Scalable Flow Synthesis of [6,6]-Phenyl-C61-butyric Acid Methyl Ester (PCBM) using a Flow Photoreactor with a Sodium Lamp

Article abstract of DOI:10.1002/ejoc.201700745

An efficient flow system was constructed for the synthesis of [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM); the process involved flow [2+1] addition of C₆₀ and subsequent flow photoisomerization of the resulting fulleroid to PCB

Full text of DOI:10.1002/ejoc.201700745

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Accepted Article
Title: Scalable flow synthesis of [6,6]-phenyl-C61-butyric acid methyl
ester (PCBM) using a flow photo-reactor with a Na lamp
Authors: Mitsuhiro Ueda, Naoyuki Imai, Shunsuke Yoshida, Hiroshi
Yasuda, Takahide Fukuyama, and Ilhyong Ryu
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To be cited as: Eur. J. Org. Chem. 10.1002/ejoc.201700745
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10.1002/ejoc.201700745
European Journal of Organic Chemistry
COMMUNICATION
Scalable flow synthesis of [6,6]-phenyl-C61-butyric acid methyl
ester (PCBM) using a flow photo-reactor with a Na lamp
Mitsuhiro Ueda,[a] Naoyuki Imai,[b] Shunsuke Yoshida,[b] Hiroshi Yasuda,*[b] Takahide Fukuyama,*[a] and
Ilhyong Ryu [a,c]
Dedication ((optional))
Abstract: An efficient flow system was constructed for the synthesis
of PCBM, which involves flow [2+1] addition of C60 and the
subsequent flow photo isomerization of the resulting fulleroid to
PCBM by using a flow photo-reactor in combination with a Na lamp.
With the present flow system, the scalable synthesis of PCBM (0.79
g/3.3 h) was achieved by the continuous operation for 3.3 h.
Jones reported the gram scale synthesis of PCBM using one-
flow system (2.6 g/ 8 h), in which heating to 250 °C was used for
the isomerization step of fulleroid 2 to PCBM 3.[7] Muccini and
Maggini used the photo-irradiative flow synthesis of PCBM[8]
using white LEDs at ambient temperature (25 °C). However, in
their flow system, due to the low power of the employed white
LEDs (1.35 W x 75), the long residence time (41 min) was
required. As the result, the system allowed for only low product
output (6 mg/ 1 h). Since our group has a long research
experience in photo-flow synthesis,[9][10] we believed that a
practical photo isomerization process would be possible with a
judicious choice of a photo flow microreactor and a light source.
Herein, we report that the scalable flow synthesis of PCBM is
achieved in short residence time of minute order over two steps
by using a serially connected flow system comprising thermal
flow reactor and a photo flow reactor combined with a Na lamp
as a light source.[11]
Introduction
PCBM ([6,6]-phenyl-C61-butyric acid methyl ester) displays
outstanding performance as
a material of n-type organic
semiconductor for organic photovoltaics (OPVs).[1,2] This
necessitates the development of effective manufacturing
protocol available for the synthesis of a large quantity of PCBM.
A general synthetic method for PCBM is composed of two steps,
(i) [2+1] cycloaddition to prepare fullenoid 2 from C60 and diazo-
alkane 1 and (ii) its isomerization leading to PCBM 3 (Scheme 1).
[3,4]
The second isomerization step has options of thermal and
Results and Discussion
photo isomerization. If we assume the latter option on scaling-up
in a batch reactor, a huge light source capable of irradiating a
large surface volume would be necessary, yet the solubility of
C60 in organic solvent is very poor[5] (Scheme 1).
In the first investigation, we examined the flow synthesis of
fulleroid 2 by the reaction of C60 with diazo-alkane 1 (Scheme 2).
