Grignard reagents undergo carboxylation to synthesize carboxylic acids with one more carbon atom than the starting Grignard reagent.

Here, the Grignard reagent acts as a nucleophile. It first attacks the electrophilic carbon of carbon dioxide to form a metal carboxylate, resulting in the formation of a new carbon–carbon bond.

Next, the metal carboxylate is acidified to generate the free carboxylic acid product.

As Grignard reagents are synthesized from organic halides, carboxylation of a Grignard reagent is a suitable method to convert an organic halide to a carboxylic acid. Here, the organyl group can be an alkyl, vinyl, or aryl.

For example, tert-butyl chloride can be converted to its corresponding one-carbon-higher carboxylic acid in substantial yield.

Recall that Grignard reagents are strong bases and powerful nucleophiles. Hence, organic halides bearing functional groups incompatible with Grignard reagents are seldom used in this two-step formation of carboxylic acids.