Mielby J.,Center for Catalysis and Sustainable Chemistry |
Mielby J.,Technical University of Denmark |
Riisager A.,Center for Catalysis and Sustainable Chemistry |
Riisager A.,Technical University of Denmark |
And 3 more authors.
Catalysis Today | Year: 2013
The one-pot formation of amides by oxidative coupling of alcohols and amines via intermediate formation of methyl ester using supported gold and base as catalysts was studied using the Hammett methodology. Determining the relative reactivity of four different para-substituted benzyl alcohol derivatives showed that the first step of the reaction generates a partial positive charge in the benzylic position (i.e. by hydride abstraction), while the second step of the reaction builds up negative charge in the rate determining step. The aminolysis of the methyl ester intermediate was further investigated by means of DFT/B3LYP. The transition state structures and energies were determined for both a concerted and a neutral two-step reaction mechanism. As expected, the base-promoted two-step mechanism was found to be the most energetically favourable and this reaction mechanism was used to construct a theoretical Hammett plot that was in good agreement with the one obtained experimentally. © 2012 Elsevier B.V. All rights reserved.
Gorbanev Y.Y.,Center for Catalysis and Sustainable Chemistry |
Kegnaes S.,Center for Catalysis and Sustainable Chemistry |
Hanning C.W.,Center for Catalysis and Sustainable Chemistry |
Hansen T.W.,Technical University of Denmark |
Riisager A.,Center for Catalysis and Sustainable Chemistry
ACS Catalysis | Year: 2012
Heterogeneous catalyst systems comprising ruthenium hydroxide supported on different carrier materials, titania, alumina, ceria, and spinel (MgAl 2O 4), were applied in selective aerobic oxidation ethanol to form acetic acid, an important bulk chemical and food ingredient. The catalysts were characterized by X-ray powder diffraction (XRPD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), and nitrogen physisorption and utilized in the oxidation of 2.5-50 wt % aqueous ethanol solutions at elevated temperatures and pressures. The effects of Ru metal loading, pretreatment of catalysts, oxidant pressure, reaction temperature, and substrate concentration were investigated. Quantitative yield of acetic acid was obtained with 1.2 wt % Ru(OH) x/CeO 2 under optimized conditions (150 °C, 10 bar O 2, 12 h of reaction time, 0.23 mol % Ru to substrate). © 2012 American Chemical Society.