In this work, protonated tungsten bronze powder (HxWO3) was synthesized by a microwave heating technique from tungsten(VI) chloride in benzyl alcohol. This material facilitates a proton-coupled electron transfer (PCET) reaction with 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) in toluene, an aprotic solvent, to form TEMPOH, evidenced by UV–vis analysis of the organic product and X-ray photoelectron spectroscopy (XPS) analysis showing the oxidation of W5+ to W6+ in the remaining powder. Then, under illumination in an acidic aqueous solution, the oxidized WO3 powder reacts photochromically to regenerate HxWO3. The regenerated HxWO3 reagent remains active for further PCET reactions.
O’Hara et al. (Tue,) studied this question.