Preparation of Grignard reagents

Preparation of Grignard reagents (e.g. phenylmagnesium bromide) Br MgBr 

The apparatus shown in Fig. 6.21a, incorporating either a mechanical or magnetic stirrer, can be used for preparation of Grignard reagents Add dry 

Purpose To execute techniques required to prepare Grignard reagents from aryl and alkyl halides. 

Diethyl ether is extre/ne/y flammable and volatile, and its vapors can easily travel several feet along the bench top or the floor and then be ignited. Consequently, be certain there are no open flames anywhere in the laboratory 

The anhydrous diethyl ether used in this experiment is contained in metal cans, and the screw or plastic cap should always be in place when the can is not in use to prevent evaporation, absorption of atmospheric moisture and oxygen, and accidental fires. 

Open containers of diethyl ether must not be kept at your laboratory bench or stored in your laboratory drawer. Estimate the total volume of ether you will need and measure it in the hood into a container that is /oose/y stoppered. 

Lubricate all ground-glass joints in the apparatus carefully and mate them tightly to prevent the escape of diethyl ether during the reaction. 

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Diethyl ether is a mobile, colourless liquid having b.p. 35° and dy 0720. It has a characteristic odour, and a burning taste. It is used chiefly as a solvent, and was formerly widely used as an anaesthetic owing to its chemical non-reactivity, it is very seldom used actually as a reagent, except in the preparation of Grignard reagents (p. 280) where probably its chemical properties reinforce its solvent action. 

HIGHLY REACTIVE MAGNESIUM FOR THE PREPARATION OF GRIGNARD REAGENTS 1-NORBORNANECARBOXYLIC ACID... 

Small amounts of cyclized products are obtained after the preparation of Grignard reagents from 5-hexenyl bromide.9 This indicates that cyclization of the intermediate radical competes to a small extent with combination of the radical with the metal. Quantitative kinetic models that compare competing processes are consistent with diffusion of the radicals from the surface.10 Alkyl radicals can be trapped with high efficiency by the nitroxide radical TMPO.11 Nevertheless, there remains disagreement about the extent to which the radicals diffuse away from the metal surface.12... 

Sato, F. Urabe, H. Preparation of Grignard Reagents from Olefins and Acetylenes. In Handbook of GrignardReagents Silverman, G. S., Rakita, P. E., Eds. Dekker New York, 1996 chapter 3, pp 23-52. 

There remains to be mentioned a secondary reaction which often takes place, undesired, in the preparation of Grignard reagents, but is also sometimes aimed at. 

Preparation of Grignard reagents is frequently beset by practical difficulties in establishing the reaction (i.e. is usually subject to an induction period). Improved equipment and control methods for safer preparations have been described [2], Initiation of the Grignard reaction has been studied in a heat flow calorimeter [3],... 

The ( /4-bicyclo[2.2.1]hepta-2,5-diene)bis( /3-2-propenyl)ruthenium(II) and (>/4-cycloocta-l,5-diene)bis(>/3-2-propenyl)ruthenium(II) complexes have previously been reported,5,6 but we present here scaled-up procedures that produce synthetically useful quantities of these compounds. The preparation of Grignard reagents is based upon the methods described by Eisch.7... 

Highly reactive powder (5, 419 7, 218). An improved procedure uses lithium together with an electron carrier (naphthalene or biphenyl, 10% based on Li) in THF, which need not be removed before preparation of Grignard reagents or other reagents.1... 

This process is similar to the formation of Grignard reagents 4 from alkyl halides and Mg(0). In the preparation of Grignard reagents, Mg(0) is oxidized to Mg(II) by the oxidative addition of alkyl halides to form two covalent bonds. 

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