The Kolbe–Schmitt reaction/Kolbe process (named after Adolph Wilhelm Hermann Kolbe

Adolph Wilhelm Hermann Kolbe

Adolph Wilhelm Hermann Kolbe was a German chemist. He never used the first two of his given names, preferring to be known as Hermann Kolbe.-Life:...

 and Rudolf Schmitt

Rudolf Schmitt

Rudolf Schmitt was a German chemist who together with Adolph Wilhelm Hermann Kolbe discovered the Kolbe-Schmitt reaction.-Biography:...

) is a carboxylation chemical reaction

Chemical reaction

A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

 that proceeds by heating sodium phenolate (the sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 salt

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

 of phenol

Phenol

Phenol, also known as carbolic acid, phenic acid, is an organic compound with the chemical formula C6H5OH. It is a white crystalline solid. The molecule consists of a phenyl , bonded to a hydroxyl group. It is produced on a large scale as a precursor to many materials and useful compounds...

) with carbon dioxide

Carbon dioxide

Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 under pressure (100 atm

Atmospheric pressure

Atmospheric pressure is the force per unit area exerted into a surface by the weight of air above that surface in the atmosphere of Earth . In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point...

, 125°C), then treating the product with sulfuric acid

Sulfuric acid

Sulfuric acid is a strong mineral acid with the molecular formula . Its historical name is oil of vitriol. Pure sulfuric acid is a highly corrosive, colorless, viscous liquid. The salts of sulfuric acid are called sulfates...

. The final product is an aromatic hydroxy acid

Acid

An acid is a substance which reacts with a base. Commonly, acids can be identified as tasting sour, reacting with metals such as calcium, and bases like sodium carbonate. Aqueous acids have a pH of less than 7, where an acid of lower pH is typically stronger, and turn blue litmus paper red...

 which is also known as salicylic acid

Salicylic acid

Salicylic acid is a monohydroxybenzoic acid, a type of phenolic acid and a beta hydroxy acid. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin...

 (the precursor to aspirin

Aspirin

Aspirin , also known as acetylsalicylic acid , is a salicylate drug, often used as an analgesic to relieve minor aches and pains, as an antipyretic to reduce fever, and as an anti-inflammatory medication. It was discovered by Arthur Eichengrun, a chemist with the German company Bayer...

).

By using the potassium

Potassium

Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

 salt

Salt

In chemistry, salts are ionic compounds that result from the neutralization reaction of an acid and a base. They are composed of cations and anions so that the product is electrically neutral...

 4-hydroxybenzoic acid is accessible, an important precursor for the versatile paraben class of biocides used e.g. in personal care products.

Reaction mechanism

The Kolbe–Schmitt reaction proceeds via the nucleophilic addition of a phenolate to carbon dioxide to give the salicylate. The final step is reaction of the salicylate with acid to form the desired salicylic acid.