Interactions of Aprotic and Functionalized Ionic Liquids with Radicals
Final Report Abstract
Various stable 2,2,6,6-tetramethylpiperidine-1-yloxyl (TEMPO) derivatives, which are called spin probes, and photogenerated lophyl radicals were used to investigate a broad variety of ionic liquids within the three funding periods of the SPP 1191. The ionic liquids include imidazolium based ionic liquids bearing various anions, such as BF4-, PF6-, triflate, bis(trifluoromethylsulfonyl)imide (NTf2-), camphorsulfonate, lactate, tosylate or tris(pentafluoroethyl)trifluorophosphate (FAP), and 1-alkyl-1-methylpyrrolidinium, 1-alkyl-1-methyl-piperidinium, 1-vinyl-3-alkyl-imidzolium, and N,N,N,N-alkyl-dimethyl-methacryloyloxyethylammonium based ionic liquids bearing NTf2- as anion. These ionic liquids differ in both their thermal properties, such as glass formation, semicrystallinity, or crystallinity, and their viscosity. Many of these ionic liquids were optically pure, and therefore, they were investigated with both spin probes and photogenerated lophyl radicals. Moreover, new cyanine dyes were synthesized with NTf2- as anion that belong to ionic liquids because their low melting point. These cyanine dyes were investigated with spin probes only. The spin probes interact via the nitroxyl group with an ionic liquid. Furthermore, an additional substituent (e.g. a hydroxyl or an acid group, a cationic or an anionic substituent) at the 4 position to the nitroxyl group causes additional interactions, such as van der Waals interactions, hydrogen bonding or Coulomb interactions, with the individual ions of the ionic liquid influencing the mobility of the spin probe in the ionic liquids that is expressed by the average rotational correlation time (τrot). Temperature dependent measurements of the spin probes in selected ionic liquids allow to describe ionic liquids either as continuum or as matrices where free volume effects significantly influence the mobility of the solute in the ionic liquids. The ionic liquid anion strongly affects this behavior. For example ionic liquids bearing a large anion with a delocalized charge, such as NTf2-, can be rather described by the Stokes Einstein equation. In contrast to this, free volume effects significantly influence mobility of spin probes in ionic liquids bearing a small anion, e.g. BF4-. Furthermore, the hyperfine coupling constant (Aiso14N) gives information about micropolarity of ionic liquids if the spin probe mobility is sufficient in the ionic liquids investigated. Comparing Aiso14N values with Kamlet Taft parameters shows a similar tendency of the Aiso 14N values as the hydrogen bond accepting ability (β) and an opposite tendency compared to the hydrogen bond donating ability (α). In contrast to this, no correlation was obtained between the Aiso14N values and the Kamlet Taft parameter π* describing the dipolarity/polarisability. Investigation of photogenerated lophyl radical recombination in ionic liquids shows that radical recombination within the solvent cage occurs to a higher extent in ionic liquids compared to molecular solvents. The fact that lophyl radical recombination is faster in ionic liquids compared to molecular solvents although the viscosity of ionic liquids is significantly higher supports this hypothesis. Temperature dependent investigation of lophyl radical recombination shows the expected increase in lophyl radical recombination rate with increasing temperature in the case of all solvents investigated that is caused by decrease in viscosity. The results obtained are highly important for understanding of processes where ionic liquids are used and radicals are formed as reactive species, e. g. radical polymerizations and photochemical processes.
