Polyvinylpyrrolidone-supported hydroperoxide for selective oxidation of aldehydes to carboxylic acids and sulfides to sulfoxides

Article abstract of DOI:10.1080/10426501003671437

The facile immobilization of hydroperoxide on the cross-linked poly(vinylpyrrolidone) is described by treatment of a poly(vinylpyrrolidone)- Vilsmeier adduct with (35%) hydrogen peroxide. The in situ-generated poly(vinyl pyrrolidone)-supported hydroperoxide reagent showed very good performance in chemoselective oxidation of aldehydes to carboxylic acids as well as sulfides to sulfoxides. Supplemental materials are available for this article. Go to the publishers online edition of Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental file. Taylor & Francis Group, LLC.

Full text of DOI:10.1080/10426501003671437

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Polyvinylpyrrolidone-Supported
Hydroperoxide for Selective Oxidation
of Aldehydes to Carboxylic Acids and
Sulfides to Sulfoxides
a
a
Moslem Mansour Lakouraj , Bahareh Aghajani & Masoud Mokhtary
a
a
Department of Organic-Polymer Chemistry, Faculty of Chemistry ,
Mazandaran University , Babolsar, Iran
Published online: 19 Nov 2010.
To cite this article: Moslem Mansour Lakouraj , Bahareh Aghajani & Masoud Mokhtary (2010)
Polyvinylpyrrolidone-Supported Hydroperoxide for Selective Oxidation of Aldehydes to Carboxylic
Acids and Sulfides to Sulfoxides, Phosphorus, Sulfur, and Silicon and the Related Elements, 185:12,
2393-2401, DOI: 10.1080/10426501003671437
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Phosphorus, Sulfur, and Silicon, 185:2393–2401, 2010
Copyright ꢀ
Taylor & Francis Group, LLC
C
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426501003671437
POLYVINYLPYRROLIDONE-SUPPORTED
HYDROPEROXIDE FOR SELECTIVE OXIDATION
OF ALDEHYDES TO CARBOXYLIC ACIDS AND SULFIDES
TO SULFOXIDES
Moslem Mansour Lakouraj, Bahareh Aghajani,
and Masoud Mokhtary
Department of Organic-Polymer Chemistry, Faculty of Chemistry, Mazandaran
University, Babolsar, Iran
The facile immobilization of hydroperoxide on the cross-linked poly(vinylpyrrolidone) is
described by treatment of a poly(vinylpyrrolidone)-Vilsmeier adduct with (35%) hydrogen
peroxide. The in situ–generated poly(vinyl pyrrolidone)-supported hydroperoxide reagent
showed very good performance in chemoselective oxidation of aldehydes to carboxylic acids
as well as sulfides to sulfoxides.
Supplemental materials are available for this article. Go to the publisher’s online edition of
Phosphorus, Sulfur, and Silicon and the Related Elements to view the free supplemental
file.
Keywords Carboxylic acid; hydrogen peroxide; poly(vinylpyrrolidone); sulfoxide; Vilsmeier
reagent
INTRODUCTION
The Vilsmeier reaction has been used for the synthesis of a variety of cyanines via
formylation of Fisher’s bases followed by Knoevenagel condensation reaction.1,2 Since
the first report appeared in 1927, the Vilsmeier–Haack reaction has been utilized for an
3
–7
immense variety of activated aromatic compounds to complex heterocycles. Recently,
t-butyldimethylsilylated alcohols were converted in one step to the corresponding formates
8
under Vilsmeier–Haack conditions. Traditionally, Vilsmeier reagents have been utilized
as a formylating agent, but in recent years their versatility has also been demonstrated
9
as an activating agent for halogenation of β-diketones and ring opening of substituted
2
,3-epoxy-1,3-diphenyl propan-1-one.10
The ability of the Vilsmeier reagent to give rise to products of substitution with
substrates bearing a labile hydrogen atom has provided some interesting applications for
the preparation of alkylhalide,11 esters, acid chloride, and nitriles.
12
13
14
Received 5 December 2009; accepted 1 February 2010.
We are grateful to Mazandaran University for financial assistance of this work.
Address correspondence to Moslem Mansour Lakouraj, Department of Organic-Polymer Chemistry, Faculty
of Chemistry, Mazandaran University, Babolsar 47416, Iran. E-mail: lakouraj@umz.ac.ir
2
393

