| The Reformatsky reaction of an alpha-bromoester and zinc dust with an aldehyde, ketone or another electrophile was one of the first organometallic reactions studied (20 years ago) under ultrasound due to problems encountered with conventional methods. These problems include low to moderate yields due to side reactions and the zinc dust must be "activated" in order for the reaction to proceed. Low intensity ultrasound (LIU) from an ultrasonic cleaning bath as the energy source gives improved rates and yields in Reformatsky reactions of simple aldehydes and ketones. However, prior activation of the zinc dust remains necessary as well as anhydrous conditions. Also, the relatively low energy of an ultrasonic cleaning bath can lead to problems with laboratory-to-laboratory reproducibility.; This dissertation presents a study of the application of high intensity ultrasound (HIU) as the energy source for Reformatsky and Reformatsky-type heterogeneous reactions and the benefits offered by this type of ultrasound over low intensity ultrasound and conventional methods. HIU-stimulated reactions of a ketone (or alpha, beta-unsaturated ketone or imine), an alpha-bromoester, zinc dust, and a catalytic amount of iodine in dioxane were investigated with particular interest on steric and electronic features of the ketone or imine and the alpha-bromoester components. The HIU-promoted Reformatsky reactions are much more rapid and produced higher yields of Reformatsky reaction products in comparison to LIU-promoted reactions and conventional methods examined. In several cases, the use of HIU gave products that were unattainable with conventional thermal methods. |
