MECHANICAL ACTIVATION OF MAGNESIUM TURNINGS FOR THE PREPARATION OF REACTIVE GRIGNARD-REAGENTS

Preactivation of magnesium by dry stirring in an inert atmosphere is highly beneficial for the clean synthesis of reactive allylic or benzylic organomagnesium chlorides. This procedure routinely produces 0.4 M solutions of the Grignard reagent in diethyl ether free from coupling products. The purity may be directly assayed by C-13 NMR spectroscopy. Using spin saturation transfer techniques, the rate constant for interconversion of the enantiomers of (1-phenyl-2-methylpropyl)magnesium chloride in Et2O at 25-degrees-C was shown to be < 0.2s-1. Electron microscopy has been used to define the surface changes occurring e during the dry stirring of magnesium turnings.