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Microwave-assisted partial hydrogenation of citral by using ionic liquid-coated porous glass catalysts.

ChemSusChem (2011-08-10)
Thomas Gallert, Martin Hahn, Martin Sellin, Christine Schmöger, Achim Stolle, Bernd Ondruschka, Thomas F Keller, Klaus D Jandt
ABSTRACT

The microwave-assisted hydrogenation of citral (3,7-dimethylocta-2,6-dienal) to citronellal with molecular hydrogen as the reducing agent was investigated. Several polar and non-polar solvents were screened and imidazolium-based ionic liquids were applied as modifiers for the palladium-containing porous glass catalysts (Pd/TP). The best results were obtained with N-ethyl-N'-methylimidazolium dicyanamide, N-ethyl-N'-methylimidazolium acetate, or N-ethyl-N'-methylimidazolium trifluoroacetate, which were used to prepare supported catalysts with an ionic liquid layer (SCILL) on Pd/TP by wet-impregnation. The influence of pressure and temperature when using these ionic liquid-containing catalysts, as well as their long-term stabilities, were examined. Working with microwave-assisted heating, high yields of citronellal were achieved under mild conditions within short reaction times. Catalyst characterization was carried out by means of BET measurements, X-ray photoelectron spectroscopy (XPS) and thermo-gravimetric analyses. The influences of the ionic liquid layer were derived from experiments carried out before and after the reactions.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
(R)-(+)-Citronellal, technical grade
Supelco
(±)-Citronellal, analytical standard
Sigma-Aldrich
(S)-(−)-Citronellal, 96%
Sigma-Aldrich
(±)-Citronellal, natural, ≥85%, FCC, FG
Sigma-Aldrich
(±)-Citronellal, ≥95.0% (GC)