Heteropoly acids as heterogeneous and reusable catalyst for α-thiocyanation of ketones

Article abstract of DOI:10.1080/00397910903320639

Simple, efficient, and mild method for -thiocyanation of ketones in presence of heteropolyacid has been developed. This methodology offered -oxothiocyanates in good to excellent yields at room temperature in a highly selective manner. The catalyst could b

Full text of DOI:10.1080/00397910903320639

This article was downloaded by: [University of Otago]
On: 23 May 2013, At: 09:51
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Synthetic Communications: An
International Journal for Rapid
Communication of Synthetic Organic
Chemistry
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/lsyc20
Heteropoly Acids as Heterogeneous and
Reusable Catalyst for α-Thiocyanation of
Ketones
Atul C. Chaskar a , Arun A. Yadav b , Bhushan P. Langi a , Anita
Murugappan a & Chetan Shah c
a C. K. Thakur Research Centre, Navi Mumbai, India
b Institute of Science, Mumbai, India
c Radiation and Photochemistry Division, Bhabha Atomic Research
Centre, Mumbai, India
Published online: 25 Aug 2010.
To cite this article: Atul C. Chaskar , Arun A. Yadav , Bhushan P. Langi , Anita Murugappan & Chetan
Shah (2010): Heteropoly Acids as Heterogeneous and Reusable Catalyst for α-Thiocyanation of
Ketones, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 40:19, 2850-2856
To link to this article: http://dx.doi.org/10.1080/00397910903320639
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Synthetic Communications1, 40: 2850–2856, 2010
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397910903320639
HETEROPOLY ACIDS AS HETEROGENEOUS
AND REUSABLE CATALYST FOR a-THIOCYANATION
OF KETONES
Atul C. Chaskar,1 Arun A. Yadav,2 Bhushan P. Langi,1
Anita Murugappan,1 and Chetan Shah3
1C. K. Thakur Research Centre, Navi Mumbai, India
2Institute of Science, Mumbai, India
3Radiation and Photochemistry Division, Bhabha Atomic Research Centre,
Mumbai, India
Simple, efficient, and mild method for a-thiocyanation of ketones in presence of
heteropolyacid has been developed. This methodology offered a-oxothiocyanates in good
to excellent yields at room temperature in a highly selective manner. The catalyst could
be efficiently recovered from the reaction and reused.
Keywords: Ketones; a-oxothiocyanates; phosphomolybdic acid; thiocyanation
INTRODUCTION
Organic thiocyanates are obtained by deglycosylation of glucosinolates,
derived from cruciferous vegetables, and are biologically important natural
products.[1] a-Oxothiocyanates are important intermediates in the synthesis of
sulfur-containing heterocycles such as thiazoles and 2-amino-1,3-thiazines.[2–4] Some
of these compounds exhibit herbicidal and other important biological activities.[5,6]
Several methods have been reported for a-thiocyanation of ketones, using a wide
variety of reagents under diverse reaction conditions.
Different thiocyanogens were used as catalysts in heterolytic and homolytic
conditions.[7–10] Dichloroiodobenzene–lead(II) thiocyanates[11] have been used for
direct thiocyanation of carbonyl compounds. However, these methods involve harsh
reaction conditions, excess use of oxidizing agents, use of toxic metal thiocyanates,
and multistep processes, which in turn practically affect the yield.
Heteropolyacids (HPAs) have both acidic and oxidative properties.[12–14] In the
past two decades, the broad utility of HPAs as catalysts in solution as well as in the
solid state for various industrial processes has been demonstrated for a wide variety
of synthetically useful transformations of organic substrates.[15,16] HPAs are stronger
than the usual mineral acids such as H2SO4, HCl, and HNO3.[17] Solid HPAs are also
Received June 4, 2009.
Address correspondence to Atul C. Chaskar, C. K. Thakur Research Centre, Navi Mumbai
410206, India. E-mail: achaskar@rediffmail.com
2850

