[tareek]

How does a carboxylic acid like benzoic acid react with two equivalents of a grignard reagent. I know for a fact that the carboxylic acid will firstly get deprotonated but then i dont know how the second equivalent reacts.

[Hunter2]

It will not react.
You get a carboxylat negative anion in first step. Another Grignard would increase the charge to -2. Its not possible.

[tareek]

It will not react.
You get a carboxylat negative anion in first step. Another Grignard would increase the charge to -2. Its not possible.

So it just forms the carboxylic acid back right ?

[Hunter2]

No it stop at the carboxylat anion. The Magnesium salt of the acid.
Its only a Kind of Neutralisation.

CH3- + RCOOH => CH4 + RCOO-

Cation ist Magnesium with half halogenid.

[tareek]

But we use H3O + as well in the solution. Sorry i didnt say it was in acidic conditions

[Hunter2]

No, the H3O + is used to destroy the Magnesium bromide alcoholate. To obtain the product. This will added after the reaction is finished.

[tareek]

Okay thanks a lot now everything is way more clear

[rolnor]

lithium carboxylates do react with alkyl- or aryllithio-reagents to form ketones, but Grignards do not give this reaction.

[tareek]

So will it stay as a carboxylat or will it stay as an acid group

[Hunter2]

It stays as Carboxylat. The acid you get if you add another stronger acid.