Microwave flash pyrolysis: C9h8 interconversions and dimerisations

Article abstract of DOI:10.1071/CH14238

The pyrolysis of 2-ethynyltoluene, indene, fluorene, and related compounds has been studied by sealed tube microwave flash pyrolysis (MFP), in concert with modelling of putative mechanistic pathways by density functional theory (DFT) computations. In the MFP technique, samples are admixed with graphite and subjected to intense microwave power (150-300 W) in a quartz reaction tube under a nitrogen atmosphere. The MFP reaction of 2-ethynyltoluene gave mostly indene, the product of a Roger Brown rearrangement (1,2-H shift to a vinylidene) followed by insertion. An additional product was chrysene, the likely result of hydrogen atom loss from indene followed by dimerisation. The intermediacy of dimeric bi-indene structures was supported by pyrolysis of bi-indene and by computational models. Benzo[a]anthracene and benzo[c]phenanthrene are minor products in these reactions. These are shown to arise from pyrolysis of chrysene under the same MFP conditions. MFP reaction of fluorene gave primarily bi-fluorene, bifluorenylidene, and dibenzochrysene, the latter derived from a known Stone-Wales rearrangement.

Full text of DOI:10.1071/CH14238

RESEARCH FRONT
CSIRO PUBLISHING
Aust. J. Chem. 2014, 67, 1301–1308
Full Paper
http://dx.doi.org/10.1071/CH14238
Microwave Flash Pyrolysis: C9H8 Interconversions
and Dimerisations
A
A
A
Aida Ajaz, Alicia C. Voukides, Katharine J. Cahill, Rajesh
A
A
A B
,
Thamatam, Sarah L. Skraba-Joiner, and Richard P. Johnson
A
Department of Chemistry, University of New Hampshire, Durham, NH 03857, USA.
Corresponding author. Email: richard.johnson@unh.edu
B
The pyrolysis of 2-ethynyltoluene, indene, fluorene, and related compounds has been studied by sealed tube microwave
flash pyrolysis (MFP), in concert with modelling of putative mechanistic pathways by density functional theory (DFT)
computations. In the MFP technique, samples are admixed with graphite and subjected to intense microwave power
(150–300 W) in a quartz reaction tube under a nitrogen atmosphere. The MFP reaction of 2-ethynyltoluene gave mostly
indene, the product of a Roger Brown rearrangement (1,2-H shift to a vinylidene) followed by insertion. An additional
product was chrysene, the likely result of hydrogen atom loss from indene followed by dimerisation. The intermediacy of
dimeric bi-indene structures was supported by pyrolysis of bi-indene and by computational models. Benzo[a]anthracene
and benzo[c]phenanthrene are minor products in these reactions. These are shown to arise from pyrolysis of chrysene
under the same MFP conditions. MFP reaction of fluorene gave primarily bi-fluorene, bifluorenylidene, and dibenzo-
chrysene, the latter derived from a known Stone–Wales rearrangement.
Manuscript received: 13 April 2014.
Manuscript accepted: 29 April 2014.
Published online: 12 June 2014.
