Oxidative photodecarboxylation of α-hydroxycarboxylic acid derivatives with FSM-16 under visible light irradiation of fluorescent lamp

Article abstract of DOI:10.1248/cpb.59.906

Hydroxycarboxylic acids were converted to the corresponding carbonyl compounds under aerobic photooxidative conditions in the presence of FSM-16 under visible light irradiation by a fluorescent lamp. This synthetic protocol is the first example of FSM-16 functioning as a photocatalyst by visible light.

Full text of DOI:10.1248/cpb.59.906

906
Note
Chem. Pharm. Bull. 59(7) 906—908 (2011)
Vol. 59, No. 7
a
Oxidative Photodecarboxylation of -Hydroxycarboxylic Acid Derivatives
with FSM-16 under Visible Light Irradiation of Fluorescent Lamp
Norihiro TADA, Yoko MATSUSAKI, Tsuyoshi MIURA, and Akichika ITOH*
Gifu Pharmaceutical University; 1–25–4 Daigaku-nishi, Gifu 501–1196, Japan.
Received April 1, 2011; accepted April 26, 2011
Hydroxycarboxylic acids were converted to the corresponding carbonyl compounds under aerobic photo-
oxidative conditions in the presence of FSM-16 under visible light irradiation by a fluorescent lamp. This syn-
thetic protocol is the first example of FSM-16 functioning as a photocatalyst by visible light.
Key words oxidative; photodecarboxylation; a-hydroxycarboxylic acid; FSM-16; visible light
The importance of environmentally friendly processes has Results and Discussion
been recognized in all fields of industry as well as in the field
Table 1 shows the results of the photoreaction of benzylic
of synthetic organic chemistry.1) Photoreactions are a promis- acid (1) in the presence of additives (100 mg) in several sol-
ing synthetic process in this context.2) In particular, the de- vents using four 22-W fluorescent lamps at room tempera-
velopment of photocatalysts is a subject that is now receiving ture. In the absence of additives, only a trace amount of ben-
significant attention. TiO2, which catalyses the oxidation of zophenone (2) was obtained (entry 1). Although the reaction
NOx and the reduction of CO2,3,4) is one example of a practi- conditions with various additives including hexagonal meso-
cal and useful photocatalyst; extensive efforts have been
made to develop photocatalysts that are effectively activated
by visible light (VIS).5) Currently, the effective use of VIS is
Table 1. Study of Reaction Conditions for Oxidative Photodecarboxyla-
tion with FSM-16
one of the most important research topics for the prospective
development of new energy conversion and energy-using
technology. The photoreactivity of microporous silicas6) con-
taining transition metals has also been studied by many
groups7); however, little is known about silica itself.8—11)
A
Yield (%)a)
similar trend is observed for mesoporous silicas6) for which
there have been a few reports on the photoreactivity of silica
itself.12—18) During our investigation in the application of
mesoporous silicas to synthetic chemistry, we found that ben-
zylic acid (1) is oxidatively decarboxylated by photoirradia-
tion to give benzophenone (2) using a 400-W high-pressure
mercury lamp in the presence of FSM-16,16) which is a
mesoporous silica developed by Inagaki et al.19,20) In general,
thermal21—28) and photolytic29,30) oxidative decarboxylation
reactions of phenylacetic acid derivatives, which have been
reported by several groups to proceed by using heavy metals
as promoters, produce a large amount of waste and thus
cause environmental problems; however, typical mesoporous
silicas are free of heavy metals, recyclable, and yield little
waste. Although this reaction has the advantages of both in-
expensive acquisition of safe reagents and easy work-up, a
400-W high-pressure mercury lamp, which is expensive and
has harmful effects on the human body, is required. This is
the driving force of our continued studies under VIS light ir-
radiation using a general-purpose fluorescent lamp. It is
known that UV light is required for the photometathesis with
FSM-1614); to the best of our knowledge, there is no prece-
dent for visible light photoreaction with FSM-16. Herein, we
report the aerobic photodecarboxylation of a-hydroxycar-
boxylic acid derivatives with FSM-16 under visible light irra-
diation of a fluorescent lamp (Chart 1).
Entry
Solvent
Additive
2
1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24b)
25c)
26d)
27d,e)
28f)
29g)
30h)
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Cyclohexane
H2O
Toluene
MeOH
AcOEt
None
Acetone
CH2Cl2
MeCN
i-Pr2O
None
1
0
2
11
1
3
5
3
8
2
61
66
59
58
50
33
24
18
17
13
13
11
5
29
79
16
53
59
67
43
55
62
55
20
34
21
42
40
52
29
59
83
79
58
59
82
29
18
7
p-TsOH·H2O
Na2CO3
SiO2
Al2O3
HMS
MCM-41
H-Y
Na-Y
FSM-8
FSM-12
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
FSM-16
THF
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
Hexane
50
50
81
88
0
2
97
31
66
0
7
a) 1H-NMR yields. b) FSM-16 (80 mg). c) FSM-16 (120 mg). d) 30 h. e) The
reaction was carried out under an air atmosphere. f) The reaction was carried out in
the dark. g) The reaction was carried out under reflux without hn. h) The reaction
was carried out under Ar.
Chart 1
∗ To whom correspondence should be addressed. e-mail: itoha@gifu-pu.ac.jp
© 2011 Pharmaceutical Society of Japan

