Grignard reagent

Grignard reagents are a type of chemical compound. They are used in the Grignard reaction, an important tool used in organic synthesis to make new chemical bonds between carbon atoms.

Grignard reagents have three parts: an organic group, written as R, a magnesium atom, and a halogen atom written X. The chemical formula for a Grignard reagent is written RMgX. These reagents are normally a coordination complex with solvent molecules, not a pure solid, so the formula is also sometimes written including them. For example, a solution of methylmagnesium chloride in tetrahydrofuran could be written CH₃MgCl(THF)₂.

Preparation

Grignard reagents are normally made from an organohalide and magnesium metal. The normal reaction mechanism starts with a single electron transfer from the magnesium atom to the organohalide, which breaks apart into a halide anion and an organic radical. The radical then bonds with the Mg⁺ radical cation, finishing the reagent.

For example, the reaction of chloromethane and magnesium:

CH₃Cl + Mg → ·CH₃ + ·Mg⁺ + Cl⁻ → CH₃MgCl

Reactions

Grignard reagents RMgX are normally treated as equivalent to the R⁻ carbanion. They are very strong nucleophiles and bases, and will react with any source of hydrogen ions to make an alkane and magnesium salts. This means they cannot be used in protic solvents like water.

The most important reaction for Grignard reagents is the Grignard reaction. In this reaction, they react with electrophilic carbon atoms in carbonyl compounds, making magnesium alkoxides. A workup with water normally changes the alkoxide into an alcohol.

Sources

This short article about chemistry can be made longer. You can help Wikipedia by adding to it.