Well-Dispersed Trifluoromethanesulfonic Acid-Treated Metal Oxide Nanoparticles Immobilized on Nitrogen-Doped Carbon as Catalysts for Friedel–Crafts Acylation

Article abstract of DOI:10.1002/asia.202001274

Although strong acid-treated metal oxides are useful heterogeneous superacid catalysts for various organic transformations, they usually have a limited density of acidic sites due to their low surface areas. Herein, heterogeneous trifluoromethanesulfonic acid immobilized nitrogen-doped carbon-incarcerated titanium nanoparticle (NP) catalysts have been developed that are composed of well-dispersed, small Ti NPs (ca 7 nm) that are otherwise difficult to achieve using acid-treated metal oxides. The catalysts showed high activity for Friedel–Crafts acylation with low titanium loading (2 mol%, <1 mg of metal for 1 mmol of substrate). A range of microscopic, spectroscopic and physicochemical studies revealed that the nitrogen-doped carbon immobilized the trifluoromethanesulfonic acid and that the addition of metals further changed the nature of the acidic species and enhanced catalytic activity.

Full text of DOI:10.1002/asia.202001274

CHEMISTRY
AN ASIAN JOURNAL
www.chemasianj.org
Accepted Article
Title: Well-Dispersed Trifluoromethanesulfonic Acid-Treated Metal
Oxide Nanoparticles Immobilized on Nitrogen-Doped Carbon as
Catalysts for Friedel–Crafts Acylation
Authors: Xi Yang, Tomohiro Yasukawa, Tei Maki, Yasuhiro Yamashita,
and Shu Kobayashi
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Asian J. 10.1002/asia.202001274
Link to VoR: https://doi.org/10.1002/asia.202001274
A Journal of
A sister journal of Angewandte Chemie
and Chemistry – A European Journal

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
Well-Dispersed Trifluoromethanesulfonic Acid-Treated Metal
Oxide Nanoparticles Immobilized on Nitrogen-Doped Carbon as
Catalysts for Friedel–Crafts Acylation
Xi Yang,[a] Tomohiro Yasukawa,*[a] Tei Maki,# [a] Yasuhiro Yamashita,[a] and Shū Kobayashi*[a]
This paper is a part of the special collection for the 20th Anniversary of the Tateshina Conference
[a]
X. Yang, Dr. T. Yasukawa, Dr. T. Maki, Dr. Y. Yamashita, Prof. Dr. Kobayashi
Department of Chemistry, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-0033, Japan
E-mail: t-yasukawa@chem.s.u-tokyo.ac.jp
E-mail: shu_kobayashi@chem.s.u-tokyo.ac.jp
Supporting information for this article is given via a link at the end of the document.
Abstract: Although strong acid-treated metal oxides are useful
heterogeneous superacid catalysts for various organic
transformations, they usually have a limited density of acidic sites due
to their low surface areas. Herein, heterogeneous
applications to organic synthesis are limited to redox type
reactions.
Scheme 1. The catalyst design of this work
trifluoromethanesulfonic acid immobilized nitrogen-doped carbon-
incarcerated titanium nanoparticle (NP) catalysts have been
developed that are composed of well-dispersed, small Ti NPs (ca 7
nm) that are otherwise difficult to achieve using acid-treated metal
oxides. The catalysts showed high activity for Friedel–Crafts acylation
with low titanium loading (2 mol%, <1 mg of metal for 1 mmol of
substrate).
A
range of microscopic, spectroscopic and
physicochemical studies revealed that the nitrogen-doped carbon
immobilized the trifluoromethanesulfonic acid and that the addition of
metals further changed the nature of the acidic species and enhanced
catalytic activity.