Introduction
MFP appears to work because of localised high temperatures on
surfaces and is quite distinct from solution-phase microwave
reactions where microwave-specific effects are unlikely. Our
work built on many earlier examples of ‘graphite-sensitised’
microwave chemistry.[32,33] In our experience, MFP approaches
the environment of combustion – high temperature and mode-
rate concentrations of reactants – but without the oxygen. By
visualisation with a reaction camera, we find that most MFP
reactions glow brightly above ,50 W of power. Microwave-
induced solution phase pyrolysis has also been reported by
Wentrup and co-workers[34] while Kappe and co-workers
have recently reported a flow technique for pyrolysis in a
microwave.[35]
One important advance in the field of pyrolytic chemistry
was Brown’s demonstration in 1974 that a 13C label in pheny-
lacetylene (1, Scheme 1) is scrambled between C1 and C2 at
high temperature.[36] As Brown noted: ‘The simplest explana-
tion of these results is that at 7008C phenylacetylene is in
equilibrium with benzylidenecarbene because of ready migra-
tion of either hydrogen or phenyl and this leads to the observed
scrambling of the labely’. This process, now appropriately
known as the Roger Brown rearrangement, lies at the centre of
many high temperature syntheses and is often cited in combus-
tion mechanisms. We have provided evidence that 1,3-diynes
undergo carbon atom topomerisation by a more complex mech-
anism which involves closure of ethynylvinylidene to tria-
lene.[37] Vinylidenes exist in very shallow energy minima; the
most recent computational studies suggest a more complex
mechanism for the rearrangement in acetylene.[38–41] Brown
and his students reported many examples of this 1,2-shift
process, paving the route for future synthetic applications and
Pyrolysis is an ancient and venerable technique for organic
synthesis, with origins rooted in alchemy. Wo¨hler’s pyrolytic
synthesis of urea in 1828 was a turning point in the history of
chemistry.[1] Early experiments by organic chemists involved
static heating to high temperature or passage of vapours through
red-hot tubes constructed of porcelain, glass, or metal. In a
classic 1929 monograph that is rich with fascinating results,
Hurd summarised known pyrolytic transformations, which
included nearly every organic functional group.[2] Badger’s
group in Adelaide carried out early pyrolytic studies on the high
temperature generation of aromatic compounds, publishing
many papers on this topic between 1958 and 1967.[3–13]
Beginning around 1960, the technique of flow or ‘flash’ vacuum
pyrolysis (FVP) developed rapidly and has been widely applied
in synthesis.[14–20] This technique was first used by Roger
Brown and his co-workers in 1966[21,22] and later developed as a
powerful route to reactive intermediates.[16,18,23] Wentrup pro-
vides a thorough review of pyrolytic techniques in this issue.[24]
In FVP, the use of moderate to high vacuum favours unim-
olecular transformations. Of course combustion is one extreme
of pyrolysis. Although combustion is primarily destructive,
the well studied formation of soot and polycyclic aromatic
hydrocarbons (PAHs) as minor combustion products shows that
flames can also synthesise complex molecular structures
through bimolecular reactions.[25–30]
We recently introduced the technique of microwave flash
pyrolysis (MFP), showing that laboratory microwave reactors,
with a nominal temperature maximum of 3008C, can easily be
used for pyrolytic chemistry by heating solid-phase substrates
with graphite, carbon nanotubes, or other solid materials.[31]
Journal compilation Ó CSIRO 2014
www.publish.csiro.au/journals/ajc

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A. Ajaz et al.
Ph
H
•
FVP
FVP
Ph
•
H
H
•
Ph
ϭ
13C
or
•
700ЊC
0.05 mm
Ph
H
700ЊC
0.05 mm
1
•
H
720ЊC
0.05 mm
insertion
1,2-H
2
3
4
1,5-H
•
Ϫ2H2
dimerisation
5
6
chrysene
H
FVP
700ЊC
ϩ
and/or
8
7
9
10
11
Scheme 1. Examples of Roger Brown rearrangement (FVP: flash vacuum pyrolysis).
red-hot tube
4
6
700ЊC
4
6
12
13
14
ϪH
H
ϪH
ϪH
6
dimerisation
15
16
17
18
19
Scheme 2. Pyrolytic chemistry of indene.
