Investigation on the trioctylphosphine oxide-based super-concentrated HCl system

We report a new super-concentrated HCl system prepared by using trioctylphosphine oxide (TOPO)-based reverse micelles. The observed molar ratio between acid and water (n(HCl)/n(H2O)) in the super-concentrated HCl are much higher than that in the saturated aqueous HCl solution (0.28). Moreover, FT-IR spectroscopic results reveal that a significant amount of HCI remains in the molecular form rather than being ionized into H+ and Cl-. As a result, two H-Cl stretching bands can be observed in the FT-IR spectrum, The super-concentrated HCI provides a unique chemical environment in which many chemical substances occur in unusual states. For example, the color of super-concentrated HCl solution containing copper ion was found to be reddish brown rather than green as in conventional state. UV-Vis-NIR spectral results indicate that both d-d transition band of Cu2+ and charge transfer band of Cl-Cu in super-concentrated HCl underwent significant variation. Additionally, copper ions bring about remarkable variation on the hydrogen bond network among HCI in the super-concentrated HCI solution as demonstrated by FT-IR spectra. According to the EXAFS results, we suggest that copper ion may occur as HCuCl3 in the super-concentrated HCl. (C) 2014 Elsevier B.V. All rights reserved.