Heat of formation of Benzophenone Oxide

The heat of formation of benzophenone oxide, Ph 2 CO 2 , was measured using photoacoustic calorimetry. The enthalpy of the reaction Ph 2 CN 2 + O 2 → Ph 2 CO 2 + N 2 was found to be −48.0 ±0.8 kcal mol −1 and ΔH f (Ph 2 CN 2 ) was determined by measuring the reaction enthalpy for Ph 2 CN 2 + EtOH → Ph 2 CHOEt + N 2 (−53.6 ±1.0 kcal mol −1 ). Taking ΔH f (PhCHOEt) = −10.6 kcal mol −1 led to ΔH f (Ph 2 CN 2 ) = 99.2 ± 1.5 kcal mol −1 and hence to ΔH f (Ph 2 CO 2 ) = 51.1 ± 2.0 kcal mol −1 . The results imply that the self‐reaction of benzophenone oxide i.e., 2Ph 2 CO 2 → 2Ph 2 CO + O 2 is exothermic by −76.0 ±4.0 kcal mol −1 .