Chemistry of Ring-Retaining Products I. Barnes Bergische University Wuppertal

Transcription

1 Mechanism of the Photooxidation of Aromatic Hydrocarbons: Chemistry of Ring-Retaining Products I. Barnes Bergische University Wuppertal

2 Photoreactor in Wuppertal Germany 6 Meter or 1080 l reactor (~ 1990) In situ FITR, GC and DMA Base optical path 6 meter, total optical path 484,7 m

3 utdoor Photoreactor, Valencia, Spain Mixing Fan Actinometers for J ( 1 D) and J (N 2) Clean Air Inlet Ports for Reactant Inlet and Sampling LIF Mounting Position Mixing Fan White System for DAS White System for FT-IR EUPHRE chamber at CEAM, Valencia, Spain

4 Primary oxidation steps CH 2 CH 2 CH CH 3 2 / N 2 abstraction + H CH 3 M H H various mechanisms to form ring-retaining and ring-cleavage products addition (+ other isomers) Recent review of the kinetics of aromatic-h-adducts with 2 and N 2 in: R. Koch, R. Knispel, M. Elend, M. Siese und C. Zetzsch, Atmos. Chem. Phys. Discuss. 2006, 6, 7623

5 Gas phase H radical photooxidation of aromatic hydrocarbons + H + 2 H. H ADDITIN N (i) + 2 (ii) (iii) (vi) 2 N 2 H 2 H-ABSTRACTIN H 2 XEPIN H N 2 N 2 H 2 H 2 H PHENLIC H (iv) N 2 N H. (v) H 2 H N 2 H N 2 H 2 β-hydrxy PERXY H H 2 EPXY-XY 1,4- ADDITIN PERXIDE BICYCLIC Simplified photooxidation mechanism from the EXACT final report Recent quantification of dienedials by IFG and EUPHRE (Berndt and Böge, PCCP 2006, 8, )

6 H oxidation of benzene / toluene Ring-retaining products H H 50-60%* *(Berndt and Böge, Phys. Chem. Chem. Phys., 2006, 8, ) CH 3 CH 3 H H + isomers 16-18%

7 H oxidation products of phenol and cresols Reactant Product Yield (% molar) Yield (lit) Major products are phenol o-cresol 1,2-dihyroxybenzene 1,4-benzoquinone 2-nitrophenol 1,2-dihyroxy-3-methylbenzene methyl-1,4-benzoquinone 6-methyl-2-nitrophenol 78.1 ± ± ± ± ± ± ± ± 1.5 1,2-dihydroxybenzenes H H and m-cresol 1,2-dihyroxy-3-methylbenzene methyl-1,4-benzoquinone 3-methyl-2-nitrophenol 5-methyl-2-nitrophenol 70.0 ± ± ± ± ± 0.1 p-cresol 1,2-dihydroxy-4-methylbenzene 4-metyl-2-nitrophenol 64.1 ± ± ± 4 benzoquinones lariu et al. Atmos. Environ., 2002, 36, Product study H + phenol: Berndt and Böge, Phys. Chem. Chem. Phys., 2003, 5,

8 H + 2 H Simplified mechanism for the reaction of phenol/cresols with H -H 2 R + N 2 R H + 2 H H R + H H + N 2 R N 2 R nitrophenols benzoquinones + 2 M R H H 2 R 1,2-dihydroxybenzenes ring opening-products

9 H oxidation of benzene / toluene Ring-retaining products H H H H H 50-60%* up to 80% CH 3 CH 3 CH 3 H H H H 16-18% + isomers up to 80% H *(Berndt and Böge, Phys. Chem. Chem. Phys., 2006, 8, )

10 Rate coefficients for the reactions of H radicals with dihydroxybenzenes and benzoquinone (Relative kinetic technique at 298 K) Compound k (10-11 cm 3 s -1 ) τ i = 1/k[H] H H H H CH 3 1,2-dihydroxybenzene 10.4 ± min 1,2-dihydroxy- 3-methylbenzene 20.5 ± min 1,4-benzoquinone (k = (0.46 ± 0.09) x ) (37 h) CH 3 H CH 3 H 1,2-dihydroxy- 4-methylbenzene 15.6 ± min (lariu et al. Int. J. Chem. Kinet., 2000, 32, ) methyl-1,4-benzoquinone (k = (2.35 ± 0.47) x ) (7.4 h)

