Houben-Hoesch reaction

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The Houben-Hoesch reaction , also known as the Hoesch synthesis , Hoesch reaction , Houben-Hoesch acylation or Houben-Hoesch synthesis , is a name reaction in organic chemistry . The reaction was named after Kurt Hoesch (1882–1932), who published it in 1915, and after Josef Houben (1875–1940) (published in 1926). With the help of the reaction, electron-rich aromatics can be acylated .

Overview reaction

Electron-rich aromatics, such as phenols with several hydroxyl groups or corresponding ethers (shown here by way of example with resorcinol ), can in the presence of hydrogen chloride and a Lewis acid (such as AlCl 3 or ZnCl 2 ) with organic nitriles [R = organyl group (e.g. . Alkyl group , aryl group )] are acylated:

Overview reaction of the Houben-Hoesch reaction

mechanism

The mechanism is shown using the example of the reaction between 1,3-dihydroxybenzene ( resorcinol ) and an organic nitrile (R = alkyl group, aryl group). As a Lewis acid, for. B. Aluminum chloride (AlCl 3 ) used:

Reaction mechanism of the Houben-Hoesch reaction;

First, the nitrile 1 forms a complex 2 with aluminum chloride and complex 3 with another aluminum chloride . This complex reacts with resorcinol in the course of an electrophilic aromatic substitution via intermediate step 4 to form molecule 5 , with AlCl 3 leaving the molecule. Additional mesomeric boundary structures can be drawn for molecule 4 , which correspond to the boundary structures in the course of a third substitution . The reaction with water leads to renewed elimination of the Lewis acid aluminum chloride. The molecule 6 finally reacts with hydrogen chloride to form the ketone 7 , in the example an acylated resorcinol.

Individual evidence

  1. ↑ Kurt Hoesch: A new synthesis of aromatic ketones. I. Representation of some phenol ketones . In: Reports of the German Chemical Society . tape 48 , no. 1 , 1915, p. 1122-1133 , doi : 10.1002 / cber.191504801156 .
  2. ↑ Grete Ronge:  Houben, Josef. In: New German Biography (NDB). Volume 9, Duncker & Humblot, Berlin 1972, ISBN 3-428-00190-7 , pp. 659 f. ( Digitized version ).
  3. ↑ J. Houben: About the nuclear condensation of phenols and phenol ethers with nitriles to phenol and phenol ether ketimides and ketones (I.) . In: Reports of the German Chemical Society (A and B Series) . tape 59 , no. 11 , 1926, pp. 2878-2891 , doi : 10.1002 / cber.19260591135 .
  4. ↑ K. Schwetlick et al .: Organikum. 23rd edition, Wiley-VCH, Weinheim 2009, ISBN 978-3-527-32292-3 , p. 385.
  5. ↑ 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 , p. 1496.