An efficient method for the synthesis of N-(4-halophenacyl)-2-substituted-benzo[d]imidazoles using PEG-400 as green reaction solvent

In this paper, we report a green and efficient method for the synthesis of N-substituted benzimidazoles under grinding conditions using PEG-400 as reaction solvent at room temperature. 2-Substituted-1H-benzimidazole was prepared from the reaction between various aromatic aldehydes and o-phenylenediamine in mortar and pestle under a grinding process using NH4Cl as catalyst in PEG-400 as green reaction solvent. Additionally, 2-substituted-1H- benzimidazole were treated with 4-halophenacylbromide in the K2CO3 / PEG system, yielding the corresponding 1-(4-fluoro/bromophenacyl)-2-susbtituted-benzo[d]imidazole (N-substituted benzimidazoles). This methodology incorporates inexpensive catalysts, suppressed reaction times, high yields, easy work-up, and the use of green reaction solvents are reported. All of the structures of products were established by spectroscopic and analytical methods. The IR spectra of 2-substituted-1H-benzimidazole (2a-e) showed the disappearance of the stretching frequency band at 1680-1695 cm-1 due to >C=O of aromatic aldehydes and the presence of stretching bands at 1610-1630 cm-1 due to -C=N stretching, which confirms the formation products. Furthermore, 1H NMR spectra of N-substituted benzimidazoles (4a-j) showed the presence of a singlet at δ 6.10-6.25 ppm, indicating the presence of -CH2 in the structure of the phenacyl ring. The mass spectra (EIMS) of the compounds also agree with their molecular formula.