Solvent-free Chemoselective Synthesis of 1,1-diacetates Catalyzed by Iron Zirconium Phosphate

Article abstract of DOI:10.1002/jccs.201500233

In the present study, a mild, rapid, and efficient method for the protection of aldehydes with acetic anhydride (AA) in the presence of iron zirconium phosphate (ZPFe), at room temperature is reported. Selective conversion of aldehydes was observed in the presence of ketones. Under these conditions, different aldehydes bearing electron-withdrawing and electron-donating substituents were reacted with AA and the corresponding 1,1-diacetates (acylals) were obtained in high to excellent yields. The steric and electronic properties of the different substrates had a significant influence on the reaction conditions. Also, the deprotection of 1,1-diacetates has been achieved using this catalyst in water. The catalyst was characterized by several physico-chemical techniques. It was recovered easily from the reaction mixture, regenerated, and reused at least 7 times without significant loss in catalytic activity. This protocol has the advantages of easy availability, stability, reusability of the eco-friendly catalyst, chemoselectivity, simple experimental and work-up procedure, solvent-free conditions and only a stoichiometric amount of AA is needed.

Full text of DOI:10.1002/jccs.201500233

JOURNAL OF THE CHINESE
CHEMICAL SOCIETY
Article
Solvent-free Chemoselective Synthesis of 1,1-diacetates Catalyzed by Iron Zirconium
Phosphate
a,b
aHirbod Karimi
Young Researchers and Elite Club, Shahreza Branch, Islamic Azad university, Shahreza, Iran
b
Pharmaceutical Research Laboratory, Department of Chemistry, Isfahan University of Technology, Isfahan 84156, IR
Iran
(Received: Jun. 13, 2015; Accepted: Sept. 7, 2015; Published Online: Oct. 8, 2015; DOI: 10.1002/jccs.201500233)
In the present study, a mild, rapid, and efficient method for the protection of aldehydes with acetic anhy-
dride (AA) in the presence of iron zirconium phosphate (ZPFe), at room temperature is reported. Selective
conversion of aldehydes was observed in the presence of ketones. Under these conditions, different alde-
hydes bearing electron-withdrawing and electron-donating substituents were reacted with AAand the cor-
responding 1,1-diacetates (acylals) were obtained in high to excellent yields. The steric and electronic
properties of the different substrates had a significant influence on the reaction conditions. Also, the
deprotection of 1,1-diacetates has been achieved using this catalyst in water. The catalyst was character-
ized by several physico-chemical techniques. It was recovered easily from the reaction mixture, regener-
ated, and reused at least 7 times without significant loss in catalytic activity. This protocol has the advan-
tages of easy availability, stability, reusability of the eco-friendly catalyst, chemoselectivity, simple exper-
imental and work-up procedure, solvent-free conditions and only a stoichiometric amount of AA is
needed.
Keywords: Iron zirconium phosphate; Nanoparticles; Heterogeneous catalysis; Diacetate;
Solvent-free.
INTRODUCTION
The electrophilic nature of carbonyl groups is a domi-
synthesis of acylals from aldehydes using acetic anhydride
6
7
8
9
2 4 3
(AA) such as SiPW-8, SiO /B(SO H) , S-CKT, SuSA,
1
0
11
12
nant feature of their extensive chemistry. Selective protec-
tion and deprotection of aromatic or aliphatic carbonyl
SBA-15-Ph-PrSO
3
H, Zr(HSO
4
14
)
4
,
PEG-SO
3
H, Sul-
1
3
2-
15
phated Zirconia, SO
4
/SnO
2
,
ZSM-5-SO H, PS/
3
1
16
17
groups are essential steps in modern organic chemistry.
