The Beckmann rearrangement of cyclododecanone oxime into omega-laurolactam has been investigated in four ionic liquids: 1-butyl-3-methylimidazolium hexafluorophosphate and tetrafluoroborate ([C(4)mim]+PF6-, [C(4)mim]+BF4-), and 1-butyl-2,3-dimethylimidazolium and 1-butyl-4-methylpyridinium hexafluorophosphates ([C(4)mpyr]+PF6-, [C(4)m(2)im]+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 [C(4)mim]+PF6- and [C(4)mpyr]+PF6- with excellent activity and selectivity, while practically null activity is observed in [C(4)m(2)im]+PF6- and [C(4)mim]+BF4-. The results obtained indicate that a very low level of hydrolysis of the PF6- anion in [C(4)mim]+PF6- and [C(4)mpyr]+PF6-occurs under reaction conditions (130 degrees C), and the HF formed at the level of ppm acts as catalyst in the Beckmann rearrangement with excellent conversion and selectivity. (C) 2010 Elsevier Inc. All rights reserved.