July 2011
907
Table 2. Oxidative Photodecarboxylation of Several Substrates with FSM-
16
Table 3. Recycling and Reuse of FSM-16
Yield (%)a)
Entry
Substrate
Products
Yield (%)a)
Entry
FSM-16
2
1
1
2
3
84
50
1
2
3
4
5
6
Initialb)
88
89
66
25
20
64
2
First reuseb)
Second reuseb)
Third reuseb)
Fourth reuseb)
Fifth reusec)
11
29
84
80
36
(17)
37
50
(6)
4
a) 1H-NMR yields. b) Recovered FSM-16 was dried at rt for 2 h under reduced
pressure and used in next reaction. c) Recovered FSM-16 after fourth reuse (entry 5)
was recalcinated at 450 °C for 4 h and used in fifth reuse (entry 6).
31
9
5
6
Table 4. Study of Efficient Wavelength of Light
(3)
7
8
9
(11)
No reaction
No reaction
Yield (%)a)
Entry
hn (nm)b)
2
1
a) Isolated yields. Numbers in parentheses are 1H-NMR yields.
1
2
3
4
5
6
7
Xe lamp (all)
73
38
57
4
27
43
53
55
99
43
55
397
445
499
558
589
618
porous silica (HMS) and MCM-41, which are mesoporous
silicas, and H-Y and Na-Y, which are microporous zeolites,
were varied to accomplish oxidative decarboxylation, the
yields of 2 were unsatisfactory except when using FSM-12
and FSM-1631) (entries 2—12). Moreover, when using FSM-
8, a large amount of 1 was recovered, which indicates that re-
action field is actually inside the pores of FSMs, because the
1
Trace
0
a) 1H-NMR yields. b) 300 W Xenon lamp (ASAHI SPECTRA MAX-301) was
used, and light with selected wavelength was irradiated through band-pass filter.
composition and the chemical properties of FSMs are basi- which possess no hydroxyl groups at the a -position, were
cally the same. Among the solvents examined, hexane was poor substrates (entries 7 and 8), and benzilic acid methyl
found to afford the best results (entry 12); however, it was ester (18) was also intact under similar conditions, and only
found that the yield of 2 cannot be correlated to the order of the starting material was recovered quantitatively (entry 9).
solubility of oxygen (entries 12—23).32) Benzophenone (2)
Next, the reuse of FSM-16 was examined (Table 3). The
was obtained in 81% yield by prolonging the reaction time to recovered FSM-16, which was dried at room temperature for
30 h (entry 26). It is noted that the reaction using four 22-W 2 h under reduced pressure after the photoreaction with 1,
fluorescent lamps requires longer reaction time (30 h) than showed high activity in the reaction on first reuse to give 2 in
the reaction using 400-W high-pressure mercury lamp 89% yield (entry 2). However, the yield of 2 decreased on
(5 h).16) Interestingly, the yield of 2 obtained in atmospheric second reuse. It was noted that the reactivity of FSM-16 was
air was nearly equal to that under an oxygen atmosphere restored to a certain extent by recalcination at 450 °C for 4 h,
(entry 27). VIS irradiation and molecular oxygen were nec- and 2 was obtained in 64% yield.
essary for oxidative photodecarboxylation because 2 was ei-
ther not obtained or was obtained only in low yield in their oxidative decarboxylation. The present experiments showed
absence (entries 28—30). that visible light, especially at 445 nm, was the most effective
Table 4 shows the results of the wavelengths effective for
The results of the oxidative decarboxylation of various a- wavelength for this reaction, and the results indicate that
hydroxycarboxylic acids under the optimized reaction condi- FSM-16 acts as a photocatalyst under visible light.
tions are summarized in Table 2. Acetophenone (4) was ob-
Although the mechanism of this reaction is not clear yet,
tained in 50% yield as the sole product when atrolactic acid the active sites, non-bonding oxygen hole center (NBOHC)
(3) was used as a substrate (entry 2). Although mandelic and Eꢀ center, produced by dehydration from silanol groups
acids (5, 8, 11), which are secondary a -hydroxycarboxylic on the wall of FSM-16 during calcination are thought to play
acids, gave a mixture of the corresponding aldehydes and car- an important role in decarboxylation.15)
boxylic acids in moderate yields (entries 3—5), 2-hydroxy-
palmitic acid (14)—an aliphatic acid—was converted to the Conclusion
corresponding aldehyde 15 only in 3% yield. Notably,
We have demonstrated the oxidative photodecarboxylation
diphenylacetic acid (16) and 2,2-diphenylpropionic acid (17), of a-hydroxycarboxylic acid derivatives with FSM-16 under

908
Vol. 59, No. 7
11) Morikawa A., Hattori M., Yagi K., Otsuka K., Z. Phys. Chem., 104,
visible light irradiation by a fluorescent lamp. This method is
significant from the viewpoint of synthetic organic chemistry
because harmless visible light irradiation from a general-pur-
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oxidant can be used. Further application of this photooxida-
tion to other reactions is now in progress in our laboratory.
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Other chemicals used were of reagent grade, obtained from Aldrich Chemi-
cal Co., Tokyo Kasei Kogyo Co., Ltd. and Wako Pure Chemical Industries,
Ltd. All products are known compounds and were identified by comparing
their NMR spectra with those of authentic samples.
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(1, 50 mg) and FSM-16 (100 mg) in dry hexane (5 ml) was irradiated with
four 22-W fluorescent lamps at room temperature in atmospheric air for
30 h. FSM-16 was then filtered off and washed with ethyl acetate, and the fil-
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(33.6 mg, 84%) was obtained after purification by preparative TLC.
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