Ozonolysis of polycyclic aromatic hydrocarbons in participating solvents

Article abstract of DOI:10.1039/c6ra26248a

Seven polycyclic aromatic hydrocarbon (PAH) compounds that can be considered small models for graphene edges have been treated with ozone in solution. The presence of participating solvents such as water or methanol had a pronounced influence on conversion and identity of the functional groups formed, whereas the regioselectivity of the ozonation remained unaffected. Six previously unreported compounds have been isolated from the ozonolysis of pyrene 1, perylene 2 and benzo[e]pyrene 4. Comparison of the experimental data with calculated local ionization energy surfaces (IES) shows a good correlation, and indicates that this computational tool would be useful to predict the regioselectivity of ozone also for larger PAHs, including graphene and graphene nanoribbons.

Full text of DOI:10.1039/c6ra26248a

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PAPER
Ozonolysis of polycyclic aromatic hydrocarbons in
participating solvents†
Cite this: RSC Adv., 2017, 7, 6152
*
Anna Lundstedt, Matthew J. Webb and Helena Grennberg
Seven polycyclic aromatic hydrocarbon (PAH) compounds that can be considered small models for
graphene edges have been treated with ozone in solution. The presence of participating solvents such as
water or methanol had a pronounced influence on conversion and identity of the functional groups
formed, whereas the regioselectivity of the ozonation remained unaffected. Six previously unreported
compounds have been isolated from the ozonolysis of pyrene 1, perylene 2 and benzo[e]pyrene 4.
Comparison of the experimental data with calculated local ionization energy surfaces (IES) shows a good
correlation, and indicates that this computational tool would be useful to predict the regioselectivity of
ozone also for larger PAHs, including graphene and graphene nanoribbons.
Received 3rd November 2016
Accepted 23rd November 2016
DOI: 10.1039/c6ra26248a
www.rsc.org/advances
terminated graphene and graphene nanoribbons (GNRs) indi-
cates a great potential for selective edge functionalizations
Introduction
leading to chemical differentiation of graphene edges. Selective
functionalization of graphene is of interest both from a funda-
mental perspective as well as for application development.18,19
In order to evaluate and rationalize the inuence of the edge
structure1 seven different PAHs were chosen; pyrene (1), per-
ylene (2), benzo[a]pyrene (B[a]P, 3), benzo[e]pyrene (B[e]P, 4),
triphenylene (5), acenaphthylene (6) and anthracene (7)
(Chart 1). Between them, PAHs 1–7 represent the most common
edge motifs for graphene,20 namely; k region (armchair), bay
region (armchair), zigzag region and ve ring defect, in different
combinations. Pyrene 1 has k regions, perylene 2 has zigzag and
bay regions, B[a]P 3 has zigzag, k region and a bay region, B[e]P 4
has bay regions and a k region, triphenylene 5 has only bay
regions, acenaphthylene 6 has a ve ring with a localized double
bond and anthracene 7 has zigzag edges.
Polycyclic aromatic hydrocarbons (PAHs) constitute a group of
compounds of interest in many different elds such as organic
dyes, ligands for asymmetric catalysis, pharmaceuticals, agro-
chemicals and have the potential to be used as both organic
conductors or semiconductors,1–3 but also as models for gra-
phene and graphene nanoribbons (GNRs).4 In previous work in
our group, graphene on graphite and graphene on SiC was
treated with ozone under dry and aqueous conditions, and an
edge selectivity for the reaction is observed with introduction of
ether/phenolic components and ester/carboxylic groups,
leaving the bulk of the material unchanged.5–7 Calculations
show that the differences in thermodynamic reactivity between
the edges and the internal plane for graphene for cycloaddition
reactions are large, with reaction at internal positions leading to
signicantly less stable states than reaction at edge positions.8,9
PAHs are constructed of sp2 hybridized carbons in fused
aromatic motifs, and can therefore be referred to as the smallest
and most well-dened members of the nanographene family.
Several graphene edge motifs are readily available (Chart 1),
which opens for studies of structure-related reactivity and
regioselectivity using soluble models.
In organic synthesis, ozone is used for oxidative cleavage
(ozonolysis) of alkenes.10 Ozonation of PAHs, has been studied
in the context of oxidative degradation in the environment,11
but also in a more synthetic perspective.12,13 Reactions between
ozone and PAHs display regioselectivity as well as position-
dependent variations in which functional groups that are
formed.14–17 Extrapolating these observations to hydrogen-
Uppsala University, Uppsala, Sweden. E-mail: Helena.Grennberg@kemi.uu.se
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra26248a
Chart 1 Pyrene (1), perylene (2), benzo[a]pyrene (B[a]P, 3), benzo[e]
pyrene (B[e]P, 4), triphenylene (5), acenaphthylene (6) and anthracene
(7).
