Tungstate sulfuric acid (TSA)/ KMnO4 as a novel heterogeneous system for rapid deoximation

Article abstract of DOI:10.3390/11090720

Neat chlorosulfonic acid reacts with anhydrous sodium tungstate to give tungstate sulfuric acid (TSA), a new dibasic inorganic solid acid in which two sulfuric acid molecules connect to a tungstate moiety via a covalent bond. A variety of oximes were oxidized to their parent carbonyl compounds under mild conditions with excellent yields in short times by a heterogeneous wet TSA/KMnO₄ in dichloromethane system.

Full text of DOI:10.3390/11090720

Molecules 2006, 11, 720-725
molecules
ISSN 1420-3049
http://www.mdpi.org
Communication
Tungstate Sulfuric Acid (TSA)/ KMnO4 as a Novel
Heterogeneous System for Rapid Deoximation
Bahador Karami * and Morteza Montazerozohori
Department of Chemistry, Yasouj University, Yasouj 75914-353, Iran
* Author to whom correspondence should be addressed; e-mail: karami@mail.yu.ac.ir
Received: 5 September 2005; in revised form: 7 June 2006 / Accepted: 30 June 2006 / Published: 28
September 2006
Abstract: Neat chlorosulfonic acid reacts with anhydrous sodium tungstate to give
tungstate sulfuric acid (TSA), a new dibasic inorganic solid acid in which two sulfuric
acid molecules connect to a tungstate moiety via a covalent bond. A variety of oximes
were oxidized to their parent carbonyl compounds under mild conditions with excellent
yields in short times by a heterogeneous wet TSA/KMnO4 in dichloromethane system.
Keywords: Tungstate sulfuric acid, Oximes, Heterogeneous conditions, Solid acid
Introduction
Heterogenization of chemical systems is currently an active field of research in industrial and
academic chemistry because of the resulting simplification in handling procedures and work-ups,
reduction of corrosion and, from a Green Chemistry point of view, easy and clean reactions and
avoidance of by-products. Considering the wide applications of acids as reagents or catalysts in
organic chemistry (for producing more than 1×108 MT/year of products), the introduction of new
inorganic solid acids can be useful in this context. Recently silica-sulfuric acid [1] and Nafion-H® [2]
have been used for a wide variety of reactions such as production of disulfides from thiols, oxidation
of 1,4-dihydropyridines [3], N-nitrosation of secondary amines [4], deprotection of acetals [5],
oxidation of alcohols [6], alkylation with olefins, alkyhalides, alkyl esters, isomerization,
transalkylation, acylation, nitration, ether and ester synthesis, acetal formation and rearrangement
chemistry [7]. In continuation of the above and our own studies [8] on the application of inorganic
solid acids, we have now found that anhydrous sodium tungstate reacts in a 1:2 mole ratio with

