Acid Dissociation Constants of the Benzimidazole Unit in the Polybenzimidazole Chain: Configuration Effects

Liudmil Antonov; Susumu Kawauchi; Kei Shirata

doi:10.3390/molecules27031064

Acid Dissociation Constants of the Benzimidazole Unit in the Polybenzimidazole Chain: Configuration Effects

Molecules. 2022 Feb 4;27(3):1064. doi: 10.3390/molecules27031064.

Authors

Liudmil Antonov^{1

2}, Susumu Kawauchi^{3

4}, Kei Shirata⁴

Affiliations

¹ Institute of Electronics, Bulgarian Academy of Sciences, 1784 Sofia, Bulgaria.
² Central Scientific Research Laboratory, University of Chemical Technology and Metallurgy, 1756 Sofia, Bulgaria.
³ Tokyo Tech Academy for Convergence of Materials and Informatics (TAC-MI), Tokyo Institute of Technology, S6-23, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.
⁴ Department of Organic and Polymeric Materials, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550, Japan.

Abstract

The acid dissociation constant of three benzimidazoles, namely 2,2'-bibenzo[d]imidazole, 2,5'-bibenzo[d]imidazole, and 5,5'-bibenzo[d]imidazole, have been investigated by means of density functional theory calculations in gas phase and in aqueous solution. The theoretical approach was validated by the comparing of predicted and experimentally determined pK_a values in imidazole, benzimidazole, and 2-phenylbenzimidazole. From the studied compounds, 2,2'-bibenzo[d]imidazole was found to be the most acidic, which made it a valuable candidate as a material for polymer electrolyte membrane fuel cells.

Keywords: benzimidazole; density functional theory; pKa; polymer electrolyte membrane fuel cells; polymer ion.