Catalytic synthesis of benzimidazole derivatives over modified forms of zirconia

Abstract

The solid acid catalysts, ZrO₂, Mo(VI)/ZrO₂ and Pt-SO₄^2-/ZrO₂have been prepared and characterized for their surface area by BET, total surface acidity by NH₃-TPD/ <em>n</em>-butyl amine back titration and crystallinity by powder XRD methods. These solid acid catalysts have been used in the synthesis of various benzimidazole derivatives. The results have been interpreted based on the variation of acidic properties and powder XRD phases of zirconia on incorporation of Mo(VI) or Pt-SO₄^2&ndash; ions. Mo(VI)/ZrO₂ is found to be an efficient solid acid catalyst for the synthesis of benzimidazoles with up to ~98% yield. These solid acids were found to be reusable up to at least 5 reaction cycles. Plausible mechanism for the formation of benzimidazoles over protonic acid sites of the solid acid catalysts is proposed.