recognition of its importance in combustion chemistry.[18] In
1974, Brown reported that indene (4) is the major product
(Scheme 1) from FVP of 2-ethynyltoluene (2).[36] The authors
proposed an initial 1,2-H shift to vinylidene 3, followed by C–H
bond insertion. They also reported a low yield (,1 %) of
chrysene (6); this was attributed to a 1,5-H shift to 5, followed
by dimerisation and thermal dehydrogenation to 6. Among other
early examples, Brown reported that pyrolysis of 7 yields 10 and
11. Although vinylidene 8 seems a likely intermediate, we have
shown that dehydropericyclic closure to cyclic allene 9 is also
energetically competitive.[42]
Interconversion of indene and isoindene (15) by a 1,5-hydrogen
shift has been studied in great detail.[44] Much less well known is
the thermal dimerisation of indene to chrysene (6), first reported
in 1893 (!) by Spilker.[45] In Spilker’s experiments, indene was
passed through a red-hot tube to yield primarily 6 as the isolated
product. Badger and Kimber reinvestigated this chemistry in
1960, reporting that gas phase pyrolysis of 4 at 7008C and
atmospheric pressure gives primarily 6, along with smaller
amounts of 12, 13, and 14.[11] They postulated that 4 undergoes
C–C bond dissociation to diradicals, which dimerise. This
mechanism was later supported by 14C labelling, although the
technology of that era left much ambiguity about product
identities and location of the isotopic label.[46] More recently,
The high temperature thermal chemistry of indene (4,
Scheme 2) is part of the well explored C9H8 potential surface.[43]

Microwave Flash Pyrolysis
1303
4
49 %
6
11 %
12
4 %
MW/graphite
300 C/50 W
Њ
2 min
2
20
2
21
2 %
2 %
28 %
1 %
14
3 %
13
Scheme 3. Microwave flash pyrolysis results for 2-ethynyltoluene (2).
MW/graphite
300ЊC/50 W
20
3 %
12
2 %
4
6
19 %
4
76 %
13 Ͻ2 %
14
Ͻ1 %
MW/graphite
4
48 %
6 8 %
300ЊC/50 W
12 4 % 20 40 %
20
Scheme 4. Microwave (MW) flash pyrolysis studies on indene and indan.
the pyrolysis of 1,3-cyclopentadiene[47–49] and indene[50–53]
have been investigated in the context of combustion chemistry
where they are believed to be intermediates; considerable
support has evolved for a radical dimerisation mechanism which
is preceded by C–H bond dissociation steps. High temperature
dimerisation of cyclopentadiene yields naphthalene. In the case
of indene, dimerisation of radical 16 to 17 would be followed by
hydrogen atom loss and a sequence of cyclopropycarbinyl
radical rearrangements which eventually forms radical 19 and
then 6. Pyrolysis in medium pressure flow systems yielded
products similar to those described by Badger four decades
earlier.[11] Lu and Mulholland proposed a dimerisation route
from 16 to 19 (Scheme 2).[54]
microwave power over 1 to 5 min.[31] The tube was extracted
with pentane or dichloromethane; products were identified by
1H NMR spectroscopy and/or capillary gas chromatography
(GC). Scheme 3 shows a typical product distribution, normal-
ised for unreacted starting material. The product distribution
depended on microwave power, time, and substrate-to-graphite
ratio, but the main products in this reaction were always indene
and chrysene, with the proportion of the latter greatly enhanced
over those observed by Brown from FVP. Minor products 20
and 21 are ascribed to hydrogen transfer reactions. Naphthalene
has been noted earlier as a product of indene pyrolysis and may
arise from addition of a carbon atom – origin unknown – to
indene or more likely through fragmentation during the dimer-
isation mechanism. The ratio of chrysene (6) and its isomers,
benzo[a]anthracene (13) and benzo[c]phenanthrene (14) was
,71 : 23 : 6 by NMR analysis. This is similar to earlier reports
by Badger from indene pyrolysis.[11]
As expected from earlier reported results,[11,54] the MFP
reaction of pure indene (Scheme 4) yielded primarily chrysene,
along with smaller amounts of naphthalene, indan, and chrysene
isomers. The MFP reaction of indan (20) to low conversion
yielded primarily indene and chrysene. This result supports the
facility of dehydrogenation under our reaction conditions.
In these reactions, we did not see evidence for the expected
dimer 17. To support the existence of a dimerisation pathway,
we prepared 1,10-bi-indene (17) by a previously described
route[55] and studied its chemistry. The MFP reaction of 17
In the present study, we have investigated the pyrolytic
chemistry of 2-ethynyltoluene, indene, fluorene, and related
compounds by sealed tube MFP, in concert with modelling of
putative mechanistic pathways by density functional theory
(DFT) computations.
