A new and highly effective method for catalytic oxidation of alcohols to the corresponding carbonyl compounds using the tris[(2-oxazolinyl)phenolato] manganese(III)/Oxone/n-Bu4NBr oxidation system

Article abstract of DOI:10.1016/j.tetlet.2003.10.018

Oxone (2KHSO₅·KHSO₄·K ₂SO₄) in the presence of mer-tris[(2-oxazolinyl)phenolato] manganese(III), Mn(phox)₃, as catalyst under biphasic reaction conditions (CH₂Cl₂/H₂O)

Full text of DOI:10.1016/j.tetlet.2003.10.018

TETRAHEDRON
LETTERS
Pergamon
Tetrahedron Letters 44 (2003) 8943–8945
A new and highly effective method for catalytic oxidation of
alcohols to the corresponding carbonyl compounds using the
tris[(2-oxazolinyl)phenolato]manganese(III)/Oxone®/n-Bu4NBr
oxidation system
Mojtaba Bagherzadeh*
Department of Chemistry, Sharif University of Technology, PO Box 11395-9516, Tehran, Iran
Received 11 August 2003; revised 25 September 2003; accepted 3 October 2003
Abstract—Oxone® (2KHSO5·KHSO4·K2SO4) in the presence of mer-tris[(2-oxazolinyl)phenolato]manganese(III), Mn(phox)3, as
catalyst under biphasic reaction conditions (CH2Cl2/H2O) and tetra-n-butylammonium bromide as phase transfer agent efficiently
oxidises alcohols to their corresponding aldehydes and ketones at room temperature with very short reaction times (5 min) and
good to quantitative yields.
© 2003 Elsevier Ltd. All rights reserved.
The oxidation of alcohols to the corresponding alde-
hydes and ketones is a key reaction in synthetic organic
chemistry and numerous oxidizing reagents are avail-
able to effect this important reaction.1 Many of these
oxidation systems require stoichiometric amounts of
metal compounds with concomitant environmental
problems, for example the chromium oxidants which
are used in vast amounts in both the laboratory and
industry.2 Recent efforts have focused on systems which
employ metal compounds only in catalytic amounts
together with a stoichiometric oxidant.3
In this paper we demonstrate the efficient oxidation of
alcohols to their corresponding aldehydes and ketones
under mild and biphasic conditions (CH2Cl2/H2O) at
room temperature with Oxone® catalysed by mer-tris-
[(2-oxazolinyl)phenolato]manganese(III), Mn(phox)3, a
complex previously used in the epoxidation of styrene
with H2O2 (Scheme 1).11
In a typical experiment, a solution of Oxone® (0.25
mmol) in H2O (5 mL) at room temperature was added
to a solution of alcohol (0.25 mmol), tetra-n-butylam-
monium bromide, (0.1 mmol), and tris[(2-oxa-
zolinyl)phenolato]manganese(III) (0.025 mmol), in
CH2Cl2 (1 mL), and the biphasic mixture stirred vigor-
ously. Formation of products and consumption of sub-
strates were monitored by GLC. The identity of
Oxone® which contains potassium peroxymonosulfate,
KHSO5 as the oxidizing species, is commercially avail-
able as the triple salt 2KHSO5·KHSO4·K2SO4. There
are reports in the literature where Oxone® is used for
the oxidation of sulfides, amines, and alkenes.4 It can
also be used for the oxidation of alcohols to aldehydes
and ketones5 and benzaldehyde to benzoic acid.6
TEMPO/Oxone®/n-Bu4NBr is effective for the oxida-
tion of alcohols.7 In preceding papers, we reported that
Oxone® as an oxidant and a source of protons, pro-
motes the nitration of phenols,8 N-nitrosation of
amines9 and the oxidation of urazoles to their corre-
sponding triazolidines.10
Keywords: Mn-oxazoline complex; alcohol; catalytic oxidation;
Oxone®.
* Corresponding author. Fax: +98-21-6012983; e-mail: bagherzadehm
@sharif.edu
Scheme 1.
0040-4039/$ - see front matter © 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2003.10.018

