Absolute rate constants for hydrocarbon autoxidation. 30. On the self-reaction of the α-cumylperoxy radical in solution

Abstract

Can. J. Chem. 59.2253 (1981. Although it is generally accepted that the self-reaction of cumylperoxy radicals is a second-order process, recent reports have cast doubt on the overall validity of this assumption. Therefore we have reinvestigated some aspects of the self-reaction to clarify the kinetic and mechanistic features.Our product studies are entirely consistent with the accepted mechanism for the self-reaction of cumylperoxy radicals and no evidence was obtained for competing reactions. Results obtained with 360, labelled materials confirm the previous conclusion that reversible scission of cumylperoxy radicals to g h e oxygen and cumyl radicals does not compete significantly with the self-reaction 1 at ambient temperatures. Kinetic studies, under both steady-state and transient conditions, establish clearly that the self-reaction of cumylperoxy radicals is a second order process. A possible explanation is proposed to account for the previous observations which indicated that the self-reaction was a first order process. Further, we show that the changes observed in the esr spectrum of the cumylperoxy radicals, which were attributed to the formation of a complex with cumyl hydroperoxide, are caused by changes in the 1 viscosity of the solution. De recentes publications ont mis en doute la validite de I'hypothbse generalement acceptee a I'effet que I'autoreaction des radicaux cumylperoxy est une reaction d'ordre 2. Nous avons donc reexamine quelques aspects de cette reaction afin d'en clarifier les caracteristiques cinetiques et mecanistiques.Nos etudes sont entitrement en accord avec le mecanisme accepte pour I'auto-reaction des radicaux cumylperoxy et nous n'avons pas trouve de donnees permettant de croire qu'il existe des reactions en competition. Les resultats obtenus avec des produits marques au 360, confirment ce qui a ete trouve anterieurement a savoir que, a la temperature ambiante la scission reversible des radicaux cumylperoxy qui donne de I'oxygene et des racidaux cumyles n'entre pas en competition de f a~o n significative avec I'auto-reaction. Des etudes cinetiques tant dans des conditions d'etat stationnaire que transitoire etablissent clairement que I'auto-reaction des radicaux cumylperoxy est d'ordre 2. On propose une explication possible des observations anterieures qui indiquent une reaction du premier ordre. De plus, nous montrons que les variations observees dans les spectres rpe des radicaux cumylperoxy, qui ont ete attribuees a la formation d'un complexe avec I'hydroperoxyde de cumyle, sont provoquees par des variations dans la viscosite de la solution.[Traduit par le journal]

Absolute rate constants for hydrocarbon autoxidation. 32. On the self-reaction of 1,1-diphenylethylperoxyl in solution

“…Phenyl benzoate was prepared from benzoyl chloride and I phenol. 2,2,3,3-Tetraphenylbutane and di-tert-butyl hyponitrite 1 had been prepared previously in our laboratory (1). Phenol, , acetophenone, benzophenone, and I, 1-diphenylethanol were commercially available and were purified by standard methods.…”

“…Phenol, , acetophenone, benzophenone, and I, 1-diphenylethanol were commercially available and were purified by standard methods. : Product studies Oxidation and decomposition products were identified by a combination of gc-ms and hplc techniques as described previously (1). Yields of most of the oxygenated products were determined by reverse-phase hplc and were accurate to -+ 10%.…”

“…relative to the value for tert-butylperoxyl are the 1 It has recently been re-established (1) that rates result of rather low efficiencies of cage escape for of self-reaction of a-cumylperoxyl in solution are the more bulky a -c u m~l o x~l and 1 l -d i~h e n~ 1-second-order with respect to the radical concentra-ethoxyl relative to the high efficiency of cage I tion at 303 K and that, although p-scission of this for tert-butOxyl. radical (reaction [I]) occurs at this temperature, the + o2…”

Absolute rate constants for hydrocarbon autoxidation. 33. A product study of the self-reaction of α-tetralylperoxyls in solution

“…The mechanism for self-reaction of tertiary alkylperoxyls has been well estabished (2)(3)(4). These radicals exist in dynamic equilibrium with a tetroxide which decomposes to give two caged alkoxyls and oxygen.…”

“…These radicals exist in dynamic equilibrium with a tetroxide which decomposes to give two caged alkoxyls and oxygen. A fraction (-10%) of these alkoxyls combine to give di-tert-alkyl peroxide while the remainder escape the solvent cage and undergo H-atom abstraction, p-scission, or rearrangement (3,4).…”