In situ IR and NMR spectroscopic investigation of the formation and structure of protonated diacetylketene tetrachloroaluminate

In situ IR and multinuclear NMR are used to monitor the formation of protonated diacetylketene tetrachloroaluminate (1) in the reaction of acetyl chloride and AlCl₃ in both dichloromethane and in 1-butyl-3-methylimidazolium chloride ([bmim]C1). The existence of a fast equilibrium between two enolic forms of protonated diacetylketene (with [AlCl₄]^- as the counterion) is established. The structure of 1 is determined by the rarely used ¹³C{¹H}-¹³C¹H} COSY experiment.