Catalysis of Organic..

216 Cavitating Ultrasound Hydrogenationdopant to facilitate the onset of cavitation. The exact mechanism by which the onsetof cavitation onset is enhanced through the use of these inert dopants is unclear, butlikely involves solvent (or solution) modification such as by viscosity or surfacetension effects. Experiments were performed at 298 K.The full reaction process is summarized in scheme 1.Scheme 1.For example, in one pathway H-atom elimination reactions generate the enolintermediate, which eventually rearranges to 2-butanone. In a second competingreaction pathway, H-atom addition results in direct hydrogenation to the saturatedalcohol 2-butanol.A kinetic analyses of the data was performed by noting the pseudo-first orderloss of substrate together with selectivity. This enabled a pseudo-first order kineticdescription of the two pathways to be obtained. Table 1 lists the lifetimes of 2-butanone and 2-butanol production for the various experiments. Here the lifetimesrefers to the inverse of the pseudo-first order reaction rate coefficients.Table 1. Results of kinetics for stirred, non-cavitating ultrasound, and cavitatingultrasound experiments.Experiment t 1 (min.)t 2 (min.) t total (min.)(to 2-butanone) (to 2-butanol)Stirred 82.0 60.7 34.9Non-cavitating 19.8 11.1 7.1ultrasoundStirred (with 1- 125.2 125.2 62.6pentanol)Cavitatingultrasound (with1-pentanol)8.9 0.71 0.66Four primary conclusions can be put forth regarding the data of Table 1. First, asmall difference in selectivity is seen for the non-cavitating ultrasound compared tothe control experiment (obtained from the inverse of the ratio of lifetimes). Forexample, the ratio of 2-butanone to 2-butanol products for the stirred without 1-pentanol is 0.74 (equal to 60.7/82.0). Second, comparing these values to the