Overall reaction
Sodium phenoxide + CO₂ (4–7 atm or more), 125 °C, then H₃O⁺ → salicylic acid
Phenoxide carboxylates at the ortho position with CO₂ under pressure.
Name reaction · mechanism
Kolbe–Schmitt Reaction (Kolbe Reaction)
In the Kolbe–Schmitt reaction (often called the Kolbe reaction in Indian syllabuses) sodium phenoxide is heated with carbon dioxide under pressure. The ring carbon ortho to O⁻ attacks CO₂, the dienone tautomerises back to an aromatic ring, and acid work-up gives salicylic acid — the industrial route to aspirin.
Mechanism step by step
- Attack on CO₂. The ortho carbon attacks; a dienone forms
- Tautomerisation. Loss of the ring H restores aromaticity
- Acid work-up. Both oxygens are protonated
Each step is checked electron by electron: the curly arrows give exactly the structures drawn.
Key points
- Industrial route to salicylic acid, then aspirin.
- Sodium phenoxide gives mainly ortho; potassium phenoxide favours para.
- CO₂ is a weak electrophile: heat and pressure are needed.
- Phenoxide is far more reactive than phenol because O⁻ donates strongly.
For JEE and NEET
- Phenoxide, not phenol, reacts: O⁻ makes the ring far more nucleophilic.
- Sodium phenoxide gives mainly ortho (salicylic acid); potassium phenoxide at higher temperature favours para.
- Salicylic acid + acetic anhydride → aspirin (acetylsalicylic acid).
- Do not confuse with Kolbe electrolysis (carboxylate salts → alkanes at the anode).
FAQ
Why does phenol need to be converted to phenoxide?
CO₂ is a weak electrophile. The negative oxygen donates strongly into the ring, so only phenoxide is nucleophilic enough to attack it.
What is the product of the Kolbe reaction?
Salicylic acid (2-hydroxybenzoic acid) after acidification; the sodium salt forms first.
What is the difference between Kolbe and Kolbe–Schmitt?
They are usually the same reaction (Schmitt added the pressure conditions). Kolbe electrolysis is a different reaction.
Draw it in MolDraw
The button above opens the complete figure — overall reaction, numbered mechanism and key points — as ordinary editable structures. Change substituents, recolour atoms, or export a PNG, SVG or chemfig code for notes and slides. The same figure is in the Templates panel under Name reactions.