Lehmstedt – Tănăsescu reaction

The Lehmstedt-Tănăsescu reaction also known as the Lehmstedt-Tănăsescu method or the Lehmstedt-Tănăsescu-acridone synthesis is a name reaction in organic chemistry . The reaction was named after the Romanian chemist Ioan Tănăsescu (1892-1959), who discovered it in 1928, and the German chemist Kurt Lehmstedt . With the help of this reaction, acridones and their derivatives can be synthesized from 2-nitrobenzaldehyde and aromatic components.

Overview reaction

In the presence of sulfuric acid and catalytic amounts of sodium nitrite , 2-nitrobenzaldehyde and chlorobenzene react to form 3-chloroacridone.

Instead of chlorobenzene, other benzene derivatives can also react with 2-nitrobenzaldehyde to form acridone or the corresponding derivatives.

mechanism

As there is only limited information about the mechanism, the following illustration is only a suggested course of the reaction. Under the acidic reaction conditions, sodium nitrite turns into nitrous acid , which reduces the nitro group and oxidizes itself to nitric acid. This later oxidizes the alcohol group and is thus reduced again to nitrous acid.

Reaction mechanism of the Lehmstedt – Tănăsescu reaction

First, the carbonyl group of 2-nitrobenzaldehyde 1 is protonated . This is followed by a nucleophilic attack by the chlorobenzene on the partially positively charged carbon atom of carbonyl group 2 . The six-membered ring of chlorobenzene 3 rearomatizes with elimination of an H ⁺ ion . In addition, a molecule of nitrous acid positions itself near the nitro group 4 . The nitrous acid reduces the nitro group via the intermediate state of a five-membered ring 5 to a nitrosyl group 6 and leaves the molecule oxidized as a nitric acid molecule. The nitrosyl group is protonated and then attacked in turn by the chlorobenzene aromatic compound 7 . The splitting off of a proton 8 then causes a further rearomatization 9 . Finally, the alcohol group is oxidized to the keto group by the nitric acid 10 , the nitric acid is again present as a catalyst and an acridone derivative is formed as product 11 .

Individual evidence

↑ ^a ^b J. J. Li: Name Reactions in Heterocyclic Chemistry II . John Wiley & Sons, Inc., Hoboken, New Jersey 2011, ISBN 978-0-470-08508-0 , pp. 368-369.
↑ ^a ^b ^c ^d Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 1731-1732.
↑ Ioan Tănăsescu: Bull Soc Chim Fri . tape 41 , 1927, pp. 528 .
↑ Kurt Lehmstedt: A simple synthesis of acridone and 3-substituted acridone (IX. Communication on acridine). In: Reports of the German Chemical Society (A and B Series). 65, No. 5, 1932, pp. 834-839, doi: 10.1002 / cber.19320650531 .
↑ Kurt Lehmstedt, Karl Schrader: Syntheses in the Acridon Series (XVII. Communication. About Acridine). In: Reports of the German Chemical Society (A and B Series). 70, No. 7, 1937, pp. 1526-1538, doi: 10.1002 / cber.19370700714 .

[Li_368-1] J. J. Li: Name Reactions in Heterocyclic Chemistry II . John Wiley & Sons, Inc., Hoboken, New Jersey 2011, ISBN 978-0-470-08508-0 , pp. 368-369.

[Wang_1731-2] Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-471-70450-8 , pp. 1731-1732.

[3] Ioan Tănăsescu: Bull Soc Chim Fri . tape 41 , 1927, pp. 528 .

[4] Kurt Lehmstedt: A simple synthesis of acridone and 3-substituted acridone (IX. Communication on acridine). In: Reports of the German Chemical Society (A and B Series). 65, No. 5, 1932, pp. 834-839, doi: 10.1002 / cber.19320650531 .

[5] Kurt Lehmstedt, Karl Schrader: Syntheses in the Acridon Series (XVII. Communication. About Acridine). In: Reports of the German Chemical Society (A and B Series). 70, No. 7, 1937, pp. 1526-1538, doi: 10.1002 / cber.19370700714 .