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Here, the regioselectivity of the reaction between PAHs and previously reported, NMR spectroscopy and MS. The structur-
ozone in setups that can be adapted also to suspensions of ally determined products are shown in Chart 2.
graphene, the types of functionalities obtained and their
dependence on edge structure and participatory solvents are
discussed and correlated to calculated local ionization energy
Results and discussion
Standard ozonolysis of PAHs
surfaces (IES) of the experimentally investigated PAHs.
The baseline experimental procedure, without any participating
ꢀ
Materials and methods
solvents, involved ozonation in dry dichloromethane at 20 C
with no additional reagents during the work up procedure. This
gave the mono-ozonides 1a and 4a as major products for pyrene
1 and B[e]P 4, both having k regions. The ozonolysis of perylene
2 lead to the generation of a black precipitate when the solvent
was removed. This black solid was not soluble in any of the
attempted solvents and are suspected to be a polymer (poly-
ozonide) similar to the polymer that are reported to form upon
treating acenaphthylene 6 with ozone.22 No perylene ozonide
was detected in the crude reaction mixture (of what was still
soluble). The soluble products was isolated using prep HPLC
and identied as unsaturated aldehyde 2a, carboxylic acid 2c
and aldehyde 2b from cleaving the inside of one of the bay
regions.
Ozone was generated by a corona discharge generator and
transported in a dioxygen gas stream to the relevant reaction
vessel (2 or 20 mL) via Teon tubing and a stainless steel
syringe. All the reactions were performed at 20 ꢀC and the
specied reaction time denotes the time that ozone was deliv-
ered to the vessel.
Ozonides can undergo thermal decomposition and to
minimize the risk, only small scale reactions (#0.1 mmol) were
performed and safety guidelines for working with peroxides
were followed.21 Dichloromethane was used as solvent since it is
ozone stable, dissolves PAHs 1–7 well and is a polar aprotic
solvent. In the reactions with water as participating solvent,
acetonitrile (which is ozone stable) was added to the mixture to
Triphenylene 5 was the most ozone-stable compound, but
with longer reaction times than for the other PAHs, it too was
eventually degraded but not to products in amounts detectable
by 1H NMR spectroscopy. For acenaphthylene 6, a white
precipitate formed during the reaction under dry conditions
and full conversion was very fast but no products were detected
support
a homogeneous solution. Dichloromethane and
methanol are miscible.
The overall conversion of starting material and the conver-
sion to products were determined by analyzing the crude reac-
tion mixtures by quantitative 1H NMR spectroscopy with 1,2-
dichloroethane as internal standard (qNMR). The results reveal
the formation of the initial products in the oxidative degener-
ation pathway for PAHs by ozone, as well as structure related
differences in reactivity. The major products for each condition
and PAH were isolated using preparative HPLC and structurally
determined using NMR spectroscopy and HRMS or, if
1
by H NMR spectroscopy. According to literature,22 this white
insoluble powder is a polyozonide. With B[a]P 3 a mixture of
1
many products was quickly obtained. Since, the H NMR spec-
trum was very crowded, the crude mixtures were not analyzed by
qNMR spectroscopy nor were any major products isolated (see
ESI, Fig. S4†). The difficulty of obtaining products in isolatable
amount by ozonolysis of B[a]P 3 have previously been noted by
Fieser23 though, isolated compounds, mainly different
quinones, have been reported in poor yields.17,24 Being highly
carcinogenic and not providing easily interpreted information,
B[a]P 3 was removed from further studies. Anthracene 7 was
reactive, and almost 90% reacted directly and the only detect-
able product by 1H NMR spectroscopy was anthraquinone 7a in
low amounts (15–16%).
Table 1 describes the conditions and results of the dry ozo-
nolysis of selected PAHs for which products were isolated and
characterized.
From these results, it can be proposed that when treating
defect-free graphene and GNRs with ozone under dry condi-
tions, there will be ozonides on the armchair edges and corners
and carbonyls that might tautomerize to phenols on the zigzag
edges. In previous study where ozone was reacted with graphite5
no ketones were observed, only phenols.
Ozonolysis of PAHs with water as participating solvent
Ozone can decompose in water resulting in a number of reactive
oxidative species (e.g. radicals).25 Water can also participate in
the reaction by trapping the carbonyl oxide intermediate
formed during ozonolysis yielding other ozonolysis
Chart 2 The products from ozonolysis of PAHs 1, 2, 4, 6 and 7 using
either water or methanol as participating solvents or under dry
conditions in DCM. The previously unreported compounds are 1d, 2a–
d, 4a.
