Chlorosulfonic acid: A high potential reagent in catalyst design

(A) Synthesis of silica sulfuric acid (SSA) as an acidic resin. Zolfigol reported silica based acidic resin namely silica sulforic acid (SSA) via reaction of neat chlorosulfonic acid with silica gel for the first time [5] The SSA is a unique heterogeneous acidic catalyst and has been used widely inorganic functional group transformation [6]. It should be mentioned that SSA used in over 300 research papers so far. Recently, they reported a new developed model of SSA in nano scale (between 60 and 90 nm) [7]. (B) Design an acidic nano magnetic particle [sulfonic acid supported ?-Fe2O3 {Fe2O3-SO3H}]. At 2012, a magnetic particle-supported sulfonic acid catalyst was prepared for the first time by Zolfigol and co-workers [8]. These particles were prepared immediately with a low cost procedure and had several positive points such as; High activity in Hantzsch synthesis, high reusability (over 5 runs), stable and high densities of functional groups. After this report, Fe3O4-SO3H (magnetite nanocatalyst) was also prepared at 2013 by Gawande [9]. (C) Sulfonic acid functionalized imidazolium salts (SAFIS). Sulfonic acid functionalized imidazolium salts were synthesized by loaded sulfonic acid groups on 1-methyl imidazole and imidazole and produced new family of ionic liquids with amazing properties. These ILs were successfully employed as catalysts in several organic transformations [10]. In continues of this research, synthesis of 1-sulfopyridinium chloride as a new, homogeneous and reusable catalyst was reported [11]. (D) Synthesis of a bio-supported catalyst. Cellulose as a very cost-effective and biodegradable compound was converted to their sulfonic acid derivative by the reaction with ClSO3H to give cellulose sulfuric acid (CSA). CSA showed catalytic properties and ?-Amino nitriles are synthesized by a one-pot three-component condensation reaction of amines, aldehydes and trimethylsilylcyanide in the presence of a catalytic amount of it as a bio-supported catalyst [12]. (E) Saccharin sulfonic acid. Reaction of chlorosulfonic acid with saccharin was designed by Shirini and yielded a bio-supported and recyclable solid acid catalyst. Several reactions were catalyzed by it such as Chemoselective trimethylsilylation of alcohols [13], preparation and deprotection of 1,1-diacetates [14] and N-Boc protection of amines and formation of tertbutyl ethers from alcohols [15]. (F) Boron Sulfonic Acid. Boron sulfonic acid (BSA) was introduced by Kiasat and co-workers as a strong acidic catalyst and used it for the regioselective ring opening of epoxides to B-hydroxy thiocyanates in the presence of BSA by NH4SCN in a solvent less media. The promising points for the presented methodology were efficiency, generality, high yield, relatively short reaction time, cleaner reaction profile, ease of product isolation, simplicity, and finally compliance with the green chemistry protocols [16].