Sulphated zirconia as an eco-friendly catalyst in acylal preparation under solvent-free conditions, acylal deprotection assisted by microwaves, and the synthesis of anhydro-dimers of o-hydroxybenzaldehydes

Article abstract of DOI:10.3390/molecules14104065

A solvent-free approach is described for the regioselective synthesis of acylals (1,1-diacetates) in shorter reaction times and higher yields, compared to conventional methodology using solvents. In the protection reaction of the o-hydroxybenzaldehyde the formation of acetyl compounds and anhydro-dimers was observed. The deprotection reaction involves microwave (MW) exposure of diluted reactants in the presence of solid sulphated zirconia (SZ) catalyst that can be easily recovered and reused. The sulphated zirconia was recycled several times without any loss of activity.

Full text of DOI:10.3390/molecules14104065

Molecules 2009, 14, 4065-4078; doi:10.3390/molecules14104065
OPEN ACCESS
molecules
ISSN 1420-3049
www.mdpi.com/journal/molecules
Article
Sulphated Zirconia as an Eco-Friendly Catalyst in Acylal
Preparation under Solvent-Free Conditions, Acylal
Deprotection Assisted by Microwaves, and the Synthesis of
Anhydro-Dimers of o-Hydroxybenzaldehydes
Laura Nadxieli Palacios-Grijalva 1, Deysi Y. Cruz-González 1, Leticia Lomas-Romero 2,
Eduardo González-Zamora 2, Gerardo Ulibarri 3 and Guillermo E. Negrón-Silva 1,*
1
Departamento de Ciencias Básicas, UAM-A, Av. San Pablo, No. 180. C.P. 02200, México, D.F.,
Mexico; E-Mails: lnpg@correo.azc.uam.mx (L.N.P.-G.); dycg@correo.azc.uam.mx (D.Y.C.-G.)
2
Departamento de Química, UAM-I, San Rafael Atlixco, No. 186. C.P. 09340, México, D.F.,
Mexico; E-Mails: llr@xanum.uam.mx (L.L.-R.); egz@xanum.uam.mx (E.G.-Z.)
3
Department of Chemistry & Biochemistry, Laurentian University, Sudbury, ON P3E2C6, Canada;
E-Mail: gulibarri@laurentian.ca
* Author to whom correspondence should be addressed; E-Mail: gns@correo.azc.uam.mx.
Received: 25 August 2009; in revised form: 21 September 2009 / Accepted: 27 September 2009 /
Published: 12 October 2009
Abstract: A solvent-free approach is described for the regioselective synthesis of acylals
(1,1-diacetates) in shorter reaction times and higher yields, compared to conventional
methodology using solvents. In the protection reaction of the o-hydroxybenzaldehyde the
formation of acetyl compounds and anhydro-dimers was observed. The deprotection
reaction involves microwave (MW) exposure of diluted reactants in the presence of solid
sulphated zirconia (SZ) catalyst that can be easily recovered and reused. The sulphated
zirconia was recycled several times without any loss of activity.
Keywords: sulphated zirconia; solvent-free; microwaves; regioselective; diacetates
Introduction
Organic transformations are frequently assisted by heterogeneous catalysts which usually provide
rate enhancements, yield and/or selectivity improvements, and easier work ups, but the most important

Molecules 2009, 14
4066
general advantage of these methods is their contribution to eco-friendly, “green”, sustainable
chemistry, which involves the design of chemical processes with a view to reducing or even
eliminating the use and production of hazardous materials. Recent efforts have focused on limiting the
use of organic solvents and their replacement with new, less polluting and cost-effective ecologically-
friendly processes, a topic of considerable interest to the chemical industry [1-3].
Functional group protection and deprotection strategies are essential to target-oriented synthesis in
organic chemistry [4,5]. Aldehydes can be protected as acylals (1,1-diacetates), which are stable
compounds in basic and neutral media and easily re-converted into parent aldehydes [6]. In general,
1,1-diacetates are prepared from aldehydes by treatment with acetic anhydride using homogeneous
catalysts [7-17]. The methods mentioned above are not entirely satisfactory, owing to the problems of
corrosion, tedious work-up, environmental pollution and non recoverable catalysts. Such
environmental problems have attracted considerable attention towards the development of alternative
processes using novel heterogeneous catalysts [18-29]. In this context, heterogeneous catalysts play a
dramatic role with their easy work-up, separation of the catalyst by filtration, high purity of the
products, and the possibility of catalyst recycling. The application of sulphated zirconia as a versatile
catalyst in organic transformations was enhanced by the comprehensive review published by
Reddy et al. [30], and other research groups in subsequent papers [31-33]. Following our work on the
application of sulphated zirconia as an eco-friendly catalyst [34-38], we proposed its application in
protection reactions under solvent free conditions, the deprotection of the protected moieties assisted
by microwaves and the synthesis of anhydro-dimers of o-hydroxy-benzaldehydes.
Figure 1. Diffraction pattern of sulphated zirconia.
2.5
2.0
1.5
1.0
0.5
20
30
40
50
60
70
80
2
Results and Discussion
The X ray powder diffraction (XRD) patterns in the 20–65º 2θ range for sulphated zirconia
catalysts showed that after calcination the tetragonal phase is the major form present (ICSD collection
code: 066787), as given by reflections in 2θ = 30.18º (with 100 as relative intensity) and the peaks

