Synthesis, Spectroscopic, X-ray Diffraction and DFT Studies of Novel Benzimidazole Fused-1,4-Oxazepines

Advances in the Synthesis of Ring-Fused Benzimidazoles and Imidazobenzimidazoles

This review article provides a perspective on the synthesis of alicyclic and heterocyclic ring-fused benzimidazoles, imidazo[4,5-f]benzimidazoles, and imidazo[5,4-f]benzimidazoles. These heterocycles have a plethora of biological activities with the iminoquinone and quinone derivatives displaying potent bioreductive antitumor activity. Synthesis is categorized according to the cyclization reaction and mechanisms are detailed. Nitrobenzene reduction, cyclization of aryl amidines, lactams and isothiocyanates are described. Protocols include condensation, cross-dehydrogenative coupling with transition metal catalysis, annulation onto benzimidazole, often using CuI-catalysis, and radical cyclization with homolytic aromatic substitution. Many oxidative transformations are under metal-free conditions, including using thermal, photochemical, and electrochemical methods. Syntheses of diazole analogues of mitomycin C derivatives are described. Traditional oxidations of o-(cycloamino)anilines using peroxides in acid via the t-amino effect remain popular.

Theoretical and experimental solid state studies of Ethyl 1-benzyl-2-(thiophen-3-yl)-1H-benzo[d]imidazole-5-carboxylate

The title compound Ethyl 1-benzyl-2-(thiophen-3-yl)-1H-benzo[d]imidazole-5-carboxylate (BI) is prepared and characterized using spectroscopic methods. The theoretical optimization and three dimensional molecular structure are confirmed by X-ray diffraction method (single crystal). The C–H…π intermolecular interactions stabilize the crystal structure. The intermolecular contacts in the crystal structure are quantified using Hirshfeld surfaces and the crystal packing is elucidated using 3D energy frameworks analysis. In the frameworks, the dispersion energy term is dominated over the electrostatic energy term. The structural optimization was carried out with B3LYP/6-311++G (d, p) level of theory. The visual representations of positive and negative potentials (electrostatic potential) are mapped on the electron density isosurface. The band gap energy (HOMO-LUMO) of the molecule is calculated to be 4.36 eV. Structural conformation of BI is compared with similar structures.

Recent advances in the use of benzimidazoles as corrosion inhibitors

Background

Benzimidazole, a key heterocycle in therapeutic chemistry, and its derivatives, are recently mentioned in the literature as corrosion inhibitors for steels (CS, MS), pure metals (Fe, Al, Cu, Zn) and alloys. Benzimidazoles are good corrosion inhibitors for extremely aggressive, corrosive acidic media such as 1 M HCl, 1 M HNO₃, 1.5 M H₂SO₄, basic media, 0.1 M NaOH or salt solutions. Benzimidazole derivatives act as mixed type inhibitors, exhibiting stronger inhibitive effect on the cathodic reaction than on the anodic one.

Conclusion

These review highlights recent research in the field of benzimidazole compounds that their role as corrosion inhibitors, the structure of the compounds, electrochemical studies, the experimental conditions, the proposed mechanisms as well as the quantum theoretical studies that predict the structure of the compounds with inhibition properties.