Photolysis of Butenedial and 4-Oxo-2-pentenal Under Atmospheric Conditions

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1 Photolysis of Butenedial and 4-xo-2-pentenal Under Atmospheric onditions Gerard Rea, Lars Thüner and John Wenger entre for Research into Atmospheric hemistry (RA) Department of hemistry University ollege ork ork Ireland

2 The Atmosphere Photochemical reactor Major reactive species zone ( 3 ) Hydroxyl Radical (H) Sunlight (λ > 290 nm)

3 Hydroxyl Radical H Formation of H radicals hν (λ<310 nm) ( 1 D) ( 1 D) + H 2 2 H Reaction with hydroxyl radical (H) is the major fate of most hydrocarbons in the troposphere Hydroxyl radical reaction can lead to the further formation of radicals (R ) and ultimately tropospheric ozone in polluted urban air

4 Why Radicals are Important HYDRARBNS (RH) H RADIALS (R ) 2 ALKYL PERXY RAD. (R 2 ) hν (<400 nm) N N 2 3 ALKXY RADIALS (R ) PRDUTS Secondary pollutants PHTHEMIAL SMG

5 Atmospheric xidation of Aromatics H 3 H 3 H H Ring retaining products Ring fragmentation Unsaturated dicarbonyls have been seen as products during the H initiated atmospheric oxidation of aromatics Unsaturated dicarbonyls due to their structure would be expected to undergo photolysis Usat.Dicarbonyls! Radical source and effect the radical balance in the atmosphere

6 Atmospheric Fate of Butenedial and 4-oxo-2-pentenal Reaction with : Hydroxyl radical (H) zone ( 3 ) Photolysis (>290 nm) Natural Atmospheric Life-time (τ H ) τ H = k H 1 [H] Reactant Butenedial τ 4-xo-2-pentenal τ H radical (k H /10-12 ) 24.1±8 a 7.1 hours 55.8±2.1 a 3.1 h zone ( 3 ) (k 3 /10-18 ) 2 a 8.3 days 4.8±0.8 b 3.5 days Photolysis (J)?? Daily [H] = 1.6x10 6 molecules cm -3 Daily [ 3 ] = 7.0x10 11 molecules cm -3 a Bierbach et al. 1994, EST 28, 715 b Liu et al. 1999, EST 33, 4212

7 bjectives of This Work Synthesis of butenedial and 4-oxo-2-pentenal at the University of Newcastle Upon Tyne Scale up preparations Determination of rate coefficient of photolysis for butenedial and 4-oxo-2-pentenal under natural light conditions Identification of products and yields Devise mechanistic data in order to assess extent of radical formation

8 Butenedial and 4-oxo-2-pentenal H 3 Unsaturated dicarbonyls Not stable Not commercially available Require reliable synthesis! ollaboration with University of Newcastle Upon Tyne

9 Preparation of Unsaturated Dicarbonyls The general procedure for the preparation, involves oxidative ring opening of substituted furan compounds. Unsaturated Dicarbonyl Preparation of 4-oxo-2-pentenal H 3 DMD / Acetone H 3 m-pba DM H 3

10 Atmospheric Photolysis da dt = Φ( λ) σ( λ)f( λ) dλ = λ J J = photochemical rate constant (s -1 ) Φ = quantum yield (molecules/photon) F = photon flux (photons cm -2 s -1 ) σ = absorption cross section (cm 2 molecule -1 ) Must measure J under natural light conditions

11 Valencia

12 European Photoreactor (EUPHRE) EAM Institute Valencia, Spain White cell mirrors

13 Photolysis and product studies Experiments in purified air Experimental Temperature range K Light intensity and spectral distribution monitored with spectral radiant meter Photolysis rates J(N 2 ) were calculated from these data. In situ long-path FTIR spectroscopy used to quantify reactant and products oncentrations determined by computer aided subtraction of calibrated reference spectra

14 First rder Photolysis Plots E-Butendial Z-4-xo-2-pentenal y = -9.7E-04x E-03 R 2 = y = -15.2E-04x + 5.7E-02 R 2 = ln c/c o -0.8 ln c/c o t/s -4.0 t/s