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Table 1 Ozonolysis of compounds 1–2, 4–5 in dry DCM (0.025 mmol scale) or dry DCM-d2 (0.01 mmol scale) at 20 ꢀC. All conversions are from
quantitative 1H NMR spectroscopy with 1,2-DCE as internal standard and the error is 1%
Scale, mmol
V, mL
Ozone time, s
Substrate (conversion of %)
Product (conversion to %)
0.01
2
4
2/2
4
5
1 (40)
1 (80)
1 (91)
2 (95)
3
4 (40)
4 (88)
4 (98)
5 (29)
5 (54)
5 (63)
6
1a (41)
1a (77)
1a (73)
0.025
0.01/2a
0.025
25
+5
25
2a (12), 2b (2), 2c (12) + polyozonide
Too many products
4a (32)
0.01
2
4
2/2
2
4
5
0.025
0.01/2a
0.01
25
+5
15
50
+15
4a (71)
4a (73)
No detectableb product
No detectableb product
No detectableb product
Polyozonide
0.025
0.01/2a
2/2
0.01
0.01
2
2
5
+5
7 (88)
7 (90)
7a (15)
7a (16)
a
The 0.01 mmol scale experiments were performed by dissolving 0.01 mmol PAH in 2 mL DCM-d2, followed by ozone treatment and leaving the
sample for 30 min at 20 ꢀC, then half the sample was transferred to a NMR tube and 1,2-DCE was added and half was treated with as much ozone
b
again before it too was transferred to a NMR tube and 1,2-DCE added. No new peaks in the 1H NMR spectrum.
products such as aldehydes, ketones, carboxylic acids, oxy- the reaction. Anthracene 7 reacted the same way as for under
hydroperoxides than the ozonide.10,12,26,27
dry conditions, only with a bit lower conversion to 7a.
With water as the participating solvent the ozonolysis of the
Table 2 describes the conditions and results of the ozonol-
PAHs progressed in a similar fashion as without, the ozonide ysis of selected PAHs for which products were isolated and
was still the major product with pyrene 1 and B[e]P 4. From characterized when water was used as participating solvent.
pyrene 1 also the aldehyde 1e, the carboxylic acid 1d and the
Mono-ozonide 1a has been reported in yields between 23–
hydroxy ester 1b are obtained. From B[e]P 4 also the aldehyde 4b 52%, and the reduced mono-ozonide 1a (the dialdehyde) in
is obtained. From perylene 2 the same products are obtained as yields of 25–28% from reductive ozonolysis of pyrene 1.28–30
for dry conditions, the unsaturated aldehyde 2a, carboxylic acid Also tetraaldehyde 1e has been reported as products from the
2c and aldehyde 2b, and in the same low conversions. The black reductive ozonolysis of pyrene 1, in yields between 46–55%
precipitate was also obtained and again no ozonide was detec- (ref. 23 and 31–33) using common reductive work-up proce-
ted in the crude mixture. For B[a]P 3 and triphenylene 5 again dures and very similar ozonolysis procedures as for the mono-
no major products were isolated. For perylene 2 and acenaph- ozonide 1a and dialdehyde synthesis. Unlike the mono-
thylene 6 same results as observed from the experiments at dry ozonide 1a, the diozonide from ozonolysis of pyrene 1,
conditions were obtained, and precipitates are formed during which upon reduction would yield the tetraaldehyde 1e, is not
Table 2 Ozonolysis of compound 1–2, 4–6 in DCM : MeCN : water (0.025 mmol scale) or DCM-d2 : MeCN-d3 : D2O (0.01 mmol scale) at
20 ꢀC. All conversions are from quantitative 1H NMR spectroscopy with 1,2-DCE as internal standard and the error is 1%
Scale, mmol
V, mL
Ozone time, s
Substrate (conversion of %)
Product (conversion to %)
0.01
2
4
2/2
4
2
4
2/2
2
4
2/2
5
1 (35)
1 (85)
1 (94)
2 (90)
4 (36)
4 (83)
4 (92)
5 (24)
5 (46)
5 (60)
6
1a (22), 1b (11), 1d (<1), 1e (1)
1a (37), 1b (15), 1d (3), 1e (5)
1a (60), 1b (14), 1d (8), 1e (12)
2a (5), 2b (10), 2c (16)
4a (21), 4b (0), 4d (8)
4a (44), 4b (0), 4d (20)
4a (36), 4b (5), 4d (0)
No detectableb product
No detectableb product
No detectableb product
Polyozonide
0.025
0.01/2a
0.025
0.01
0.025
0.01/2a
0.01
25
+5
25
5
25
+5
15
50
+15
0.025
0.01/2a
0.01
0.01
2
2
5
+5
7 (87)
7 (90)
7a (10)
7a (11)
a
The 0.01 mmol scale experiments were performed by dissolving 0.01 mmol PAH in 2 mL DCM-d2, followed by ozone treatment and leaving the
sample for 30 min at 20 ꢀC, then half the sample was transferred to a NMR tube and 1,2-DCE was added and half was treated with as much ozone
b
again before it too was transferred to a NMR tube and 1,2-DCE added. No new peaks in the 1H NMR spectrum.
