Rate-acceleration in gold-nanocluster-catalyzed aerobic oxidative esterification using 1,2- and 1,3-diols and their derivatives

Article abstract of DOI:10.1002/asia.201000624

Aerobic oxidation of aldehydes to 1,2- and 1,3-diol monoesters was catalyzed by polymer-incarcerated gold nanoclusters under ambient conditions. The esterification proceeded much faster with 1,2- and 1,3-diols and their derivatives rather than with methanol. Magnum PI: Gold-nanocluster catalysts, PI-Au, that were immobilized on polystyrene-based polymers with cross-linking moieties, were used to catalyze the syntheses of 1,2 and 1,3-diol monoesters and their derivatives from aldehydes. The effect of neighboring-group participation in the esterification reaction is also described. Copyright

Full text of DOI:10.1002/asia.201000624

DOI: 10.1002/asia.201000624
Rate-Acceleration in Gold-Nanocluster-Catalyzed Aerobic Oxidative
Esterification Using 1,2- and 1,3-Diols and Their Derivatives
Tomohiro Yasukawa, Hiroyuki Miyamura, and Shu Kobayashi*[a]
¯
Dedicated to Professor Eiichi Nakamura on the occasion of his 60th birthday
Abstract: Aerobic oxidation of aldehydes to 1,2- and 1,3-diol monoesters was cata-
Keywords: gold
heterogeneous catalysis
boring-group effects · oxidation
·
esterification
·
lyzed by polymer-incarcerated gold nanoclusters under ambient conditions. The
esterification proceeded much faster with 1,2- and 1,3-diols and their derivatives
rather than with methanol.
·
neigh-
Introduction
monoesterification of aldehydes in which molecular oxygen
has been used as an oxidant.
Esters are generally prepared from carboxylic acids or acti-
vated carboxylic acids, such as acid chlorides or acid anhy-
drides.[1] Alternatively, several research groups have recently
reported the gold-nanocluster-catalyzed[2,3] aerobic oxidative
esterification of alcohols or aldehydes.[4] This reaction pro-
ceeds under mild conditions, requires molecular oxygen as
the only oxidant, and has potential industrial applications as
a sustainable chemical process.
The synthesis of glycol monoesters is useful for the inter-
mediates of pheromones of Lepidoptera,[5] cross-linking
agents for polyesters or fungicides,[6] miticides,[7] and emulsi-
fiers.[8] Conventionally, they are synthesized by the oxidation
of cyclic acetals to avoid the formation of diesters[6,9] or by
the addition of carboxylic acids to ethylene oxide.[10] Howev-
er, these methods involve two steps and require more than
stoichiometric amounts of oxidants or employ ethylene
oxide, which is difficult to handle in the laboratory. Recent-
ly, a one-step direct glycol monoesterification of aldehydes
or carboxylic acids was reported.[11] However, to the best of
our knowledge, there are no examples of the catalytic glycol
Recently, we disclosed that gold-nanocluster catalysts im-
mobilized on polystyrene-based polymers with cross-linking
moieties, that is, polymer-incarcerated gold-nanocluster cata-
lysts (PI-Au),[12] were effective in the direct aerobic oxida-
tion of alcohols in methanol to afford methyl esters under
ambient conditions (under atmospheric oxygen conditions
and at room temperature).[13] This procedure has advantages
in terms of atom and energy efficiency, the E factor, and en-
vironmental friendliness, when compared to traditional
esterification procedures. However, the rate of esterification
reactions catalyzed by gold nanoclusters in other alcohols,
such as ethanol, 1-propanol, and benzyl alcohol, is still
low.[4g,h]
Herein we report the aerobic oxidative formation of
glycol monoesters from aldehydes catalyzed by PI-Au under
mild conditions. Results of the comparison of the use of dif-
ferent diols on the reactivity of the esterification reaction,
which suggests the existence of effective neighboring group
participation between oxygen in diols or its derivatives and
gold nanoclusters, are also described.
Results and Discussion
[a] T. Yasukawa, Dr. H. Miyamura, Prof. Dr. S. Kobayashi
Department of Chemistry
The PI-Au nanoparticles were prepared according to a pre-
viously reported procedure (Scheme 1).[12a] We investigated
the oxidative esterification of para-methylbenzaldehyde
using this gold catalyst. When ethanol was used as solvent,
the yield of the ethyl ester was 60% (Scheme 2). On the
other hand, when para-methylbenzaldehyde was treated
with ethylene glycol, the reaction proceeded smoothly to
School of Science and Graduate School of Pharmaceutical Sciences
The University of Tokyo, Hongo, Bunkyo-ku
Tokyo 113-0033 (Japan)
Fax : (+81)3-5684-0634
E-mail: shu_kobayashi@chem.s.u-tokyo.ac.jp
Supporting information for this article, including detailed experimen-
tal procedures, is available on the WWW under http://dx.doi.org/
10.1002/asia.201000624.
