Question

Why is ether used as the solvent during Grignard reactions?

Answer 1

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

Explanation:

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.

Answer 2

the very simple reason is that in ether, there is no acidic Hydrogen present on which the Grignard reagent `RMgX` can attack and get itself converted to `R-H`.

Explanation:

thus to prevent Grignard from decomposing simply to an alkane/ene/yne, we use ether.