TiCl
4
1
,
Schiff base complex of Cr(III), Solid sulfuric
8
19
20
21
22
The protection of aldehydes, as acetals, acylals, oxathio-
acetals, or dithioacetals, is a common practice for manipu-
lation of other functional groups during multisteps synthe-
sis. Geminal diacetates (acylals) are one of the essential
carbonyl protecting groups due to their stability under both
neutral and basic media as well as acidic conditions and
also, they are easily converted into parent aldehydes, which
acid, SBSSA, CPTS–HOAc,
H
25
2
NSO
3
4
H, ZrCl ,
2
3
24
26
4 3
Zeolite Y, [bmpy]HSO , InCl , SPDTSA, sulfated
2
7
28
29
30
SnO
2
,
DBSA, P(4-VPH)ClO
4
,
H
6
3
P
1
2
W
18
O
62·24H
2
O,
O,
32
36
zirconium sulfophenyl phosphonate, La(NO ) ·6H
3 3
2
3
3
34
35
(NH
4
)
3
PW12
O
40
,
PBBS, SbCl
3
,
2
Cu3/2PMo12O40/SiO ,
3
7
38
Si–[SbSipim][PF
6
], DOWEX(R)50WX4, [bmim]
3
9
40
41
[FeCl
4
42
], Mo/TiO
2
–ZrO
43
2
2
,
Cyanuric chloride, CuSO
4
45
·
1
-2
44
are frequently used as protecting groups for aldehydes.
5H
2
O,
H
3
PW12
O
40
6-47
,
H
SO
4
-silica, Supported POM,
4
Furthermore, the acylals functionality can be converted
into other useful functional groups by reaction with appro-
priate nucleophiles and also are useful intermediates in in-
dustries, such as cross linking agent for cellulose in cotton
and P
2
O
5
/SiO
2
.
Although some of these methods have
convenient protocols with good to high yields, some of
these methods suffer at least from one of the following dis-
advantages: reaction under oxidizing conditions, use of
harmful organic solvents, long reaction times, use of excess
AA, unrecyclable catalysts, high cost, and high toxicity.
Also, very few reports are applicable to both the synthesis
3
-5
or used as stain-bleaching agents. In addition, the prepa-
ration of 1,1-diacetates from the corresponding aldehydes,
in the presence of ketones, can be very important due to
3
-4
14-15,22,31,48
their involvement in various natural products synthesis.
Several reagents and catalysts have been reported for the
as well as deprotection of 1,1-diacetates.
a-Zirconium phosphate (ZP) is one of the most im-
*
Corresponding author. Tel: 0098-0311-3913262; Email: h_karimi11x@yahoo.com; h.karimi11@ch.iut.ac.ir
Supporting information for this article is available on the www under http://dx.doi.org/10.1002/jccs.201500233
1000
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Chemoselective Synthesis of 1,1-diacetates
portant compounds in inorganic chemistry, and the layered
structure of this material has led to its use in a variety of dif-
ZPFe materials. The results show some characteristic re-
flections in the 2q range of 5°–40°. The diffraction peak in
ZP at 2q~12° was assigned to a d002 basal spacing of 7.5 Å
between the planes, which was consistent with the patterns
previously reported for ZP and its derivatives with a hexag-
4
9-51
ferent fields.
ZP behaves as a unique ion exchanger be-
cause of its exceptionally poor aqueous solubility, high
thermal stability, resistance to radiation and abrasive pro-
5
2-53
+
50
perties.
exchanged for various other ions, resulting in an enlarge-
The H of the P–OH moiety in ZP can be
onal crystal system. It shows that the d-spacing of the
(002) plane of ZPFe had increased, which indicated that the
5
4-58
3+
ment of the interlayer distance.
Several studies pertain-
Fe ions had intercalated into the interlayer of ZP and in-
ing to the successful exchange of this proton with various
divalent and trivalent cations have been presented in the lit-
creased the d002 basal interlamellar spacing of ZP from 7.5
3
+
to 9.3 Å. It is well known that the ion radii of Fe (0.64 Å)
5
8-62
3+
erature.
cellent selectivity towards Pb , Zn , and Fe as an ion
It has also been reported that ZP possesses ex-
and hydrated Fe (3.9 Å) are smaller than the basal spacing
2
+
2+
3+
73-74
of ZP (7.5 Å).
These results therefore indicated that
6
3-64
3+
exchanger.
hibit antibacterial activity when it was loaded with Cu ,
Furthermore, ZP has been reported to ex-
Fe ions had inserted into the interlayer of ZP and in-
2
+
creased the basal spacing of the modified ZP after the ex-
2
+
3+ 53,60-62
52,56-58
Zn , or Ce .
There have also been several reports
change.