Chem. Asian J. 2011, 6, 621 – 627
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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FULL PAPERS
When 10 equivalents of ethylene glycol was used, the cor-
responding ester was obtained in 83% yield (Table 1,
entry 1). The yield decreased as the alkyl chain between the
two hydroxy groups increased (Table 1, entries 2–5). These
results could be explained by the neighboring-group partici-
pation effect, in which the hemiacetal intermediates are sta-
bilized by the two hydroxy groups on the surface of the gold
nanoclusters to accelerate the pathway to glycol esterifica-
tion. In the case of long alkyl chains, it is entropically unfav-
orable for the two hydroxy groups to coordinate to the gold
surface over the alkyl chain. Comparison of the results ob-
tained when using 1,6-hexanediol and 1,2-hexanediol clearly
demonstrated the neighboring-group effect where, in the
presence of two hydroxy groups at the 1 and 2-positions, the
reactivity improved significantly (Table 1, entries 5 versus
6). The neighboring-group effect was observed not only with
hydroxy groups but also with ethereal oxygen atoms
(Table 1, entries 7 and 8). It is interesting to note that in the
case of a sulfur-containing alcohol, no reaction occurred, in
spite of the good affinity of sulfur for gold (Table 1,
entry 9). When alcohols were used as the solvent instead of
acetonitrile, the yields of the corresponding monoesters in-
creased significantly (Table 1, entries 2, 7, 8, and 10). Al-
though stirring of a glycerol solution did not proceed very
smoothly, owing to its high viscosity, a mixture of the corre-
sponding monoesters was obtained in moderate yield
(Table 1, entry 10). The products shown in Table 1, entries 7
and 8 were difficult to synthesize by conventional methods,
that is, by the opening of cyclic acetals.[9] The esterification
reactions were dramatically accelerated by the neighboring-
group effect when compared to the simple esterification re-
actions in which ethanol and 2-propanol were used (Table 1,
entries 11 and 12, also see below).
Scheme 1. Preparation of PI-Au nanoclusters.
Scheme 2. Esterification of an aldehyde with ethanol and ethylene glycol.
afford the corresponding monoester product in 85% yield
(Scheme 2). These results were remarkable because it has
been reported that polyols, such as ethylene glycol[4p,14] and
glycerol[15] itself, are oxidized in the presence of gold nano-
clusters. However, in the esterification reaction, ethylene
glycol functioned well as a counterpart in oxidative esterifi-
cation with an aldehyde. We then examined the esterifica-
tion of benzaldehyde with 10 equivalents of various diols
and their derivatives as counterparts, using this catalyst, in
the presence of potassium carbonate under atmospheric
oxygen and at room temperature in acetonitrile (Table 1).[16]
Table 1. Monobenzoylation of various diols and alcohols in acetonitrile.
Several examples of the aerobic oxidative formation of
ethylene glycol monoesters are summarized in Table 2. In
the presence of electron-withdrawing groups on the aromat-
ic rings, the reactions proceeded smoothly, but both the de-
sired ester and carboxylic acids were formed. To suppress
the formation of carboxylic acids, the reactions were then
conducted in the presence of a small amount of a base at
lower temperature. We were pleased to see that the yield
then improved to about 70% (Table 2, entries 3–4). On the
other hand, the presence of electron-donating groups on the
aromatic rings decreased the initial hemiacetal formation. In
particular, the reaction was rather slow when para-methoxy-
benzaldehyde was used. The desired ester was obtained in
75% yield when ethylene glycol was used as the solvent
(Table 2, entry 6). Furthermore, an aliphatic substrate and
other aromatic substrates were smoothly converted into the
corresponding esters under the standard conditions (Table 2,
entries 7–10).
À
Entry
Alcohol (R OH)
Conversion [%][a]
Yield [%][b] PhCOOH
[%][b]
1
2[c]
100
86 (91)[d]
83
64 (74)[d]
16
11
2
3
25
7
20
4
4
1
5
14
9
5
6
40
32[e]
5
7
8
9
>99 (>99)[d] 65 (78)[d]
13
6
54 (99)[d]
48(78)[d]
0
0
0
10
85(91)[d]
3
25 (56)[d,f]
1
28
11
12
EtOH
iPrOH
trace
no reaction
[a] Determined by GC analysis. [b] Yield of isolated product. [c] Compound 2
was obtained as a by-product in 3% yield. [d] The yield in parenthesis was ob-
tained under the conditions: 1 mol% PI-Au and 2 mL alcohol instead of aceto-
nitrile as solvent. [e] The ratio of 1-substituted monoester to 2-substituted
monoester was 18:14. [f] The ratio of 1-substituted monoester to 2-substituted
monoester was 50:6.
