Reduction of citral in water under typical transfer hydrogenation conditions—Reaction mechanisms with evolution of and hydrogenation by molecular hydrogen

The reduction of an α,β-unsaturated aldehyde, citral, was investigated over a 10 wt% Pd catalyst under transfer hydrogenation (TH) conditions in a closed system with microwave assistance. Surprisingly, it was found that hydrogen was produced quite fast under the microwave irradiation during the reaction, and the reduction of citral was proved to go mainly through consecutive pathways of hydrogen production – hydrogenation rather than those commonly considered for TH reactions. Similar reaction pathways were also observed with a homogeneous catalyst of [RuCl2(C6H6)]2 and other typical hydrogen donors like formate salts and isopropanol, which are usually used in the typical transfer hydrogenations.

Graphical abstractUnusual reaction mechanisms are proved for selective reduction of an α,β-unsaturated aldehyde of citral under typical transfer hydrogenation (TH) reaction conditions. The reaction goes through consecutive pathways of hydrogen production – hydrogenation than those commonly considered for TH reactions.Figure optionsDownload full-size imageDownload high-quality image (150 K)Download as PowerPoint slideHighlights► Hydrogen is produced promptly from HCOONa and H2O over Pd/C under microwave assistant. ► Citral was hydrogenated by the hydrogen produced in situ efficiently. ► A consecutive hydrogen production and hydrogenation process was confirmed.