PEG-supported sulfonic acid as an efficient and recyclable catalyst for the synthesis of 1,1-diacetates under solvent-free conditions

Article abstract of DOI:10.1080/00397910601168264

An operationally simple, efficient, and environmentally benign synthesis of 1,1-diacetates in good yields by reaction of different aldehydes with acetic anhydride in the presence of PEG-supported sulfonic acid under solvent-free conditions is described. C

Full text of DOI:10.1080/00397910601168264

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PEG‐Supported Sulfonic Acid as an Efficient
and Recyclable Catalyst for the Synthesis of
1,1‐Diacetates under Solvent‐Free Conditions
Qiu‐Ying Wang a , Shou‐Ri Sheng a , Mei‐Hong Wei a , Zhong‐Li Xie a &
Xiao‐Ling Liu a
a College of Chemistry and Chemical Engineering, Jiangxi Normal
University , Nanchang, China
Published online: 24 Feb 2007.
To cite this article: Qiu‐Ying Wang , Shou‐Ri Sheng , Mei‐Hong Wei , Zhong‐Li Xie & Xiao‐Ling Liu (2007)
PEG‐Supported Sulfonic Acid as an Efficient and Recyclable Catalyst for the Synthesis of 1,1‐Diacetates under
Solvent‐Free Conditions, Synthetic Communications: An International Journal for Rapid Communication of
Synthetic Organic Chemistry, 37:6, 1019-1026, DOI: 10.1080/00397910601168264
To link to this article: http://dx.doi.org/10.1080/00397910601168264
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Synthetic Communicationsw, 37: 1019–1026, 2007
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910601168264
PEG-Supported Sulfonic Acid
as an Efficient and Recyclable Catalyst
for the Synthesis of 1,1-Diacetates under
Solvent-Free Conditions
Qiu-Ying Wang, Shou-Ri Sheng, Mei-Hong Wei,
Zhong-Li Xie, and Xiao-Ling Liu
College of Chemistry and Chemical Engineering, Jiangxi Normal
University, Nanchang, China
Abstract: An operationally simple, efficient, and environmentally benign synthesis of
1,1-diacetates in good yields by reaction of different aldehydes with acetic anhydride in
the presence of PEG-supported sulfonic acid under solvent-free conditions is described.
Keywords: PEG-supported sulfonic acid, 1,1-diacetate, solvent free, environmentally
benign
Polymer-supported organic reagents and catalysts have been rapidly applied in
the preparation of organic molecules. The most important point is that the gene-
ration and reuse of the recovered polymeric reagents and catalysts are possible,
thus providing an environmentally benign system.[1] Soluble polymeric
supports of this nature, with applications in liquid-phase organic synthesis
(LPOS), can have several advantages over insoluble polymer-based
supports:[2] solubility in solvents such as dichloromethane and methanol
gives a more solution-like environment for reactions and also enables the moni-
1
toring of polymer-bound intermediates by solution H NMR spectroscopy.
Received in Japan June 26, 2006
Address correspondence to Shou-Ri Sheng, College of Chemistry and Chemical
Engineering, Jiangxi Normal University, Nanchang, China. E-mail: shengsr@jxnu.
edu.cn
1019

