Reaction of Cumene with Ozone To Form Cumyl Hydrotrioxide and the Kinetics of Decomposition of Cumyl Hydrotrioxide

Article abstract of DOI:10.1021/ja00349a044

Cumene forms a charge-transfer complex with ozone in a number of solvents (e.g. with absorption at 360 nm in acetone).When this CT complex is photolyzed at -75 deg C or warmed above -40 deg C, reaction occurs to form both cumyl hydrotrioxide and ring-ozonated products (in ratio of about 70/30).The decomposition of the hydrotrioxide, PhCMe2OOOH, can be monitored by proton NMR in acetone-d₆ using either the CH3 or the OOH hydrogens; the decomposition is first order and gives activation parameters of E = 16.0 +/- 0.1 kcal/mol and log A = 10.4 +/- 0.1.These values agree with literature data on the decomposition of aroyl hydrotrioxide (from the reaction of ozone with aromatic aldehydes) and on the decomposition of trioxides of cyclic and acyclic acetals, but they are far from the values of E = 23 kcal/mol and log A = 16 calculated using thermokinetic methods.The low activation parameters undoubtedly result from a chain decomposition of the trioxide.Therefore, we also studied the decomposition in the presence of an inhibitor, 2,6-di-tert-butyl-4-methylphenol (BHT), to eliminate the chain decomposition.In the presence of BHT, the activation parameters become E = 23.9 +/- 0.1 kcal/mol and log A = 16.4 +/- 0.1, in agreement with theory.In addition, we can follow the disappearance of the phenolic hydrogen of BHT, and it disappears with the same rate constant as does cumyl hydrotrioxide, indicating that every decomposition of the hydrotrioxide leads to two scavengeable free radicals.In the presence of BHT, the hydrotrioxide decomposes to give cumyl alcohol as the only organic product; in the absence of BHT a small yield of acetophenone also is formed, perhaps as a result of the production of the cumyltrioxyl radical in a chain process and its exothermic loss of dioxygen and subsequent β-scission of the cumyloxyl radical.This is the first time that the hydrotrioxide of a hydrocarbon has been charaterized by NMR and that Arrhenius parameters for decomposition of a hydrotrioxide have been obtained that agree with thermokinetic predictions.