Revisiting the role of sulfated oxides for the synthesis of pharmaceutically important heterocycles: Understanding, challenges, and future prospects

The development of sustainable catalytic processes is the requirement of the future to replace traditional protocols involving hazardous, non-green, non-benign reagents/solvents, and cost ineffectiveness. Metal and mixed metal oxides due to their redox properties make them potential substitutes for conventional homogeneous catalysts. The acidity can be enhanced further by the sulfation process to form sulfated oxides representing a new class of solid acid catalysts. This review is the revisiting of sulfated solid acid catalysts, with major emphasis on understanding, methods, applications, and their role in the syntheses of heterocycles of pharmaceutical importance. The present review also discusses factors affecting the acidity of the catalysts, possibilities of leaching in reaction media, methods of sulfation to arrest leaching, other challenges, and future prospects.