The reaction profiles of the respective oxidative esterifica-
tions with methanol, ethanol, and ethylene glycol were com-
pared under the reaction conditions that included PI-Au
(1 mol%), K2CO3 (0.5 equiv), and the alcohol (10 equiv) in
acetonitrile at 308C (see Figure 1). We had previously ob-
served that the corresponding esters were obtained in good
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2011, 6, 621 – 627

Gold-Nanocluster-Catalyzed Diol Esterification
Table 2. Scope of aerobic oxidative formation of ethylene glycol monoesters.
Entry[a]
R
Base [equiv]
T [8C]
Conv. [%][b]
Yield [%][c]
Acid [%][c]
1[d,e]
2
3
Ph
4-BrC6H4
0.5
0.5
0.1
0.1
0.5
0.5
0.25
0.25
0.25
0.25
30
30
0
>99
>99
>99
96
92
94
96
94
>99
83
83
82
72
70
78
75
71
73
80
70
16
8
15
10
8
7
13
8
4-CF3C6H4
4-NO2C6H4
4-MeC6H4
4-MeOC6H4
PhCH2CH2
PhCH=CH
2-Napthyl
4
5
0
30
30
0
30
0
6[e,f]
7
8
9[e]
10[e]
11
8
4-(1,1’-Biphenyl)
0
[a] 0.25 mmol scale and 0.25m. [b] Determined by GC analysis. [c] Yield of isolated product. [d] 0.5m. [e]0.5 mol% PI-Au was used. [f] Ethylene glycol
(1 mL) was used instead of acetonitrile.
alcohol was converted into the corresponding ester in 68%
yield.[12f] Control experiments, using a cyclic acetal as sub-
strate and ethylene glycol, were also performed. Under both
conditions, namely Conditions A, using 10 equivalents ethyl-
ene glycol and acetonitrile as solvent, and Conditions B,
using 1 mL ethylene glycol, the formation of the correspond-
ing ester was not observed (Scheme 4).
Scheme 4. Control experiments with a cyclic acetal and ethylene glycol.
Conditions A: ethylene glycol (2.5 mmol), MeCN (1 mL), starting materi-
als were fully recovered. Conditions B: ethylene glycol (1 mL), starting
materials were fully recovered.
Figure 1. Reaction profiles of oxidative esterification of aldehydes in the
presence of 10 equiv ethylene glycol, methanol, and ethanol.
On the basis of these results, we have proposed the cata-
lytic cycle shown in Figure 2. Based on the results of the
control experiment in which a cyclic acetal was used, the re-
to high yields when methanol or ethanol was used as sol-
vent.[13] In contrast, the methyl ester and ethyl ester hardly
formed when 10 equivalents alcohol in acetonitrile was
used. On the other hand, the ethylene glycol ester formed
readily under the same conditions. These results clearly il-
lustrate the remarkable effect of the neighboring-group par-
ticipation between gold nanoclusters and the two hydroxy
groups in oxidative esterification with ethylene glycol.
action pathway that involved the formation of a cyclic acetal
was ruled out. According to Haruta and co-workers and
Tsukuda and co-workers, gold nanoclusters immobilized on
polymer supports are sufficiently electron rich to activate
molecular oxygen, and the subsequent alcohol adsorption
on the gold nanoclusters is facilitated by a weak base, such
as K2CO3 (or even no base).[4e,17,18] In the case of our PI-Au
catalysts, a similar mechanism, in which gold nanoclusters
adsorb molecular oxygen and possess Lewis acidity
(Figure 2, A), is assumed.[19] This is because we had already
confirmed that PI-Au was sufficiently active in 1) the aero-
bic oxidation of alcohols and aerobic oxidative methyl
esterification with K2CO3 at room temperature,[12f,13] and
2) in the aerobic oxidation of alcohols without base at room
temperature.[12d]
The direct aerobic oxidative esterification of glycol from
an alcohol was also investigated (Scheme 3). In the presence
of 0.5 mol% PI-Au and 0.5 equiv K2CO3, para-methylbenzyl-
The remarkable acceleration of the rate of diol esterifica-
tion has been explained by two main factors, which pertain
Scheme 3. Glycol esterification from an alcohol.