Solid acids are increasingly favored as catalysts for several
organic transformations because of their noncorrosive and
nontoxic nature, reusability, and the ease with which they can be
handled and separated. Among the range of common solid acids,
metal oxides, sulfonated metal oxides, heteropolyacids and resin
acids exhibit outstanding catalytic activity in a wide range of
organic transformations.[1,2] In particular, sulfated metal oxides
such as zirconia and titania are promising catalysts for various
reactions, including esterification, acylation of aromatics,
alkylation and isomerization because of their significant acidity.[3]
However, these types of catalysts usually have a limited density
of acidic sites and low surface areas.[3b] To expand their surface
area, the preparation of small metal oxide particles and the
formation of porous structures have been examined.[4]
Unfortunately, although the size of the particles can be kept small
(<10 nm), particle agglomeration often occurs during catalyst
preparation to form assembled structures, leading to
compromised catalytic performance.
Previously, our group developed nitrogen-doped carbon-
incarcerated (NCI) metal NP catalysts, with poly(4-vinylpyridine)
as the nitrogen precursor.[6] In this polymer-incarceration method,
NPs were stabilized through encapsulation by nitrogen-doped
carbon layers, and the NP sizes were controlled and well
distributed on the support. Cobalt-based catalysts prepared using
this method showed high catalytic activities for various organic
reactions, including aerobic oxidative esterification,[6] aerobic
ammoxidation[7] and oxygenation of styrene.[8] During these
investigations, we found that active species with very small NP
sizes were present that were tolerant of strong acid treatment.
These results demonstrated that N-doped carbon can strongly
stabilize small metal NPs. Inspired by our previous results, we
wanted to combine the NCI method with sulfated metal oxides to
generate active solid acid catalysts bearing well-dispersed small
NPs. Namely, we hypothesized that small metal oxide particles
could be dispersed on a nitrogen-doped carbon and a treatment
of these supported catalysts with strong acids expressed acidic
sites without causing leaching of metals (Scheme 1). One of the
challenges was that the basic sites of generated nitrogen species
on the support might reduce the acidity of the catalysts.[9] We
hypothesized that treatment of metal oxides with much stronger
To address these issues, incorporation of well-dispersed
metal nanoparticles (NPs) on nitrogen-doped carbon support has
been conceived. N-Doped carbon materials have been widely
applied in electrochemistry, and recently, N-doped carbon-
supported metal NPs have become established as promising
catalysts in organic transformations because of their low cost,
unique catalytic activities and robustness.[5] However,
1
This article is protected by copyright. All rights reserved.

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
acids than sulfuric acid, such as trifluoromethanesulfonic acid
(TfOH), would offset this issue. Wei et al. reported that a metal–
organic framework-derived N-doped carbon matrix can be treated
with a large excess of concentrated TfOH to generate a solid
superacid for hydrocracking reactions.[10] Balanco et al. and Khder
et al. reported the use of TfOH-supported zirconia to catalyze
esterification reactions.[11,12] Nonetheless, expensive zirconium
precursors (zirconium propoxide and zirconium isopropoxide,
respectively) were required and agglomeration of zirconia was
observed, resulting in reduced surface area and low efficiency of
the catalysts.
performance in the model reaction (entry 5). Further optimization
of the poly(4-vinylpyridine) (PVP)/Ketjenblack (CB) ratio revealed
that an improved yield of 83% was achieved using a PVP/CB ratio
of 1:2 (entry 6). Control studies showed that catalysts that were
not treated with TfOH (NCI-Ti and nitrogen-doped carbon)
possessed no catalytic activity toward the target reaction (entries
7 and 9). However, TfOH-treated N-doped carbon alone (NC-
TfOH) catalyzed the reaction, albeit with only a 51% yield of the
desired product (entry 8). This result indicated a concerted
catalytic pathway with more than one active species involved in
NCI-Ti-TfOH 3. In addition, the TfOH treated titanium catalyst with
only ketjenblack (CB) as support (CB-Ti-TfOH) exhibited almost
no catalytic activity (entry 10). In addition, ICP analysis showed
that Ti loading of CB-Ti-TfOH was significantly decreased after
TfOH treatment (from 0.454 mmol/g to 0.160 mmol/g). In contrast,
NCI-Ti-TfOH 3 showed a similar metal loading compared to NCI-
Ti. Thus, nitrogen in the support could stabilize Ti nanoparticles
and prevent Ti leaching during the acid treatment.
