Microwave-assisted acetalization of pentaerythritol catalyzed by 12-tungstophosphoric acid

Article abstract of DOI:10.1081/SCC-100108222

Efficient conversion of carbonyl compounds and pentaerythritol to corresponding diacetals in the presence of 12-tungstophosphoric acid under microwave irradiation is described.

Full text of DOI:10.1081/SCC-100108222

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MICROWAVE-ASSISTED ACETALIZATION
OF PENTAERYTHRITOL CATALYZED BY 12-
TUNGSTOPHOSPHORIC ACID
Yanqing Peng a , Gonghua Song b & Xuhong Qian a
a Institute of Pesticides and Pharmaceuticals, East China University of Science and
Technology , Shanghai, 200 237, P. R. China
b Institute of Pesticides and Pharmaceuticals, East China University of Science and
Technology , Shanghai, 200 237, P. R. China
Published online: 09 Nov 2006.
To cite this article: Yanqing Peng , Gonghua Song & Xuhong Qian (2001) MICROWAVE-ASSISTED ACETALIZATION OF
PENTAERYTHRITOL CATALYZED BY 12-TUNGSTOPHOSPHORIC ACID, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 31:24, 3735-3738, DOI: 10.1081/SCC-100108222
To link to this article: http://dx.doi.org/10.1081/SCC-100108222
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SYNTHETIC COMMUNICATIONS, 31(24), 3735–3738 (2001)
MICROWAVE-ASSISTED
ACETALIZATION OF
PENTAERYTHRITOL CATALYZED
BY 12-TUNGSTOPHOSPHORIC ACID
Yanqing Peng,Gonghua Song, * and Xuhong Qian
Institute of Pesticides and Pharmaceuticals,
East China University of Science and
Technology, Shanghai 200 237, P.R.China
ABSTRACT
Efficient conversion of carbonyl compounds and pentaerythri-
tol to corresponding diacetals in the presence of 12-tungsto-
phosphoric acid under microwave irradiation is described.
The diacetals of pentaerythritol are a series of useful organic com-
pounds.1 They have been used as plasticizers and vulcanizers, as physio-
logically active substance, and as potential protective groups in organic
synthesis.The preparation of these compounds has been well investigated.
A variety of acidic catalysts, such as hydrochloric acid, sulfuric acid,
p-toluenesulfonic acid,1 zinc chloride,2 acidic cation exchanger,3 Montmori-
llonite clay,4 expansive graphite5 and anhydrous ferrous sulfate6 have been
used for this purpose.
*Corresponding author. E-mail: ghsong@ecust.edu.cn
3735
Copyright & 2001 by Marcel Dekker, Inc.
www.dekker.com

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PENG,SONG,AND QIAN
Microwave dielectric heating has become an important technique in
organic synthesis.7 Wang et al.have presented their method by which the
diacetals of pentaerythritol were prepared in the presence of p-toluene-
sulfonic acid in a domestic microwave oven.8 We report herein a rapid
and facile procedure for the synthesis of pentaerythritol diacetals under
microwave irradiation catalyzed by 12-tungstophosphoric acid9 (Scheme 1).
Up to now, there is no report of the use of heteropolyacids as catalysts in
microwave-prompted organic reactions.The 12-tungstophosphoric acid
showed excellent activity in the acetalization reaction, hence, the amount
of catalyst used here (molar ratio of catalyst to substrate ¼ 1/200) is much
less than that in the reported process (the molar ratio of catalyst to
substrate ¼ 1/36).8
In experiment, carbonyl compounds were treated with 0.5 equivalent
of pentaerythritol in the presence of 12-tungstophosphoric acid under
microwave irradiation leading to diacetals in satisfactory yields, except
for benzophenone.Acetonitrile was used as solvent because of its high
dielectric constant and outstanding solubility.The results are summarized
in the table.
Scheme 1.
Table. Microwave-Assisted Acetalization of Pentaerythritol
M.P. (ꢀC)
Power Time Yielda
Entry
Carbonyl Compounds
(W)
(min)
(%)
Foundb
Lit.
1
2
3
4
5
6
7
8
9
10
Benzaldehyde
300
400
400
400
400
400
300
400
400
400
8
2
6
5
5
5
2
12
12
12
80
90
81
93
72
78
66
67
62
0
159–160 155–1568
199–200 197–1988
180–181 178–1808
180–182 179–1808
111–112 109–1108
171–172 170–1714
4-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
3-Nitrobenzaldehyde
4-Hydroxybenzaldehyde
Vanillin
Cinnamaldehyde
Cyclohexanone
Cyclopentanone
196–198
19510
115–116 113–1144
154–155 153–1542
Benzophenone
–
–
b
aIsolated yield; Recrystallization from n-butanol.

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ACETALIZATION OF PENTAERYTHRITOL
3737
The acetalization of both aldehydes and ketones have been investi-
gated.In many cases (except for 4-hydroxybenzaldehyde), our protocol
gave shorter reaction time and higher yields than presented literature.8
Aromatic aldehydes with strong electron-donor groups, such as hydroxy,
show less reactivity and give lower yields.Cinnamaldehyde with pentaery-
thritol for 2 min at 300 W microwave irradiation afforded a moderate yield
(66%) of the corresponding diacetals.Prolonged reaction time and higher
microwave power level resulted in dark-brown polymeric by-products.
Ketones show less reactivity than aldehydes.Benzophenone failed to give
the desired diacetal under above reaction conditions perhaps due to higher
steric hindrance.
In conclusion, this process for the synthesis of pentaerythritol diace-
tals is rapid, convenient and provides products in high yields with simple
work-up procedure.
EXPERIMENTAL SECTION
Melting points (uncorrected) were taking in open capillary on a
WRS-1 digital melting point apparatus manufactured in Shanghai.IR spec-
tra were recorded as KBr pellets on a Model 7650 spectrometer.All reagents
were commercially available and used without purification.Reactions were
conducted in a MW-800 II multimode cavity refluxing system made by
Microwave Research Center of East China Normal University.
Typical procedure. A solution of 4-chlorobenzaldehyde (2.81 g,
20 mmol), pentaerythritol (1.36 g, 10 mmol), 12-tungstophosphoric acid
(0.33 g, 0.1 mmol) in acetonitrile (20 mL) is refluxed during 2 min under
microwave irradiation.The solvent was evaporated in vacuo and the residue
was washed with hot water.Recrystallization from n-butanol gave 3.44 g
(90% yield) of corresponding diacetal as white needles.Mp 199–200 ꢀC (Lit.8
197–198ꢀC).
IR (KBr, cmꢁ1): 2860, 1600, 1495, 1385, 1340, 1205, 1170, 1080, 815.
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PENG,SONG,AND QIAN
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Received in the USA February 7, 2001

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