Chem. Asian J. 2011, 6, 621 – 627
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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623

S. Kobayashi et al.
FULL PAPERS
tives or hemiacetals and the surface of gold nanoclusters has
been discussed. This is the first report of such an effect ob-
served in aerobic oxidation using gold nanoclusters. Further
investigations, which include consideration of the mecha-
nism, other possibilities of neighboring group participation,
and synthetic applications, are currently underway in our
laboratory.
Experimental Section
General
Melting points are uncorrected. JEOL JMN-LA400, 500 or 600 spectrom-
eters were used for NMR spectroscopic measurements. Tetramethylsilane
(d=0) was used as an internal standard for 1H NMR spectroscopy and
CDCl3 (d=77.0) for 13C NMR spectroscopy. ICP analysis was performed
on Shimadzu ICPS-7510 equipment. IR spectra were measured on a
JASCO FT/IR-610 spectrometer. GC analysis was performed on a Shi-
madzu GC-2010 apparatus (Column: GL Science, TCWAX, 0.25 mm ID,
0.25 mm, 60.0 m; Gas pressure: 214.2 kPa; Total flow: 90.6 mLminÀ1
Column flow: 1.86 mLminÀ1
Velocity: 30.8 cm/sec; Purge flow:
;
;
3.0 mLminÀ1; Sprit ratio: 46.0; Injector: 250 8C, FID: 250 8C; Column
program: starting from 50.08C, 10 min hold, 108C/min to 2208C, 20 min
hold). STEM/EDS images were obtained using a JEOL JEM-2100F in-
strument operated at 200 kV. All STEM specimens were prepared by
placing a drop of the solution on carbon-coated copper grids and allowed
to dry in air (without staining).
Figure 2. Proposed catalytic cycle.
The PI-Au was prepared according to a previously reported procedur-
e.[11a] AuClPPh3 was purchased from Strem Chemical Inc. NaBH4 was
purchased from Wako Pure Chemical Company and recrystallized from
diglyme by heating according to the literature procedure1 and stored in a
glove box. It is important to manipulate all operations under an argon at-
mosphere during recrystallization. The activity of the catalysts and its re-
producibility were influenced by the purity of NaBH4 in the course of
catalyst preparation.
to the neighboring-group coordination to the gold surface,
namely, decreasing the activation energy to form a hemiace-
tal on the surface of gold nanoclusters, and stabilization of
the hemiacetal intermediate by multidentate coordination to
the surface of gold nanoclusters.
Although there may be no special stabilization effect in
the hemiacetal formation from an aldehyde and ethylene
glycol or 2-methoxy ethanol in the liquid phase without
gold,[20] a hemiacetal formed from an aldehyde and a diol
can be stabilized on the surface of gold nanoclusters by the
dual coordination of oxygen atoms to gold (Figure 2, B).[21]
In contrast to 1,2- or 1,3-diols, these effects are decreased
in diols that have longer alkyl chains between the two hy-
droxy groups. This decrease is because it is entropically un-
favorable for the two hydroxy groups to coordinate to gold.
Furthermore, ethereal oxygen atoms may coordinate to gold
nanoclusters too. Finally, b-hydride elimination occurs to
afford the corresponding ester along with reoxidation of hy-
drogen to water on the surface of gold nanoclusters, thus
completing this catalytic cycle.[22]
The structures of known compounds were confirmed by comparison with
commercially available compounds or data shown in literature.
Typical Procedure for The PI-Au-Catalyzed Aerobic Esterification of
Aldehyde in Polyol
(Table 1, entry 2) Benzaldehyde (53.0 mg, 0.5 mmol), K2CO3 (34.6 mg,
0.25 mmol), PI-Au (1 mol%), and propane-1,3-diol (2.0 mL) were com-
bined in a round-bottomed flask. After the mixture was stirred for 24 h
under an O2 atmosphere at 308C, the catalyst was collected by filtration
and washed with dichloromethane using a Kiriyama Rohto funnel. Brine
(40 mL) was added and the whole aqueous layer was extracted with ethyl
acetate (20~30 mL). The conversion of aldehyde was determined by GC
analysis with reference to an internal standard (anisole). The solvent was
removed in vacuo and the residue was purified by preparative TLC to
afford the mixture of 3-hydroxypropyl benzoate and 2-formyl-3-hydroxy-
prop-1-enyl benzoate as a by-product (68.7 mg). The ratio of the amounts
of the substances was determined by 1H NMR analysis, and then the
yield of the ester and the by-product was calculated as 74% and 3%, re-
spectively.
