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 reaction in 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 ions having 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 order to 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 peculiar features, whose effects can be rationalized only considering all parameters affecting their three-dimensional structure

CIAO: wavefront sensors for GRAVITY

International audienc

CIAO: wavefront sensors for GRAVITY

International audienc

CIAO: wavefront sensors for GRAVITY

International audienc

Extended scale for the hydrogen-bond basicity of ionic liquids

In the past decade, ionic liquids (ILs) have been the focus of intensive research regarding their use as potential and alternative solvents in many chemical applications. Targeting their effectiveness, recent investigations have attempted to establish polarity scales capable of ranking ILs according to their chemical behaviours. However, some major drawbacks have been found since polarity scales only report relative ranks because they depend on the set of probe dyes used, and they are sensitive to measurement conditions, such as purity levels of the ILs and procedures employed. Due to all these difficulties it is of crucial importance to find alternative and/or predictive methods and to evaluate them as a priori approaches capable of providing the chemical properties of ILs. Furthermore, the large number of ILs available makes their experimental characterization, usually achieved by a trial and error methodology, burdensome. In this context, we firstly evaluated COSMO-RS, COnductor-like Screening MOdel for Real Solvents, as an alternative tool to estimate the hydrogen-bond basicity of ILs. After demonstrating a straight-line correlation between the experimental hydrogen-bond basicity values and the COSMO-RS hydrogen-bonding energies in equimolar cation-anion pairs, an extended scale for the hydrogen-bond accepting ability of IL anions is proposed here. This new ranking of the ILs' chemical properties opens the possibility to pre-screen appropriate ILs (even those not yet synthesized) for a given task or application