Friedel–Crafts acylation has been used extensively as an
efficient synthetic method for the generation of aromatic ketones,
which are crucial precursors for agrochemicals, pharmaceuticals
and fine chemicals.[13] Conventionally, Lewis acids (e.g., BF3,
AlCl3, FeCl3 or TiCl4) are widely used as promoters for
electrophilic acylations.[1] However, stoichiometric amounts of
metal halides are required because of the formation of strong
complexes with the ketone products. Homogeneous Lewis acid
catalysts such as Hf(OTf)4 were then developed; however, a
relatively high loading of metals, which were difficult to recover,
was required.[14] As a result, solid acids have become increasingly
favored as catalysts for Friedel–Crafts acylations because of their
noncorrosive and nontoxic nature, reusability, and the ease with
which they can be handled and separated.[15] Sulfated zirconia,
titania or hafnia have been used for this purpose; however, the
limited surface area of these catalysts meant that high loadings of
metals, substoichiometric amounts in most cases, and/or excess
amounts of arenes were required.[1,2d,4b,16] Recently, Zhang and
Jia et al. reported that N-doped porous carbon-supported iron
carbides nanoparticles catalyzed Friedel-Crafts acylation with
acyl chlorides as acylation agents. However, activation of
anhydrides with this catalyst was unsuccessful.[17] Herein, we
report the use of TfOH-immobilized NCI titania NP catalysts for
Friedel–Crafts acylation. Metal NPs can be stabilized by the
polymer through multiple interactions, and inexpensive and
readily available TiCl4 and low concentration of triflic acid were
used for catalyst construction. Arenes were used as the limiting
reagents with anhydrides as the acylation agents.
Inspired by the construction of NCI metal NP catalysts and
previous reports on TfOH-treated zirconia catalysts, a catalyst
preparation method was first optimized with zirconium NPs in the
initial trials (Table S1, see the Supporting Information (SI)).[6,12]
The metal salt was treated with basic reagents to exchange the
counter anion and form small particles in the presence of polymer
and carbon black; a poor solvent was then added to generate
polymer-capsulated NPs as a precipitate. The precipitate was
further pyrolyzed to form metal oxide NPs on nitrogen-doped
carbon followed by treatment with TfOH to generate acidic sites
on the metal NPs (NCI-M-TfOH). The catalytic activities were
evaluated with respect to the acylation of anisole. Examination of
the catalysts in the target reaction showed that treatment with
both sodium borohydride and an aqueous ammonia solution in
the initial step of the catalyst preparation and use of TfOH (Table
S2) was essential for improved catalytic activity (Scheme 2).
Further catalyst optimization was performed by solvent screening,
wherein the use of nitromethane as a solvent was found to be
optimal (Table 1). Several metal salts were examined, including
zirconium, titanium, scandium and hafnium, and all showed
similar catalytic activities (entries 1–4). However, as the metal
loading was decreased, NCI-Ti-TfOH 2 showed increased
Scheme 2. Preparation of NCI-M-TfOH catalysts
Table 1. Optimization of NCI-M-TfOH Catalysts
Metal loading Yield
Entry Catalyst
PVP:CB Metal salt
(mmol/g)a
(%)b
1
NCI-Zr-TfOH
ZrCl4
TiCl4
0.795 (13 mg) 61
0.744 (13 mg) 51
2
NCI-Ti-TfOH 1
NCI-Sc-TfOH
NCI-Hf-TfOH
NCI-Ti-TfOH 2
NCI-Ti-TfOH 3
NCI-Ti
3
1:1
ScCl3·6H2O 0.776 (13 mg) 59
4
HfCl4
TiCl4
TiCl4
TiCl4
–
0.695 (14 mg) 50
0.305 (33 mg) 68
0.330 (30 mg) 83
0.359 (28 mg) N.D.
5
6
7
1:2
8c
9c
10
NC-TfOH
– (50 mg)
51
N-doped C
–
– (50 mg)
N.D.
2
CB-Ti-TfOH
-
TiCl4
0.160 (63 mg)
a
Determined by ICP analysis. Weight of the catalyst incorporated was shown
b
in paratheses.
Determined using gas chromatography analysis with
nitrobenzene as the internal standard. c 50 mg of catalyst was incorporated.
