Selective Monoacetylation of Symmetrical Diols and Selective Monodeacetylation of Symmetrical Diacetates Using HY-Zeolite as Reusable Heterogeneous Catalyst

Article abstract of DOI:10.1055/s-2003-42468

HY-Zeolite has been found to be an efficient and reusable catalyst for selective monoacetylation of symmetrical diols and selective monodeacetylation of symmetrical diacetates to form the products in high yields.

Full text of DOI:10.1055/s-2003-42468

LETTER
2419
Selective Monoacetylation of Symmetrical Diols and Selective Monode-
acetylation of Symmetrical Diacetates Using HY-Zeolite as Reusable
Heterogeneous Catalyst1
HY-Zeolite as
R
eu
.
sable Hetero
V
geneous Catalyst . N. S. Srinivas, I. Mahender, Biswanath Das*
Organic Chemistry Division-I, Indian Institute of Chemical Technology, Hyderabad-500 007, India
Fax +91(40)27160512; E-mail: biswanathdas@yahoo.com
Received 11 July 2003
monoacetylation was required. Here we report the facile
preparation of monoacetates of symmetrical diols using
HY-Zeolite as a catalyst (Scheme 1).
Abstract: HY-Zeolite has been found to be an efficient and reus-
able catalyst for selective monoacetylation of symmetrical diols and
selective monodeacetylation of symmetrical diacetates to form the
products in high yields.
Reactions carried out under heterogeneous catalysis have
Key words: monoacetylation, symmetrical diols, monodeacetyla- recently gained increasing attention because of the use of
tion, symmetrical diacetates, HY-Zeolite
inexpensive and non-corrosive catalysts, highly efficient
transformations, easy experimental procedures and high
purity of the products. Several heterogeneous catalysts
have now been introduced to perform various chemical
transformations.11 Acidic zeolites are important and use-
ful heterogeneous catalysts due to the ease of their separa-
tion, their reusability and ability to carry out the
transformations with higher yields and selectivity than
when homogeneous catalysts are used.12 We have recently
observed that HY-Zeolite is an efficient heterogeneous
catalyst for the preparation of monoacetylated symmetri-
cal diols.
Selective protection of multiple identical functional
groups is very important in organic synthesis. Monopro-
tected symmetrical diols are suitable starting materials for
the preparation of various sex pheromones and medicinal-
ly important compounds.2 The yields of the final products
depend on the efficient preparation of these starting mate-
rials from the corresponding symmetrical diols. However,
hydroxyl groups in similar chemical environments react at
similar rates with the protecting reagents often leading to
the formation of diprotected products. Thus the function-
alization of only one hydroxyl group of a symmetrical diol
is not an easy process. Monoprotection of polyols can be
achieved by carefully controlled reaction conditions,3
continuous extraction,4 the use of solid-supported re-
agents,5 alumina,6 lanthanum halides,7 phase transfer
catalysts8 and insoluble polymer supports9 or via the for-
mation of cyclic compounds.10 However, some of the
methods require special experimental set ups, some of the
catalysts are not readily available or have to be freshly
prepared at the time of use and some of the protocols are
not straightforward. The reusability of several catalysts
has also not been verified. Hydroxy compounds are fre-
quently protected by acetylation in organic synthesis.
Monoacetylated symmetrical diols were prepared earlier
for the synthesis of sex pheromones of Lepidoptera by
treatment of symmetrical diols with acetic anhydride
(Ac2O) under strongly basic and refluxing conditions.2b
The yields were moderate and the method involved te-
dious experimental procedure. Improvement in yields of
Several symmetrical diols were treated with HOAc for 2–
6 hours in the presence of HY-Zeolite under refluxing
conditions. The monoacetates of the diols were formed in
high yields (Table 1).
Using HOAc as acetylating agent no diacetates could be
detected under the reaction conditions. However, acetyla-
tion with Ac2O afforded a little diacetate (7–12%) along
with monoacetate (75–80%) in each case.3 Moreover,
from an industrial point of view, anhydrides are more ex-
pensive than the corresponding carboxylic acids. Transes-
terification of diols with EtOAc was also achieved by
heating under reflux (3.5–8.0 h) with HY-Zeolite. In this
case the monoacetates were also produced selectively.4
This method is of particular convenience since the react-
ing ester (EtOAc) is readily available and is also used as
the solvent. Corrosive acetylating reagents are avoided
and the reaction work up is very simple. However, the
yields of the products were somewhat lower and the times
of conversion somewhat longer than when HOAc was em-
ployed (Table 1).
Scheme 1
SYNLETT 2003, No. 15, pp 2419–2421
0
1
.1
2
.2
0
0
3
Advanced online publication: 07.11.2003
DOI: 10.1055/s-2003-42468; Art ID: D16903ST.pdf
© Georg Thieme Verlag Stuttgart · New York

