Desorption electrospray ionization (DESI) is a recently developed ambient mass spectrometric method where analytes on surfaces are sprayed with charged microdroplets; reflected secondary microdroplets enter a mass spectrometer.  If reagents are added to the spray solutions and a catalyst or catalyst precursor is absorbed to the surface, short-lived catalytic intermediates formed on the surface or in the secondary microdroplets can be intercepted and characterized.  The millisecond timescales of the DESI process, coupled with the selectivity and sensitivity of high resolution mass spectrometry (HRMS), provides a powerful strategy for detecting reactive species.  We describe the application of DESI-HRMS to identify intermediates in a regio- and chemoselective oxidation of a variety of vicinal polyols with [(neocuproine)Pd(OAc)]2(OTf)2 (neocuproine = 1,9-dimethylphenanthroline).  The Pd-mediated catalytic oxidation of vicinal diols occurs readily at room temperature to generate a-hydroxy ketones in gram and multi-gram scaled reactions.  Several reactive intermediates had been proposed from mechanistic, kinetic, and theoretical investigations; the application of DESI-HRMS enabled us to directly identify and characterize many of these key intermediates.

Desorption electrospray ionization mass spectrometry studies of the chemoselective Pd-catalyzed aerobic oxidation of polyols

245th National Meeting (2013)

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