Dehydrogenation of primary aliphatic alcohols by Au/TiO2 photocatalysts

Article abstract of DOI:10.1246/cl.161195

Dehydrogenation reaction of primary aliphatic alcohols to aldehydes and molecular hydrogen was achieved under UV-vis light irradiation in the presence of gold-loaded titanium dioxide (Au/TiO₂) photocatalysts.

Full text of DOI:10.1246/cl.161195

Advance Publication Cover Page
2
Dehydrogenation of Primary Aliphatic Alcohols by Au/TiO Photocatalysts
Masaki Shibata, Ryoko Nagata, Susumu Saito, and Hiroshi Naka*
Advance Publication on the web February 10, 2017
doi:10.1246/cl.161195
©
2017 The Chemical Society of Japan
Advance Publication is a service for online publication of manuscripts prior to releasing fully edited, printed versions. Entire
manuscripts and a portion of the graphical abstract can be released on the web as soon as the submission is accepted. Note that the
Chemical Society of Japan bears no responsibility for issues resulting from the use of information taken from unedited, Advance
Publication manuscripts.

1
2
Dehydrogenation of Primary Aliphatic Alcohols by Au/TiO Photocatalysts
Masaki Shibata, Ryoko Nagata, Susumu Saito, and Hiroshi Naka*
Graduate School of Science and Research Center for Materials Science, Nagoya University, Chikusa, Nagoya 464-8602
(
E-mail: h_naka@nagoya-u.jp)
Dehydrogenation reaction of primary aliphatic alcohols
to aldehydes and molecular hydrogen was achieved under
UV–vis light irradiation in the presence of gold-loaded
Table 1. Photocatalytic dehydrogenation of 3-phenylpropanol (1a) to 3-
phenylpropanal (2a) and H .
2
a
hν (λ = 300–470 nm)
M/TiO2
OH
O
2
titanium dioxide (Au/TiO ) photocatalysts.
+
H2
ethyl acetate, N2
1
a
2a
Keywords: Dehydrogenation | Aldehyde | Photocatalysis
Entry
M
T
t
Conv.
Yield
Yield
(
loading in (°C)
(h)
of 1a
(%)
10 ± 2
of 2a
(%)
11 ± 1
of H
(%)
13 ± 1
2
b
b
b
wt %)
Pd (5)
Acceptorless dehydrogenation of primary alcohols
1
2
3
4
45
45
45
45
45
45
45
25
65
45
45
45
1
1
(
(
RCH
2
OH) to aldehydes (RCHO) and molecular hydrogen
1−3
Pt (5)
14 ± 2
12 ± 1
12 ± 1
H
2
) is an important reaction in synthetic chemistry.
c
c
c
Ag (4)
1
4
3
2
Emerging alternatives to conventional thermal methods
include photocatalytic dehydrogenation using (metal-loaded)
Au (5)
1
17 ± 2
17 ± 1
14 ± 1
17 ± 1
16 ± 2
17 ± 3
4
5
6
inorganic photocatalysts such as Pt/TiO
2
,
Pt/CdS, CdS,
5
6
Au (0.6)
None
1
7
8
9
10
d
d
d
1
2
1
< 1
3 2 2
Ru/SrTiO :Rh, Pd/CdS–TiO , Au–Pd/ZrO , and Ni/CdS ;
e
d
d
d
the photocatalytic dehydrogenation proceeds at around room
temperature (25–50 °C) under ultraviolet (UV) or visible (vis)
light irradiation, producing aldehydes in a chemoselective
7
Au (0.6)
Au (0.6)
Au (0.6)
Au (0.6)
Au (0.6)
Au (0.6)
1
< 1
< 1
< 1
8
9
1
9 ± 1
23 ± 2
69 ± 7
98 ± 1
87 ± 7
9 ± 1
20 ± 1
55 ± 9
51 ± 4
76 ± 5
4 ± 2
1
18 ± 1
4
–10
f
manner.
converting
Although these methods are effective for
benzyl and allyl alcohols, selective
10
10
10
10
N.D.
g
g
f
11
N.D.
h
f
dehydrogenation of simple aliphatic primary alcohols to
aldehydes remains elusive due to the lower reactivity of
unactivated alcohols and the instability of aliphatic aldehydes
N.D.