Taken together, these data indicated that
concerning the catalytic activities of ion-exchanged mate-
rials of this type, including the use of copper zirconium
phosphate (ZPCu) as catalysts in the acetylation of alco-
hols and phenols and the use of potassium iron zirconium
phosphate as a catalysts in Friedel–Crafts benzoylation re-
ZPFe had been formed successfully. The XRD pattern of
the ZPFe catalyst after the 8th run showed that the basal
spacing of ZP was about 10.5 Å, which was only a little
larger than that of the fresh ZPFe catalyst. This increase
3
+
may have occurred because of the presence of less Fe on
the surface of ZP, and an increase in the number of water
molecules between the layers following the seventh run
6
5-72
action.
To the best of our knowledge, there is no report avail-
able in the literature for using ZPFe as catalyst for prepara-
tion of 1,1-diacetates from carbonyl compounds. There-
fore, in continuation of our reports using various catalysts
for organic transformations, we report a convenient, recy-
clable and chemoselective procedure for conversion of al-
dehydes to the corresponding acylals in the presence of
AA. The reaction was easily carried out at room tempera-
ture under solvent-free condition with short reaction times
for a wide range of aldehydes.
3
+
(i.e., Fe ions may have been washed off during the regen-
eration of the catalyst, Table 1).
2
Using N adsorption-desorption isotherms at liquid
nitrogen temperature, the specific surface areas of the sam-
ples were determined by the Brunauer–Emmett-Teller
(BET) method on a Quantachrome ChemBET 3000 instru-
ment. Prior to analysis, each sample was degassed at 350
°C for 2 h to remove any adsorbed species on the surface.
Fig. 2 shows the N
ZPFe, as a representative example, in the relative pressure
range (P/P ) of 0.1–1.0. The surface area of ZPFe was de-
2
adsorption-desorption isotherm of
RESULTS AND DISCUSSION
0
2
All products were characterized by comparison with
authentic samples and by spectroscopy data FT-IR,
termined to be 132.5 m /g. The isotherm for ZPFe shows
three adsorption stages. The first of these stages was ob-
1
HNMR and GC-Mass (Agilent 5975C) analysis (Supple-
0
served at P/P < 0.41, whereas the second stage was ob-
1
mentary Information). HNMR spectra were recorded at
4
3
00 MHz. The spectra were measured in CDCl unless
Table 1. Element contents of ZPFe (atm.%) and physical
properties of the catalysts before and after reaction
otherwise stated, relative to TMS (0.00 ppm).
Characterization of catalyst
2
Total acidity
mmol NH /g)
3
The ICP-OES analyses of ZP and ZPFe are shown in
Table 1. The results obtained in the current study for ZPFe
were compared with those reported previously in the litera-
Sample Fe
O
Zr
P
BET (m /g)
(
ZP
-
63.1 13.6 23.3
158.7
132.5
131.8
61.2
3.1
2.3
2.26
0.48
ZPFe
ZPFe
ZPFe
a
9.1 59.3 11.9 19.7
9.0 59.6 11.8 19.6
2.8 63.6 13.8 19.8
5
6-58
ture.
Our results revealed that there was a negligible
a
b
leach of iron ions into the reaction media after the reaction
(
i.e., following the first use of the catalyst).
After the first cycle.
After the 8th cycle.
b
Fig. 1 shows the powder XRD patterns of the ZP and
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Fig. 1. XRD patterns of powder ZP (down), ZPFe (up).
sites using FTIR. Prior to the measurements, 20 mg of a cat-
alyst was pressed in self-supporting disc and activated in
the IR cell attached to a vacuum line at 350 °C for 4 h. The
adsorption of pyridine was performed at 150 °C for 30 min.
The excess of probe molecules was further evacuated at
1
50 °C for 0.5 h. The adsorption–evacuation was repeated
several times until no changes in the spectra were observed
(
Fig. 3). The main bands observed over the samples are as-
7
6-77
signed according to the literature data.
Pyridine de-
sorbed FTIR spectra of the ZPFe shows the strong bands at
-
1
1
631 and 1540 cm , indicating typical pyridinium ion. The
-
1
band at 1488 cm is a combination band between those at
Fig. 2. N2 adsorption-desorption isotherm of ZPFe.
-1
1
540 and 1444 cm , corresponding to Brønsted and Lewis
acid sites, respectively.
served in the range of 0.41 < P/P
was observed at higher relative pressures (P/P
adsorption-desorption isotherm of ZPFe exhibited a
typical “type IV” isotherm shape with a distinct hysteresis
0
< 0.95, and the third stage
0
> 0.95). The
N
2
7
5
loop, which is characteristic of a mesoporous material.
