Salt-Type Organic Acids: A Class of Green Acidic Catalysts in Organic Transformations

Salt-Type Organic Acids (STOA) catalysts consisting of organic components and acidic sites, possessing salt characteristics simultaneously, have been paid much attention from the whole world as reaction promoters to acid-catalyzed reactions. In recent years, the replacement of the conventional mineral acids with environmentally benign ones has become one of the prime concerns of the chemists for the sake of the development of green strategy for the industrial production. Of special interests to this review are acidic ionic liquids, sulfamic acid and polyaniline salts, the three important representatives for STOA catalysts. Using these catalysts for organic and catalytic reactions possesses the advantages like simple and convenient product isolation, reduced equipment corrosion, and minimized contamination of the waste streams combined with reusability of the catalysts. Importantly, some special features such as regio- or chemo-selectivity could be obtained using STOA catalysts. To some extent, it seems that they are the perfect combination of heterogeneous solid acid and homogeneous organic acid catalysts. Therefore, STOA catalysts may be in principle served as a new generation of green acidic catalysts, and very interesting applications in many organic reactions and scientific research fields are addressed in this review. The category, characteristics and applications of STOA catalysts were described in details.