Solar driven uphill conversion of dicyclopentadiene to cyclopentadiene: An important synthon for energy systems and fine chemicals

Article abstract of DOI:10.1039/c4ra09599e

The retro Diels-Alder conversion of endo-dicyclopentadiene to cyclopentadiene (Cp)-which is thermodynamically uphill under ambient conditions (ΔG = +9.7 kcal mol^-1; values based on computation at 273 K following CBS-QB3 methodology)-was carried out at 175-190 °C in neat state using solar energy. The reaction is thermodynamically favorable at elevated temperature. Considering heat release from the reverse reaction (ΔH = -23.4 kcal mol^-1), the energy storage efficiency was computed to be ca. 5.5% with respect to the IR component in concentrated solar radiation. Solar energy was further utilized for preparation of a model 2,5-norbornadiene derivative (75% isolated yield) through the cycloaddition reaction of Cp with 4-phenylbut-3-yn-2-one at 150-185 °C. The norbornadiene-quadricyclane system has been proposed for solar energy storage, and its solar assisted synthesis would help reduce its carbon footprint over its life cycle. Norbornadiene synthesis using solar energy may also be of interest for greener processing of fuels derived from this compound. Cookson's cage ketone, which too has been proposed as an energy storage medium, was additionally synthesized from the Diels-Alder adduct of Cp and p-benzoquinone employing concentrated solar photo-thermochemical conditions. The reaction proceeded rapidly (15 min) and gave the desired product in 96% isolated yield. Besides the above applications, Cp is an important synthon in the preparation of fine chemicals.

Full text of DOI:10.1039/c4ra09599e

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PAPER
Solar driven uphill conversion of dicyclopentadiene
to cyclopentadiene: an important synthon for
energy systems and fine chemicals†
Cite this: RSC Adv., 2014, 4, 54558
Milan Dinda,a Supratim Chakraborty,a Mrinal Kanti Si,a Supravat Samanta,a
b
ab
Bishwajit Ganguly,ab Subarna Maiti and Pushpito K. Ghosh
*
*
The retro Diels–Alder conversion of endo-dicyclopentadiene to cyclopentadiene (Cp) – which is
thermodynamically uphill under ambient conditions (DG values based on
+9.7 kcal molꢀ1
¼
;
computation at 273 K following CBS-QB3 methodology) – was carried out at 175–190 ꢁC in neat state
using solar energy. The reaction is thermodynamically favorable at elevated temperature. Considering
heat release from the reverse reaction (DH ¼ ꢀ23.4 kcal molꢀ1), the energy storage efficiency was
computed to be ca. 5.5% with respect to the IR component in concentrated solar radiation. Solar energy
was further utilized for preparation of a model 2,5-norbornadiene derivative (75% isolated yield) through
the cycloaddition reaction of Cp with 4-phenylbut-3-yn-2-one at 150–185 ꢁC. The norbornadiene–
quadricyclane system has been proposed for solar energy storage, and its solar assisted synthesis would
help reduce its carbon footprint over its life cycle. Norbornadiene synthesis using solar energy may also
be of interest for greener processing of fuels derived from this compound. Cookson's cage ketone,
which too has been proposed as an energy storage medium, was additionally synthesized from the
Diels–Alder adduct of Cp and p-benzoquinone employing concentrated solar photo-thermochemical
conditions. The reaction proceeded rapidly (15 min) and gave the desired product in 96% isolated yield.
Besides the above applications, Cp is an important synthon in the preparation of fine chemicals.
