Catalytic transfer hydrogenation of hydrophobic substrates by water-insoluble hydrogen donors in aqueous microemulsions

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.

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► “Green” hydrogenation of water insoluble compounds in aqueous media.
► Replacement of harmful organic solvents by aqueous microemulsions.
► Elucidation of factors that influence transfer hydrogenation in aqueous microemulsions.