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to be found in the literature. Surprisingly, in our experiments the methoxy peroxide 6c was detected and now also the ozonide
neither the dialdehyde nor the diozonide from ozonolysis of 6a was obtained and only traces of white polymer precipitate
pyrene 1 was observed in the crude reaction mixture under any were observed. The mono-ozonide 6a was isolated as a white
conditions. An explanation for this discrepancy was found by solid using prep HPLC in 11% yield (qNMR conversion was 17%
Vollman et al.,24 who reported that ozonolysis of pyrene during to 6a). The peroxide 6c was detected in the crude 1H NMR
longer times gives the tetraaldehyde 1e upon reduction and spectrum, attempting to isolate it by preparative HPLC was not
shorter times the aldehyde–carboxylic acid (as 1b) upon red successful. Since this compound is known and its 1H NMR
work up of the mono-ozonide 1a. Here, no longer times were shis,27 qNMR of the crude spectrum could still be done and
attempted and all experiments were stopped before 100% a conversion of 40% to the methanol trapped peroxide 6c was
conversion of 1, explaining the lack of dialdehyde and di- obtained. Sugimoto et al.,27 reported yields of 13% of 6a and
ozonide.
66% of 6c at 0 ꢀC, and 7% 6a and 69% 6c at ꢁ70 ꢀC when
From these results, it can be proposed that when treating performing the ozonolysis of 6 in DCM : MeOH. Ozonolysis of 1
defect free graphene and GNRs with ozone and water, there will in DCM : MeOH, was also reported in that study, and at 0 C
ꢀ
be ozonides, aldehydes, hydroxy esters and carboxylic acids on with a 66% conversion of 1, they isolated ozonide 1a in 9% and
the armchair edges and corners and carbonyls that might tau- 1c in 35%. Anthracene 7 reacted the same way as for under dry
tomerize to phenols on the zigzag edges. Ozone can also conditions.
degrade in water, forming radical oxidative species,25 these
Table 3 describes the conditions and results of the ozonol-
radicals can also be expected to react. In this study with ozone ysis of selected PAHs for which products were isolated and
and PAHs, no products from degenerated ozone were observed characterized when methanol was used a participating solvent.
in the crude NMRs (when compared to NMR spectra predicted
in MestReNova 8.1.4).
From these results, it can be proposed that when treating
defect free graphene and GNRs with ozone and methanol, there
will be ozonides, aldehydes, methoxy esters and carboxylic acids
on the armchair edges and corners and carbonyls that might
tautomerize to phenols on the zigzag edges.
Ozonolysis of PAHs with methanol as participating solvent
When methanol is used as the participating solvent during
ozonolysis of the PAHs signicant variations on the standard
procedure were observed. Pyrene 1 and B[e]P 4 reacted at the
Edge structure–reactivity correlation of ozonolysis of PAHs
same position as without a participating solvent, however, the In summary, ozone reacts k regions (part of armchair edges) and
ozonides 1a and 4a were obtained in smaller amounts and were alkene ‘defect’ motifs, resulting in ozonides, aldehydes, esters
no longer the major product. Instead the methoxy ester 1c and and carboxcylic acids depending on reaction conditions (e.g.
4c from the acid degraded peroxide (degrading in the HPLC by solvents) when ozone reacts with zigzag motifs, ketones form
TFA buffer) were identied as the major products. For perylene regardless of conditions.
2, again the aldehyde 2b, saturated aldehyde 2a, carboxylic acid
Zigzag edges has been reported to be more reactive towards
2c were obtained, and also the acid-degenerated methanol oxidation than armchair edges.1 The acenes, a group of PAHs
trapped carbonyl oxide 2d is obtained in small amounts. The which are all linear and contain zigzag edges, have been re-
black precipitate from perylene 2 still formed. For triphenylene ported to be very reactive towards ozone. Ozone can undergo
5, still no major products were isolated. For acenaphthylene 6, electrophilic aromatic substitution (EAS) with zigzag edges and
Table 3 Ozonolysis of compound 1–2, 4–6 in DCM : MEOH (1 : 1, 0.025 mmol scale) or DCM-d2 : MeOD (1 : 1, 0.01 mmol scale) at 20 ꢀC. All
1
conversions are from quantitative H NMR spectroscopy with 1,2-DCE as internal standard and the error is 1%
Scale, mmol
V, mL
Ozone time, s
Substrate (conversion of %)
Product (conversion to %)
0.01
2
4
2/2
4
2
4
2/2
2
4
2/2
2
5
1 (38)
1 (78)
1 (88)
2 (92)
4 (38)
4 (78)
4 (92)
6 (100)
5 (24)
5 (48)
7 (85)
7 (86)
1a (9), 1c (22), 1e (0)
1a (18), 1c (29), 1e (0)
1a (19), 1c (30), 1e (10)
2a (8), 2b (3), 2c (12), 2d (4)
4a (4), 4b (0), 4c (11), 4d (0)
4a (16), 4b (0), 4c (37), 4d (6)
4a (12), 4b (10), 4c (36), 4d (0)
6a (8), 6c (20)
0.025
0.01/2a
0.025
0.01
0.025
0.01/2a
0.01
0.025
0.01/2a
0.01
25
+5
25
5
25
+5
15
50
+15
5
No detectableb product
No detectableb product
7a (17)
0.01
2
+5
7a (17)
a
The 0.01 mmol scale experiments were performed by dissolving 0.01 mmol PAH in 2 mL DCM-d2, followed by ozone treatment and leaving the
sample for 30 min at 20 ꢀC, then half the sample was transferred to a NMR tube and 1,2-DCE was added and half was treated with as much ozone
b
again before it too was transferred to a NMR tube and 1,2-DCE added. No new peaks in the 1H NMR spectrum.