1
2
a
Conditions: 1a (2.0 mmol, 269.7 ± 1.2 mg), UV–vis light (300 W Xe
lamp with a UV cold mirror, λ = 300–470 nm), M/TiO2 (39 mg), ethyl
acetate (5 mL), N . Determined by GC analysis, average of 3 runs with
standard deviation. Average of 2 runs. Result of a single run. Without
light irradiation. Not determined due to evolution of larger amounts of
1
1,12
b
under the reaction conditions.
light-promoted dehydrogenation of 1-decanol with
Ru/SrTiO :Rh photocatalyst gives 1-decanal in 51% yield
25 °C, 24 h), but is accompanied with over-oxidation to 1-
For example, our visible-
2
c
d
e
a
f
3
g
h
2
hydrogen. Au/TiO loading: 117 mg. Ethyl acetate (25 mL).
(
7
–1
decanoic acid (15%). A Au–Pd/ZrO
2
photocatalyst developed
selectivity (Entry 5). The reaction rate of 340 µmol h in this
by Zhu and coworkers promotes selective conversion of 3-
phenylpropanol to 3-phenylpropanal under visible light
case was higher than in previously reported examples [4.3
–
1
7
–1
9
µmol h (Ru/SrTiO :Rh) ; 19 µmol h (Au–Pd/ZrO ) ; 0.3
3
2
–
1
10
irradiation but the reaction proceeds in low yield (31% yield,
µmol h (Ni/CdS) ], and the Au loading-based turnover
frequency (TOF) was 310 h . Dehydrogenation hardly
9
–1
4
5 °C, 16 h). Here, we report selective dehydrogenation of
primary aliphatic alcohols to aliphatic aldehydes and H
UV–vis light irradiation using gold-loaded titanium dioxide
Au/TiO ) photocatalysts.
We first prepared several metal-loaded titanium dioxide
photocatalysts (M/TiO , M = Pd, Pt, Ag, or Au) by means of
an impregnation–reduction method using Aeroxide TiO P25
Evonik) and sodium borohydride (Table S1), and we tested
2
under
proceeded in the absence of photocatalyst (Entry 6) or without
light irradiation (Entry 7). Decreasing the temperature from
45 °C to 25 °C significantly reduced the reaction rate (Entry
8), and the reactivity at 65 °C was slightly higher than that at
(
2
–
1
2
45 °C (reaction rate: 400 µmol h , Au loading-based TOF:
–1
2
360 h , Entry 9). Conversion of 1a reached 69% and 98%
1
3
(
when the reaction mixture was irradiated for 10 h in the
their photocatalytic activity for dehydrogenation of 3-
phenylpropanol (1a, 2.0 mmol) in ethyl acetate at 45 °C for 1
h under UV–vis irradiation (300 W Xe lamp with a UV cold
mirror, λ = 300–470 nm) under a nitrogen atmosphere (Table
presence of 39 mg and 117 mg of Au/TiO , respectively
(Entries 10 and 11). Lower selectivity in these cases could be
2
overcome by diluting the reaction mixture, and the aldehyde
1
6
2a was obtained in 76% GC yield (Entry 12).
1
). The palladium, platinum and gold-loaded photocatalysts
The scope of the photocatalytic dehydrogenation of
primary aliphatic alcohols is illustrated in Table 2. Straight-
chain fatty alcohols could be effectively converted to
aldehydes 2b and 2c in good yield, whereas β- or γ-branched
primary alcohols 1d–1f were less reactive under these
conditions, though the aldehydes were formed under the
reaction conditions in moderate yields. Major side products in
these experiments were alkanes (R–H). Carboxylic acids
showed high reactivity and selectivity for this transformation,
generating 3-phenylpropanal (2a) in 11–14% GC yield with
nearly equimolar amounts of H
Entries 1, 2, and 4). Ag/TiO was less effective than the other
three photocatalysts (Entry 3). The metal loading amount of
the most reactive photocatalyst, Au/TiO
reduced to 0.6 wt % without affecting the reactivity and
2
(12–16% GC yield, Table 1,
2
1
3b
1
4,15
2
,
could be

2
a
Table 2. Photocatalytic dehydrogenation of alcohols.
unchanged in the presence of ketone or aryl chloride (Entries
2
and 3), but the presence of nitrile slightly retarded
hν (λ = 300–470 nm)
Au (0.6 wt %)/TiO2
dehydrogenation of 1a (Entry 4). More reactive nitrobenzene
markedly inhibited dehydrogenation of 1a with partial
conversion of the impurity, yet 2a was still formed in 23%
yield (Entry 5).
