In the grand scheme of things, carbon-carbon bonds are pretty stable. They don’t just break.
But there’s one important exception to this.
Carboxylic acids that have a carbonyl group two carbons over (this is called the “beta” position) can lose carbon dioxide quite readily – heating above 150 degrees C will do the trick.
Most carboxylic acids won’t lose CO2 this way, because it would lead to formation of an unstable carbanion. But when a carbonyl is present, two carbons over, an enol can be formed, which is resonance-stabilized.
Here’s what the reaction looks like.
You might notice that these types of molecules (beta-keto acids) can be obtained through the Claisen condensation. So later on, we’ll see how the decarboxylation reaction can be combined with the Claisen (and related reactions) to make different molecules.
Tomorrow – another reaction that the “resonance stabilization” of enolates makes possible.
Thanks for reading! James