Abstract
IT has been shown recently1 that methanol and isopropanol are more basic than water in dilute aqueous solutions containing mineral acids, in contrast to the basicity of alcohols in alcohol-rich solutions2,3. The concentration of p-nitroaniline determined spectrophotometrically in mineral acids with and without added alcohol, CR and c, respectively, in dilute aqueous solution, obeys the relationship1: c0 is the initial concentration of p-nitroaniline without added acid or alcohol, r is the concentration of added alcohol and w = [H2O] before addition of alcohol. This expression can be deduced from the three equilibria: where N and NH are unprotonated and protonated p-nitroaniline respectively, K1F1 = [NH][H2O]/[N][H3+O] and all hydroxylated species, protonated and unprotonated, are assumed to be complex hydrates4. The foregoing expression was tested for methanol and isopropanol by obtaining linear plots1 for CCR/(CR–c) against CR/(C0–CR) : values for were calculated from Kb′ = c0w/rwR × slope. Kb′ was constant for methanol and isopropanol over the concentration range2–10 per cent v/v alcohol.
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References
Wells, C. F., Nature, 196, 770 (1962).
a, Braude, E. A., J. Chem. Soc., 1971 (1948). b, Braude, E. A., and Stern, E. S., ibid., 1976 (1948).
Stability Constants, Part 2, Chem. Soc. Spec. Pub., 7, 66 (1958).
Wells, C. F., Farad. Soc. Disc., 29, 219 (1960).
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GILES, G., WELLS, C. Acid-base Equilibria involving Oxygen-containing Molecules in Dilute Aqueous Solution. Nature 201, 606–607 (1964). https://doi.org/10.1038/201606a0
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DOI: https://doi.org/10.1038/201606a0
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