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Fig. 1 PAHs 1–6 calculate local ionization energy (IE, in eV) surfaces. The values for the two-three lowest IE values for bonds (b) and atoms (a) are
shown. The brighter areas between two atoms are predicted to be more reactive toward oxidative addition. Property range: 9.0–9.4 eV. See ESI†
for all values.
both B[a]P 3 and anthracene 7 have been reported to yield the
quinones upon ozonolysis.15,17,24,34
Calculations of local IES for PAHs 1–7 was performed as
described by Brown and Cockro37 and the results compared to
Here, both B[a]P 3 and anthracene 7 was observed to be the experimental ndings (previous sections). Generally, the
very reactive towards ozone and from PAH 7, anthraquinone calculated local IES correlates well to the experimental results.
7a was observed. Pyrene 1 and B[e]P 4 (k region) have The major products from PAH 1, 4 and 6's were easily obtained
a similar reactivity towards ozone, triphenylene 5 (bay region) under the right conditions; all have one double bond that is
is less ozone reactive, and anthracene 7 (zigzag) is more clearly more reactive than the others. The major product from
reactive than 1 and 4. This corresponds nicely with the study perylene 2 was a polymer, possibly this formed from the initial
by Pryor et al.16 were the relative ozone reactivity of PAHs, product from ozone either adding to the bond with the lowest IE
including 1, 2, 5 and 7 in dichloromethane was investigated. value or substituted to the atom with the lowest IE value. B[a]P
The least reactive was PAH 5, followed by 1, 2, then 7 being 3, where many different products were observed, have four
the most reactive PAH.
different bonds with similar IE values, and a zigzag edge. This
For hydrogen-terminated graphene, ozonation could correlates well with the observation of many different products
possible lead to chemical differentiation of the edges which forming already at short reaction times. Triphenylene 5 has six
could be used for covalent stitching of graphene sheets and equal bonds with the same IE values and the observation of no
a study35 recently showed that the electron mobility of the major product, only slow degradation to many minor products
connection depends on how the edges of two graphene sheets is also in accordance with these calculations. Lastly, from
are connected (e.g. zigzag–zigzag or armchair–armchair etc.) as anthracene 7 the quinone 7a was the only identied product,
well as the entity connecting the sheets.
although the conversion of 7 was high.
PAHs 1–7 local IES are shown in Fig. 1, and the numbers are
the most reactive positions for EAS and oxidative addition.
Calculated local ionization energy surfaces
Both regiochemical and functional group outcome from the
ozone treatment will depend on if the ozone attaches to the
Conclusions
C]C bond (addition) or at a C atom (initial EAS) and ozone can Six previously unreported compounds have been isolated from
react with sp2 carbon motifs by both,10,34 although the preferred the ozonation of pyrene 1, perylene 2, benzo[e]pyrene 4.
route for alkenes is cycloaddition of the electrophilic ozone 1,3- Studying different PAHs reaction with ozone, calculated local
dipole.36
IESs and the literature indicate that ozone reacts with zigzag
Predicting reactivity for PAHs and possible also for larger regions forming ketones regardless of any co-reagents and with
systems (e.g. graphene and GNRs) are of importance for devel- the k region of the armchair edge, resulting in ozonide-, alde-
opment of safe and selective processes. Local ionization energy hyde-, carboxylic acid- or ester-groups depending on co-
surfaces (IES) is one computational tool, by which the most reagents. Ozone has a preference for zigzag edges over
nucleophile sites in PAHs can be predicted. Depending on the armchair edges. In practice, since ozone reacts with both, the
localization of the minimum, the likely reaction outcome will reaction time and relative abundance of the edge motif are key
either be electrophilic aromatic substitution (if the minimum is factors for achieving regioselectivity.
localized over an atom) or electrophilic addition (if the
minimum is localized between two atoms).37
The calculated local IESs correlates well against the experi-
mental results indicating that this computational tool can be
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used for predicting regioselectivity of ozone addition to larger
PAH systems e.g. hydrogen-terminated graphene and GNRs.
General procedure “small scale” (0.01 mmol) for quantitative
1H NMR spectroscopy
Stock solutions of PAHs 1, 2, 4 and 5 (0.1 mmol mlꢁ1) using
DCM-d2 as solvent were prepared and of internal standard 1,2-
DCE (20 mL in 4000 mL) using MeCN-d3 as solvent.
Experimental section
General
PAH stock solution (100.0 mL, 0.01 mmol), internal standard
stock solution (100 mL, 0.006 mmol 1,2-DCE) and deuturated
solvent (tot. 1800 mL of D2O, MeOD, DCM-d2 and/or MeCN-d3)
was added to the vial. The vial was sealed with a cap.
