Modified Paal-Knorr Synthesis of Novel and Known Pyrroles Using Tungstate Sulfuric Acid as a Recyclable Catalyst

Tungstate sulfuric acid (TSA) as a solid acid catalyst has been synthesized and used in Paal–Knorr synthesis of some novel and known pyrroles under solvent-free conditions. Catalyst loadings can be as low as 1 mol % to give high yields of the corresponding pyrroles at 60 °C. To make the catalyst, sodium tungstic reacted with chlorosulfonic acid in nhexane.