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.

Examples:

Notes:

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(+) .