All reagents were commercially available and used without further
purication. NMR spectra were recorded on a Varian UNITY (1H at
399.97 MHz, 13C at 100.58 MHz) or a Varian INOVA (1H at 499.93
MHz, 13C at 125.71 MHz) spectrometer. The chemical shis are
reported using the residual solvent signal as an indirect reference
to TMS 1H: CHCl3: 7.26, acetone-d6: 2.05, DCM-d2: 5.32, MeCN-d3:
1.94 13C: CDCl3: 77.0. The vials used in all experiments were
heavy-walled glass Emrys process vials (2–5 mL) sealed with
aluminium crimp caps tted with a septum. Ozone generator
(Pilodist OGF 505) settings for all experiments were 5W, 0.25 bar,
0.5 L minꢁ1. See ESI† for HPLC UV traces and NMR spectra.
The cap was removed and the reaction mixture bubbled
ꢀ
through with ozone (PAH 1: 5 s, 4: 5 s, 5: 15 s) at 20 C. The
ꢀ
mixture was le at 20 C for 30 min and half the total volume
was transferred to an NMR tube. The mixture in the vial was
again bubbled through with ozone (1: 5 s, 4: 5 s, 5: 15 s) and le
to stand at 20 ꢀC for 30 min before being transferred to a NMR
tube. Reference samples for the internal standard were done for
all experiments, were O2 was used insted of O3. All NMR
samples were analyzed by 1H NMR spectroscopy with a d1 of
30 s.
Calibration of the quantitative 1H NMR spectroscopy method
Mixed stock solutions in vials with screw cap. Stored all stock
solutions in freezer until use. Stock solution A: weighted
20.0 mg pyrene into a 2 mL vial. Added 1000 mL DCM-d2 to the
vial, sonicated until all pyrene dissolved. Stock solution B:
added 3 ꢂ 1000 mL MeCN-d3 into a 4 mL vial (screw cap), added
10.0 mL 1,2-DCE. Stock solution C: added 4 mL MeCN-d3 into a 4
mL vial.
General procedure “medium scale” (0.025 mmol) for
quantitative H NMR spectroscopy
1
To a vial, PAH (0.025 mmol) was added, the vial was sealed with
a cap and solvents (tot 4 mL) was added via a syringe through
the cap. The reaction mixture was bubbled through with ozone
(PAH 1: 25 s, 2: 25 s, 4: 25 s 5: 50 s) at 20 ꢀC. The mixture was le
at 20 ꢀC for 30 min and the solvent was removed in vacu and any
isolated solid or liquid was re-dissolved in acetone-d6 (1 mL)
and 1,2-DCE as internal standard and analyzed by 1H NMR
spectroscopy with d1 ¼ 30 s.
Prepared samples. To ve (1–5) 4 mL vials, 2500 mL stock
solution C was added (500 mL per vial). Added 2500 mL of
stock solution B to vials 1–5 (500 mL per vial). Treated vial 1–3
with ozone at 20 ꢀC for 15 s per vial. Standing at 20 ꢀC for
10 min with cap on. Added 500 mL of stock solution A to vial
1–5 (100 mL per vial). The ve solutions were transferred to
General procedure “large scale” (0.1 mmol) for isolation of
products
1
NMR tubes and analyzed by H NMR spectroscopy with d1 ¼
30 s.
To a vial, PAH (0.1 mmol) was added, the vial was sealed with
a cap and solvents (total volume: 20 mL) was added via a syringe
through the cap. The reaction mixture was bubbled through
with ozone (1: 90 s, 2: 90 s, 3: 70 s, 4: 90 s 5: 300 s). The mixture
was le at 20 ꢀC for 1–2 hours and le in the freezer (ꢁ18 ꢀC) if
le over night or longer. The solvent was removed in vacu and
all isolated solid or liquid was re-dissolved in acetone-d6 (1.0
Setting internal standard integral (4H) to 400 resulted in
pyrene (4H) integral or pyrene (4H) + 1a (4H) integral values of:
1: 158 (140 + 18), 2: 157 (140 + 17), 3: 154 (138 + 16), 4: 154, 5: 156
(std dev 1%).
Acceptable inaccuracies for precise, accurate quantication
using qNMR are 2%.38
1
mL) and analyzed by H NMR spectroscopy.
Preparative HPLC
The solution was puried by preparative HPLC.
As solvents acetonitrile and water was used with 0.01% TFA.
For all mixtures the same conditions were used.
Additional procedures for the different conditions
1
Aer crude H NMR spectroscopy, the NMR solution was
Dry conditions. Dry DMC, vials dried in oven over night. SM
added upon taking them out of oven and capped, cooled down
under Ar(g).
injected in the prep HPLC. Injected volume: 600 mL,
collected volume: 5 mL, ow rate: 20 mL minꢁ1, gradient: 20
to 90 (MeCN) over 20 min, 15 min isocratic (90% MeCN), UV
detector: 254 nm, column: C18-PFP, 25 mm, 150 mm, 5 m,
Water as a co-solvent. DCM : MeCN : H2O (8 : 11 : 1).