11 Rate coefficients at 298 K for the reactions of 3 with Dihydroxybenzenes (relative kinetic technique at 298 K) Compound k (10-17 cm 3 s -1 ) H H 1,2- dihydroxybenzene 0.96 ± 0.0 H H CH 3 H CH 3 H 1,2-dihydroxy- 3-methylbenzene 2.80 ± ,2-dihydroxy- 4-methylbenzene 2.63 ± 0.34 (Tomas et al, Int. J. Chem. Kinet., 2003, 35, )

12 Rate coefficients at 298 K for the reactions of N 3 radicals with dihydroxybenzenes Compound 1080 l reactor k (10-11 cm 3 s -1 ) EUPHRE k (10-11 cm 3 s -1 ) k(average) (10-11 cm 3 s -1 ) H H 1,2- dihydroxybenzene 9.03 ± ± ± 5.0 H H CH 3 H CH 3 H 1,2-dihydroxy- 3-methylbenzene 17.3 ± ± ± 5.6 1,2-dihydroxy- 4-methylbenzene 16.0 ± ± ± 6.5 (lariu et al. Int. J. Chem. Kinetics, 2004,36, )

13 Lifetimes of aromatic compounds H H H τ(h) 9.5 d 5.1 h 1.3 h τ( 3 ) >4.5 yr d τ(n 3 ) >4 yr 8.8 min 20.4 s Atmospheric lifetimes calculated using: [H] a 12-h daytime average of 2 x 10 6 molecule cm -3 [ 3 ] a 24-h average of 7 x molecule cm -3 [N 3 ] a 12-h nightime average of 5 x 10 8 molecule cm -3

14 Trend of rate coefficients for the reaction of methylated hydroxyaromatic compounds with N 3 radicals. 1.8e e e e-11 K N3 (cm 3 s -1 ) 6.0e e e e e ls methylcatechols catechol dimethylphenols cresols phenol trimethylbenzenes xylenes toluene benzene For the isomers an average of the rate coefficients has been used. For benzene an upper limit of k N3 = cm 3 s 1 has been used.

15 Rate coefficients for the reaction of Cl with catechols (relative kinetic technique at 298 K) compound reference k 1 /k 2 k 1 (10-10 cm 3 s -1 ) k 1 (average) (10-10 cm 3 s -1 ) H H ethene 3.8± ±0.1 isoprene 1.8± ±0.1 (6.6 ± 0.1) 1,2-dihydroxybenezene H H ethene 3.7± ±0.3 3-methyl-1,2- dihydroxybenzene H H CH 3 CH 3 4-methyl-1,2- dihydroxybenzene isoprene 2.1± ±0.7 ethene 3.1± ±0.8 (6.7 ± 0.8) (6.2 ± 0.8)

16 Dihydroxybenzene (catechol) H oxidation products (analysis with long path FTIR) H 2 / -H 2 o-benzoquinone abstraction + H 2 evidence for formation* H H H H ring-opening / other products C maleic anhydride addition H H H H observed H H 2 / -H 2 ther Products? -H / -H 2 H H H H H not formed Ipso H addition? An intermediate ketene absorption is observed (*4-methyl-ortho-benzoquinone identified in H + 4-methyl-1,2-dihydroxybenzene)

17 Dihydroxybenzene (catechol) H oxidation products Main observations: 1,2,3-trihydroxybenzene and 1,2,4-trihydroxybenzene not formed An intermediate infrared absorption due to a ketene group (-C=C=) is observed Infrared evidence for the formation of o-benzoquinone (and methylated derivatives) Positive identification of maleic anhydride (4-7%) (probable precursor butenedial) maleic anhydride Formation of C observed, yield increases with time, Detection of C shows ring opening is occurring maleic anyhdride may also indicate ring-opening Identification of 4-nitrocatechol

18 Dihydroxybenzene (catechol) H oxidation products (C and maleic anhydride) 0.25 maleic acid anhydride C maleic acid anhydride and C yield catechol

