Effect of two Macrocyclic Aminals on the Temperature of Maximum Density of Water

Densities of several aqueous solutions of two macrocyclic aminals, 1,3,5,7-tetraazatricyclo[3.3.1.1(3,7)]decane (HMT) and 1,3,6,8-tetraazatricyclo[4.4.1.1(3,8)]dodecane (TATD) at concentrations from 0.001 up to 0.2 mol⋅kg −1 (molal) between 2.0 and 5.0 °C every 0.5 °C, were obtained using a magnetic float densimeter designed, constructed and calibrated according to the available literature. The effect of the two solutes on the temperature of the maximum density of the water θ was established. The dependence of density with molality is linear in the entire range of concentration, at all temperatures, and the dependence of Δ θ with composition, for both aqueous systems, does not follow the Despretz law. Based on the variation of Δ θ with composition, the solutes are classified as liquid water structure breakers; the effect of TATD on the solvent is greater. The results are discussed in terms of solute–solvent and solute–solute interactions.