Mild oxidation of alcohols with O-lodoxybenzoic acid (IBX) in ionic liquid 1-butyl-3-methyl-imidazolium chloride and water

Article abstract of DOI:10.1021/ol0351549

(Matrix presented) A mild, efficient, and eco-friendly procedure for the oxidation of alcohols with IBX in ionic liquid [bmim]Cl and water has been developed. Simply stirring of a solution of the alcohol and IBX in [bmim]Cl/water at room temperature followed by extraction with ether or ethyl acetate and removal of the solvent gives excellent yields of the corresponding carbonyl compounds. Recycling and reuse of the oxidant and ionic liquid have also been reported.

Full text of DOI:10.1021/ol0351549

ORGANIC
LETTERS
2003
Vol. 5, No. 18
3321-3323
Mild Oxidation of Alcohols with
O-Iodoxybenzoic Acid (IBX) in Ionic
Liquid 1-Butyl-3-methyl-imidazolium
Chloride and Water
Zhi Liu, Zhen-Chu Chen,* and Qin-Guo Zheng
Department of Chemistry, Zhejiang UniVersity (XiXi Campus),
Hangzhou, 310028, P. R. China
zhenchuc@mail.hz.zj.cn
Received June 23, 2003
ABSTRACT
A mild, efficient, and eco-friendly procedure for the oxidation of alcohols with IBX in ionic liquid [bmim]Cl and water has been developed.
Simply stirring of a solution of the alcohol and IBX in [bmim]Cl/water at room temperature followed by extraction with ether or ethyl acetate
and removal of the solvent gives excellent yields of the corresponding carbonyl compounds. Recycling and reuse of the oxidant and ionic
liquid have also been reported.
Hypervalent iodine reagents have attracted increasing interest
during the past decade because of their selective, mild, and
environmentally friendly properties as oxidizing agents in
organic synthesis.1 IBX (o-iodoxybenzoic acid) has gained
great popularity as a mild oxidant for the conversion of
alcohols to aldehydes or ketones.2,3 IBX is virtually insoluble
in most organic solvents, which accounts for the great length
of time between the discovery of IBX and the first practical
applications of it in DMSO (the only solvent in which it
does dissolve).1,5 While not entirely inconvenient, the limita-
tions of DMSO as a solvent are apparent and sufficient to
have motivated two independent syntheses of solid-phase
analogues of IBX (polystyrene- and silica-bound).6 In each
case, the authors correctly note that these solid-phase reagents
expand the range of viable solvents, simplify separation of
oxidation byproducts, and facilitate recovery and reuse of
the oxidant. However, it is obvious that the synthesis of these
solid-phase reagents is laborious and time-consuming. Most
recently, researchers have turned their attention to carrying
out the oxidation in common, low boiling point molecular
solvents by elevating the reaction temperature or using a
suitable catalyst.7 These two improvements are effective
(1) (a) Varvoglis, A. HyperValent Iodine in Organic Synthesis; Academic
Press: London, 1997. (b) Stang, P. J. J. Org. Chem. 2003, 68, 2997. (c)
Zhdankin, V. V.; Stang, P. J. Chem. ReV. 2002, 102, 2523. (d) Wirth, T.;
Hirt, U. H. Synthesis 1999, 1271.
(4) IBX was first prepared over 100 years ago: Hartman, C.; Mayer, V.
Chem. Ber. 1893, 26, 1727.
(2) (a) Frigerio, M.; Santagostino, M. Tetrahedron Lett. 1994, 35, 8019.
(b) Frigerio, M.; Santagostino, M.; Sputore, S.; Palmisano, G. J. Org. Chem.
1995, 60, 7272. (c) De Munari, S.; Frigerio, M.; Santagastino, M. J. Org.
Chem. 1996, 61, 9272. See also ref 3a.
(3) IBX has also found use in several other oxidative transformations.
For an overview, see: (a) Wirth, T. Angew. Chem., Int. Ed. 2001, 40, 2812.
For more recent developments, see: (b) Nicolaou, K. C.; Baran, P. S.;
Zhong, Y.-L.; Barluenga, S.; Hunt, W. K.; Kranich, R.; Vega, J. A. J. Am.
Chem. Soc. 2002, 124, 2233. (c) Nicolaou, K. C.; Montagnon, T.; Baran,
P. S.; Zhong, Y.-L. J. Am. Chem. Soc. 2002, 124, 2245.
(5) Prior to its use as a terminal oxidant in its own right, IBX was
identified as a valuable precursor to Dess-Martin Periodinate: Dess,
D. B.; Martin, J. C. J. Am. Chem. Soc. 1991, 113, 7277 and references
therein.
(6) (a) Mu¨lbaier, M.; Giannis, A. Angew. Chem., Int. Ed. 2001, 40, 4393.
(b) Sorg, G.; Mengel, A.; Jung, G.; Rademan, J. Angew. Chem., Int. Ed.
2001, 40, 4395.
(7) (a) More, J. D.; Finney, N. S. Org. Lett. 2002, 4, 3001. (b) Surendra,
K.; Krishnaveni, N. S.; Reddy, M. A.; Nageswar, Y. V. D.; Rao, K. R. J.
Org. Chem. 2003, 68, 2058.
10.1021/ol0351549 CCC: $25.00 © 2003 American Chemical Society
Published on Web 08/13/2003

