Carboxylic Acids and Their DerivativesReactions of Alcohols

The Reaction of Grignard and Organolithium Reagents with Carbon Dioxide

We have seen in many examples how Grignard and organolithium reagents react with various carbonyl compounds such as aldehydes, ketones, esters, and more. So, let’s discuss what happens when we react a Grignard or organolithium reagent with carbon dioxide. Although CO₂ may be seen as an unreactive gas because of its abundance in the atmosphere and its relative rarity in classic organic reaction textbooks, its central carbon atom is highly electrophilic.

 

 

Each C=O bond is a polarized π bond. Oxygen, being more electronegative, pulls electron density away from carbon, leaving it with a partial positive charge (δ⁺). This makes it a linear molecule primed for attack by strong nucleophiles such as the Grignard and organolithium reagents.

Remember, these are organometallics where the carbon is connected to a metal and, because of their low electronegativities, they render the carbon atom rich in electron density, thus making them strong bases and nucleophiles.

 

The Mechanism of Grignard and Organolithium Reagents with Carbon Dioxide

In the first step, the nucleophilic carbon chain of your organometallic reagent (R⁻ from RMgX or RLi) attacks the electrophilic carbon atom of CO₂, breaking one of its π bonds. That attack pushes the π electrons onto one oxygen, giving you a metal‑stabilized carboxylate ion. The carboxylate ion is simply treated with an aqueous acidic work‑up (H₃O⁺), converting the carboxylate into the corresponding carboxylic acid:

 

 

Notice that the carbon chain is extended by one carbon atom coming from the carbon dioxide, so this is a great synthetic strategy for introducing a new functional group and extending the carbon chain.

 

 

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