Application of a cross-linked Pd–chitosan catalyst in liquid-phase-hydrogenation using molecular hydrogen

Chitosan was cross-linked with hexamethylendiisocyanate and loaded with Pd which was subsequently reduced with NaBH4. The prepared catalyst was characterized by FT-IR and elemental analysis. The metal content was determined by ICP-MS measurements. Several substrates (cyclohex-2-enone, benzalacetophenone, 1,2-diphenylacetylene, and N-benzylidenaniline) were hydrogenated successfully in ethanol at mild conditions (50 °C, p(H2) ∼6 bar) utilizing a microwave reactor. Reaction parameters like temperature, hydrogen pressure, and the solvent were varied. It was shown that the reduction of the catalyst is crucial for catalytic activity. The catalyst was reused ten times for the hydrogenation of cyclohex-2-enone, without showing a dramatic loss in immobilized metal content. Also the polymeric support material did not show any decomposition.

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► A Pd-catalyst based on cross-linked chitosan was prepared.
► The reduction of unsaturated carbonyl compounds proceeded with high selectivities.
► Imines and alkynes were hydrogenated rapidly.
► Catalyst was reused for ten times.