Reilly-Hickinbottom rearrangement
The Reilly-Hickinbottom rearrangement is a name reaction in organic chemistry . It is the acid-catalyzed rearrangement of an N - alkyl aniline into alkyl-substituted anilines . It was named after Joseph Reilly and Wilfred John Hickinbottom (1896–1979), who reported on this for the first time in 1920.
The reaction is a variant of the Hofmann rearrangement Martius in which, instead of metal halides such as zinc chloride , most inorganic acids and Lewis acids are used.
Overview reaction
The reaction will be explained using the example of N -methylaniline . This leads to a rearrangement of the methyl group. The p -substituted aniline 1 and the o -substituted aniline 2 are obtained as products. A Lewis acid such as zinc chloride serves as the catalyst .
Instead of N -methylaniline, other N -alkylanilines can also be used, so the alkyl radical is variable. In addition, instead of an N -alkylaniline, an N, N -dialkylaniline can also be selected as the starting material.
Reaction mechanism
The mechanism is described in the literature and exemplified using N- methylaniline.
First, the zinc chloride is attached to the N -methylaniline 3 , so that the intermediate 4 is formed. By rearrangement of the binding electrons between the methyl group and the nitrogen, the methyl group is split off. In the next step, this is bound to the molecule again in the para position, so that molecule 5 is obtained. Two different electron rearrangements can occur in this molecule, which are indicated by the colored electron shift arrows.
Path A leads to a [1,3] rearrangement of the methyl group. A deprotonation follows, whereby the anion 6 is obtained. As a result of the attachment of the proton to the nitrogen, the zinc chloride is split off in the last step. The para -substituted aniline 7 is obtained as the product .
In path B, the electron rearrangement in molecule 5 results in hydrogen being attached to the nitrogen. This leads to the splitting off of the zinc chloride and the ortho -substituted aniline 8 is obtained as the product .
In the reaction, the yield of the para -substituted aniline is relatively higher than that of the ortho -substituted aniline. It is therefore assumed that the para -substituted aniline arises at least partially from further rearrangements of the alkyl group in the ortho -substituted aniline.
Individual evidence
- ↑ a b c Zerong Wang: Comprehensive Organic Name Reactions and Reagents , Wiley, 2010, ISBN 9780470638859 , pp. 2326-2328, doi: 10.1002 / 9780470638859 .
- ^ J. Reilly and WJ Hickinbottom: Intramolecular rearrangement of the alkylarylamines: formation of 4-amino-n-butylbenzene In: Journal of the Chemical Society 117, 1920, p. 103, doi: 10.1039 / CT9201700103 .
- ↑ AW Hofmann: Methylirung the phenyl group in the aniline In: Journal of the American Chemical Society 4, 1871, pp 742-748, doi: 10.1002 / cber.18710040271 .