Flash Pyrolysis of t-Butyl Hydroperoxide and Di-t-butyl Peroxide: Evidence of Roaming in the Decomposition of Organic Hydroperoxides

Abstract

Thermal decomposition of t-butyl hydroperoxide and di-t-butyl peroxide was investigated using flash pyrolysis (in a short reaction time of <100 μs) and vacuum-ultraviolet (λ = 118.2 nm) single-photon ionization time-of-flight mass spectrometry (VUV-SPI-TOFMS) at temperatures up to 1120 K and quantum computational methods. Acetone and methyl radical were detected as the predominant products in the initial decomposition of di-t-butyl peroxide via O-O bond fission. In the initial dissociation of t-butyl hydroperoxide, acetone, methyl radical, isobutylene, and isobutylene oxide products were identified. The novel detection of the unimolecular formation of isobutylene oxide, as supported by the computational study, was found to proceed via a roaming hydroxyl radical facilitated by a hydrogen-bonded intermediate. This new pathway could provide a new class of reactions to consider in the modeling of the low temperature oxidation of alkanes.

Copper‐Catalyzed Allylic C−H Alkynylation by Cross‐Dehydrogenative Coupling

“…Nevertheless, under our reaction conditions the formed tert ‐butoxy radicals can decompose into methyl radicals and acetone [Scheme , Eq. (2)] . The produced open‐shell species may then react with the copper(I) catalyst [LCuI] + in a reductive fashion to produce the oxidized copper(II) complex 5 .…”

“…(2)]. [30] Thep roduced open-shell species may then react with the copper(I) catalyst [LCuI] + in ar eductive fashion to produce the oxidized copper(II) complex 5. [31] This single electron transfer (SET) reaction should be feasible consideringt he inherente lectrophilicity of the alkoxy radical [32] and the reductivep ower of [LCu I ] + (for reference:E 1/2 Cu(II)/CuI in water is À0.093 Vv s. SCE).…”

Mechanistic Study of Thermal Decomposition of Hexamethyldisilane by Flash Pyrolysis Vacuum Ultraviolet Photoionization Time-of-Flight Mass Spectrometry and Density Functional Theory

“…The pyrolysis products were formed when the HMDS precursors passed through the heated microreactor. The conditions of the SiC tube microreactor were similar to those well characterized in the previous studies; 31,34,37 the short residence time, the modestly low pressure, and the low concentration of the precursor molecules in inert gas strongly favored unimolecular reactions and minimized bimolecular and surface reactions. As shown in the Results section, the lack of the H atom abstraction product peak (parent mass minus 1) from the parent molecule and any adducts peaks higher than the parent peak indicated a minimum amount of bimolecular reactions in the microreactor.…”

“…The pyrolysis experimental setup has been described previously − and used to investigate thermal decomposition of silicon-containing compounds. , HMDS (99%, Sigma-Aldrich) was used without further purification and was diluted to <1% by bubbling the liquid sample using helium as the carrier gas. The <1% HMDS in He gas sample (at a total pressure of 1.2 atm) was introduced by a pulsed nozzle into a SiC tube attached in front of the pulsed valve and expanded sonically through the SiC tube microreactor (∼40 mm long, 2 mm O.D., 1 mm I.D.)…”

Cu-Catalyzed Oxidative Allylic C–H Arylation of Inexpensive Alkenes with (Hetero)Aryl Boronic Acids

“…Our first mechanistic hypothesis, pathway A, begins with the decomposition of DTBP initiated by LCu I via a single-electron transfer (SET) reaction to produce a tert -butoxy radical and the oxidized copper­(II) complex I , LCu II -O t Bu . The formed tert -butoxy radical can either decompose by β-scission into acetone and a methyl radical, which can be trapped by TEMPO, or be involved in hydrogen atom abstraction (HAA) step from an alkene to form an allyl radical . In parallel, the copper­(II) complex II is generated by the transmetelation reaction of aryl boronic acid with LCu II -O t Bu ( I ) .…”