Scale-Up of Microwave-Assisted Reactions in a Multimode Bench-Top Reactor

An evaluation of a new bench-top microwave batch reactor that uses a single 1 L reaction vessel is presented. Several microwave-assisted organic reactions have been scaled-up, including Newman Kwart and Diels–Alder reactions, Pd-catalyzed cross-couplings, heterocycle synthesis, aromatic substitution, and a Knoevenagel condensation. A range of different solvents (high and low microwave absorbing), varying reaction times (4 s up to 2 h), and temperatures (120–250 °C) have been explored in these investigations. For all studied transformations, it was possible to perform a direct scale-up (up to 720 mL reaction volume) without changing the previously optimized reaction conditions achieved in a laboratory-scale single-mode microwave instrument (2–20 mL processing volume), obtaining similar isolated product yields. A scalability up to 360-fold, when moving from 3 mmol up to 1.08 mol, was demonstrated, and isolated product yields up to 300 g (2.5 mol scale) in a single run could be accomplished, providing the potential for a kilogram output per day for specific transformations by performing multiple sequential runs.