Molecules 2009, 14
4067
located at 34.616º, 35.283º, 43.002º, 50.214º, 50.770º, 59.291º, 60.187º, 62.724º, 72.894º, 74.617º and
81.768º [35] (Figure 1).
The study of the nitrogen physisorption provides information regarding the textural properties of
the catalysts (Figure 2). The adsorption/desorption isotherm relative to calcinated sample belongs to
type IV IUPAC classification, with a type H2-H3 hysteresis loop [39]. It is an isotherm with a steep
increment of the adsorbed volume at low pressure and a second one at around P/Po = 0.35,
corresponding to pore filling and the existence of mesopores [40]. The textural properties of sulphated
zirconia are shown in Table 1. The surface area (SBET) was calculated by the BET method, the
cumulative pore volume (Vp) and the average pore diameter (Dp), were obtained by the BJH data
analysis [41].
Figure 2. Nitrogen adsorption-desorption plot of sulphated zirconia.
Adsorption
100
Desorption
80
60
40
20
0,0
0,2
0,4
0,6
0,8
1,0
Relative Pressure (p/pO)
Table 1. Sulphated zirconia surface features.
Surface area (SBET
Pore volume (Vp)
Pore diameter (Dp)
)
90 m²/g
0.12 cm³/g
52.7 Å
For testing recyclability, the sulphated zirconia catalyst was filtered after the benzaldehyde
protection-deprotection reaction and activated at 500 ºC for 1 hr in air flow; the reactivated sulphated
zirconia samples were analyzed by XRD. We observed the presence and increase of the monoclinic
phase from the second to the fourth recalcination cycles (2θ = 28.16º and 2θ = 31.44º reflexions), due
to the effect of the reactivation process (Figure 3). In a previous work we demonstrated a similar
behavior in the synthesis of β-amino alcohols. [37-38]

Molecules 2009, 14
4068
Figure 3. XRD Patterns of reactivated sulphated zirconia.
+
6
5
4
3
2
1
0
Monoclinic
*
+
Tetragonal
+
+
+
4th cycle
+
+
+
+
*
*
*
*
+
+
+
3rd cycle
*
*
2nd cycle
1st cycle
80
20
30
40
50
60
70
2
The basic scheme of the acylal protection and deprotection reactions of using sulphated zirconia as
acid catalyst is shown in Scheme 1.
Scheme 1. Reaction of protection and deprotection of acylals.
R= aryl, alkyl
Table 2 shows isolated yields using some different aldehydes in the solvent free protection reaction
at 0 ºC, in the presence of sulphated zirconia catalyst.
Table 2. Aldehydes protection under solvent-free conditions.
Entry
1
Substrate
Time (hr)
Product
Yield (%)
5.00a
6.00b
99c
97d
4.20a
5.00b
100c
99d
2
3
4.30a
8.00b
99c
90d

Molecules 2009, 14
4069
Table 2. Cont.
4.30a
5.00b
97c
94d
4
5
4.00a
5.00b
99c
97d
7.00a
4.30b
95c
90d
6
5.00a
5.00b
99c
95d
7
8
5.00a
5.00b
99c
85d
5.00a
5.00b
100c
90d
9
5.00a
5.00b
99c
85d
10
11
8.00a
5.00b
99c
95d
a Reaction conditions: aldehyde (0.83 mmol), acetic anhydride (2.5 mmol), SZ (25 mg) and no
b
c
solvent at 0 °C; Reaction conditions of the published data [35]. Yields of solvent free reactions.
1
d
The products were characterized by IR, H-NMR and Mass Spectroscopy; Yields refer to the
published data [35].
Table 3 shows the yield of the 1,1-diacetate deprotections to the corresponding aldehydes using
catalytic amounts of sulphated zirconia in CH3CN at 60 ºC in a microwave reactor.
Table 3. 1,1-Diacetates deprotection reaction to aldehydes.
Entry
1
Substrate
Time(hr)
Product
Yield (%)
100c,d
0.45a
6.00b
0.45a
6.00b
100c,d
2

