An efficient method for the synthesis of N-tert-butyl amides by reaction of nitriles with tert-butyl acetate or tert-butanol is described using oxalic acid dihydrate in solvent-free condition. The result showed that tert-butyl acetate served as a relatively better source of tert-butyl carbocation than tert-butanol. 1. Introduction Solvent-free reactions obviously reduce pollution and bring down handling costs due to simplification of experimental procedure, work-up technique, and saving energy. These would be especially important during industrial production [1]. The Ritter reaction makes possible the conversion of a group, capable of giving a relatively stable carbonium ion, to a substituted amide by reaction with a nitrile in the presence of a strong acid [2]. The classical Ritter reaction is the reaction of alkenes and tertiary or benzylic alcohols with nitriles in the presence of concentrated sulfuric acid [3–5]. Several modifications have been attempted to improve Ritter reaction conditions. However, as an alternative to sulfuric acid, other acid catalysts such as (CF3SO2)2O [6], BF3-Et2O [7], Fe3+-Montmorillonite [8], Mg(HSO4)2 [9], Bi(OTf)3 [10], CeCl3 7H2O/AcCl [11], P2O5/SiO2 [12], and Nafion [13] are employed in the classical Ritter reaction. Ritter reaction using tert-butyl acetate instead of alcohol was also reported to be catalyzed by sulfuric acid [14, 15], FeCl3 6H2O [16], ZnCl2-SiO2 [17], and I2 [18]. However, most of these methods suffer from at least one of the following disadvantages such as vigorous reaction conditions, high cost and toxicity of the reagent, tedious work-up procedures, and instability and hygroscopic nature of the reagent. Also, the use of tert-butanol can be complicated by the melting point (26°C) leading to a semisolid at room temperature. An attractive alternative is tert-butyl acetate due to its ease of handling (bp 97-98°C), availability as a common solvent, and low cost [15]. Recently, oxalic acid was efficiently used as catalyst in variety of chemical reactions like imino Diels-Alder reaction [19], Beckmann rearrangement [20], protection of carbonyl to thioacetal, and deprotection of thioacetal to carbonyl as well [21]. The conversion of a nitrile to the corresponding N-tert-butyl amide is a very important transformation in organic synthesis. The N-tert-butyl amides are pharmaceutically useful [22] and also serve as precursors to the corresponding amines. In connection of our research to develop application of oxalic acid dihydrate for oxygenation of sulfides to sufoxides in the presence of H2O2 [23], herein,
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