Formation of Grignard Reagents from Alkyl Halides

by James

Description: Treatment of alkyl halides with magnesium metal leads to formation of a Grignard reagent.
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Notes: X here is a halide. This reaction works with alkyl chlorides, bromides, or iodides. Sometimes “ether” is also written. This is the solvent, it doesn’t actually participate in the reaction.

Examples: 

Notes: Note that in example 2 the structure below the reaction is diethyl ether. This is just a solvent, it doesn’t take part in the reaction.

Mechanism: Note that the mechanism of this reaction is generally not considered important for Org 1/ Org 2.

The first step here is donation of an electron to Br from the Mg. This leads to fragmentation of the C–Br bond, forming a radical. The second step is reformation of the C–Mg bond to give the Grignard reagent.

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{ 1 comment… read it below or add one }

Polina Porotsky

Would I be correct in stating that the Grignard reagent is so basic, with such a high pKa (approx. 50) that it is able to de-protonate any hydrogen with a lower pKa? Additionally, that in a synthesis it will de-protonate the most acidic hydrogen?

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