Molecules 2009, 14
4070
Table 3. Cont.
0.30a
6.00b
100c,d
100c,d
100c,d
3
4
5
0.30a
6.00b
0.30a
6.00b
1.00a
6.00b
100c,d
6
0.30a
6.00b
100c,d
100c,d
100c,d
7
8
9
2.00a
6.00b
0.60a
6.00b
2.00a
6.00b
100c,d
100c,d
10
11
2.00a
6.00b
O2N
CHO
O
a Reaction conditions: A solution of 1,1-diacetates (1 mmol) in HPLC acetonitrile (0.5 mL) and SZ (25 mg)
were irradiated at 60 ºC (initial power of 100 W) for 10 min in a self tuning mode CEM lab mate ®
b
c
d
microwave synthesizer; Reaction conditions of the published data [35]; Yields of microwave reactions;
Yields refer to the published data [35].
When the recycled catalysts were tested in the benzaldehyde protection-deprotection reaction, no
significant yield changes were observed (Table 4).
Table 4. Aldehyde protection-deprotection reactions in the presence of reactivated
sulphated zirconia.
% Yield
Protection Deprotection
% Yield
Cycle No.
1st
2nd
3rd
4th
92
90
90
86
90
89
89
87

Molecules 2009, 14
4071
We have recently applied the experimental conditions described above to o-hydroxybenzaldehyde
(1). We observed a 12% production of the triacetate 2, and 88% of the anhydro dimer of
o-hydroxybenzaldehyde (6,12-epoxy-6H,12H-dibenzo[b,f][1,5]dioxocin, 3) (Scheme 2).
The classic method of dimerization employs acetic anhydride as the dehydrating agent and solvent
using a catalytic amount of sulfuric acid [42], this method provides a 65% of the dimer 3. Clearly, the
advantages with our experimental conditions are the reusability of the catalyst, the easy separation of
pure products and carrying out the reaction in conditions of green chemistry.
Scheme 2. Acylation and autocondensation reaction of 1 under classic conditions and by
microwaves.
If the reaction is assisted by microwave radiation at 0 °C, the formation of the dimer of o-hydroxy-
benzaldehyde, 3, increases to 93% and the formation of the triacetate, 2 decreases to 7% (Scheme 2).
In our last work, we demonstrated that some aliphatic and aromatic ketones do not form acylals
under the described conditions [35]. From this evidence we studied the dimerization reaction of o-
hydroxybenzaldehyde and o-hydroxyacetophenone.
The dimer 3 of o-hydroxybenzaldehyde has been previously described as the result of an aggressive
procedure involving H2SO4, and the dimer 5 (6-methyl-6,12-epoxy-6H,12H-dibenzo[b,f][1,5]-
dioxocin), is formed in two steps: aggressive dimerization reaction with THF (tetrahydrofuran) at
-78 ºC, n-butyllithium (n-BuLi ) and H2SO4, followed by a methylation with methyl iodide [43]. Based
on the last the last evidence, our aim was the dimerization reaction between o-hydroxybenzaldehyde,
1, and o-hydroxyacetophenone, 4 employing sulphated zirconia as catalyst; we observed the formation
of 5% of the corresponding triacetate 2, 17%yield of the dimer 3 of o-hydroxybenzaldehyde and an
18% yield of dimer 5 (Scheme 3).
Scheme 3. Acylation and condensation reaction of the mixture composed of 1 and 4 under
classical conditions and by microwaves.
Further, when we applied microwave radiation at 0 ºC (initial power 100 W), 5% of product 2 is
obtained, 12%of product 3 and 18% of product 5 (Scheme 3).