Molecules, 2006, 11
721
chlorosulfonic acid (Scheme 1) to give tungstate sulfuric acid (TSA, I) in a simple and clean reaction
that did not require any work-up.
Scheme 1.
O
O
HO3SO
OSO3H
+
W
NaCl
2
NaO
ONa
ClSO H
3
W
O
+ 2
O
I
After preparation of TSA (I), we were interested in examining its use as a proton source in
combination with KMnO4 and water in dichloromethane as a heterogeneous system for the cleavage of
oximes to regenerate the corresponding aldehydes or ketones. This is an important reaction because
oximes serve as efficient carbonyl protective groups and are used extensively for the purification and
characterization of such compounds. A number of methods have been reported for deoximation,
among which we may mention chromium trioxide [9], 3-carboxypyridinium chlorochromate [10],
sodium perborate [11], peroxymonosulphate ion [12], tert-butylhydroperoxide [13], ammonium
persulphate-alumina under microwave irradiation [14] Dess-Martin periodinane [15], l-benzyl-4-aza-1-
azonia-bicyclo[2.2.2]-octane periodate [16], microwave assisted sodium periodate supported on silica
[17] and KMnO4-dicyclohexyl-18-crown-6 [18, 19]. Classically, the recovery of the parent carbonyl
compounds from oximes involves a hydrolytic cleavage which removes the hydroxylamine from
equilibrium [20]. However; many of these existing methods either employ highly toxic reagents or, in
the case of aldoximes, result in further oxidation of liberated aldehydes to their corresponding
carboxylic acids.
Results and Discussion
In this article we wish to report a new, simple and convenient method for the effective deprotection
of the oximes under mild and heterogeneous conditions using wet TSA (I)/KMnO4 in dichloromethane
(Scheme 2). Different kinds of oximes were subjected to this oxidative deprotection reaction and the
results are summarized in Table 1.
Scheme 2
R1
R2
R1
R2
Wet TSA(I)
/ KMnO4
O
C
N
C
OH
, RT
CH2Cl2
As evident from the results, aldoximes were generally deprotected relatively faster than ketoximes
(cf. entries 1-2, 14 and 16-18). It was also interesting to note that by controlling the amounts of
reagents used, it was possible to avoid further oxidation of the liberated aldehydes to the
corresponding carboxylic acids (entries 1-3 and 14-18), therefore this system behaves
chemoselectively towards the oxime function with controlled amounts of reagents. Oximes bearing
substituents susceptible to acidic media (entries 14 and 15) did not undergo hydrolysis of these
functional groups.

Molecules, 2006, 11
722
Table 1. Regeneration of carbonyl compounds from oximes using a heterogeneous wet
TSA (I)/ KMnO4 system in dichloromethane
Time
Yield (%) b
Entry
Oxime substrate
Product a
(min.)
NOH
CHO
1
2
3
H
C
10
5
91
90
92
NOH
O
Cl
Cl
CH
CH
O
NOH
CH
CH
5
O3N
O3N
O
NOH
4
12
10
90
93
5
6
NOH
O
NOH
O
NH2
HO
CH3
CH3
C
C
10
8
90
92
NOH
O
7
8
NOH
O
CH3
CH3
C
10
94
C
NOH
O
Cl
Cl
Br
CH3
9
CH3
C
12
8
90
90
C
O
NOH
Br
CH3
10
C
CH3
C
NOH
O
11
12
8
94
91
15
O
NOH
C
C
O
C
NOH
CH3
13
10
92
Ph
C
Ph
CH3

Molecules, 2006, 11
723
Table 1. Cont.
NOH
CH
O
CH
14
15
5
90
OMe
NOH
OMe
CHO
H
C
12
8
90
92
OCOEt
OCOEt
NOH
O
16
17
CH
CH
S
N
S
N
O
NOH
CH
10
8
90
90
CH
O
NOH
18
n-C7H15
n-C7H15
C
H
CH
a
1
Characterized by H-NMR and IR spectral analysis and comparison of TLC
and physical data with authentic samples [22].
b
Yields refer to isolated and purified products.
To identify of the nature of the agent responsible for deoximation in our conditions, three parallel
control experiments were designed using the oximes of entries 1, 3, 5 and 13: a first reaction in the
presence of wet TSA, another using only wet KMnO4 and the third one in the presence of the proposed
wet TSA/KMnO4 combination. The results showed that neither wet TSA nor wet KMnO4 alone could
accomplish the deoximation reactions to any great extent, even after reaction times of up to 10 h, while
as the results in Table 1 show, deoximation was complete in 15 min. or less when the wet
TSA/KMnO4 system was used. It is well known that KMnO4 requires an acidic medium to function as
an oxidant, consequently we propose an oxidative mechanism for this reaction in which the wet TSA
acts as a proton source for the KMnO4 to oxidize the oximes.
Conclusions
In summary, we think TSA (I) represents a good solid acid for reactions in which protons are need
as catalysts or reagents due to its efficiency, easy preparation, low cost and availability, insolubility
towards all organic solvents, simplicity of handling, convenient work–up of products, clean reactions,
short reaction times and high reaction yields. In this paper we have reported a convenient, efficient and
practical method for the oxidative cleavage of oximes. Structural investigation of TSA (I) and similar
solid acids and other applications of these reagents in various organic reactions are current research
objectives in our laboratory.

