Stainless Steel-Mediated Hydrogen Generation from Alkanes and Diethyl Ether and Its Application for Arene Reduction

Article abstract of DOI:10.1021/acs.orglett.8b00931

Hydrogen gas can be generated from simple alkanes (e.g., n-pentane, n-hexane, etc.) and diethyl ether (Et₂O) by mechanochemical energy using a planetary ball mill (SUS304, Fritsch Pulverisette 7), and the use of stainless steel balls and vessel is an important factor to generate the hydrogen. The reduction of organic compounds was also accomplished using the in-situ-generated hydrogen. While the use of pentane as the hydrogen source facilitated the reduction of the olefin moieties, the arene reduction could proceed using Et₂O. Within the components (Fe, Cr, Ni, etc.) of the stainless steel, Cr was the metal factor for the hydrogen generation from the alkanes and Et₂O, and Ni metal played the role of the hydrogenation catalyst.

Full text of DOI:10.1021/acs.orglett.8b00931

Letter
Cite This: Org. Lett. XXXX, XXX, XXX−XXX
pubs.acs.org/OrgLett
Stainless Steel-Mediated Hydrogen Generation from Alkanes and
Diethyl Ether and Its Application for Arene Reduction
Yoshinari Sawama,* Naoki Yasukawa, Kazuho Ban, Ryota Goto, Miki Niikawa, Yasunari Monguchi,
Miki Itoh, and Hironao Sajiki*
§
Laboratory of Organic Chemistry, Gifu Pharmaceutical University, 1-25-4 Daigaku-nishi, Gifu 501-1196, Japan
*
S Supporting Information
ABSTRACT: Hydrogen gas can be generated from simple alkanes (e.g., n-pentane,
n-hexane, etc.) and diethyl ether (Et O) by mechanochemical energy using a
2
planetary ball mill (SUS304, Fritsch Pulverisette 7), and the use of stainless steel
balls and vessel is an important factor to generate the hydrogen. The reduction of
organic compounds was also accomplished using the in-situ-generated hydrogen.
While the use of pentane as the hydrogen source facilitated the reduction of the
olefin moieties, the arene reduction could proceed using Et O. Within the
2
components (Fe, Cr, Ni, etc.) of the stainless steel, Cr was the metal factor for the
hydrogen generation from the alkanes and Et O, and Ni metal played the role of the
2
hydrogenation catalyst.
ydrogen technology is becoming of increasing impor-
tance as an alternative manner to avoid global climate
Meanwhile, we have also recently accomplished a stainless-steel
(SUS304) and mechanochemical energy-mediated quantitative
hydrogen generation reaction from water (water splitting),
H
7a
changes, which are mainly based on the emission of carbon
1
dioxide (CO ) derived from the combustion of fossil fuels.
and the in-situ-generated hydrogen could be utilized as a
reductant of the coexisting reducible functional groups (alkyne,
alkene, aromatic halides, nitro group, azide, ketone, etc.) in a
2
Because industrial hydrogen production methods using fossil
fuels such as methane (CH ) as its raw materials emit
4
7b
substantial quantities of CO2 as a byproduct, it is quite
planetary ball milling vessel. We now report the stainless-steel
(SUS304) and mechanochemical energy-mediated CO -free
hydrogenation reaction of alkenes, alkynes, and ketones using
alkanes and diethyl ether (Et O) to generate the appropriate
quantities of H gas; the process is accompanied by the
formation of gaseous molecular hydrocarbons such as CH
generated by C−C bond cleavage of the parent alkanes and
Et O. It is noteworthy that the hydrogenation of resonance-
important to spur the development of new CO -free practical
2
2
technologies for hydrogen production resulting in the
2
coproduction of elemental carbon. The transition-metal-
2
catalyzed CO -free hydrogen generation consisting of dehy-
2
2
drogenation and C−C bonds cleavage reactions (decomposi-
,
4
2
,3
tion) of alkanes is an useful strategy to produce H gas.