19 Photolysis of butenedials CH 3 ~20% C R 9-10% 0-18% (R=CH 3 ) 18-20% 0-10% (R=H) ~80% R R C H C From: Thüner, Rea and Wenger 4th EUPHRE Report 2001 R? Z-4-oxo-pent-2-enal system (R= CH 3 ) E-butendial system (R = H ) α-angelicalactone 31-35% (3H)-Furan-2-one 45-55% Maleic Anhydride 4-5% Maleic Anhydride 20-21% Unknown C= 20% Unknown C= 6-14%

20 Ketene and benzoquinone formation work on Cl + catechols has shown H-atom abstraction from an H group Is a major channels to ketene and benzoquinone formation H H H H H + Cl - HCl H 2 H 2 2 N N 2 2 H 2 2 N N 2 2 H 2 H H KETENE formation

21 Generation of phenoxy radicals H H H H CH + Cl H H N 2 N 2 + Cl main product

22 bservation of intermediate ketene absorptions Phenoxy radicals generated from benzaldehyde, phenol and catechol by reaction with Cl atoms a - Benzaldehyde reaction with Cl b - Catechol reaction with Cl c - Phenol reaction with Cl Initial dark Visible lamps Absorbance ketene (c) Wavelenght (cm -1 ) Absorbance ketene (b) Absorbance ketene (a) Phenol (ppm), Ketene (factor) Phenol (ppm) 0.2 Ketene (factor) HCl (ppm) C (ppm) Final dark Time (s) T 1/2 =90s HCl, C (ppm)

23 Ketene identity? H H H H Cl H H HCl H ring opening 2 + H 2 2-butene-1,4-diketene H C ring size reduction + H 1,4-cyclopentadienyl-5-ketene

24 Dihydroxybenzene (catechol) - N 3 reaction products (work 2006) H H H N 3 H + HN 3 N 2 nly observe 4-nitro-1,2-dihydroxybenzene and nitric acid as gas phase products No indication of other products in the residual infrared spectrum Aerosol is formed still to be quantified

25 Dihydroxybenzene (catechol) - N 3 reaction Mechanism? (work 2006) H H N 3 H 2N H -HN 3 H H H N 2 H H H N 2 2 N H

26 xidation of aromatics to nitrophenols CH 3 H/Nx H N 2 H H 3 C N 2 H CH 3 H CH 3 H H N 3 H CH 3 H H H H/Nx N 2 N 2 H Nitrophenol formation

27 Gas phas chemistry of nitrophenols Status up to 2005: nly a rate coefficient available for the reaction of H with 2-nitrophenol obtained by Zetzsch (1985 Report) using FP-RF Estimated rate coefficients for H with 3-, 4- and 5-methyl-2-nitrophenol Photolysis in solution was reported to be very slow

28 Plot of the kinetic data for the reaction of 3-methyl-2-nitrophenols (3M2N) with H radicals 0.3 H N 2 Ln([3M2N] t0 /[3M2N] t )-k (wall, hν) *t CH Ln([reference] t0 /[reference] t )/k H (reference)(10 12 cm -3 s) Data obtained at 1000 mbar total pressure of synthetic air by 298 K using with the relative kinetic technique and ( ) ethene as reference hydrocarbon

29 Rate coefficients for the reactions of H with 2-nitrophenols (NP) at 298 K obtained with the relative kinetic technique Compound k H (10-12 cm 3 s -1 ) k (literature) (10-12 cm 3 s -1 ) H N 2 NP ~ a H N 2 3M2NP (3.69±0.16) 11.2 b CH 3 H N 2 4M2NP (3.46±0.18) 5.38 b H CH 3 N 2 5M2NP (7.34±0.52) 11.2 b H 3 C H 3 C H N 2 6M2NP (2.70±0.17) - a) Zetzsch and coworkers using FP-RF; b) computer estimate by Meylan and Howard, Chemosphere, 1993, 26(12)

30 UV spectra of 2-nitrophenols

31 UV spectra of 3-methyl-2-nitrocresol 2.0E log10 (σ, cm 2 /molec -1 )( ) 1.6E E E E Absorbance ( ) 0.0E Wavelength (nm)

32 N 2 + hν Proposed nitrophenol atmospheric photolysis pathways H N + ( 3 P) (minimum energy 389 KJ mol-1 = threshold of 307 nm H H + N 2 (minimum energy 297 kj mol-1 = 403 nm) N 2 + H (minimum energy 362 kj mol-1 = 330 nm)