Molecules 2009, 14
4072
The importance of these anhydro dimers is that they have four of the six rings present in some
natural products, and for this reason, Taylor and co-workers have used them as starting materials in the
formation of the preussomerins [43].
Furthermore, if m-benzaldehyde (6) is used as substrate, the formation of the β-hydroxyaldehyde
dimerization product is not observed and rather the triacetate 7 is obtained quantitatively (Scheme 4).
Scheme 4. Acylation and acetylation reactions of m-hydroxybenzaldehyde.
In the case of p-hydroxybenzaldehyde (8), it does not form the dimer but, also the triacetal 9 and
diacetal 10 are formed in 62% and 18% yield, respectively (Scheme 5).
Scheme 5. Acylation and acetylation reactions of p-hydroxybenzaldehyde.
Experimental
General
Powder X ray diffraction (XRD) was performed with a Philips X´Pert Instrument using Cu K-alpha
radiation (45 kV, 40 mA). Nitrogen adsorption/desorption isotherms were obtained at -196 ºC on
Micrometrics ASAP 2020 equipment. The reaction products were analyzed by GC-FID (Agilent
Technologies 6890N) equipped with a HP-5 column with the program 70-180 ºC (20 ºC/min) for 6.50
min then 180-280 ºC (15 ºC/min) for 7 min, injector 250 ºC , detector 280 ºC; the detector was set in
the Chemical Ionization mode using methane as reactive gas. Mass spectra were obtained by GC-MS
13
(Agilent Technologies 6890N, Detector 5973) using methane chemical ionization. 1H-NMR and C-
NMR spectra was measured at 500 MHz and 125 MHz, respectively, on a Bruker Avance DMX-500
spectrometer using CDCl3 as solvent and tetramethylsilane as internal standard. Infrared (IR) spectra
were recorded on a Bruker Vector 33 ATR spectrometer. All aldehydes, reagents and solvents were
provided by Aldrich and all products were identified by IR, 1H-NMR, 13C-NMR, mass spectra and by
comparison of their corresponding melting points.

Molecules 2009, 14
4073
Sulphated zirconia synthesis
Zirconium n-propoxide (20 mL, 70% n-propanol) was mixed with 2-propanol (30 mL) and stirred
with a magnetic bar. Then, an acid solution (1 mL 98% sulfuric acid in 3.2 mL of distilled water) was
added dropwise in order to cause the hydrolysis and gelation of the zirconium n-propoxide. The solid
was filtered and dried at 80 ºC until complete alcohol evaporation, then calcinated in air at 600 ºC for 6 h.
Procedure for the conversion of aldehydes to geminal diacetates under solvent free conditions
A mixture of aldehyde (0.83 mmol), acetic anhydride (2.50 mmol), and sulphated zirconia (25 mg)
were placed in a screw-cap vial at 0 ºC. The suspension was stirred for the appropriate time (see
Table 1). After completion of the reaction, the catalyst was recovered by filtration and the filtrate was
extracted with EtOAc (3x10 mL) and water (2 × 10 mL). The organic extracts were combined and
washed with 10% NaHCO3 and dried over anhydrous Na2SO4. The solvent was evaporated under
reduced pressure and the residue was purified on silica gel using light petroleum-ether as eluent to give
the pure product 1,1-diacetates. All products were identified via GC-FID mass spectra and analyzed
GC-MS, 1H-NMR, 13C-NMR.
Procedure for the deprotection of 1,1 diacetates to aldehydes using Microwave synthesizer
A solution of 1,1-diacetate (1 mmol) in HPLC-grade acetonitrile (0.5 mL) and sulphated zirconia
(25 mg) was introduced into a pressurized reaction tube (10 mL) equipped with a magnetic stirrer and
the mixture was irradiated at 60 ºC (initial power of 100 W) for 10 min in a self tuning mode CEM
Labmate ® microwave synthesizer. After the reaction, the catalyst was recovered by filtration and the
filtrate was extracted with EtOAc and washed with water. The organic extracts were combined and
washed with 10% NaHCO3 and dried over anhydrous Na2SO4. Then was filtered and evaporated under
reduced pressure to give the corresponding aldehyde.
Procedure for the formation of o-hydroxybenzaldehyde dimer (6,12-epoxydibenzo-6H,12H-
dibenzo[b,f][1,5] dioxocin, 3) using the conventional thermal method
A mixture of o-hydroxybenzaldehyde (0.1738 mL, 1.66 mmol), acetic anhydride (0.1181 mL,
1.25 mmol) and sulphated zirconia (50 mg) were stirred for 3 h. under solvent free conditions. After
completion of the reaction, the catalyst was recovered by filtration and the filtrate was extracted with
EtOAc (3 × 10 mL) and washed with water (2 × 10 mL). The organic extracts were combined and
washed with 10% NaHCO3 and dried over anhydrous Na2SO4. The solvent was evaporated under
reduced pressure and the residue was chromatographied on silica gel (light petroleum-ether as eluent)
to give the corresponding dimer 3 as a white solid in 80% yield; m.p. 127-130 ºC (lit. [44] m.p.
130 ºC); GC-MSD for C14H10O3 (m.w.: 226g/mol): [M+1]+ = 227, [M+29]+ = 255, [M+41]+ = 267;
IR (cm-1):1590, 1455, 1069, 1611, 1217. 1H-NMR: δ (ppm) 7.28 (dd, 2H, J = 1.6, J = 7.7 Hz), 7.21-
1
2
7.26 (m, 2H), 6.95 (ddd, 2H, J = 1.1, J = 7.5, J = 8.6 Hz), 6.87 (d, 2H, J = 8.2 Hz), 6.35 (s, 2H);
1
2
3
13
13C-NMR: δ (ppm) 150.50, 130.94, 127.47, 121.51, 119.98, 116.59, 90.13. (lit. [45] C-NMR (125
MHz, CDCl ): δ (ppm) 150.55, 130.89, 127.42, 121.46, 120.00, 116.58, 90.14).
3

