Unexpected Roles of Molecular Sieves in Palladium-Catalyzed Aerobic Alcohol Oxidation

Methods for palladium-catalyzed aerobic oxidation of alcohols often benefit from the presence of molecular sieves. This report explores the effect of molecular sieves on the Pd(OAc)2/pyridine and Pd(OAc)2/DMSO (DMSO = dimethyl sulfoxide) catalyst systems by performing kinetic studies of alcohol oxid...

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Bibliographic Details
Published in:	Journal of organic chemistry 2006-03, Vol.71 (5), p.1861-1868
Main Authors:	Steinhoff, Bradley A, King, Amanda E, Stahl, Shannon S
Format:	Article
Language:	eng
Subjects:	Acetates - chemistry Aerobiosis Alcohols - chemistry Catalysis Catalysts: preparations and properties Chemistry Dimethyl Sulfoxide - chemistry Exact sciences and technology Gases - chemistry General and physical chemistry Heterocyclic compounds Heterocyclic compounds with only one n hetero atom and condensed derivatives Kinetics Kinetics and mechanisms Organic chemistry Organometallic Compounds - chemistry Oxidation-Reduction Oxygen - chemistry Preparations and properties Pyridines - chemistry Reactivity and mechanisms Spectroscopy, Fourier Transform Infrared Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
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Summary:	Methods for palladium-catalyzed aerobic oxidation of alcohols often benefit from the presence of molecular sieves. This report explores the effect of molecular sieves on the Pd(OAc)2/pyridine and Pd(OAc)2/DMSO (DMSO = dimethyl sulfoxide) catalyst systems by performing kinetic studies of alcohol oxidation in the presence and absence of molecular sieves. Molecular sieves enhance the rate of the Pd(OAc)2/pyridine-catalyzed oxidation of alcohols, and the effect is attributed to the ability of molecular sieves to serve as a Brønsted base. In contrast, no rate enhancement is observed for the Pd(OAc)2/DMSO-catalyzed reaction. Both catalyst systems exhibit improved catalyst stability in the presence of molecular sieves, manifested by higher catalytic turnover numbers. Control experiments indicate that neither of these beneficial effects is associated with the ability of molecular sieves to absorb water, a stoichiometric byproduct of these reactions. Finally, the use of simultaneous gas-uptake and in-situ IR spectroscopic studies reveal that molecular sieves inhibit the disproportionation of H2O2, an observation that contradicts a previous suggestion that the beneficial effect of molecular sieves may arise from their ability to promote H2O2 disproportionation.
ISSN:	0022-3263 1520-6904