Synthesis of Novel Gemini Dicationic Acidic Ionic Liquids and Their Catalytic Performances in the Beckmann Rearrangement

Abstract

Abstractmagnified imageA series of novel gemini dicationic acidic ionic liquids (GDAILs), compounds 1–3 carrying two SO3H groups at the cation moieties and having anions of the type CF3SO$\rm{ _3^ - }$, were synthesized in good yields (Scheme 1). Some physicochemical properties of 1–3 were determined; due to their unique structures, these novel GDAILs showed noticeable hydrophilic properties and strong acidities (Table 1). Beckmann rearrangements of oximes catalyzed by 1, 2, or 3/zinc chloride (GDAIL/ZnCl2) were investigated (Scheme 2); the corresponding amides were formed in up to 99% yield in the presence of 5 mol‐% of GDAIL/ZnCl2 catalyst under optimized conditions (Tables 2 and 3). The peculiar solubilities of 1–3 made the separation of the catalysts from the products very facile, and the catalytic system could be recycled and reused for three times.

Protic Ionic Liquids Based on Oligomeric Anions [(HSO4)(H2SO4)x]− (x = 0, 1, or 2) for a Clean ϵ-Caprolactam Synthesis

“…[13] Brønsted-acidic ILs bearing sulfonic acid group (-SO 3 H) have been extensively studied as catalysts for -caprolactam transformations, for example in one-step synthesis of -caprolactam from cyclohexanone and hydroxylamine. [14] The combination of sulfonated ILs with either ZnCl 2 or phosphotungstate was investigated in both the Beckmann rearrangement of cyclohexanone oxime [15][16][17] and direct synthesis of -caprolactam from cyclohexanone. [18] With respect to Beckmann rearrangement, the best results reported so far were achieved using an aprotic ionic liquid with [HSO 4 ]anion and a sulfonic acid appended to the alkyl chain of the cation, in a dual role of both the solvent and the catalyst.…”

Task-Specific Organic Salts and Ionic Liquids Binary Mixtures: A Combination to Obtain 5-Hydroxymethylfurfural From Carbohydrates

“…On this subject, we found a similar behavior performing the mononuclear rearrangement of heterocycles in the presence of dicationic TSILs (Rizzo et al, 2014). Previously, Chen et al studying the Beckmann rearrangement in the presence of some acidic dicationic ILs, obtained comparable yields in amides regardless of the acidic strength of ILs, as accounted for by H 0 values (Liu et al, 2009). On the other hand, also for the dehydration of fructose, the trend in yield has been ascribed to the concomitant action of several factors on the transformation, different from the Hammett acidity (Dam et al, 1986).…”

Amidinium based ionic liquids

“…The preparation of the bisamidinium salts (series C) is justified by the fact that only very few examples of ionic liquids based on dicationic units have been reported. [26][27][28][29][30][31][32][33] Finally, it is worth noting that, the three series spotted in this investigations can be obtained easily in large quantities and at rather low cost.…”