3-Hydroxypropyl benzoate:[11c] IR (neat): n˜ =3421, 3066, 1710, 1456,
Conclusions
1279, 714 cmÀ1 1H NMR (CDCl3): d=1.94 (tt, 2H, J=6.0 Hz, 12.0 Hz),
;
2.02 (t, 1H, J=5.4 Hz), 3.71 (dt, 2H, J=5.4 Hz, 11.4 Hz), 4.42 (t, 2H, J=
6.0 Hz), 7.37 (dd, 2H, J=8.4 Hz), 7.50 (dd, 1H, J=7.2 Hz), 7.97 ppm (d,
2H, J=6.6 Hz); 13C NMR: d=31.8, 59.0, 61.8, 128.3, 129.5, 130.0, 133.0,
166.9 ppm.
2-Formyl-3-hydroxyprop-1-enyl benzoate:[23] 1H NMR (CDCl3): d=4.32
(s, 2H), 7.42–7.46 (m, 3H), 7.49 (s, 1H), 8.03 (d, 2H, J=7.2 Hz),
9.62 ppm (s, 1H).
We have found that aerobic oxidative esterification of alde-
hydes or an alcohol with 1,2- and 1,3-diols and its deriva-
tives proceeds smoothly in the presence of PI-Au under am-
bient conditions. It is of interest to note that esterification
proceeded much faster with 1,2- and 1,3-diols and its deriva-
tives than with methanol. The effect of neighboring group
participation between the oxygens of diols and its deriva-
2-(2-Hydroxyethoxy)ethyl benzoate[11c] and diethylene glycol: (Table 1,
entry 7) 2-(2-Hydroxyethoxy)ethyl benzoate and diethylene glycol
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Chem. Asian J. 2011, 6, 621 – 627

Gold-Nanocluster-Catalyzed Diol Esterification
(81.3 mg, 78%). IR (neat): n˜ =3439, 3067, 1716, 1454, 1277, 1112,
2-Hydroxyhexyl benzoate:[28] 1H NMR (CDCl3): d=0.90 (t, 3H, J=
7.2 Hz), 1.31–1.57 (m, 6H), 2.16 (d, 1H, J=4.8 Hz), 3.97 (m, 1H), 4.21
(dd, 1H, J=6.9, 12.3 Hz), 4.37 (dd, 1H, J=3.0, 5.4 Hz), 7.43 (dd, 2H, J=
8.1 Hz), 7.55 (dd, 1H, J=7.5 Hz), 8.04 ppm (d, 2H, J=8.4 Hz);
13C NMR: d=14.0, 22.6, 27.5, 33.1, 69.2, 70.1, 128.4, 129.6, 129.8, 133.2,
166.7 ppm.
714 cmÀ1 1H NMR (CDCl3): d=3.48 (br, 1H), 3.60 (t, 2H, J=4.5 Hz),
;
3.70 (t, 2H, J=4.5 Hz), 3.79 (t, 2H, J=4.5 Hz), 4.44 (t, 2H, J=4.5 Hz),
7.39 (dd, 2H, J=8.4 Hz), 7.51 (dd, 1H, J=7.2 Hz), 8.01 ppm (d, 2H, J=
7.2 Hz); 13C NMR: d=61.7, 64.0, 69.2, 72.3, 128.3, 129.6, 129.9, 133.0,
166.6 ppm.
2-Methoxyethyl benzoate:[24] (Table 1, entry 8) IR (neat): n˜ =3066, 1722,
1-Hydroxyhexan-2-yl benzoate:[29] 1H NMR (CDCl3): d=0.91 (m, 3H),
1.32–1.76 (m, 6H), 2.09 (br, 1H), 3.97 (m, 1H), 3.75 (dd, 1H, J=6.3,
12.0 Hz), 3.82 (dd, 1H, J=3.0, 12.0 Hz), 5.15 (m, 1H), 7.45 (dd, 2H, J=
8.7 Hz), 7.55 (dd, 1H, J=7.5 Hz), 8.03 ppm (d, 2H, J=7.8 Hz);
13C NMR: d=13.9, 22.5, 27.5, 30.3, 65.0, 76.4, 128.4, 129.7, 130.1, 133.1,
166.9 ppm.
1455, 1275, 1110, 712 cmÀ1 1H NMR (CDCl3): d=3.41 (s, 3H), 3.71 (t,
;
2H, J=5.1 Hz), 4.46 (t, 3H, J=4.5 Hz), 7.41 (dd, 2H, 7.5 Hz), 7.54 (dd,
1H, J=7.8 Hz), 8.05 ppm (d, 2H, J=4.8 Hz); 13C NMR: d=59.1, 64.0,
70.5, 128.3, 129.7, 130.0, 133.0, 166.6 ppm.
