Acidity of Solid and Liquid Acids Probed by P-31 NMR Chemical Shifts of Phosphine Oxides

A novel method for acidity characterization of solid and liquid acids is proposed. Surpassing conventional methods, this technique employs 31P nuclear magnetic resonance (NMR) of adsorbed phosphine oxides is capable of monitoring a wide range of acidic strengths from weak to super acids with superior sensitivity.