Effect of N-Methyl Substitution in the Glycine Molecule on the Enthalpy of Dissolution in Mixed Water–Alcohol Solvents at 298.15 K

Abstract

The enthalpies of dissolution of N-methylglycine in water + ethanol, water + (1-propanol) and water + (2-propanol) are determined via calorimetry at an alcohol concentration of x₂ = 0–0.25 mole fraction. The standard values of enthalpies of dissolution (\({{\Delta }_{{{\text{sol}}}}}H^\circ \)) and transfer (\({{\Delta }_{{{\text{tr}}}}}H^\circ \)) of N-methylglycine from water to solution are calculated. The effect the structure and properties of N-methylglycine and the composition of a water–alcohol mixture have on N-methylglycine’s enthalpy characteristics is examined. The enthalpy coefficients of pair interactions (h_xy) between N-methylglycine and alcohol molecules are calculated. They have positive values and grow in the series ethanol (EtOH) < 1-propanol (1-PrOH), < 2-propanol (2-PrOH). A comparative analysis is performed of the enthalpy characteristics of dissolution and transfer of N-methylglycine and the analogous characteristics of glycine and DL-α-alanine in similar mixtures.