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 using cinchonidine (CD), indicate that CD activates pyruvate (through enol formation) and modifies the unsaturated acid (salt formation), but not the catalyst, and that CD may even poison the catalyst (palladium more than platinum). Therefore, the modifierʹs properties must fit the substrateʹs properties and not be a catalyst poison, the best sequence for addition of the reactants being: first a mixture of substrate/CD and then the supported Pt and/or Pd catalyst.