2,3-Dimethyl-2-butene: Thermodynamic Properties in the Solid, Liquid and Vapor States

Abstract

Various thermodynamic properties of 2,3-dimethyl-2-butene were studied experimentally. The entropy of the liquid a 298.16/sup 0/K (S/sub satd/ = 64.58 cal deg /sup 1/ mole/sup -1/) was computed from calorimetric values of the heat capacity in the solid and liquid states (11 to 318/sup 0/K) and of the heats of transition and fusion (844 cal mole/sup -1/ at 196.82/sup 0/K and 1542 cal mole/sup -1/ at the triple point, 198.92/sup 0/K, respectively). Results obtained for the heat capacity of the liquid (C/sub satd/), vapor pressure (p), heat of vaporization (..delta..H/sub v/), heat capacity in the ideal gas state (C/sup 0//sub p/), and the second virial coefficient (B = (PV - RT)/P) are represented as a function of temperature by the following empirical equations: (1) C/sub satd/ = 48.178 - 0.16068T + 6.2188 x 10/sup -4/T/sup 2/ - 5.2083 x 10/sup -7/T/sup 2/, cal deg/sup -1/ mole/sup -1/) (200 to 320/sup 0/K); (2) log/sub 10/p (mm) = 6.93324 - 1206.037/(t + 224.400), (29 to 73/sup 0/); (3) ..delta..H/sub v/ = 10,674 - 5.713T - 0.01344T/sup 2/, cal mole/sup -1/ (292 to 346/sup 0/K); (4) C/sup 0//sub ..nu.. = 4.454 + 0.087361T - 1.1983 x 10/sup -4/T/sup 2/, cal deg/sup -1/ mole/supmore » -1/ (334 to 473/sup 0/K); and B = -2764 - 4.93 exp (1100/T), cc mole/sup -1/ (292 to 473/sup 0/K). The entropy in the ideal gas state at 298.16/sup 0/K (S/sup 0/ = 87.16 cal deg/sup -1/ mole/sup -1/) was computed from these data. A vibrational assignment was made for 2,3-dimethyl-2-butene, and the average height of the potential barriers hindering internal rotation of the methyl groups, 680 cal mole/sup -1/, was evaluated from the calorimetric data. Values of the functions (F/sup 0/ - H/sub 0//sup 0/)/T, (H/sup 0/ - H/sub 0//sup 0/)/T, H/sup 0/ - H/sub 0//sup 0/, S/sup 0/ and C/sup 0//sub p/ were calculated at selected temperatures to 1500/sup 0/K.« less