Molecules 2009, 14
4074
Procedure for the formation of o-hydroxybenzaldehyde dimer (6,12-epoxydibenzo-6H,12H-
dibenzo[b,f][1,5] dioxocin, 3) using microwave irradiation
A mixture of o-hydroxybenzaldehyde (0.1738 mL, 1.66 mmol), acetic anhydride (0.1181 mL,
1.25 mmol) and sulphated zirconia (50 mg) were introduced into a pressurized tube (10 mL) equipped
with a magnetic stirrer, which was irradiated in solvent free conditions to 0 ºC (initial power of 100 W)
for 30 min. After reaction, the catalyst was recovered by filtration and the filtrate was treated as
described in the conventional thermal method described above for dimer 3.
Procedure for the preparation of the dimer 6-methyl-6,12-epoxy-6H,12H-dibenzo[b,f][1,5]dioxocin
(5) using the conventional thermal method
A mixture of o-hydroxybenzaldehyde (0.0869 mL, 0.83 mmol), o-hydroxyacetophenone
(0.2260 mL, 1.66 mmol), acetic anhydride (0.11801 mL, 1.25 mmol) and sulphated zirconia (50 mg)
was magnetically stirred in solvent-free conditions at 0 ºC for 6 h. After completion of the reaction, the
catalyst was recovered by filtration and the filtrate was extracted with EtOAc (3x10 mL) and washed
with water (2x10 mL). The organic layer was washed with 10% NaHCO3 and dried over anhydrous
Na2SO4. The solvent was evaporated under reduced pressure and the residue was purified by silica gel
chromatography using 100% light petroleum-ether as eluent to give the corresponding dimer 5 in 15%
as a white solid with a m.p. 80-83 °C, GC-MSD for C15H12O3 (m.w.: 240 g/mol): [M+1] + = 241,
1
[M+29]+ = 269, [M+41]+ = 281; IR (cm-1): 1383, 1590, 1455, 1069, 1611, 1217; H-NMR: δ (ppm)
7.33 (ddd, 1H, J = 0.4, J = 1.6, J = 7.8 Hz), 7.27 (dtd, 1H, J = 0.5, J = 1.7, J = 7.7 Hz), 7.14-
1
2
3
1
2
3
7.19 (m, 2H), 6.91 (dd, 1H, J = 1.2, J = 7.4, Hz), 6.88 (dd, 1H, J = 1.2, J = 7.4, Hz), 6.83 (ddd,
1
2
1
2
1H, J = 0.4, J = 1.2, J = 8.2 Hz), 6.79-6.81 (m, 1H), 6.33 (s,1H), 2.01 (s, 3H);13C-NMR: δ (ppm)
1
2
3
151.98, 150.23, 130.32, 130.71, 127.26, 126.01, 123.42, 121.62, 121.22, 119.55, 116.76, 116.29,
95.45, 90.97, 25.05.
Procedure for the preparation of the dimer 6-methyl-6,12-epoxy-6H,12H-dibenzo[b,f][1,5]dioxocin
(5) using microwave irradiation
In a glass tube for microwave reactions equipped with a magnetic stirrer were introduced a
suspension of sulphated zirconia (50 mg), o-hydroxybenzaldehyde (0.0869 mL, 0.83 mmol),
o-hydroxyacetophenone (0.2260 mL, 1.66 mmol) and acetic anhydride (0.1181 mL, 1.25 mmol) in
under solvent free conditions at 0 ºC and the mixture was irradiated (initial power of 100 W) for 1 h.
After the reaction time, the catalyst was recovered by filtration and the filtrate was treated as described
in the conventional thermal method described above for dimer 5.
Conclusions
We have demonstrated the high activity of sulphated zirconia in the solvent-free formation of
glycals (1,1-diacetates or acylals), and in the corresponding microwave assisted deprotection reactions.
The catalyst can be recycled several times without significant loss of activity, it is highly stable,

