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Regioselective catalytic hydrogenation of citral with ionic liquids as reaction modifiers

Arras, Jürgen ; Steffan, Martin ; Shayeghi, Yalda ; Ruppert, Dominik ; Claus, Peter :
Regioselective catalytic hydrogenation of citral with ionic liquids as reaction modifiers.
[Online-Edition: http://dx.doi.org/10.1039/b822992a]
In: Green Chemistry, 11 pp. 716-723. ISSN 14639262
[Artikel], (2009)

Offizielle URL: http://dx.doi.org/10.1039/b822992a

Kurzbeschreibung (Abstract)

Silica and polyaniline supported palladium catalysts prepared by different techniques (incipient-wetness impregnation, deposition precipitation) using Pd(OAc)2 or H2PdCl4 as precursors were studied in the liquid-phase hydrogenation of citral under addition of several ionic liquids ([BMIM][NTf2], [BMIM][PF6], [BMPL][NTf2], [BMIM][DCA], [BMPL][DCA], [B3MPYR][DCA]) either as catalyst coating or as additive. By an incipient-wetness technique, the catalysts were coated with a mixture of IL in acetone. The catalysts were characterized by nitrogen physisorption, whereby a decrease of surface area and pore volume was detected by the IL coated catalysts. Furthermore, ICP-OES, TEM and IR spectroscopy were performed to analyze metal content, particle size and coverage of the catalyst with ionic liquid. Citral hydrogenation was performed at 323 K and under 2.0 MPa H2 in an autoclave with off-line GC analysis of the product mixtures. Beside stirrer speed, catalyst mass and citral concentration, the type and quantity of ionic liquid were also varied to elucidate their influence on activity and selectivity of the Pd/SiO2 catalysed citral hydrogenation. The results show that treatment of the catalyst with ionic liquids—independent of catalyst coating or additive—leads to a selectivity enhancement of the desired product, citronellal. With [PF6]− or [NTf2]− as the IL anion, maximum selectivities were (60 ± 2)% at 70% conversion. In particular, dicyanamide (DCA) containing ionic liquids allow, under optimised conditions, the quantitative one-pot synthesis of citronellal, at least if the Pd/SiO2 catalyst was coated with 29 wt% [B3MPYR][DCA]. By using polyaniline supported Pd catalysts and [BMIM][DCA] as additive, the consecutive hydrogenation towards dihydrocitronellal was less pronounced and the influence of metal precursor, support material and preparation technique of the catalyst could be excluded. Hydrogenation of pure citral on [BMIM][DCA] coated palladium catalysts offers a solvent-free, green route to citronellal in reasonable selectivities (S = 86%).

Typ des Eintrags: Artikel
Erschienen: 2009
Autor(en): Arras, Jürgen ; Steffan, Martin ; Shayeghi, Yalda ; Ruppert, Dominik ; Claus, Peter
Titel: Regioselective catalytic hydrogenation of citral with ionic liquids as reaction modifiers
Sprache: Englisch
Kurzbeschreibung (Abstract):

Silica and polyaniline supported palladium catalysts prepared by different techniques (incipient-wetness impregnation, deposition precipitation) using Pd(OAc)2 or H2PdCl4 as precursors were studied in the liquid-phase hydrogenation of citral under addition of several ionic liquids ([BMIM][NTf2], [BMIM][PF6], [BMPL][NTf2], [BMIM][DCA], [BMPL][DCA], [B3MPYR][DCA]) either as catalyst coating or as additive. By an incipient-wetness technique, the catalysts were coated with a mixture of IL in acetone. The catalysts were characterized by nitrogen physisorption, whereby a decrease of surface area and pore volume was detected by the IL coated catalysts. Furthermore, ICP-OES, TEM and IR spectroscopy were performed to analyze metal content, particle size and coverage of the catalyst with ionic liquid. Citral hydrogenation was performed at 323 K and under 2.0 MPa H2 in an autoclave with off-line GC analysis of the product mixtures. Beside stirrer speed, catalyst mass and citral concentration, the type and quantity of ionic liquid were also varied to elucidate their influence on activity and selectivity of the Pd/SiO2 catalysed citral hydrogenation. The results show that treatment of the catalyst with ionic liquids—independent of catalyst coating or additive—leads to a selectivity enhancement of the desired product, citronellal. With [PF6]− or [NTf2]− as the IL anion, maximum selectivities were (60 ± 2)% at 70% conversion. In particular, dicyanamide (DCA) containing ionic liquids allow, under optimised conditions, the quantitative one-pot synthesis of citronellal, at least if the Pd/SiO2 catalyst was coated with 29 wt% [B3MPYR][DCA]. By using polyaniline supported Pd catalysts and [BMIM][DCA] as additive, the consecutive hydrogenation towards dihydrocitronellal was less pronounced and the influence of metal precursor, support material and preparation technique of the catalyst could be excluded. Hydrogenation of pure citral on [BMIM][DCA] coated palladium catalysts offers a solvent-free, green route to citronellal in reasonable selectivities (S = 86%).

Titel der Zeitschrift, Zeitung oder Schriftenreihe: Green Chemistry
Band: 11
Fachbereich(e)/-gebiet(e): Fachbereich Chemie
Fachbereich Chemie > Technische Chemie > Technische Chemie II
Fachbereich Chemie > Technische Chemie
Hinterlegungsdatum: 02 Mai 2009 13:00
Offizielle URL: http://dx.doi.org/10.1039/b822992a
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First published on the web 27. Februar 2009

ID-Nummer: 10.1039/b822992a
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