Grignard reactions

The Grignard Reaction

The Grignard reaction is an organometallic chemical reaction in which alkyl or aryl-magnesium halides (Grignard reagents) act as nucelophiles and attack electrophilic carbon atoms that are present within polar bonds (e.g. in a carbonyl group as in the example shown below) to yield a carbon-carbon bond, thus altering hybridisation about the reaction center. The Grignard reaction is an important tool in the formation of carbon-carbon bonds as well as for the formation of carbon-phosphorus, carbon-tin, carbon-silicon, carbon-boron and other carbon-heteroatom bonds.

The reaction is irreversible due to the high pKₐ (see notes on equilibrium) value of the alkyl component (pKₐ =~45). Such reactions are not ionic; the Grignard reagent exists as an organometallic cluster (in ether).

The disadvantage

The disadvantage of Grignard reagents is that they readily react with protic solvents (e.g. water) or with functional groups with acidic protons, such as alcohols and amines. In fact, the atmospheric humidity in the laboratory can dictate the success of synthesis of a Grignard reagent from magnesium turnings and an alkyl halide.

Another disadvantage…