Received 1st September 2014
Accepted 14th October 2014
DOI: 10.1039/c4ra09599e
www.rsc.org/advances
required in the process poses the challenge of cost-effective
reactor design besides the signicant problem of higher levels
1. Introduction
of reradiation. Many other solar thermochemical schemes
based on inorganic chemicals have also been proposed for
energy storage but these too are high temperature processes for
the most part.6 Schemes operating at relatively lower tempera-
tures have also been investigated, for example the thermal
dehydration of inorganic hydroxides such as Ca(OH)2, which
can release heat on rehydration.7
Organic systems are also reported for energy storage. In
particular, photochemical conversion of 2,5-norbornadiene (1)
to quadricyclane (2) (eqn (1)) has been studied extensively.8 DH
for the process was reported to be 21.4 kcal molꢀ1.9 Solar energy
is not an ideal light source for the reaction since photons in the
ultraviolet region are required. However, efforts have been
made to employ sensitizers that extend the absorption to longer
wavelengths.10 2 can interconvert thermally to 1 releasing the
strain energy as usable heat, and studies are reported on
substituent effects to maximize the harvesting of solar energy in
this manner.11 1 has also been employed for the preparation of a
missile fuel.12 The process involved synthesis of the endo–endo
homodimer (3), followed by its acid-catalyzed isomerization at
elevated temperature to the fuel, 4 (eqn (2)). The fuel reportedly
has a density of 1.02 g mLꢀ1, caloric value of 160 000 BTU
Storage of solar energy in the form of chemical energy is of
profound importance. A much sought aer goal is the splitting
of water into hydrogen and oxygen.1,2 Photoelectrolytic conver-
sion in a system wherein amorphous FeOOH was coupled to an
amorphous Si solar cell reportedly gave an efficiency of 4.3% in
a recent study.3 Solar thermochemical splitting of water is also
of interest. Starting with its splitting on a zirconia surface at
temperatures exceeding 2500 K, several improvements have
been realized over the years through a two-step approach
involving reduction and reoxidation of suitable metal oxides.4
An important advance made recently is the development of an
isothermal water splitting route employing the hercynite cycle
based on cobalt ferrite, which overcomes the drawbacksꢁ of
temperature swing.5 However, the high temperature (1350 C)
aAcademy of Scientic & Innovative Research, CSIR-CSMCRI premises, G. B. Marg,
Bhavnagar 364 002, India. E-mail: pushpitokghosh@gmail.com
bCentral Salt and Marine Chemicals Research Institute, Council of Scientic &
Industrial Research, G. B. Marg, Bhavnagar 364 002, India. E-mail: smaiti@csmcri.
org; Fax: +91-278-2567562
† Electronic supplementary information (ESI) available: Analytical data; NMR,
FT-IR and HR-MS data of some selective compounds. See DOI:
10.1039/c4ra09599e
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gallonꢀ1, and freezing temperature below ꢀ45 ꢁC, making it preparation of heterocycles.18 The present work reports the solar
well suited for the intended application.
driven synthesis of Cp from 5. Solar assisted preparation of
Cookson's cage ketone and a compound akin to 1 from Cp is
also reported. Production of energy systems in this manner
would reduce the overall carbon footprint, providing the moti-
vation for this study.
(1)
(2)
2. Experimental section
2.1. Materials and methods
All reagents were of commercial grade and puried according to
established procedure. 1H and 13C NMR were recorded in CDCl3
with TMS as the internal standard using Model BrukerAvance II
spectrometer. FT-IR spectra were recorded in KBr using Perkin
Elmer spectrometer. Melting point was recorded using Mettler
Toledo instrument and the data were uncorrected.