For this reaction, we used a MiChS’s DH micromixer (channel
width = 60 µm) as a micromixer and a residence time unit (i.d. =
1 mm, length = 2.46 m, inner volume: 2 mL). The flow reaction of
C60 with 1 at 25 °C with a residence time of 80 sec gave fulleroid
2 in 59% yield, in which the yield based on the consumed C60
was 86%.[12] A shorter residence time of 40 sec gave 2 in 52%
yield, in which the yield based on the consumed C60 was
83%.[13]
Ph
OMe
Ph
OMe
Ph
OMe
N
N
O
O
O
1
hν /
C60
− N2
fulleroid (2)
[6,6]-PCBM (3)
([5,6]-PCBM)
Ph
OMe
Scheme 1. General synthetic method of PCBM (3) via fulleroid (2)
BPR
(75 psi)
C60 (15.0 mM)
1,2,4-TMB
O
MiChS DH
OMe
Recently, the use of continuous flow system[6] for the synthesis
of PCBM has attracted much attention. In 2011, Wong and
Ph
1 mm i.d.
lenght = 246 cm
V = 2 mL
N
N
O
fulleroid (2)
1 (12.0 mM)
25 °C
residence time (sec) HPLC yield (%)
1,2,4-TMB
*1,2,4-TMB: 1,2,4-trimethylbenzene
59 (86)a
52 (83)a
a Values in parentheses were
based on consumed C60
[a]
Dr. Mitsuhiro Ueda, Prof. Takahide Fukuyama, Prof. Ilhyong Ryu
Department of Chemistry, Graduate School of Science,
Osaka Prefecture University
80
40
Sakai, Osaka 599-8531, Japan
E-mail: fukuyama@c.s.osakafu-u.ac.jp.
http://www.c.s.osakafu-u.ac.jp/~ryu/?lang=en
Dr. Naoyuki Imai, Sunsuke Yoshida, Hiroshi Yasuda
Institute for Advanced & Core Technology, Showa Denko K.K
Chiba 267-0056, Japan.
E-mail: yasuda.hiroshi.xhnuc@showadenko.com.
Prof. lhyong Ryu
Department of Applied Chemistry, National Chiao Tung University
Hsinchu 30010, Taiwan
Scheme 2. Flow synthesis of fulleroid (2) by the reaction of C60 and 1
[b]
[c]
Encouraged by these nice results for flow synthesis of fulleroid 2,
we then moved on the isomerization of 2 to PCBM 3 using a flow
photo-reactor (Scheme 3). A 1,2,4-trimethylbenzene solution of
fulleroid (2, 4.1 mM) was irradiated using a flow photo-reactor
(MiChS L-1; inner volume: 3 mL, width = 2 mm, length = 3 m,
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
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10.1002/ejoc.201700745
European Journal of Organic Chemistry
COMMUNICATION
depth = 0.5 mm, quartz). After a survey of various light sources
(See the Supporting Information), we were delighted to find that
the use of a Na lamp (589 nm, 360 W) gave excellent results
(Scheme 3).[4,14] For example, the flow photo isomerization of 2
Having promising results over two flow steps in hand, we then
embarked on a challenge to develop the continuous one-flow
two-step synthesis of PCBM 3 from C60 and diazo-alkane 1, for
which we used an automated flow reactor system (MiChS X-
1)[16] combined with the photo flow reactor (MiChS L-1) and Na
lamp (for details, see SI) (Scheme 4). A 1,2,4-trimethylbenzene
solution of C60 (0.96 mL/min) and a 1,2,4-trimethylbenzene
solution of 1 (0.96 mL/min) were mixed using a micromixer at
25 °C, and the resultant mixture was guided to the residence
time unit at the same temperature with residence time of 52 sec.
