Beckmann Rearrangement with Improved Atom Economy, Catalyzed by Inexpensive, Reusable, Bro̷nsted Acidic Ionic Liquid

Abstract

Inexpensive protic ionic liquids, synthesized from di- or triamines and excess sulfuric acid, were used as solvents and catalysts for the Beckmann rearrangement. The use of ionic liquids in place of oleum or sulfuric acid allowed the base neutralization step, which is required in the conventional Beckmann rearrangement, to be entirely avoided, thereby dramatically improving the atom economy. Using a biphasic water/organic solvent extraction system, it was possible to recover and reuse the ionic liquid. The proposed method was found applicable for the synthesis of a range of primary and secondary amides.

The structure of protic ionic liquids based on sulfuric acid, doped with excess of sulfuric acid or with water

“…The composition of the Brønsted acidic PIL, [Hpy][HSO 4 ]·H 2 SO 4 , was one of the two standard acidic compositions used in our earlier catalytic studies. 5,8–10 The aim of this work was to elucidate its structure (3D network vs . discrete anionic clusters) and understand how differences in the liquid structure of this PIL and sulfuric acid account for their different miscibilities with the ester product.…”

“…A technoeconomic assessment concluded that triethylammonium hydrogensulfate, [HN 222 ][HSO 4 ], could be produced for as little as US$0.78 kg −1 , comparable to many organic solvents in commercial use. 1–4 Ionic liquids formulated from di- and tri-alkylamines with excess sulfuric acid were postulated to be even cheaper, 5 dispensing with the still-popular misconception that ionic liquids are, generically, too expensive for mainstream industrial use. 6…”

Comprehensive updates on Beckmann Rearrangement

“…Du et al [93] described the Beckmann rearrangement for the synthesis of caprolactam in the presence of ionic liquid made up of sulfonyl chloride functionalized ionic materials. BMImPF 6 , can also be utilized as medium to facilitate the contact between substrate and catalyst but the yield produced was not good.…”

Untapped Potential of Deep Eutectic Solvents for the Synthesis of Bioinspired Inorganic–Organic Materials

“…Further, it is predicted that DESs can be successfully adapted for various applications, including dissolution and processing biopolymers, inorganic synthesis, or 3D printing . Alongside the aforementioned reasons, low costs and low maintenance make DESs excellent candidates for utilization on the industrial scale, which is the main barrier in the case of most ILs. − …”