Environ. Sci. Technol. 1900, 22, 1044-1048
Nitration of Acephenanthrylene under Simulated Atmospheric Conditions and in Solution and the Presence of Nitroacephenanthrylene(s) in Ambient Particles Barbara Zlelinska, * Janet Arey, Roger Atkinson, and Patricia A. McElroy
Statewide Air Pollution Research Center, University of California, Riverside, California 9252 1 H The nitration products resulting from the gas-phase reactions of acephenanthrylene with OH radicals in the presence of NO, and with N2O5 were studied in an environmental chamber. The nitroacephenanthrylenes formed from the OH radical initiated reaction were compared with those produced from solution-phase nitrations of acephenanthrylene with N204,N205,and the nitronium ion and shown to be isomers other than those formed in these solution-phase reactions. The more abundant nitroacephenanthrylene formed in the OH radical initiated reaction was observed in an ambient particulate sample, suggesting that it was formed from this atmospheric reaction of gas-phase acephenanthrylene.
Introduction Acephenanthrylene is a polycyclic aromatic hydrocarbon (PAH) of molecular weight (M,) 202, isomeric with fluoranthene and pyrene, and is similarly emitted from combustion sources (I). Prior to its synthesis, ace-
7
6
ACEPHENANTHRYLENE
7
6
FLUORANTHENE
6
5
PYRENE
phenanthrylene had been tentatively identified in several combustion emission sources (2-4) and ambient air (5). Recently, the presence of acephenanthrylene in ambient air particulate samples has been confirmed through comparisons of its gas chromatographic relative retention time with that of an authentic standard (6; see also below). The dominant nitroarenes observed in ambient particulate organic matter (POM) are 2-nitrofluoranthene and 1- and 2-nitropyrene, all of MI 247 (7-10). Lesser amounts of other nitrofluoranthenes and 4-nitropyrene (7,10-12), as well as a t least one other M , 247 nitroarene, are also observed in ambient air. It has been shown that the most abundant of these nitroarenes are formed from atmospheric reactions of gas-phase fluoranthene and pyrene (11, 13,14). Thus, it is now known that those PAH not containing cyclopenta-fused rings, such as fluoranthene and pyrene, when present in the gas phase will be removed from the atmosphere by reaction with the OH radical and, to a lesser extent, with N205(15-19), with these gas-phase reactions leading to the formation of nitroarenes (11,13, 14, 17,19,'20). Recently we have shown that acenaphthylene (a PAH of M , 152 containing a cyclopenta-fused ring) also reacts in the gas phase with O3 and the NO3 radical (with the NO3 radical reaction dominating over any N206reaction) (18). Thus, the major atmospheric reactions for acenaphthylene are with 03,NO3 radicals, and OH radicals, with the O3 and NO3 radical reactions, and a significant portion of the OH radical reaction, being postulated to proceed by initial addition to the double bond in the cyclopenta-fused ring (18). The atmospheric reactions of gaseous acephenanthrylene are expected to be analogous to those of acenaphthylene (18). 1044
Envlron. Sci. Technol., Vol. 22, No. 9, 1988