Methanol as a co-solvent. DCM : MeOH (1 : 1).
˚
100 A. Removed solvent from collected fractions in vacu,
redissolved in 0.5 mL acetone-d6.
Characterization data for isolated compounds
Calculation of local ionization energy surfaces
From pyrene 1
The structures was optimized using B3LYP/6-311G(d) with
Monoozonide 1a. 1H NMR (500 MHz, acetone-d6) d 8.15 (d, J ¼
Gaussian 09 rev C.01 and Spartan 10. Local ionization energy 7.2 Hz, 2H), 7.98 (s, 2H), 7.85 (d, J ¼ 7.2 Hz, 2H), 7.73 (dd, J ¼
surfaces were calculated at the same level using Spartan 10.
7.2 Hz, 2H), 6.89 (s, 1H) ppm.
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13C NMR from HMBC (126 MHz, acetone) d 106.8, 128.5,
128.8, 130.8, 132.8, 135.6, 135.9, 136.4 ppm.
Methyl ester 2d. 1H NMR (500 MHz, acetone-d6) d 8.83 (d, J ¼
7.4 Hz, 1H), 8.77 (d, J ¼ 8.1 Hz, 1H), 8.69 (dd, J ¼ 7.4, 1.4 Hz,
1H), 8.50 (dd, J ¼ 8.1, 1.4 Hz, 1H), 8.29 (d, J ¼ 8.1 Hz, 1H), 7.95
(dd, J ¼ 8.1 Hz, 2H), 7.88 (dd, 1H), 7.58 (dd, J ¼ 7.4, 1.1 Hz, 1H),
3.98 (s, 3H) ppm.
Shis and assignments in accordance with literature.39
m/z [APCI+]: 251 (M+), 235, 236, 237, 205, 206, 207.
Hydroxy ester 1b. 1H NMR (500 MHz, acetone-d6) d 8.32 (d, J ¼
7.7 Hz, 2H), 8.14 (d, J ¼ 7.7 Hz, 2H), 7.97 (s, 2H), 7.86 (dd, J ¼
7.7 Hz, 2H), 7.41 (s, 1H), 6.79 (s, 1H) ppm.
13C NMR from HMBC (126 MHz, acetone) d 177.2, 165.5,
131.9, 131.1, 130.8, 130.7, 128.3, 126.2, 125.5, 124.7, 123.1,
123.0, 122.6, 122.6, 122.5, 121.4, 120.4, 119.9, 47.0, ppm.
m/z [APCI+]: 289 (M)+, 290, 291.
13C NMR from HMBC (126 MHz, acetone) d 95.8, 124.1,
124.3, 127.2, 127.5, 127.7, 129.7, 130.6, 132.2, 133.2, 133.5,
133.6, 134.6, 134.8, 137.0, 168.4.
HRMS [TOF MS ES+]: C19H12O3, calculated: 289.0865 found:
289.0871.
Shis and assignments in accordance with literature (except
the 7.41 PhCHOH shi in the 1H NMR spectrum which was
reported at 3.35 and mixed up with the PhCHOH shi at 6.79).40
m/z [APCI+]: 251 (M+), 252, 253.
From benzo[e]pyrene 4
Benzo[e]pyrene monoozonide 4a. H NMR (500 MHz, acetone-
1
d6) d 9.04 (dd, J ¼ 8.2, 1.5 Hz, 2H), 8.82 (dd, J ¼ 6.3, 3.3 Hz, 2H),
7.86 (dd, J ¼ 8.2, 1.5 Hz, 2H), 7.79 (dd, J ¼ 8.2, 7.2 Hz, 1H), 7.75
(dd, J ¼ 6.3, 3.3 Hz, 1H), 6.87 (s, 1H) ppm.
1
Methoxy ester 1c. H NMR (500 MHz, acetone-d6) d 8.39–8.31
(m, 2H), 8.17 (dd, J ¼ 7.9, 1.4 Hz, 1H), 8.02 (d, J ¼ 7.9 Hz, 1H),
7.99 (ds, 2H), 7.87 (dd + dd, J ¼ 22.3, 7.8 Hz, 2H), 6.40 (s, 1H),
3.79 (s, 3H) ppm.
13C NMR from HMBC (126 MHz, acetone) d 130.6, 127.0,
122.9, 122.2, 120.7, 130.6, 118.8, 124.6, 122.1, 100.4.
HRMS [TOF MS ES+]: C20H12O3, calculated: 301.0865 found:
301.0866.
Shis and assignments in accordance with literature.41
m/z [APCI+]: 265 (M+), 266, 267.
Trialdehydecarboxylic acid 1d. 1H NMR (500 MHz, acetone-d6)
d 9.74 (s, 2H), 9.68 (s, 1H), 8.41 (d, J ¼ 9.2 Hz, 1H), 8.26 (d, J ¼
7.7 Hz, 2H), 7.94–7.82 (m, 2H) ppm.
Benzo[e]pyrene dialdehyde 4b and benzo[e]pyrene acid-
1
degenerated water trapped carbonyl oxide 4c only as H NMR
spectra on crude products. Shis used for qNMR spectroscopy;
4b: 8.79, 8.68, 8.03, 6.16, 4c: 8.74, 7.92 6.20, 5.60, 3.79.
