Reactions of hydroperoxy radicals. Liquid-phase oxidation of 1,4-cyclohexadiene

Abstract

The autoxidation of 1,4-cyclohexadiene proceeds exclusively through a free radical chain dehydrogenation to form benzene and hydrogen peroxide. The key step is the reaction of the cyclohexadienyl radical with oxygen to give benzene and hydroperoxy (HO2•) radicals directly. Estimated Arrhenius parameters exclude other routes. The bond energy of the active carbon-hydrogen bonds in various carbon radicals correlates directly with the amount of olefin formed in competition with organic hydroperoxide upon reaction with oxygen.The formation of benzene and hydrogen peroxide from the oxidation of 1,4-cyclohexadiene1'2 is one of the few cases of dehydrogenation by a simple autoxidation process at room temperature. While this oxidation is atypical because of the thermodynamic advantage associated with benzene formation, other hydrocarbons show the same behavior at higher temperatures. Because of the potential of this reaction as a source of hydroperoxy radicals near room temperature, we have made a careful study of the reaction.

Aromatic C–H amination in hexafluoroisopropanol

“…2a: an ammoniumyl radical, generated either through N-O bond homolysis or iron-mediated single electron reduction, adds to an arene to generate a putative cationic cyclohexadienyl radical (A). Intermediate A then rearomatizes to the aniline product through one of three pathways: single electron oxidation by iron(III), [43][44][45] aerobic oxidation [46][47][48][49][50] or chain propagation. 51 We identied a hydrogen bond in reagent 1 between one N-H and the triate counterion in the solid state (Fig.…”

Inhibition of hydrocarbon autoxidation by nitroxide-catalyzed cross-dismutation of hydroperoxyl and alkylperoxyl radicals

“… 28 Hendry and Schuetzle subsequently argued that the reaction must involve direct H-atom transfer from the cyclohexadienyl radical to O 2 . 40 Subsequent reports seem split between the two mechanisms. 41 – 45 …”

Mechanistic Insight into the Dehydro-Diels–Alder Reaction of Styrene–Ynes

“…This hypothesis is supported by the work of Hendry et al, who used kinetic data and quantitative water analysis to reveal that only substoichiometric amounts of oxygen were required for the thermal dehydrogenation of 1,4-cyclohexadiene to benzene (Scheme 6D). 40 When we performed the IMDDA reaction in the presence or absence of oxygen, the same product selectivity for naphthalene 31a…”