title: Microwave-specific acceleration of a Friedel-Crafts reaction: evidence for selective heating in homogeneous solution.
abstract: Thermally promoted Friedel-Crafts benzylation of arene solvents has been examined under both conventional convective heating with an oil bath and heating using microwave (MW) energy. Bulk solution temperatures-as measured by internal and external temperature probes and as defined by solvent reflux-were comparable in both sets of experiments. MW-specific rate enhancements were documented under certain conditions and not others. The observed rate enhancements at a given temperature are proposed to arise from selective MW heating of polar solutes, perturbing thermal equilibrium between the solute and bulk solution. Central to MW-specific thermal phenomena is the difference between heat and temperature. Temperature is a measure of the ensemble average kinetic molecular energy of all solution components, but temperature does not provide information about solute-specific energy differences that may arise as a consequence of selective MW heating. Enhanced chemical reactivity of the MW-absorbing solute can be described as a MW-specific "extra-temperature thermal effect", because the measurable solution temperature only captures a portion of the solute kinetic molecular energy. Experimental factors that favor MW-specific rate enhancements are discussed with an eye toward future development of MW-actuated organic reactions, in which the observed thermal reactivity exceeds what is predicted from temperature-based Arrhenius calculations.
authors: Department of Chemistry and Biochemistry, Florida State University , Tallahassee, Florida 32306-4390, United States.
authors: Michael R
authors: MR
authors: Rosana
authors: Jacob
authors: J
authors: Hunt
authors: Anthony
authors: A
authors: Ferrari
authors: Taylor A
authors: TA
authors: Southworth
authors: Yuchuan
authors: Y
authors: Tao
authors: Albert E
authors: AE
authors: Stiegman
authors: Gregory B
authors: GB
authors: Dudley