Mixture of 2,3-dihydroxypropyl benzoate and 1,3-dihydroxypropan-2-yl
benzoate: (Table 1, entry 10) IR (neat): n˜ =3439, 3070, 1708, 1455, 1279,
714 cmÀ1 (a mixture of two compounds).
2-Hydroxyethyl benzoate:[9h,11c] (Table 2, entry 1) IR (neat): n˜ =3439,
3066, 1712, 1453, 1279, 714 cmÀ1 1H NMR (CDCl3): d=2.21 (t, 1H, J=
;
2,3-dihydroxypropyl benzoate:[25] 1H NMR (CDCl3): d=2.24 (t, 1H, J=
6.3 Hz), 2.69 (d, 1H, J=5.4 Hz), 3.63 (m, 2H), 3.72 (m, 1H), 4.01 (m,
1H), 4.33–4.40 (m, 2H), 7.39 (dd, 2H, J=7.8 Hz), 7.52 (dd, 1H, J=
7.5 Hz), 7.98 ppm (d, 2H, J=7.8 Hz); 13C NMR: d=63.4, 65.6, 70.3,
128.4, 129.5, 129.7, 133.3, 166.9 ppm.
6.0 Hz), 3.94 (dd, 2H, J=5.4, 9.0 Hz), 4.44 (t, 2H, J=4.8 Hz), 7.42 (dd,
2H, J=7.8 Hz), 7.55 (dd, 1H, J=7.5 Hz), 8.04 ppm (d, 2H, J=7.8 Hz);
13C NMR: d=61.2, 66.6, 128.3, 129.6, 129.8, 133.1, 166.9 ppm.
2-Hydroxyethyl 4-bromobenzoate:[9b] (Table 2, entry 2) IR (neat): n˜ =
1
3438, 3096, 1717, 1453, 1277, 757 cmÀ1; H NMR (CDCl3): d=2.14 (t, 1H,
1,3-Dihydroxypropan-2-yl benzoate:[26] 1H NMR (CDCl3): d=1H NMR
(CDCl3) d=3.91 (dd, 4H, J=5.1 Hz), 5.11 (t, 1H, J=4.8 Hz), 7.39 (dd,
2H, J=7.8 Hz), 7.52 (dd, 1H, J=7.5 Hz), 7.98 ppm (d, 2H, J=7.8 Hz);
13C NMR: d=62.0, 75.6, 128.4, 129.5, 129.7, 133.3, 166.7 ppm.
J=6.0 Hz), 3.93 (m, 2H), 4.43 (t, 2H, J=4.8 Hz), 7.56 (d, 2H, J=
9.0 Hz), 7.88 ppm (d, 2H, J=7.2 Hz); 13C NMR: d=61.3, 66.8, 128.3,
128.7, 131.2, 131.7, 166.2 ppm.
2-Hydroxyethyl 4-(trifluoromethyl)benzoate: (Table 2, entry 3) IR (neat):
3439, 1724, 1464, 1281 773 cmÀ1 1H NMR (CDCl3): d=2.22 (s, 1H), 3.95
;
(s, 2H), 4.47 (t, 2H, J=4.8 Hz), 7.67 (d, 2H, J=8.4 Hz), 8.14 ppm (d,
2H, J=9.0 Hz); 13C NMR: d=61.1, 67.0, 124.5, 125.4, 130.1, 133.1, 134.7,
165.7 ppm; DART-MS: m/z (%) calcd for C10H10F3O3: 235.05820 [MH+];
found: 235.05737.
A typical procedure for aerobic oxidation of aldehyde to ethylene glycol
ester in acetonitrile catalyzed by PI-Au[9b,11c]
(Table 1, entry 1) Benzaldehyde (53.0 mg, 0.5 mmol), K2CO3 (34.6 mg,
0.25 mmol), PI-Au (0.5 mol%), ethylene glycol (310.4 mg, 5 mmol), and
acetonitrile (1 mL) were combined in a round-bottomed flask. After the
mixture was stirred for 24 h under O2 atmosphere at 308C, the catalyst
was collected by filtration and washed with dichloromethane using a Kir-
iyama Rohto funnel. Aqueous sodium hydroxide solution (1m, 5 mL) was
added and the aqueous layer was extracted with dichloromethane (20~
30 mL). The combined organic layers were washed with brine and dried
over sodium sulfate. The conversion of the aldehyde was determined by
GC analysis with reference to an internal standard (IS=anisole). The sol-
vent was removed in vacuo and the residue was purified by preparative
TLC to afford 2-hydroxyethyl benzoate (61.0 mg, 83%). On the other
hand, hydrochloric acid (1m, 10 mL) was added to the aqueous layer and
it was extracted with dichloromethane (20~30 mL). The combined organ-
ic layers were washed with brine and dried over sodium sulfate and the
solvent was removed in vacuo to afford benzoic acid (9.4 mg, 16%). The
purity of benzoic acid was determined by NMR analysis (polyol could
sometimes be detected by 1H NMR). IR (neat): n˜ =3439, 3066, 1712,
2-Hydroxyethyl 4-nitrobenzoate:[9h] (Table 2, entry 4) m.p. 77–798C. IR
(KBr): n˜ =3332, 3113, 1726, 1531, 1465, 1356, 1289, 717 cmÀ1 1H NMR
;
(CDCl3): d=2.07 (t, 1H, J=5.7 Hz), 3.98 (t, 2H, J=4.5 Hz), 4.50 (t, 2H,
J=4.8 Hz), 8.21 (d, 2H, J=9.0 Hz), 8.26 ppm (d, 2H, J=9.0 Hz);
13C NMR: d=61.0, 67.3, 123.5, 130.8, 135.2, 150.6, 164.9 ppm.
