Partial molar volumes and isentropic compressibilities in mixtures of γ-butyrolactam (n = 5) with 2,2,2-trichloroethanol or 2,2,2-trifluoroethanol or 1,1,1,3,3,3-hexafluoropropan-2-ol

Abstract

The partial molar volumes and isentropic compressibilities of 2,2,2-trichloroethanol, 2,2,2-trifluoroethanol and 1,1,1,3,3,3-hexafluoropropan-2-ol have been obtained in pyrrolidin-2-one at 303.15 K from measurements of excess volume and ultrasonic velocity. In the mixture of pyrrolidin-2-one and 2,2,2-trifluoroethanol the V^E is negative throughout the composition range, with a tendency to become positive at large x. The other two mixtures present an S-shaped behaviour of V^E with composition, being negative at low x and positive at high x. Quantitative estimation of different contributions viz. interactional, free volume and P* effect to V^E have been obtained by utilizing the well known Prigogine–Flory–Patterson theory. The ultrasonic velocity data have been combined with excess volume to compute molar isentropic compressibility K_s and its excess values K_s^E. K_s^E is negative in all the mixtures over the whole composition range and the values vary in the order 2,2,2-trichloroethanol < 2,2,2-trifluoroethanol < 1,1,1,3,3,3-hexafluoropropan-2-ol. Several related quantities have been calculated and presented graphically. The results are compared and discussed to gain insight into the changes in molecular association equilibria and structural effects in these systems.