Atmospheric Oxidation of Selected Aromatic Hydrocarbons

143 Pages·2002·1.33 MB·English

by  Physikalische Chemie

Atmospheric Oxidation of
Selected Aromatic Hydrocarbons
Thesis submitted to the Faculty of Chemistry
Bergische Universität Gesamthochschule Wuppertal
for the Degree of Doctor of Science
(Dr. rerum naturalium)
by
Romeo Iulian Olariu
October, 2001

The work described in this thesis was carried out in the Department of Physical Chemistry,
the Bergische Universität Gesamthochschule Wuppertal under the scientific supervision of
Prof. Dr. K. H. Becker, during the period of March, 1998 - October, 2001.
Referee: Prof. Dr. K. H. Becker
Co-referee: Prof. Dr. E. H. Fink

soţiei mele, Irina
şi
fiicei noastre, Ana

I would like to express my sincere thanks to Prof. Dr. Karl Heinz Becker for the opportunity
of doing this Ph.D. in his research group and for the supervision of this work.
I would like to thank Prof. Dr. Ewald Fink for agreeing to co-referee the thesis and for his
useful comments.
My sincere gratitude also to Dr. Ian Barnes who not only helped me to understand at least a
part of the immense and fascinating domain of the atmospheric chemistry but also followed
with special care my scientific work.
I express my thanks to Prof. Dr. Raluca Delia Mocanu for trusting me and making many
valuable suggestions.
The help given by Dr. Björn Klotz, especially at the beginning of my Ph.D. work, is much
appreciated.
Thanks are also due to my colleague Cecilia Arsene for suggestions and critical observations.
Many colleagues helped by supplying advanced information, suggestions and comments on
laboratory work. Of these I would like to mention particularly Dr. Klaus Brockmann, Markus
Spittler, Dr. Jörg Kleffmann, Dr. Klaus Wirtz (Valencia) and the technical staff of this group.

Abstract
This work presents investigations on the gas-phase chemistry of phenol and the cresol isomers
performed in a 1080 l quartz glass reactor in Wuppertal and in a large-volume outdoor
photoreactor EUPHORE in Valencia, Spain. The studies aimed at clarifying the oxidation
mechanisms of the reactions of these compounds with OH and NO radicals.
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Product investigations on the oxidation of phenol and the cresol isomers initiated by
OH radicals were performed in the 1080 l quartz glass reactor with analyses by in situ FT-IR
absorption spectroscopy. The primary focus of the investigations was on the determination of
product yields. This work represents the first determination and quantification of 1,2-
dihydroxybenzenes in the OH oxidation of phenolic compounds. Possible reaction pathways
leading to the observed products have been elucidated. The products observed and their
respective yields were as follows:
reactant products yield (%)
phenol 1,2-dihydroxybenzene 80.4 ± 12.1
1,4-benzoquinone 3.7 ± 1.2
2-nitrophenol 5.8 ± 1.0
ortho-cresol 1,2-dihydroxy-3-methylbenzene 73.4 ± 14.6
methyl-1,4-benzoquinone 6.8 ± 1.0
6-methyl-2-nitrophenol 6.8 ± 1.5
meta-cresol 1,2-dihydroxy-3-methylbenzene 68.6 ± 13.4
1,2-dihydroxy-4-methylbenzene 9.7 ± 2.7
methyl-1,4-benzoquinone 11.3 ± 2.5
5-methyl-2-nitrophenol 4.4 ± 1.5
3-methyl-2-nitrophenol 4.3 ± 1.6
para-cresol 1,2-dihydroxy-4-methylbenzene 64.1 ± 11.3
4-methyl-2-nitrophenol 7.6 ± 2.2
The rate constants for the reaction of OH radicals with dihydroxy(methyl)benzenes
and (methyl)benzoquinones were determined using the relative rate technique. All of the
following data represent first-time determinations of the rate constants. At 1000 mbar total
pressure and 300± 2 K, the following rate constants (in 10-11 cm3 molecule-1 s-1) were obtained:
reactant k
OH
1,2-dihydroxybenzene 10.4 ± 2.1
1,2-dihydroxy-3-methybenzene 20.5 ± 4.3
1,2-dihydroxy-4-methylbenzene 15.6 ± 3.3
1,4-benzoquinone 0.46 ± 0.1
methyl-1,4-benzoquinone 2.35 ± 0.47
The following products and respective yields were observed from the NO radical
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reaction with phenol and the cresol isomers:
reactant products yield (%) 1080 l yield (%) EUPHORE
phenol 2-nitrophenol 24.2 ± 3.7 21.3 ± 3.3
4-nitrophenol 50.0 ± 3.8 50.0 ± 10.0
HNO 89.7 ± 13.0 73.8 ± 8.3
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ortho-cresol 6-methyl-2-nitrophenol 11.5 ± 0.8 -
methyl-1,4-benzoquinone 4.4 ± 0.3 -
HNO 77.2 ± 6.3 95.9 ± 4.8
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meta-cresol 3-methyl-2-nitrophenol 21.2 ± 1.4 22.3 ± 1.6
3-methyl-4-nitrophenol 22.8 ± 1.8 25.4 ± 1.7
5-methyl-2-nitrophenol 23.5 ± 1.8 22.4 ± 1.5
methyl-1,4-benzoquinone 4.2 ± 0.7 -
HNO 72.3 ± 6.4 91.1 ± 6.3
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para-cresol 4-methyl-2-nitrophenol 41.3 ± 3.7 44.3 ± 3.3
HNO 85.0 ± 10.2 86.2 ± 7.0
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This work has vastly improved the knowledge on the distribution of oxidation
products from the reaction of OH with phenol and the cresol isomers and also significantly
improved it for the NO reactions. The product studies have allowed the construction of
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tentative oxidation mechanisms for these selected aromatic compounds which are required for
atmospheric chemical transport models.