Anal. Chem. 1982, 5 4 , 2379-2380 ..
192
5.8
U L 0.34 0.38 OA2 0.46 050 0.54 0.58 A IC I
0.62
c
0.66
M OLEFR ACT 10N
Flgure 1. Chemical shift of 6-2 and -6 protons in 1-(1-buty1)pyridinium chloride:AICI, (A)at 35 O C , and C-2 proton in I-methyl-3-ethylimidazoiium:AICI, (0)mixtures at 34 OC as a function of AICi, mole fraction.
plicable for XAICla < 0.5.. Apparently aluminum is oxidized by the melt cation at thlese compositions ( 4 , 6, 7). The changes in chemical shifts may be explained by assuming that each organic cation is closely associated with two anions and is in fast exchange on the NMR time scale. k detailed analysis of the effect of such ion pairing interactions has been made and will be reported separately. A reasonably good fit to the data may be made by a quadratic fit to eq 1,
where h o h d is the measured chemical shift, and a, b, and c are fitted parameters. The principal source of error in the method is in the precision of the NMR chemical shift measurement. A f0.05 ppm precision is readily achieved with most spectrometers, which corresponds to f0.001 mole fraction A1C13 in basic melts. The method applies well only to the Xhc13C 0.5 (basic) melts, since the acidic compositions show a less pronounced dependence of chemical shifts on composition. Note that the range of compositions shown for the pyridinium melt is not as extensive as for the imidazalium melt. This is because pyridinium mel1,s are liquid only in the range 0.44