From acenaphthylene 6
m/z [APCI+]: 283 (M+), 282, 267, 265.
HRMS [TOF MS ES+]: C16H10O5, calculated: 283.0606, found:
283.0597.
Acenaphthylene monoozonide 6a. Isolated as a white solid
(4.5 mg, 11%) by preparative HPLC by following the general
procedure for larger scale, performing this in duplicates and
pooling the crudes prior to purication.
Tetraaldehyde 1e. 1H NMR (500 MHz, acetone-d6) d 9.78 (s,
4H), 8.35 (d, J ¼ 7.7 Hz, 4H), 7.98 (dd, J ¼ 7.7 Hz, 2H) ppm.
Shis and assignments in accordance with literature.31
m/z [APCI+]: 267(M+), 269.
1H NMR (500 MHz, acetone-d6) d 8.00 (dd, J ¼ 8.2, 1.2 Hz,
2H), 7.64 (dd, J ¼ 6.9, 1.2 Hz, 2H), 7.59 (dd, J ¼ 8.2, 6.9 Hz, 2H),
6.96 (s, 2H) ppm.
From perylene 2
Unsaturated aldehyde cis-2a. H NMR (500 MHz, acetone-d6)
1
Shis and assignments in accordance with literature.27
Acenaphthylene methoxyperoxide 6c. Not isolated. Used the
NMR literature values for the integration of the qNMR spectrum
of the crude product. 1H NMR: d 3.69 (s, 3H), 6.09 (s, 1H), 6.49 (s,
1H), 7.2–7.9 (m, 6H), 9.45 (s, 1H) ppm.27
d 9.92 (d, J ¼ 7.8 Hz, 1H), 8.86 (d, J ¼ 15.8 Hz, 1H), 8.81 (d, J ¼
7.3 Hz, 1H), 8.79 (d, J ¼ 7.8 Hz, 1H), 8.69 (dd, J ¼ 7.3, 1.3 Hz,
1H), 8.26 (d, J ¼ 7.6, 1H), 7.93 (td, J ¼ 7.6, 4.2 Hz, 2H), 7.85 (dd,
1H), 7.77 (d, J ¼ 7.5 Hz, 1H), 6.54 (dd, J ¼ 15.8, 7.8 Hz, 1H) ppm.
13C NMR from HMBC (126 MHz, acetone) d 194.2, 185.5,
155.2, 139.2, 138.5, 138.3, 136.0, 132.9, 131.5, 130.8, 130.3,
129.5, 129.3, 129.2, 128.1, 128.0, 127.5, 127.0, 126.6, 124.9 ppm.
m/z [APCI+]: 285 (M)+, 286, 287.
From anthracene 7
Anthraquinone 7a. Not isolated. Used the NMR values form
a bought sample of 7a for the integration of the qNMR spectrum
of the crude product. 1H NMR: d 7.81 (m, 4H), 8.32 (m, 4H) ppm.
HRMS [TOF MS ES+]: C20H12O2, calculated: 285.0916, found:
285.0910.
1
Aldehyde 2b. H NMR (500 MHz, acetone-d6) d 10.74 (s, 1H),
Conflict of interest
8.85 (dd, J ¼ 11.9, 8.2 Hz, 2H), 8.72 (dd, J ¼ 7.3, 1.2 Hz, 1H), 8.51
(dd, J ¼ 8.2, 1.2 Hz, 1H), 8.28 (d, J ¼ 8.2 Hz, 1H), 7.97 (dt, J ¼
14.0, 7.6 Hz, 2H), 7.87 (dd, J ¼ 7.9, 1H), 7.70 (dd, J ¼ 7.7, 1.1 Hz,
1H) ppm.
The authors declare no competing nancial interests.
Acknowledgements
m/z [APCI+]: 259 (M+), 260.
Carboxcylic acid 2c. 1H NMR (500 MHz, acetone-d6) d 8.80 (d, J
¼ 7.1 Hz, 1H), 8.72 (dd, J ¼ 8.2, 1.0 Hz, 1H), 8.66 (dd, J ¼ 7.3,
1.3 Hz, 1H), 8.46 (d, J ¼ 9.1 Hz, 1H), 8.25 (d, J ¼ 8.1 Hz, 1H), 7.91
(ddd, J ¼ 8.2, 7.4, 2.1 Hz, 2H), 7.85 (dd, ¼ 7.4, 1H), 7.58 (dd, J ¼
7.4, 1.0 Hz, 1H) ppm.
˚
The Swedish Research Council (Vetenskapsradet), the Uppsala
University KoF Priority Project on Graphene, and the Knut and
Alice Wallenberg Foundation (KAW graphene) for nancial
support.
m/z [APCI+]: 275 (M)+, 276, 277.
References
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