2
Although such alkane-decomposition techniques have been the
subject of active investigations in the past two decades,
industrial practical hydrogen production (hydrogen recovery)
processes have still not been developed. On the other hand, the
reduction of organic compounds is a fundamental reaction in
organic chemistry. In particular, the catalytic hydrogenation of
2
stabilized aromatic nuclei could also be achieved by using Et O
2
as the hydrogen source to give the cyclohexane derivatives
without the use of any noble-metal catalysts.
Liquid alkanes as a part of the LOHCs are easily available
and inexpensive, because of their production from fossil fuels,
in most cases, and their frequent use as solvents in synthetic
organic chemistry. First, the reactivity of alkanes in the
hydrogen generation was investigated (see Table 1). Pentane
4
,5
resonance-stabilized arenes
is an important method for
accessing the corresponding cyclohexane derivatives, which are
utilized as functional materials and are expected to be used for
hydrogen storage as liquid organic hydrogen carrier (LOHC)
(
(
n-C H , 15 mmol) could be smoothly transformed to H
5
1
2
2
6
0.93 mmol), along with the generation of CH (2.36 mmol)
systems in the energy field. However, the use of large amounts
4
and trace amounts of ethane and propane by the
mechanochemical reaction using a planetary ball milling device
of industrially produced flammable H gas under high pressure
2
4
and temperature is constantly required. From the point of view
equipped with stainless steel (SUS304) balls and a vessel at a
of safety, easy handling, and the reduction of environmental
8
8
00 rpm rotation speed for 1 h (entry 1 in Table 1). Hexane
burdens, the development of a CO -free direct arene
2
(
n-C H ) and heptane (n-C H ) could also serve as hydrogen
hydrogenation (hydrogen transfer) method from a LOHC is
extremely attractive. We have previously developed a
6 14 7 16
heterogeneous noble metal-catalyzed arene hydrogenation
Received: March 21, 2018
5
reaction using isopropanol as the CO -free hydrogen source.
2
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.orglett.8b00931
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
Table 1. Hydrogen Generation Activity of Alkanes under
Ball Milling Conditions
hydrogenation activities, in comparison to n-C H and n-
5
12
a
C H . The use of n-C H (20 equiv) for a longer rotation
6 14 5 12
time (24 h) completed the reduction of 1a to give 2aa in
8
moderate yield (Table 2, entry 7). A 1.0 mol scale reaction of
1
a using the same vessel (12 mL) and number of balls (50
b
Generated Gas (mmol)
pieces) lowered the reactivity (Table 2, entry 8), which
indicated that the internal capacity of the vessel and the ball
number might need to be increased for scaleup.
entry
alkane
H2
CH4
1
2
3
4
n-C H
0.93
1.06
2.36
0.84
5
12
Et O also proved to be an efficient hydrogen source under
2
n-C H
6
14
16
the same reaction conditions, as shown in Table 1, and 3.01
mmol H gas and 0.84 mmol CH were produced from 15
mmol Et O in 1 h (eq 1). Intriguingly, and contrary to our
n-C H
2.05
0.62
7
n-C H
22
not detected
not detected
2
4
10
a
2
The reaction was carried out using a Fritsch Pulverisette 7 Premium
Line 7 Ball Mill (PLP-7) that was equipped with a 80 mL SUS304
vessel and 100 SUS304 balls (diameter: ca. 5 mm). Alkanes were
purchased from commercial sources and used without further
b
purification. The total quantity of the generated gas and the
proportion of hydrogen, methane, etc., including nitrogen and oxygen
contaminated from the air during operation are described in the
Supporting Information. Trace amounts of ethane and propane were
also detected by the GC analysis.
expectations, the hydrogenation of 1a could be accomplished at
sources (entries 2 and 3 in Table 1), while no hydrogen
8
00 rpm in the presence of 20 equiv of Et O as a hydrogen
2
generation was observed using decane (n-C H ) as a substrate
1
0
22
source to generate 1,1-dicyclohexylethane (2ab). Here, hydro-
genation of the olefin moiety, as well as the aromatic nuclei,
occurred (eq 2).
(
entry 4 in Table 1).
