Heat capacities of chlorocyclohexane and bromocyclohexane between the temperatures 10 K and 300 K, and phase transitions in the crystalline state for chlorocyclohexane

✍ Scribed by Kazuhisa Kobashi; Masaharu Oguni

• Publisher: Elsevier Science
• Year: 1995
• Tongue: English
• Weight: 502 KB
• Volume: 27
• Category: Article
• ISSN: 0021-9614
• DOI: 10.1006/jcht.1995.0103

✦ Synopsis

Heat capacities of chlorocyclohexane (CAS[542-18-7]), c-CHCL(CH2)5, and bromocyclohexane, (CAS[108-85-0]), c-CHBr(CH2)5, were measured with adiabatic calorimeters in the temperature range between T=8 K and T=300 K and the standard thermodynamic functions were evaluated. For chlorocyclohexane, temperatures, molar enthalpies, and molar entropies were determined to be (220.24 2 0.03) K, (8.11 2 0.02) kJ•mol -1 , and (36.8 2 0.1) J•K -1 •mol -1 , respectively, for the crystal-to-(orientationally disordered crystal) (denoted by II-to-I) phase transition; and (228.01 2 0.05) K, (2.02 2 0.01) kJ•mol -1 , and (8.9 2 0.1) J•K -1 •mol -1 , respectively, for fusion. Moreover, two other heat-capacity anomalies were found at T=(118.620.1) K and T=(14821) K and are suggested to be successive (denoted by IV-to-III and III-to-II, respectively) phase transitions of the superstructural commensurate-to-incommensurate-to-(normal commensurate) phase-sequence type. Molar entropies of the IV-to-III and III-to-II phase transitions were estimated to be (0.7 2 0.1) J•K -1 •mol -1 and (0.05 2 0.01) J•K -1 •mol -1 , respectively. Large orientational disorder amounting to S°m14.6 J•K -1 •mol -1 was suggested to exist even in phase II of the ''globular molecule'' chlorocyclohexane. Bromocyclohexane, on the other hand, displayed only fusion at T=(216.8720.03) K. The molar enthalpy and molar entropy of fusion were determined to be (10.79 2 0.03) kJ•mol -1 and (49.8 2 0.1) J•K -1 •mol -1 , respectively.