Hydrogenation reactions in ionic liquids: Finding solutions for tomorrow's world

Ionic liquids are excellent solvents for conducting biphasic hydrogenation reactions offering many advantages over both related homogeneous processes and biphasic reactions in other alternative solvents. The relevant physicochemical properties of ionic liquids that lend themselves to hydrogenation catalysis are summarised and key hydrogenation reactions/protocols conducted using ionic liquids are discussed. Two new heterogeneous catalyst systems for the hydrogenation of benzene are described. One employs a well known rhodium nanoparticle catalysts, and compared to its use in molecular solvents, reaction rates, ease of use and recyclability, are all improved. The other comprises a new simple platinum-chloroaluminate catalyst system. The preparation of the chloroaluminate ionic liquid on a moderate scale is described together with the chloride salt precursor and the tetrafluoroborate salt. Potentially these ionic liquids (and others) could be prepared by Lonza on a 100 ton scale.