A comprehensive study on low-temperature oxidation chemistry of cyclohexane. I. Conformational analysis and theoretical study of first and second oxygen addition

Free‐radical catalyzed oxidation reactions with cyclohexene and cyclooctene with peroxides as initiators

“…One of these, featuring a unimolecular mechanism, involves a 1,3‐hydrogen atom migration on the cyclohexene peroxy radical, 2 , with an activation energy of 37.59 kcal/mol (similar to that for the 1,3‐hydrogen shift for CH 3 CH 2 OO˙, which was calculated [ 47 ] at the CBS‐QB3 level to be 39.2 kcal/mol) as shown on the top right of Scheme 1 and Figure S6, followed by rapid OO bond cleavage resulting in 2‐cyclohexen‐1‐one and a hydroxy radical. In comparison, the transformation of the cyclohexyl peroxy radical into cyclohexanone and a hydroxy radical was estimated to have an activation energy of 39.23 (i.e., for the 1,3‐hydrogen atom shift) and enthalpy of −27.23 kcal/mol [ 48 ] (at the CBS‐QB3 level) in contrast to the 37.59 and −37.50 kcal/mol (APFD/6‐311 + G(d) level) respectively for the transformation of the cyclohexene peroxy radical, 2 , into cyclohexanone and a hydroxy radical, Scheme 1. Also, the R −αH ˙ OOH is known to decompose to ketone and ˙OH spontaneously.…”

“…[15] This reaction does not proceed in the presence of BHT, suggesting that freeradical species are involved. [15] In contrast to the mechanisms presented in Schemes 1 and 2, the proposed mechanism, in this case, consists of the formation of an acyl radical from isobutyraldehyde with subsequent formation d,p)) [41] D(O O) in t BuOOH 33.12 33.12 36.87 (B3LYP/6-311 + G(d,p), 43.93-47.14 (G4, CBS-QB3 and CBS-APNO) [39] H atom abstraction 4.28 2.22 8.89 (B3LYP/6-311 + g(3df,2p)-D3//B3LYP/6-31 + g(d)) [42] Alkene radical + O 2 1.36 0.80 À0.9 for CH 3 CH 2 ˙+ O 2 (CCSD(T)/DZP) [43] 1,3-H atom shift on 37.59 33.32 39.2 for CH 3 CH 2 OO˙(CBS-QB3) [47] 39.23 for cyclohexyl peroxy à cyclohexanone (CBS-QB3) [48] H atom abstraction with 2 or 9 15.28 14.72 15.4 for (i-C 3 H 7 ˙from C 3 H 8 + HO 2 ˙) (def2-TZVP) [50] of a peroxide by reaction with oxygen that results in the formation of a manganese oxide that transfers the O atom to the alkene resulting in the epoxide. This shows that very complex mechanisms possibly pertain for oxidation reactions.…”

Product Identification in the Low-Temperature Oxidation of Cyclohexane Using a Jet-Stirred Reactor in Combination with SVUV-PEPICO Analysis and Theoretical Quantum Calculations

“…The electronic footprints of both species were detected in the SPES spectrum of m / z 98 (see Figure ). γQOOH is the most likely formed radical due to the low energy barrier for its formation . It is mainly consumed via reaction with a second oxygen molecule.…”

“…They identified and quantified stable products and reactive intermediates such as hydroperoxides by using both synchrotron vacuum ultraviolet PIMS (SVUV-PIMS) and GC–MS. With the support of Rice–Ramsperger–Kassel–Marcus (RRKM)/master-equation simulations, they developed a new kinetic model including for the first time conformational effects of the cyclohexane ring. The most stable conformers of cyclohexane contain H-atoms in axial and equatorial positions.…”

Probing combustion and catalysis intermediates by synchrotron vacuum ultraviolet photoionization molecular-beam mass spectrometry: recent progress and future opportunities

“…More recently, the delicate conformational kinetics information during low-temperature oxidation was investigated experimentally based on the observation of alkenal-hydroperoxides and keto-hydroperoxides in low-temperature oxidation of cyclohexane and alkylcyclohexanes. [58][59][60][61] Fig. 5a shows a representative mass spectrum recorded in the low temperature oxidation of ethylcyclohexane (ECH) conducted in a jet-stirred reactor.…”