Catalysis of Organic..

498 Transition Metal Removalreduced to single-digit ppm levels.Table 4 summarizes these results. Theconcentration levels obtained in thisexperiment are comparable to thoseobtained when similar conditions wereused for studying adsorption of Pd inthe fixed bed mode (see section “Effectof temperature”). However, in the fixedbed mode the experiment time was 20min vs. 3 h in batch mode. In addition,an extra step for filtration of thescavenger from the process solution wasrequired when batch mode was employed.Table 4 Results from batch study ofDeloxan ® scavenging of Ru(II). [a]Toluene DMFDeloxan® ppm Ru [b] ppm Ru [b]MP 3 6THP II 1 6.5[a] Cl 2 Ru(PPh 3 ) 3[b] initial concentration 20 ppm RuEach mode of use has its own advantages and disadvantages. In batch mode, theentire amount of process solution and the entire amount of scavenger are in contactwith each other from the beginning. Metal adsorption starts off quick because thereare a large number of free sites available. However, over time the most easilyaccessible available sites become occupied leading to a decrease in the rate ofadsorption of the metal contaminant. In fixed bed mode, the concentration of themetal contaminant decreases as the process solution moves down the columnbecause, if the column is long enough, the process solution is constantly exposed tofresh adsorbent. If the metal contaminant forms a colored complex with theadsorbent, the zone of reaction of the metal with the scavenger is easily observable.Usually the reaction zone is much darker colored at the inlet than the outlet of thecolumn. In the present work, the reaction zone for all Pd complexes was verynarrow compared to the reaction zone for Ru(II). The orange-colored reaction zonefor Pd complexes was not observed to go below half the filling of metal scavenger.The brown-colored reaction zone for Ru(II), however, was observed to go down tonear the bottom frit of the column.Experimental SectionGeneral Procedure: All columns were packed with Deloxan ® THP II or Deloxan ®MP Metal Scavenger from Degussa and conditioned before use. The columns wereconditioned by passing MeOH (methanol, Acros, extra dry) followed by either DMF(dimethylformamide, Fisher ACS certified) or toluene (Fisher ACS certified)through the column. 20 ppm solutions of H 2 PdCl 4 in DMF, trans-di(µ-acetato)bis[o-(di-o-tolylphosphino)benzyl]dipalladium(II) (3) in toluene and Cl 2 Ru(PPh 3 ) 3 intoluene or DMF were prepared by standard procedures. 3 and 4 were purchasedfrom Strem.Metal Analysis: The concentration of Pd in the effluent was determined by ICP orAA and the concentration of Ru was extrapolated from a UV-Vis calibration curve.A Leeman Labs, Inc. Direct Reading Eschelle ICP-AES was used for Pdconcentration determination in the Deloxan ® MP studies while a Varian Spectra AA55B flame atomic absorption spectrophotometer was used to determine the Pdconcentration in the Deloxan ® THP II pilot studies. Once the organic solvent was