Cation exchange resin supported oxidation of alkylbenzenes and olefins using potassium permanganate

Article abstract of DOI:10.3184/030823400103165617

Rapid and efficient oxidation of alkylbenzene side chains at the benzylic positions as well as oxidative cleavage of olefins with potassium permanganate in presence of solid polymeric cation exchange resins in good yields is reported.

Full text of DOI:10.3184/030823400103165617

38 J. CHEM. RESEARCH (S), 2000
J. Chem. Research (S),
2000, 38–39
SHORT PAPER
Cation exchange resin supported oxidation of
alkylbenzenes and olefins using potassium permanganate†
Padmaker L. Joshi* and Braja G. Hazra
Division of Organic Chemistry (Synthesis), National Chemical Laboratory, Pune 411008, India
Rapid and efficient oxidation of alkylbenzene side chains at the benzylic positions as well as oxidative cleavage of olefins
with potassium permanganate in presence of solid polymeric cation exchange resins in good yields is reported.
Potassium permanganate (KMnO4) is an oxidising agent used
in organic chemistry, is one of the most versatile and vigorous
of the commonly used oxidants, and has been extensively
employed in acid, alkaline and neutral medium. The oxidation
products can be glycols, hydroxy ketones, diketones, epoxides
or cleavage products dependent on the reaction conditions.
Unfortunately, the conditions under which these reactions take
place are not sharply defined and mixture of products are often
obtained.1 To induce some sort of selectivity and control, sev-
eral modified means of carrying out permanganate oxidations
have been reported which involve solubalisation of perman-
ganate in organic solvents with the help of phase transfer cata-
lysts,2 crown ether,3 or preparing quarternary ammonium salts.4
One recent development that has significantly expanded the
scope of this reagent is its use in presence of inorganic supports.
The effectiveness of a particular support material for a given
reagent and reaction is likely to be the result of combition of
factors including surface area, porosity, acidity, basisity as well
as the crystalline or amorphous nature of the material. The poly-
meric support provides a particular reaction environment capa-
ble of enhancing the reactivity of many reagents and moreover,
turns out to be very profitable in the working up, which
becomes reduced to a mere filtration. One major and only
recently appreciated advantage of supported reagents is their
potential as environmentally friendly alternatives to corrosive,
wasteful and difficult to dispose of conventional reagents.5
Regan and Koteel6 have reported that various types of mole-
cular sieves, silica and K-catalysts can easily be impregnated
with KMnO4 and the resulting reagents are useful for alcohol
oxidations. Hydrated copper sulfate supported KMnO4 oxi-
dises secondary alcohols to ketones,7 however alkenes are con-
verted into ␣-diketones or ␣-hydroxy ketones when treated
with KMnO4 and copper sulfate pentahydrate in presence of
t-butyl alcohol.8 KMnO4 impregnated on silica gel is reagent of
choice for the cleavage of ethylenic double bond to get acids,9
while alkenes when treated with KMnO4 in presence of moist
alumina ends up into corresponding aldehydes or ketones.10
Moreover, simple addition of certain supports to a reaction
mixture can have a dramatic effect on reaction rate as the in situ
mixing of support (silica gel) and reagent (NaBH4) in the
reduction of nitrostyrene.11 Oxidation of alkylbenzene side
chains at the benzylic positions using KMnO4 supported on
alumina and copper sulfate has been reported12 to produce
corresponding alcohols and ketones. However in these oxida-
tions the reaction times are quite long (few days).
