Question

Why does the glassware have to be dry in a grignard reaction?

Answer 1

Because water is the natural enemy of the Grignard reagent.

Explanation:

Grignard reagents (and organometallic reagents in general) are usually formed with the strict exclusion of water. A Grignard reagent is strongly nucleophilic and will react with water rapidly and irreversibly:

`R-MgX + H_2O rarr R-Huarr + MgXOH`

Note that sometimes we can exploit this reactivity if we wanted to put a deuterium label (`""^2H`) on the molecule, i.e.

`R-MgX + ""^2H_2O rarr R-""^2H + MgXO-""^2H`

This would be much cheaper than buying the labelled reagent from a commercial supplier. `D_2O` is (as labelled solvents go) very cheap.

I am sure that there are similar answers on Socratic, but it's always hard to find the one you need.