Acidity of HCl in Neutral Buffered Chloroaluminate Molten Salts

The Brønsted acidity of HCl in neutral buffered AlCl 3:1-ethyl-3-methylimidazolium chloride (EMIC) melts has been compared to the Brønsted acidity of HCl in acidic (55 mol % AlCl 3 ) melts. The acidities were compared using the spectrophotometric indicator method. Arenes were used as the weak indicator bases. The acidity of HCl in the neutral buffered melts was found to be dependent on both the type of buffering agent (LiCl, KCl, and NaCl) and on the concentration of the metal cation in the melt. An enhancement in Brønsted acidity of HCl is observed in the neutral buffered melts, although to a lesser degree than that in the acidic melts. A Hammett acidity function was determined for a NaCl (originally 55 mol % AlCl 3 ) buffered melt and a LiCl (originally 55 mol % AlCl 3 ) buffered melt. For a HCl (1 atm)/NaCl/AlCl 3:EMIC (originally 55 mol % AlCl 3 ) buffered melt, H o = −11.3. H o = −12.7 for a HCl (1 atm)/LiCl/AlCl 3:EMIC (originally 55 mol % AlCl 3 ) buffered melt.