Abstract

Aldimines can be readily formed in aprotic solvents from the reaction of amines with aldehydes. However, the true reaction mechanism has not be fully elucidated yet. In this work, the mechanism of methylamine addition to acetaldehyde catalyzed by a second amine, water molecules and the carbinolamine intermediate was investigated by reliable theoretical methods. Although all of these species were able to catalyze this reaction via proton shuttle mechanism, none of them have led to ΔG‡ compatible with experimental data. An additional species presents in the reaction mixture as impurity, acetic acid, which is formed by the contact of acetaldehyde with the oxygen of the air, was also investigated as a catalyst. The calculation of the free energy profile and a microkinetic analysis indicated that a small concentration of acetic acid present in solution is able to promote a very effective catalyst, leading to reaction kinetics compatible with experimental data. Thus, the present study suggest that trace amount of carboxylic acids present in aldehydes catalyze this kind of reaction.

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