The preparation of 1
(eqn (3)).13
̲ involves the use of cyclopentadiene (Cp)
2.2. Temperature and weather related measurements
The thermal imager used for temperature proling was TESTO
876. It gave the temperature distribution on the surface of the
round bottom ask and condenser assembly. It had a wide
angle lens with 32ꢁ ꢂ 23ꢁ eld of vision. The thermal sensitivity
of this device was < 80 mK at 30 ꢁC. The spectral range was 8–14
mm and it could measure the range of temperature from 0ꢁ to
280 ꢁC. The accuracy of the instrument was ꢃ2 ꢁC. A micro-
controller based automatic weather station with data logging
facility was used to capture the weather data during the course
of the experiment. Global radiation was measured on CM4
pyranometer having spectral range of 305–2800 nm and
nominal sensitivity of 15 mV Wmꢀ2. Diffused and infrared
radiation were measured using a CMP22 pyranometer with
shaded ring and CGR4 pyrgeometer (4500–42 000 nm spectral
range), respectively. Air temperature in the weather station was
recorded with a digital sensor having measurement range of
ꢀ40 to 123.8 ꢁC. A 3 cup anemometer measured the wind speed
and had the range of measurement from 5 kph to 200 kph. The
sensing was done by a reed switch/magnet and provided 1 pulse
per rotation. The wind direction was sensed using a magnetic
Hall Effect sensor having range 360ꢁ (zero dead band). The
accuracy was ꢃ0.3 to 0.5 % of signal range. The wind direction
was considered in terms of angle with respect to the North
direction, measured clockwise. The air pressure sensor was a
barometer of piezo-resistive silicon membrane type having
range of measurement as 0.150 Bar to 1.15 Bar. The temperature
at the focus of the parabolic dish was determined by K-type
(3)
Cp, in turn, is obtained from endo-dicyclopentadiene (5)
through a retro Diels–Alder reaction at elevated temperature
(eqn (4)).
(4)
The kinetics of the forward reaction of eqn (4) was investi-
gated by Khambata and Wassermann.14 Studies were carried out
at atmospheric pressure in the temperature range of 50–175 ꢁC,
both in paraffin solution and in pure liquid state. The non-
exponential factor of the velocity coefficient was found to be
of the same order of magnitude (4 ꢂ 1013 sꢀ1) as the interatomic
vibrational frequency, leading the authors to propose a unim-
olecular reaction pathway. The rate constant, k, in paraffin
solution was estimated to be 4.8 ꢂ 10ꢀ5, 7.2 ꢂ 10ꢀ4 and 8.0 ꢂ
10ꢀ3 minꢀ1 at 120, 145 and 175 ꢁC, respectively, and the values
were similar for neat liquid. Practical conversion rates are thus
ꢁ
feasible only for T $ 175 C. The DH of the process has been
estimated to be 21.4 kcal molꢀ1 experimentally.15 The rate
constant, k, of the reverse reaction of eqn (4) has been computed
to be 2.71 ꢂ 10ꢀ4, 5.84 ꢂ 10ꢀ3 and 6.75 ꢂ 10ꢀ2 L molꢀ1 minꢀ1
at 40, 80 and 120 ꢁC, respectively.16 The moderately good kinetic
stability of Cp at lower temperatures makes it amenable to
storage.
ꢁ
thermocouple of ꢃ0.5 C accuracy.
2.3. Computational method
Full geometrical optimizations were carried out in the gas phase
employing the complete basis set CBS-QB3 method at the
temperature 273 K, unless mentioned otherwise.19,20 Frequency
calculations were performed at the same level of theory to
conrm that each stationary point is a local minimum with zero
imaginary frequency. DG and DH of reactions were computed by
complete basis set CBS-QB3 method. All calculations were per-
formed with Gaussian 09 suite of programmes.21
Solar photo-thermochemical C(sp3)–H bromination, con-
ducted efficiently in a specially designed reactor, was reported
by us recently.17a The scope of the reaction was expanded
subsequently to include the solar syntheses of more complex
organic molecules such as 2,5-oxazole derivatives from simple
building blocks.17b Several publications also reported the
application of similar solar thermochemical reactions for the
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2.4. Solar mediated retro Diels–Alder reaction of 5
3. Results and discussion
The retro Diels–Alder reaction of 5 was carried out using a solar
parabolic dish concentrator with geometrical concentration
ratio of 20 X (Fig. S1†). Experiments were conducted during
11.15 am to 2.15 pm on a typical sunny day in March. Details of
the concentrator and ambient conditions on the day of the
experiment are provided under Section S1 of ESI.† 500 g of 5 was
charged into a 1 L RB ask placed at the focus of the dish. A PV
panel was used to operate a pump to circulate cool water
through a condenser to facilitate condensation of Cp. The
distillate was collected in a 250 mL RB ask placed inside an ice
bag. It was stored in the refrigerator and used as required.
