The standard molar enthalpy of formation of 2,3-dichlorodibenzo-p-dioxin

The standard molar enthalpy of combustion of crystalline 2,3-dichlorodibenzo-p-dioxin was determined by rotating-bomb calorimetry: ΔcHm°=−(5406.4±6.6) kJ·mol−1. Using this result and the standard molar enthalpy of sublimation, ΔsubHm°=(108.6±1.0) kJ·mol−1, the values of the standard molar enthalpies of formation of 2,3-dichlorodibenzo-p-dioxin in the crystalline and gaseous states were found to be −(220.5±6.8) kJ·mol−1and −(111.9±6.9) kJ·mol−1, respectively. The standard molar enthalpy of formation of gaseous 2,3,7,8-tetrachlorodibenzo-p-dioxin was estimated: ΔfHm°(g)≈−164.6 kJ·mol−1.