1020
Q.-Y. Wang et al.
However, their low solubility in the other solvents, such as propan-2-ol and
diethyl ether, allows ease of purification using simple crystallization
techniques. 1,1-Diacetates (acylals) are one of the useful carbonyl protecting
groups because of their stability under both neutral and basic media as well as
under acidic conditions.[3] The diacetates of a,b-unsaturated aldehydes are
important starting materials for Diels–Alder reactions and also are useful inter-
mediates in industry.[4,5] Moreover, the acylal functionality can be converted into
other functional groups by reaction with appropriate nuclephiles.[6,7] Many
methods for the preparation of 1,1-diacetates from aldehydes and acetic
anhydride using sulfuric acid,[8] PCl3,[9] I2,[10] NBS,[11] FeCl3,[12] Sc(OTf)3,[13]
Cu(OTf)2,[14] Bi(OTf)3,[15] In(OTf)3,[16] CAN,[17] b-zeolite,[18] LiBF4,[19]
AlPW12O40,[20] NH12SO3H,[21] amberlyst-15,[22] ZrCl4,[23] Wells–Dawson
[25]
acid,[24] Bi(BO3)3 5H2O,
and silica sulfuric acid[26] as reagents and
.
catalysts were reported. Although some of these methods have convenient
protocols with good to high yields, the majority of these methods suffer at
least from one of the following disadvantages: reaction under oxidizing con-
ditions, high temperature, long reaction times, moisture sensitivity of the used
reagent, high cost, and hightoxicity. Hence, a practical and more efficientalterna-
tive using an inexpensive and environmentally friendly reagent is still of interest.
To our knowledge, there have been no reports about the use of PEG-supported
sulfonic acid as catalyst for the preparation of 1,1-diacetates. We herein report
a facile method for the formation of 1,1-diacetates by reaction of an aldehyde
with acetic anhydride in the presence of PEG-supported sulfonic acid.
Among the various soluble polymers, polyethylene glycol (PEG) has
increasingly become an attractive support.[27] The dimesylation of PEG 4000
was carried out as previously reported and then conversion to the corresponding
dibromide was achieved under standard conditions.[28] Reaction with 4-hydro-
xybenzenesulfonic acid and sodium hydroxide, then acidification with concd.
HCl gave the difunctionalized PEG-supported sulfonic acid 2 (Scheme 1).
To optimize the reaction conditions, initially the reaction of benzaldehyde
3a with an excess of acetic anhydride to the corresponding 1,1-diacetate 4a
(Scheme 2) was carried out with PEG-supported sulfonic acid as catalyst
using various solvents such as dichloromethane (88%), acetonitrile (78%),
or diethyl ether (45%). However, a high yield of the product (92%) was
obtained under solvent-free conditions. By using this catalyst, various
aldehydes 3a–3l were converted to their corresponding diacetates 4a–4l in
Scheme 1.

PEG-Supported Sulfonic Acid as Catalyst
1021
Scheme 2.
moderate to good yields within short reaction times by employing the above
conditions (Table 1). As seen from Table 1, both aromatic (entries 1–12
and 15) aliphatic (entry 14), and a,b-unsatured (entry 13) aldehydes
afforded their corresponding diacetates in equally good yields, but the acid-
sensitive substrate furfural is converted to its 1,1-diacetate in moderate
yield (entry 12), and the 4-(N,N-dimethylamino)benzaldehyde failed to give
corresponding 1,1-diacetate. The starting materials were quantitatively
recovered under the same conditions. The explanation for this result may be
the strong electron donation of the dimethylamino group in 3m, which will
reduce the reactivity (Table 1, entry 16). A degree of tautomerisation may
occur in 3m with formation of a quininoid structure and thus decrease the
Table 1. Synthesis of 1,1-diacetates in the presence of PEG-supported sulfonic acid
Time
(min)
Entry
Substrate (3a–m)
Benzaldehyde (3a)
Benzaldehyde (3a)
Comp.
Yield (%)a
1
2
35
35
35
35
40
40
90
30
30
25
30
35
30
40
50
150
4a
4a
4a
4a
4b
4c
4d
4e
4f
92
90b
90c
88d
91
88
85
94
86
96
93
70
90
78
85
—
3
Benzaldehyde (3a)
Benzaldehyde (3a)
4
5
4-Methylbenzaldehyde (3b)
3-Methoxybenzaldehyde (3c)
2-Hydroxybenzaldehyde (3d)
4-Chlorobenzaldehyde (3e)
2,6-Dichlorobenzaldehyde (3f )
4-Nitrobenzaldehyde (3g)
4-Cyanobenzaldehyde (3h)
Furfural (3i)
6
7
8
9
10
11
12
13
14
15
16
4g
4h
4i
Cinnamaldehyde (3j)
Hexanal (3k)
4j
4k
4l
4-Acetylbenzaldehyde (3l)
4-(N,N-Dimethylamino)
benzaldehyde (3m)
—
aYields refer to the isolated pure products based on aldehydes.
bWith the first regenerated resin.
cWith the second regenerated resin.
dWith the fourth regenerated resin.