The in-situ-generated H in a SUS304 ball milling vessel
2
could be utilized for the reduction of olefin (see Table 2). 1,1-
Via this protocol, a wide variety of arene derivatives were
mechanochemically hydrogenated in the presence of Et O as a
2
Table 2. Hydrogenation of Olefin Using Alkane as a
Hydrogen Source
a
hydrogen source (see Table 3). The detailed optimization using
n-heptylbenzene (1b, 0.5 mmol) as a simple arene substrate has
been described in the Supporting Information (Table S2). The
aromatic nucleus of 1b was thoroughly hydrogenated to
produce 2b in 67% yield (Table 3, entry 1). Biphenyl (1c)
and diphenylmethane (1d) bearing two aromatic rings within
the molecule were also hydrogenated to the corresponding
biscyclohexane derivatives (2c and 2d) in moderate yields
Yield (%)
entry
alkane
recovered 1
2aa
1
2
n-C H
60
92
24
6
5
12
(
(
Table 3, entries 2 and 3). Diphenylacetylene (1e) and stilbene
1f) were transformed to 1,2-dicyclohexylethane (2e) with
n-C H
6
14
16
b
3
b
n-C H
no reaction
no reaction
7
complete hydrogenation of the aromatic nuclei as well as the
alkyne and alkene moieties (Table 3, entries 4 and 5).
Naphthalene (1g) was also entirely hydrogenated to give
bicyclo[4,4,0]decane (decaline, 2ga and 2gb) as a mixture of cis
and trans isomers (Table 3, entry 6). Benzophenone (1h) also
efficiently underwent arene hydrogenation to give dicyclohexyl-
methane (2d), along with hydrogenolysis of the ketone
function (Table 3, entry 7). 2-Dodecanone (1i) as an aliphatic
ketone was less reactive, and 2-dodecanol (2i) as a secondary
alcohol was obtained in 32% yield in association with the
recovery of the unchanged starting material (61%, 1i).
Meanwhile, the aliphatic alkyne functionalities of 1j and 1l
were efficiently hydrogenated to the corresponding alkanes (2j
and 2l) in good yields (Table 3, entries 9 and 10).
4
n-C H
10 22
5
6
c-C H
76
85
0
10
6
5
10
c-C H
6
12
c
7
cd
,
n-C H
55
16
5
12
12
8
n-C H
68
5
a
The reaction was carried out using a Fritsch Pulverisette 7 Classic
Line Ball Mill (PL-7) that was equipped with a 12 mL SUS304 vessel
and 50 SUS304 balls (diameter: ca. 5 mm). Alkanes were purchased
b
from commercial sources and used without further purification. The
c
use of distilled n-C H or n-C H resulted in no reaction. 20 equiv
7
16
10 22
d
of n-C H were used, and the reaction was carried out for 24 h. 1.0
5
12
mol of 1a was used using a Fritsch Pulverisette 7 Classic Line Ball Mill
(
PL-7) equipped a 12 mL SUS304 vessel and 50 SUS304 balls
(
diameter: ca. 5 mm).
