# What's the purpose of a Grignard reagent initiation?

Preface: I've read this question about water preventing an initiation from occurring.

I understand why it's important to slowly add the alkyl halide to the dry ether and magnesium for exotherm control. But why is the first addition called an initiation and what's its purpose?

Is it just to confirm that the conditions are ready to continue slowly adding the rest of the reagent? I know it's a free-radical reaction, maybe that's where the term "initiation" comes from. But I've seen the reaction described as "self-sustaining" after the initiation, but it's not a chain reaction. Perhaps that's referring to a predictable reaction proceeding forward instead of stalling then blowing up your glassware.

First, you are mixing magnesium metal with an alkyl halide. The product of this reaction is $\ce{R-Mg-I}$, where $\ce{R}$ is the alkyl group and $\ce{I}$ is the halide. It is called an initiation reaction because you first need to make the reactive compound.