Tungstate sulfuricacid (TSA) as a solid acid catalyst has been synthesized and used in Paal–Knorr synthesis of some novel and knownpyrroles 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.
Abstract Water was a suitable medium for Paal–Knorrpyrrole cyclocondensation. Hexa-2,5-dione was reacted with several aliphatic and aromatic primary amines, affording N-substituted 2,5-dimethyl pyrrole derivatives in good to excellent yields. An efficient, green method using water either as environmentally friendly solvent or catalyst was presented. GRAPHICAL ABSTRACT