The substrate scope was examined with the optimized
catalyst (Table 2). Acetic anhydride, propionate anhydride and
valeric anhydride were successfully activated at elevated
temperature to give the desired product in high yields with trace
amounts of ortho-acylated byproducts. The reaction with benzoic
2
This article is protected by copyright. All rights reserved.

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
anhydride required an excess of anisole to achieve a high yield.
Other electron-rich aryl substrates, mesitylene and o-
dimethoxybenzene, were also acylated in high yields. The
reaction of toluene with benzoic anhydride could not give the
desired product.
BET surface area analysis of NCI-Ti-TfOH 3 was conducted
(Figure S15). The BET surface area of NCI-Ti-TfOH 3 was
calculated as 177 m2g-1, which was compromised compared to
ketjen black, given that the structure of the catalyst surface would
likely be affected by the nitrogen dopant (from polyvinylpyridine)
as well as the pyrolysis temperature.
Table 2. Substrate Scopea
NCI-Ti-TfOH 3
Fourier transform infrared (FT-IR) spectroscopy was
conducted to characterize the catalysts further (Figure 2). In
contrast to the untreated catalysts, NCI-Ti, NCI-Ti-TfOH 3 showed
a clear peak at 1036 cm–1, which was assigned to the C–F
stretching mode.[12] This indicated that TfOH was attached to the
surface of NCI-Ti. However, signals corresponding to S=O and
titanium oxide were not clear in the spectra. To elucidate whether
the acidic sites on the catalysts have Lewis acidic or Brønsted
acidic nature, FT-IR analysis of pyridine-absorbed samples was
conducted using Nujol mull or KBr pellet methods.[3a,18] The
catalysts were treated with pyridine at room temperature and then
dried in vacuo before FT-IR analysis. No clear peak difference
around 1450 cm–1 that was associated with Lewis acidic sites was
observed in the spectra of pyridine-treated NCI-Ti-TfOH 3, NC-
TfOH and NCI-Ti (Figures S11–S13, see SI). On the other hand,
a tiny peak at ca 1540 cm–1 that was associated with Brønsted
acidic sites was observed in the spectra of pyridine-treated NCI-
Ti-TfOH 3 and NC-TfOH (Figures S8 and S9, see SI) whereas no
peak was observed in the spectra of pyridine-treated NCI-Ti
(Figure S10). Although peaks derived from carbon black
significantly hindered the observation of these pyridine derived
peaks, we conclude that Brønsted acidic sites are the major
species in NCI-Ti-TfOH 3 and NC-TfOH.
According to thermogravimetric (TG) analysis, a significant
decrease in weight percentage of NCI-Ti-TfOH 3 was observed at
around 290 °C due to decomposition of triflic acid anchored on
the catalyst support (Figure 3). In contrast, NCI-Ti showed no
weight loss during the increase in temperature. Based on the
weight loss, 0.357 mmol/g of TfOH loading was estimated.
The amount of TfOH estimated from TG analysis diagrams
was consistent with that calculated from elemental analysis. With
a comparable amount of TfOH as NC-TfOH, NCI-Ti-TfOH 3
showed better catalytic activity, suggesting that interaction
between triflic acid and Ti NPs was the key to the elevated
catalytic performance.
O
O
(Ti: 2 mol%)
R1
R2
R1
+
100 °C, 16 h, Ar
MeNO2 (1 M)
R2
R2
O
O
2 equiv.
Et
OMe
OMe
OMe
Me
nBu
O
O
O
87% yield
73% yield
70% yieldb
OMe
OMe
Me
Me
OMe
Ph
Me
Me
O
O
Me
O
87% yieldc
78% yieldb
96% yield
a
b
c
Isolated yield. At 120 °C. Neat conditions with 0.5 mL of anisole and 0.5
mmol of benzoic anhydride, at 120 °C.
