Zeolitic Imidazolate Framework-8 in Piezo-Assisted Mechanochemical Oxidation Reactions

Piezocatalysis, in combination with mechanochemical reactions, can create a respectable revolution in organic synthesis by enhancing product yield. In this study, ball milling merging with the synthesized zeolitic imidazolate framework-8 (ZIF-8), possessing a specific surface area of 1097 m²/g, was explored to catalyze the oxidative mechanochemical solventless homocoupling reaction of thiols (R-SH) to disulfides (R-S-S-R) at 450 rpm within 120 min, as well as the oxidative mechanochemical solvent-assisted reaction of toluene to phenol at 450 rpm within 180 min. 1-butanethiol and 4-aminothiophenol, as the models of thiol compounds, were oxidized to 1,2-dibutyldisulfane and 4,4'-disulfanediyldianiline, respectively, with the yields of 40% and 64%. The production of disulfides was monitored by ¹H-NMR, ¹³C-NMR, and gas chromatography-mass spectrometry. Gas chromatography-flame ionization detection qualitatively and quantitatively explored the phenol production, as the phenol concentration was determined to be 5.550 mmol/L at a pH of 5 and 5.533 mmol/L under the condition of no adjusted pH (the initial pH of ≈3). In the toluene oxidation, O₂ ^•- species were detected as the main species, through radical trapping experiments. The ZIF-8 particles could be reused after three cycles with no significant loss in the yield of thiol oxidation product, as further confirmed by their recorded Fourier transform infrared spectrum, powder X-ray diffraction pattern, and field emission scanning electron microscopy images.