CBS-QB3 method was employed to calculate the changes in DH
and DG of the various reactions considered in the present study.
The data are compiled in Table 1. The method was tested
initially for the formation of quadricyclane from norborna-
diene. The calculated DH of 22.8 kcal molꢀ1 was in good
agreement with the experimental DH value of 21.4 kcal molꢀ1
reported for this process.9 The free energy of reaction was
computed to be 22.7 kcal molꢀ1. The reaction of eqn (4) was
studied next. The computed DH of 23.4 kcal molꢀ1 at 273 K was
again in good agreement with the experimentally determined
value of 21.4 kcal molꢀ1
. Corresponding value of DG was 9.7
15
kcal molꢀ1. The computed DG reduced to 2.0 kcal molꢀ1 at 423
K (Table 1), suggesting that the equilibrium of eqn (4) moves to
the right at higher temperature, in line with the reported
observations. Since the values of DH were similar at 273 K and
423 K, the shi in DG is due to changes in the TDS term in the
free energy equation (DG ¼ DH ꢀ TDS). This term would be
expected to increase with temperature on account of the posi-
tive DS expected from the cracking of one molecule of 5 into two
molecules of Cp.
2.5. Solar mediated synthesis of 1-(3-phenylbicyclo [2.2.1]
hepta-2,5-dien-2-yl) ethanone (7) (see eqn (5))
An offset parabola of concentration ratio 59 X (Fig. S2†) was
employed for the synthesis and the reaction was conducted over
5.5 h (10.00 am to 3.30 pm) on a typical day in March. Details of
the concentrator and ambient conditions on the day of the
experiment are provided in Section S1.† 0.46 g of Cp prepared
above was added along with 1 g of 4-phenylbut-3-yn-2-one (6)
and 15 mL of diphenyl ether (solvent) into a 25 mL single neck
RB ask. The ask was placed at the focal point of the
concentrator which served as source of thermal energy. The
reaction temperature over the reaction period was in the range
of 150–185 ꢁC. Aer termination of the reaction the contents
were charged on a silica gel column and eluted with 5% ethyl
acetate in hexane. 1.1 g (75% isolated yield) of pure 7 was
obtained. 1H NMR (500 MHz, CDCl3) d 7.36–7.35 (d, 2H), 7.33–
7.31 (m, 1H), 7.29–7.28 (d, 2H), 6.98 (s, 1H), 6.88 (s, 1H), 4.09 (s,
1H), 3.77 (s, 1H), 1.99 (s, 3H); 13C NMR (125 MHz, CDCl3) d
196.5, 166.5, 149.4, 143.7, 141.2, 137.0, 128.5, 127.1, 70.3, 59.3,
52.2, 29.1; IR (in KBr, cmꢀ1) 3435, 2931, 2362, 1651, 1443, 1359,
1237, 1022, 759, 699; HRMS (ESI): found 211.1135 (calcd for
Drawing on the kinetics data reported earlier on the retro
Diels–Alder reaction of 5,14 the parabolic dish of Fig. S1† was
designed and fabricated to achieve 175 ꢁC # T # 200 ꢁC under
peak insolation condition (850–1000 W mꢀ2) prevailing in the
summer months in the western part of India. Initially, the
reactor assembly of Fig. S1(A)† was taken, and entries 1 and 2
in Table 2 provide data for experiments conducted on
cracking of 5 on two separate sunny days during March 2014.
The second set of data were taken for further analysis.
