Urech hydantoin synthesis

The Urech- hydantoin is a name reaction in organic chemistry. It was named after Friedrich Urech, who published the reaction in 1873. With this reaction, hydantoins from α -amino acids can be produced.

Overview reaction

In acidic reaction medium to react α - amino acids with potassium cyanate (blue) to give 5- substituted hydantoins:

If amino acids used in the reaction with a substituted amino group ( green), arise 1-N- substituted hydantoins.

Mechanism

In this named reaction is a two-step reaction in which hydantoic 8 can be isolated. This can then be reacted with hydrochloric acid, and so also Hydanoine 11 are prepared.

First, the amino group is deprotonated carboxyl group of the amino acid 1 and forms the zwitterion 2 The ammonium group 2 is deprotonated by the cyanate ion to form a carboxylate 3. The amino group then accesses nucleophile to the carbon atom of the cyanuric acid (4). Followed by a 1.3 - proton transfer from nitrogen to the negatively charged nitrogen atom of the cyanate former 5, and thus the formation of an imine by a further 6 proton transfer, the amide 7 is the protonation of the carboxylate group in the amide 7 leads to intermediate 8 hydantoic The following is an intramolecular attack of the amino group 8 on the carbonyl group resulting in the closure of a heterocyclic five-membered ring 9. The formation of a diol 10 by proton transfer, the product hydantoin formed after elimination of water 11

The reaction is even today still an important variant for the preparation of hydantoins.