In this work we have investigated the nitroacephenanthrylenes formed from the gas-phase reactions of acephenanthrylene with the OH radical in the presence of NO, and with NO3 radicals and N205. Since the nitro products observed from the gas-phase reactions of fluoranthene and pyrene with the OH radical in the presence of NO, (10, 11, 19) and with N205 (10, 13, 14, 19) are isomers distinct from those formed by certain nitration reactions in solution, including electrophilic nitration (21), we also carried out the solution-phase nitration of acephenanthrylene with N204, N205, and the nitronium (NO,') ion for comparison with the gas-phase nitration products. The nitroacephenanthrylenes we observed from these reaction systems are compared with the MI 247 species in an ambient air sample. Experimental Section Collection and Analysis of Ambient POM. The ambient POM sample was collected a t El Camino Community College in Torrance, CA, on January 28, 1986, 0500-1700, with standard high-volume samplers. The sample collection, extraction, fractionation, and final gas chromatography/mass spectrometry (GC/MS) analysis for the M I 247 nitroarenes have been described in detail previously (9). Nitroacephenanthrylenes from Gas-Phase Reactions. The gas-phase reactions of acephenanthrylene with OH radicals, in the presence of NO,, and with NO3 radicals and/or N205were carried out in a 6400-L all-Teflon environmental chamber equipped with black light irradiation, as described previously (11). Fluoranthene-dlo was also included in these reaction mixtures to serve as a reference compound since we have previously investigated the OH radical and N206reactions of this PAH (11,13,14). To optimize the amounts of acephenanthrylene and fluoranthene-dIo present in the gas phase, they were introduced into the chamber by spraying a solution of these PAH ( 18 mg each) in 100 mL of methanol onto the chamber walls, followed by flushing the chamber with dry (55% relative humidity at room temperature) pure air to remove the methanol. The first exposures conducted were to OH radicals, which were generated in the chamber from the photolysis of methyl nitrite (at an initial concentration of -2.4 X 1014 molecules ~ m - in ~ )air at wavelengths >300 nm: CH30N0 + hv CH30 + NO CH30 + O2 HCHO + HO2 HOz + NO -.+OH + NO2
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Nitric oxide (also a t a concentration of -2.4 X 1014molecules ~ m - was ~ ) added to the reaction mixtures to avoid the formation of 03,and hence of NO3 radicals and N206. After the introduction and mixing of the reactants, the lights were turned on at the maximum intensity for 3.0 min. Sampling from the chamber volume onto a polyurethane foam (PUF) plug was started as soon as the lights were turned on and continued during the irradiation period, yielding an -4000-L gas sample. The chamber was
0013-938X/88/0922-1044$01.50/0
0 1988 American Chemical Society
NMR Chemical Shifts (ppm) for Acephenanthrylene and for Nitroacephenanthrylenes Produced Table 1. The 500-MHz from the Reactions of Acephenanthrylene with NzOd in CHzClz and Nz05in CClf
compound
H-1
H-2
H-3
H-4
H-5
H-6
H-7
H-8
H-9
H-10
8.41 (d) 7.7 (m) 7.7 (m) 7.12b (d) 7.22b (d) 8.01 (s) 8.02 (d) 7.62 (t) 7.7 (m) 8.66 (d) 4-nitroacephenanthrylene (peak l)c 8.41 (d) 7.84 (m) 8.57 (d) 8.44 (s) 8.10 (s) 8.12 (d) 7.72 (m) 7.84 (m) 8.72 (d) 5-nitroacephenanthrylene(peak 2)c 8.41 (d) 7.84 (m) 8.01 (d) 8.21 (s) 8.82 (s) 8.18 (d) 7.72 (m) 7.84 (m) 8.69 (d)
acephenanthr ylene
= singlet; d = doublet; m = multiplet; t = triplet. See Figure 3.
These chemical shifts were not unequivocally assigned; Le., they may be reversed.