Experimental Studies on C8H9 Isomers
We initially explored the closed vessel MFP of 2 using
powdered graphite as a thermal sensitiser. As described earlier,
these experiments were carried out in nitrogen-purged tubes,
with use of a quartz tube placed inside standard Pyrex reaction
tubes.[31] In typical experiments, admixed substrate and sen-
sitiser (weight ratio 2–10) were subjected to 50–150 W of

1304
A. Ajaz et al.
MW/graphite
150 W
17
4
66 %
3 %
12
22 19 %
(1) n-BuLi
(2) CuCl2
20
11 %
Ͻ1 %
6
4
Scheme 5. Microwave (MW) flash pyrolysis studies on bi-indene.
H
phenyl migration
TS1
MW/graphite
55.0
[57.3]
2
300 W
3 min
3
0 kcal molϪ1
45.3
[44.8]
7
13 7.5 %
[0 kcal molϪ1
]
14 0.5 %
TS2
43.7
40.5
Scheme 6. Microwave (MW) flash pyrolysis studies on chrysene.
54.9
[60.4]
insertion
60.4]
54.8 [
1,5-H shift
TS4
TS3
hydrogen migration
yielded the products shown in Scheme 5, all identified by high
field 1H NMR analysis of the crude product mixture. No 17 was
recovered. Indene is clearly the product of homolysis and
hydrogen atom scavenging, while 22 presumably arises from
two 1,5-H atom shifts. Chrysene is also present but the dominant
reaction is fragmentation to indene; this does not permit us to
determine unequivocally that 6 arises directly from 17.
The origin of chrysene isomers 13 and 14 in these reactions is
problematic and has required previous authors to propose
unusual mechanistic routes. We wondered whether these
might be secondary products from isomerisation of chrysene.
The MFP reaction of pure chrysene (Scheme 6) reproducibly
resulted in low conversions into 13 and 14, as confirmed by
NMR analysis. Given the demonstrated facility of hydrogen
atom transfer in these mixtures, we believe these reactions are
catalysed by hydrogen atom addition and rearrangement.
Hydrogen atom catalysed isomerisation of azulene to naphtha-
lene has been reported by Alder[56]and there are other cases of
radical-catalysed Stone–Wales rearrangement.[57,58] Badger
described the pyrolytic interconversion of anthracene[5] and
phenanthrene[6] by vapour phase pyrolysis at moderate pre-
ssure. Although purely thermal isomerisation is rare,[59] we
believe that arene skeletal isomerisations are common in high
temperature hydrogen atom rich environments.
•
TS6
[63.9]
TS7
43.6 [51.2]
1,2-H shift
57.9
closure
4
5
23
34.1
[38.5]
Ϫ26.6 [Ϫ19.4]
23.6 [23.2]
46.2 [50.4]
electrocyclic
ring opening
11.1 [19.4]
1,5-H shift
TS5
TS8
22
24
Ϫ5.5 [2.4]
2.4 [7.5]
Scheme 7. B3LYP/6–311þG(d,p) energies and, in boldface, free energies
at 898 K for thermal rearrangements of o-ethynyltoluene.
must also occur but do not appear to be chemically productive
under these conditions. Our computations thus show two ener-
getically competitive routes to indene from alkyne 2.
