Aspects of the Chemistry of Water in Ambient-Temperature Chloroaluminate Ionic Liquids: 17O NMR Studies

摘要

Room-temperature ionic composed of mixtures of chloroaluminate and organic chloride salts, RCL(R = N-(1-butyl)pyridinium cation (Bupy+) or 1-ethyl-3-methylimidazolium cation (Im+), have been used as solvents for a wide variety of chemical studies. These molten salts have several desirable properties. The primary source of protonic impurities in the room-temperature chloroaluminate melts is water with the organic chloride component of the melts. The latter salts are extremely hygroscopic, and it has proven extremely difficult to remove water completely. Associated with the protonic impurities in the melts is oxide from water and additionally from impurities in AlCl3. A study of the reduction of protons on a Pt electrode in melts has been reported. The limiting currents for proton reduction increased in a roughly linear fashion with the concentration of water added to basic melts. Less current was observed for an equivalent amount of water added to an acidic melt. Finally, the addition of water to nearly neutral melts apparently results in a release of 2 protons per water molecule. As part of an ongoing effort to study the chemistry of water in the room-temperature chloroaluminate melts, we have used oxygen 17 NMR spectra of water added to the melt to obtain information on the speciation of oxide and protons. Reprints. (aw)