Scheme 1a
Table 1. Oxidation of Alcohols with IBX in [bmim]Cl/Water
a Reagents and conditions: (a) IBX (1.1 equiv), [bmim]Cl/H2O,
20 °C.
alternatives to classical procedure by avoiding the use of the
high boiling point, difficultly removed solvent DMSO.2a
However, the elevation of reaction temperature may cause
decomposition of starting materials and bring about side
reactions.
Ambient-temperature ionic liquids have been emerging as
promising green solvents for the past decade.8 Their non-
volatile nature gives them significant advantage in minimiz-
ing solvent consumption. Their polarity renders them good
solvents for various organic, inorganic, and polymeric
compounds and therefore good media for homogeneous
reactions.8c Because of their unique solubility properties, i.e.,
miscibility gap between water and organic solvents, they have
become interesting candidates for separation processes by
simple liquid-liquid extraction with either aqueous or
conventional organic solvents.9
In our efforts to investigate the range of organic reactions
possible in ionic liquids,10 we report herein a simple, mild,
efficient, and practical method for the oxidation of alcohols
and diols with IBX using 1-butyl-3-methylimidazolium
chloride ([bmim]Cl) as the solvent (Schemes 1 and 2).
Scheme 2a
([bmim]Cl), 1-butyl-3-methylimidazolium tetrafluoroborate
([bmim][BF4]), and 1-butyl-3-methylimidazolium hexafluo-
rophosphorate [bmim][PF6]. None of these ionic liquids can
dissolve IBX even when heated to 80 °C except [bmim]Cl,
which can readily dissolve IBX in the presence of a small
amount of water at room temperature to form a homogeneous
solution.
The reactions were carried out by dissolving IBX in
[bmim]Cl and water at room temperature followed by the
addition of corresponding alcohol. All the alcohols investi-
gated gave excellent yields ranging from 88 to 99%, and
the products were substantially pure as indicated by 1H NMR
and HPLC analysis (Table 1, purities as assessed by HPLC
>95%).11 No overoxidation to acids was observed in the case
of aldehyde products (entries 1-8, Table 1). Both aryl-
a Reagents and conditions: (a) IBX (1.1 equiv), [bmim]Cl/H2O,
20 °C; (b) IBX (2.5 equiv), [bmim]Cl/H2O, 20 °C.
We examined the reaction in six ambient-temperature ionic
liquids, butylpyridinium tetrafluoroborate (bpyBF4), butylpy-
ridinium hexafluorophosphorate (bpyPF6), butylpyridinium
chloride (bpyCl), 1-butyl-3-methylimidazolium chloride
(8) (a) Zhao, H.; Malhotra, S. V. Aldrichimica Acta 2002, 35, 75. (b)
Dupont, J.; De Souza, R. F.; Suarez, P. A. Z. Chem. ReV. 2002, 102, 3667.
(c) Wasserscheid, P.; Keim, W. Angew. Chem., Int. Ed. 2000, 39, 3772.
(d) Welton, T. Chem. ReV. 1999, 99, 2071.
(9) Huddleston, J. G.; Willauer, H. D.; Swatloski, R. P.; Visser, A. E.;
Rogers, R. D. Chem. Commun. 1998, 1765.
(10) (a) Xie, Y.-Y.; Chen, Z.-C.; Zheng, Q.-G. Synthesis 2002, 1505.
(b) Xie, Y.-Y.; Chen, Z.-C.; Zheng, Q.-G. J. Chem. Res., Synop. 2002, 618.
(c) Su, C.; Chen, Z.-C.; Zheng, Q.-G. Synthesis 2003, 555.
(11) Alcohols in Table 1 are commercially available and were used as
received.
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Org. Lett., Vol. 5, No. 18, 2003