15 Photolysis Rates of E-Butenedial and Z-4-xo-2-pentenal J (aldehyde) J (N2) J (aldehydes) 10-4 s s -1 J (N2) 9.7± ± ± ± ± ±0.017 * quoted errors cover error limits of individual values, result averaged over two experiments

16 Product Studies In situ FTIR allowed: Time resolved concentration-time profiles during the photolysis reaction Providing information about intermediate products and direct or delayed product formation Long path length (553.5 m) low detection limit

17 FTIR Spectra of E-Butenedial Reaction system R H ketene 2(5H)-Furanone Butenedial (a) before photolysis (b) after photolysis (c) residual spectrum Absorbance (3H)-Furanone (a) 0.2 (b) 0.1 (c) wavenumber cm

18 oncentration-time Profile E-Butenedial Reaction System ppb reactant ppb products Ketene time/s

19 Product Yield Diagram E-Butenedial Reaction System hange in conc. product Ketene intermediate onc. reactant

20 Product Yields of Butenedial Photolysis Major products 2(3H)furanone Maleic anhydride delayed 55±2% delayed 20±1% direct 18±3 % Minor products 2(5H)furanone Acrolein Glyoxal Methylglyoxal H H H 2 H 3 max 3% max 2% max 10% max 2% max 2%

21 Product Yields of 4-xo-2-pentenal Photolysis Major products α- angelicalactone H 3 Maleic anhydride delayed 50±7% delayed 5.6±1.3% direct 12±4% Minor products Acrolein Formaldehyde MVK Glyoxal Methylglyoxal H 2 H H H 2 H 3 H 3 max 8% max 1% max 18% max 1.5% max 1.5%

22 Ketene Intermediate From 4-oxo-2-pentenal From butendial Absorbance Wavenumbers (cm-1) 2120

23 500 haracterisation of the Ketene Intermediate ppb reactant H ppb products R 50 H :00 10:10 10:20 10:30 10:40 10:50 11:00 11:10 11:20 11:30 11:40 11:50 12:00 12:10 12:20 12:30 12:40 12:50 13:00 13:10 time

24 Possible Mechanism Formation of Ring losure Products H H H H H 3 h υ sun π * n H H H R h υ sun π * n H H H R H γ-h abstraction R H H R H H R Ketene R α-angelicalactone (R = H 3 ) 2(3H)Furanone (R = H) H 2

25 Summary H 3 or H Sunlight Sunlight R R HH R R nπ H H H R R 2(5H)furanone b-angelicalactone 2(3H)furanone a-angelicalactone

26 Summary Reactant Butenedial τ 4-xo-2-pentenal τ H radical (k H /10-12 ) 24.1±8 a 7.1 hours 55.8± h zone ( 3 )(k 3 /10-18 ) 2 a 8.3 days 4.8± days Photolysis (J/10-4 s -1 ) 9.7± min 15.9± min No high concentrations expected in ambient air Unsaturated dicarbonyl! Ketene Intermediate! products Photolysis leads mainly to ring closure products Little or no formation of radicals

27 Acknowledgements Prof. Bernard Golding Alistair Henderson Klaus Wirtz (EUPHRE) John Wenger Lars Thüner This work was part of the EU research project EXAT

28 Preparation of Butenedial Br 2 /MeH Me Me Me Amberlyst 15 Acetone/water Me

29 Unsaturated Dicarbonyls Parent Aromatic Unsaturated Dicarbonyl H 3 Butenedial H 3 H 3 H 3 H 3 4-oxo-2-pentenal 2-methyl-butenedial H 3 H 3 H 3 H 3 2-methyl-4-oxo-pentenal H 3 Hexene-2,5-dione H 3 H 3 H 3 3-methyl-hexene-2,5-dione H 3

30 Ketene Formation and Decay H 3 H 3 H J = 0.20±0.04xJ(N 2 ) hν sun k = 4.2±0.3 s -1 dark products H H H J = 0.14±0.03xJ(N 2 ) hν sun k = 2.0±0.4 s -1 dark products