HETEROPOLY ACIDS AS CATALYST FOR a-THIOCYANATION OF KETONES
2851
Scheme 1. Synthesis of 2-oxo cyclohexyl thiocyanate.
stronger than conventional solid acids such as SiO2=Al2O3, H3PO4=SiO2, and HX or
HY zeolites.[18]
Considering the properties and importance of the HPAs as the catalysts in
organic synthesis, we herein report a-thiocyanation of ketones using a catalytic
amount of HPA. HPA not only oxidized the ammonium thiocyanate to thiocyano-
gen [(SCN)2] but also enolized the carbonyl group to get a-thiocyanate. Cyclohexa-
none (1 mmol), ammonium thiocyanate (2 mmol), and phosphomolybdic acid in
ethylene dichloride were stirred for 20 min at room temperature to get 2-oxo
cyclohexyl thiocyanate (Scheme 1). At the end of the reaction, the catalyst could
be recovered by filtration. The recovered catalyst was washed with dichloromethane
and reused.
We studied the effects of various organic solvents on the yield of product and
rate of the reaction. Organic solvents [viz., dichloromethane, tetrahydrofuran
(THF), ethylene dichloride, methanol, chloroform, carbon tetrachloride, and
acetonitrile] were selected for the study. It was observed that maximum yields were
obtained when ethylene dichloride was used as solvent (Table 1). Solubility of HPA
in a few organic solvents did not show significant effect on the outcome of the
reaction.
Considering the effectiveness of the HPA, we decided to generalize the protocol
by treating a broad range of ketones with ammonium thiocyanate in the presence of
HPA. All the selected ketones afforded corresponding a-oxothiocyanates in good to
excellent yields. Thiocyanation of cyclic ketones occurred with excellent yields,
whereas that of b-dicarbonyl compounds occurred in moderate yields. The presence
of a heteroatom in the ring did not affected the yield of a-oxothiocyanates. Physical
and spectral data of known compounds are in agreement with those reported in the
literature[19,20] (Table 2).
Table 1. Solvent effects on the reaction of cyclohexanone and ammonium
thiocyanate catalyzed by HPA
Entry
Solvent
Time (min)
Yield (%)
1
2
3
4
5
6
7
CHCl2
THF
25
30
20
30
25
30
20
75
70
86
75
82
78
80
ClCH2CH2Cl
MeOH
CHCl3
CCl4
CH3CN

2852
A. C. CHASKAR ET AL.
Table 2. HPA-catalyzed a-thiocyanation of ketones
Entry
Carbonyl compound
a-Oxothiocyanates
Time (min)
Yield (%)
1
2
20
86
35
35
75
68
3
4
30
45
40
30
73
68
68
75
5
6
7
8
40
65
(Continued )

HETEROPOLY ACIDS AS CATALYST FOR a-THIOCYANATION OF KETONES
Table 2. Continued
2853
Entry
Carbonyl compound
a-Oxothiocyanates
Time (min)
Yield (%)
9
30
78
10
40
80
11
12
35
40
70
65
13
14
30
30
75
75
65
15
16
35
45
65
(Continued )

2854
Entry
17
A. C. CHASKAR ET AL.
Table 2. Continued
a-Oxothiocyanates
Carbonyl compound
Time (min)
Yield (%)
45
60
18
40
70
EXPERIMENTAL
All commercial reagents were used as received without purification, and all
solvents were of reagent grade. The reaction was monitored by thin-layer chromato-
graphy (TLC) using 0.25-mm E. Merck silica-gel 60 F254 precoated plates, which
were visualized with ultraviolet light. Melting points were observed using open capil-
laries. The infrared (IR) spectra were recorded on a Perkin-Elmer 257 spectrometer
using KBr discs. 1H NMR and 13C NMR spectra were recorded on a VXR 300-MHz
instrument using tetramethylsilane (TMS) as internal standard.
General Experimental Procedure
A mixture of ketone (1 mmol), ammonium thiocyanate (2 mmol), and phos-
phomolebdic acid (0.0002 mol) with a pinch of CuCl2 in ethylene dichloride
(15 ml) was stirred at room temperature for the appropriate time, as indicated in
Table 2. After completion of reaction, as monitored by TLC, the solution was fil-
tered, and the filtrate was dried on sodium sulfate and concentrated under reduced
pressure. The product obtained was purified by column chromatography.
Representative Spectral Data for Products
Compound 1. IR (KBr): 3045, 2851, 2156, 1705, 1690, 1438, 1120 cmꢀ1.1H
NMR CDCl3 (d ppm): 4.42–4.47 (m, 1H), 2.82–2.87 (m, 1H), 2.56–2.62 (m, 1H),
2.28–3.34 (m, 1H), 1.82–2.23 (m, 5H). 13C NMR CDCl3(d ppm): 24.13, 26.18,
34.09, 40.21, 50.47, 112.14, 206.80.
Compound 6. IR (KBr): 3058, 2960, 2927, 2125, 1685, 1585, 1520, 792,
1
650 cmꢀ1. H NMR CDCl3 (d ppm): 8.12 (s, 1H), 7.87 (d, J ¼ 7.0 Hz, 1H), 7.52
(d, J ¼ 7.0 Hz, 1H), 7.28(t, 1H, J ¼ 7.0 Hz), 4.70 (s, 2H). 13C NMR CDCl3 (d ppm):
42.96, 111.32, 125.87, 128.20, 131.10, 132.25, 134.80, 138.15, 189.70.