8944
M. Bagherzadeh / Tetrahedron Letters 44 (2003) 8943–8945
Table 2. Oxidation of alcohols by the Mn(phox)3/Oxone®/
n-Bu4NBr catalytic systema
1
products was determined by IR and H NMR spectral
data and by comparison with authentic samples using
gas–liquid chromatography.
In order to choose a suitable solvent, the oxidation of
benzyl alcohol was carried out in dichloromethane,
chloroform, acetonitrile, benzene, and ethyl acetate.
Our findings showed that CH2Cl2 was generally the best
of the solvents tested in terms of yields (Table 1).
Important effects of a nitrogen base acting as the axial
ligand to the metal in manganese complex-catalysed
oxidation is well-known in some systems.11,12 In the
present oxidation method, however, the same yields
were obtained for benzyl alcohol oxidation in the pres-
ence or in the absence of various nitrogen donor bases
such as imidazole and pyridine.
In order to find the optimum conditions for the oxida-
tion, various molar ratios of the catalyst, phase transfer
agent, benzyl alcohol, and Oxone® were used. The
optimization of the reaction conditions revealed that
simple stirring of a solution of the catalyst (1 equiv.),
tetra-n-butylammonium bromide (10 equiv.), benzyl
alcohol (10 equiv.) and Oxone® (10 equiv., which con-
tains 20 equiv. of the oxidizing component of Oxone®,
i.e. potassium peroxymonosulfate, KHSO5) in a bipha-
sic medium (CH2Cl2/H2O) effected the formation of
benzaldehyde in quantitative yield within 2 min at 0°C
to room temperature. However, in the absence of the
Mn-complex catalyst, benzaldehyde was only formed in
15% yield. Over-oxidation of aldehydes to their corre-
sponding carboxylic acids which has been observed in
the oxidation of aldehydes with Oxone®6 did not occur
in our system.
We showed that this oxidation method could be applied
to a wide range of benzylic, allylic, alicyclic, primary
and secondary alcohols (Table 2). Oxone® is a poor
oxidant for all types of alcohols in the absence of
Mn(phox)3 over a period of 5 min. However various
alcohols were converted to the corresponding aldehydes
or ketones in quantitative yield in the presence of the
catalyst (Table 2). While alicyclic alcohols were oxi-
dised in upwards of 80% yields (entries 3–5), the acyclic
aliphatic alcohols, 1-octanol and 2-octanol, were less
efficiently oxidised (entries 1 and 2). Although, intro-
ducing a nitro group to the phenyl ring of benzyl
alcohols often reduces the reactivity of the alcohol in
oxidation processes, with the Mn(phox)3/Oxone®/n-
Bu4NBr oxidation system, both nitro benzyl alcohols
were oxidised in good yields (entries 11 and 12).
Table 1. The effect of the nature of solvent on the oxida-
tion of benzyl alcohol by Mn(phox)3/Oxone®/n-Bu4NBr
catalytic system
The marked reduction of the benzaldehyde yield (41%)
when the benzyl alcohol oxidation reaction is carried
out in the presence of 2,6-di-tert-butyl-p-cresol as an
inhibitor, suggests that a radical intermediate is formed
during the oxidation reaction. A radical intermediate
could be formed via a one-electron transfer process
between the Mn-complex and substrate as Oakes et al.
have reported in Calmagite dye oxidation catalysed by
manganese(II) ions.13
Solvent
Benzaldehyde (%)
CH2Cl2
CH3Cl
100
90
C6H6
80
CH3COOC2H5
CH3CN
78
71

