Isomerization and Fragmentation of Cyclohexanone in a Heated Micro-Reactor.
J Phys Chem A
; 119(51): 12635-47, 2015 Dec 24.
Article
em En
| MEDLINE
| ID: mdl-26617252
ABSTRACT
The thermal decomposition of cyclohexanone (C6H10âO) has been studied in a set of flash-pyrolysis microreactors. Decomposition of the ketone was observed when dilute samples of C6H10âO were heated to 1200 K in a continuous flow microreactor. Pyrolysis products were detected and identified by tunable VUV photoionization mass spectroscopy and by photoionization appearance thresholds. Complementary product identification was provided by matrix infrared absorption spectroscopy. Pyrolysis pressures were roughly 100 Torr, and contact times with the microreactors were roughly 100 µs. Thermal cracking of cyclohexanone appeared to result from a variety of competing pathways, all of which open roughly simultaneously. Isomerization of cyclohexanone to the enol, cyclohexen-1-ol (C6H9OH), is followed by retro-Diels-Alder cleavage to CH2âCH2 and CH2âC(OH)-CHâCH2. Further isomerization of CH2âC(OH)-CHâCH2 to methyl vinyl ketone (CH3CO-CHâCH2, MVK) was also observed. Photoionization spectra identified both enols, C6H9OH and CH2âC(OH)-CHâCH2, and the ionization threshold of C6H9OH was measured to be 8.2 ± 0.1 eV. Coupled cluster electronic structure calculations were used to establish the energetics of MVK. The heats of formation of MVK and its enol were calculated to be ΔfH298(cis-CH3CO-CHâCH2) = -26.1 ± 0.5 kcal mol(-1) and ΔfH298(s-cis-1-CH2âC(OH)-CHâCH2) = -13.7 ± 0.5 kcal mol(-1). The reaction enthalpy ΔrxnH298(C6H10âO â CH2âCH2 + s-cis-1-CH2âC(OH)-CHâCH2) is 53 ± 1 kcal mol(-1) and ΔrxnH298(C6H10âO â CH2âCH2 + cis-CH3CO-CHâCH2) is 41 ± 1 kcal mol(-1). At 1200 K, the products of cyclohexanone pyrolysis were found to be C6H9OH, CH2âC(OH)-CHâCH2, MVK, CH2CHCH2, CO, CH2âCâO, CH3, CH2âCâCH2, CH2âCH-CHâCH2, CH2âCHCH2CH3, CH2âCH2, and HC≡CH.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Cicloexanonas
/
Temperatura Alta
/
Calefação
Idioma:
En
Revista:
J Phys Chem A
Assunto da revista:
QUIMICA
Ano de publicação:
2015
Tipo de documento:
Article
País de afiliação:
Estados Unidos