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], [C4mim]), and 1-butyl-2,3-dimethylimidazolium and 1-butyl-4-methylpyridinium hexafluorophosphates ([C4mpyr], [C4m2im]), 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] and [C4mpyr] with excellent activity and selectivity, while practically null activity is observed in [C4m2im] and [C4mim]. The results obtained indicate that a very low level of hydrolysis of the PF6- anion in [C4mim] and [C4mpyr] 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.