Poly [N-(4-pyridinium dichromate)-P-styrene sulphonamide] as an efficient reagent for oxidation of alcohols

Article abstract of DOI:10.1080/10426500490262603

Poly [N-(4-pyridinium dichromate)-p-styrene sulphonamide] is readily prepared. It is a stable, mild, and efficient oxidizing reagent that can be used for oxidation of different alcohols to their corresponding carbonyl compounds in approtic solvents. This polymer can be synthesized from the reaction between poly [N-(4-pyridyl)-p-styrene sulphonamide] and CrO₃ in a minimum amount of water. The latter polymer was prepared by free radical polymerization of [N-(4-pyridyl)-p-styrene sulphonamide] by using azobis(isobutyronitrile) (AIBN) as an initiator. N-(4-pyridyl)-p-styrene sulphonamide was synthesized from commercial 4-vinyl benzene sulphonic acid sodium salt and 4-amino pyridine. Poly[N-(4-pyridinium dichromate)-p-styrene sulphonamide] can oxidize both aliphatic and aromatic alcohols in good yields at a temperature of 38°C and in CH₂Cl₂ as solvent. One advantage in using this reagent is the mild condition of the reaction system. The synthesized compounds including polymeric reagent and carbonyl compounds were identified by HNMR and IR spectroscopy.

Full text of DOI:10.1080/10426500490262603

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Phosphorus, Sulfur, and Silicon and the Related
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POLY [N-(4-PYRIDINIUM DICHROMATE)-P-STYRENE
SULPHONAMIDE] AS AN EFFICIENT REAGENT FOR
OXIDATION OF ALCOHOLS
Ardeshir Khazaei a , Ebrahim Mehdipour b & Soleiman Yadegari a
a Bu Ali Sina University, Hamadan, Iran
b University of Lorestan, Khorram Abbad, Iran
Published online: 12 Aug 2010.
To cite this article: Ardeshir Khazaei , Ebrahim Mehdipour & Soleiman Yadegari (2004): POLY [N-(4-PYRIDINIUM DICHROMATE)-
P-STYRENE SULPHONAMIDE] AS AN EFFICIENT REAGENT FOR OXIDATION OF ALCOHOLS, Phosphorus, Sulfur, and Silicon and the
Related Elements, 179:3, 437-441
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Phosphorus, Sulfur, and Silicon, 179:437–441, 2004
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Copyright Taylor & Francis Inc.
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500490262603
POLY [N-(4-PYRIDINIUM DICHROMATE)-P-STYRENE
SULPHONAMIDE] AS AN EFFICIENT REAGENT
FOR OXIDATION OF ALCOHOLS
Ardeshir Khazaei,a Ebrahim Mehdipour,b
and Soleiman Yadegaria
Bu Ali Sina University, Hamadan, Irana and University
of Lorestan, Khorram Abbad, Iranb
(Received August 5, 2003; in final form September 9, 2003)
Poly [ N-(4-pyridinium dichromate)-p-styrene sulphonamide] is read-
ily prepared. It is a stable, mild, and efficient oxidizing reagent that
can be used for oxidation of different alcohols to their correspond-
ing carbonyl compounds in approtic solvents. This polymer can be
synthesized from the reaction between poly [ N-(4-pyridyl)-p-styrene
sulphonamide] and CrO3 in a minimum amount of water. The latter
polymer was prepared by free radical polymerization of [ N-(4-pyridyl)-
p-styrene sulphonamide] by using azobis(isobutyronitrile) (AIBN) as an
initiator. N-(4-pyridyl)-p-styrene sulphonamide was synthesized from
commercial 4-vinyl benzene sulphonic acid sodium salt and 4-amino
pyridine. Poly [ N-(4-pyridinium dichromate)-p-styrene sulphonamide]
can oxidize both aliphatic and aromatic alcohols in good yields at a
temperature of 38◦C and in CH2Cl2 as solvent. One advantage in using
this reagent is the mild condition of the reaction system. The synthe-
sized compounds including polymeric reagent and carbonyl compounds
were identified by HNMR and IR spectroscopy.
Keywords: Alcohols; oxidation; polymer support; reagent; synthesis
An increasing number of polymeric reagents have been developed for
synthetic use. Polymeric reagents are greatly used in single step reac-
tions. Their main advantages over monomeric reagents is their insolu-
bility in the reaction medium and consequently the easier separation of
products from the reaction mixtures, in most cases by simple filtration.
The reaction often can be driven to completion by using excess of
these reagents without fear of separating the unspent reagents or the
polymeric by-products from the desired reaction products. In addition,
Address correspondence to Ardeshir Khazaei, Department of Chemistry, Faculty
of Sciences, Bu-Ali Sina University, Hamadan, Iran.
437

