Charged microdroplets produced by spray-based ionization techniques, such as electrospray ionization, have been widely used as a means to probe both reaction mechanisms and kinetics. I have shown that the same microdroplets can have an increased chemical reactivity compared to corresponding bulk solution-phase. This apparent conundrum and the exploitation of droplet-accelerated reactions will be the foci of this talk. Controlling variables in the electrospray process, such as pH, concentration, sheath gas flow and distance between the ion source and the ion transfer capillary of the mass spectrometer, has allowed the selection between monitoring reactions by mass spectrometry with or without reaction rate acceleration. Comparisons to “on-water” chemistry of the Sharpless group, including the cycloaddition reaction of diethyl azodicarboxylate and quadricyclane, demonstrates the role of the droplet surface using theta-tip nanoelectrospray ionization mass spectrometry. Using larger Leidenfrost droplets, which are created by levitating reaction mixtures on superheated surfaces, provides reaction acceleration. The applications of these accelerated reactions include the collection of organic products from the spray process, or more practically from Leidenfrost droplet experiments as well as the screening of novel chemistry in droplets. Using the Leidenfrost experiment, it was demonstrated that the synthesis of ca. 18 mg of reaction product in the Katritzky pyrylium to pyridinium conversion could be achieved. This makes the Leidenfrost and other levitated droplet techniques an intriguing route for scale-up of these accelerated reactions.
Dr. Ryan M. Bain attained his B.S. in chemistry from Saint Xavier University (Chicago, IL) in 2012 and his Ph.D. in chemistry from Purdue University (West Lafayette, IN) in 2017, working under the advisement of Professor R. Graham Cooks. Subsequently, he worked as a Postdoctoral Fellow between the Stanford University Medical School and Department of Chemistry (Stanford, CA) with Professors James Brooks and Richard N. Zare. Ryan is currently a Senior Scientist in Core Research and Development at the Dow Chemical Company in Midland, MI.