Catalysis of Organic..

494 Transition Metal Removalmetal residue permitted to remain in pharmaceutical products is strictly regulated andfor Pd and other platinoid metals this level should be below 5 ppm.[2]Several methods of metal removal from process solutions exist. Some of theseapproaches include crystallization, distillation and extraction. However, thesemethods can be very time-consuming and often result in loss of some valuableproduct. To overcome these shortcomings, Degussa has developed Deloxan ® MetalScavengers as an attractive option to solve problems associated with transition metalcontamination of process solutions.[3, 4, 5] Two resins are commercially available.Deloxan ® THP II (1) is a thiourea functionalized, macroporous, organofunctionalpolysiloxane while Deloxan ® MP (2) is mercapto functionalized.These Deloxan ® beads have an inert siloxane matrix which is advantageous overother adsorbents such as activated carbon or organic polymer-based resins and fibersbecause (1) valuable API product is not adsorbed and lost as is the case whenactivated carbons are used and (2) they are chemically resistant to most solvents andstable over a wide pH range (0–12).OOOOSiOSiOCH 2 CH 2CH 2 CH 2CH 2CH 2NHNHCSOOSiOSiOCH 2 CH 2CH 2 CH 2CH 2CH 2SHSH1 2In addition to these, Deloxan ® THP II and MP possess many othercharacteristics that are essential for good metal scavenging. First, they have good toexcellent scavenging properties for most transition metals. They are structurallystable showing no shrinking or swelling and compatible with all solvents. These arehighly attrition resistant and thermally stable. Deloxan ® Metal Scavengers have awell-defined pore structure and due to the bead size (0.4–1.4 mm) and shape theycan be applied in either fixed bed or batch mode. They can be refined allowing forrecovery of precious metals. Importantly, Deloxan ® THP II and MP arecommercially available in large quantities.Results and DiscussionDue to the particle size of Deloxan ® THP II and MP, these resins can be used ineither batch or fixed bed mode to scavenge transition metals from contaminatedprocess solutions. In this work both modes of operation were investigated. Inaddition to mode of use, many other variables can influence the effectiveness of ametal scavenger. Oxidation state of the metal, solvent characteristics (polar ornonpolar) and nature of the metal complex (ligands) are just a few of these variablesand these were chosen for investigation in this body of work.