Mechanochemical energy could be effectively applied to
9
Diphenylethane (2aa) as a hydrogenated product was produced
by the rotation (800 rpm) of a mixture of 1,1-diphenylethene
various reactions, and the metallic component of the ball mill
10
system sometimes facilitated the desired reaction. The
present SUS304 and mechanochemical energy-mediated hydro-
(
1a; 0.5 mmol), 10 equiv of n-C H12 and 5 mm diameter
5
SUS304 balls (50 pieces) in a 12 mL SUS304 vessel for 6 h in
gen generation from alkanes and Et O in a SUS304 ball milling
2
2
4% yield, together with 60% of unchanged 1a (Table 2, entry
vessel never proceeded when using ZrO balls (diameter 5
2
1
). n-C H was the apparent hydrogen source in this instance
mm) and a vessel (20 mL, Table 4, entry 1). Stainless steel
(SUS304) is composed of Fe, Cr, and Ni as the main
components (Fe, 69%; Cr, 18%−20%; Ni, 8%−10%). There-
6
14
(Table 2, entry 2), since n-C H and n-C H were ineffective
7 16 10 22
as reaction solvents (Table 2, entries 3 and 4). The
hydrogenation activity was not correlated with the in-situ-
fore, the metal efficiencies to promote the H gas generation
2
generated H amount (compare Tables 1 and 2). The cyclic
using Et O (3.75 mmol) under the stated ball milling
conditions were next investigated via the addition of zerovalent
2
2
alkanes, such as c-C H and c-C H , possessed similar
5
12
6
14
B
DOI: 10.1021/acs.orglett.8b00931
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
a
Table 3. Scope of Substrates
Furthermore, the role of the metal components of SUS304
that influenced the hydrogenation were also investigated under
atmospheric H conditions (Table 5). 1,1-Diphenylethene (1a)
2
a
Table 5. Essential Metals for Hydrogenation
a
The reaction was carried out using a Fritsch Pulverisette 7 Premium
Line 7 Ball Mill (PLP-7) equipped a 20 mL ZrO vessel and 25 ZrO
balls (diameter: ca. 5 mm). Recovery of the substrate. The reaction
2
2
b
c
was carried out under H (5 atm) using 75 ZrO balls.
2
2
was never hydrogenated by ball milling (800 rpm for 3 h) in a
ZrO vessel (20 mL) in the presence of ZrO balls (25 pieces)
2
2
(
Table 5, entry 1). While the addition of Fe or Cr powder (1
equiv) was ineffective for the hydrogenation (Table 5, entries 2
and 3), 1 equiv of Ni powder as an additive did facilitate the
hydrogenation of the olefin function of 1a to the alkane
product (2aa) (Table 5, entry 4). While the arene hydro-
genation of 1b never proceeded without an additive or the
addition of Fe, Cr, or Ni powder (1 equiv) (Table 5, entry 5), it
could proceed in the presence of Ni powder under pressurized
H conditions (5 atm) using 75 ZrO balls. Therefore, the
a
The reaction was carried out using a Fritsch Pulverisette 7 Classic
Line Ball Mill (PL-7) equipped a 12 mL SUS304 vessel and 50
SUS304 balls (diameter: ca. 5 mm). Et O was purchased from
commercial sources and used without further purification. Recovery
of the substrate.
2
b
2
2
progression of the mechanochemically mediated arene hydro-
genation requires the appropriate internal pressure of the
SUS304 ball milling vessel. Since the internal temperature of
the SUS304 ball milling vessel under 800 rpm rotation
Table 4. Essential Metal To Generate Hydrogen and
Methane
a
7a
conditions reaches ∼60 °C, the use of several organic
solvents with low boiling points, such as n-pentane (boiling
point (bp) = 36.1 °C), c-pentane (bp = 49 °C), and diethyl
ether (bp = 34.6 °C), indicated a good progression of the
hydrogenation (see Table 2 and eq 2). Therefore, n-heptane
Generated Gas (mmol)
entry
additive
H2
CH4
(
bp = 98.3 °C) as a higher-boiling-point solvent may be
1
2
3
4
not detected
not detected
0.52
not detected
not detected
0.075
inefficient, as shown in entry 3 in Table 2. These results
indicate that Cr metal is an absolutely essential metal for the H2
generation, and the hydrogenation is thoroughly catalyzed by
Ni metal. However, both reactions were much more effectively
facilitated by stainless steel 304 as an alloy of Fe, Cr, and Ni, in
comparison to the independent use of Cr or Ni. Actually, a
small amout of SUS304 alloy was collisionally eroded from balls
in the mixture as a fine powder during the arene reduction in
Fe
Cr
Ni
not detected
not detected
a
The reaction was carried out using a Fritsch Pulverisette 7 Premium
Line 7 Ball Mill (PLP-7) that was equipped with a 20 mL ZrO vessel
2
and 25 ZrO balls (diameter: ca. 5 mm). Et O was purchased from
2
2
commercial sources and used without further purification.
the presence of Et O (eq 2), although the precise role of each
metal is still under investigation.