Molecules, 2006, 11
Experimental
General
724
Chemicals were purchased from the Merck, Fluka and Aldrich chemical companies. Oximes were
prepared from the corresponding carbonyl compounds according to the reported procedure [21]. The
reactions were monitored by TLC. The products were isolated and identified by comparison of their
physical and spectral data with authentic samples. IR spectra were recorded on a Jasco FT-IR 680
1
instrument. H-NMR data were obtained on a Bruker-DPX-300 MHz Avance 2 instrument. Mass
spectra were recorded on an AMD 604 spectrometer, operating in EI-mode at 70 ev and FT-mode at
0.005 V.
Preparation of tungstate sulfuric acid (TSA, I).
Anhydrous sodium tungstate (29.38 g, 0.1 mol) was added gradually to chlorosulfonic acid
(23.304 g, 13.31 mL, 0.2 mol) contained in a 250 mL round bottomed flask placed in an ice-bath. After
the completion of the addition the mixture was shaken for 1 h. A yellowish-white solid of TSA was
obtained (40.2 g, 98.0 %), m.p. 285°C (dec.); IR (KBr, cm-1); 3600-2200 (OH, bs), 1240-1140 (S=O,
bs), 1060 (S-O, m), 1005 (S-O, m), 880-840 (W=O, m), 450 (W-O, m).
Typical deoximation procedure: oxidation of 3-nitrobenzaldoxime (Table 1, entry 3).
To a solution of 3-nitrobenzaldoxime (0.152 g, 1 mmol) in dichloromethane (10 mL), wet TSA (I,
10% w/w, 1.05 g, 2 mmol) and KMnO4 (0.316 g, 2 mmol) were added. The reaction mixture was
stirred at room temperature and the transformation was determined to be finished after 5 min. by TLC
(1:1 n-hexane-ethyl acetate). The reaction mixture was filtered and the solids washed with
dichloromethane (2 × 4 mL). The filtrate was evaporated under reduced pressure and the resulting
crude material was purified by flash chromatography on SiO2 (eluent: CH2Cl2) to afford 3-
nitrobenzaldehyde (0.139 g, 92%), m.p= 42-43 ºC (lit.[22] mp 42 oC); IR (KBr, cm-1): 3050 (m), 2950
(m), 1685 (s), 1610 (m), 1570 (m), 828 (m), 760 (m) ; 1H-NMR (CDCl3): 7.9 (s, 1H), 8.0-8.4 (m, 4H)
ppm; MS: m/z=151.
References
1.
2.
3.
Zolfigol, M. A. Tetrahedron 2001, 57, 9509-9511.
Olah, G. A.; Molhotra, R.; Narang, S. C. J. Org. Chem. 1987, 43, 4628.
Zolfigol, M. A.; Shirin, F.; Ghorbani Choghamarani, A.; Mohammadpoor-Baltork, I. Green
Chem. 2002, 4, 562.
4.
5.
Zolfigol, M. A.; Bamoniri, A. Synlett 2002, 1621.
(a) Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A. J. Korean Chem. Soc. 2001, 45, 546; (b)
Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A. Molecules 2002, 7, 751.

