Thermodynamics Research Center / ThermoML | Thermochimica Acta

ABSTRACT

The molar enthalpies of solution of racemic (with enantiomer ratio of 1:1) 2-monomethyl-, 2,6-dimethyl-, and 2,4,6-trimethylglycolurils (2-MMGU, 2,6-DMGU and 2,4,6-TMGU, respectively) in water were measured calorimetrically in the temperature range between (278.15 and 313.15) K and at p = 99.6 kPa. Derived from experimental data, the standard (at infinite dilution) molar enthalpic characteristics of the dissolution process are positive by sign and increase with rising temperature as well as in a sequence of 2,4,6-TMGU less than 2,6-DMGU less than 2-MMGU. In the same way, the standard heat capacity of solution decreases distinctly, leading to the conclusion that the effect of hydrophobic hydration is more pronounced for the more N-methylated solute. It was suggested that, despite the presence of hydrophobic moieties (N-sited methyl groups) in the molecules considered, a hydrophilic constituent (via H-bonding) seems to be the predominant one in the total enthalpy effect of a solute hydration.