[kolly]

I still don't quite understand the main difference between Grignard and Barbier reactions based on their definitions. Is it the metal used? Substrate? Mechanism?

Suppose I want to make an alpha-benzyl alcohol from benzaldehyde and an alkyl bromide. If I use magnesium. Would that automatically make it a Grignard reaction instead of Barbier?
And how come Barbier reaction is less sensitive to water?

Thank you so much in advance

[Hunter2]

The reaction is similar to the Grignard reaction but the crucial difference is that the organometallic species in the Barbier reaction is generated in situ, whereas a Grignard reagent is prepared separately before addition of the carbonyl compound.[1] Unlike many Grignard reagents, the organometallic species generated in a Barbier reaction are unstable and thus cannot be stored or sold commercially. Barbier reactions are nucleophilic addition reactions that involve relatively inexpensive, water insensitive metals (e.g zinc powder) or metal compounds. For this reason, it is possible in many cases to run the reaction in water, making the procedure part of green chemistry. In contrast, Grignard reagents and organolithium reagents are highly moisture sensitive and must be used under an inert atmosphere without the presence of water. The Barbier reaction is named after Philippe Barbier, who was Victor Grignard's teacher.

[rolnor]

I gave you a Mole snack Hunter2