The hysteresis loop (type H3) is associated with the occur-
rence of capillary condensation in the mesopores, which in-
dicates the presence of a mesoporous structure in the ZPFe
catalyst. The observed increase in adsorption at the higher
P/P
sample.
found to be 61.2 m /g.
Pyridine adsorption was used to determine the acidic
0
value indicated the presence of larger mesopores in the
5
7-58
The surface area of ZPFe after the 8th run was
2
Fig. 3. Pyridine-desorbed FTIR spectra of the calcined
ZPFe.
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Chemoselective Synthesis of 1,1-diacetates
Total acidity of the samples was determined by tem-
ca. 2.3 mmol NH
3
/g of catalyst. ATPD experiment was car-
perature-programmed desorption of ammonia (TPD-NH
3
)
ried out after the 8th cycle by recovering the catalyst, in or-
der to magnify the difference from the fresh catalysts (Ta-
ble 1).
with a Quantachrome ChemBET 3000. Before the adsorp-
tion of ammonia, the samples were pre-treated in He at 250
°
C for 30 min and then, 1 h at 350 °C and cooled to 100 °C.
Then ammonia was adsorbed on the samples for 1 h. The
TPD-NH was carried out between 150 and 550 °C, at 10
C/min, and analyzed by a thermal conductivity detector
TCD) for continuous monitoring of the desorbed ammo-
nia. TPD-NH provides a quantitative estimation of the to-
tal number of acid sites and the distribution of acid st-
rengths. Because of the strong basicity of NH gas, it was
expected that all acid sites on the catalysts interact with
NH . The total amount of NH desorbed after saturation
The surface morphology of the ZP and ZPFe was
studied by SEM (SEM, Philips XL) (Fig. 5). The SEM im-
age of ZP (Fig. 5(a)) revealed the presence of hexagonal
plates with well-defined shapes and very smooth surfaces.
Fig. 5(b) and (c) (different magnification) show the SEM
images of ZPFe. These images revealed that the structure
of ZPFe was much less ordered than that of ZP, and that the
ZPFe particles had aggregated to form both sheets and
3
°
(
3
3
5
0,58
spheres of different shapes and sizes.
3
3
Fig. 6 shows the TEM (CENTRA 100, Zeiss) images
of ZPFe. It shows that ZPFe catalyst retained the original
morphology of ZP (layered structure) and that the particles
were approximately 120 nm in size. These images also
showed nanoparticles of different sizes on the smooth sur-
face of the ZP. The presence of metallic crystal nano-
particles on the surface of ZP indicated that the iron depos-
ited on the surface of the ZP had agglomerated. Similar ob-
servations have also been reported for copper, zinc, and ce-
permits the quantification of the number of acid sites on the
surface, while the position of the peak, desorption tempera-
ture, indicates the strength of the catalyst, i.e., the higher
7
8
temperature of desorption, the stronger the acid strength.
The TPD-NH curves of ZPFe are shown in Fig. 4.
3
ZPFe desorbed ammonia in a wide range of temperatures
from 212 to 538 °C, which mostly corresponds to the me-
dium and the strong acidic sites. The NH
at temperatures below 250 °C belongs to the physisorption/
chemisorptions of NH molecules on weak acidic sites. The
3
desorption peak
6
0,70
rium with ZP.
Figures 5(d) and 6(c) show the SEM and
3
TEM images of the catalyst following its 8th run, respec-
tively. Both of these images showed that the sheets and par-
ticles had conglomerated to a much greater extent follow-
ing the 8th run because of the process used to regenerate the
catalyst.
peak at about 250-450 °C shows the existence of intermedi-
ate strength acidic sites and finally the peak at 450-538 °C
demonstrates the presence of strong acidic sites on the sur-
face of ZPFe. Fig. 4 shows that the desorption of ammonia
starts at almost 212 °C, centered at 317. The NH
3
-TPD
Synthesis of 1,1-diacetates
curves subsequently decreased with further increase in
temperature and almost complete at 538 °C. This indicates
that ZPFe contains a considerable number of acid sites
In order to find the most appropriate reaction condi-
tions and evaluate the catalytic efficiency of ZPFe on the
protection of aldehydes to the corresponding 1,1-diacet-
ates, we tried to convert benzaldehyde (5 mmol) to its cor-
responding acylal with ZPFe (0.5 mol%) and AA (10
mmol) in various solvents and also under solvent-free con-
ditions. We observed that the yield of the reaction under
solvent-free condition is higher and the reaction time is
shorter as compared to the other methods (Table 2).