+
H2
R
OH
R
O
ethyl acetate, N2
45 °C, 10 h
1
2
Conv.
Yield
b,c
(%)
RCH
2
OH (1)
b
RCHO (2)
(
%)
1
00
OH
O
dark
dark
9
8
85 (66)
8
0
1
a
2a
(a)
n-C12
n-C18
H
H
25OH (1b)
37OH (1c)
94
89
n-C11
n-C17
H
H
23CHO (2b)
35CHO (2c)
82 (74)
70 (59)
60
4
0
0
0
(b)
>
99
69 (64)
OH
O
2
1
1
1
d
2d
(
c)
(
)6
OH
( )6
d
O
5
(
4
6
8
0
2
4
6
8
45)
(
)4
( )4
time (h)
e
2e
Figure 1. Molar compositions of (a) 1a, (b) 2a, and (c) ethylbenzene in
photocatalytic dehydrogenation of 1a with Au (0.6 wt %)/TiO . The
reaction mixture was left in the dark during 2–4 and 6–8 h. See Table 1,
Entry 12 for reaction conditions and Table S4 for detailed results.
d
7
8
46
OH
O
2
f
2f
Cl
Cl
(
)7 OH
97
( )7
71 (55)
83 (63)
O
1
g
2g
2h
To
better
characterize
dehydrogenation reaction, we conducted
this
photocatalytic
series of
a
9
8
OH
O
experiments using cutoff filters (λ > 350, 370, and 400 nm).
The results indicated that this reaction is mainly promoted by
UV light irradiation (λ = 350–470 nm, yield of 2a: 64%; 370–
470 nm, 51%; 400–470 nm, 2% Table S3). This finding is
broadly in line with the band gap of TiO
apparent quantum yield for
dehydrogenation of alcohols using UV light (365 nm
monochromatic light) was 20% (average of 2 runs), which
was higher than we had previously with Ru/SrTiO :Rh (0.9%,
20 nm monochromatic light). The high apparent quantum
yield for Au/TiO -promoted dehydrogenation of alcohols
under UV-light irradiation would be a main reason for the
higher TOF of this reaction. Monitoring of Au/TiO -promoted
dehydrogenation of 1a with or without UV–vis light
irradiation indicated that both consumption of 1a and
formation of 2a occurred only when the reaction mixture was
irradiated (Figure 1). The composition of 1a and 2a remained
unchanged when the reaction mixture was left in the dark (2–4
h and 6–8 h), indicating that formation of 2a is due to light-
promoted dehydrogenation of 1a. Although small amounts of
ethylbenzene was detected in the late stage of reaction (<
1
h
a
Conditions: 1 (2.0 mmol), UV–vis light (300 W Xe lamp with a UV cold
mirror, λ = 300–470 nm), Au (0.6 wt %)/TiO (117 mg), ethyl acetate (25
mL). Determined by H NMR analysis, average of 2 runs. Isolated yield
2
b
1
c
1
4,17
(Figure S1).
The
d
2
of 2 in parentheses, result of a single run. Result of a single run.
Au/TiO -promoted
2
a
Table 3. Compatibility of functional groups.
hν, Au/TiO2
recovered
impurity
1
a + impurity
2a +
3
ethyl acetate
N , 45 °C, 10 h
7
4
2
Recovery
impurity (%)
–
of
2
b
Entry Impurity
Yield of 2a (%)
b
1
2
3
4
5
None
76 ± 5
2
Cyclohexanone 77
> 98
> 98
> 98
89
Chlorobenzene
Benzonitrile
79
57
23
Nitrobenzene
a
Conditions: 1a (2.0 mmol), impurity (2.0 mmol), UV–vis light (300 W
Xe lamp with a UV cold mirror, λ = 300–470 nm), Au (0.6 wt %)/TiO
117 mg), ethyl acetate (25 mL). Determined by GC analysis.
2
b
(
(
2 2 2
RCO H) and esters (RCO CH R) were not observed.
1
0%), the dehydrogenation continuously gave 2a with good
Reactions with allyl alcohols (e.g. cinnamyl alcohol), benzyl
alcohols (e.g. 3-methoxybenzyl alcohol), or secondary
alcohols (e.g. 2-tetradecanol) were sluggish, and the desired
aldehydes or ketones were detected in low yields (< 40%).