Scanning transmission electron microscopy (STEM)
analysis showed the formation of Ti NPs with small sizes (6.6 ±
2.7 nm, for n = 329) (Figure 1 and S1). Notably, well-dispersed
NPs were achieved with limited aggregation (ca <20 nm). Ti
particle size in CB-Ti-TfOH was also measured to be 9.1 ± 5.2 nm
(n = 91) and aggregates were observed (Figure S3). These
observations indicated that introduction of nitrogen-containing
polymer was the key for forming small-size nanoparticles with well
dispersion. Energy dispersive X-ray spectroscopy (EDS) mapping
revealed that titanium and oxygen were present in the same
region, indicating the formation of TiOx. On the other hand, sulfur
was spread on the entire surface of the N-doped carbon support,
giving a clue for the allocation of anchored TfOH. This
phenomenon could explain the catalytic reactivity of TfOH-treated
N-doped carbon.
Figure 1. STEM and EDS mapping analysis of NCI-Ti-TfOH 3.
3
This article is protected by copyright. All rights reserved.

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
Figure 2. FT-IR analysis of NCI-Ti-TfOH 3.
To clarify the nature of the acid sites, NH3-temperature-
programmed desorption (TPD) analysis was conducted for NCI-
Ti-TfOH 3 and for NCI-Ti and NC-TfOH as a comparison (Figure
5). Catalysts were pretreated at 200 °C before analysis. Two
peaks for NCI-Ti-TfOH 3 and three peaks for NC-TfOH were
observed in the medium-temperature region (300–500 °C), which
could be assigned as the medium acid sites. Compared with NC-
TfOH, NCI-Ti-TfOH 3 showed a stronger desorption peak at
around 417 °C, which may correspond to the active catalytic acid
site for the desired Friedel–Crafts acylation pathway. The inactive
NCI-Ti catalyst presented two broad peaks in the medium- and
high-temperature regions (>500 °C), likely corresponding to the
Lewis acidic sites.[16d] However, these acid sites showed weak
desorption peaks and exhibited no catalytic activity toward the
Friedel–Crafts acylation. Given the evidence from TPD analysis,
the deposition of titanium NPs led to an increase in the number of
acidic sites and their nature might differ from TfOH anchored only
on N-doped carbon. We speculated that the TfOH strongly
absorbed on both the surface of the N-doped carbon support and
the titania NPs.
Figure 3. TG analysis of NCI-Ti-TfOH 3 and NCI-Ti.
Table 3. Elemental Analysis of Catalysts
Estimated
TfOH
Catalyst
C (%)
H (%)
N (%)
S (%)
F (%)
(mmol/g)
NCI-Ti-TfOH 3 87.32
1.05
0.97
1.29
1.10
0.92
1.04
1.50
1.66
1.25
–
2.06
–
0.361
–
NCI-Ti
91.84
89.16
93.88
NC-TfOH
N-doped C
1.34
–
2.09
–
0.367
–
X-ray photoelectron spectroscopy (XPS) analysis was
conducted to establish the surface composition of NCI-Ti and
NCI-Ti-TfOH 3 (Figure 4). Supporting the other characterization
data, attachment of TfOH to NCI-Ti-TfOH 3 was confirmed by
observation of a peak on the F 1s spectrum. Spectra of N 1s
showed that the ratio of pyrrolic nitrogen and pyridinic nitrogen
(81:19) remained the same before and after the acid treatment.
The Ti 2p3/2 XPS spectra indicated the formation of TiO2.[4f]
Figure 5. NH3-TPD analysis of NCI-Ti-TfOH 3, NC-TfOH and NCI-Ti.
Reusability of NCI-Ti-TfOH 3 catalyst was examined, and
the recovery of the catalyst could be easily achieved by
centrifugation with minimum catalyst lost (Table S3). A slight loss
of activity in the second run and a complete loss of activity in the
third run were observed. The deactivation of the catalyst is
probably due to the absorbance of byproducts or water on the
Brønsted acidic sites. Retreatment of the reused catalyst with
TfOH via the general TfOH treatment method could regenerate
the catalyst.