2420
K. V. N. S. Srinivas et al.
LETTER
Table 1 Preparation of Monoacetates of Symmetrical Diols
Table 2 Selective Monodeacetylation of Symmetrical Diacetates
Entry Diol
Acetylating Time
Isolated
Yield (%)
Entry
Diacetate
Time
(h)
Isolated
Yield%
agent
(h)
HO(CH2)nOH
n = 2
AcO(CH2)nOAc
1
2
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
HOAc
EtOAc
2
90
83
89
82
98
91
95
86
96
87
93
84
92
81
94
85
95
81
92
78
93
85
92
83
1
2
n = 2
2.5
2.5
3
88
85
97
93
96
94
91
93
91
90
93
92
3.5
2
n = 3
n = 3
3
n = 4
3.5
3
4
n = 5
3
3
n = 4
5
n = 6
3.5
4
5
6
n = 8
4
n = 5
3
7
n = 9
4
5
8
n = 10
4.5
5
5
n = 6
3.5
5.5
3.5
6
9
n = 12
10
11
12
n = 16
6.5
4.5
5
6
n = 8
AcOCH2CH=CHCH2OAc
AcOCH2C≡CCH2OAc
The structures of the products were confirmed from spectral (IR, 1H
NMR and MS) data.
7
n = 9
3.5
6
8
n = 10
4
changed under the present experimental conditions to
yield the corresponding monoacetates in high yields (81–
87%). However, compound I (Figure 1) with Me3Si ether
group afforded a mixture of products.
7
9
n = 12
4.5
7
The present methodology was again examined with sym-
metrical secondary and tertiary diols. The yields of
monoacetates obtained either directly by acetylation of
the symmetrical secondary diols (II) (Figure 1) or by
deacetylation of the corresponding diacetates using HY-
Zeolite were found to be poor (33–41%). On the other
hand, symmetrical tertiary diols did not afford any acety-
lated product. Some unsymmetrical substituted 1,2-diols
(III) (Figure 1) were also studied. Acetylation of the com-
pounds under the described conditions (5–7.5 h) produced
only the monoacetates formed by acetylation of the prima-
ry hydroxyl group. Thus the present method offers excel-
lent selectivity for protection of primary hydroxyl group
in the presence of secondary hydroxyl group.
10
11
12
n = 16
6
8
HOCH2CH=CHCH2OH
HOCH2C≡CCH2OH
3.5
5
4
5.5
The structures of the products were confirmed from spectral (IR, 1H
NMR and MS) data.
The monoacetates of symmetrical diols were also pre-
pared by selective monodeacetylation of diacetates by
heating under reflux (2.5–6.5 h) with commercial MeOH
over HY-Zeolite (Table 2). The yields of the monoace-
tates were very high. The structures of the products were
confirmed from their spectral (IR, 1H NMR and MS) data.
The scope and limitation of the developed methodology
have been studied. Carbon-Carbon multiple bonds present
in the symmetrical diols are unaffected during acetylation
of the compounds or deacetylation of the corresponding
diacetates (Tables 1 and 2). Several 2-oxy-derivatives of
1,2,3-propane triol (I) were acetylated with HOAc or
EtOAc. Alkyl ethers (like MeO, EtO, BnO) were un-
Figure 1
The catalyst HY-Zeolite is non-hazardous and environ-
mentally benign. It can easily be removed from the reac-
tion mixture by simple filtration. Acetylation of alcohols
Synlett 2003, No. 15, 2419–2421 © Thieme Stuttgart · New York

