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Efficient and Green Ritter Reaction for the Synthesis of N-(t-Butyl)- and N-Benzylamides from t-Butyl and Benzyl Acetates

The amido function is recurring feature of many organic bio-molecules such as peptides and proteins and is also found in various synthetic materials especially in greater than 25% of known drugs and pharmaceuticals. N-(t-Butyl)amides are important not only from a medicinal standpoint but they also serve as precursors of the corresponding t-butylamine and t-alkylamines as well as important building block in synthetic chemistry. Several methods for their preparation have been reported. The Ritter reaction is important for the preparation of amides substituted with bulky N-substituents and involves the reaction of t-butyl or of benzylic cations with nitriles in concentrated sulfuric acid. Other acidic reagents such as Fe(ClO4)3/SiO2, 7 MeSO3H/Al2O3, 8 (CF3SO2)2O, 9 Nafion-H, CoCl2/Ac2O, 11 BF3/Et2O, 12 Fe3C-K10 Montmorillonite, heteropoly acids, and zeolites have been used for this purpose. However, there are many disadvantages of these methods e. g. difficult availability and/or high cost of the reagent, drastic reaction conditions, unsatisfactory yields, long reaction times, the use of strong protic acids in aqueous media, toxicity and tedious work-up Either isobutylene or t-butanol in the presence of acid is employed to generate the tbutyl cation. In spite of this widely used method, some inherent problems exist; for example, the exothermic reaction of isobutylene, a gas, with acids and its susceptibility to subsequent cationic polymerization. Another complication involves in the use of t-butanol whose melting point makes it a semi-solid at room temperature. Although t-butyl acetate has been used as an alternative reagent because of its ease of handling, ready availability and low cost, there are only limited examples of Ritter reactions in which t-butyl acetate and benzyl acetate are employed to generate the tert-butyl or benzyl cation. Solid acid catalysts, especially heteropoly acids play a key role in organic synthesis under heterogeneous conditions, because of environmental, economic and industrial considerations. 23 Silica sulfuric acid (SSA) is a re-usable heterogeneous solid catalyst that it easily prepared by treatment of silica gel with chlorosulfonic acid at room temperature. Silica sulfuric acid has been utilized successfully as a catalyst in many reactions such as carbon–carbon bond formation, cycloadditions, oxidation, protection and deprotection of functional groups. Similarly, p-toluenesulfonic acid (p-TSA), a strong organic acid