In summary, we have developed TfOH-immobilized NCI
titanium NP catalysts, which were well characterized and showed
good catalytic activity for Friedel–Crafts acylation. It was revealed
that nitrogen-doped carbon could disperse and stabilize strong
acid-treated titania NPs well while retaining a small size, whereas
the conventional acid-treated-metal oxides had bulk species or
larger particles. As a result, the catalyst showed a high turnover
number and required less than 1 mg of metal per 1 mmol of
substrate to complete the reactions. TPD analysis indicated that
the catalytically active species in NCI-Ti-TfOH 3 differ from those
of TfOH anchored on the support. This indicates that TfOH
interacted strongly with both the N-doped carbon support and the
surface of titania NPs, and that a concerted catalytic pathway with
both possible active species was probable.
Figure 4. XPS analysis of NCI-Ti-TfOH 3.
Acknowledgements
4
This article is protected by copyright. All rights reserved.

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
[17] (a) H. Zhang, X. Song, C. Zhao, D. Hu, W. Zhang, M. Jia, ACS Appl.
Nano Mater. 2020, 3, 6664–6674; (b) H. Zhang, X. Song, D. Hu, W.
Zhang, M. Jia, Catal. Sci. Technol. 2019, 9, 3812-3819.
This work was supported in part by a Grant-in-Aid for Scientific
Research from the Japan Society for the Promotion of Science
(JSPS KAKENHI, Grant No. 18K14208 and 20K15274) and the
Japan Science and Technology Agency (JST). We thank Central
Glass Co., Ltd. for providing TfOH.
[18] W. H. Chen, H. H. Ko, A. Sakthivel, S. J. Huang, S. H. Liu, A. Y. Lo, T.
C. Tsai, S. Bin Liu, Catal. Today 2006, 116, 111–120.
Keywords: Heterogeneous catalyst • Solid acid • Nitrogen-
doped carbon • Friedel–Crafts acylation • Metal nanoparticles
# EM Business Unit, EM Application Department, JEOL Ltd.
[1] G. Sartori, R. Maggi, Chem. Rev. 2006, 106, 1077–1104.
[2] (a) F. Liu, K. Huang, A. Zheng, F. S. Xiao, S. Dai, ACS Catal. 2018, 8,
372–391; (b) M. K. Gnanamani, L. Z. Linganiso, G. Jacobs, R. A. Keogh,
W. D. Shafer, B. H. Davis, Catal. Lett. 2012, 142, 1180–1189; (c) M. A.
Ahmed, Fuel Process. Technol. 2011, 92, 1121–1128; (d) K. Arata, H.
Nakamura, M. Shouji, Appl. Catal., A 2000, 197, 213–219; (e) W. Hua,
Y. Xia, Y. Yue, Z. Gao, J. Catal. 2000, 196, 104–114; (f) S. Kobayashi,
S. Nagayama, J. Am. Chem. Soc. 1998, 120, 2985–2986.
[3] For sulfated zirconia: (a) V. S. Marakatti, S. Marappa, E. M. Gaigneaux,
New J. Chem. 2019, 43, 7733–7742; (b) B. M. Reddy, M. K. Patil, Chem.
Rev. 2009, 109, 2185–2208; (c) K. Arata, Green Chem. 2009, 11, 1719–
1728; For sulfated titania: (d) M. Fan, Z. Si, W. Sun, P. Zhang, Fuel 2019,
252, 254–261; (e) M. Hosseini-Sarvari, E. Sodagar, M. M. Doroodmand,
J. Org. Chem. 2011, 76, 2853–2859; (f) J. L. Ropero-Vega, A. Aldana-
Pérez, R. Gómez, M. E. Niño-Gómez, Appl. Catal., A 2010, 379, 24–29;
(g) H. Jensen, A. Soloviev, Z. Li, E. G. Søgaard, Appl. Surf. Sci. 2005,
246, 239–249.
[4] (a) K. Saravanan, B. Tyagi, H. C. Bajaj, Appl. Catal., B 2016, 192, 161–
170; (b) G. Chen, C. Y. Guo, H. Qiao, M. Ye, X. Qiu, C. Yue, Catal.
Commun. 2013, 41, 70–74; (c) S. K. Das, S. A. El-Safty, ChemCatChem
2013, 5, 3050–3059; (d) J. B. Joo, A. Vu, Q. Zhang, M. Dahl, M. Gu, F.
