The Doebner reaction is the

chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the pos ...

of an

aniline Aniline is an organic compound with the formula C6 H5 NH2. Consisting of a phenyl group attached to an amino group, aniline is the simplest aromatic amine In organic chemistry, an aromatic amine is an organic compound consisting of an aroma ...

with an

aldehyde In organic chemistry, an aldehyde () is an organic compound containing a functional group with the structure . The functional group itself (without the "R" side chain) can be referred to as an aldehyde but can also be classified as a formyl grou ...

and

pyruvic acid Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...

to form

quinoline Quinoline is a heterocyclic aromatic organic compound with the chemical formula C9H7N. It is a colorless hygroscopic liquid with a strong odor. Aged samples, especially if exposed to light, become yellow and later brown. Quinoline is only sli ...

-4-

carboxylic acid In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxylic ...

s.Bergstrom, F. W. ''

Chem. Rev. ''Chemical Reviews'' is peer-reviewed scientific journal published twice per month by the American Chemical Society. It publishes review articles on all aspects of chemistry. It was established in 1924 by William Albert Noyes (University of Illinoi ...

'' 1944, ''35'', 156. (Review) The reaction serves as an alternative to the

Pfitzinger reaction The Pfitzinger reaction (also known as the Pfitzinger-Borsche reaction) is the chemical reaction of isatin with base and a carbonyl compound to yield substituted quinoline-4-carboxylic acids. Several reviews have been published. Reaction mechan ...

.W. Pfitzinger: ''Chinolinderivate aus Isatinsäure.'' In: ''Journal für Praktische Chemie.'' Band 33, Nr. 1, 1886, S. 100, doi:10.1002/prac.18850330110.Oscar Doebner: ''Ueber α-Alkylcinchoninsäuren und α-Alkylchinoline.'' In: ''Justus Liebigs Annalen der Chemie.'' Band 242, Nr. 3, 1887, S. 265–388, doi:10.1002/jlac.18872420302.

Reaction mechanism

The reaction mechanism is not exactly known, two proposals are presented here. One possibility is at first an

aldol condensation An aldol condensation is a condensation reaction in organic chemistry in which two carbonyl moieties (of aldehydes or ketones) react to form a β-hydroxyaldehyde or β-hydroxyketone (an aldol reaction), and this is then followed by dehydration to ...

, starting from the enol form of the pyruvic acid (1) and the aldehyde, forming an ''β,γ''-unsaturated α-ketocarboxylic acid (2). This is followed by a

Michael addition In organic chemistry, the Michael reaction or Michael addition is a reaction between a Michael donor (an enolate or other nucleophile) and a Michael acceptor (usually an α,β-unsaturated carbonyl) to produce a Michael adduct by creating a carbon ...

with aniline to form an aniline derivative (3). After a cyclization at the benzene ring and two proton shifts, the quinoline-4-carboxylic acid (4) is formed by water elimination: RMV5 Doebner-Reaktion 60

An alternative mechanism is based on the aniline and the aldehyde forming at first the

Schiff base In organic chemistry, a Schiff base (named after Hugo Schiff) is a compound with the general structure ( = alkyl or aryl, but not hydrogen). They can be considered a sub-class of imines, being either secondary ketimines or secondary aldimine ...

upon water elimination. The subsequent reaction with the enol form of pyruvic acid (1) leads to the formation of the above-mentioned aniline derivative (3) followed by the above-described reaction mechanism:
RMAV2 Doebner-Reaktion 60

Side reactions

It is reported in the literature that the Doebner reaction fails in case of 2-chloro-5-aminopyridine. In this case the cyclization would take place at the amino group instead of the

benzene ring Benzene is an organic chemical compound with the molecular formula C6H6. The benzene molecule is composed of six carbon atoms joined in a planar ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, ...

and lead to a

pyrrolidine Pyrrolidine, also known as tetrahydropyrrole, is an organic compound with the molecular formula (CH2)4NH. It is a cyclic secondary amine, also classified as a saturated heterocycle. It is a colourless liquid that is miscible with water and most ...

derivative.Martin J. Weiss, Charles R. Hauser: ''Failure of the Doebner Reaction with 2-Chloro-5-

aminopyridine Aminopyridine may refer to any of several chemical compounds: * 2-Aminopyridine * 3-Aminopyridine 3-Aminopyridine is an aminopyridine. It is a colorless solid. Preparation 3-Aminopyridine is prepared by heating nicotinamide with sodium hypobr ...

. Synthesis of a Pyrrolidine Derivative.'' In: ''Journal of the American Chemical Society.'' Band 68, Nr. 4, 1946, S.722–723, doi:10.1021/ja01208a513.

Alternative reactions

Alternative syntheses of quinoline derivatives are for example: *

* Conrad-Limpach reaction * Doebner-Miller reaction *

Combes quinoline synthesis The Combes quinoline synthesis is a chemical reaction, which was first reported by Combes in 1888. It involves the condensation of unsubstituted anilines (1) with β-diketones (2) to form substituted quinolines (4) after an acid-catalyzed ring closu ...

References

{{Reflist Carbon-carbon bond forming reactions Condensation reactions Quinoline forming reactions Multiple component reactions Name reactions