438
A. Khazaei et al.
the spent polymeric reagents can usually be recovered quantitativilly
at the end of the reactions and in ideal cases they can be regenerated
to their initial activities.
A variety of polymer-supported oxidizing reagents with different
functionalities have been reported in literature.1−12
Among these, polymer-bound metallic oxidants and specially
polymer-supported chromium (VI) reagents have received considerable
attention.
In connection with studies on the preparation and application of recy-
clable polymeric reagents for use in simple one-step processes, we have
described the polymeric reagent poly [N-(4-pyridinium dichromate)-p-
styrene sulphonamide] which is an efficient reagent in the oxidation of
alcohols to the corresponding aldehydes and ketones.
RESULTS AND DISCUTION
This nonacidic polymeric reagent can be prepared easily by treatment
of poly [N-(4-pyridyl)-p-styrene sulphonamide] with a slight excess of
CrO3 in water at room temperature (Scheme 1). After being washed
with water to remove any unbound chromium (VI), the reagent can be
used directly without drying in oxidation reaction or dried in vacuum
to a yellow-brown powder, which is quite stable to prolonged storage.
The IR spectrum of the polymer showed peaks at 765 and 930 cm−1
,
which confirmed that it was a dichromate.13
SCHEME 1
It should be noted that the reagent could be prepared and handled
safely in molar amount, a definite advantage over more classical CrO3
based reagents.

Oxidation of Alcohols
439
TABLE I Oxidation of Alcohols with Poly [N-(4-Pyridinium
dichromate)-p-styrene Sulphonamide]
Alcohol
Product
Molar ratio
Reaction times (h)
Yield (%)
Benzyl alcohol
1-Butanol
2-Butanol
1-Pentanol
1-Hexanol
1-Heptanol
1-Octanol
Benzaldehyde
Butanal
2-Butanone
Pentanal
Hexanal
Hepanal
Octanal
Cyclopentanone
Cyclohexanone
1.1:1
1.1:1
1.1:1
1.1:1
1.1:1
1.1:1
1.1:1
1.1:1
1.1:1
2
6
10
9
10
10
10
8
95
80
80
90
90
85
85
90
90
Cyclopentanol
Cyclohexanol
8
aProducts were characterized by their physical constants, comparison with authentic
samples, and by spectroscopic methods.
The best results were obtained by using the wet reagent in the oxida-
tion reaction (Table I). The reaction of alcohols with polymeric reagent
afforded carbonyl compounds without the formation of side products
(Scheme 2). As expected, in the absence of water the dry reagent is
ineffective. Isolation of the aldehydes after reaction was greatly facili-
tated by the fact that no chromium ions were leached from the polymer.
The results obtained in the oxidation of a number of different alcohols
are reported in Table I. As expected the rate of reaction increased when
the molar ratio of Cr(VI) to alcohol was increased, and very fast reac-
tions could be obtained by using four-fold excess of reagent. However,
the reagent was still quite effective in almost equimolar amount. As ex-
pected, the initial rate of the reaction with the polymer is usually quite
high but the reaction slows down as the reactive sites are consumed. It
should be noted that, although the reaction times are sometimes quite
long, no products of overoxidation were detected with any of the alcohols
tested.
SCHEME 2
Recycling of the reagent can be accomplished by using a simple
washing-reactivation procedure in which the spent reagent is washed
to remove the spent chromium salts. After regeneration of the polymer
addition of CrO3 and water reactivates the polymer.

440
A. Khazaei et al.
EXPERIMENTAL
Apparatus
IR and H NMR spectra were recorded using a Shimadzu 435-U04 spec-
trophotometer, (KBr pellets) and a 90 MHz Jeol FT-NMR spectrometer,
respectively.
General Reagents
Commercial 4-vinylbenzenesulphonic acid sodium salt was obtained
from Fluka AG. All other chemicals were obtained from Merck.
Procedure for the Preparation of Poly
[ N-(4-pyridyl)-p-styrene sulphonamide]
To a solution of 0.02 mmol of [N- (4-pyridyl)-p-styrene sulphonamide]
in 100 ml of DMSO was added 1.5 mmol of AIBN and then heated at
100◦C for 27 h under a N2 atmosphere. Then addition of water precipi-
tated the polymer. The yield of product was 80%.
Procedure for the Preparation of Poly [ N-(4-pyridinium
dichromate)-p-styrene sulphonamide]
To a suspension of 0.05 mmol of poly [N-(4-pyridyl)-p-styrene
sulphonamide] in 100 ml of water was added 0.06 mmol of CrO3. For-
mation of the reagent occurred very smoothly and no heat was evolved
when the mixture was stirred for several hours. After filtration, the
reagent was washed repeatedly with water until the filtrate was color-
less. In general the reagent was used without drying.
Procedure for the Oxidation of Alcohols
The standard procedure involved the reaction of 2.2 mmol of poly-
meric reagent with 2 mmol of alcohols in 10 ml of CH2Cl2 at 38◦C.
The progress of some reactions was monitored by TLC. After comple-
tion of the reaction the products could be obtained after filtration of the
polymer in the filtrate.
The main advantage associated with the use of a polymeric reagent is
the ease of purification of the final product since both the initial polymer,
which may be used in excess to help drive the reaction to completion and
its by-product are insoluble and can be separated by simple filtration.
CONCLUSION
The procedure reported here is a convenient and high-yielding method
for the oxidation of alcohols to their corresponding carbonyl compounds.

Oxidation of Alcohols
441
Furthermore, another important advantage of this work is that the
polymeric reagent can be stored for months without losing its activity. It
is not hygroscopic or light sensitive. The insoluble polymer was removed
by filtration after reaction.
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