Unconventional approaches to driving chemical reactions using light, ultrasound, plasma, mechanical forces, and microwaves, are having a renaissance with the expected electrification of the chemical industry. Among these approaches, ultrasound irradiation is particularly promising, given its ability to generate free radicals (oxidants) at 300 K and atmospheric pressure. These radicals are generated during the violent collapse of gas cavities in acoustic fields and initiate chemistries that otherwise do not occur under ambient conditions. Ultrasound irradiation is already used in the industry for mixing, cleaning, and wastewater treatment. Recent studies have shown the promise of ultrasound irradiation for fine chemicals synthesis.

First principles calculations, microkinetic modelling, bubble dynamics models, kinetic experiments, and EPR spectroscopy are combined to elucidate the mechanism of the ultrasound-driven oxidation of aqueous glyoxal to C¬1/C2 acids, and CO2 in the absence of any catalyst. These C2 acids like oxalic acid are the building blocks of bio-degradable polymers. Glyoxal, a C2 dialdehyde, is an intermediate formed during the depolymerization of polyethylene terephthalate (PET). The mechanistic insights are established using analogous oxidation reactions that occur in atmospheric chemistry. Our mechanism explains how sonochemistry can selectively form C2 acids over less desired C1 acids and undesired CO2. Such selectivity trends are in contrast to the electrocatalytic oxidation of glyoxal that favors C1 acids and CO2, showing how using sonochemistry can improve selectivity. After calibrating the microkinetic model with experiments, this model is leveraged to determine reaction environments (pH, radical formation rates) that favor C2 acids.