1022
Q.-Y. Wang et al.
Scheme 3.
reactivity of the aldehyde group (Scheme 3). Furthermore, in the reaction of
2-hydroxybenzaldehyde under these conditions, both carbonyl and phenolic
OH group of substrate were acylated (Table 1, entry 7). On the other hand,
the chemoselectivity of this method was demonstrated using 4-acetylbenzal-
dehyde (Table 1, entry 15). Smooth conversion of the aldehyde to the corre-
sponding diacetate was observed while the ketone functionality remained
unaffected.
After finishing the reaction, the recovered PEG-bound sulfonic acid was
precipitated with cold diethyl ether and can be used repeatedly for the prep-
aration of the present 1,1-diacetates without obvious decreases in the yield,
as shown in Table 1 (entries 1–4). It should be noted that when the
catalytic activity of polymeric sulfonic acid decreased, the resin could be
treated with concd. HCl again to keep its catalytic activity. In some cases, a
trace amount of the PEG residue, which might contaminate the final
products 4, was easily removed by passing the crude product through a pad
of silica-gel column (ethyl acetate/hexane, 1:9 as the eluent).
In conclusion, we have reported a mild, efficient, and environmentally
benign method for preparation of acylals from aldehydes and acetic
anhydride in the presence of PEG-supported sulfonic acid in good yields
within short reaction times. The use of cheap, recyclable PEG-bound
sulfonic acid as catalyst is another advantage of this method.
EXPERIMENTAL
Melting points were determined on an X4 melting-point apparatus and are
1
uncorrected. H NMR spectra were recorded on Bruker Avance 400-MHz
spectrometer. IR spectra were determined on a Perkin-Elmer SP One FT-IR
spectrophotometer. All reagents were purchased from commercial sources
and were used without further purification.
Preparation of PEG-Supported Sulfonic Acid 2
PEG 4000 (10.0 g, 2.5 mmol) was dissolved in CH2Cl2 (100 mL) and cooled
to 08C. Methanesulfonylchloride (2.0 mL, 25.0 mmol) and triethylamine
(1.5 mL) was then added dropwise. The reaction mixture was stirred at rt
overnight and concentrated in vacuo. The crude product was dissolved in

PEG-Supported Sulfonic Acid as Catalyst
1023
CH2Cl2 (100 mL) and added dropwise with vigorous stirring to diethyl ether
(1.0 L). The resulting precipitate was collected by filtration, washed with
diethyl ether (3 Â 30 mL) and then dried under high vacuum to give the
desired PEG 4000 dimesylate as a white solid (9.76 g, 94% based on
polymer recovery). 1H NMR (400 MHz; CDCl3) d 3.50–3.66 (m, PEG
CH2), 3.06 (s, 6H SO2CH3).
PEG 4000 dimesylate (10.0 g, 2.40 mmol) in acetone (50 mL) and lithium
bromide (1.47 g, 16.9 mmol) were heated at reflux for 18 h. The solution was
cooled, and a white solid was removed by filtration. The filtrate was evapor-
ated in vacuo; the crude product dissolved in hot propan-2-ol (50 mL) and then
cooled to 58C. The precipitate formed was collected by filtration, washed with
propan-2-ol (10 mL) and Et2O (2 Â 25 mL), and dried in vacuo to afford PEG
1
4000 dibromide as a colorless solid (9.90 g, 100%). H NMR (400 MHz;
CDCl3) d 3.40–3.86 (m, PEG CH2), 3.45 (t, J ¼ 6.3 Hz, CH2Br).
To a solution of PEG 4000 dibromide (8.25 g, 2.0 mmol) in propan-2-ol/
water (1:1, 100 mL), 4-hydroxybenzenesulfonic acid (mono sodium salt)
(4.65 g, 20.0 mmol) and sodium hydroxide (800 mg, 20.0 mmol) were
added. The reaction mixture was heated at reflux for 24 h. The solvent was
removed in vacuo, and the crude product dissolved in hot propan-2-ol
(100 mL), from which an insoluble white solid was removed by filtration.
The filtrate was cooled to 58C, and the precipitate that formed was collected
by filtration. This was washed with propan-2-ol (10 mL) and Et2O
(2 Â 25 mL) and dried in vacuo to afford PEG 4000 disulfonic acid sodium
1
salt as a white solid (8.10 g, 93%). H NMR (400 MHz; CDCl3) d 3.41–
3.84 (m, PEG CH2), 4.15 (t, J ¼ 5.1 Hz, 4H, CH2OAr), 6.84 (d, J ¼ 8.7 Hz,
4H, Ar-H), 7.85 (d, J ¼ 8.7 Hz, 4H, Ar-H).
To a solution of PEG 4000 disulfonic acid sodium salt (21.8 g, 5.0 mmol)
in propan-2-ov/water (1:1, 100 mL), concd. HCl (2.5 mL) was added and
stirred for 5 h at rt. The solvent was removed in vacuo, and the crude product
dissolved in hot propan-2-ol (100 mL). The solution was cooled to 08C, and
the precipitate that formed was collected by filtration. The precipitation step
was repeated; the combined precipitates were washed with propan-2-ol
(10 mL) and Et2O (2 Â 25 mL) and then dried in vacuo to afford PEG 4000 dis-
ulfonic acid (2) as a white solid (20.3 g, 94%). 1H NMR (400 MHz; CDCl3) d
3.38–3.88 (m, PEG CH2), 4.22 (t, J ¼ 4.6 Hz, 4H, CH2OAr), 7.05
(d, J ¼ 9.0 Hz, 4H, Ar-H), 7.94 (d, J ¼ 9.0 Hz, 4H, Ar-H), 11.26 (s, 2H).
General Procedure for Preparation of 1,1-Diacetates 4
To a stirred solution of aldehyde (2.0 mmol) in freshly distilled Ac2O
(20.0 mL), PEG 4000 disulfonic acid (0.1 mmol, 0.45 g) was added, and the
reaction mixture was stirred at room temperature for the time given in
Table 1. After completion of the reaction (thin-layer chromatography,
TLC), the excess of Ac2O was distilled. The mixture was cooled to 08C,

