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

Jan 1, 2016

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:

$R - M g X + {H}_{2} O \rightarrow R - H \uparrow + M g X O H$

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

$R - M g X + {\text{^2H_2O rarr R-""^2H + MgXO-}}^{2} H$

This would be much cheaper than buying the labelled reagent from a commercial supplier. ${D}_{2} O$ 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.