Cyclization of aromatic aldehydes and phenylenediamines under reduced pressure: A convenient, environmentally friendly, and simple procedure for benzimidazole precursors

ABSTRACT

The condensation of phenylenediamines with aromatic aldehydes in the presence of catalysts to obtain benzimidazoles under harsh condition is achieved by various reported conditions. The present work demonstrates a convenient, environmentally friendly, and simple procedure to obtain benzimidazoles through the cyclization between phenylenediamines and aromatic aldehydes under reduced pressure. By simply adding aromatic aldehydes to diaminobenzene derivatives and allowing the stoichiometric reaction at room temperature under reduced pressure at 66.6 Pa, the dehydrogenation leads to benzimidazoles with the yield as high as 80–90%. In addition, the purging of H₂ gas to benzimidazoles results in the hydrogenation of imidazole to obtain the intermediate benzimidazolidine form. This confirms how the cyclization relies on the reduced pressure. This synthesis pathway not only gives the aromatic aldehydes with high yield under the mild condition but also the selection of benzaldehydes with reactive functional groups leads to the precursors for other chemical modifications and polymerizations.

GRAPHICAL ABSTRACT

KEYWORDS:

• Aromatic aldehydes
• cyclization
• heterocycles
• reduced pressure

Acknowledgment

One of the authors, Choltirosn Sutapin acknowledges the scholarship from Center of innovative nanotechnology, Chulalongkorn University.

Additional information

Funding

The research work was supported by The Thailand Research Fund (BRG5380010) and Government Budget Grant, National Research Council of Thailand (2559A10102134).