Catalysis of Organic..

Disselkamp et al. 21324. Cavitating Ultrasound Hydrogenation ofWater-Soluble Olefins Employing Inert Dopants:Studies of Activity, Selectivityand Reaction MechanismsRobert S. Disselkamp, Sarah M. Chajkowski, Kelly R. Boyles, Todd R. Hart,and Charles H.F. PedenInstitute for Interfacial Catalysis, Pacific Northwest National Laboratory,Richland, WA 99352 USAAbstractrobert.disselkamp@pnl.govHere we discuss results obtained as part of a three-year investigation at PacificNorthwest National Laboratory of ultrasound processing to effect selectivity andactivity in the hydrogenation of water-soluble olefins on transition metal catalysts.We have shown previously that of the two regimes for ultrasound processing, highpowercavitating and high-power non-cavitating, only the former can effect productselectivity dramatically (>1000%) whereas the selectivity of the latter wascomparable with those obtained in stirred/silent control experiments [R.S.Disselkamp, Y.-H. Chin, C.H.F. Peden, J. Catal., 227, 552 (2005)]. As a means ofensuring the benefits of cavitating ultrasound processing, we introduced the conceptof employing inert dopants into the reacting solution. These inert dopants do notpartake in solution chemistry but enable a more facile transition from high-powernon-cavitating to cavitating conditions during sonication treatment. With cavitationprocessing conditions ensured, we discuss here results of isotopic H/D substitutionfor a variety of substrates and illustrate how such isotope dependent chemistriesduring substrate hydrogenation elucidate detailed mechanistic information aboutthese reaction systems.IntroductionUsing ultrasound to enhance activity, and to a lesser extent to alter selectivity, inheterogeneous condensed phase reactions is well known [1-7], with the first paper onsonocatalysis having been published over 30 years ago [8]. In principle, there existstwo separate domains for sonochemistry, these are non-cavitating and cavitatingultrasound regimes. For commercially available instruments, bath systems by virtueof their lower acoustic intensity are usually non-cavitating whereas probe (e.g., horn)systems can be either (high power) non-cavitating or cavitating. One objective ofthis paper is to contrast differences in a heterogeneous catalytic reaction for noncavitatingand cavitating ultrasound compared to a control (stirred and silent) system.Only through “doping” our solution were we able to initiate the rapid onset of