Aminopropyl silica gel supported iodine as catalyst in nucleophilic ring opening of epoxides and episulfides

Article abstract of DOI:10.1081/SCC-120003617

Silica gel functionalized by aminopropyl group was prepared. Iodine was then supported on this inorganic polymer and used as a stable and efficient heterogeneous catalyst for nucleophilic ring opening reactions of epoxides and episulfides in different nucleophilic solvents such as alcohols, water and acetic acid.

Full text of DOI:10.1081/SCC-120003617

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AMINOPROPYL SILICA GEL SUPPORTED IODINE AS
CATALYST IN NUCLEOPHILIC RING OPENING OF
EPOXIDES AND EPISULFIDES
B. Tamami a , N. Iranpoor a & H. Mahdavi a
a Chemistry Department , Shiraz University , Shiraz, Iran
Published online: 16 Aug 2006.
To cite this article: B. Tamami , N. Iranpoor & H. Mahdavi (2002) AMINOPROPYL SILICA GEL SUPPORTED IODINE AS CATALYST
IN NUCLEOPHILIC RING OPENING OF EPOXIDES AND EPISULFIDES, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 32:8, 1251-1258, DOI: 10.1081/SCC-120003617
To link to this article: http://dx.doi.org/10.1081/SCC-120003617
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SYNTHETIC COMMUNICATIONS, 32(8), 1251–1258 (2002)
AMINOPROPYL SILICA GEL
SUPPORTED IODINE AS CATALYST IN
NUCLEOPHILIC RING OPENING OF
EPOXIDES AND EPISULFIDES
B. Tamami, N. Iranpoor,y and H. Mahdavi
*
Chemistry Department, Shiraz University, Shiraz, Iran
ABSTRACT
Silica gel functionalized by aminopropyl group was prepared.
Iodine was then supported on this inorganic polymer and used
as a stable and efficient heterogeneous catalyst for nucleo-
philic ring opening reactions of epoxides and episulfides in
different nucleophilic solvents such as alcohols, water and
acetic acid.
Polymer supported catalysts are a very important category of cata-
lysts. A wide variety of catalysts has been supported on polymeric sup-
ports.1–3 In most cases the supports are organic polymers. However, these
systems suffer from two main drawbacks, lack of accessibility due to the
viscous character of the polymeric medium when swollen by a suitable
solvent, and lack of thermal, mechanical and/or chemical stability. On the
other hand, inorganic supports such as silica gel may have morphologies
*Corresponding author. E-mail: Tamami@chem.susc.ac.ir
yCorresponding author. E-mail: iranpoor@chem.susc.ac.ir
1251
Copyright & 2002 by Marcel Dekker, Inc.
www.dekker.com

1252
TAMAMI, IRANPOOR, AND MAHDAVI
well suited for good accessibility, and in addition they offer to the supported
catalysts both thermal and mechanical stability.4 They are inexpensive and
readily available with wide ranges of purities and physical properties,
including surface area, pore size distribution and particle size.
No reaction of epoxides has been more thoroughly studied and widely
used in organic synthesis than the addition of nucleophilic agents to form
1,2-disubstituted products.5
Among these nucleophilic reactions, solvolysis of epoxides in the pres-
ence of a catalyst, has been the subjects of intense investigations. For ex-
ample catalysts such as 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ),6
cerium (IV) salt,7,8 and ferric salt,9 were used in solvolysis reactions of
epoxides. Solvolytic ring opening reactions of thiiranes have also been cat-
alyzed with Ce(IV) and DDQ.10 Recently we have also shown that iodine
and iodine supported on poly(N-vinylpyrrolidone) can be utilized as efficient
catalysts for the solvolysis of epoxides and episulfides.11
In order to decrease the toxicity nature of iodine and modification of
its catalytic activity, in this paper we report the use of iodine supported on
aminopropyl silica gel as a heterogeneous catalyst in solvolytic ring opening
reactions of epoxides and episulfides.
Aminopropyl silica gel was prepared (via a sol–gel reaction) from
the reaction of activated silica gel with aminopropyl triethoxy silane in
toluene at room temperature. The absorption at 2950 and 3649 cmꢀ1 in
FT.IR spectrum of aminopropyl silica gel was characterized for methylene
and amino groups respectively. Supporting iodine on aminopropyl silica gel
(APSG) was carried out with stirring APSG in solution of I2/THF at room
temperature. The amount of iodine supported on APSG was determined
iodometrically. The capacity was 0.14 mmol iodine per gram of silica support.
It is worthwhile to mention that iodine absorbed on silica gel is not
stable and slowly evaporated from the silica surface even at room tempera-
ture. However, aminopropyl functionalized silica gel supported iodine was
stable without losing any iodine at room temperature or even at 80ꢁC in
vacuum. This stability is presumably due to the formation of a charge
transfer complex between the amino groups and iodine.19
Ring opening reactions of epoxides in primary, secondary and tertiary
alcohols were performed in the presence of 0.06–0.2 molar equivalent of
iodine supported on aminopropyl silica gel. The molar ratio of iodine to
the substrate depends on the structure of epoxide and the nucleophile.
The corresponding b-alkoxy alcohols were formed in high to excellent
yields. The results showed that the reactions were highly regioselective. The
product obtained from cyclohexene oxide showed the formation of trans-
isomer as the sole product of the reaction (Table 1). The reaction of these
epoxides in water and acetic acid also occurred efficiently and in the pres-