Therefore, to establish the generality and scope of the
method, we employed the above conditions for conversion
of various aldehydes (aromatic, heterocyclic, aliphatics
and a,b-unsaturated aldehydes) to the corresponding di-
acetates, Table 3. Both aromatic and aliphatic aldehydes re-
act smoothly with AA to afford the corresponding 1,1-
diacetates in good to excellent yields in short reaction times
at room temperature (Table 3, entries 1-23), which are, in
general, similar or higher than those described in the litera-
3
+
which is attributed to the presence of Fe groups on the
surface of zirconium phosphate layers and make it suitable
solid acid catalyst. The extent of desorptions is found to be
Fig. 4. NH3-TPD profile of ZPFe.
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Fig. 6. TEM images of regular morphology of pre-
pared ZPFe (a,b) (different magnification) and
after the 8th run (c).
6
-47
ture.
The reactions did not proceed in the absence of
Fig. 5. SEM images of regular morphology of prepared
ZP (a) and ZPFe (b, c) and after 8th run (d).
ZPFe even under heating conditions (Table 3, entry 27).
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Chemoselective Synthesis of 1,1-diacetates
Table 2. Conversion of benzaldehyde to its corresponding
diacetate in different solvents and under solvent-free
conditions in the presence of ZPFe
Under these reaction conditions, various functional groups
(
2
Me, OMe, OH, Cl, Br, CN, NO ) were tolerated. The elec-
tronic properties of the substituents on the aromatic alde-
hydes have a major effect on the reaction yield and time.
a
b
Entry
Solvent
Yield (%)
Time (min)
1
2
3
4
5
6
a
Diethylether
Cyclohexane
Dichloromethane
Acetonitrile
51
38
56
67
55
90
90
120
90
120
120
5
The aldehydes with electron-withdrawing groups (NO
2
,
CN, Br and Cl), afforded the corresponding diacetates in
7
9
higher yields (Table 3, entries 10–16). But, aldehydes
bearing electron-donating groups (Me and OMe) gave the
corresponding 1,1-diacetates in lower yields and longer re-
action times (Table 3, entries 2-9). This may be due to the
reduced electrophilicity of the aldehyde group as a result of
the electron-rich nature of the phenyl ring to which the al-
dehyde is attached. Also, the reaction rate was found to be
Ethylacetate
c
Solvent-free
The reaction was carried out in 5 ml of solvents at reflux
conditions.
b
The yields refer to isolated pure products.
c
The reaction was carried out at r.t.
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dependent on steric crowding surrounding the aldehyde
group. Thus, the presence of substitutes at the para or meta
position (Table 3, entries 4, 5, 8, 11, 13) made the reaction
faster with better yields than those with substitutes at the
ortho position (Table 3, entries 3, 9, 10, 12).
Scheme 1 Competitive acylal formation of aldehydes
in the presence of ZPFe
The acid-sensitive compounds such as furfural and
cinnamaldehyde were also protected as 1,1-diacetates in
good yields without any side products (Table 3, entries 18
and 19). We investigated the reaction of 2-hydroxybenzal-
dehyde and 4-hydroxybenzaldehyde under above condi-
tions (Table 3, entries 8, 9); it should be mentioned that the
phenolic group was also protected as acetate in hydroxyl
containing aromatic aldehyde under such conditions (3
Scheme 2 Cleavage of acylal to benzaldehyde in water
2
equiv. of Ac O). 4-(dimethylamino) benzaldehyde failed to
catalyzed by ZPFe
give 1,1-diacetate under the same conditions which may be
due to the electron donation of dimethylamino group (Ta-
ble 3, entry 17). The explanation for this result may be due
to the strong electron donating properties of the dimethyl-
amino group which will reduce the reactivity. Moreover,
the protocol could also equally work with aliphatic alde-
hydes (Table 3, entries 20-23). Because of aldol condensa-
tion as a competitive reaction, the yields of corresponding
acylals of aliphatic aldehydes were low. Ketones proved
completely resistant to acylal synthesis with AA under
outlined in Scheme 3 the possible mechanism of this reac-
tion may be involved either intermolecular or intramole-
cular transfer of the second acetate group after the initial at-
tack by AA. We suggest that ZPFe, as a Lewis acid, in-
creases the electrophilicity of the carbonyl group on the al-
dehyde. Then AA attacks complex (I) to produce the final
1,1-diacetate.
