Abstract
The dissociation constant of acetic acid in N-methylpropionamide (NMP) has been determined at 11 temperatures from 5 to 55°C by measurement of the electromotive force of cells without liquid junction containing hydrogen gas electrodes and silver-silver chloride electrodes. The pK at 25°C was found to be 7.995 (molal scale) as compared with 4.756 in water; thus, acetic acid is much weaker in NMP than in water despite the higher dielectric constant of the nonaqueous solvent (176 as compared with 78.3 at 25°C). The standard changes of enthalpy and entropy for the dissociation of acetic acid were calculated from the temperature coefficient of pK, and thermodynamic functions for the transfer dissociation process were obtained. The weakness of acetic acid in NMP is discussed in terms of electrostatic effects and solute-solvent interactions.
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Etz, E.S., Robinson, R.A. & Bates, R.G. Dissociation constant of acetic acid in N-methylpropionamide from 5 to 55°C and related thermodynamic quantities. J Solution Chem 1, 507–516 (1972). https://doi.org/10.1007/BF00651727
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DOI: https://doi.org/10.1007/BF00651727