STOICHIOMETRY OF LATENT ACIDITY IN BUFFERED CHLOROALUMINATE IONIC LIQUIDS

Chloroaluminate ambient temperature ionic liquids consisting of AlCl3 and 1-ethyl-3-methylimidazolium chloride can be both neutralized and b uffered by the addition of an alkali halide to an acidic melt, one con taining excess AlCl3. Such melts possess an electrochemical window of similar to 4.4 V. The ionic composition of a NaCl-buffered neutral mel t is modified such that [Im(+)] + [Na+] = [AlCl4-]. We have observed t hat these buffered melts exhibit a ''latent acidity''. Weak Lewis base s, B:, which are uncomplexed by AlCl3 in an unbuffered neutral melt, f orm AlCl3 adducts in a buffered melt. This occurs because the equilibr ium B: + AlCl4- + Na+ reversible arrow B:AlCl3 + NaCl(s) is driven to the right by the precipitation of NaCl(s); in the absence of Na+, this reaction does not take place. The reaction was observed for the weak bases acetylferrocene, dimethylaniline, and pyrrole with use of electr ochemical and techniques and is limited by the amount of Na+ present i n solution in the initially buffered neutral melt.