O−O Bond Dissociation Enthalpy in Di(trifluoromethyl) Peroxide (CF₃OOCF₃) as Determined by Very Low Pressure Pyrolysis. Density Functional Theory Computations on O−O and O−H Bonds in (Fluorinated) Derivatives

The thermal decomposition of di(trifluoromethyl) peroxide (between 575 and 900 K) and di- tert -butyl peroxide (between 425 and 650 K) has been investigated by means of a very low pressure pyrolysis method. The Arrhenius equations for homolytic oxygen−oxygen bond rupture obey log( k 1 /s -1 ) = 15.30−45.0 kcal mol -1 /2.303 RT for CF 3 O−OCF 3 and log( k 2 /s -1 ) = 15.30−37.4 kcal mol -1 /2.303 RT for Me 3 CO−OCMe 3 . The oxygen−oxygen bond dissociation enthalpies, BDE(O−O), at 298 K for the peroxides are derived to be 47.5 ± 0.5 (CF 3 O−OCF 3 ) and 38.9 ± 0.5 kcal mol -1 (Me 3 CO−OCMe 3 ). Various density functional theory calculations have been utilized to compute the BDEs for XO−H, XO−OH, and XO−OX, with X = H, CF 3, and Me 3 C. Expansion of the basis set and the application of the restricted open-shell (RO) formalism for the radical species affords better agreement with experimental values. Using isodesmic reactions, a convergence is obtained for the BDE(O−H) in trifluoromethanol (CF 3 O−H) toward 118.8 ± 0.5 kcal mol -1 . Reevaluation of literature thermokinetic data leads to BDE(F−CF 2 O • ) of 27 ± 1, and BDE(CF 3 O−F) of 48 ± 1 kcal mol -1 .