Ion associations of lithium and sodium nitrophenolates (2-, 4-, 2,4-, 2,5-, and 2,4,6-derivatives) were examined by means of conductometry at 25°C in several aprotic solvents (MeCN, DMF, acetone, and PhCN). The molar conductivities (Λ) of lithium 2,4-dinitrophenolate in acetonitrile were explained by the formation of "symmetrical" triple ions (M 2 X + and MX 2 -) as well as ion pairs (MX); however, those of the sodium salt were explained by the formation of ion pairs alone. The salts of 2,5-dinitrophenol in acetonitrile gave larger formation constants than those of 2,4-dinitrophenol. The molar conductivities of lithium 2-nitrophenolate in acetonitrile were explained by the strong formation of quadrupoles (M 2 X 2 ) in addition to triple ions and ion pairs, although the (direct) Shedlovsky analysis gave a "pseudo" value of K a ) 0 (no association between simple ions). Any species from lithium 2-nitrophenolate could not be ignored even at lower concentrations because the ratio of the concentration of a species (e.g., [X -]/C s ) to the salt concentration (C s ) was greater than ca. 1% for C s ) (0.16-2.0) × 10 -3 mol dm -3 . Lithium 4-nitrophenolate gave formation constants smaller than those of the 2-nitrophenolate because of no nitro-group at the ortho-position. Ion aggregations occurred to the higher extent for salts of ortho-substituted nitrophenols with weaker (Brønsted) acidities of phenols (2,4,6-< 2,4-< 2,5-< 2-). In the stronger solvating solvent, DMF, the high ion aggregation above ion pair formation was observed only for lithium 2-nitrophenolate but not for other salts. The logarithms of the formation constants for lithium 2,4-dinitrophenolate decreased linearly with increasing value of the (geometric) average between the donor and acceptor numbers [(DN × AN) 1/2 ] of the solvents. The results of the present study provided the quantitative interpretation for the promotion of proton transfer from nitrophenols to amine or pyridine bases by the addition of LiClO 4 or NaClO 4 in acetonitrile.

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