The reaction mixture including unconverted C60 was then passed
through the flow photo-reactor (MiChS L-1) at 55 °C with
residence time of 95 sec under Na lamp irradiation (589 nm, 360
W). Consequently, we obtained 0.79 g of PCBM (3) in 3.3 h
(37% yield, PCBM/others/C60 = 30/28/42, Scheme 4).[17]
to
3 with a residence time of 5 min gave the desired
isomerization product 3 in 100% yield. Whereas a much shorter
residence time of 1 min gave 3 in poor yield, we found that even
with the short residence time of 45 sec, in the presence of C60,
PCBM 3 was formed in excellent yield. We assume that C60
would behave as a photo-sensitizer in the present photo
isomerization reaction as well as the reported cases.[15]
Na lamp
(589 nm, 360 W)
Ph
OMe
Ph
OMe
O
O
BPR (20 psi)
MiChS L-1, 55 °C
width = 2 mm, depth = 0.5 mm
length = 3 m, V = 3 mL
Conclusions
fulleroid (2 : 4.1 mM)
[6,6]-PCBM (3)
In summary, we demonstrated one flow synthesis of PCBM 3
from C60 and diazo-alkane 1, in which photo-isomerization of in
situ formed fulleroid 2 to PCBM 3 was successfully carried out in
very short residence time by the irradiation of a Na lamp. The
presence of excess C60 contributed to accelerate the photo-
isomerization presumably as a photo-sensitizer and the obtained
output (0.79 g/3.3 h) is promising for scalable synthesis of
PCBM.
1,2,4-TMB
residence time (min) yield (%)
5
1
100
4
0.75 (45 sec)
100a
a In the presence of
1 equiv of C60
Scheme 3. Photo-isomerization of fulleroid (2) to PCBM (3).
Na lamp
(589 nm, 360 W)
Ph
OMe
0.96 mL/min
MiChS DH
(15.1 mM)
C60
O
BPR (20 psi)
2 + C60
1,2,4-TMB
Ph
OMe
1 mm i.d.
MiChS L-1
width = 2 mm
depth = 0.5 mm
length = 3 m
55 °C
N
N
O
lenght = 210 cm
V = 1.65 mL
25 °C
0.96 mL/min
1 (12.2 mM)
[6,6]-PCBM (3)
1,2,4-TMB
37% yield
0.79 g in 3.3 h
(240 mg/h)
52 sec
95 sec
Scheme 4. Continuous one-flow synthesis of PCBM (3). Picture of the flow reactor system (MiChS® System XL-1)
conditions were sampled (1 mL) automatically in vials by a fraction
collector, and the yields of product 2 were determined by HPLC analysis.
Experimental Section
Photo-isomerization of fulleroid (2) to PCBM (3): An 80 mL 1,2,4-
trimethylbenzene solution of fulleroid (2: 0.3 mmol, 0.3 g, 4.1 mM) was
prepared and placed in a glass-made bottle. The bottle was connected
by PTFE tube to the HPLC pumps of the automated microflow system,
MiChS® system X-1, equipped with a MiChS L-1 as a flow photo-reactor
(inner volume 3 mL, width 2 mm, length 3 m, depth 0.5 mm, quartz, 55
°C), which was irradiated with a Na lamp (589 nm, 360 W), a back-
pressure regulator (20 psi), and an automated fraction collector. The
reaction mixtures for each conditions were sampled (1 mL) automatically
Flow synthesis of fulleroid (2): A 60 mL 1,2,4-trimethylbenzene
solution of C60 (0.9 mmol, 0.65 g, 15.0 mM) and a 60 mL 1,2,4-
trimethylbenzene solution of diazo-alkane 1 (12.0 mM, 0.8 equiv) were
prepared and placed in glass-made bottles respectively. These two
bottles were connected by PTFE tube to the HPLC pumps of the
automated microflow reactor, MiChS® system X-1, equipped with a
MiChS DH micromixer, a residence time unit (RTU, inner volume: 2 mL,
1 mm i.d., length: 246 cm, 25 °C), a back-pressure regulator (75 psi), and
an automated fraction collector. The reaction mixtures for each
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10.1002/ejoc.201700745
European Journal of Organic Chemistry
COMMUNICATION
in vials by a fraction collector, and the yields of product 3 were
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determined by HPLC analysis.
