An Examination of the H/D Isotope Substitution Effect on Selectivity and Activity in the Cavitating Ultrasound Hydrogenation of Aqueous 3-Buten-2-ol and 1,4-Pentadien-3-ol on Pd-black

In this study, cavitating ultrasound (CUS) processing is compared to the traditional (stirred/silent, SS) method in the aqueous phase hydrogenation, via H/D isotope substitution of 3-buten-2-ol (3B2OL) and 1,4-pentadien-3-ol (14PD3OL) using a Pd-black catalyst, all at 298 K. The products that are formed include 2-butanol and 2-butanone for 3B2OL, and 3-pentanol and 3-pentanone for 14PD3OL. The H and D isotope-dependent chemistries are accomplished using H2- versus D2-mediated H/D addition, as well as H2O versus D2O solvents for alcohol -OH and -OD isotope substitution. Several conclusions are presented. For example, the H2-CUS processing of 3B2OL in water compared to D2O reveals ketone selectivities that are twice as large. This suggests that the alcohol-dependent enol tautomerization to ketone reaction is slower with deuterium, and possibly a rate-controlling event. In addition, for CUS processing of both 3B2OL and 14PD3OL in water, the similarity in ketone selectivities (all ~17%) for H2 compared to D2 addition suggests that adsorbed H and D isotopes have comparable surface diffusion rates and, hence, result in almost-equal selectivities.