Transfer hydrodechlorinations

Y Ukisu, TJ Miyadera. Hydrogen transfer hydrodechlorination of aromatic halides with alcohols in the presence of noble metal catalysts. Mol. Catal. A Chemical 125 135-142,1997. 

Transfer Hydrodechlorination. [Cp RhCl2]2-catalyzed transfer hydrodechlorination of aryl chlorides is developed using 2-butanol as a hydrogen source and KOH as a base. ... 

Actual metal contents were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES). Metal particles were examined by X-ray diffraction, transmission electron microscopy and CO chemisorption. Details about the procedures used can be found elsewhere [9]. In the case of Pd-Ag/C catalysts, the combination of these three techniques enabled us to obtain the metal particles size and their bulk and surface composition [9, 13]. Finally, the Pt/C catalysts were tested for benzene hydrogenation, and the Pd-Ag/C catalysts were used to study mass transfer in the support during a well-known reaction the selective hydrodechlorination of 1,2-diehloroethane into ethylene. 

After drying and reduction, the Pd-Ag/C catalysts are composed of bimetallic Eilloy nanoparticles ( 3 nm). CO chemisorption coupled to TEM and XRD analysis showed that that, for catalysts 1.5% wt. in each metal, the bulk composition of the alloy is close to 50% in each metal, whereas the surface is 90% in Ag and 10% in Pd [9]. Mass transfer limitations can be detected by testing the same catalyst with various pellet sizes [18]. Indeed, if the reactants diffusion is slow due to small pore sizes, the longer the distance between the pellet surface and the metal particle, the larger the influence of the difiusion rate on the apparent reaction rate. Pd-Ag catalysts with various pellet sizes were thus tested in hydrodechlorination of 1,2-dichloroethane. Results were compared to those obtained with a Pd-Ag/activated charcoal catalyst. Fig. 4 shows the evolution of the effectiveness factor of the catalysts, i.e. the ratio between the apparent reaction rate and the intrinsic reaction rate, as a function of the pellet size. The intrinsic reaction rate was considered equal to the reaction rate obtained with the smallest pellet size. When rf = 1, no diffusional limitations occur, and the catalyst works in chemical regime. When j < 1, the observed reaction rate is lower than the intrinsic reaction rate due to a slow diffusion of the reactants and products and the catalyst works in diffusional regime [18]. 

Chlorinated acetophenones and benzophenones were hydrodechlorinated selectively under phase transfer conditions without the hydrogenation of the ketone (Scheme 70).t ... 

Job J, Heinrichs B, Lambert S et al (2006) Carbon Xerogels as Catalyst Supports Study of Mass Transfer. American Institute of Chemical Engineers Fluid Mechanics and Transport Phenomena 52 2663-2676 Job N, Heinrichs B, Ferauche F et al (2005) Hydrodechlorination of 1,2-dichloroethane on Pd-Ag catalysts supported on tailored texture carbon xerogels. Catalysis Today 102 234—241... 

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