An efficient catalytic aerobic oxidation of alcohols in water using hypervalent iodine(V)

Article abstract of DOI:10.1002/adsc.200505102

A transition metal-free aerobic oxidation of alcohols to the corresponding aldehydes or ketones can be effectively catalysed by iodoxybenzene (PhIO ₂)/Br₂/NaNO₂ in water.

Full text of DOI:10.1002/adsc.200505102

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An Efficient Catalytic Aerobic Oxidation of Alcohols in Water
Using Hypervalent Iodine(V)
Ruizhu Mu, Zhongquan Liu, Zhanjun Yang, Zhengang Liu, Longmin Wu,
Zhong-Li Liu*
National Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou, Gansu 730000, Peopleꢀs Republic of
China
Phone: (þ86)-931-891-1186, fax: (þ86)-931-862-5657, e-mail: liuzl@lzu.edu.cn
Received: March 4, 2005; Accepted: April 29, 2005
Abstract: A transition metal-free aerobic oxidation
of alcohols to the corresponding aldehydes or ke-
tones can be effectively catalysed by iodoxybenzene
(PhIO2)/Br2/NaNO2 in water.
ing 1 mol % of iodoxybenzene as the active oxidant
(Scheme 1 and Table 1). To the best of our knowledge,
this is the first example of a hypervalent iodine(V)-cat-
alyzed transition metal-free aerobic oxidation of alco-
hols in water.
Keywords: alcohols; aldehydes; hypervalent iodine;
ketones; oxidation; water as solvent
Scheme 1.
The development of a selective alcohol oxidation that
It is seen from Table 1 that benzyl alcohols gave excel-
uses environmentally benign and low-cost oxidants is a lent yields of the corresponding benzaldehydes and no
critical challenge for synthetic organic chemists. Recent- over oxidation by-products were found (entries 1–5).
ly, the use of molecular oxygen as the terminal oxidant Primary aliphatic alcohols also produced the corre-
has received great attention, and many catalytic systems sponding aldehydes as the unique product, but the yields
have been developed for aerobic alcohol oxidation using were low due to the lower conversion (entries 6 and 7).
palladium,[1] copper,[2] or ruthenium catalysts.[3] Of Aromatic and aliphatic secondary alcohols gave excel-
particular interest are catalytic systems involving nitrox- lent yields of the corresponding ketones (entries 8–
À
yl radicals (e.g., 2,2,6,6-tetramethyl-piperidyl-1-oxyl, 15). Benzoin and meso-hydrobenzoin gave the C C
TEMPO).[4,5] However, many of these systems suffer bond cleavage product benzaldehyde (entries 16 and
from expensive transition metal catalysts, relatively 17). The efficiency and selectivity are similar to the pre-
high catalyst loadings and use of organic solvents.[6,7] viously reported catalytic procedures,[1–7] but the transi-
We wish to report herein an efficient selective catalytic tion metal-free, low catalyst loading and the organic sol-
aerobic oxidation of primary and secondary alcohols vent-free features make this procedure very attractive.
to the corresponding aldehydes and ketones in water
A plausible mechanism for this catalytic oxidation is
by using iodoxybenzene (PhIO2) as the active oxidant. depicted in Scheme 2 that comprises three redox cycles,
Hypervalent iodine reagents, such as o-iodoxybenzoic similar to that proposed previously for the TEMPO-
acid (IBX) and the Dess–Martin periodinane (DMP), mediated oxidation.[7c] In the scheme iodoxybenzene is
have been successfully used for oxidation of alcohols the active oxidant that oxidizes the alcohol to the corre-
to the corresponding carbonyl compounds,[8] while sponding carbonyl compound. The acid-catalyzed oxi-
only limited reports dealt with use of iodoxybenzene dation of alcohols by the stoichiometric iodoxybenzene
as the oxidant.[9] In addition, most of these procedures in organic solvents has been reported previously.[9a] The
used stoichiometric hypervalent iodine, and were con- running of the cycle I continuously provides iodoxyben-
ducted in organic solvents, apart from the stoiochiomet- zene by oxidizing the intermediate dihydroxyiodoben-
ric alcohol oxidation using IBX in an ionic liquid and wa- zene,[11] the reduced form of iodoxybenzene, with Br2,
ter[8 h] and in water/acetone mixture in the presence of b- which in turn, is reduced to HBr. Although NaNO2 can-
cyclodextrin,[8i] as well as the oxidation of sulfides to not directly react with HBr, it can disproportionate in
À
sulfoxides in water by using 55 mol % of iodoxybenze- acidic aqueous solution to produce NO3 and NO