1024
Q.-Y. Wang et al.
and then diethyl ether (20.0 mL) was added with vigorous stirring. The
resulting precipitate was collected by filtration and washed with cold
diethyl ether (2 Â 20 mL). The filtrate was washed successively with aq.
10% NaHCO3, aq. saturated NaHSO3 solution, and water (20 mL each) and
dried over sodium sulfate. The solvent was evaporated under reduced
pressure to give the corresponding 1,1-diacetates, which were further
purified by passing the crude product through a pad of silica-gel column
(10% ethyl acetate in hexane), if necessary.
When the catalytic activity of the recovery PEG-bound sulfonic acid
decreased, the resin could be treated with concd. HCl (0.5 mL) with stirring at
rt overnight, and then the polymeric sulfonic acid was precipitated by addition
of diethyl ether (100 mL) to the mixture. The recovered white precipitate was
collected, washed with diethyl ether (2 Â 5 mL), and dried in vacuo for reuse.
Data
1,1-Diacetoxy-1-phenylmethane (4a): mp 44–458C (lit.[20] mp 44–458C);
1H NMR: d ¼ 7.61 (s, 1H), 7.40–7.37 (m, 3H), 7.30–7.25 (m, 2H), 1.93
(s, 6H); IR (KBr): 3060, 1756, 1604, 1470, 1376, 1245, 1205, 1064, 1009,
760, 699 cm21
.
1,1-Diacetoxy-1-(4-methylphenyl)methane (4b): mp 80–818C (lit.[20] mp
81–828C); 1H NMR: d ¼7.50 (s, 1H), 7.28 (d, J ¼ 8.6 Hz, 2H), 6.87
(d, J ¼ 8.6 Hz, 2H), 2.30 (s, 3H), 1.97 (s, 6H); IR (KBr): 3032, 2944, 1756,
1609, 1500, 1378, 1221, 1205, 788, 718 cm21
.
1
1,1-Diacetoxy-1-(3-methoxyphenyl)methane (4c): oil (lit.[15] oil); H NMR:
d ¼ 7.54 (s, 1H), 7.30–7.05 (m, 3H), 6.85 (s, 1H), 3.85 (s, 3H), 2.00
(s, 6H); IR (neat): 3030, 2944, 2801, 1756, 1611, 1500, 1380, 1221, 1205,
1014, 790, 721 cm21
.
1,1-Diacetoxy-1-(2-acetoxyphenyl)methane (4d): mp 100–1018C (lit.[25] mp
1
100–1028C); H NMR: d ¼ 7.74 (s, 1H), 7.26–7.05 (m, 2H), 7.10–7.00
(m, 2H), 2.18 (s, 3H), 1.95 (s, 6H); IR (KBr): 3050, 2950, 1769, 1750,
.
1610, 1500, 1466, 1384, 1250, 1205, 1069, 990, 780 cm21
1,1-Diacetoxy-1-(4-chlorophenyl)methane (4e): mp 81–828C (lit.[20] mp 82–
838C); 1H NMR d ¼ 7.55 (s, 1H), 7.32 (d, J ¼ 7.6 Hz, 2H), 7.20
(d, J ¼ 7.6 Hz, 2H), 2.09 (s, 6H); IR (KBr): 3058, 3020, 1758, 1608, 1485,
1210, 1012, 821, 620 cm21
.
1,1-Diacetoxy-1-(2,6-dichlorophenyl)methane (4f): mp 87–888C (lit.[19] mp
1
85–868C); H NMR: d ¼ 8.28 (s, 1H), 7.35–7.12 (m, 3H), 2.11 (s, 6H); IR
(KBr): 3075, 1765, 1600, 1489, 1386, 1250, 1200, 1018, 930, 616 cm21
.