IBX at room temperature with [bmim]Cl and water as a
solvent. Compared with the classical procedure in DMSO,
this procedure in ambient-temperature ionic liquid [bmim]-
Cl and water shares the advantage of mild reaction condi-
tions, homogeneous solution, facile recovery of the oxidant,
and excellent yields of products and is, to some extent,
superior in terms of the ready separation of products, small
degree of consumption of the solvent, and recycling of the
ionic liquid without decreasing the yields of products. We
anticipate that this protocol will be of broad interest and use
to the chemical community.14
Table 2. Results Obtained Using Recycled Ionic Liquid
Acknowledgment. We thank the analytical center of
chemistry department, Zhejiang University for providing the
spectra data.
a Isolated yields based on benzyl alcohol.
carbinols and aliphatic alcohols gave good to excellent yields.
Various functionalities such as methoxy and nitro groups,
alkene double bonds, and a furan ring can tolerate the
oxidation. 1,2-Diols were cleanly oxidized, with a stoichio-
metric amount of IBX, to R-dicarbonyls (entries 14-15,
Table 1) or R-ketol (entry 13, Table 1) without cleavage of
the 1,2-diol bond. All of the compounds were characterized
Supporting Information Available: Experimental pro-
cedure and spectral data for all compounds. This material is
available free of charge via the Internet at http://pubs.acs.org.
OL0351549
(13) In a representative (and unoptimized) case, IBA was recovered
essentially quantitatively by first extracting out benzaldehyde with ether (3
× 10 mL) from the reaction mixture and then adding 10 mL of water to
the remaining solution to precipitate IBA followed by filtration. Oxidation
of IBA to IBX was carried out in deionized water at 70 °C using Oxone as
the oxidant. For details, see: Frigerio, M.; Santagostino, M.; Sputore, S. J.
Org. Chem. 1999, 64, 4537. About 55% yield of IBX was recovered, which
is identical to authentic IBX as indicated by 1H NMR (DMSO-d6) and
elemental analysis (>99% purity by HPLC). Ionic liquid [bmim]Cl was
recovered by evaporating the filtrate under vacuum to remove water, and
more than 95% yield of recovered [bmim]Cl was obtained and reused
(containing trace IBX, which did not affect the oxidation at all).
(14) Representative Experimental Procedure. To a mixture of [bmim]-
Cl (3 mL) and water (0.6 mL) was added IBX (0.31 g, 1.1 mmol). The
resulting mixture was stirred at room temperature for 5-10 min, and benzyl
alcohol (0.11 g, 1 mmol) was added. The reaction mixture was stirred at
room temperature for 5 min, and then the product was extracted with ether
(3 × 10 mL). The organic phase was dried over anhydrous sodium sulfate
and concentrated under vacuum to yield 0.11 g (99% yield, >98% pure by
HPLC) of benzaldehyde as a pale yellow liquid.
1
by mass, H NMR, and IR and by comparison with the
known compounds.7b,12
In these reactions, iodosobenzoic acid (IBA), obtained
from the reduction of IBX, can be reoxidized to active IBX
using standard procedures.13 The regenerated IBX is indis-
tinguishable from IBX freshly prepared from o-iodobenzoic
acid. Ionic liquid [bmim]Cl has also been recovered and
reused without decreasing the yields of products (Table 2).13
As a final point, we have presented an elegant and simple
methodology for the oxidation of a variety of alcohols using
(12) Most of the spectral data for the products can be obtained from
Sigma-Aldrich via the Internet at http://www.Sigmaaldrich.com. Data for
the rest of the products are available in ref 7b.
Org. Lett., Vol. 5, No. 18, 2003
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