A study of the influence of ionic liquids properties on the Kemp elimination reaction

The morpholino-induced elimination of 5-nitrobenzisoxazole into the relevant 2-cyano-4-nitrophenolate has been used as a sample reactionin order to investigate molecular properties of some room temperature ionic liquids. The kinetic study was carried out at 298 K by means of spectrophotometric measurements. Ionic liquids,which differ in both their cation and anion properties, were used as solvent systems. In particular, aliphatic (pyrrolidinium, piperidinium, and ammonium)and aromatic (imidazolium and pyridinium) ionic liquids were used. For aromatic cations, imidazolium ionshaving different hydrogen-bond donor ability or a different alkyl-chain length were taken into account. The anions chosen ([BF4 ], [PF6 ], [SbF6 ], and [NTf2 ]; where NTf2=bis(trifluoromethansulfonyl)imide) showed different shape, size, and coordination ability.Solvent parameters of all ionic liquids used were determined by using spectroscopic probes, such as 4-nitroaniline, N,N-diethyl-4-nitroaniline, Nile Red, and Reichardt s dye. Finally, in orderto obtain information on the structural organization of the solvent systems, resonance light-scattering measurements were carried out. The collected data provide evidence that ionic liquids are solvent media which exhibit peculiarfeatures, whose effects can be rationalized only considering all parameters affecting their three-dimensional structure.