The DFT potential surface connecting bi-indene (18) with
chrysene is summarised in Scheme 8. Dimerisation of indenyl
radical 16 to 17 is followed by hydrogen atom loss and a series of
cyclopropylcarbinyl radical rearrangements.[60] The largest bar-
rier along this path is ring opening of 25. A similar profile has
been predicted for dimerisation of 1,3-cyclopentadiene and
formation of naphthalene.[61]
Computational Studies
We used density functional methods to characterise potential
reaction mechanisms. Our B3LYP/6–311þG(d,p) computa-
tional results on the C9H8 reaction surface are summarised in
Scheme 7. Boldfaced numbers represent free energies calcu-
lated at 898 K. Vinylidene 3 is accessible by either phenyl or
hydrogen migration (TS1 or TS2, respectively) with the latter
clearly the lower energy pathway. A surprisingly high barrier
(TS4) for vinylidene insertion into the benzylic ortho-methyl
group slows the route to indene and allows a 1,5-shift (TS3) to
become energetically competitive. As a consequence, ortho-
xylallene (5) provides an alternative route to indene by closure
(TS6) to carbene 23. Interconversions with isomers 22 and 24
Pyrolysis of Fluorene
Fluorene (28) is also a likely intermediate in combustion
chemistry[30] but its reaction pathways have not been closely
analysed. Following several early studies in which only rubicene
(32) was characterised,[62,63] Lang and co-workers investigated
the hot-tube pyrolysis of fluorene in 1961.[64] Products identi-
fied by UV spectroscopy included bi-fluorenylidene (30),
dibenzochrysene (31), and rubicene (32).[64] We examined the

Microwave Flash Pyrolysis
1305
35.5
TS10
TS9
16.5
TS12
TS11
16.1
15.0
ϪH
6
15.1
17
8.5
ϪH
3.5
H
H
18
H
0 kcal molϪ1
25
H
27
H
26
Scheme 8. B3LYL/6–31G(d) results for the bi-indene to chrysene pathway.
19
Ϫ11.3
MW/graphite
150 W
1 min
28
32
31
4.6 % conversion
29
30
0.5 %
1 %
3 %
0.1 %
28
30
31
32
MW/graphite
150 W
0.5 min
43 %
6 % 34 %
1 %
91 % conversion
33
34
29
5 %
0.5 %
MW/graphite
28
31
32
33
34
150 W
1 min
1 % 22 % 0.5 %
2 %
0.5 %
26 % conversion
30
Scheme 9. Microwave (MW) flash pyrolysis results for fluorene and its dimers.
MFP reaction of 28 and find clear evidence for the expected
dimerisation route. Conversions were kept low to minimise
secondary chemistry; product ratios from high field NMR
analysis are shown in Scheme 9. The products were identified by
MFP reaction of bi-fluorenylidene (30)[74] yielded primarily
dibenzochrysene. Our results support a mechanism in which
reversible dimerisation of a fluorenyl radical to 29 is followed
by dehydrogenation to 30 and then Stone–Wales rearrangement
to 31. Under the reaction conditions, radical catalysis seems
likely. Secondary cyclisation to 33 and 34 is also observed and
might be further optimised.
1
comparison to reported H NMR spectra of the known com-
1
pounds.[65–72] The major products observed by high field H
NMR analysis of the crude reaction mixture are 29, 30, and 31.
When the reaction is run at lower power (100 W), 29 and 30 are
the major products; this clearly supports a radical dimerisation
mechanism. At higher power (150 W), 31 becomes the major
product and small amounts of rubicene (32) are present as well.
The conversion of 30 into 31 is one of the few known examples
of a Stone–Wales rearrangement[57,58,73] and may also proceed
here by free radical catalysis. Independent pyrolysis of bi-
fluorene (29) led to a rapid reaction, yielding primarily fluorene,
in addition to 30 and 31. Smaller amounts of 32, 33, and 34 could
also be seen in the NMR spectra of the product mixture. Finally,
Conclusions
MFP with graphite[31] provides an alternative to the FVP
methods developed over many years by Roger Brown[16,18,23]
and others.[14–20,24] The use of graphite in microwave reactions
was demonstrated earlier by Laporterie;[33] we find that apply-
ing higher microwave power moves graphite from a thermal
sensitiser to an effective medium for pyrolysis. This microwave
technique is applicable to both volatile and non-volatile sub-
strates and effectively contains all reaction products in a closed

1306
A. Ajaz et al.
tube. One important difference in MFP is the higher effective
concentration of reactants, which favours bimolecular reaction.
