In the course of our attempts to replace harmful organic solvents used in organic processes by environmentally favored media, we investigated the transfer hydrogenation of various, unsaturated substrates by cyclohexene and similar water-insoluble hydrogen donors. The catalyst in these reactions was Pd(0) in form of nanoparticles, stabilized by hydrophobic silica sol-gel which can be reused at least 4-6 times without significant loss of activity. The process was shown to depend on the electronic nature of the surfactants. Marlipal ® 24/70 gave in most experiments the best results. Except for the hydrolysable 1-chloromethylnaphthalene, where chlorine can be substituted by a hydroxyl group, the aqueous medium does not take part in the catalytic process.
Bibliographical noteFunding Information:
We thank Dr. Inna Popov for performing the TEM measurements and Dr. Vitaly Gutking for the XPS analyses. We also acknowledge the financial support of the Deutsche Forschungsgemeinschaft (DFG) for a trilateral grant No. SCHO687/8-2 .
- Aqueous microemulsion
- Heterogeneous catalysis
- Sustainable chemistry
- Transfer hydrogenation