Influence of H/D Isotope Substitutio on Physicochemical Properties of Aqueous Solutions of Urea and Thiourea

The influence of the H/D isotope substitution on excess volumes, partial molar volumes, viscosity and ultrasound speed in aqueous solutions of urea and thiourea are studied at 20 C. The excess volume of the solutions studied is relatively small - however, it is negative in urea and positive in thiourea solutions. On the other hand, the deuteration affects the excess volume in both solutions in the same way: deuterated systems show smaller deviation from additivity than regular ones. The speed of sound in the systems studied increases monotonously with concentration, but its isotope effect decreases as the concentration increases. The curves of viscosity are monotonous too, but isotope effect of kinematic viscosity is practically the same in the whole concentration range studied. The present results for urea and thiourea aqueous solutions are compared with those previously obtained for amide-water systems.