PEG-Supported Sulfonic Acid as Catalyst
1025
1,1-Diacetoxy-1-(4-nitrophenyl)methane (4g): mp 124–1258C (lit.[20] mp
1
125–1278C); H NMR: d ¼ 8.12 (d, J ¼ 8.9 Hz, 2H), 7.56 (d, J ¼ 8.9 Hz,
2H), 7.50 (s, 1H), 2.06 (s, 6H); IR (KBr): 3092, 1764, 1610, 1530, 1354,
.
1210, 1200, 1088, 1000, 961, 848, 732 cm21
1,1-Diacetoxy-1-(4-cyanophenyl)methane (4h): mp 101–1028C (lit.[2] mp
1
98–1028C); H NMR: d ¼ 7.70 (d, J ¼ 8.6 Hz, 2H), 7.10 (d, J ¼ 8.6 Hz,
2H), 7.31 (s, 1H), 2.15 (s, 6H); IR (KBr): 3068, 2210, 1758, 1609, 1380,
.
1231, 1205, 1010, 828 cm21
1,1-Diacetoxy-1-(2-furyl)methane (4i): mp 52–538C (lit.[20] mp 52–538C); 1H
NMR: d ¼ 7.68 (s. 1H), 7.40 (d, J ¼ 7.3 Hz, 1H), 6.45–6.28 (m, 2H), 2.10
(s, 6H); IR (KBr): 3100, 1751, 1500, 1240, 1201, 1058, 936, 828, 750 cm21
.
1,1-Diacetoxy-3-phenylprop-2-ene (4j): mp 85–868C (lit.[20] mp 85–868C;
1H NMR: d ¼ 7.66–7.15 (m, 6H), 6.84 (d, J ¼ 15.8 Hz, 1H), 5.96
(d, J ¼ 15.8 Hz, 1H), 2.07 (s, 6H); IR (KBr): 3086, 2928, 1760, 1654, 1610,
1495, 1376, 1241, 1205, 1110, 1003, 941, 752, 690 cm21
.
1
1,1-Diacetoxyhexane (4k): oil (lit.[2] oil); H NMR: d ¼ 6.62 (t, J ¼ 5.6 Hz,
1H), 2.02 (s, 6H), 1.80–1.22 (m, 8H), 0.92 (t, J ¼ 7.1 Hz, 1H); IR (neat):
2972, 1756, 1460, 1376, 1235, 1205, 1091, 1021, 990, 652 cm21
.
1,1-Diacetoxy-1-(4-acetylphenyl)methane (4l): mp 56–598C (lit.[15] mp 56–
578C); 1H NMR: d ¼ 7.97 (d, J ¼ 8.4 Hz, 2H), 7.68 (s, 1H), 7.62
(d, J ¼ 8.4 Hz, 2H), 2.61 (s, 3H), 2.10 (s, 6H); IR (KBr): 3085, 2926, 1760,
1695, 1608, 1500, 1376, 1240, 1202, 1110, 1002, 940, 824, 960 cm21
.
ACKNOWLEDGMENT
We gratefully acknowledge financial support from the National Natural
Science Foundation (NSF) of China (No. 20562005) and NSF of Jiangxi
Province (No. 0620021).
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