The ionicity value, which is a key property of protic ionic liquids, was obtained by attenuated total reflection Fourier transform infrared spectroscopy and nuclear magnetic resonance, respectively, for a protic ionic liquid: n-propylammonium acetate. The method of potentiometric titration is found to not be suitable for such a kind of ionic liquid, as the ΔpK of the compositing acid and base is relatively small. In the IR spectrum, molecular species can be directly observed in the range 1200-1800 cm, and the ratio of ionic and molecular species can be quantitatively calculated by the area of characteristic absorption peaks calibrated by a standard curve from NaAc/HAc solutions. The results show that 93% components in n-propylammonium acetate are ionic species. The NMR method was also introduced to test and verify the result. Despite that only one mixed peak can be observed for molecular and ionic species, the observed H chemical shift can be assumed to be the weighted average of them. In this way, the ionicity can be calculated and it fits well with the IR approach. It indicates that, for a protic ionic liquid with a relatively small ΔpK value, spectroscopic methods such as IR and NMR could be applied to determine the ionicity.

The degree of proton transfer and thermodynamic parameters of six acetate-based protic ionic liquids (PILs) were measured using nuclear magnetic resonance spectroscopy and calculated by van't Hoff analytical method, respectively. The degree of proton transfer of these PILs at 298 K spread over a large range, which is from 39.6% (1-methylpyrrolidinium acetate, [MpyrH][AcO]) to 94.4% (1-butylimidazolium acetate, [BuimH][AcO]). The calculated standard enthalpy change of the reaction (ΔH) is from -23.30 to -7.80 kJ mol and the standard entropy change of the reaction (ΔS) is from -42.70 to -8.07 J mol K. The correlation between the degree of proton transfer and aqueous ΔpK or ΔH was investigated as well. Furthermore, in some special cases, ΔS, especially the entropy change of symmetry, also plays an important role in affecting the degree of proton transfer.

Phenoxyl radical was generally suggested as the intermediate during copper-catalyzed aerobic oxygenation of phenols. However, the substrate-dependent selectivity has not been well interpreted, due to insufficient characterization of the radical intermediate under reaction conditions. When studying the CuCl-LiCl-catalyzed aerobic phenol oxidation, we obtained EPR spectra of phenoxyl radicals generated by oxidizing phenols with the preactivated catalyst. Upon correlation to the selectivity of benzoquinone, the hyperfine coupling constant of para-site proton (a H, para ) was found to be better than the Hammett constant. The catalysis mechanism was studied based on EPR detection and the reaction results of phenoxyl radicals under N 2 or O 2 atmosphere. It appeared that the chemoselectivity depended on the attack of activated dioxygen on phenoxyl radicals, and the activation of dioxygen by [Cu n Cl n+1 ] − (n = 1, 2, 3) was suggested as the rate-determining step. Understanding of the substrate-dependent selectivity contributed to predicting the chemoselectivity in the aerobic oxidation of phenols.

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