Quelet reaction

The Quelet reaction (or Blanc-Quelet reaction ) is a name reaction in organic chemistry . The reaction was named after the chemist R. Quelet who discovered it. In this synthesis, an electron-rich aromatic (e.g. anisole ) is substituted in the para position by an α-haloalkyl radical. In the case of a haloalkane (or haloalkyl radical), one or more hydrogen atoms of an alkane (or alkyl) have been replaced by halogen atoms. For example, chloromethane (CH ₃ Cl) is a haloalkane derived from methane and chloromethyrest (-CH ₂ Cl) is a haloalky group.

Overview reaction

Haloalkylated aromatics are produced by reacting dry hydrochloric acid with anisole (methylphenyl ether) and an aliphatic aldehyde in the presence of a Lewis acid (here ZnCl ₂ ). If the aromatic is blocked in the para position, the reaction takes place in the ortho position of the aromatic.

The radical R is an alkyl radical , for example a methyl radical. The reaction creates a bicyclic by-product.

Reaction mechanism

The possible reaction mechanism comes from the book " Comprehensive Organic Name Reactions and Reagents " and is carried out here using anisole - an electron-rich aromatic - as an example :

The aldehyde 1 now reacts with the Lewis acid (here the ZnCl ₂ ) and forms a secondary valence bond to the zinc. The phenyl group of the anisole also forms such a bond, so that intermediate 2 is formed. (At this point an already chlorinated derivative can also be bound to the zinc, whereby the by-product from the overview reaction is created with an analogous mechanism.) As a result, the carbon atom of the carbonyl group can now be attacked by a double bond and the result is, with elimination of chloride , Carbenium ion 3 . During rearomatization, a hydroxyl group is formed with the elimination of zinc chloride . The benzyl alcohol 4 is reacted with hydrogen chloride, during which the hydroxyl group is protonated. The chloride ion is now substituted on the carbon atom with elimination of water . This creates the chloroalkylated aromatic 5 .

See also

• Blanc reaction
• Hammick reaction

Individual evidence

1. ↑ ^{a b} Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 2 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-470-28663-0 , p. 2290.
2. ↑ R. Quelet: preparation d'un derive chloro-methyl du para-bromo-anisole (methoxy-2 bromo-2 α-chlorotoluene) . In: Comptes rendus hebdomadaires des séances de l'Académie des sciences . tape 37 , 1932, p. 155 ff . ( Digitized on Gallica ).
3. ↑ M. Windholz (Ed.): The Merck Index, Ninth Edition . Merck & Co., 1976, ISBN 978-0-911910-26-1 , p. ON-720.
4. ↑ Z. Wang (Ed.): Comprehensive Organic Name Reactions and Reagents, 2 Volume Set . John Wiley & Sons, Hoboken, New Jersey 2009, ISBN 978-0-470-28663-0 , p. 2291.