryl halides and 1 in toluene or ether at elevated temperatures, is not caused by the reaction of 1 but by the "active magnesium" (Mg*) formed by decomposition of 1 in these solvents.In contrast, allyl, propargyl, and benzyl halides react with 1 independently of the solvent under mild conditions to produce 5 and 6.Allyl- and the difficultly accessible allenylmagnesium chloride can be prepared in THF at -78 and 0 deg C, respectively, from the corresponding halides and ordinary Mg powder via catalytic amounts of 1.
- Bogdanovic, Borislav,Janke, Nikolaus,Kinzelmann, Hans-Georg
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p. 1507 - 1515
(2007/10/02)
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- Process for using finely divided highly reactive magnesium
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The present invention relates to a process for preparing a finely divided, highly reactive magnesium from magnesium hydride, magnesium anthracene and/or its derivatives or magnesium butadiene and/or its alkyl or phenyl derivatives, which process is characterized in that the respective magnesium-containing compound is thermally decomposed at a pressure from 10-6 to 1 bar, the decomposition being carried out in the presence of a co-reactant of a consecutive reaction, or such co-reactant being added only after completion of the precipitation of the magnesium, or in the absence of such co-reactant, the magnesium obtained by said decomposition being isolated as a powder, and to the use of the finely divided, highly reactive magnesium for inserting magnesium into poorly reactive C--X bonds, wherein X denotes heteroatoms such as halogen, oxygen, sulfur, nitrogen, phosphorus, and the resulting organomagnesium compound may be used in a consecutive reaction according to a per se known method, and for the reversible preparation of active magnesium hydride by reaction with molecular hydrogen at a pressure of from 1 to 2 bar and at a temperature of from 150° C. to 250° C.
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