Superconcentrated hydrochloric acid.

We report the discovery of a potentially useful superconcentrated HCl at ambient temperature and pressure by using a simple surfactant-based reversed micelle system. Surprisingly, the molar ratios of H+ to H2O (denoted as nH+/nH2O) in superconcentrated HCl can be larger than 5, while the maximum achievable nH+/nH2O value for conventional saturated HCl aqueous solution (37 wt %) is only about 0.28. Furthermore, both NMR and FT-IR results indicate that a significant amount of HCl remains in the molecular form rather than being ionized into H+ and Cl–. The superconcentrated HCl may promote some organic reactions that are not feasible by using conventional 37 wt % HCl solution. For example, addition reaction between C═C and HCl occurs in superconcentrated HCl solution without using catalysts.