Fig. S3(A)† provides data on global insolation, ambient
temperature and temperature in the reaction zone during
10.00 am to 2.00 pm on the day of the experiment pertaining
to entry 2, Table 2. Other weather related data are presented
in Table S1.† The reaction temperature rose gradually from
11.15 am to 12.00 noon and thereaer remained in the range
of 175–190 ꢁC. A thermal image recorded during this period is
shown in Fig. 1. The total volume of Cp collected over 3 h was
154 mL which worked out to an average hourly collection of
51.3 mL hꢀ1 (Table 2). Although hour-wise data were not
collected, the output was highest during 12.30 pm to 1.00 pm.
Based on the collector aperture area (1.83 m2) and average
global insolation (857 W mꢀ2) during the duration of the
experiment, the total energy captured by the parabolic dish
was 1344 kcal hꢀ1. However, the energy available at the
reaction zone was only 5142 kcal hꢀ1 based on pyranometer
reading of the concentrated radiation. This was ascribed to
C
15H14O [M + H], 211.1123).
2.6. Solar mediated synthesis of pentacyclo-
[5.4.0.02,6.03,10.05,9]undecan-8, 11-dione(9) from8 (see eqn (6)).
8 was prepared as a yellow crystalline solid from solar generated
Cp and benzoquinone following literature procedure.22 1 g of 8
was taken in 10 mL of ethyl acetate and placed in a quartz RB
ask positioned at the focus of an 8ꢂ parabolic dish.17a 9 was
obtained as a brown solid (m.p. 240 ꢁC) in 96% yield within 15
min. The reaction temperature was ca. 90 ꢁC. 1H NMR (500
MHz, CDCl3) d 3.18 (s, 2H), 2.94 (s, 2H), 2.82 (d, 2H), 2.71 (s, 2H),
2.06–2.04 (d, 1H), 1.90–1.88 (d, 1H); 13C NMR (125 MHz, CDCl3):
d 212.1, 54.7, 44.6, 43.7, 40.4, 38.7; IR (in KBr, cmꢀ1) 3448, 2990,
2930, 2868, 1753, 1728, 1454, 1267, 1224, 1191, 1056, 966, 911,
860, 823, 755, 600, 525, 453. Observed mass (M + H) 174.96,
calculated mass (M + H) 175.08.
the following reasons: (i) diffuse radiation (ca. 100 W mꢀ2
)
was not concentrated and (ii) there were considerable
reection losses during concentration. Further, in the
experiment as conducted using a glass RB ask, heating
would have been effected mainly by the infrared component
(4500–42 000 nm) in the concentrated radiation. This
component was estimated to be 2424 kcal hꢀ1 based on
measurement of IR intensity in the solar insolation. Taking
Note: safety precautions must be taken while performing
experiments with concentrated solar radiation.
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Table 1 Free energy and enthalpy values of substrates and products computed by CBS-QB3 method, along with data on free energy and
enthalpy changes for reactions of interesta
G (ꢂ10ꢀ3
H (ꢂ10ꢀ3
DG
DH
Compounds
kcal molꢀ1
)
kcal molꢀ1
)
Reaction and remarks
(kcal molꢀ1
)
(kcal molꢀ1
)
ꢀ170.037
ꢀ170.018
(1)
+22.8
+22.9
light-driven thermodynamically uphill conversion
ꢀ170.014
ꢀ169.995
(2)
ꢀ121.572
ꢀ121.582b
ꢀ121.554
ꢀ121.551b
+9.7
+23.4
(Cp)
ꢀ243.153
ꢀ243.166b
ꢀ243.131
ꢀ243.125b
+2.0b
+23.0b
solar thermal driven thermodynamically uphill conversion
(5)
ꢀ48.446
ꢀ121.572
ꢀ48.433
ꢀ121.554
Cp
ꢀ19.2
ꢀ19.7
ꢀ31.3
ꢀ35.0
ꢀ170.037
ꢀ288.82
ꢀ170.018
ꢀ288.793
solar thermal mediated thermodynamically spontaneous reaction
(1)
(6)
ꢀ410.411
ꢀ410.381
solar thermal mediated thermodynamically spontaneous reaction
(7)
ꢀ360.599
ꢀ360.607
ꢀ360.573
ꢀ360.584
(8)
ꢀ8.1
ꢀ10.4
solar photon-mediated thermodynamically spontaneous reaction
(9)
a
b
Unless otherwise stated all calculations were at 273 K. Calculations at 423 K.
