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The solvent effect of methanol on the dissociation of Bis·H+ from 10 to 40°C

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Abstract

The solvent effect on the acidic dissociation of the protonated base tris(hydroxymethyl)aminomethane (Tris) has been studied in aqueous mixtures of several organic constituents with qualitatively similar results. The dissociation constant of protonated 2-amino-2-methyl-1,3-propanediol (Bis), the analog of Tris with two hydroxy groups, has now been determined in 50 mass % methanol by emf measurements of cells without liquid junction in the temperature range 10 to 40°C. The conventional treatment of the data indicated abnormally low values for the activity coefficient of BisHCl, but an alternate method of calculation with allowance for ion pairing provided no advantage. The pKa in the range from T=283.15 to 313.15 K is given by

$$pK_a = 3755.63/T - 24.5127 + 3.56855 In T$$

with a standard deviation of 0.0006 at the seven temperatures. Thermodynamic quantities for the dissociation process and corresponding quantities for the transfer from water to 50 mass % methanol were derived. The implications of the results in terms of selective solute-solvent stabilization are discussed.

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On leave 1979–80 from the Institute of Physical and Chemical Research, Saitama, Japan.

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Bates, R.G., Tanaka, K. The solvent effect of methanol on the dissociation of Bis·H+ from 10 to 40°C. J Solution Chem 10, 155–162 (1981). https://doi.org/10.1007/BF00653092

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Key words

  • Acidic dissociation
  • basic dissociation
  • Bis
  • dissociation constant
  • ionization constant
  • methanol
  • solute-solvent effects
  • solvent effect