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 investig ated by means of a very low pressure pyrolysis method. The Arrhenius equati ons for homolytic oxygen-oxygen bond rupture obey log(k(1)/s(-1)) = 15.30-4 5.0 kcal mol(-1)/2.303RT for CF3O-OCF3 and log(k(2)/s(-1)) = 15.30-37.4 kca l mol(-1)/2.303RT for Me3CO-OCMe3. The oxygen-oxygen bond dissociation enth alpies, BDE(O-O), at 298 K for the peroxides are derived to be 47.5 +/- 0.5 (CF3O-OCF3) and 38.9 +/- 0.5 kcal mol(-1) (Me3CO-OCMe3). Various density f unctional theory calculations have been utilized to compute the BDEs for XO -H, XO-OH, and XO-OX, with X = H, CF3, and Me3C. Expansion of the basis set and the application of the restricted open-shell (RO) formalism for the ra dical species affords better agreement with experimental values. Using isod esmic reactions, a convergence is obtained for the BDE(O-H) in trifluoromet hanol (CF3O-H) toward 118.8 +/- 0.5 kcal mol(-1). Reevaluation of literatur e thermokinetic data leads to BDE(F-CF2O.) of 27 +/- 1, and BDE(CF3O-F) of 48 +/- 1 kcal mol(-1).