Kolbe-Schmitt reaction
The synthesis of ortho - hydroxybenzoic acid and its derivatives by heating alkali metal phenolates with carbon dioxide under high pressure is known as the Kolbe-Schmitt reaction or Kolbe synthesis . The reaction was discovered in 1860 by A. W. H. Kolbe as a method for the synthesis of salicylic acid , where he carried out the conversion of the above components at 180-200 ° C.
This synthesis was improved in 1885 by Rudolf Schmitt .
mechanism
A complex of sodium phenolate and carbon dioxide is postulated for the mechanism of this reaction , which together with the stability of the chelate complex formed as an intermediate product also explains the high ortho selectivity of this reaction. As a result of the complexation, the carbon dioxide molecule experiences a polarization, whereby its electrophilic character is increased, and it is fixed in a position that only allows the ortho attack on the ring. This is also referred to as the chelate effect . Rearomatization occurs with the formation of an OH group on the carbonylene oxygen atom. Now the negatively charged oxygen atom attacks the sulfuric acid. Emerge with sodium bisulfate and ortho -hydroxybenzoic acid (salicylic acid).
The corresponding para- hydroxybenzoic acid and its derivatives can be synthesized from the respective potassium phenates.
The Kolbe-Schmitt reaction is restricted to phenols and substituted phenols (also more highly fused phenols such as naphthols ). This reaction is still used today for the technical synthesis of salicylic acid from sodium phenolate, which is why the Kolbe-Schmitt reaction is often referred to simply as salicylic acid synthesis .
literature
- HR Christen, Fritz Vögtle : Organic Chemistry, From the Basics to Research . Volume I. Otto Salle Verlag, 1988, ISBN 3-7935-5397-3
- Alexander R. Surrey: Name Reactions in Organic Chemistry . 2nd edition. Academic Press, 1961, ISBN 0-12-677450-1
- Heinrich Schwarz: An important chemical discovery . In: The Gazebo . Issue 7, 1875, pp. 123 ( full text [ Wikisource ]).
Web links
Individual evidence
- ↑ H. Kolbe: About a new method of representation and some remarkable properties of salicylic acid. In: Journal für Praktische Chemie , 10, 1874, pp. 89-112.
- ↑ Patent US334290 : Manufacture of salicylic acid. Published January 12, 1886 , inventor: R. Schmitt.
- ^ László Kürti and Barbara Czakó: Strategic Applications of Named Reactions in Organic Synthesis: Background and Detailed Mechanisms , Elsevier Academic Press, 2005, ISBN 978-0-12-429785-2 , pp. 248-249.