2
1
these reaction conditions. 2-Oxo-2-phenylacetaldehyde
substrate was exposed to the reaction conditions that only
aldehyde group was protected and carbonyl group re-
mained unchanged (Table 3, entry 24). Cyclohexanone,
acetophenone, and 4-nitroacetophenone were checked for
the reactivity. No diacetate formation was observed for
these compounds, neither under room temperature nor re-
flux conditions (Table 3, entries 25-27). Encouraged by
this result, we suggest that the chemoselective protection of
aldehydes in the presence of ketones can be achieved by
this method (Scheme 1). We found that benzaldehyde was
converted to the related gem-diacetate while the aceto-
phenone remained unaffected.
Scheme 3 Plausible mechanism
In addition to these results, we further studied the
possibility of deprotection of resulting acylals in this cata-
lytic system by addition of water as a green solvent. Indeed,
deprotection of phenylmethylene diacetate to the benzal-
dehyde was performed by treatment of acylals in water at
6
0 °C. By this procedure, related acylal has been com-
We were interested in studying the reusability of the
catalyst because of economic and environmental aspects.
Hence, the reaction of benzaldehyde with AA was chosen
as a model reaction in the presence of regenerated ZPFe un-
der the optimum reaction conditions and the results are
pletely transformed into benzaldehyde in short reaction
time (Scheme 2).
On the basis of literature studies, a plausible catalytic
cycle for the regeneration, of ZPFe has been proposed. As
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Chemoselective Synthesis of 1,1-diacetates
summarized in Table 4. Used ZPFe gave a similar yield of
product as the fresh catalyst till the 8th cycle. The lowered
activity of the used catalyst sample confirms the catalyst
deactivation during the reaction. The regenerated catalyst
was characterized for its chemical composition by elemen-
tal analysis (Table 1). No significant change in composition
of ZPFe was observed after regeneration (till the 8th cycle).
It could be seen from Table 4 that the ZPFe was utilized re-
peatedly over seven times without any apparent loss of the
conversion. In order to compare the catalytic potentiality of
ZPFe nanoparticles with some recently reported proce-
dures in the literature, we have shown the results of the syn-
thesis of acylal from benzaldehyde in the presence of vari-
ous catalysts with respect to the amounts of AA, reaction
time and the yield of the products (Table 5).
out further purification.
Catalyst synthesis: All of the reagents and solvents used in
the current study were purchased from Merck Chemical Com-
pany and used without further purification. The catalyst was pre-
pared according to previously published procedures, with minor
5
0,56-58
modifications.
procedure. ZrOCl
of H PO (50 mL, 12 mol/mL) for 24 h. The resulting mixture was
ZP was prepared according to the following
2
·8H O (5 g) was heated at reflux in a solution
2
3
4
cooled to ambient temperature to give a suspension, which was
filtered, and the filter cake was then washed with a solution of
3 4
H PO (0.1 mol/mL) until the filtrate was free of chloride ions.
The filter cake was then washed several times with distilled water
until the pH of the filtrate was neutral. The solid was then col-
5
0
lected and dried in an oven at 110 °C for 24 h. ZPFe was pre-
5
6-58
pared through an ion-exchange reaction.
dispersed in deionized water (50 mL) at 50 °C, and the resulting
suspension was treated with a solution of Fe(OAc) (100 mL, 0.1
Briefly, ZP (3 g) was
The results show that, ZPFe is an equally or competi-
tive more efficient catalyst for this reaction with regards to
reaction conditions and yield. The better efficacy of ZPFe
nanoparticles in solvent-free synthesis of 1,1-diacetate
from aldehydes might be due to the presence of Lewis acis
3
Table 5. Comparison of the effect of catalysts for 1,1-diacetate
synthesis from benzaldehyde
3
+
sites (Fe ) on the surface of the catalyst. Moreover, this
procedure offers advantages over some of the methodolo-
gies in terms of efficiency, deprotection as well as protec-
tion, reusability of the catalyst and we found that ZPFe is a
selective catalyst in solvent-free conditions, which thus,
makes it environmentally more acceptable.
a
Ac
2
O
Time Yield
Catalyst
Ref.
