Magnesium, reactive forms

Formation of aryl Grignard reagents (Section 14.4) Aryl halides react with magnesium to form the corresponding arylmagnesium halide. Aryl iodides are the most reactive, aryl fluorides the least. A similar reaction occurs with lithium to give aryllithium reagents (Section 14.3). 

CAUTION The flammability of magnesium is well known, and appropriate precautions must be taken when handling it (see note concerning fire extinguishers on p. 18). The more finely divided the magnesium, the greater the hazard, and the very reactive forms, especially the slurries described below, are PYROPHORIC in contact with air). 

The highly reactive form of magnesium obtained by dry stirring (see under Activation of magnesium , below, may also be regarded as a slurry. 

Magnesium anthracene. Syntheses of organomagnesium compounds from the magnesium-anthracene adduct (see p. 40) proceed via dissociation of the adduct to give magnesium in a highly reactive form [9, 10]. Indeed, anthracene may be used to catalyse the reactions of other forms of magnesium (see below). 

Alternative routes to unimolecular reduction include hydrogen abstraction by ketyls (see (ii)), Meerwein-Ponndorf reduction by alkoxides [A]f and reduction by a reactive form of magnesium hydride... 

The alkaline earths, beryllium, magnesium, calcium, strontium, barium, and radium, together constitute Group 2 of the periodic table. They are usually found in relatively un-reactive forms, bound to oxygen the free metals still have a tendency to lose their outer electrons, but less easily than the Group 1 elements, and are a little less reactive. 

An alternative to the use of magnesium oxide as the additive is to inject magnesium hydroxide into the high temperature zone to provide a highly reactive form of magnesium oxide, i.e. 

Highly reactive form (5, 419). Details for the preparation of Rieke s activated and pyrophoric magnesium have been submitted to Organic Synthesis. The powder should be kept under argon. The preparation includes synthesis of benzoic acid in 70-897o yield from bromobenzene. 

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