Solventless Ultrasonic Assisted Synthesis Of 1H-Benzo[d]imidazoles

Introduction

Benzimidazoles are considered privileged structures due to their wide range of reported biological activities. In our aim to obtain benzimidazoles, herein we report a novel methodology to their synthesis. Methodology proceeds solvent free under ultrasonic conditions by the condensation of o-phenylenediamine with several aldehydes.

Experimental part

In a test tube o-phenylenediamine is added , followed by the aldehyde of interest. This reaction mixture is allowed to react in a Cole Parmer ultrasonic processor (Input:50-60 Hz), which has a water bath that was already checked to be stable at 60ºC. After the reaction time has elapsed, the reaction crude is washed with methanol. The desired product within the crude mixture is isolated using column chromatography.

Results and Discussion

First, o-phenylenediamine was reacted with benzaldehyde under aqueous conditions giving the desired 1H-benzo[d]imidazole with a 40% yield. Aiming to increase the yield, conditions were changed, and molecular iodine was used to catalyze the reaction under solvent-free and ultrasonic conditions, which resulted in an 80% yield. To maxime the yield, molecular iodine was removed from the reaction, giving a 97% yield. Following this procedure, 10 compounds were synthesized with yields ranging from 17-83%. Compounds with electron-withdrawing groups in both the benzene ring of the aldehyde and the diamine gave the highest yields.

Conclusions

In conclusion, the catalysis-free ultrasonic solventless synthesis of 1-H-benzo[d]imidazoles, by the condensation of o-phenylenediamine with several aldehydes, depends on the chemical substituents and the position of them within the benzene ring of both the aldehyde and the diamine.