M. Bagherzadeh / Tetrahedron Letters 44 (2003) 8943–8945
8945
In conclusion, the results obtained in this research
show that tris[(2-oxazolinyl)phenolato]manganese(III),
Mn(phox)3, is an excellent catalyst for the simple, selec-
tive and very fast oxidation of alcohols to the corre-
sponding carbonyl compounds with Oxone® under mild
conditions in CH2Cl2/H2O.
1287–1290; (c) Evans, T. L.; Grade, M. M. Synth. Com-
mun. 1986, 16, 1207–1216; (d) Trost, B. M.; Braslau, R. J.
Org. Chem. 1988, 53, 532–537; (e) De Poorter, B.; Ricci,
M.; Meunier, B. Tetrahedron Lett. 1985, 26, 4459–4462;
(f) De Poorter, B.; Meunier, B. J. Chem. Soc., Perkin
Trans. 2 1985, 1735–1740.
5. (a) Koo, B. S.; Lee, K. L.; Lee, K. J. Synth. Commun.
2002, 32, 2115–2123; (b) Kennedy, R. J.; Stock, A. M. J.
Org. Chem. 1960, 25, 1901–1906.
Acknowledgements
6. (a) Webb, K. S.; Ruszkay, S. J. Tetrahedron 1998, 54,
401–410; (b) Baumstark, A. L.; Beeson, M.; Vasquez, P.
C. Tetrahedron Lett. 1989, 30, 5567–5570.
I gratefully acknowledge financial support from the
Research Council of Sharif University of Technology.
7. Bolm, C.; Magnus, A. S.; Hilderbrand, J. P. Org. Lett.
2000, 2, 1173–1175.
8. Zolfigol, M. A.; Bagherzadeh, M.; Madrakian, E.;
Ghaemi, E.; Taqian-Nasab, A. J. Chem. Res. (S) 2001,
140–142.
9. Zolfigol, M. A.; Bagherzadeh, M.; Ghorbani Choghama-
rani, A.; Keypour, H.; Salehzadeh, S. Synth. Commun.
2001, 31, 1161–1166.
10. Zolfigol, M. A.; Bagherzadeh, M.; Chehardoli, G.;
Malakpour, S. E. Synth. Commun. 2001, 31, 1149–
1154.
11. Hoogenraad, M.; Ramkisoensing, K.; Kooijman, H.;
Spek, A. L.; Bouwman, E.; Haasnoot, J. G.; Reedijk, J.
Inorg. Chim. Acta 1998, 279, 217–220.
12. (a) Meunier, B. Chem. Rev. 1992, 92, 1411–1456; (b)
Davoras, E. M.; Coutsolelos, A. G. J. Inorg. Biochem.
2003, 94, 161–170; (c) Mohajer, D.; Bagherzadeh, M. J.
Chem. Res. (S) 1998, 556–557.
References
1. (a) Hudlicky, M. Oxidation in Organic Chemistry; Ameri-
can Chemical Society: Washington, DC, 1990; pp. 114–
163; (b) Mirafzal, G. A.; Lozera, M. Tetrahedron Lett.
1998, 39, 7263–7266; (c) Corey, E. J.; Kim, C. U. J. Am.
Chem. Soc. 1972, 94, 7586–7587; (d) Lou, J. D.; Lou, W.
X. Synth. Commun. 1997, 27, 3697–3699.
2. Comprehensive Organic Synthesis; Trost, B. M.; Fleming,
I. Eds.; Pergamon Press: UK, 1991; Vol. 7 (Oxidation).
3. (a) Zondervan, C.; Hage, R.; Feringa, B. L. Chem. Com-
mun. 1997, 419–420; (b) Coleman, K. S.; Lorber, C. Y.;
Osborn, J. A. Eur. J. Inorg. Chem. 1998, 1673–1675; (c)
Moody, C. J.; Palmer, F. N. Tetrahedron Lett. 2002, 43,
139–141; (d) Dijksman, A.; Marino-Gonzales, A.;
Payeras, A. M. I.; Arends, I. W. C. E.; Sheldon, R. A. J.
Am. Chem. Soc. 2001, 123, 6826–6833.
13. Oakes, J.; Gratton, P.; Weil, I. J. Chem. Soc., Dalton
Trans. 1997, 3805–3809.
4. (a) Brik, M. E. Tetrahedron Lett. 1995, 36, 5519–5522; (b)
Trost, B. M.; Curran, D. P. Tetrahedron Lett. 1981, 22,