Solvent-free oxidation of alcohols with potassium persulphate in the presence of bronsted acidic ionic liquids

Article abstract of DOI:10.1080/00397910802374117

An efficient conversion of alcohols to aldehydes was achieved using potassium persulphate and 3-methylimidazolinium methane sulfonate. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910802374117

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Solvent-Free Oxidation of
Alcohols with Potassium
Persulphate in the Presence of
Brönsted Acidic Ionic Liquids
a
b
a
A. C. Chaskar , S. R. Bhandari , A. B. Patil , O.
a
c
P. Sharma & S. Mayeker
a
C. K. Thakur Research Center, Mumbai, India
Amoly Organic Pvt. Limited, Mumbai, India
Institute of Science, Mumbai, India
b
c
Published online: 22 Dec 2008.
To cite this article: A. C. Chaskar , S. R. Bhandari , A. B. Patil , O. P. Sharma & S.
Mayeker (2008): Solvent-Free Oxidation of Alcohols with Potassium Persulphate in the
Presence of Brönsted Acidic Ionic Liquids, Synthetic Communications: An International
Journal for Rapid Communication of Synthetic Organic Chemistry, 39:2, 366-370
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Synthetic Communications , 39: 366–370, 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910802374117
Solvent-Free Oxidation of Alcohols with
Potassium Persulphate in the Presence of
Br o¨ nsted Acidic Ionic Liquids
1
A. C. Chaskar, S. R. Bhandari, A. B. Patil, O. P. Sharma,
2
1
1
3
and S. Mayeker
C. K. Thakur Research Center, Mumbai, India
1
2
Amoly Organic Pvt. Limited, Mumbai, India
3
Institute of Science, Mumbai, India
Abstract: An efficient conversion of alcohols to aldehydes was achieved using
potassium persulphate and 3-methylimidazolinium methane sulfonate.
Keywords: Alcohols, aldehydes, Br o¨ nsted acidic ionic liquid, oxidation,
potassium persulphate
INTRODUCTION
Transformation of alcohols to aldehydes is one of the most fundamental
reactions for which various methods have been developed. The oxidants
[1]
used for this purpose include chromium(VI) reagents, transition-metal
[2]
[3]
nitrates on solid supports, hypervalent iodine compounds, dimethyl
[4]
[5]
[6]
sulfoxides=HBr, ionic liquid, and microwave irradiation. Nitric acid
attracted much attention for the conversion of alcohols to the carbonyl com-
pounds mainly because of its ready availability of strong oxidizing power.
[7]
The reaction system of aqueous 20% nitric acid=nitromethane, nitric acid=
[8]
dichloromethane, and nitric acid=ytterbium(III) triflate=1,2-dichloro-
[9]
ethane system has been successfully utilized for the oxidation of alcohols.
Ionic liquid is used as an alternative to traditional solvents for
organic reactions particularly in the area of green chemistry. Br o¨ nsted
Received April 22, 2008.
Address correspondence to A. C. Chaskar, C. K. Thakur Research Center,
Navi Mumbai 410 206, India. E-mail: achaskar@rediffmail.com
366

Solvent-Free Oxidation of Alcohols
367
Scheme 1. Synthesis of aldehyde.
acidic ionic liquids have been successfully applied to a variety of reactions
[10]
including the esterification of carboxylic acids, protection of aldehydes
[
11]
[12]
and ketones,
Br o¨ nsted acidic ionic liquid 3-methylimidazolinium methane sulfonate
[Hmim] CH SO ) and used it as both catalyst and reaction medium in
and cleavage of ethers.
Here we have synthesized
(
3
3
the oxidation of alcohols with potassium persulfate (Scheme 1).
RESULTS AND DISCUSSION
A broad range of benzylic and aliphatic alcohols have been used. Electron-
donating substituents on the benzene ring accelerate the reaction rate
whereas electron-withdrawing groups reduce the reaction rate and also
require higher temperature. Oxidation of alcohols using potassium persul-
phate without 3-methylimidazolinium methane sulfonate was unsuccessful.
In this reaction, [Hmim] CH SO plays a dual role of acidic catalyst as well
3
3
as solvent. Use of such a reaction medium should be appreciated because of
its easy preparation, convenient separation, and ecofriendly nature. The
ionic liquid can be reused after washing with diethyl ether to remove the
unreacted starting materials and products. Physical and spectral data of
[
5]
known compounds are in agreement with those reported in the literature.
The results of oxidation of variety of alcohols are summarized in Table 1.
CONCLUSION
In conclusion, it is an efficient, simple, and fast method for the oxidation
of alcohols to the corresponding aldehydes. Relatively short reaction
times, utilization of cheap and recyclable reagent, and high yield of
products are some of the advantages of the present protocol.
EXPERIMENTAL
Melting points were taken in open capillaries. The IR spectra were rec-
1
orded on a Perkin-Elmer 257 spectrometer using KBr discs. H NMR

3
68

Solvent-Free Oxidation of Alcohols
369
1
and C NMR spectra in DMSO-d were recorded on a VXR 300-MHz
3
6
instrument using TMS as internal standard. The homogeneity of
the compounds was described by thin-layer chromatography (TLC) on
silica-gel plates. The spots are developed in an iodine chamber.
+
Preparation of [Hmim] CH3SO3
ꢁ
1
-Methylimidazole (0.01 mol) was placed in a round-bottom flask and
ꢀ
cooled to 0 C. Methane sulfonic acid (0.01 mol) was added slowly with
stirring. The mixture was stirred for 5 min at room temperature to get
3
-methylimidazolinium methane sulfonate.
Typical Procedure
Alcohol (0.01 mol), potassium persulfate (0.01 mol), and 3-methylimida-
zolinium methane sulfonate (0.01 mol) were stirred for the time and
temperature shown in Table 1. The reaction was monitored by TLC using
ethyl acetate–petroleum ether (1:1) solvent system. The reaction mixture
was cooled to room temperature and extracted with diethyl ether, dried
over sodium sulfate, and evaporated under reduced pressure.
5
-Amino-2-chloro Benzaldehyde (1)
ꢁ
1
1
. H NMR
IR (KBr): 3300–3500, 2730, 1724, 1590, 1500, 960 cm
DMSO-d (d ppm): 10.54 (s, 1H, CHO), 7.65 (d, 1H, J ¼ 7.2 Hz), 7.20
6
1
3
(
s, 1H), 6.80 (d, 1H, J ¼ 7.2 Hz), 4.80 ( s, 2H, NH ). C NMR
2
DMSO-d (d ppm): 190.85, 148.10, 139, 129.80, 125.10, 124.20, 116.10.
6
Elem. anal. calcd. C, 55.04; H, 3.89; N, 9.00; O, 10.28; Cl, 22.79. Found:
C, 55.10; H, 3.92; N, 8.92; O, 10.25; Cl, 22.83.
3
-Methyl Butanal (28)
1
IR (KBr): 2720, 1725, 1423, 1410. H NMR DMSO-d (d ppm): 9.81
(
6
1
s, 1H, CHO), 2.64 (d, 2H), 1.87 (m, 1H), 1.21 (d, 6H). C NMR
3
DMSO-d (d ppm): 202.00, 54.00, 29.60, 24.80.
6
ACKNOWLEDGMENT
The authors are grateful to Amoly Organic (India) Ltd., Mumbai, for
providing gift samples and the University Grant Commission for

3
70
A. C. Chaskar et al.
financial support. The authors are thankful to Dr. S. T. Gadade, principal,
C. K. Thakur College, Navi Mumbai, for providing the laboratory and
other facilities.
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