Role of the Solvent in the Adsorption−Desorption Equilibrium of Cinchona Alkaloids between Solution and a Platinum Surface:  Correlations among Solvent Polarity, Cinchona Solubility, and Catalytic Performance

Zhen Ma and Francisco Zaera*
Department of Chemistry, University of California, Riverside, California 92521
J. Phys. Chem. B, 2005, 109 (1), pp 406–414
DOI: 10.1021/jp046017b
Publication Date (Web): December 7, 2004
Copyright © 2005 American Chemical Society
*

 Corresponding author. E-mail:  zaera@ucr.edu.

Abstract

The role that the nature of the solvent plays in defining the extent of cinchona alkaloid adsorption−desorption equilibrium on platinum surfaces has been studied both by testing their solubility in 54 different solvents and by probing the stability of adsorbed cinchona in the presence of those solvents. The solubilities vary by as much as 5−6 orders of magnitude, display volcano-type correlations with solvent polarity and dielectric constant, and follow a cinchonine < cinchonidine < quinine, quinidine sequence. The adsorption−desorption equilibrium shifts toward the solution with increasing dissolving power of the solvent. The relevance of these results to the behavior of cinchona as chiral modifiers in hydrogenation catalysis is discussed.

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History

  • Published In Issue January 13, 2005
  • Received September 3, 2004
    Revised October 21, 2004

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