the computed DH of 23.4 kcal molꢀ1 for the forward reaction 2.97% [energy storage efficiency (%) ¼ (heat output from
of eqn (4), the re-formation of endo-dicyclopentadiene from dimerization of Cp)/(energy supply by concentrated IR radi-
51.3 mL of Cp (specic gravity ¼ 0.8) would release 7.27 kcal ation incident on the reactor) ꢂ 100] for the experiment of
of heat, corresponding to an energy storage efficiency of entry 2, Table 2. To improve the capture of the solar radiation
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Table 2 Retro Diels–Alder reaction of 5 undertaken using the para-
bolic dish concentrator in Fig. S1
(5)
Entry
no.
Amount of 5 Amount of Cp Yield/
Time period
charged/mL
collected/mL
mL hꢀ1
1a
2b
3c
12.30 pm–2.00 pm 500
11.15 am–2.15 pm 500
12.30 pm–1.30 pm 500
60
154
94.8
40.0
51.3
94.8
The reaction temperature could be maintained in the
range of 150–185 ꢁC during the peak insolation period of
10.00 am to 3.30 pm (5.5 h) (Fig. S4†). In view of the small
scale (1 g of 6) at which the reaction was undertaken, the
solvent volume could not be optimized as a minimum reac-
tion volume had to be maintained. 7 was isolated from the
crude reaction mixture in 75% yield through column chro-
matographic separation. The reaction of eqn (5) is thermo-
dynamically favored (DH ¼ ꢀ34.7 kcal molꢀ1; DG ¼ ꢀ19.7
kcal molꢀ1) (Table 1), and the role of solar thermal energy was
mainly to overcome the activation barrier. Although product
isolation in the reaction with the model substrate was
through chromatographic separation, a more practical solu-
1 March, 2014. b 3 March, 2014. c 30 September, 2014.
a
tion would be required in
a commercial process. As
mentioned above, the ultimate aim is the preparation of 2,5-
norbornadiene (eqn (3)) which has a boiling point of 89.5 ꢁC.
It can thus be isolated through fractional distillation, leaving
ꢁ
behind the high boiling diphenyl ether solvent (b.p. 258 C)
Fig. 1 Thermal image recorded during solar driven retro Diels–Alder
reaction of 5 (entry 2, Table 2) using a parabolic dish having 20ꢂ
concentration ratio.
for recycle. Further, even if some dicyclopentadiene were to
form in the reaction from the dimerization of Cp, it can be
cracked at a temperature well below the boiling point of the
solvent to regenerate and recover Cp.
Another application of Cp in the context of energy is toward
synthesis of Cookson's cage ketone, 9.22 The Diels–Alder adduct
of Cp and benzoquinone, 8, which was formed spontaneously in
crystalline form in 94.2% yield at room temperature, was con-
verted rapidly (15 min) under neat condition into 9 through
solar driven [2 + 2] photo-cycloaddition (eqn (6)).22 Conversion
under photochemical conditions in the laboratory using arti-
cial light source seemingly takes much longer,23 indicating that
the concentrated solar radiation used in the present study was
benecial. Cookson's cage ketone can be employed for solar
energy storage, as reported for the cyclic scheme of eqn (7).22
and to reduce heat losses, the RB ask was painted black and
inserted in a wooden box with transparent bottom and other
interiors of the box painted black, as shown in Fig. S1(B).† An
experiment conducted on 30 September, 2014 with this
assembly gave a much higher yield of 94.8 mL of Cp during
the 1 h period between 12.30 pm and 1.30 pm (entry 3, Table
2), even while the average global insolation during the period
of the experiment [Fig. S1(B)†] was comparable to that
recorded for the experiment of entry 2, Table 1 [Fig. S1(A)†].