Molecules 2009, 14
4075
chemoselective, and environmentally friendly, which could open the possibility for an environmentally
benign approach for the synthesis of acylals and triacetals under mild reaction conditions.
In case of o-hidroxybenzaldehyde, we observed the formation of the corresponding anhydro dimer,
as well as the formation of an acetylation product. For m-hydroxybenzadehyde and p-hydroxy-
benzaldehyde, aside from the acylation reaction, acetylation also occurs. On the other hand, when we
used o-hydroacetophenone with the o-hydroxybenzaldehyde, we observed the formation of the
corresponding anhydro dimer methylated on the six position.
Acknowledgements
The authors would like to thank Consejo Nacional de Ciencia y Tecnología, CONACyT (project
59417) for financial support. L. Nadxieli Palacios is indebted to CONACyT, for the Postgrade
Scholarship No. 204780 granted. LLR, EGZ and GNS wish to acknowledge the SNI for the distinction
of their membership and the stipend received.
References
1. Yadav, G.D.; Pujari, A.A. Friedel-Crafts acylation using sulfated zirconia as a catalyst. Green
Chem. 1999, 1, 69–74.
2. Ahmed, A.I.; Hakam, E.I.; Samra, S.E.; EL-Khouly, A.A.; Khder, A.S. Structural characterization
of sulfated zirconia and their catalytic activity in dehydration of ethanol. Colloids Surf. A
Physicochem. Eng. Asp. 2008, 317, 62–70.
3. Das, B.; Krishnaiah, M.; Laxminarayana, K.; Reddy, K.R. A simple and efficient one-pot
synthesis of β-acetamido carbonyl compounds using sulfated zirconia as a heterogeneous
recyclable catalyst. J. Mol. Catal. A. Chem. 2007, 270, 284–288.
4. Greene, T.W.; Wuts, P.G.M. Protective Groups in Organic Synthesis, 3rd ed.; Wiley-Interscience:
New York, NY, USA, 1999; p. 306.
5. Kocienski, P.J. In Protecting Groups; Georg Thieme Verlag: Stuttgart, Germany; New York, NY,
USA, 1994; pp. 156–164.
6. Manjula, K.; Pasha, M.A. Rapid and efficient method for the synthesis of acylals from aldehydes
and their deprotection catalyzed by p-toluene sulfonic acid. Synth. Commun. 2007, 37,
1563–1569.
7. Yin, L.; Zhang, Z.H.; Wang, Y.M. A stable intermediate: a new insight into the mechanism of
Lewis acids promoted formation of acylals from aldehydes. Tetrahedron Lett. 2007, 48,
3119–3122.
8. Yadav, J.S.; Reddy, B.V.S.; Sreedhar, P.; Kondaji, G.; Nagaiah, K. Mild and efficient conversion
of aldehydes to gem-diacetates using 2nd generation ionic liquids. Catal. Commun. 2008, 9,
590–593.
9. Hajipour, A.R.; Nasreesfahani, Z.; Ruoho, A.E. An efficient and chemoselective synthesis of
aldehyde 1,1 diacetate using morpholinum bisulfate as a Brönsted acid ionic liquid under solvent
free conditions. Org. Prep. Proc. Int. 2008, 40, 385–391.

