ATMOCHEM - Novel Approaches in the Understanding of Aromatic Compound Degradation in the Atmosphere: From Theoretical Studies to Simulation Chamber Experiments
Zusammenfassung der Projektergebnisse
The ipso‐type addition of hydroxyl radicals to substituted benzenes was investigated at the high‐pressure limit by studying the reaction of OH with polymethylated benzenes in helium as a function of temperature. Total rate constants (addition + abstraction) were obtained for p‐xylene, mesitylene, the three tetramethylbenzenes, pentamethylbenzene and p‐cymene by pulsed vacuum UV flash photolysis of water vapour in the presence of various levels of the aromatic for production of OH and time resolved resonance‐fluorescence for detection. Isothermal data sets consisting of typically 10 different levels of the aromatic were generated by computer control of the mass flows of He (utilizing the gas saturation technique), triggering of the flash lamp (typically 50 flashes) and collecting and saving the signal between 1 ms and 4 s after the flash and the relevant reaction conditions. Photon counting, combined with multichannel scaling, allowed us to obtain signal/noise ratios sufficient for evaluating the sets of isothermal decays of the intensity for their triexponential components over the temperature range of 25 to about 80 °C, resulting from the reversible formation of two OH adducts with different thermal stability. Symmetry of the 1,4‐dimethyl‐, 1,3,5‐trimethyl ‐ and 1,2,4,5‐tetramethylbenzenes clearly demonstrates the contribution of ipso adducts to the triexponential decays, and the thermal properties of these ortho and ipso OH‐substituted adducts are characterized. The thermodynamic quantities and Arrhenius parameters imply that isomerization of the adducts occurs. Similar data were obtained for the remaining tetramethylbenzenes (1,2,3,5‐, and 1,2,3,4‐) and pentamethylbenzene, but less conclusive due to more than two possibilities of adduct formation. Triexponential decays, observed in the presence of p‐cymene, are assigned to arise from the two possible ortho‐OH adducts to the isopropyl and methyl substituents on the benzene ring. The contribution from the ipso adducts is considered unimportant for this molecule, supported by theoretical calculations (DFT and RRKM) by the project partners at Bordeaux.
Projektbezogene Publikationen (Auswahl)
- Rate and pathways for the reaction of OH with the biogenic p‐cymene, an alkylated aromatic. Annual Assembly of the European Geophysical Union, Vienna, Austria, April 19th ‐24th 2009, Geophysical Research Abstracts 11, EGU 2009‐13131, 2009
- Novel Approaches in the Understanding of Aromatic Compound Degradation in the Atmosphere: From Theoretical Studies to Simulation Chamber Experiments, Colloquium CNRS‐DFG Bilateral Project: Joint French‐German Projects on Innovative Basic Research in Atmospheric Chemistry, Lyon, 2010
C. Zetzsch (with contributions by C. Jain, C. Schoemaecker, C. Fittschen, S. Nehr, B. Bohn and the SAPHIR‐Team, P. Morajkar, J.‐C. Loison, A. Gratien, P.‐M. Flaud, M‐T. Rayez, J.‐C. Rayez, E. Villenave, P. Alarcon, R. Atkinson, J. von Buttlar, R. Koch, M. Siese, R. Strekowski, T. Riedl, S. Zhang)
- Studies of aromatics with OH radicals in a smog chamber and by flash photolysis with resonance fluorescence detection of OH. Sino‐German Workshop Chemical Processes in the Troposphere: Implications for Air Pollution and Climate Change in Large Urban Areas, Beijing, China, October 25th ‐28th 2010
P. Alarcón, J. von Buttlar, R. Koch, M. Siese, C. Zetzsch, B. Bohn
- Experimental and theoretical study of the reaction of OH radicals with the aromatic molecule p‐cymene, proceeding via two adducts. 110th Annual Assembly of the German Bunsen‐Society for Physical Chemistry, Berlin, June 2nd ‐ 4th 2011
P. Alarcón, B. Bohn, M.T. Rayez, J.C. Rayez, C. Zetzsch
- Experimental and theoretical study of the reaction of OH with the aromatic molecule p‐cymene, proceeding via two adducts. Annual Assembly of the European Geophysical Union, Vienna, Austria, April 3rd –8th 2011, Geophysical Research Abstracts 13, EGU 2011‐7849‐1, 2011
P. Alarcón, B. Bohn, M. T. Rayez, J. C. Rayez, R. Strekowski, C. Zetzsch
- Kinetics and mechanism of the reaction of OH with the trimethylbenzenes. Experimental evidence for the formation of adduct isomers, Phys. Chem. Chem. Phys. 14, 13933‐ 13942, 2012
Bohn, B., Zetzsch, C.
(Siehe online unter https://doi.org/10.1039/c2cp42434g) - Rate constants for the reaction of OH with durene (1,2,4,5‐tetramethylbenzene), leading to two types of adducts: ortho and ipso. 22nd International Symposium on Gas Kinetics, Boulder, Colorado, USA, June 18th ‐22nd 2012
P. Alarcón, B. Bohn, C. Zetzsch
- Addition of OH to 1,2,4,5‐tetramethylbenzene and reactions of the adducts with O2. 8th International Conference on Chemical Kinetics, Seville, Spain. July 8th ‐12th 2013
P. Alarcón, B. Bohn, C. Zetzsch
- How Important is the ipso addition of OH to methylated benzenes? European Combustion Meeting, Lund, Sweden, June 26th‐28th 2013
P. Alarcón, C. Zetzsch, B. Bohn
- Rate constants for the reaction of mesitylene‐OH adducts with O2. 8th International Conference on Chemical Kinetics, Seville, Spain. July 8th ‐12th 2013
P. Alarcón, B. Bohn, C. Zetzsch
- Reversible addition of OH to polymethylated benzenes: Contribution of ipso adducts. 30th Informal Symposium on Kinetics and Photochemical Processes in the Atmosphere, Pasadena, CA, USA, March 3rd‐6th 2013
P. Alarcón, B. Bohn, C. Zetzsch
- Reversible addition of the OH radical to p‐cymene in the gas phase: kinetic analysis assuming formation of a single adduct. Part 1. Phys. Chem. Chem. Phys. 15, 20105‐20114, 2013
Alarcón, P., Strekowski, R., Zetzsch, C.
(Siehe online unter https://doi.org/10.1039/c3cp53040j) - Reversible addition of the OH radical to p‐ cymene in the gas phase: multiple adduct formation. Part 2. Phys. Chem. Chem. Phys. 16, 17315‐17326, 2014
Alarcón, P., Bohn, B., Zetzsch, C., Rayez, M.T., Rayez, J.C.
(Siehe online unter https://doi.org/10.1039/c4cp02073a) - Kinetic and mechanistic study of the reaction of OH radicals with methylated benzenes: 1,4- dimethyl-, 1,3,5-trimethyl-, 1,2,4,5 -, 1,2,3,5- and 1,2,3,4-tetramethyl-, pentamethyl- and hexamethylbenzene. Phys. Chem. Chem. Phys., 2015,17, 13053-13065
Alarcón, P., Bohn, B., Zetzsch, C.
(Siehe online unter https://doi.org/10.1039/c5cp00253b)
