Why is ether used as the solvent during Grignard reactions?

Ether is used as a solvent because it is aprotic and can solvate the magnesium ion.

A Grignard reaction involves the reaction of an alkyl (or aryl halide) with magnesium metal to form an alkylmagnesium halide.

##"R-X" + "Mg" stackrelcolor(blue)("dry ether"color(white)(X))(→) "R-MgX"##

Diethyl ether is an especially good solvent for the formation of Grignard reagents for two reasons.

(a) Ether is an aprotic solvent

The ##"R-Mg"## bond is highly polar: ##stackrelcolor(blue)(δ^(-))("R"color(white)(l))-stackrelcolor (blue)(δ^+)("Mg")"X"##

The Grignard carbon is highly basic and reacts with the acidic protons of polar solvents like water to form an alkane.

##stackrelcolor (blue)(δ^(-))("R"color(white)(l))"-"stackrelcolor (blue)(δ^+)("Mg")"X" + "H-OH" → "R-H" + "HO-MgX"##

Ether has no acidic protons, so Grignard reagents are stable in ether.

(b) Ether is a great solvating agent

The ##"MgX"## bond in a Grignard reagent is ionic: ##"R-Mg"^+ color(white)(l)"X"^-##.

Hence, it is difficult to form a Grignard reagent in a nonpolar solvent.

The ##"C-O"## bond in an ether is quite polar, and the oxygen of the dipole can solvate and stabilize the ##"R-Mg"^+## ion.

Thus, Grignard reagents are soluble in ether.