Zaera, Y. Yin, ChemSusChem 2013, 6, 2001–2008; (e) E. Liu, A. J.
Locke, R. L. Frost, W. N. Martens, J. Mol. Catal. A: Chem. 2012, 353–
354, 95–105; (f) A. Sinhamahapatra, N. Sutradhar, M. Ghosh, H. C.
Bajaj, A. B. Panda, Appl. Catal., A 2011, 402, 87–93; (g) X. R. Chen, Y.
H. Ju, C. Y. Mou, J. Phys. Chem. C 2007, 111, 18731–18737; (h) Y.
Sun, S. Ma, Y. Du, L. Yuan, S. Wang, J. Yang, F. Deng, F. S. Xiao, J.
Phys. Chem. B 2005, 109, 2567–2572.
[5] L. He, F. Weniger, H. Neumann, M. Beller, Angew. Chem. Int. Ed. 2016,
55, 12582–12594.
[6] T. Yasukawa, X. Yang, S. Kobayashi, Org. Lett. 2018, 20, 5172–5176.
[7] T. Yasukawa, X. Yang, S. Kobayashi, J. Org. Chem. 2020, 85, 7543–
7548.
[8] T. Yasukawa, S. Kobayashi, Bull. Chem. Soc. Jpn. 2019, 92, 1980–
1985.
[9] B. Li, X. Y. Sun, D. Su, Phys. Chem. Chem. Phys. 2015, 17, 6691–6694.
[10] Z. Yang, X. Y. Wei, Z. X. Li, M. Zhang, Z. M. Zong, Z. H. Wei, Y. Li, Fuel
Process. Technol. 2018, 180, 180–188.
[11] M. Gorsd, L. Pizzio, M. Blanco, Appl. Catal., A 2011, 400, 91–98.
[12] H. M. Altass, A. E. R. S. Khder, J. Mol. Catal. A: Chem. 2015, 411, 138–
145.
[13] G. Sartori, R. Maggi, Advances in Friedel-Crafts Acylation Reactions:
Catalytic and Green Processes, CRC Press, 2009.
[14] (a) H. Ishitani, H. Suzuki, Y. Saito, Y. Yamashita, S. Kobayashi, Eur. J.
Org. Chem. 2015, 2015, 5485–5499; (b) I. Hachiya, M. Moriwaki, S.
Kobayashi, Bull. Chem. Soc. Jpn. 1995, 68, 2053–2060.
[15] (a) X. Rao, H. Ishitani, W. J. Yoo, S. Kobayashi, Asian J. Org. Chem.
2019, 8, 316–319. (b) M. I. M. Al - Zeer, K. J. D. Mackenzie, Catalysts
2019, 9, 372. (c) V. Morizur, D. Hector, S. Olivero, J. R. Desmurs, E.
Duñach, Eur. J. Org. Chem. 2016, 2016, 3126–3129.
[16] (a) K. Arata, Green Chem. 2009, 11, 1719–1728; (b) M. Hosseini-
Sarvari, E. Safary, J. Sulfur Chem. 2011, 32, 463–473; (c) Z. Miao, J.
Zhou, J. Zhao, D. Liu, X. Bi, L. Chou, S. Zhuo, Appl. Surf. Sci. 2017,
411, 419–430; (d) D. A. Vargas, L. J. Méndez, A. S. Cánepa, R. D. Bravo,
Catal. Lett. 2017, 147, 1496–1502.
5
This article is protected by copyright. All rights reserved.

10.1002/asia.202001274
Chemistry - An Asian Journal
COMMUNICATION
Entry for the Table of Contents
Trifluoromethanesulfonic acid-immobilized nitrogen-doped carbon-incarcerated titanium nanoparticle catalysts for the Friedel–Crafts
reaction were developed. The nitrogen-doped carbon enabled the stable formation of well-dispersed, small (ca 7 nm), strong acid-
treated titanium nanoparticles that are difficult to achieve using conventional acid-treated metal oxides. The catalysts showed high
activity with low metal loading.
Institute and/or researcher Twitter usernames: @ShuKobayashiLab
6
This article is protected by copyright. All rights reserved.