Brown first showed that pyrolysis of 2-ethynyltoluene gives
indene, an early example of the reaction named after him.[36]
Our computational models fully support the intermediacy of a
vinylidene intermediate in this reaction but also suggest a sec-
ond pathway through 1,5-sigmatropic shift and ring closure of
o-xylallene (5, Scheme 7). Formation of chrysene is clearly due
to initial formation of indene; dimerisation is a minor process in
FVP but becomes important at higher reactant concentration. It
is astonishing that the thermal dimerisation of indene has now
been known for 121 years![11,45] Computations reported here
support a radical dimerisation pathway and are consistent with
recent proposals by Lu and Mulholland based on related com-
bustion mechanisms.[54] We have shown for the first time that
minor isomers of chrysene, 13 and 14, may arise from a sec-
ondary isomerisation. Further work on arene isomerisations is in
progress. In this series, the pyrolysis of fluorene yields the
clearest evidence for radical dimerisation, with direct observa-
tion of the initial product 29.
spectroscopy and capillary GC. The product consisted of indan
(3 %), indene (76 %), naphthalene (2 %), and chrysene (19 %).
Small amounts of isomers benzo[a]anthracene (13) and benzo
[c]phenanthrene (14) were also seen by NMR spectroscopy.
MFP of 1,1-Bi-indene (17)
Bi-indene (17, 46 mg) and graphite (106 mg) were pyrolysed as
described above. Pyrolysis was carried out using dynamic power
(150 W) for 1 min. 1H NMR and capillary GC analysis showed
the products to be indene (4, 66 %), 3,30-bi-indene (22, 19 %),
naphthalene (12, 3 %), chrysene (7, 11 %), and indan (20,
,1 %). Spectroscopic data for bi-indene isomers 17 and 22
were in agreement with literature values.[55]
MFP of Indan (20)
Indan (20, 30 mg, 0.25 mmol) and graphite (153 mg) were mixed
and pyrolysed as above at 3008C (50 W) for 5 min. The crude
mixture was extracted with dichloromethane, filtered through
neutral alumina, and concentrated to yield 26 mg of oil. Capil-
lary GC analysis showed the following product distribution:
indene (4, 48 %), naphthalene (12, 4 %), chrysene (6, 8 %), and
starting material (30 %).
Experimental
Computational Methods
MFP of Chrysene (7)
All calculations were carried out with Gaussian or Spartan.
Structures were optimised and characterised by frequency
analysis at the B3LYP/6–311þG(d,p) or B3LYP/6–31G(d)
level of theory. Unscaled zero point corrections were applied
to DFT energies.
Caution: To minimise risks of explosion or ruptured reaction
vessels, microwave pyrolysis experiments should be carried out
using quartz reaction tubes and with nitrogen purging before
pyrolysis.
Chrysene (50 mg, 0.22 mmol) and graphite (250 mg) were
mixed by light grinding. Pyrolysis was carried out using fixed
power (300 W) for 3 min. The crude product mixture was fil-
tered through a silica plug using chloroform. 1H NMR integra-
tion indicated chrysene (6, 92 %), benzo[a]anthracene (13,
7.5 %), and benzo[c]phenanthrene (14, 0.5 %).