33 H-bonding in 2-nitrophenols H H N 2 + hν N + HN photolytic assisted H-atom transfer radical product + nitrous acid H N H N H N H N I I II III

34 Flow system used for study of nitrophenol photolysis alternative to FTIR LPAP (HN) Nx - monitor (N and N 2 ) optical cell FTIR (nitrocresols) excess nitrocresol source fan flowcontr. lamps lamps photoreactor heating system with temperature controlled syn. air, N 2, 2 Ar He

35 For Harvey (and others) LPAP (HN) instrument costs around EUR. More information can be found at:

36 Experiments on the photolysis of 2-nitrophenols (Bejan, et al., J. Phys. Chem. Chem. Phys., , ) HN [ppbv] HN 3M2N blank: lamps on lamps off nitrophenol source connected lamps on lamps off M2N [ppmv] :00 15:00 18:00 time [hh:mm] 0

37 Photolysis of 2-nitrophenols Extensive tests performed to test mechanism of HN formation Tested effects of: Number of photolysis lamps HN(large photoreactor) [ppbv] large photoreactor small photoreactor [HN] (large) = x [3M2N] [HN] (small) = x [3M2N] M2N [ppmv] HN(small photoreactor) [ppbv] Concentration of the nitrophenols 8 7 Change in surface to volume ratio Bath gas (Ar, N 2, 2, syn air) HN [ppbv] No. of lamps

38 Photolysis of 2-nitrophenols H N 2 CH 3 7 H HN [ppbv] H 3 C H N 2 H N 2 N ortho-nitrohydroxylated aromatic compounds [ppmv] CH 3 All observations are in line with a purely photolytic production of HN No formation of N 2 observed 2 is not only a quench gas but appears to be active in the mechanism

39 Photolysis of 2-nitrophenols 80 CH 3 nitrotoluene N 2 HN-formation [ppt ppm-1 s-1] H N 2 CH 3 3-Methyl-2- nitrophenol H N 2 2-Nitrophenol H 3 C H 5-Methyl-2- nitrophenol N 2 H CH 3 N 2 4-Methyl-2- nitrophenol HN formation rate (ppt ppm -1 s -1 ) from the different ortho-nitrohydroxylated monoaromatic compounds observed in the flow system.

40 Photolysis of 2-nitrophenols products + HN d)uni-molecular decomposition H N a) + hν b) + M 2 > N 2 > Ar > He H N * * H * c) energy transfer N II III III * e) + 2 Mechanism proposed to explain HN formation + HN (Bejan, et al., J. Phys. Chem. Chem. Phys., , ) products

41 Atmospheric lifetimes of 2-nitrophenols Approximate atmospheric lifetimes of the 2-nitrocresols with respect to photolysis and reaction with H radicals. compound 2-nitrophenol 3-methyl-2- nitrophenol 4-methyl-2- nitrophenol 5-methyl-2- nitrophenol τ hν (a) (min) ~ 25 min ~ 23 min ~ 44 min ~ 37 min τ H (b) 7.2 d ~ 47 h ~ 50 h ~ 24 h (a) Calculated for atmospheric conditions against J(N 2 ) (b) Daily average H = 1.6 x 10 6 cm-3 (Prinn et al., 1995).

42 Assuming 1 ppb total 2-nitrophenols in the atmosphere and a J(N 2 ) of 10-2 s -1 would support a gas phase HN product rate of 100 pptv/h

43 Time dependence of the aerosol size distribution measured during a typical photolysis experiment on 2-nitrophenol Background 5.0e+8 1.0e+9 1.5e+9 2.0e+9 2.5e+9 Lamps FF Dp, nm 150 Lamps N :48:00 20:08:00 20:28:00 20:48:00 21:08:00 Time Conversion of ver low concentrations (1 ppb) results in aerosol formation

44 Rate coefficients for the reactions of Cl atoms with 2-nitrophenol, methyl-2-nitrophenols and 2-chlorophenol at 298 K Compound k (cm 3 molecule -1 s -1 ) 2-nitrophenol (0.69 ± 0.02) 3-methyl-2-nitrophenol (14.97 ± 0.38) 4-methyl-2-nitrophenol (4.92 ± 0.03) 5-methyl-2-nitrophenol (2.13 ± 0.03) 6-methyl-2-nitrophenol (3.04 ± 0.07) 2-chlorophenol (0.63 ± 0.05)