then refilled and flushed for several hours with pure dry air, and a replicate experiment was carried out. Since N205is in equilibrium with NO3 radicals and NO2, addition of N206to the chamber exposed the fluoranthene-dlo and acephenanthrylene to N205and NOs radicals, with the N205/N03radical concentration ratio being lo3. Prior to beginying these N205/N03radical exposures, the chamber was flushed for several hours with pure dry air, and a chamber blank consisting of an -4000-L gas sample was collected onto a PUF plug. After refilling the chamber with pure dry air, N205(at an initial concentration of -2.4 x l O I 4 molecule cm-3 in the chamber) was added to the acephenanthrylene and fluoranthene-dloremaining in the chamber, and the reaction was allowed to proceed in the dark for 25 min before taking an -4000-L PUF plug sample. The PUF plug samples from each exposure and the chamber blank were individually Soxhlet extracted for -6 h with CH2C12,and the products were analyzed by highperformance liquid chromatography (HPLC) (Beckman Model 334 HPLC with Model 164 UV detector) and GC/MS with a Finnigan 3200 GC/MS interfaced to a Teknivent data system and a Hewlett-Packard 5970 mass selective detector (MSD), as described below. An internal standard (phenanthrene) was added to 10% of each extract, and fluoranthene-dlo,acephenanthrylene, and 2-nitrofluoranthene-dewere quantified on the basis of their UV absorptions at 254 nm with a Vydac 201TP5415 (4.6 mm X 15 cm) column with isocratic elution by acetonitrile/water (52%/48%) at a 1mL m i d flow rate. The remaining 90% of the extracts was fractionated on a semipreparative HPLC Altex Ultrasphere ODS column (methanol/water, 80%/20% at 3 mL min-l). The HPLC fractions in which the nitroarenes, if present, would elute were collected and analyzed with the Finnigan GC/MS in the electron impact mode (70 eV) using multiple ion detection (MID). The ions monitored were those typical of the M , 247 nitroarenes (7): m/z 247, [MI+; m/z 217, [M - NO]+;m/z 201, [M - NO2]+;m/z 200, [M - HN02]+;and m / z 189, [M - NO - CO]'. The corresponding molecular and fragment ions fdr the deuteriated species (M, 256) at 8 or 9 amu higher were also monitored. For chromatographic separation, a cool on-column injector and either a 30-m or 60-m DB-5 fused silica capillary column eluting directly into the ion source was used. The nitroarene product identifications were confirmed using a HewlettPackard 5890 GC (equipped with a 28-m DB-5 column) interfaced to the H P 5970 MSD operated in the scanning mode (40-300 amu). Nitroacephenanthrylenes from Solution-Phase Reactions. The reaction of acephenanthrylene with N205 in CCl., solution was carried out at 25 OC, as described previously (14), with an acephenanthrylene:N2O5molar ratio of unity. The nitroacephenanthrylene products were isolated from the reaction mixture (with an -20% yield) by chromatography on silica gel 60 (Merck) with CC14/ CH,C12 (90%/lo%) elution. The products were identified using the Finnigan GC/MS system described above in the
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RETENT ION TIME (mtn) Figure 1. GC/MS-MID trace of the molecular ion (mlz 202) of the fluoranthene (FL), acephenanthrylene (AC), and pyrene (PY) present in an ambient POM sample collected at Torrance, CA, on January 28, 1986 (0500-1700). GC conditions: 30 m DB-5 capillary COlurnn, programmed from 50 to 300 OC at 8 OC min-'.
scanning mode (40-400 amu) and by lH NMR, recorded with a General Electric GN500 500-MHz Fourier transform NMR spectrometer. The reaction of acephenanthrylene with N2O4 in CHzC12 solution was carried out as described by Radner (22), with methanesulfonic acid as a catalyst and a 30-min reaction time. The nitroacephenanthrylene products were isolated (with an -40% yield) and identified as described above. The reaction of acephenanthrylene with the NO2' ion was carried out by placing a single drop of a "03 (70%)/H2S04(90%)/H20(1:l:l v/v/v) mixture onto 100 pg of solid acephenanthrylene and heating the reaction mixture to 50-60 "C for -20 min. The nitroacephenanthrylene products were isolated by semipreparative HPLC, with a 1 