Protonation of p-methoxybenzhydryl cations; a new series of indicators for superacid acidity measurements by nuclear magnetic resonance spectroscopy
Abstract
The behaviour of (p-substituted phenyl)(p-methoxyphenyl)methanol derivatives dissolved in superacid mixtures (HF, HFSO3, or CF3SO3H with various proportions of SbF5) has been studied by n.m.r. spectroscopy. Increasing the SbF5 concentration causes drastic changes in Chemical shifts due to stable O-protonation of the methoxy group in the highest acidity media. By using these bases as indicators for superacid acidity measurements we have shown that the acidity of these three systems does not increase as fast as previously claimed, and also that the acidity of the CF3SO3H–SbF5 system remains lower than that of the HFSO3–SbF5 system in the 0–50% SbF5 range.