Koch reaction

The Koch reaction is an organic reaction for the synthesis of tertiary carboxylic acids from alcohols or alkenes and carbon monoxide. Some commonly industrially produced Koch acids include pivalic acid, 2,2-dimethylbutyric acid and 2,2-dimethylpentanoic acid. The Koch reaction employs carbon monoxide as a reagent and can therefore be classified as a carbonylation. The carbonylated product is converted to a carboxylic acid, so in this respect the Koch reaction can also be classified as a carboxylation.

Pivalic acid is produced from isobutene using the Koch reaction, as well as several other branched carboxylic acids. An estimated 150,000 tonnes of "Koch acids" and their derivatives annually.

Koch–Haaf-type reactions have been used to carboxylate adamantanes.

The reaction is a strongly acid-catalyzed carbonylation and typically proceeds under pressures of CO and at elevated temperatures. The commercially important synthesis of pivalic acid from isobutenes operates near 50 °C and 50 kPa (50 atm). Generally the reaction is conducted with strong mineral acids such as sulfuric acid, HF, or phosphoric acid in combination with BF₃.

Formic acid, which readily decomposes to carbon monoxide in the presence of acids, can be used instead of carbon monoxide. This method is referred to as the Koch–Haaf reaction. This variation allows for reactions at nearly standard room temperature and pressure.

The mechanism has been intensively scrutinized. The mechanism involves generation of a tertiary carbenium ion, which binds carbon monoxide. The resulting acylium ion is then hydrolysed to the tertiary carboxylic acid:

The carbenium ion can be produced either by protonation of an alkene or protonation/elimination of a tertiary alcohol:

Standard acid catalysts are sulfuric acid or a mixture of BF₃ and HF.