Titanium dioxide as a mild and efficient catalyst for conversion of epoxides to thiiranes

Article abstract of DOI:10.1081/SCC-200026239

Titanium dioxide (TiO₂) efficiently catalyze the reaction of a variety of epoxides with ammonium thiocyanate in refluxing acetonitrile to afford the corresponding thiirane in high to excellent yields.

Full text of DOI:10.1081/SCC-200026239

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Titanium Dioxide as a Mild
and Efficient Catalyst for
Conversion of Epoxides to
Thiiranes
Bahram Yadollahi a , Shahram Tangestaninejad b
Mohammad Hossein Habibi b
&
a Department of Chemistry, Institute for Advanced
Studies in Basic Sciences (IASBS), P.O. Box
45195‐159, Gava Zang, Zanjan, Iran
b Department of Chemistry, Esfahan University,
Esfahan, Iran
Published online: 10 Jan 2011.
To cite this article: Bahram Yadollahi , Shahram Tangestaninejad & Mohammad
Hossein Habibi (2004) Titanium Dioxide as a Mild and Efficient Catalyst for
Conversion of Epoxides to Thiiranes, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 34:15, 2823-2827,
DOI: 10.1081/SCC-200026239
To link to this article: http://dx.doi.org/10.1081/SCC-200026239
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SYNTHETIC COMMUNICATIONSw
Vol. 34, No. 15, pp. 2823–2827, 2004
Titanium Dioxide as a Mild and Efficient
Catalyst for Conversion of Epoxides
to Thiiranes
2
Bahram Yadollahi,1, Shahram Tangestaninejad,
*
and Mohammad Hossein Habibi2
1Department of Chemistry, Institute for Advanced Studies in Basic
Sciences (IASBS), Gava Zang, Zanjan, Iran
2Department of Chemistry, Esfahan University,
Esfahan, Iran
ABSTRACT
Titanium dioxide (TiO2) efficiently catalyze the reaction of a variety of
epoxides with ammonium thiocyanate in refluxing acetonitrile to afford
the corresponding thiirane in high to excellent yields.
Key Words: Titanium dioxide; Catalysis; Epoxide; Thiirane;
Ammonium thiocyanate.
*
Correspondence: Bahram Yadollahi, Department of Chemistry, Institute for
Advanced Studies in Basic Sciences (IASBS), P.O. Box 45195-159, Gava Zang,
Zanjan, Iran; Fax: þ98 (241) 4248013; E-mail: yadollahi@iasbs.ac.ir.
2823
DOI: 10.1081/SCC-200026239
0039-7911 (Print); 1532-2432 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

2824
Yadollahi, Tangestaninejad, and Habibi
INTRODUCTION
The most general procedure for the synthesis of thiiranes is the conversion
of epoxides by an oxygen–sulfur exchange reaction. Sulfur introducing
reagents, such as inorganic thiocyanates,[1–3] thiourea,[3,4] phosphine
sulfide,[5] 3-methyl benzothiazole-2-thione,[6] dimethylthioformamide,[7]
silica-gel supported KSCN,[8] and polymer supported thiocyanate,[9] have
been used for this purpose. Very recently, conversion of epoxides to thiiranes
in the presence of one electron transfer and the Lewis acid catalysts such
as ceric ammonium nitrate,[10] ruthenium trichloride,[11] and metallopor-
phyrins,[12–14] have also been reported.
However, some of these methods suffer from disadvantages such as long
reaction times, low yields of the products, formation of polymeric by-pro-
ducts, requirement for aqueous reaction conditions, and presence of sulfuric
and trifluoroacetic acids.
There are a few methods that used from the Ti(IV) compounds in conver-
sion of epoxides to thiiranes,[15] but these Ti(IV) compounds are expensive
reagents. Therefore, we decided to use from titanium dioxide in this trans-
formation. In our studies, we found that titanium dioxide can act as an efficient
catalyst for conversion of various epoxides to thiiranes with ammonium thio-
cyanate in refluxing acetonitrile (Sch. 1).
The reaction of styrene oxide as a model substrate with ammonium
thiocyanate in the presence of titanium dioxide was studied in refluxing aceto-
nitrile for 30 min without polymerization (Table 1, entry 1). Different types of
aliphatic as well as cyclic epoxides including those with electron-withdrawing
substituents were also converted to their thiiranes performed in refluxing aceto-
nitrile and in the presence of only 0.05 M eq. of TiO2 (Table 1, entries 2–7).
The effects of other solvents such as acetone, chloroform, dichloro-
methane, carbon tetrachloride, and n-hexane were also investigated. In com-
parison with acetonitrile, the reaction times were longer and the yields of
thiiranes were considerably lower in all other solvents. Control experiments
carried out on the epoxides showed that in the absence of the catalyst, no con-
version of epoxides to thiiranes compounds takes place at short reaction times.
In conclusion, titanium dioxide (TiO2) and ammonium thiocyanate can
act as a mild and as efficient catalytic system for conversion of epoxides to
Scheme 1.

TiO2 as Catalyst for Conversion of Epoxides to Thiiranes
2825

2826
Yadollahi, Tangestaninejad, and Habibi
thiiranes. High yields, short reaction times, stability, and easy work-up make
this method a suitable procedure for conversion of epoxides to thiiranes.
EXPERIMENTAL
All chemicals used were of reagent grade.
General Procedure for Conversion of Epoxides to Thiiranes
In a typical experiment, a solution of epoxide (1 mmol) in CH3CN (5 mL)
was prepared. Ammonium thiocyanate (0.152 g, 2 mmol) and TiO2 (4 mg,
0.05 mmol) were added to this solution, and the reaction mixture was stirred
magnetically under reflux conditions. After completion of the reaction
(monitored by GC), the mixture was directly passed through a short column
of silica gel [eluent: 1/1 (hexane/ethyl acetate)] to remove the catalyst. The
eluent was evaporated under reduced pressure and the crude product was
obtained in 89–96% yields without any polymerization by-products. Distilla-
tion of the product from one experiment with 5 mmol of styrene epoxide under
reduced pressure resulted the corresponding thiirane in 92% yield.
ACKNOWLEDGMENTS
We thank the Institute for Advanced Studies in Basic Sciences (IASBS)
and Isfahan University Research Council for support of this work.
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Received in Poland May 13, 2003