Molecules, 2006, 11
725
6.
(a) Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A.; Zarei, A. Bull. Korean Chem. Soc. 2003, 24,
400; (b) Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A.; Zaghaghi, Z. J. Chem. Research (S). 2003,
273; (c) Mirjalili, B. F.; Zolfigol, M. A.; Bamoniri, A.; Zaghaghi, Z.; Hazar, A. Acta Chem. Slov.
2003, 50, 563; (d) Shirini,; F. Zolfigol, M. A.; Mohammadi, K. Bull. Korean Chem. Soc. 2004,
25, 325.
7.
8.
Harmer, M. A.; Sun, Q. Appl. Catal. A: General 2001, 221, 45.
(a) Heydari, A.; Larijani, H.; Emami, J.; Karami, B. Tetrahedron Lett. 2000, 41, 2471; (b)
Asgarian Damavandi, J.; Zolfigol, M. A.; Karami, B. Synth. Commun. 2001, 31, 129; (c) Niknam,
K.; Karami, B.; Kiasat, A. R. Bull. Korean Chem. Soc. 2005, 26, 975-978; (d) Karami, B.;
Montazerozohori, M.; Habibi, M. H. Bull. Korean Chem. Soc. 2005, 26, 1125-1128.
Hamal, S., Santosh, K. M.; Chhabilal, G. Ind. J. Chem. 1996, 35B, 1116.
9.
10. Mohammadpoor-Baltork, I.; Pouranshirani. S. Synth. Commun. 1996, 26, 1.
11. Bandgar, B. P.; Shaikh, S. I.; Iyer, S. Synth. Commun. 1996, 26, 1163.
12. Bose, S. D.; Srinivas, P. Synth. Commun. 1997, 27, 3835.
13. Barhate, N. B.; Gajare, A. S.; Wakharkar, R. D.; Sadalai, A. Tetrahedron Lett. 1997, 38, 653.
14. Verma, R.S.; Meshram H. M. Tetrahedron Lett. 1997, 38, 5427.
15. Chaudhari, S. S.; Akamanchi, K. G. Tetrahedron Lett. 1998, 39, 3209.
16. Hajipour, A. R.; Mahboubghah, N. J. Chem. Res. (S). 1998, 123.
17. Verma, R. S.; Dahia, R.; Saini, R. K. Tetrahedron Lett. 1997, 38, 8819.
18. House, H. O. “Modern Synthetic Reactions”, 2nd ed.; W. A Benjamin: San Francisco, CA, USA,
1972; pp 275.
19. Sam, D. J.; Simmons, H. F. J. Am. Chem. Soc. 1972, 94, 4024.
20. (a) Hershberg, E. B. J. Org. Chem. 1984, 13, 542; (b) Drabowiez, J. Synthesis 1980, 125; (c) Rao,
C. G.; Radhakrishna, A. S.; Singh, R. B.; Bhatnagar, S. P. Synthesis 1983, 808; (d) Bandgar, B.
P.; Kunde, M. L. B.; Thote, J. L. Synth. Commun. 1997, 27, 1149; (e) Butler, R. N.; Morris, G. J.;
Odonohue, A. M. J. Chem. Res. (S). 1981, 61; (f) Shim, S. B.; Kim, K.; Kim, Y. H. Tetrahedron.
Lett. 1987, 28, 645 ; (g) Salmon, M.; Miranda, R.; Angeles, E. Synth. Commun. 1986, 16, 1827;
(h) Moriarty, R. M.; Prakash, O.; Vavilikolanu, R. Synth. Commun. 1986, 16, 1247; (i) Vankar,
P.; Rathore, R.; Chandrasekaran, S. J. Org. Chem. 1986, 51, 3063; (j) Chidambaram, N.;
Satyanarayana, K.; Chandrasekaran, S. Synth. Commun. 1989, 19, 1724; (k) Mona, D.; Cramman,
P.; Spranzo, G.; Tagliapietra, P.; Manam, P. Synth. Commun. 1986, 16, 803.
21. Vogel’s Text Book of Practical Organic Chemistry, 4th ed.; Longman Group Limited: London,
1978.
22. Dictionary of Organic Compounds, 6th ed.; Chapman and Hall: London, 1982.
Sample Availability: Available from the authors.
© 2005 by MDPI (http:www.mdpi.org). Reproduction is permitted for non commercial purposes.