Molecules 2009, 14
4076
10. Bhattacharya, A.K.; Mujahid, M.; Natu, A.A. An efficient method for the synthesis of acylals
from aldehydes under solvent free conditions catalyzed by antimony trichloride. Synth. Commun.
2008, 38, 128–134.
11. Ono, F.; Nishioka, K.; Itami, S.; Takenaka, H.; Sato, T. An improved method for the synthesis of
allylic gem diacetates from α,β unsatured aldehydes catalyzed by lithium tetrafluoroborate. Chem.
Lett. 2008, 37, 1248–1249.
12. Wang, M.; Song, Z.; Gong, H.; Jiang, H. Synthesis of 1,1 diacetates using a new combined
catalytic system, copper p- toluensulfonate/HOAc. Synth. Commun. 2008, 38, 961–966.
13. Kumar, S.; Saini, A.; Sandhu, J.S. Gallium (III) chloride: an efficient catalyst for facile
preparation of gem diacetates from aldehydes. ARKIVOC 2007, 14, 27–33.
14. Hajipour, A.R.; Khazdooz, L.; Ruoho, A.E. Brönsted acidic ionic liquid as an efficient catalyst for
chemoselective synthesis of 1,1 diacetates under solvent free. Catal. Commun. 2007, 9, 89–96.
15. Mirjalili, B.F.; Zolfigol, M.A.; Bamoniri, A.; Amrollahi, M.A.; Sheikhan, N. Chemoselective
synthesis of 1,1 diacetates from aldehydes in the presence of Al(HSO4)3 under mild solvent free
conditions. Russ. J. Org. Chem. 2007, 43, 852–854.
16. Bandgar, B.P.; Joshi, N.S.; Kamble, V.T. A versatile and practical synthesis of 1,1-diacetates
fromaldehydes catalyzed by cyanuric chloride. J. Chin. Chem. Soc. 2007, 54, 489–492.
.
17. Heravi, M.M.; Bakhtiari, K.; Benmorad, T.; Oskoore, H. V5O4 5H2O A mild and efficient catalyst
for chemoselective conversion of aldehydes to 1, 1 diacetates. J. Chin. Chem. Soc. 2007, 54,
273–275.
18. Sartori, G.; Ballini, R.; Bigi, F.; Bosica, G.; Maggi, R.; Righi, P. Protection and deprotection of
functional groups in organic synthesis by heterogeneous catalysis. Chem. Rev. 2004, 104,
199–250.
19. Desai, U.V.; Thopate, T.S.; Pore, D.M.; Wadgaonkar, P.P. An efficient solvent-free method for
the chemoselective synthesis of acylals from aldehydes and their deprotection catalyzed by silica
sulfuric acid as a reusable solid acid catalyst. Catal. Commun. 2006, 7, 508–511.
20. Li, T.S.; Zhang, Z.H.; Fu, C.G. Montmorillonite clay catalysis V: An efficient and facile
procedure for deprotection of 1,1-diacetates. Tetrahedron Lett. 1997, 38, 3285–3288.
21. Barua, A.; Das, P.J. Solvent free diacetylation of aldehydes using solid acid under microwave
irradiation and a simple route to their regeneration. Indian J. Chem. 2008, 47B, 938–941.
22. Hajipour, A.R.; Zarei, A.; Ruoho, A.E. P2O5/Al2O3 as an efficient heterogeneous catalyst for
chemoselective synthesis of 1,1-diacetates under solvent free. Tetrahedron Lett. 2007, 48,
2881–2884.
23. Romanelli, G.; Dimitroff, P.; Vázquez, P.; Autino, J.C. Chemoselective preparation of 1,1-
diacetates of aldehydes, mediated by a Keggin heteropolyacid under solvent free conditions at
room temperature. Eur. J. Chem. 2007, 4, 83–89.
24. Kamble, V.T.; Jamode, V.S.; Joshi, N.S.; Biradar, A.V.; Deshmukh, R.Y. An efficient method for
synthesis of acylals from aldehydes using silica supported perchloric acid. Tetrahedron Lett.
2006, 47, 5573–5576.
25. Khan, A.T.; Choudhury, L.H.; Ghosh, S. Silica supported perchloric acid: A highly efficient and
reusable catalyst for germinal diacylation of aldehydes under solvent free conditions. J. Mol.
Catal. A.: Chem. 2006, 255, 230–235.