45 THANKS FR LISTENING

46 Ketene identity? Absorbance (Base 10) Ketene formation from: 1. E,E-2-Methyl-2.4-hexadiendial UV-photolysis 2. E,E-2.4-hexadiendial UV-photolysis 3. E.Z-2,4-hexadiendial UV-photolysis 4. Benzene oxid-oxepin VIS-photolysis Z-oxopentenal UV-photolysis 6. Benzoloxid UV-photolysis 7. Catechol H/Nx system Wavenumber (cm -1 ) 4 7 6

47 Laboratory photolysis rates and steady-state H radical concentrations observed for 2-nitrophenols in a photoreactor. Compound 2-nitrophenol 3-methyl-2- nitrophenol 4-methyl-2- nitrophenol 5-methyl-2- nitrophenol Photolysis (a) (s -1 ) (1.5 ± 0.5) 10-4 (1.67 ± 0.11) 10-4 (8.86 ± 1.07) 10-5 (1.07 ± 0.14) 10-4 H concentration (cm -3 ) ~ ~ ~ ~ (a) Values for the photolysis rate obtained in the 1080 L quartz glass reactor. Lamps: Philips TL05 40W superactinic lamps, emit in the range nm and have a maximum intensity at 360 nm. Value for 2-nitrotoulene s -1 )

48 N H N H N N N N H H H H CC TC CT TT Matrix-isolation infrared spectroscopy in combination with density Function (DFT) calculations Identification of the aci-nitro form of 2-nitrophenol (Nagaya, Kudoh and Nakata, Chem. Phys. Letter, 2006, 427, 67-71) hν

49 H H H k(h) cm 3 molecule -1 s -1 k( 3 ) < not known cm 3 molecule -1 s -1 k(n 3 ) < cm 3 molecule -1 s -1 CH 3 CH 3 CH 3 H H k(h) cm 3 molecule -1 s -1 k( 3 ) < cm 3 molecule -1 s -1 k(n 3 ) cm 3 molecule -1 s -1 H

50 Primary oxidation products 1 H H 4 H H 2 hν H 13 2 H 14 bzw. 15 H H 2 2,N H N 2 H N N 2 H 2 H 2 H, 2 2 H 2 N N 2 2 H H 2 H 2 Recent quantification of dienedials by IFG and EUPHRE (Berndt and Böge, PCCP 2006, 8, )

51 Comparison of estimated atmospheric J-values for 2-nitrocresols with those measured by Bardini (2006) in the EUPHRE chamber, Valencia, Spain. 3.0E-04 Photolysis frequency (s -1 ) 2.0E E E+00 Bardini, M2N this study 4M2N 5M2N 6M2N

52 Dark, with chlorine VIS lamps ( nm ) Dark Nitrophenol, 2Cl-phenol, HCl(ppm Dark initial, without chlorine 2NitroPhenol 2ClPhenol HCl C ClN2 N ClN 2, C, N 2 (ppm) Time (s)

53 Comparison between the product spectrum obtained from the reaction of catechol with chlorine atoms with that from the reaction with H radicals. The lower trace is a spectrum of 4-nitrocatechol identified as product.

54 * C N 2 N 2 Formation of cyclopentadiene ketene from the phototransformation of 2-nitrophenol in aqueous solution (Alif et al., 1991)

55 Aerosol yields from the ozonolysis of dihydroxybenzenes (DHB) Reaction Mass catechol reacted (mg m3) Mass aerosol (mg m3) Aerosol yield (%) 1,2-DHB (cyclohexane) ,2-DHB (cyclohexane) ,2-DHB ,2-DHB ,2-DHB M-1,2-DHB (cyclohexane) M-1,2-DHB M-1,2-DHB (cyclohexane) M-1,2-DHB

56 (Benzene) Toluene + H Adduct (+ 2 ) (+ 2 ) (Phenol) Cresols Adducts- 2 (+ H) (+ N 3 ) N N 2 Catechol /Methylcatechols (+ H)? Nitrophenols (+ H) Ring Fragmentation Semi Volatile Products? Non Volatile Products Semi Volatile Products ther Products