The presence of the Csp3–Cl bond in 1g or the C=C bond in 1h
was well tolerated under the photocatalytic conditions, and the
functionalized aldehydes 2g and 2h were obtained in good
yields.
Functional group compatibility was further examined by
adding impurities to the reaction mixture (Table 3).
Functional groups such as cyclic ketone, CAr–Cl bond, and
cyano group did not react under the photocatalytic conditions
selectivity. The Au/TiO photocatalyst was found to be
recyclable at least for four consecutive dehydrogenation of 1a
by separating the photocatalyst after each run and re-
2
activating it with NaBH
4
(Table S5). The activity of the
recycled Au/TiO remained essentially unchanged in these
2
–1
four runs [TOF = 74, 88, 71, and 84 h (t = 2 h)].
In summary, selective dehydrogenation of primary
aliphatic alcohols to aldehydes was effectively promoted by
Au/TiO
2
photocatalysts under mild conditions. This
platform for in situ
photocatalytic system provides
a
generation of aliphatic aldehyde and hydrogen, both of which
1,13
play key roles in so-called borrowing hydrogen chemistry.
(
Entries 2–4). Compared with the data in Table 3, Entry 1, the
This work was supported by
a Grant-in-Aid for
efficiency of dehydrogenation of 1a remained essentially
Scientific Research C (General, 26410115, to H.N.) from
2

3
MEXT, funds from the Tobe Maki Scholarship Foundation (to
H.N.), and funds for the ACT-C program from JST (to S.S.).
The authors wish to thank Professors R. Noyori (NU) and A.
Kudo (Tokyo University of Science) for fruitful discussions
as well as L. Wang and Y. Morioka (NU) for their technical
assistance.
Ohtani, Phys. Chem. Chem. Phys. 2010, 12, 2344–2355. b) D.
Tsukamoto, Y. Shiraishi, Y. Sugano, S. Ichikawa, S. Tanaka, T.
Hirai, J. Am. Chem. Soc. 2012, 134, 6309–6315.
Alkane (R–H, ethylbenzene) is a major side product in Table 1,
Entries 10–12. This side reaction could be suppressed by light
irradiation with longer wavelength (λ = 370–470 nm, yield of 2a:
51%, yield of ethylbenzene: 1%, Table S3, Entry 2).
D.C. Hurum, A. G. Agrios, K. A. Gray, T. Rajh, M. C. Thurnauer,
J. Phys. Chem. B. 2003, 107, 4545–4549.
Supporting Information is available electronically on the CSJ-
Journal Web site, http://www.csj.jp/journals/chem-lett/index.html.
1
6
1
1
7
8
References and Notes
1
a) G. E. Dobereiner, R. H. Crabtree, Chem. Rev. 2010, 110, 681–
7
1
03. b) C. Gunanathan, D. Milstein, Science 2013, 341, 1229712-
–11.
2
a) K. Fujita, T. Yoshida, Y. Imori, R. Yamaguchi, Org. Lett. 2011,
3, 2278–2281. b) A. Prades, E. Peris, M. Albrecht,
1
Organometallics 2011, 30, 1162–1167. c) R. Kawahara, K. Fujita,
R. Yamaguchi, J. Am. Chem. Soc. 2012, 134, 3643–3646. d) R.
Kawahara, K. Fujita, R. Yamaguchi, Angew. Chem. Int. Ed. 2012,
5
1, 12790–12794. e) K. F. Donnelly, C. Segarra, Li-X. Shao, R.
Suen, H. Müller-Bunz, M. Albrecht, Organometallics 2015, 34,
076–4084. f) S. Chakraborty, P. E. Piszel, W. W. Brennessel, W.
4
D. Jones, Organometallics 2015, 34, 5203–5206. g) M. Valencia,
H. Müller-Bunz, R. A. Gossage, M. Albrecht, Chem. Commun.
2
016, 52, 3344–3347. h) I. Dutta, A. Sarbajna, P. Pandey, S. M. W.
Rahaman, K. Singh, J. K. Bera, Organometallics 2016, 35, 1505–
513.
1
3
a) W.-H. Kim, I.-S. Park, J. Park, Org. Lett. 2006, 8, 2543–2545. b)
T. Mitsudome, Y. Mikami, H. Funai, T. Mizugaki, K. Jitsukawa, K.
Kaneda, Angew. Chem. Int. Ed. 2008, 47, 138–141. c) T.
