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Reusable Task‐Specific Ionic Liquids for a Clean ε‐Caprolactam Synthesis under Mild Conditions
Author(s) -
Turgis Raphaël,
Estager Julien,
Draye Micheline,
Ragaini Vittorio,
Bonrath Werner,
Lévêque JeanMarc
Publication year - 2010
Publication title -
chemsuschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.412
H-Index - 157
eISSN - 1864-564X
pISSN - 1864-5631
DOI - 10.1002/cssc.201000203
Subject(s) - caprolactam , ionic liquid , beckmann rearrangement , chemistry , cyclohexanone oxime , sulfonic acid , catalysis , hydrogen sulfate , viscosity , hydrogen bond , organic chemistry , inorganic chemistry , cyclohexanone , materials science , molecule , composite material
Brønsted‐acidic ionic liquids that bear a sulfonic acid group, known as Forbes acids, show a good catalytic activity for the Beckmann rearrangement, used to prepare ε‐caprolactam, which is a precursor of Nylon 6. The activity essentially stems from the acidity of the sulfonic acid group. Although these task specific ionic liquids suffer from a high viscosity, this drawback can be circumvented at higher temperatures. A combination of the hydrogen sulfate anion and the sulfonic acid group of the cation is needed to obtain the rearrangement product rapidly under mild conditions. When using an excess of ionic liquid, we postulate that the internal pressure of the ionic medium, generated by the high viscosity and the high number of hydrogen‐bonds, is strong enough to contribute to a decrease of the thermodynamic barrier. In accordance with the “Principles of Green Chemistry,” we have developed a synthesis of ε‐caprolactam that requires no additional chemicals except cyclohexanone oxime and the reusable TSIL.