Aerobic oxidation of 2-hydrazinyl-1-methyl-1H-benzo[d]imidazole in situ: A quantum chemical insight into the reaction background

Abstract

Herein, attempts at hydrazinolysis of 1-methyl-1H-benzo[d]imidazole-2-sulfonic acid 6 and its potassium salt 9 have been reported. None of them resulted in the isolation of 2-hydrazinyl-1-methyl-1H-benzo[d]imidazole 3. Instead, 1-methyl-1H-benzo[d]imidazol-2(3H)-one 10 was obtained in some cases. The hydrazinolysis failure may be due to the aerobic oxidation of hydrazine 3 in situ. To get into the background for the reaction, the highest occupied molecular orbitals (HOMOs) of compound 3 and relatively oxidation-resistible 2-hydrazinyl-1H-benzo[d]imidazole 11 were comparatively considered. Based on the analysis of the regions of highest density of HOMOs in both hydrazines, the aminoguanidine moiety in compound 3 appeared to be more susceptible to oxidation as compared to the moiety in compound 11.