Kinetics and equilibria in the system Br + t‐BuO₂H ⇆ HBr + t‐BuO₂. OH bond dissociation energy in t‐BuO₂‐H

The kinetics and equilibria in the system Br + t ‐BuO 2 H ⇆ HBr + t ‐BuO 2 · have been measured in the range of 300–350 K using the very low pressure reactor (VLPR) technique. Using an estimated entropy change in reaction (1) Δ S 1 = 3.0 ± 0.4 cal/mol·K together with the measured Δ G 1 , we find Δ H 1 = 1.9 ± 0.2 kcal/mol and DH º ( t ‐BuO 2 ‐H) = 89.4 ± 0.2 kcal/mol Δ H f ·( t BuO 2 ·) = 20.7 kcal/mol and DH º ( t ‐Bu‐O 2 ) = 29.1 kcal/mol. The latter values make use of recent values of Δ H f ·( t ‐Bu) = 8.4 ± 0.5 kcal/mol and the known thermochemistry of the other species. The activation energy E 1 is found to be 3.3 ± 0.6 kcal/mol, about 1 kcal lower than the value found for Br attack on H 2 O 2 . It suggests a bond 1 kcal stronger in H 2 O 2 than in t BuO 2 H.