2-Hydroxyethyl 4-methylbenzoate:[9h] (Table 2, entry 5) IR (neat): n˜ =
1
3439, 3036, 1709, 1453, 1279, 755 cmÀ1; H NMR (CDCl3): d=2.28 (t, 1H,
J=6.3 Hz), 2.38 (s, 3H), 3.92 (dd, 2H, J=6.3, 9.3 Hz), 4.42 (t, 2H, J=
4.5 Hz), 7.21 (d, 2H, J=8.4 Hz), 7.92 ppm (d, 2H, J=7.8 Hz); 13C NMR:
d=21.7, 61.5, 66.5, 127.0, 129.1, 129.7, 143.9, 167.0 ppm.
2-Hydroxyethyl 4-methoxybenzoate:[11d] (Table 2, entry 6) IR (KBr): n˜ =
1
3452, 3085, 1709, 1462, 1280, 772 cmÀ1; H NMR (CDCl3): d=2.19 (t, 1H,
J=6.0 Hz), 3.84 (s, 3H), 3.92 (dd, 2H, J=5.7, 9.9 Hz), 4.29 (t, 2H, J=
4.8 Hz), 6.90 (d, 2H, J=8.4 Hz), 7.99 ppm (d, 2H, J=9.0 Hz); 13C NMR:
d=21.7, 61.5, 66.5, 127.0, 129.1, 129.7, 143.9, 167.0 ppm.
2-Hydroxyethyl 3-phenylpropanoate:[30] (Table 2, entry 7) IR (neat): n˜ =
1453, 1279, 714 cmÀ1 1H NMR (CDCl3): d=1H NMR (CDCl3): d=2.21
;
1
3440, 3029, 1732, 1454, 749 cmÀ1; H NMR (CDCl3): d=2.00 (s, 1H), 2.71
(t, 1H, J=6.0 Hz), 3.94 (dd, 2H, J=5.4, 9.0 Hz), 4.44 (t, 2H, J=4.8 Hz),
7.42 (dd, 2H, J=7.8 Hz), 7.55 (dd, 1H, J=7.5 Hz), 8.04 ppm (d, 2H, J=
7.8 Hz); 13C NMR d=61.2, 66.6, 128.3, 129.6, 129.8, 133.1, 166.9.
(t, 2H, J=7.5 Hz), 3.00 (t, 2H, J=7.5 Hz), 3.78 (dd, 2H, J=5.4, 9.0 Hz)
4.21 (t, 2H, J=4.5 Hz), 7.24 (m, 3H), 7.32 ppm (dd, 2H, J=7.5 Hz);
13C NMR d=30.9, 35.7, 61.1, 66.0, 126.3, 128.2, 128.5, 140.3, 173.2 ppm.
4-Hydroxybutyl benzoate:[11c] (Table 1, entry 3) IR (neat): n˜ =3415, 3065,
2-Hydroxyethyl cinnamate:[31] (Table 2, entry 8) IR (neat): n˜ =3439, 3061,
1711, 1455, 1278, 714 cmÀ1 1H NMR (CDCl3): d=1.72 (m, 2H), 1.85 (m,
;
1708, 1637, 1453, 1278, 768 cmÀ1 1H NMR (CDCl3): d=2.29 (t, 1H, J=
;
2H), 3.71 (m, 2H), 4.35 (t, 2H, J=6.3 Hz), 7.42 (dd, 2H, J=8.1 Hz), 7.54
(dd, 1H, J=7.8 Hz), 8.02 ppm (d, 2H, J=8.4 Hz); 13C NMR: d=25.2,
29.2, 62.4, 64.7, 128.3, 129.5, 130.3, 132.9, 166.6 ppm.