Mitsudome, Y. Mikami, K. Ebata, T. Mizugaki, K. Jitsukawa, K.
Kaneda, Chem. Commun. 2008, 4804–4806. d) K. Shimizu, K.
Sugino, K. Sawabe, A. Satsuma, Chem. Eur. J. 2009, 15, 2341–
2
351. e) W. Fang, J. Chen, Q. Zhang, W. Deng, Y. Wang, Chem.
Eur. J. 2011, 17, 1247–1256. f) B. Feng, C. Chen, H. Yang, X.
Zhao, L. Hua, Y. Yu, T. Cao, Y. Shi, Z. Hou, Adv. Synth. Catal.
2
012, 354, 1559–1565. g) Y. Zhu, M. Shen, Y. Xia, M. Lu, Appl.
Organometal. Chem. 2015, 29, 152–156. h) D. Damodara, R.
Arundhathi, P. R. Likhar, Adv. Synth. Catal. 2014, 356, 189–198. i)
A. Bayat, M. Shakourian-Fard, N. Ehyaei, M. M. Hashemi, RSC
Adv. 2015, 5, 22503–22509.
4
5
a) W. Zhai, S. Xue, A. Zhu, Y. Luo, Y. Tian, ChemCatChem 2011,
3
, 127–130. b) K. Imamura, H. Tsukahara, K. Hamamichi, N. Seto,
K. Hashimoto, H. Kominami, Appl. Catal. A 2013, 450, 28–33.
T. P. Ruberu, N. C. Nelson, I. I. Slowig, J. Vela, J. Phys. Chem.
Lett. 2012, 3, 2798−2802.
6
7
8
9
1
1
T. Mitkina, C. Stanglmair, W. Setzer, M. Gruber, H. Kisch, B.
König, Org. Biomol. Chem. 2012, 10, 3556–3561.
Z. Liu, J. Carner, A. Kudo, H. Naka, S. Saito, Chem. Eur. J. 2013,
1
9, 9452–9456.
S. Higashimoto, Y. Tanaka, R. Ishikawa, S. Hasegawa, M. Azuma,
H. Ohue, Y. Sakata, Catal. Sci. Technol. 2013, 3, 400–403.
S. Sarina, S. Bai, Y. Huang, C. Chen, J. Jia, E. Jaatinen, G. A.
Ayoko, Z. Bao, H. Zhu, Green Chem. 2014, 16, 331–341.
Z. Chai, T.-T. Zeng, Q. Li, L.-Q. Lu, W.-J. Xiao, D. Xu, J. Am.
Chem. Soc. 2016, 138, 10128–10131.
Over-oxidation of aldehydes to esters or carboxylic acids is a major
side reaction. Aldehydes and alcohols can also give acetals in situ:
H. Zhang, Z. Zhu, Y. Wu, T. Zhao, L. Li, Green Chem. 2014, 16,
0
1
4
076–4080.
1
2
Dehydrogenation of simple aliphatic alcohols is more endothermic
than that of allylic or benzylic alcohols. Calculated changes of
Gibbs free energy from ethanol, allyl alcohol, and benzyl alcohol to
2
corresponding aldehydes and H are +37.7, +21.7, and +26.9 kJ
–
1
mol , respectively (25°C, 1 atm, at the M06-2X/6-311++G**
level).
1
1
1
3
4
5
a) J. Caner, Z. Liu, Y. Takada, A. Kudo, H. Naka, S. Saito, Catal.
Sci. Technol. 2014, 4, 4093–4098. b) V. N. Tsarev, Y. Morioka, J.
Caner, Q. Wang, R. Ushimaru, A. Kudo, H. Naka, S. Saito, Org.
Lett. 2015, 17, 2530–2533.
2
Au/TiO photocatalysts for hydrogen production: a) K. A. Connelly,
H. Idriss, Green Chem. 2012, 14, 260–280. b) B. Gupta, A. A.
Melvin, T. Matthews, S. Dash, A. K. Tyagi, Renewable Sustainable
Energy Rev. 2016, 58, 1366–1375.
Au/TiO
2
plasmonic photocatalysts for aerobic oxidation of
alcohols: a) E. Kowalska, O.-O. Prieto-Mahaney, R. Abe, B.
3