AMINOPROPYL SILICA GEL SUPPORTED IODINE
1253
ence of 0.05–0.1 molar equivalent of iodine supported on APSG. The cor-
responding b-diols and b-acetoxy alcohols were obtained in high to excellent
yields (Table 2). Identification of the products were done by a comparison of
their physical constants with those of their authentic samples.
The reaction of thiiranes in alcohols and aqueous acetonitrile, was
performed in the presence of 0.5 molar equivalent of iodine supported on
APSG at room temperature or under reflux conditions (Table 3).
In these reactions ring opening of thiranes and dimerization occurred
together with the formation of the corresponding disulfides in good yields.
Comparison of results obtained from the solvolysis reactions of epox-
ides and episulfides in the presence of aminopropyl silica gel supported
iodine as a catalyst, and those reported10 for iodine and iodine supported
on poly(N-vinylpyrrolidone) show that the efficiency of the former catalyst
is higher than the latter. It should also be mentioned that, when APSG
supported iodine was used as a catalyst during the reaction, there was no
free iodine in the reaction system compared to when poly(N-vinylpyrolid-
one) supported iodine or iodine alone was used.10
In conclusion this stable and efficient modified inorganic supported
iodine catalyst proved to be a valuable addition to the already present
catalysts for ring opening reactions of epoxides and episulfides.
Further studies are in progress for the synthesis of silica gel grafted
functional polymers as inorganic supports for a variety of catalysts to be
used in different organic reactions.

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TAMAMI, IRANPOOR, AND MAHDAVI

AMINOPROPYL SILICA GEL SUPPORTED IODINE
1255

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TAMAMI, IRANPOOR, AND MAHDAVI

AMINOPROPYL SILICA GEL SUPPORTED IODINE
EXPERIMENTAL
1257
Chemicals were either prepared in our laboratory or were purchased
from Fluka, BDH and Merck chemical companies. Products were charac-
terized by comparison of their physical data, IR, NMR, and mass spectra
with those reported in the literature. All yields refer to isolated products. IR
spectra were recorded on a Perkin Elmer IR-157G and a Perkin Elmer 781
spectrometer. NMR spectra were recorded on a Bruker DPX 250 MHz
spectrometer. Mass spectra were recorded on a Shimadzu GCMS-QP
1000EX. Determination of the purity of the substrates and reaction mon-
itoring were accomplished by TLC on silica gel polygram SILG/UV254
plates or by GLC on a Shimadzu GC-14A instrument.
Procedure for Preparation of Iodine Supported on
Aminopropyl Silica Gel (I2/APSG)
Silica gel (Fluka 100, P.S. 0.015–0.035 nm) was activated by refluxing
in concentrated HCl for 4 h, followed by washing with water repeatedly and
dried overnight under vacuum at 80ꢁC. To this activated silica gel (13.39 g),
a toluene solution (70 ml) of 3-aminopropyltriethoxy silane (10.0 g,
0.045 mol) was added and then stirred for 30 m at 80ꢁC. The modified
silica was washed successively with toluene, dichloromethane, and ether
respectively and then dried overnight under vacuum at 80ꢁC.
The prepared Aminopropyl silicagel (5 g) was placed in a flask and to
it a solution of iodine (4 g), in THF (50 ml) was added and the resulting
suspension was stirred magnetically at room temperature for 12 h. The mix-
ture was filtered and washed with THF repeatedly using a Soxhlet appara-
tus, until the solvent became colorless. The resulting brown precipitate was
dried overnight under vacuum at 70ꢁC. The aminopropyl silica gel sup-
ported iodine was obtained as a yellow solid. The amount of iodine sup-
ported on aminopropyl silica gel was determined iodimetrically. It was
0.14 mmol iodine per gram of the supported catalyst.
General Procedure for the Solvolysis Reactions of Epoxides and
Episulfides in the Presence I2/APSG
I2/APSG (0.6–5 mmol) was added to a solution of epoxide or episulfide
(10 mmol) in the appropriate solvent (60 ml). The reaction mixture was
stirred for the specified time at the appropriate temperature according to
Tables 1–3. Progress of the reaction was monitored by GLC and TLC. After

1258
TAMAMI, IRANPOOR, AND MAHDAVI
completion of the reaction, the mixture was filtered, and the solvent was
evaporated to give the pure product.
ACKNOWLEDGMENT
The authors are grateful to Shiraz University Research Council for the
partial support (Grant No. 78-SC-1234-667) of this work.
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Received in the UK February 8, 2001