2
11
Fe, Cr, or Ni powder (0.5 equiv) in the ZrO vessel (20 mL)
2
with ZrO balls (25 pieces). As a result, significant amounts of
In conclusion, hydrogen transfer utilizing alkanes and Et O
2
2
generated hydrogen could be observed in the presence of Cr
powder (Table 4, entry 3), while the addition of Fe or Ni
powder proved totally ineffective (Table 4, entries 2 and 4).
as hydrogen sources has been accomplished under mechano-
chemical (ball milling) conditions using SUS304 balls and an
SUS304 vessel. The in-situ-generated hydrogen could be used
C
DOI: 10.1021/acs.orglett.8b00931
Org. Lett. XXXX, XXX, XXX−XXX

Organic Letters
Letter
to hydrogenate a variety of reducible functionalities on the
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(
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pseudo-reductant for the hydrogenation of aromatic nuclei to
produce the materially useful cycloalkane derivatives. The
present reaction is an innovative hydrogenation method for the
direct (one-pot) utilization of hydrogen atoms on LOHC
molecules and it can also be expected to contribute to the
further application of alkanes and ethers as clean energy
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(
processes without CO production for the next generation.
2
5
ASSOCIATED CONTENT
Supporting Information
■
(
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.or-
glett.8b00931.
(
Suarez, E. J. Dalton Trans. 2016, 45, 19368−19373. (e) Morioka, Y.;
Matsuoka, A.; Binder, K.; Knappett, B. R.; Wheatley, A. E. H.; Naka,
H. Catal. Sci. Technol. 2016, 6, 5801−5805. (f) Pel
Denicourt-Nowicki, A.; Roucoux, A. ACS Sustainable Chem. Eng. 2016,
, 1834−1839. (g) Shi, J.; Zhao, M.; Wang, Y.; Fu, J.; Lu, X.; Hou, Z. J.
ss-Fink, G. J.
Organomet. Chem. 2016, 812, 81−86. (i) Baghbanian, S. M.; Farhang,
M.; Vahdat, S. M.; Tajbakhsh, M. J. Mol. Catal. A: Chem. 2015, 407,
́
isson, C.-H.;
Synthetic procedures and spectroscopic data for the
products (PDF)
4
Mater. Chem. A 2016, 4, 5842−5848. (h) Sun, B.; Su
̈
AUTHOR INFORMATION
Corresponding Authors
■
*
*
1
28−136. (j) Martinez-Prieto, L. M.; Urbaneja, C.; Palma, P.;
Campora, J.; Philippot, K.; Chaudret, B. Chem. Commun. 2015, 51,
647−4650. (k) Kang, X.; Zhang, J.; Shang, W.; Wu, T.; Zhang, P.;
Han, B.; Wu, Z.; Mo, G.; Xing, X. J. Am. Chem. Soc. 2014, 136, 3768−
771. (l) Maegawa, T.; Akashi, A.; Yaguchi, K.; Iwasaki, Y.; Shigetsura,
M.; Monguchi, Y.; Sajiki, H. Chem. - Eur. J. 2009, 15, 6953−6963.
m) Maegawa, T.; Akashi, A.; Sajiki, H. Synlett 2006, 2006, 1440−
1442.
E-mail: sawama@gifu-pu.ac.jp (Y. Sawama).
E-mail: sajiki@gifu-pu.ac.jp (H. Sajiki).
́
4
ORCID
3
Yoshinari Sawama: 0000-0002-9923-2412
Yasunari Monguchi: 0000-0002-2141-3192
Hironao Sajiki: 0000-0003-2792-6826
Present Address
§Laboratory of Organic Chemistry, Daiichi University of
Pharmacy, 22-1 Tamagawa-cho, Minami-ku, Fukuoka 815−
511, Japan (E-mail: monguchi@daiichi-cps.ac.jp).
Author Contributions
‡These authors contributed equally.
(
(5) Sawama, Y.; Mori, M.; Yamada, T.; Monguchi, Y.; Sajiki, H. Adv.
Synth. Catal. 2015, 357, 3667−3670.