HETEROPOLY ACIDS AS CATALYST FOR a-THIOCYANATION OF KETONES
2855
1
Compound 16. IR (KBr): 3040, 2849, 2110, 1715, 1645. H NMR CDCl3
(d ppm): 2.48 (s, 6H), 4.90 (s, 1H). 13C NMR CDCl3 (d ppm): 29.10, 61.78,
112.12, and 202.69.
CONCLUSION
In conclusion, we have developed an alternative and simple protocol for the
synthesis of a-oxothiocyanates using HPA as an ecofriendly, reusable, inexpensive,
and efficient catalyst. Excellent yields, relatively short reaction times, and easy
workup are some of the advantages of this protocol.
ACKNOWLEDGMENTS
The authors are grateful to the University Grant Commission, New Delhi, for
financial support. Thanks also go to Dr. S. T. Gadade, principal, C. K. Thakur
College, for providing the laboratory and other facilities.
REFERENCES
1. Mehta, R. G.; Liu, J.; Constantinou, A.; Thomas, C. F.; Hawthorne, M.; You, M.;
Gerhaeusers, C.; Pezzuto, J. M.; Moon, R. C.; Moriarty, R. M. Cancer chemopreventive
activity of brassinin, a phytoalexin from cabbage. Carcinogenesis 1995, 16, 399.
2. Wood, J. L. Organic Reactions; R. Adams (Ed.); John Wiley & Sons: New York, 1946;
vol. 3, chap. 6.
3. Metzer, J. B. Comprehensive Heterocyclic Chemistry; A. Katrizky (Ed.); Pergamon:
Oxford, 1984; vol. 6, p. 235.
4. Yadav, L. D. S.; Patel, R.; Rai, V. K.; Srivastava, V. P. An efficient conjugate hydrothio-
cyanation of chalcones with a task-specific ionic liquid. Tetrahedron Lett. 2007, 48, 7793.
5. LeBlanc, B. W.; Jursic, B. S. Preparation of 5-alkylthio and 5-arylthiotetrazoles from
thiocyanates using phase transfer catalysis. Synth. Commun. 1998, 28, 3591.
6. Newman, A. A. Chemistry and Biochemistry of Thiocyanic Acid and Its Derivatives, 1st ed.;
Academic Press, New York, 1975.
7. Christopfel, W. C.; Miller, L. L. Octahydroanthracene as a bridging unit for juxtaposed
aromatic rings. J. Org. Chem. 1984, 49, 5198.
8. Guillerm, D.; Guillerm, G. Enantioselective synthesis of episulfide analogues of
L-methionine. Tetrahedron Lett. 1992, 33, 5047.
9. Nikiforov, T. T.; Connolly, B. A. 50-O-(4–40-Dimethylthoxytrityl)-4-thiocyanatothymi-
dine: A useful intermediate for the preparation of various 4-substituted thymidine
analogues. Tetrahedron Lett. 1991, 32, 2505.
10. Kagabu, S.; Maehara, M.; Sawahara, K.; Saito, K. Facile synthesis of thiocyanate using
trimethylsilyl cyanide. J. Chem. Soc., Chem. Commun. 1988, 1485.
11. Prakash, O.; Kaur, H.; Batra, H.; Rani, N.; Singh, S. P.; Moriarty, R. M. a-Thiocyana-
tion of carbonyl and b-dicarbonyl compounds using (dichloroiodo)benzeneꢀlead(II)
thiocyanate. J. Org. Chem. 2001, 66, 2019.
12. Heravi, M. M.; Sadjadi, S.; Oskooie, H. A.; Shoar, R. H.; Bamoharram, F. F. Heteropo-
lyacids as heterogeneous and recyclable catalysts for the synthesis of benzimidazoles.
Catal. Commun. 2008, 9, 504.
13. Bamoharram, F. F.; Roshani, M.; Alizadeh, M. H.; Razvi, H.; Moghayadi, M. Novel
.
oxidation of aromatic aldehydes catalyzed by Preyssler’s anion, [NaP5W30O110]14-
J. Braz. Chem. Soc. 2006, 17, 505.

2856
A. C. CHASKAR ET AL.
14. Heravi, M. M.; Sadjadi, S.; Oskooie, H. A.; Shoar, R. H.; Bamoharram, F. F. Hetero-
polyacids as green and reusable catalysts for the synthesis of 3,1,5-benzoxadiazepines.
Molecules 2007, 12, 255.
15. Kozhevnikov, I. V. Catalysis by heteropoly acids and multicomponent polyoxometalates
in liquid-phase reactions. Chem. Rev. 1998, 98, 171, and references 2–16 cited therein.
16. Misono, M.; Nojiri, N. Recent progress in catalytic technology in Japan. Appl. Catal.
1990, 64, 1.
17. Kozhevnikov, I. V. Advances in catalysis by heteropoly acids. Russ. Chem. Rev. 1987,
56, 811.
18. Misono, M.; Misono, N.; Katamura, K.; Kasai, A.; Konishi, Y.; Sakata, K.; Okuhara, T.;
Yoneda, Y. Catalysis by heteropoly compounds, III: The structure and properties of
12-heteropolyacids of molybdenum and tungsten (H3 PMo12 ꢀ xWxO40) and their salts
pertinent to heterogeneous catalysis. Bull. Chem. Soc. Jpn. 1982, 55, 400.
19. Yadav, J. S.; Subba Reddy, B. V.; Subba Reddy, U. V.; Chary, D. N. Iron(III) chloride
as mild and efficient reagent for the a-thiocyanation of ketones: An expedient synthesis of
a-oxo thiocyanates. Synthesis 2008, 8, 1283.
20. Kumar, A.; Ahamd, P.; Maurya, R. A. Direct a-thiocyanation of carbonyl and
b- dicarbonyl compounds using potassium peroxydisulfate–copper(II). Tetrahedron Lett.
2007, 48, 1399.