Excess molar heat capacities and excess molar volumes of some mixtures of propylene carbonate with aromatic hydrocarbons

Abstract

Excess molar volumes V E and excess molar heat capacities C at constant pressure have been measured, at 25°C, as a function of composition for the four binary liquid mixtures propylene carbonate (4-methyl-1,3-dioxolan-2-one, C4H6O3; PC) + benzene (C6H6;B), + toluene (C6H5CH3;T), + ethylbenzene (C6H5C2H5;EB), and + p-xylene (p-C6H4(CH3)2;p-X) using a vibrating-tube densimeter and a Picker flow microcalorimeter, respectively. All the excess volumes are negative and noticeably skewed towards the hydrocarbon side: V E (cm3-mol−1) at the minimum ranges from about −0.31 at x1=0.43 for {x1C4H6O3+x2p-C6H4(CH3)2}, to −0.45 at x1=0.40 for {x1C4H6O3+x2C6H5CH3}. For the systems (PC+T), (PC+EB) and (PC+p-X) the C s are all positive and even more skewed. For instance, for (PC+T) the maximum is at x 1,max =0.31 with C =1.91 J-K−1-mol−1. Most interestingly, C of {x1C4H6O3+x2C6H6} exhibits two maxima near the ends of the composition range and a minimum at x 1,min =0.71 with C =−0.23 J-K−1-mol−1. For this type of mixture, it is the first reported case of an M-shaped composition dependence of the excess molar heat capacity at constant pressure.