Continuous one-flow synthesis of PCBM (3): A 243 mL 1,2,4-
trimethylbenzene solution of C60 (3.7 mmol, 2.6 g, 15.1 mM) and a 275
mL 1,2,4-trimethylbenzene solution of diazo-alkane 1 (12.2 mM, 0.8
equiv) were prepared and placed in bottles respectively. These two
bottles were connected by PTFE tube to the HPLC pumps of the
automated microflow system, MiChS® system X-1, equipped with a
MiChS DH as a micromixer, a residence time unit (Inner volume: 1.65 mL,
1 mm i.d., length: 210 cm, 25 °C), MiChS L-1 as a flow photo-reactor
(inner volume 3 mL, width 2 mm, length: 3 m, depth 0.5 mm, quartz, 55
°C), which was irradiated with Na lamp (589 nm, 360 W), a back-
pressure regulator (20 psi), and an automated fraction collector. A 1,2,4-
trimethylbenzene solution of C60 (0.96 mL/min) and
a
1,2,4-
[7]
[8]
[9]
H. Seyler, W. W. H. Wong, D. J. Jones, A. B. Holmes, J. Org. Chem.
2011, 76, 3551.
trimethylbenzene solution of 1 (0.96 mL/min) were mixed using MiChS
DH mixer at 25 °C, and the resultant mixture was guided to the residence
time unit (residence time, 52 sec). The reaction mixture was then passed
through the flow photo-reactor (MiChS L-1, 55 °C, residence time, 95
sec) under Na lamp irradiation (589 nm, 360 W) in the presence of
unconverted C60. The reaction mixture was collected during 3.3 h and the
evaporation of the solvent gave a crude reaction mixture, which was
purified by column chromatography on SiO2 to give PCBM (3: 0.79 g,
37% yield).
E. Rossi, T. Carofiglio, A. Venturi, A. Ndobe, M. Muccini, M. Maggini,
Energy Environ. Sci. 2011, 4, 725.
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Acknowledgements
This work was supported by Grants-in-Aid for Scientific
Research (A) (26248031) from JSPS and Scientific Research on
Innovative Areas 2707 Middle Molecular Strategy (15H05850)
from MEXT.
Keywords: Flow synthesis • PCBM • Isomerization • Photo-
reactor • Na lamp
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[2]
Cyclobutane- and cyclopentane-annulated fullerenes also have
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have high-lying LUMO levels, which gave a high open-circuit voltage
compared with the PCBM-based devices in organic solar cell
applications. see: M. Ueda, T. Sakaguchi, M. Hayama, T. Nakagawa, Y.
Matsuo, A. Munechika, S. Yoshida, H. Yasuda, I. Ryu, Chem. Commun.
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[12] In reference 3, the reaction of 1 with C60 for 24 h gave fulleroid (2) in
50% yield. The yield of based on consumed C60 was 70% yield.
[13] Further reducing the residence time resulted in low yield (a residence
time: 20 sec, 44% yield)
[14] In reference 3, the isomerization of 2 at 180 °C for 2 h gave PCBM (3)
in 98% yield. In reference 4, under irradiation conditions with an Ar ion
laser (488 nm, 50 mW), the isomerization of 2 for 1 h gave 3 in
quantitative conversion.
[3]
[4]
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[16] http://www.michs.jp/index_en.html.
[17] Conventional batch reaction gave 32% yield of PCBM with similar
product distribution.
[6]
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in Organic Synthesis and Catalysis, Wiley-VCH, Weinheim, 2013; b) V.
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Entry for the Table of Contents (Please choose one layout)
Layout 1:
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*
Page No. – Page No.
*one or two words that highlight the emphasis of the paper or the field of the study
Layout 2:
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One-Flow synthesis*
Mitsuhiro Ueda, Naoyuki Imai, Hiroshi
Yasuda,* Takahide Fukuyama,* and
Ilhyong Ryu
We found that the photo-isomerization of fulleroid to PCBM proceed very efficiently
by using a flow photo-reactor with a Na lamp. As the result, the scalable synthesis
of PCBM was achieved by continuous-flow synthesis (0.79 g/3.3 h).
Page No. – Page No.
Scalable flow synthesis of [6,6]-
phenyl-C61-butyric acid methyl ester
(PCBM) using a flow photo-reactor
with a Na lamp
*one or two words that highlight the emphasis of the paper or the field of the study
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