Substrate-modifier but not catalyst-modifier: heterogeneous hydrogenation of C=O and C=C using cinchonidine

Literature results and our own, concerning hydrogenation of ethyl pyruvate and 2-methyl pentenoic acid over Al2O3-supported platinum and palladium usi ng cinchonidine (CD), indicate that CD activates pyruvate (through enol For mation) and modifies the unsaturated acid (salt formation), but not time ca talyst, and that CD may even poison the catalyst (palladium more than plati num). Therefore. time modifier's properties must fit the substrate's proper ties and not be a catalyst poison, the brst sequence Tor addition of the re actants being first a mixture of substrate/CD and then the supported Pt and /or Pd catalyst. (C) 2001 Elsevier Science Ltd. All rights reserved.