exchange resin and KMnO4, we were successful in carrying
out the oxidations just by mixing the resins with KMnO4 in a
suitable solvent system.
Here we present out results on the oxidation of olefins under
very mild conditions with KMnO4, in presence of cation
exchange resins (H+ form) to afford the corresponding aldehy-
des or ketones in high yields and not the acids which are usual
products in aqueous medium1 or when the support material is
silica gel.9 Also we report the oxidations of alkylbenzene side
chains under similar reaction conditions in which the products
are alcohols if the benzylic carbon is tertiary and ketones if it is
secondary, in excellent yields. The alkyl sidechain oxidations are
significantly more selective under our reaction conditions than
permanganate alone, where carbon-carbon bond cleavage
occurs. The reaction times are also short (0.5 to 8 h). Another
observation is that the oxidations carried out using potassium
permanganate in presence of p-toluene sylfonic acid instead of
cation exchange resin, are found to proceed much slowly. This
indicates that the role of cation exchange resin is not just to pro-
vide protons. The reactions are performed using batch technique
by stirring an excess of cation exchange resin (H+ form), the
olefin or alkylbenzene and finely powdered KMnO4 in a mixed
solvent system t-butyl alcohol and dichloromethane at room
temperature. Products are isolated by removal of the spent
reagent system by filtration, drying over anhydrous Na2SO4,
evaporation of the solvent and purification by column chro-
matography. The products are identified either by comparison
with authentic samples or by NMR and IR spectroscopy. The use
of cation exchange resins in the oxidation of olefins and alkyl-
benzenes with KMnO4 has not been reported so far.
Oxidation of cinnamic acid was studied in detail by chang-
ing solvents, resins and stoitiometric quantities of KMnO4.
Solvents like chlorinated hydrocarbons, actone and
diethylether are found to be equally effective, the reaction in
benzene is sluggish while no reaction takes place when
hexane is used as a solvent. Moreover, systematic examination
of eight different support systems (Table 1) has established
that Tulsion T-40 is by far the most suitable for the oxidation
of olefins and superior to others in handling and general
experimental simplicity. Similarly Tulsion T-42 is the resin of
choice of the oxidation of diphenyl methane, so it has been
used for all the oxidations of alkylbenzenes.
Experimental
All melting points are uncorrected. IR spectra are recorded on a
Perkin-Elmer Infrared 599-B spectrophotometer model using NAC1
optics. 1H NMR are run in CDCl3 solution on a Bruker AC-200 NMR
spectrophotometer operating at 200Hz using tetramethylsilane as an
internal standard. Mass spectra are recorded on Finnigan Mat 1020C
Mass spectrophotometer at 70eV. TLC is performed using precoated
aluminium sheets with silica gel 60F254, Merck, Germany. For col-
umn chromatography ACME silica gel 100–200 mesh size is used.
Methylene chloride is freshly distilled over clacium hydride. Cation
exchange resins are procured from Thermax (India). Ltd. Pune. All
oxidation products are known compounds and the identity is con-
firmed by comparison of their physical and spectral data.
In continuation of our studies regarding the applications of
cation exchange resins,13 we have found that commercial
cation exchange resins without any modification are found to
be very useful in oxidations with KMnO4. Despite the failure
in preparation of an impregnated reagent using cation
* To receive any correspondence: e-mail:hazra@ems.ncl.res.in
† This is a Short Paper, there is therefore no corresponding material in
J Chem. Research (M).

