Preparation of Grignard Reagents
Grignard reagents are produced when an organic halide, such as an alkyl, aryl, or vinyl halide, is treated with small pieces of magnesium metal in the presence of a completely dry ether solvent, like diethyl ether or tetrahydrofuran. The reaction takes place in specially dried glassware because even a trace of moisture can destroy the reagent.
To start the reaction, the magnesium surface is sometimes activated by gentle heating or by adding a small crystal of iodine. Once the reaction begins, it proceeds quite vigorously, releasing heat. The ether solvent plays an essential role: it not only dissolves the reactants but also stabilizes the newly formed Grignard reagent by surrounding the magnesium atom.
The product of this process is the Grignard reagent, which consists of an organic group directly bonded to magnesium along with a halogen atom. The reagent is obtained as a solution in ether and is never isolated in pure form because of its high reactivity.
In short: Grignard reagents are prepared by reacting an organic halide with magnesium metal in a dry ether solvent under moisture-free conditions.