Development of Brönsted–Lewis acidic solid catalytic system of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides for the preparation of bis(indolyl)methanes

• Brönsted and Lewis acidic three heterogeneous 3-methyl-1-sulfonic acid imidazolium transition metal chlorides were synthesized.
• All compounds were characterized by NMR, FT-IR, RAMAN, XRD, SEM-EDX, BET, AAS, powder XRD and elemental analysis techniques.
• Acidity of these compounds was measured by Hammett function.
• Higher catalytic activity was observed in solution for the preparation of bis(indolyl)methane at room temperature.
• All compounds were recycled for three consecutive runs without reactivation.

Three new heterogeneous catalysts of 3-methyl-1-sulfonic acid imidazolium transition metal chlorides [Msim][X] (where X = [FeCl4]−, [ZnCl3]−, [CuCl2]−) were synthesized containing both Lewis and Brönsted acidic sites. These solid acids were fully characterized by various analytical tools such as FT-IR, Raman, 1H NMR, 13C NMR, SEM-EDX, TGA, Powder XRD, AAS, BET, UV–vis and elemental analysis. All of them were efficiently utilized as reusable catalysts (5–10 mol%) for the selective synthesis of bis(indolyl)methane derivatives in ethylacetate at room temperature within short time with excellent yields.

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