MFP of Fluorene (28)
Fluorene (50 mg) and graphite (70 mg) were mixed by light
grinding. Pyrolysis was carried out using fixed power (100 W)
for 1 min. The crude product mixture was filtered over a
silica plug using chloroform. 1H NMR analysis indicated
95.4 % of fluorene remaining, with 0.5 % bi-fluorene (29), 1 %
bi-fluorenylidene (30), 3 % dibenzo[g,p]chrysene (31), and
0.1 % rubicene (32). Longer runs showed decreasing pro-
portions of 30, and an increase in 31. All products 29–34
were identified by comparison to known spectra from the
literature.[65–68,71,72]
MFP of 2-Ethynyltoluene (2)
In a typical experiment, 2-ethynyltoluene (2, 30 mg, 0.26 mmol)
was mixed with graphite (50 mg, Aldrich synthetic graphite, 20
microns) by light grinding and then transferred to a quartz tube
(12 ꢀ 70 mm). A small plug of glass wool was placed above the
graphite. The quartz tube was inserted into a Pyrex microwave
reaction tube, purged with nitrogen, and sealed. The pyrolysis
was run in a CEM microwave reactor at 3008C (50 W) for 1–
5 min hold time. After cooling, the crude product mixture was
extracted with dichloromethane, filtered through a small plug of
neutral alumina, and carefully concentrated. Mass recovery was
,50 % in all cases. The product mixture was analysed by a
combination of capillary GC and 400 MHz 1H NMR spectros-
copy. In a typical run held for 2 min at maximum temperature,
GC analysis showed the following: starting alkyne (28 %), 2-
vinyl toluene (2 %), indan (2 %), indene (49 %), naphthalene
(4 %), and chrysene (11 %). NMR analysis further revealed
chrysene isomers benzo[a]anthracene (13, ,3 %) and benzo[c]
MFP of Bi-fluorene (29)
Bi-fluorene (30 mg) and graphite (100 mg) were mixed by light
grinding. Pyrolysis was carried out using fixed power (150 W)
for 30 s. The crude product mixture was filtered over a silica
plug using chloroform. 1H NMR intergration indicated 9 % bi-
fluorene (29), 43 % fluorene (28), 6 % bi-fluorenylidene (30),
34 % dibenzo[g,p]chrysene (31), 1 % rubicene (37), 5 % benz[e]
indeno[1,2,3-h,i]acephenanthrylene (33), and 2 % benz[p]
indeno[1,2,3,4-d,e,f,g]chrysene (34).
1
phenanthrene (14, ,1 %) as determined by H NMR analysis.
These were identified by comparison to known spectra in the
literature.[41,42]
MFP of Bi-fluorenylidene (30)
Bi-fluorenylidene (50 mg) and graphite (100 mg) were mixed by
light grinding. Pyrolysis was carried out using fixed power
(150 W) for 1 min. The crude product mixture was filtered over a
MFP of Indene (4)
Indene (4, 30 mg, 0.26 mmol) was mixed with graphite (150 mg)
by light grinding and pyrolysed as above at 3008C (50 W) for
5 min. After cooling, the crude product mixture was extracted
with dichloromethane, filtered through neutral alumina, and
1
silica plug using chloroform. H NMR integration indicated
74 % bi-fluoreneylidene (30) remaining, 1 % fluorene (28),
22 % dibenzo[g,p]chrysene (31), 0.5 % rubicene (32), 2 % 33,
and 0.5 % 34.
1
concentrated. The crude mixture was analysed by H NMR

Microwave Flash Pyrolysis
1307
Supplementary Material
[28] M. Frenklach, Phys. Chem. Chem. Phys. 2002, 4, 2028. doi:10.1039/
B110045A
[29] H. Richter, J. B. Howard, Pror. Energy Combust. Sci. 2000, 26, 565.
doi:10.1016/S0360-1285(00)00009-5
[30] V. V. Kislov, A. I. Sadovnikov, A. M. Mebel, J. Phys. Chem. A 2013,
117, 4794. doi:10.1021/JP402481Y
Z-matrices or Cartesian coordinates and summary energetics for
stationary points from computations and selected NMR spectra
from pyrolysis are available on the Journal’s website.
Acknowledgements
[31] H. Y. Cho, A. Ajaz, D. Himali, P. A. Waske, R. P. Johnson, J. Org.
Chem. 2009, 74, 4137. doi:10.1021/JO900245V
[32] T. Besson, V. Thiery, J. Dubac, in Microwaves in Organic Synthesis,
2nd edn (Ed. A. Loupy) 2006, Ch. 9, pp. 416–455 (Wiley-
VCH: Weinheim).
The authors are grateful for support from the National Science Foundation
(CHE-9616388) and to Professor Curt Wentrup for the kind invitation to
submit an article for this special issue honoring Professor Roger Brown. This
research used the Extreme Science and Engineering Discovery Environment
(XSEDE), supported by NSF Grant No. OCI-1053575.
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