J. CHEM. RESEARCH (S), 2000 39
Tulsion T-42, KMnO4
Table 1 Oxidation of cinnamic acid by permanganate- cation
exchange resins
Alkylbenzenes
→ Alcohol or ketone
Entry Resina
Time (min)
Remarksb
t-BuOH, CH2Cl2, R.T.
1
2
3
4
5
6
7
8
Tulsion T-40c
Amberlyst-15
Amberlyte IR-100
IR-120
Tulsion T-42
Indion-130
Zeocarb-225
CXO-18c
30
20
30
35
15
35
45
90
Wet (52% moisture)
Dry
Scheme 2
Dry
Dry
Dry
Table 3 Oxidation of alkylbenzenes
Dry
Substrate
Product
KMnO4 Time Yielda
(eq.)
Dry
(h) (%)
Wet (52% moisture)
aEntries 1–7 are strongly acidic cation exchange resins
(H+ forms) having matrix structure with styrene divinylbenzene
copolymer having sulfonicacid groups. Entry No. 8 is in a
weakly acidic cation exchange resin (H+ form) having matrix
structure with styrene divinylbenzene copoluymer having car-
boxylic acid functional groups. bWhile conducting the reactions
with dry resins, equal quantity of water is added to the reaction
mixture. cSince the distribution of water is uniform throughout
the polymer matrix, the reactions carried out using this resin are
smooth, associated with batch to batch consistency and the
work-up is more convenient, hence in general Tulsion T-40 resin
is preferrred even though the time required for complete
conversion is a little more as compared to some of the dry
resins.
Diphenylmethane Benzophenone
3
3
3
3
3
92
86
90
88
Ethylbenzene
Tetralin
Acetophenone
a-Tetralone
Isopropylphenyl
ketone
4.5
4
Isobutylbenzene
5
Cumene
2-Phenyl-
3
4
82
2-propanol
Phenethylalcohol Acetophenone
Benzoin
Stilbene-1,2-diol
3
6
6
6
0.5
7
8
No
94
Benzil
Benzil
76b
75b
Phenylacetic-acid Benzoyl-
formicacid
reactionc
Menthol
methone
6
No
reaction
aIsolated yields, product identity is confimed by comparison
with 1 H-NMR and IR spectra of authentic compounds.b About
10–15% of benzoin is recovered in the column chromato-
praphic purification. cOnly 60% of the starting material is
recovered back.
Table 2 Oxidative cleavage of olefins
Entry Reactant
Reaction Product (%yield)a
time (h)
1
2
3
4
5
Cinnamic acid
Cyclooctene
␤-Pinene
trans-Stilbene
␣-Methyl styrene
0.5
4
3.5
3
4
Benzaldehyde (86%)
1,8-Octanediol (73%)b
Nopinone (65%)
Benzaldehyde (82%)
Acetophenone (81%)
with the use of only three mole equivalents of KMnO4, under
simple reaction conditions and in very short time. The oxida-
tion products can be isolated very easily in relatively pure
form. The oxidiation of olefins and alkylbenzenes with
KMnO4 in presence of cation exchange resins has been
reported for the first time. The fact that the manganese ions in
these reactions remain firmly bound to the resin after the reac-
tion, may be valuable in preventing environmental pollution.
These results suggest that activiation of KMnO4 in presence of
cation exchange resins may provide an attractive synthetic
alternative to related techniques such as phase transfer, use of
quarternary ammonium salts or inorganic supports. In view of
its optional simplicity, efficiency, the method described above
will hopefully prove to be of wide synthetic use.
aIsolated yields, product identity is confirmed by comparison
with 1H-NMR and IR spectra of authentic compounds. bThe
yield is based on the quantity of 1,8-Octanediol obtained by
subsequent reduction of the dialdehyde intermediate with
sodium borohydride.
Typical procedure for oxidative cleavage of olefins: KMnO4 (2.37g,
15 mmol) is added to a suspension of Tulsion T-40 resin (4g), t-butyl
alcohol (4ml), trans-stilbene (900mg, 5mmol) in dichloromethane
(25ml) in lots during 5 min. The reaction mixture was stirred at room
temperatuire for 3h, filtered and dried over anhydrous Na2SO4. After
removing the solvent, the product obtained shows single spot on TLC
and found to have identical spectral properties with benzaldehyde
(870mg, 82%).
We are grateful to Dr K. N. Ganesh for encouragement. We
are thankful to Thermax(India) Ltd. for the supply of cation
exchange resins, and DST, New Delhi, for financial support
Typical procedure for oxidation of alkylbenzenes: KMnO4 (0.948g.,
6mmol) is added to a suspension of Tulsion T-42 resin (2g), t-butyl alco-
hol (4ml), water (1ml), tetralin (264mg, 2mmol) in dichloromethane
(20ml) in lots during 10 min time. The reaction mixture was stirred at
room temperature for 4 h, filtered and dried over anhydrous Na2SO4.
After removing the solvent, the product obtained is purified by column
chromatography to get ␣-tetralone (263mg, 90%).
Received 19 July 1999; accepted 21 October 1999
Paper 9/05785D
References
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of the reaction is extended to few days.
In conclusion the cleavage of olefins and selective oxidation
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Tulsion T-40, KMnO4
Olefins
→ Aldehydes or ketones
t-BuOH, CH2Cl2, RT
Scheme 1