Angeli–Rimini reaction

Angeli the Rimini - specific detection reaction is a reaction of aldehydes, in which a hydroxamic acid is formed by reaction of the aldehyde with a derivative of the hydroxylamine, which gives an intensely red complex with iron ( III) chloride. The reaction was discovered by the Italian chemist Angelo Angeli and Enrico Rimini and published in 1896.

Mechanism

For the exact course of several hydroxamic acid reaction pathways are discussed:

The N- Hydroxybenzoesulfonamid 1 or the deprotonated form 2 acts as a nucleophile in the reaction with the aldehyde 3 to give intermediate 4 by intramolecular proton exchange to a 5 Benzolsulfinatanion is split off and formed over the nitrone 6 and the intermediate 7, the hydroxamic acid 8.

Alternatively, it is discussed that from 4 after elimination of the Sulfinsäureanions an aziridine intermediate 9 is formed, which further reacts directly to the hydroxamic acid 8.

Originally unstable Nitrohydroxylamin or its disodium salt ( disodium trioxodinitrat (II), Angeli salt) used as a reagent; here the nitrite ion acts as a leaving group. Since this salt decomposes to form the highly unstable Nitrosowasserstoffs ( ENT, nitroxyl ), a reaction mechanism is discussed, which extends over free nitroxyl.