Microwave induced synthesis of geminal diacetates from aldehydes using envirocat EPZ10 without solvent

Article abstract of DOI:10.1007/PL00010311

A simple, efficient, and environmentally friendly synthesis of geminal diacetates using Envirocat EPZ10 under microwave activation and solvent-free conditions is described. Easy separation and recyclability of the catalyst, high reaction rates, high yields, and easy work-up are important advantages of this method.

Full text of DOI:10.1007/PL00010311

Monatshefte fuÈr Chemie 131, 417±420 (2000)
Microwave Induced Synthesis of Geminal
Diacetates from Aldehydes Using Envirocat
EPZ101 Without Solvent
Ã
Babasaheb P. Bandgar , Sangita S. Makone, and Sulakshana R. Kulkarni
School of Chemical Sciences, Swami Ramanand Teerth Marathwada University, Nanded-431606,
India
Summary. A simple, ef®cient, and environmentally friendly synthesis of geminal diacetates using
Envirocat EPZ101 under microwave activation and solvent-free conditions is described. Easy
separation and recyclability of the catalyst, high reaction rates, high yields, and easy work-up are
important advantages of this method.
Keywords. Envirocats: Microwaves: Aldehydes; Geminal diacetates.
Introduction
Geminal or 1,1-diacetates are synthetically useful as aldehyde protecting groups
[1] as alternatives to acetals. These diacetates are stable towards aqueous acids and
mild bases [2] and are useful as important building blocks for the synthesis of
dienes for Diels-Alder cycloaddition reactions [3]. Diacetates of some aldehydes
are reported to be good cross-linking reagents for cellulose in cotton [4] and
activators in the composition of a bleaching mixture for wine stained fabric [5]. A
patent claims the utility of 1,1-diacetates as protecting groups in the synthesis of an
intermediate for chrysanthemic acid [6].
Usually, the formation of 1,1-diacetates is catalyzed by protic acids [7] such as
sulfuric, methanesulfonic, or phosphoric acid, by Lewis acids, e.g. FeCl3 [2],
PCl3 [8], BF3 [9], ZnCl2 [10], etc. and by the super acid Na®on-H [11]. More
recently, Me3SiCl-NaI [12], I2 [13], sulfated zirconia [14], and zeolites [15] of
different types have also been used as catalysts for this conversion. However, the
application of conventional protic or Lewis acid catalysts entail the problems of
corrosivity, tedious work-up, and ef¯uent pollution. In some cases, either low
yield of product or long reaction times have been observed [8]. Therefore,
the development of new reagents providing higher ef®ciency, better yields,
environmentally more friendly procedures, high reaction rates, and easy work-up is
of more interest.
Ã
Corresponding author

418
B. P. Bandgar et al.
There has been a considerable growth in interest in recent years in the catalysis
of organic reactions by inorganic reagents supported on high surface area inorganic
materials [16]. Envirocats1, a new family of supported reagents, constitute a
signi®cant breakthrough in environmentally friendly chemistry. These reagents,
non-toxic powders which can be ®ltered off easily and may be reused after
activation, are capable of catalyzing various reactions [17]. Envirocat EPZ101
exhibits both Brùnsted and Lewis acid characteristics [17]. We report herein the
®rst example of Envirocat EPZ101 applied for the synthesis of 1,1-diacetates
under solvent-free conditions using microwave irradiation.
Results and Discussion
The results of the reaction geminal diacetates (cf. Scheme) are summarized in
Table 1. When aldehydes were mixed with Envirocat EPZ101 and Ac2O and
exposed to microwaves, the corresponding diacetates were obtained in excellent
yields and high purity. The reaction worked equally well for a dialdehyde (entry
13) The ef®ciency of Envirocat EPZ101 can be clearly visualized in the case of
aromatic aldehydes with an electron withdrawing group where the corresponding
diacetates have been obtained in excellent yields (entries 8±11), whereas e.g. the
phosphorus trichloride catalyzed reaction gave poor yields in this case and required
a very long reaction time (120 h) [8].
1
RCHO ‡ Ac2OEnvirocat EPZ1!0 RCHꢀOAc†
2
MW
Scheme
In conclusion, Envirocat EPZ101 has been found to be a convenient and very
effective heterogenous catalyst for the synthesis of 1,1-diacetates from a variety of
aldehydes under microwave irradiation and solvent-free conditions. The reaction is
quite general. The obivious advantages of this methodology are easy separation and
recyclability of the catalyst, high reaction rates, high yields, easy work-up, and an
eco-friendly procedure.
Experimental
Envirocat EPZ101 was obtained from Contract Chemicals, England, and used without activation.
Commercially available aldehydes were used as obtained. IR spectra were recorded on a Bomem MB
104 FT-IR spectrometer and 1H NMR spectra on a Perkin-Elmer 90 MHz spectrometer using TMS as
an internal standard.
General Procedure
A mixture of the aldehyde (5 mmol), acetic anhydride (10 mmol for monoaldehyde or 20 mmol for
dialdehyde) and Envirocat EPZ101 (100 mg) was irradiated with microwaves for the speci®ed time
(Table 1). After completion of the reaction (TLC), diethyl ether (2Â10 cm3) was added to the
reaction mixture, and EPZ101 was ®ltered off. After drying (Na2SO4), the ether was evaporated
under reduced pressure to give the products in high yield and in almost pure form.

Geminal Diacetates from Aldehydes
419
Table 1. Microwave induced EPZ101 catalyzed synthesis of geminal diacetates
Entry Aldehyde
Product [7±15]
Reaction Yielda
time (sec) (%)
1
2
3
4
5
Propanal
Propanal-1,1-diacetate
Butyraldehyde-1,1-diacetate
Hexanal-1,1-diacetate
Nonanal-1,1-diacetate
4-Bromobenzaldehyde-
1,1-diacetate
10
12
40
55
30
89
85
87
89
87
Butyraldehyde
Hexanal
Nonanal
4-Bromobenzaldehyde
6
7
4-Chlorobenzaldehyde
2,4-Dichlorobenzaldehyde
2-Nitrobenzaldehyde
4-Chlorobenzaldehyde-
1,1-diacetate
10
40
50
30
40
20
30
45
92
90
90
83
89
90
85
89
2,4-Dichlorobenzaldehyde-
1,1-diacetate
8
2-Nitrobenzaldehyde-
1,1-diacetate
9
3-Nitrobenzaldehyde
3-Nitrobenzaldehyde-
1,1-diacetate
10
11
12
4-Nitrobenzaldehyde
4-Nitrobenzaldehyde-
1,1-diacetate
3-Nitro, 4-chlorobenzaldehyde
3,4,5-Trimethoxybenzaldehyde
3-Nitro-4-chlorobenzaldehyde-
1,1-diacetate
3,4,5-Trimethoxybenzaldehyde-
1,1-diacetate
13
OHC
CHO
(AcO)2HC
CH(OAc)2
a
Products were characterized by their physical constants [7±15], their spectroscopic characteristics
(IR, 1H NMR), and by comparison with authentic samples; the yields refer to pure isolated products
Acknowledgements
We thank UGC, New Delhi, for ®nancial assistance and Contract Chemicals, England, for a generous
gift of Envirocat EPZ101.
References
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B. P. Bandgar et al.: Geminal Diacetates from Aldehydes
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Received November 3, 1999. Accepted November 24, 1999
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