The very low‐pressure pyrolysis of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether and the enthalpy of formation of the phenoxy radical

Abstract

A value of the enthalpy of formation of the phenoxy radical in the gas phaae, A H " , l e s~ (@., g) = 11.4 f 2.0 kcal/mol, has been obtained from the kinetic study of the unimolecular decompositions of phenyl ethyl ether, phenyl ally1 ether, and benzyl methyl ether1 a t very low pressures. Bond fission, producing phenoxy or benzyl radicals, respectively, is the only mode of decomposition in each case. The present value leads to a bond dissociation energy BDE(+O-H) = 86.5 f 2 kcal/mol,' in good agreement with recent estimates made on the basis of competitive oxidation steps in the liquid phase. A comparison with bond dissociation energies of aliphatic alcohols, BDE (RO-H) = 104 kcal/mol, reveals that the stabilization energy of the phenoxy radical (17.5 kcal/mol) is considerably greater than the one observed for the isoelectronic benzyl radical (13.2 kcal/mol). Decomposition of phenoxy radicals intci cyclopentadienyl radicals and CO has been observed at temperatures above 1000"K, and a mechanism for this reaction is proposed.

Reaction of 2,2?-azinobis (3-ethylbenzothiazoline-6-sulfonic acid (ABTS) derived radicals with hydroperoxides. Kinetics and mechanism

“…(13) (14) are also very poorly correlated, indicating that neither this simplified mechanism is able to explain the experimental data.…”

“…The main differences are the lack of equilibration in the first step and a considerably slower rate when hydroperoxides are employed instead of the phenols. The faster rate observed with the latter compounds can be related to the smaller bond strength in the phenols [13,14]. This could favor the occurrence of the initial reaction with the ABTS radical cation.…”

Unimolecular isomerization/decomposition of cyclopentadienyl and related bimolecular reverse process:ab initio MO/statistical theory study

“…27 -29 As for the relative ordering of these two minima, no consensus has been reached, because it depended on the MO method employed. Experimentally, the reversed ordering was observed for two cyclopentadienyl isotopomers, C 5 H 4 D and C 5 HD 4 . 38 However, the observed splitting of ∼9 cm −1 , which should be mainly due to zero point energy splitting, can only suggest that the splitting of classical electronic levels is also very small.…”

Detailed chemical kinetic models for the low-temperature combustion of hydrocarbons with application to gasoline and diesel fuel surrogates

“…Other channels can also be considered at low temperature as will be discussed in paragraph 5.4.b. Phenol can react by H-abstraction to give phenoxy radicals, which can decompose to give carbon monoxide and cyclopentadienyl radicals, through a two or three-step process [239]. The resonance stabilised phenol and cyclopentadiene [240].…”