ne.[9c] Taking advantage of the high solubility of iodoxy- [Eq. (1)].[12] Oxidation of NO by atmospheric oxygen
benzene in water,[10] we successfully accomplished an ef- produces NO2 which reoxidizes HBr to Br2 as illustrated
ficient catalytic aerobic alcohol oxidation in water by us- in the cycle II,[12] and the NO2 is reduced back to NO(cy-
Adv. Synth. Catal. 2005, 347, 1333–1336
DOI: 10.1002/adsc.200505102
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Ruizhu Mu et al.
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Table 1. Catalytic aerobic alcohol oxidation in water.[a]
Entry
Substrate
Product
Time [h]
1
Conv.[b] [%]
100
Yield[c] [%]
94
1
2
1
100
94
3
4
1
1
100
100
97
94
5
1.5
100
98
6
7
2
2
48.0
73.6
42
67
8
9
1.5
1.5
1.5
1
100
100
100
100
98
97
95
93
10
11
12
13
1.5
1.5
100
100
94
95
14
15
2
2
100
100
92
93
16
8
7
100
100
91
96
17
[a]
Reaction conditions, see Experimenal Section. All products were identified by comparing their MS and 1H NMR data with
those in the literature.
Conversion determined by GC-MS.
Isolated yield of pure products.
[b]
[c]
cle III).[12] The coupling of these three redox cyclesare so can also oxidize HBr to Br2 [Eq. (2)] as reported recen-
efficient that only 1 mol % of iodoxybenzene, 2 mol % tly.[7d]
of Br2 and 1 mol % of NaNO2 are sufficient to complete
the overall catalytic process. In addition, HNO3 pro-
duced from Eq. (1) and from dissolving NO2 in water
ð1Þ
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Catalytic Aerobic Oxidation of Alcohols in Water
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Scheme 2. Our proposed mechanism.
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ð2Þ
In conclusion, this work demonstrates that PhIO2/Br2/
NaNO2 is a very efficient catalytic system for selective
aerobic oxidation of alcohols in water. Extension of
this procedure to other substrates is underway in this
laboratory.
[4] For reviews of TEMPO-catalyzed alcohol oxidation, see:
a) A. E. J. de Nooy, A. C. Besemer, H. van Bekkum,
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Experimental Section
1H NMR spectra were recorded on a Varian Mercury Plus-300
spectrometer in CDCl3 with TMS as internal standard. Mass
spectra were determined on a Hewlett Packard 5988A spec-
trometer by direct inlet at 70 eV. GC/MS were determined us-
ing a Finnigan Trace 2000 GC/MS system. All products were
identifiedby NMR, MS and/or comparison with authentic sam-
ples. Iodoxybenzene was prepared according to the literature
procedure.[10] Alcohols and other reagents were all purchased
from commercial sources.
[5] For transition-metal-assisted TEMPO-catalyzed aerobic
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Lett. 2001, 42, 6651; d) A. Dijksman, A. Marino-Gonza-
lez, A. Mairata i Payeras, I. W. C. E. Arends, R. A. Shel-
don, J. Am. Chem. Soc. 2001, 123, 6826; e) R. Ben-Dan-
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In a typical experiment an alcohol (10 mmol) was mixed
with iodoxybenzene (0.1 mmol), Br2 (0.2 mmol) and NaNO2
(0.1 mmol) in water (40 mL). The mixture was heated to
558C to facilitate dissolution of iodoxybenzene and kept at
this temperature under vigorous stirring and a balloon pressure
of air until the reaction was completed as monitored by TLC.
Extraction of the reaction mixture with ether followed by re-
moval of the solvent under reduced pressure and column chro-
matographic separation gave the pure product which was iden-
tified by MS and 1H NMR. The conversion and selectivity were
determined by GC-MS.
[6] Catalytic aerobic alcohol oxidation in water by a water-
soluble palladium catalyst[2b, d] or an amphiphilic resin-
dispersion of a nanopalladium catalyst[2 h] has recently
been reported.
[7] For transition metal-free catalytic alcohol oxidation in
organic solvents, see: a) H.-R. Bjørsvik, L. Liguori, F.
Costantino, F. Minisci, Org. Process Res. Dev. 2002, 6,
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J. Am. Chem. Soc. 2004, 126, 4112; d) F. Minisci, O. Por-
ta, F. Recupero, C. Punta, C. Gambarotti, M. Pierini, L.
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Acknowledgements
We thank the National Natural Science Foundation of China
(grant No. 20372030) for financial support.
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1336
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