Abstract: Highlights • Transformation of fluorinated 1,2-phenylenediamines was investigated in PPA. • Asymmetrically fluorinated 2,2′-bibenzimidazoles were obtained. • Under similar conditions phenazine-2,3-diamines were obtained. • The direction of the reaction depends on the number and position of f atoms. • Hydrodefluorination of initial diamines occurs when f contain at 4 and 5 positions. Abstract A series of asymmetrically fluorinated 2,2′-bibenzimidazoles were obtained by reaction of benzimidazole-2-carboxylic acid with fluorinated 1,2-phenylenediamines in polyphosphoric acid at elevated temperature. The tautomers of fluorinated 2,2′-bibenzimidazoles with a predominance of isomers containing F atoms in distant position relative to the NH group of the benzimidazole fragment are detected in DMSO‑d6 using NMR spectroscopy. The ratio of tautomers depends on the number and arrangement of F atoms in the initial fluorinated 1,2-phenylenediamines. Under similar conditions fluorinated 1,2-phenylenediamines in the presence of benzimidazole-2-carboxylic acid, but without its participation as well as without it, give fluorinated phenazine-2,3-diamines. The direction of transformation of fluorinated 1,2-phenylenediamines depends on the number and position of F atoms. Under similar conditions phenazine-2,3-diamine is not formed from non-fluorinated 1,2-phenylenediamine, but it is obtained with the presence of fluorinated 1,2-phenylenediamines. When fluorinated 1,2-phenylenediamines contain F atoms simultaneously at the positions 4 and 5, the hydrodefluorination of initial fluorinated 1,2-phenylenediamines occurs, resulting in less fluorinated 2,2′-bibenzimidazoles and phenazine-2,3-diamines. Hydrodefluorination of fluorinated 1,2-phenylenediamines in a polyphosphoric acid at elevated temperatures is the first example of the hydrodefluorination of fluorinated aromatic compounds containing strong donor substituents, such as amino groups. Polyphosphoric acid is shown to be a suitable medium for redox processes.

Cite: Li J. , Krasnov V.I. , Karpova E.V. , Andreev R.V. , Shundrina I.K. , Bagryanskaya I.Y. , Selivanova G.A.
Transformation of fluorinated 1,2-phenylenediamines in polyphosphoric acid medium with or without the benzimidazole 2-carboxylic acid: synthesis of fluorinated 2,2′-bibenzimidazoles and phenazine-2,3-diamines
Journal of Fluorine Chemistry. 2024. V.277. 110313 . DOI: 10.1016/j.jfluchem.2024.110313

Dates:

Submitted:	May 14, 2024
Accepted:	Jul 2, 2024
Published print:	Jul 9, 2024
Published online:	Jul 9, 2024

Identifiers:

OpenAlex

W4400468328

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