In situ multinuclear solid-state NMR spectroscopy study of Beckmann rearrangement of cyclododecanone oxime in ionic liquids: The nature of catalytic sites

The Beckmann rearrangement of cyclododecanone oxime into ω-laurolactam has been investigated in four ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate ([C4mim]+PF6-, [C4mim]+BF4-), and 1-butyl-2,3-dimethylimidazolium and 1-butyl-4-methylpyridinium hexafluorophosphates ([C4mpyr]+PF6-, [C4m2im]+PF6-), in a batch reactor as well as by ‘in situ’ multinuclear solid-state NMR spectroscopy. The Beckmann rearrangement reaction of cyclododecanone oxime takes place in [C4mim]+PF6- and [C4mpyr]+PF6- with excellent activity and selectivity, while practically null activity is observed in [C4m2im]+PF6- and [C4mim]+BF4-. The results obtained indicate that a very low level of hydrolysis of the PF6- anion in [C4mim]+PF6- and [C4mpyr]+PF6- occurs under reaction conditions (130 °C), and the HF formed at the level of ppm acts as catalyst in the Beckmann rearrangement with excellent conversion and selectivity.

Graphical abstract[C4mim]+PF6- and [C4mpyr]+PF6- ionic liquids can supply in a controlled way ppms of HF in the reaction media, which catalyze the Beckmann rearrangement of cyclododecanone oxime with excellent conversion and selectivity.Figure optionsDownload full-size imageDownload high-quality image (22 K)Download as PowerPoint slide