Formation of carboxylic acids from Grignard reagents and CO2
Description: Grignard reagents will add to carbon dioxide, forming carboxylate salts. After acidic workup, carboxylic acids are formed.
Notes: X here is unimportant – could be Cl, Br or I. The type of acid for workup is not crucial – could also write “H+” or HCl, etc.
Notes: Note that the type of Grignard reagent is unimportant for the reaction; each ends up giving the carboxylic acid.
Mechanism: The reaction proceeds through 1,2-addition of the Grignard reagent to the carbonyl carbon of carbon dioxide (Step 1, arrows A and B) to form a carboxylate salt. When acid is added, the oxygen of the carboxylate is protonated (Step 2, arrows C and D).
Notes: There is nothing special about Br(–) here, it’s just the counter-ion of H3O(+) .