Gas-phase reaction of OH radicals with benzene: products and mechanism

Authors
Citation
T. Berndt et O. Boge, Gas-phase reaction of OH radicals with benzene: products and mechanism, PHYS CHEM P, 3(22), 2001, pp. 4946-4956
Citations number
32
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
ISSN journal
1463-9076 → ACNP
Volume
3
Issue
22
Year of publication
2001
Pages
4946 - 4956
Database
ISI
SICI code
1463-9076(2001)3:22<4946:GROORW>2.0.ZU;2-0
Abstract
The gas-phase reaction of OH radicals with benzene was studied in O-2/He mi xtures under flow conditions in the temperature range 276-353 K and at pres sures of 100 and 500 mbar using on-line FT-IR spectroscopy and GC-MS measur ements. The reaction conditions were chosen so that the initially formed OH /benzene adduct predominantly reacted either with O-2 or O-3. Under conditi ons of a predominant reaction of the OH/benzene adduct with O-2 the product formation was studied for variable NO concentrations. Identified products were the isomers of hexa-2,4-dienedial, phenol, nitrobenzene, p-benzoquinon e and glyoxal. Furan was found in small amounts. For increasing NO concentr ations there was a decrease of the phenol yield and the yields of trans,tra ns-hexa-2,4-dienedial and nitrobenzene increased, resulting in maximum valu es of 0.36 +/- 0.02 and 0.11 +/- 0.02, respectively (100 mbar, 295 K). The p-benzoquinone yield of 0.08 +/- 0.02 was found to be independent of the NO concentration. The temperature dependence of the phenol yield was measured in the range of 276-353 K for initial ratios of [NO]/[O-2] = 1-20 x 10(-6) at 500 mbar. For a fixed [NO]/[O-2] ratio, a distinct increase of the phen ol yield with increasing temperature was observed; initial [NO]/[O-2] = 1-1 .2 x 10(-6), phenol yield : 0.18 +/- 0.04 (276 K) and 0.68 +/- 0.05 (353 K) . Generally, the total yield of carbonylic substances was found to be anti- correlated to the phenol yield. When the OH/benzene adduct reacted with O-3 , trans,trans-hexa-2,4-dienedial, phenol and formic acid were identified as main products with formation yields of 0.28 +/- 0.02, 0.20 +/- 0.05 and 0. 12 +/- 0.02, respectively (100 mbar, 295 K). Further products were p-benzoq uinone, CO and unidentified carbonylic substances. For the different experi mental conditions, reaction mechanisms are proposed explaining the formatio n of the observed products. A simple model describing the temperature and N Ox-dependence of the phenol yield is presented.