LETTER
HY-Zeolite as Reusable Heterogeneous Catalyst
2421
was heated under reflux for 3.5 h and after cooling this was filtered.
The filtrate on concentration afforded a residue, which on purifica-
tion by column chromatography over silica gel yielded 6-acetoxy
hexane-1-ol as a colorless viscous mass (154 mg, 96%). IR (neat):
3428, 1744, 1336, 1047 cm–1. 1H NMR (200 MHz, CDCl3): d = 4.05
(t, J = 7.0 Hz, 2 H), 3.55 (t, J = 7.0 Hz, 2 H), 2.02 (s, 3 H), 1.62–
1.44 (m, 4 H), 1.42–1.26 (m, 4 H). FABMS: m/z = 160 [M+].
can be achieved by treatment with carboxylic acids in the
presence of a conventional Lewis acid but the catalyst is
destroyed in the work-up procedure. We have observed
that HY-Zeolite can be reused at least three times without
losing its activity. The process is thus economic. The cat-
alyst is commercially available (PQ Corporation, USA). It
has the following physico-chemical parameters: Si/Al, 2.6
and surface area, 457.19 m2/g. The experimental proce-
dures for both the monoacetylation of symmetrical diols
and monodeacetylation of symmetrical diacetates using
this catalyst are very simple. The catalytic activity of HY-
Zeolite is independent of the length of the diols.
Acknowledgment
The authors thank CSIR, New Delhi and IICT for financial assi-
stance.
In conclusion, we have developed a novel practical meth-
od for the preparation of monoacetates of saturated and
unsaturated symmetrical diols starting from the diols
themselves or from their diacetates in the presence of HY-
Zeolite as a convenient and efficient catalyst. The opera-
tional simplicity, high yields of the products, high selec-
tivity and reusable property of the catalyst are the
advantages of the present protocol. We feel the developed
method is an attractive alternative to the existing process-
es for the selective preparation of monoacetates of sym-
metrical diols.
References
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Treatment of Diols with HOAc: Dodecane-1,12-diol (Table 1, en-
try 9) (202 mg, 1 mmol) was dissolved in HOAc (0.5 mL). HY-Zeo-
lite (PQ Corporation, USA) (150 mg) and CHCl3 (8 mL) were
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(t, J = 7.0 Hz, 2 H), 3.54 (t, J = 7.0 Hz, 2 H), 2.00 (s, 3 H), 1.56–
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Treatment of Diols with EtOAc: Decane-1,10-diol (Table 1, entry
8) (174 mg, 1 mmol) was dissolved in EtOAc (8 ml). HY-Zeolite
(150 mg) was added to the solution and the mixture was heated un-
der reflux for 7 h. After filtration of the catalyst the reaction mixture
was concentrated under reduced pressure. The residue was purified
by column chromatography over silica gel to produce 10-acetoxy
decane-1-ol as a white solid (183 mg, 85%). IR (KBr): 3442, 1745,
1365, 1240, 1041 cm–1. 1H NMR (200 MHz, CDCl3): d = 4.04 (t, J
= 7.0 Hz, 2 H), 3.60 (t, J = 7.0 Hz, 2 H), 2.03 (s, 3 H), 1.64–1.46 (m,
4 H), 1.42–1.22 (m, 12 H). FABMS: m/z = 216 [M+].
Treatment of Diacetates with MeOH: 1,6-Diacetoxyhexane diac-
etate (Table 2, entry 5) (202 mg, 1 mmol) was dissolved in commer-
cial MeOH (10 mL). HY-Zeolite (150 mg) was added. The mixture
Synlett 2003, No. 15, 2419–2421 © Thieme Stuttgart · New York