Dakin reaction

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The Dakin reaction or Dakin oxidation is a name reaction in organic chemistry, it was first introduced in 1909 by Henry Drysdale Dakin and is used to synthesize dihydric phenols from 2- or 4- hydroxybenzaldehyde . Instead of the substituted benzaldehyde, hydroxy- substituted aryl ketones can also be used as starting material.

Overview of the Dakin reaction in which a phenolic hydroxyl group is formed by the action of hydrogen peroxide from an aromatic aldehyde (above) or ketone (below) in a basic medium ( sodium hydroxide solution ) ; R denotes an alkyl group in aryl ketones or a hydrogen atom in aryl aldehydes.

The hydroxyl group in the starting material can also be replaced by other substituents with a + M effect on the ring, e.g. B. an amino group . In addition, this group can be in both the ortho and the para position to the carbonyl group. The Dakin reaction is a special case of the Baeyer-Villiger oxidation .

mechanism

The reaction takes place as described above with every functional group with + M effect, but here the mechanism is only shown with one hydroxyl group as an example. In addition, the remainder can be in both the ortho and the para position, but this is only demonstrated in the mechanism as an example for the para position.

Mechanism of the Dakin reaction; R denotes a hydrogen atom or an alkyl radical.

First, the hydroxyl group of the aryl ketone (R = organyl group ) or of the aryl aldehyde (R = H) is deprotonated in 1 to form the phenolate 2 . Under the action of hydrogen peroxide in an alkaline medium, the hydroperoxide 3 is formed , which is rearranged into the quinoid epoxide 4 . The ester 5 is formed under rearomatization . The alkaline saponification of 5 produces a carboxylic acid via intermediate 6 and the 1,4-diphenolate 7 . The stepwise protonation of 7 finally yields hydroquinone ( 9 ).

Individual evidence

  1. ↑ Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009 , p. 829, ISBN 978-0-471-70450-8 .
  2. ^ Siegfried Hauptmann : Organic chemistry . 2nd reviewed edition, VEB Deutscher Verlag für Grundstoffindindustrie, Leipzig, 1985 , p. 337, ISBN 3-342-00280-8 .
  3. ↑ Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 3 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009 , p. 830, ISBN 978-0-471-70450-8 .