(
mmol) (min)
%
SiO /B(SO
2
4
H)
3
2
5
2
1.2
3
10
2.5
2
1
1.2
3
15
15
4
4
5
12
5
5
15
5
15
1
40
15
5
97
96
98
100
90
89
99
97
97
93
96
83
84
92
90
90
90
97
95
95
91
94
98
90
98
[7]
[8]
[9]
S-CKT
SuSA
SBA-15-Ph-PrSO
Zr(HSO
PEG-SO
Sulphated Zirconia
3
H
[10]
[11]
[12]
[13]
[14]
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
[29]
[32]
[33]
4
)
4
In summary, in this paper, we reported a mild, sol-
vent-free and efficient protocol for the protection of alde-
hydes by their conversion to 1,1-diacetates. ZPFe was used
for this reaction at room temperature. This method is selec-
tive for the preparation of 1,1-diacetates from aldehydes in
the presence of ketones. Also, 1,1-diacetates can be conve-
niently deprotected by using ZPFe in water. Other advan-
tages of this catalyst are good to excellent yields and reus-
ability of the catalyst. Further applications of this catalyst
to other transformations are currently under investigation.
3
H
b
2
-
SO
4
/SnO
ZSM-5-SO
2
3
H
c
PS/TiCl
4
Schiff base complex of Cr (III)
Solid sulfuric acid
SBSSA
4
CPTS–HOAc
42
60
30
180
5
30
4
60
5
H
2
NSO
ZrCl
Zeolite Y
bmpy]HSO
InCl
SPDTSA
3
H
3
3
3
3
4
d
[
4
3
5
EXPERIMENTAL
15
12
3
5
2.2
2
All of the reagents and solvents used in the current study
were purchased from Merck Chemical Company and used with-
sulfated SnO
DBSA
P(4-VPH)ClO
2
4
1
La(NO
NH
3
)
3
×6H
2
O
90
90
5
Table 4. The catalyst re-used under the optimum reaction
conditions for for 1,1-diacetate synthesis
(
4
)
3
PW12
O
40
ZPFe
2
90 This work
a
Substrate Fress run 1 run 2 run 3 run 4 run 5 run 6 run 7 run 8
a
Reaction conditions: r.t, solvent-free.
b
c
d
C
6
H
5
CHO 90
90 90 89 88 88 85 84 68
CHO (5 mmol), AA (10 mmol),
Reaction temperature: 0 °C.
Cl as solvent.
2 2
Ultrasonic irradiation, 30 °C.
a
CH
6 5
Reaction conditions: C H
catalyst (0.5 mol%), r.t. and 10 min.
J. Chin. Chem. Soc. 2015, 62, 1000-1010
© 2015 The Chemical Society Located in Taipei & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.jccs.wiley-vch.de
1007

Article
Karimi
3
+
mol/L) in water (excess amount of Fe ). This mixture was then
heated at reflux for 4 d. It is noteworthy that the acetate ion per-
formed effectively as a base to keep the hydrogen ion concentra-
tion in solution sufficiently low to achieve high loadings of the
hydrous CaCl
2
. The solvent was evaporated under reduced pres-
sure to give the corresponding aldehyde.
Recyclability studies of catalyst: To examine the recycl-
ability of the catalyst, the used ZPFe was recovered from the reac-
tion media and re-used. For recycling, after the first use, the cata-
lyst was separated from the reaction mixture by centrifugation,
washed sequentially with ethanol and water before being dried at
110 °C for 2 h, and then activated at 450 °C for 2 h.
8
0
catalyst. A complete exchange between the cations and the hy-
drogen ions of the P–OH groups could not be achieved in less than
7
0
3
d or at temperatures below 80 °C. The resulting slurry was fil-
tered hot to give a light yellow solid, which was washed with dis-
3
+
tilled water until no Fe ions could be detected in the filtrate (i.e.,
until the filtrate was colorless). The solid product was then dried
at 100 °C for 24 h before being calcined at 600 °C for 4 h to give
ACKNOWLEDGEMENTS
We gratefully acknowledge the funding support re-
ceived for this project from the Isfahan University of Tech-
nology (IUT), IR Iran.
the final product, Fe1/3[Zr
).
2 4 3
(PO ) ], as a pale yellow solid (Scheme
4
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