The reaction of acetaldehyde, glyoxal, and ammonia to yield 2-methylimidazole: thermodynamic and kinetic analyses of the mechanism

Abstract

The most thermodynamically and kinetically favorable pathways for the formation of 2-methylimidazole (2MI) in the reaction of glyoxal and acetaldehyde with ammonia in aqueous solution have been determined. The formation...

Nature or number of species in a transition state: the key role of catalytically active molecules in hydrogen transfer stages in atmospheric aldehyde reactions

“…The stage of intramolecular cyclization of the mechanism of 2-methylimidazole formation is rate-determining for this process. 22 The search for its TS leads to the discovery of TSs only with the involvement of one and two water molecules; Fig. 3 shows the corresponding structures.…”

“…The previously proposed and justified mechanism 22 for the 2-methylimidazole formation in the reaction of acetaldehyde and glyoxal with ammonia consists of parallel stages of ammonization of the carbonyl groups of acetaldehyde and glyoxal (stages A1 and A2) with the formation of the corresponding aminoalcohols, which, when interacting with each other, lead to the formation of a precyclic intermediate (stage B). The subsequent proceeding of the reaction consists in intramolecular cyclization (stage C) followed by dehydration steps (stages D and E) and ends with the stage of intramolecular hydrogen transfer with the formation of the aromatic structure of 2-methylimidazole (stage F).…”

“…To establish the catalytic role of the factors described, our research goal was to determine the priority of the nature or the number of molecules of the catalyzing species in the reaction of 2-methylimidazole formation (Scheme 1). 22 The mechanism developed of this reaction includes characteristic types of reactions occurring in atmospheric aerosols.…”

“…To date, the focus of theoretical studies of the above processes occurring in atmospheric aerosols is the catalytic properties of various species in the reactions of ammonization and/or amination and hydration of atmospheric carbonyl compounds. 5–25 It is known that all reactions of hydration and ammonization/amination of carbonyl compounds include stages of hydrogen atom transfer. Quantum-chemical studies have shown that the simulation of these processes without accounting for water molecules leads to high energy barriers, which contradicts the conditions for the carrying out of these reactions at moderate temperatures and without a catalyst in solution.…”

Spectroscopic identification of interstellar relevant 2-iminoacetaldehyde

“…13 In further condensation reactions of 1 with aldehydes in aqueous ammonia containing solutions a variety of imidazole or oxazole based heterocycles might form. 14 Even the synthesis of 5 via the insertion of excited state oxygen atoms into the aldehyde C–H bond seems feasible (Fig. 1).…”