5.4 Hz), 3.88 (d, 2H, J=4.2 Hz), 4.33 (t, 2H, J=4.5 Hz), 6.46 (d, 1H, J=
15.6 Hz), 7.36 (d, 3H, J=1.8 Hz), 7.50 (dd, 2H, J=3.3 Hz), 7.70 ppm (d,
1H, J=16.8 Hz); 13C NMR: d=61.3, 66.2, 117.5, 128.1, 128.9, 130.4,
134.2, 145.4, 167.2 ppm.
5-Hydroxypentyl benzoate:[27] (Table 1, entry 4) IR (neat): n˜ =3439, 1708,
1465, 1274, 675 cmÀ1 1H NMR (CDCl3): d=1.48–1.67 (m, 4H), 1.80 (m,
;
2-Hydroxyethyl 2-naphthoate:[11c] (Table 2, entry 9) m.p.: 176–1798C; IR
1
(KBr): n˜ =3452, 3052, 1692, 1466, 1264, 784, 675 cmÀ1; H NMR (CDCl3):
2H), 3.67 (dt, 2H, J=6.2, 11.4 Hz), 4.32 (t, 2H, J=3.0 Hz), 7.42 (dd, 2H,
J=7.4 Hz), 7.52–7.56 (m, 1H), 8.02 ppm (d, 2H, J=5.2 Hz); 13C NMR:
d=22.3, 28.5, 32.3, 62.7, 64.9, 128.3, 129.5, 130.4, 132.9, 166.7 ppm.
d=2.28 (s, 1H), 3.99 (s, 2H), 4.51 (t, 2H, J=4.8 Hz), 7.51 (dd, 1H, J=
7.5 Hz), 7.57 (dd, 1H, J=7.2 Hz), 7.85 (d, 2H, J=7.8 Hz), 7.92 (d, 1H,
J=7.2 Hz), 8.04 (dd, 1H, J=1.4, 8.2 Hz), 8.60 ppm (s, 1H); 13C NMR:
d=61.4, 66.8, 125.1, 126.7, 127.0, 127.7, 128.2, 128.3, 129,3 131.2, 132.4,
135.6, 167.1 ppm.
6-Hydroxyhexyl benzoate:[27] (Table 1, entry 5) IR (neat): n˜ =3439, 1709,
1465, 1277, 675 cmÀ1 1H NMR (CDCl3): d=1.40–1.49 (m, 4H), 1.59 (m,
;
2H), 1.77 (m, 2H), 3.64 (t, 2H, J=6.3 Hz), 4.32 (t, 2H, J=6.6 Hz), 7.42
(dd, 2H, J=7.8 Hz), 7.53 (dd, 1H, J=7.5 Hz), 8.02 ppm (d, 2H, J=
7.2 Hz); 13C NMR: d=25.4, 25.8, 28.7, 32.6, 62.8, 64.9, 128.3, 129.5, 130.4,
132.8, 166.7 ppm.
2-Hydroxyethyl [1,1’-biphenyl]-4-carboxylate: (Table 2, entry 10) m.p.:
96–978C; IR (KBr): n˜ =3495, 3061, 1697, 1454, 1291, 743, 692 cmÀ1
;
1H NMR (CDCl3): d=2.26 (s, 1H), 3.96 (s, 2H), 4.47 (t, 2H, J=2.4 Hz),
7.38 (dd, 1H, J=6.5 Hz), 7.39 (dd, 2H, J=12.6 Hz), 7.60 (d, 2H, J=
6.8 Hz), 7.64 (d, 2H, J=8.4 Hz), 8.11 ppm (d, 2H, J=8.4 Hz); 13C NMR:
d=61.4, 66.7, 127.0, 127.2, 128.2, 128.5, 128.9, 130.2, 139,9 145.9,
Mixture of 2-hydroxyhexyl benzoate and 1-hydroxyhexan-2-yl benzoate:
(Table 1, entry 6) IR (neat): 3392, 3069, 1709, 1456, 1279, 714 cmÀ1 (a
mixture of two compounds).
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S. Kobayashi et al.
FULL PAPERS
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Acknowledgements
This work was supported by a Grant-in-Aid for Scientific Research from
the Japan Society of the Promotion of Science (JSPS), ERATO (JST),
NEDO, and GCOE. H.M. thanks the JSPS fellowship for Japanese
Junior Scientist. Mr. Noriaki Kuramitsu (The University of Tokyo) is ac-
knowledged for electronic microscopy analysis.
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Received: August 31, 2010
Published online: November 26, 2010
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