Abstract

The thermodynamic properties of 135 polybrominated phenoxathiins (PBPTs) in the ideal gas state at 298.15 K and 1.013×10⁵ Pa have been calculated at the B3LYP/6-31G* level using Gaussian 03 program. The isodesmic reactions were designed to calculate standard enthalpy of formation (Δ_fH^Ó©) and standard free energy of formation (Δ_fG^Ó©) of PBPTs congeners. The relations of these thermodynamic parameters with the number and position of Br atom substitution (N_PBS) were discussed, and it was found that there exist good correlations between thermodynamic parameters (entropy (S^Ó©), Δ_fH^Ó© and Δ_fG^Ó©) and N_PBS. According to the relative magnitude of their Δ_fG^Ó©, the order of relative stability of PBPT congeners was theoretically proposed. Moreover, using a statistical thermodynamics calculation program based on Gaussian output files, the values of molar heat capacity at constant pressure (C_p,m) from 200 to 1800 K for PBPT congeners were calculated, and the temperature dependence relation of them was obtained using the least-squares method.

Key words: Polybrominated phenoxathiins, the number and position of Br atom substitution (N_PBS), thermodynamic property, relative stability, molar heat capacity at constant pressure (C_p,m).