Maintaining the same basis of computation as above, the
energy storage efficiency was 5.49%.
As mentioned above, the norbornadiene–quadricyclane
system holds promise for energy storage. Synthesis of 1 from
Cp (eqn (3)) using solar energy was of interest. However, due
to difficulties in handling acetylene, the substituted acety-
lene, 4-phenylbut-3-yn-2-one (6), was chosen as a model
substrate for the experiment (eqn (5)). Studies were con-
ducted initially in the laboratory under neat condition using
an oil bath. No reaction was observed either at room
(6)
ꢁ
temperature or at 100 C. When the temperature was raised
(7)
ꢁ
further to ca. 160 C and the reaction le overnight, the 2,5-
norbornadiene derivative, 7, was obtained in satisfactory
yield and purity. The reaction was thereaer attempted using
an offset-parabolic dish (Fig. S2†), which was found to be well
suited to small scale reactions at 150–200 ꢁC. Diphenyl ether
was taken as high boiling solvent.
Besides the above uses, Cp nds numerous other applica-
tions in ne chemicals synthesis making it a versatile synthon
(Scheme 1).24 Hence its solar driven synthesis from the
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Acknowledgements
The referees are acknowledged for helpful suggestions. P. Patel,
J. N. Bharadia, P. S. Bapat and J. P. Makwana are acknowledged
for fabrication of the solar devices and assistance during solar
experiments. Analytical support provided by the Discipline of
Analytical Science and Centralized Instrument Facility is
gratefully acknowledged. MD, SC and SS thank CSIR for their
research fellowships. Authors are grateful to CSIR India for
supporting the study as part of an in-house laboratory project.
This is communication number 076/2014 from CSIR-CSMCRI.
Notes and references
1 (a) M. G. Walter, E. L. Warren, J. R. McKone, S. W. Boettcher,
Q. Mi, E. A. Santori and N. S. Lewis, Chem. Rev., 2010, 110,
6446; (b) A. Kudo and Y. Misekia, Chem. Soc. Rev., 2009, 38,
253; (c) A. Steinfeld, Sol. Energy, 2005, 78, 603.
Scheme 1 Schematic depiction of various uses of Cp.24
2 (a) W. J. Youngblood, S. A. Lee, Y. Kobayashi, E. A. Hernandez-
Pagan, P. G. Hoertz, T. A. Moore, A. L. Moore, D. Gust and
T. E. Mallouk, J. Am. Chem. Soc., 2009, 131, 926; (b)
D. V. Esposito, S. T. Hunt, A. L. Stottlemyer, K. D. Dobson,
B. E. McCandless, R. W. Birkmire and J. G. Chen, Angew.
Chem., Int. Ed., 2010, 49, 9787.
universally employed precursor, 5, would help reduce the
carbon footprint of such ne chemicals also.
3 W. D. Chemelewski, H. Lee, J. Lin, A. J. Bard and
C. B. Mullins, J. Am. Chem. Soc., 2014, 136, 2843.
4 S. Abanades and G. Flamant, Sol. Energy, 2006, 80, 1611.
5 C. L. Muhich, B. W. Evanko, K. C. Weston, P. Lichty, X. Liang,
J. Martinek, C. B. Musgrave and A. W. Weimer, Science, 2013,
341, 540.
6 A. Steinfeld and R. Palumbo, Encyclopedia of Physical Science
& Technology, ed. R. A. Meyers, Academic Press, 2001, vol. 15,
pp. 237.
4. Conclusions
The thermodynamically uphill cracking of neat endo-dicy-
clopentadiene to Cp using solar thermal energy was demon-
strated. The energy storage efficiency was 5.5% with respect
to IR component in global insolation during peak period. The
efficiency can be enhanced in the future by (i) minimizing
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