Molecules 2009, 14
4077
26. Jin, T.S.; Zhao, Y.; Gu, S.Q.; Liu, L.B.; Li, T.S. An efficient procedure for the synthesis of 1,1-
diacetates from aldehydes with acetic anhydride catalyzed by silica sulfate. Ind. J. Chem. Sec. B
Org. Chem. 2006, 45B, 1054–1056.
27. Kumar, R.; Tiwari, P.; Maulik, P.R.; Misra, A.K. HClO4-SiO2 catalyzed chemoselective synthesis
of acylals from aldehydes under solvent free conditions. J. Mol .Catal. A. Chem. 2006, 247,
27–30.
28. Hajipour, A.R.; Zarei, A.; Khazdooz, L.; Mirjaili, B.B.; Sheikhan, N.; Zahmatkesh, S.; Ruoho,
A.E. Silica sulfuric acid as an efficient heterogeneous catalyst for the synthesis of acylals from
aldehydes under solvent free conditions. Synthesis 2005, 20, 3644–3648.
29. Hydarzadeh, S.; Salavati-Niasari, M. An efficient method for the selective synthesis of germinal
diacetates (acylals) from aromatic aldehydes using alumina supported InCl3. J. Mol. Catal. A
Chem. 2005, 237, 254–258.
30. Reddy, B.M.; Patil, M.K. Organic Syntheses and Transformations Catalyzed by Sulfated Zirconia.
Chem. Rev. 2009, 109, 2185–2208.
31. Xinhua, Q.; Masaru, W.; Taku, M.A. Sulfated zirconia as a solid acid catalyst for the dehydration
of fructose to 5-hydroxymethylfurfural. Catal. Commun. 2009, 10, 1771–1775.
32. Murata, M.; Takamiya, N. Method to produce zirconia particles and zirconia transparent
dispersion. Jpn. Kokai Tokkyo Koho. 2009, 16.
33. Reddy, B.M. Reddy, G.K.; Rao, K.N.; Katta, L. Influence of alumina and titania on the structure
and catalytic properties of sulfated zirconia: Beckmann rearrangement. J. Mol. Catal. A Chem.
2009, 306, 62–68.
34. Negrón, G.; Angeles, D.; Lomas, L.; Martínez, A.; Ramírez, M.; Martínez, R. An efficient
synthesis of 6,6 dimethyl-2- (4-nitrophenyl)-1-(R-phenyl)-4,5,6,7-tetrahydro-1H-4-indolones
using solid sulphated zirconia catalyst. Heterocycles 2004, 63, 367–372.
35. Negrón, G.E.; Palacios, L.N. Angeles, B.; Lomas, L.; Gaviño, R. A mild efficient method for
chemoselective synthesis of acylals from aromatic aldehydes and their deprotections catalyzed by
sulfated zirconia. J. Braz. Chem. Soc. 2005, 16, 490–494.
36. Negrón, G.; Angeles, D.; Lomas, L.; Lara, V.H.; Gonzalez, E. Sulfated zirconia-catalyzed
synthesis of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs) under solventless conditions.
Competitive multicomponent Biginelli vs. Hantzsch reactions. Molecules 2006, 11, 731–738.
37. Negrón, G.; Hernández, C.X.; Angeles, D.; Lomas, L.; Gónzalez, E.; Méndez, J. Comparative
study of regioselective synthesis of beta-aminoalcohols under solventless conditions catalyzed by
sulfated zirconia and SZ/MCM-41. Molecules 2007, 12, 2515–2532.
38. Negrón, G.; Hernández, C.X.; Angeles, D.; Lomas, L.; Gónzalez, E.; Méndez, J. Microwave-
enhanced sulphated zirconia and SZ/MCM-41 catalyzed regioselective synthesis of beta-amino
alcohols under solvent-free conditions. Molecules 2008, 13, 977–985.
39. Zane, F.; Melada, S.; Signoretto, M.; Pinna, S. Active and recyclable sulphated zirconia catalysts
for the acylation of aromatic compounds. Appl. Catal. A. 2006, 299,137–144.
40. Yang, X.; Jentoft, F.C.; Girgsdies, F.; Ressler, T. Sulfated zirconia with ordered mesopores as an
active catalyst for n-butane isomerization. Catal. Lett. 2002, 81, 25–31.
41. Webb, P.A.; Orr, C. Analytical Methods in Fine Particle. Technology Micrometrics Instrument
Corporation Norcross: Georgia, USA, 1997; p. 301.

Molecules 2009, 14
4078
42. Kulkarni, V.S.; Hosangadi, B.D. A facile synthesis of anhydro dimers of o-
hydroxybenzaldehydes. Synth. Commun. 1986, 16, 191–193.
43. Ragot, J.P.; Prime, M.E.; Archibald, S.J.; Taylor, R.J.K. A novel route to Preussomerins via 2-
Arylacetal anions. Org. Lett. 2000, 2, 1613–1616.
44. Adams, R.; Fogler, M.F.; Kreger, W. The structure of disalicyl aldehydes. J. Am. Chem. Soc.
1922, 44, 1126–1133.
45. Jones, P.R.; Gelinas, R.M. The first spectral confirmation for the structures of anhydro dimers of
o-hydroxybenzaldehydes. J. Org. Chem. 1981, 46, 194–196.
Sample Availability: Samples of the compounds are available from the authors.
©2009 by the authors; licensee Molecular Diversity Preservation International, Basel, Switzerland.
This article is an open-access article distributed under the terms and conditions of the Creative
Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).