Publications
- Synthesis of 4-sulfonatooxy-2,2,6,6-tetramethylpiperidine-1-yloxyl derivatives for investigation of ionic liquids, Tetrahedron Letters 49 (2008), 586-588
Veronika Strehmel, Hans Rexhausen, Peter Strauch
- Synthesis of 4-trimethylammonio-2,2,6,6-tetramethylpiperidine-1-yloxyl with various anions for investigation of ionic liquids, Tetrahedron Letters 49 (2008), 3264-3267
Veronika Strehmel, Hans Rexhausen, Peter Strauch
- Synthesis of a new ionic spin probe for investigation of polar and non-polar solvents, Tetrahedron Letters 49 (2008), 7143-7145
Veronika Strehmel, Hans Rexhausen, Peter Strauch
- Temperature Dependence of Interactions between Stable Piperidine-1-yloxyl Derivatives and an Ionic Liquid, ChemPhysChem 9 (2008), 1294-1302
Veronika Strehmel, Hans Rexhausen, Peter Strauch, Eckhard Görnitz, Bernd Strehmel
- Recombination of Photogenerated Lophyl Radicals in Imidazolium-Based Ionic Liquids, ChemPhysChem 10 (2009), 3112-3118
Veronika Strehmel, James F. Wishart, Dmitry E. Polyansky, Bernd Strehmel
- 2,2,6,6-Tetramethylpiperidine-1-yloxyl bound to the imidazolium ion by an acetamido group for investigation of ionic liquids, Tetrahedron Letters 51 (2010), 747-750
Veronika Strehmel, Hans Rexhausen, Peter Strauch
- Influence of imidazolium bis(trifluoromethylsulfonylimide)s on the rotation of spin probes comprising ionic and hydrogen bonding groups, PhysChemChemPhys 12 (2010), 1933-1940
Veronika Strehmel, Hans Rexhausen, Peter Strauc
- Relationship between Hyperfine Coupling Constants of Spin Probes and Empirical Polarity Parameters of Ionic Liquids, New J. Chem. 34 (2010), 2125-2131
Veronika Strehmel, Ralf Lungwitz, Hans Rexhausen, and Stefan Spange
- Temperature Dependence of Interactions between Stable Piperidine-1-yloxyl Derivatives and a Semicrystalline Ionic Liquid, ChemPhysChem 11 (2010), 2182-2190
Veronika Strehmel, Hans Rexhausen, Peter Strauch, Bernd Strehmel
- The dipolarity/polarisability of 1-alkyl-3-methylimidazolium ionic liquids as function of anion structure and the alkyl chain length, New J. Chem. 34 (2010), 1135-1140
Ralf Lungwitz, Veronika Strehmel, Stefan Spange
- Diffusion in ionic liquids: the interplay between molecular structure and Dynamics, Soft Matter 7 (2011), 1678-1681
J. R. Sangoro, C. Iacob, S. Naumov, R. Valiullin, H. Rexhausen, J. Hunger, R. Buchner, V. Strehmel, J. Kärger and F. Kremer
- New spin probes starting from 4-amino-2,2,6,6-tetramethylpiperidine-1-yloxyl, Tetrahedron Letters 53 (2012), 1587-1591
Veronika Strehmel, Hans Rexhausen, Peter Strauch
(See online at https://doi.org/10.1016/j.tetlet.2012.01.063) - Radicals in Ionic Liquids, ChemPhysChem 13 (2012) 1649-1663
Veronika Strehmel
- Recombination of Lophyl Radicals in Pyrrolidinium-Based Ionic Liquids, ChemPhysChem 14 (2013) 1899-1908
Stefan Berdzinski, Joachim Horst, Petra Straßburg, Veronika Strehmel
(See online at https://doi.org/10.1002/cphc.201300098) - Interactions between Ionic Liquids and Radicals. Journal of Molecular Liquids, Volume 192, April 2014, Pages 153-170
Veronika Strehmel, Stefan Berdzinski, Hans Rexhausen
(See online at https://doi.org/10.1016/j.molliq.2013.12.007) - Structure–property relationships in ILs: Vaporization enthalpies of pyrrolidinium based ionic liquids. Journal of Molecular Liquids, Volume 192, April 2014, Pages 171-176
Dzmitry H. Zaitsau, Andrei V. Yermalayeu, Vladimir N. Emel'yanenko, Andreas Heintz, Sergey P. Verevkin, Christoph Schick, Stefan Berdzinski, Veronika Strehmel
(See online at https://doi.org/10.1016/j.molliq.2013.07.018)
