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Thermodynamic Behavior of Electrolytes in Mixed Solvents Downloaded from pubs.acs.org by CALIFORNIA INST OF TECHNOLOGY on 09/18/17. For personal use only.
Acidity Functions in Solutions of Strong Bases in Mixed Solvents T. J. M. POUW, W. J. BOVER, and P. ZUMAN Department of Chemistry, Clarkson College of Technology, Potsdam, Ν. Y. 13676
The addition of hydroxide ions to substituted benzaldehydes (ArCHO + OH ArCH(OH)O ) is used to establish J -acidity scales in water-ethanol and water-DMSO mixtures containing sodium hydroxide as a base. The pK-values in such mixtures are linearly correlated with Hammett substituent constants. The independence of reaction constant ρ of sol vent composition confirms that substituted benzaldehydes are suitable J- indicators for hydroxide solutions in water-ethanol and water-DMSO mixtures. Dependence of J- values on so dium hydroxide concentration is only slightly affected by etha nol up to 90 % and at a constant sodium hydroxide concentra tion shows only small increase between 90 and 98 % ethanol. J- increases more with increasing DMSO concentration, but the effect is much smaller than that of DMSO on H- values based on proton abstraction from aniline. -
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he electrochemical oxidation of aromatic aldehydes ( i ) must be studied in strongly alkaline media. A c i d i t y functions for strongly alkaline aqueous solutions of alkali metal a n d quaternary a m m o n i u m hydroxides, corresponding to dissociation of proton ( H _ ) , are w e l l established (2, 3). Substituted anilines and diphenylamines (4,5) and indoles (6) were used as acid-base indicators f o r establishment of such scales, but whether a n a c i d i t y scale based o n one type of indicator can be rigorously applied to acid-base equilibria i n v o l v i n g structurally different acidic groups for reactions i n strongly alkaline m e d i a remains questionable. F o r substituted anilines, behavior both parallel (7) a n d nonparallel (8) to the H _ scale based on indole derivatives has been reported. T h e l i m i t e d solubility of anilines i n aqueous solutions of alkali metal hydroxides, the reactions of the aniline derivative w i t h more than one h y d r o x i d e ion, irreversible substitution reactions (9), a n d the possibility of h y d r o x i d e i o n a d d i t i o n rather than 343
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THERMODYNAMIC BEHAVIOR OF ELECTROLYTES
proton abstraction—in particular for nitro derivatives (10)—complicate terpretation of experimental data.
the i n -
Nevertheless, v a l i d i t y of a c i d i t y f u n c t i o n H _ cannot be expected to extend to reactions i n v o l v i n g a d d i t i o n of h y d r o x i d e ions rather than dissociation of a proton. F o r addition of hydroxide ions, the acidity function J _ has been defined (