(6) For selected papers and reviews, see: (a) Patel, R.; Patel, S. Clean
Energy 2017, 1, 90−101. (b) Sordakis, K.; Tang, C.; Vogt, L. K.; Junge,
8
H.; Dyson, P. J.; Beller, M.; Laurenczy, G. Chem. Rev. 2018, 118, 372−
4
33. (c) Broicher, C.; Foit, S. R.; Rose, M.; Hausoul, P. J. C.; Palkovits,
R. ACS Catal. 2017, 7, 8413−8419. (d) Chen, Y.-R.; Tsuru, T.; Kang,
D.-Y. Int. J. Hydrogen Energy 2017, 42, 26296−26307. (e) Lin, L.;
Zhou, W.; Gao, R.; Yao, S.; Zhang, X.; Xu, W.; Zheng, S.; Jiang, Z.; Yu,
Q.; Li, Y.-W.; Shi, C.; Wen, X.-D.; Ma, D. Nature 2017, 544, 80−83.
Notes
The authors declare no competing financial interest.
(f) Preuster, P.; Papp, C.; Wasserscheid, P. Acc. Chem. Res. 2017, 50,
7
4−85. (g) Yolcular, S. Energy Sources, Part A 2016, 38, 2031−2014.
ACKNOWLEDGMENTS
■
(h) Nagatake, S.; Higo, T.; Ogo, S.; Sugiura, Y.; Watanabe, R.;
Fukuhara, C.; Sekine, Y. Catal. Lett. 2016, 146, 54−60. (i) Itoh, N.;
Watanabe, S.; Kawasoe, K.; Sato, T.; Tsuji, T. Desalination 2008, 234,
261−269.
This study was partially supported by a Grant-in-Aid for
Scientific Research (B) (No. 16H05075), the Canon
Foundation, Koshiyama Science Technology Foundation and
ESPEC Foundation for Global Environment Research and
Technology (Charitable Trust) (ESPEC Prize for the
Encouragement of Environmental Studies). We are grateful
for the kind assistance provided by Fritsch Japan Co, Ltd.,
relevant to the Fritsch Pulverisette 7 Premium Line 7 Ball Mill
(
7) (a) Sawama, Y.; Niikawa, M.; Yabe, Y.; Goto, R.; Kawajiri, T.;
Marumoto, T.; Takahashi, T.; Itoh, M.; Kimura, Y.; Sasai, Y.;
Yamauchi, Y.; Kondo, S.-i.; Kuzuya, M.; Monguchi, Y.; Sajiki, H.
ACS Sustainable Chem. Eng. 2015, 3, 683−689. (b) Sawama, Y.;
Kawajiri, T.; Niikawa, M.; Goto, R.; Yabe, Y.; Takahashi, T.;
Marumoto, T.; Itoh, M.; Kimura, Y.; Monguchi, Y.; Kondo, S.;
Sajiki, H. ChemSusChem 2015, 8, 3773−3776.
(
PLP-7).
(
8) Time courses of hydrogen generation from n-pentane and the
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Letter
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e) Stefanic, G.; Krehula, S.; Stefanic, I. Chem. Commun. 2013, 49,
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245−9247. (f) Yu, J.; Li, Z.; Jia, K.; Jiang, Z.; Liu, M.; Su, W.
Tetrahedron Lett. 2013, 54, 2006−2009. (g) Su, W.; Yu, J.; Li, Z.; Jiang,
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(
11) 50 balls (5 mm diameter, total 22.9 g) was used for the reaction
of eq 2, and total 21.9 g of balls was recovered. These results indicated
that all metallic components (Fe, Cr, Ni, etc.) were eroded in the
reaction mixture as a fine powder during the milling. Meanwhile, the
weight of vessel fairly remained unchanged. The residual metals of
product (2ab) were measured by atomic absorption spectrometry.
Consequently, a quite trace amount of Fe species was detected [0.3
ppm of Fe metal was observed in 50 mL Et O solution of 0.55 mmol
2
product 2ab (106.9 mg)], while other metals were not detected.
E
DOI: 10.1021/acs.orglett.8b00931
Org. Lett. XXXX, XXX, XXX−XXX