abstract
This paper reports thermodynamic properties of phase transitions of 2,4,6-trichloro and 2,4,6-tribromo anisoles and of 2,4,6-tribromophenol. The vapor pressures of both crystalline and liquid phases (including supercooled liquid) of the three compounds were measured, respectively, in the temperature ranges T = (297.1 to 368.3) K, T = (330.7 to 391.7) K, and T = (336.5 to 401.7) K, using a static method based on capacitance diaphragm manometers. Moreover, the sublimation vapor pressures of 2,4,6-tribromophenol were also measured in the temperature interval (307.2 to 329.2) K, using a Knudsen mass-loss effusion technique. The standard molar enthalpies, entropies, and Gibbs energies of sublimation and of vaporization, at reference temperatures, were derived from the experimental results as well as the (p,T) values of the triple point of each compound. The temperatures and molar enthalpies of fusion of the three benzene derivatives were determined using differential scanning calorimetry and were compared with the values derived indirectly from the vapor pressure measurements. The thermodynamic results were discussed together with the available literature data for 2,4,6-trichlorophenol. To help rationalize the phase behavior of these substances, the crystallographic structure of 2,4,6-tribromophenol was determined by single crystal X-ray diffraction.
keywords
HEAT-CAPACITY; OFF-FLAVORS; VAPOR-PRESSURES; CORK; 2,4,6-TRICHLOROANISOLE; THERMOCHEMISTRY; TEMPERATURE; ENTHALPIES; CRYSTAL; IDENTIFICATION
subject category
Thermodynamics; Chemistry; Engineering
authors
Almeida, ARRP; Pinheiro, BDA; Lima, CFRAC; Santos, AFLOM; Ferreira, ACS; Paz, FAA; Monte, MJS
our authors
Filipe Alexandre Almeida Paz
Principal Researcheracknowledgements
This work was developed within the scope of the projects UID/QUI/00081/2013, POCI-01-0145-FEDER-006980, and NORTE-01-0145-FEDER-000028 (Sustained Advanced Materials, SAM), awarded to CIQUP, financed by Fundacao para a Cfencia e Tecnologia (FCT, Portugal) and cofinanced in the framework of Operational Programme for Competitiveness and Internationalisation (COMPETE, Portugal), with community funds (FEDER, Portugal) and national funds of MEC. This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. A.R.R.P.A. also thanks FCT, European Social Fund (ESF) and national funds of MEC for the award of the postdoctoral grant (SFRH/BPD/97046/2013). We are grateful to Prof. Artur Silva (CICECO) for his kind help.