Koch reaction

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The Koch reaction or Koch-Haaf carbonylation is a name reaction in organic chemistry that was named after its discoverer, the German chemist Herbert Koch (1904–1967).

Overview reaction

The Koch reaction allows the atom-economical production of tertiary , saturated carboxylic acids (" Koch acids ") from alkenes - in the example isobutene - with carbon monoxide :

A carbon monoxide molecule is integrated into the alkene with the addition of water and sulfuric acid. The resulting carboxylic acids are called cooking acids.

Reaction mechanism

In the first step, the double bond of alkene 1 is protonated by the addition of sulfuric acid , which creates the formally positively charged tertiary carbenium ion 2 . The carbon atom of carbon monoxide is formally negatively charged, which is why it can attack the carbenium ion. The creation of a new CC single bond creates a mesomeric-stabilized acylium ion 3 . The addition of water to 3 produces the oxonium ion 4 :

Reaction mechanism of the Koch reaction

In the last step 4 is deprotonated, whereby the carboxylic acid 5 is formed.

Practical meaning

The alkyl branches in the α-position to the carboxy group lead to strong steric hindrance , which, among other things, results in strong thermal stability and heavy saponifiability. That is why esters of the “cooking acids” are particularly stable. Cooking acids per se are often processed into resins and paints , while metal salts of highly branched cooking acids can be used as drying accelerators. In addition, the starting materials (alkene, carbon monoxide) are cheap and easily accessible, which is why the Koch reaction is of considerable industrial importance.

alternative

Alternatively, the Koch reaction can also start from a tertiary alcohol such as tert- butanol :

Alternative reaction scheme for the Koch reaction based on tert-butanol

Individual evidence

  1. ↑ H. Koch, W. Haaf: About the synthesis of branched carboxylic acids by the formic acid method , Liebigs Ann. Chem . 1958 , 618, 251-266.
  2. ↑ a b J. Arpe: Industrial organic chemistry: important preliminary and intermediate products . Wiley-VCH, 2007, ISBN 3-52731540-3 .
  3. ↑ Jie Jack Li: Name reactions: A collection of detailed mechanisms and synthetic applications . 5th ed.Springer, Cham 2014, ISBN 978-3-319-03979-4 , pp. 349 , doi : 10.1007 / 978-3-319-03979-4 .
  4. ↑ Bradford P. Mundy; Michael G. Ellerd; Frank G. Favaloro: Name reactions and reagents in organic synthesis . 2nd ed. Wiley, Hoboken (NJ) 2005, ISBN 0-471-73987-1 , pp. 368 .