title: Para-hydrogen induced polarization in homogeneous phase--an example of how ionic liquids affect homogenization and thus activation of catalysts.
abstract: Para-hydrogen induced polarization (PHIP) is observed in an organic solvent-free homogeneous catalyst/substrate system using ionic liquids. The hydrogenation reactions are performed employing a Rh-catalyst/ionic liquid system without further organic solvents. The PHIP phenomenon is demonstrated for the ethyl acrylate system. Small amounts of ionic liquids (ILs) containing weakly coordinating anions such as [Tf2N]- act as homogenizing cosolvents for the catalyst in ethyl acrylate, leading to a dramatic activation of the catalytic process and a high PHIP signal enhancement. The achieved enhancement depends strongly on the viscosity of the ethyl acrylate/IL mixture. Furthermore, by deliberate choice of the IL constituents it was possible to design a model system exhibiting both sufficient catalyst solubility and biphasic liquid-liquid behavior. This shows that in ionic liquids PHIP enhancements followed by a fast quantitative removal of the para-hydrogenated product from the catalyst phase is in principle possible. The possible PHIP enhancement factors will depend strongly on the design of a suitable hydrogenation reactor.
authors.affiliation: Institute of Physical Chemistry, Technical University Darmstadt, Petersenstrasse 20, D-64287 Darmstadt, Germany.
authors.forename: Torsten
authors.initials: T
authors.lastname: Gutmann
authors.forename: Martin
authors.initials: M
authors.lastname: Sellin
authors.forename: Hergen
authors.initials: H
authors.lastname: Breitzke
authors.forename: Annegret
authors.initials: A
authors.lastname: Stark
authors.forename: Gerd
authors.initials: G
authors.lastname: Buntkowsky