Preparation of Silica-Bonded S-Sulfonic Acid: A Recyclable Catalyst for the Synthesis of Bis-Indolylmethanes

Abstract

Silica bonded S-sulfonic acid (SBSSA) was prepared by the reaction of 3-mercaptopropylsilica (MPS) and chlorosulfonic acid in chloroform. Silica-bonded S-sulfonic acid, as a reusable solid acid catalyst, was used for the condensation reactions of indole with carbonyl compounds at ambient temperature. Tetra-(indolyl)methanes were also obtained by the condensation reaction of indole with dialdehyde compounds. Silica bonded S-sulfonic acid was recovered and reused.

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Keywords:

• Bis(indolyl)methanes
• carbonyl compounds
• indole
• silica-bonded S-sulfonic acid
• tetra(indolyl)methanes

Acknowledgments

We are thankful to the Persian Gulf University Research Council for the partial support of this work.

Notes

^a Conversion.

^a Conversion.

^a Reaction conditions: indole (2 mmol), carbonyl compound (1 mmol), and SBSSA (0.1 g) in 2 mL of CH₃CN at room temperature.

^bIsolated yield.