Why is Grignard dry?

1 Answer
Jun 13, 2016

Because the natural enemy of a Grignard reagent, and of organometallic reagents in general is water.

Explanation:

Grignard reagents, though not as water-sensitive as lithium reagents are reactive to water. Dry ethers are generally used in their synthesis.

RX+MgRδMgXδ+

Once the Grignard has been prepared, quenching with water gives back the hydrocarbon:

RδMgXδ++H2ORH+MgXOH

Sometimes, we can exploit that reactivity. Suppose, for another experiment we needed the deuterated alkane, we could quench the Grignard with heavy water:

RδMgXδ++2H2OR2H+MgXO2H

Deuterium oxide, D2O, is quite cheap as labelled solvents go.