cm X 25 cm Altex Ultrasphere ODS column eluted with methanol/water (85%/15%) at 2 mL min-l. Reagents. Acephenanthrylene was synthesized from acenaphthene according to a method described in the literature (23, 24) and was characterized on the basis of its melting point (140.5-141.5 "C), lH NMR spectrum (Table I), GC retention time, and mass spectrum (m/z 202, [MI+,loo%), all of which were in good agreement with the literature data (1, 24). N206was prepared from the gas-phase reaction of NO2 with 03,with collection of the product at -77 "C (25). Methyl nitrite was prepared as described by Taylor et al. (26). Fluoranthene-d,, (99.2%, MSD Isotopes) and acenaphthene (99%, Aldrich Chemical Co.) were used as received. N204 was of commercial grade (Matheson Inc.). All solvents were of HPLC grade (Burdick and Jackson, high purity). Results Ambient POM Analysis. Figure 1shows a GC/MSMID trace of the m/z 202 ion obtained from the analysis of the PAH-containing HPLC fraction of the extract of a Environ. Sci. Technol., Vol. 22, NO. 9, 1988
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m / z 247
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RELATIVE RETENTION TIME Flgure 3. GC/MS-MID traces of the molecular ions of the nitroacephenanthryienes ( m l r 247) and the nitrofiuoranthene-d, (NF-da) isomers (m/z 256) formed from (A) reaction of acephenanthryiene with N204in CH2C12solution; (B) reaction of acephenanthrylene with N20, in CCi4 solution; (C) and (D) gas-phase reactlon of acephenanthryiene and fluoranthene-d,, with the OH radical in the presence of NO,. GC conditions are as given in Figure 2.
fragment ion at m/z 217 was very low, as is the case for 2-nitrofluoranthene and 2-nitropyrene (9.1 Furthermore, this m/z 247 peak was also present in negative ion chemical ionization (NICIMS) (28) and negative ion atmospheric pressure ionization (NIAPIMS) (29) mass spectrometry analyses of this sample. Both of these ionization techniques are selective for nitroarenes, and these analyses confirmed that this peak has a molecular ion at m/z 247. Thus, NICIMS has been reported to give intense molecular ions which are generally the base peaks in the nitroarene spectra (30),and NIAPIMS is expected to give nitroarene spectra consisting solely of the molecular ion (12,31). Our evidence for suggesting that this peak is a nitroacephenanthrylene formed from the OH radical initiated reaction of acephenanthrylene is discussed below. Solution- a n d Gas-Phase Reactions of Acephenanthrylene. Figure 3 gives the ion chromatograms obtained from the GC/MS-MID analyses for the nitroacephenanthrylenes produced from the reaction of acephenanthrylene with N204in CH2C12solution (Figure 3A) and N206in CC14 solution (Figure 3B), showing that the same two nitroacephenanthrylenes (although in different relative abundances) were formed from these nitration reactions. The two isomers have very similar mass spectra, with the main peaks having the following mlz (re1 intensity) values: 247 (60%), [MI+;231 (lo%), [M - 01'; 217 (70%), [M - NO]+; 201 (40%), [M - NO2J'; 200 (60%), [M - HN02]+;and 189 (loo%), [M - NO - CO]'. These same two nitroacephenanthrylenes were also formed from the nitration of acephenanthrylene with the NOz' ion. The nitro products observed from the gas-phase reactions of acephenanthrylene and fluoranthene-dlo with OH radicals in the presence of NO, (carried out simultane1046
Environ. Sci. Technoi., Vol. 22, No. 9, 1988
ously) are shown in Figure 3C and D. The amount of 2-nitrofluoranthene-d9sampled from this reaction mixture was 5.5 pg, and it can be estimated from the abundances of the molecular ions shown in Figure 3C and D that the more abundant nitroacephenanthrylene (peak 3) was -25% of the 2-nitrofluoranthene-dg. The chamber blank PUF sample following the OH radical reactions contained no measurable amount of 2nitrofluoranthene-dg. The ratio of fluoranthene-dlo to acephenanthrylene in this blank sample was 2:l. The 30-min dark exposure of acephenanthrylene and fluoranthene-dlo to N205 resulted in 2.6 pg of 2-nitrofluoranthene-dg on the PUF plug sample and no detectable amount of nitroacephenanthrylene(s) (
