Pyrazinyl and pyridinyl bis-azomethines formation: an experimental and computational study

Formation of bis-azomethines from hydrazine and heterocyclic aromatic carbaldehydes, namely pyridine-2-carbaldehyde and pyrazine-2-carbaldehyde, is studied using density functional theory. The theoretical investigation is correlated with experimental results obtained by means of NMR spectroscopy. The presence of bis-hemiaminal intermediates is evidenced by NMR spectra while surprisingly stable hemiaminal intermediate was isolated experimentally. Water, methanol and acetic acid were outlined to play a crucial role as active catalysts of elementary steps of the reaction mechanisms. The possible reaction sequences, i.e. addition-dehydration-addition-dehydration or addition-addition-dehydration-dehydration are investigated and discussed. Also, alternative mechanistic path via ionic mechanism was proposed for the formation of hemiaminals.

Automated summary

The formation of bis-azomethines from hydrazine and heterocyclic aromatic carbaldehydes using water, methanol, and acetic acid as catalysts was studied through density functional theory and experimental results. The presence of stable hemiaminal intermediates was confirmed, and multiple possible reaction sequences and alternative mechanisms were proposed.