Fischer–Hepp rearrangement

In organic chemistry, the Fischer–Hepp rearrangement is a rearrangement reaction in which an aromatic N-nitroso (−N=O) or secondary nitrosamine (>N−N=O) converts to a carbon nitroso compound:[1][2] This organic reaction was first described by the German chemist Otto Philipp Fischer (1852–1932) and Eduard Hepp (June 11, 1851 – June 18, 1917) [3] in 1886, and is of importance because para-NO secondary anilines cannot be prepared in a direct reaction.

The rearrangement reaction takes place by reacting the nitrosamine precursor with hydrochloric acid.

The chemical yield is generally good under these conditions, but often much poorer if a different acid is used.

There is evidence suggesting an intramolecular reaction, similar to that seen in the Bamberger rearrangement.

The final step, in which a proton eliminates from the Wheland intermediate, appears to be rate-limiting, and the rearrangement is also suppressed in excessive (e.g. >10M sulfuric) acid.