2394
M. M. LAKOURAJ ET AL.
Treatment of a monomeric Vilsmeier reagent with hydrogen peroxide affords a
highly electrophilic hydroperoxy methylenedimethyl-ammonium salt, which could effi-
ciently produce 1,2-dichloro compounds of corresponding alkenes or act as a powerful
15
epoxidizing reagent, depending on the reaction conditions. A Vilsmeier reagent of N-
methylpyrrolidone (I) prepared by reaction of NMP with POCl3 affords an active oxygen
transfer reagent (II) by reaction with hydrogen peroxide, which epoxidizes the double bonds
of alkenes exclusively.16 However, this reagent is a highly reactive salt, and attempts to
isolate it were unsuccessful.
+
+
-
-
PO Cl
2
2
PO Cl
2 2
N
Cl
N
OOH
(
I)
(
II)
Polymer-supported catalysts and reagents have become popular in organic synthesis
17
over the past few decades. Their high catalytic activity, low toxicity, stability, recyclability,
and environmentally safe conditions make the use of polymer-supported reagents attractive
alternatives to conventional reagents. Hydrogen peroxide has been used for the oxidation
of aldehydes to their corresponding carboxylic acids under basic conditions, alone or
in combination with other reagents.1
8–21
Indeed, several methods have been reported for
22–27
the transformation of aldehydes to carboxylic acids.
However, these methods are all
deficient in some respect, such as strong acidic or basic conditions, use of heavy metal as a
catalyst, low yield, or high cost. Furthermore, most of them suffer from low selectivity. On
the other hand, there are several methods for the oxidation of alcohols to aldehydes using
polymer-supported reagents, whereas their further oxidation to corresponding acids has
not been well demonstrated. Although the wide variety of polymer-supported catalysts and
reagents have been well established for organic transformation, to the best of our knowledge
there is no literature report on the use of a H2O2 adduct of a polymer-supported Vilsmeier-
type reagent. Therefore, in continuation of our studies on the development of novel synthetic
28–30
methodologies using polymeric systems and of oxidative transformations,
in this article
we introduce the use of a polymeric Vilsmeier reagent (III) as an environmentally benign
promoter for the oxidation of aldehydes and sulfides using hydrogen peroxide (Scheme 1).
RESULTS AND DISCUSSION
The poly(vinylpyrrolidone)-supported Vilsmeier reagent (PVPP-POCl3) is obtained
as a white powder by treatment of a suspension of cross-linked polyvinylpyrrolidone(PVPP)
withPOCl3 indichloromethaneat roomtemperature. Incontrast tothemonomericVilsmeier
reagents, which are extremely hygroscopic, this reagent is nonhygroscopic powder. How-
ever, the use of linear poly(vinylpyrrolidone) was not satisfactory for the reaction with
POCl3 due to the formation of a sticky resin. Characterization of the chloropyrrolid-
inum dichlorophosphate groups on the cross-linked reagent was performed by record-
ing the Fourier transform infrared spectroscopy (FTIR) spectra (Supplemental Materials,

POLYVINYLPYRROLIDONE-SUPPORTED HYDROPEROXIDE
2395
Scheme 1
−
1
Figure S1, available online). The IR spectrum shows a broad absorption at 1250–1293 cm
−1
−1
for the P O bond and 750 cm for P Cl, 1027 and 532 cm due to the C Cl bond, and
−1
31
absorption at 1643 cm corresponds to the C N of iminium in the ring. Indeed, the
P
NMR spectrum of the linear polyvinylpyrrolidone-supported reagent clearly indicated the
characteristic δp of a dichlorophosphate anion3 by a signal at −13.6ppm in DMSO.
To show the role of the Vilsmeier adduct in these oxidation reactions, the oxidation
of p-methoxybenzaldehyde was carried out in the absence of the Vilsmeier reagent. The
oxidation was very slow, and the p-methoxybenzoic acid was obtained in very poor yield.
Also, the oxidation of sulfide, e.g., methylphenylsulfide, without using the Vilsmeier reagent
was not successful, and a low yield of corresponding sulfoxide was formed. As seen in
Table I, the optimized stoichiometric ratio of RCHO:H2O2 for the conversion of aldehydes
1
◦
to carboxylic acids was found to be 1:3, using 0.5 g of the reagent in acetonitrile at 45 C. In
the oxidation of methylphenylsulfides, a ratio of 1:2 of sulfide to hydrogen peroxide in the
presence of 0.25 g of the reagent produces the corresponding sulfoxide in excellent yield
in methanol at room temperature.
To select the best solvent, the oxidation of the p-methoxybenzaldehyde and
methylphenylsulfide were studied in a variety of organic solvents such as methanol,
acetonitrile, dioxane, and dichloromethane. Among them, acetonitrile and methanol were
found to be the best solvents for oxidation of aldehydes and sulfides, respectively (Table II).
The oxidation reaction of aldehydes was found to be slow at room temperature, and very
low yield of product was obtained, even at longer reaction times. A protic solvent such
as methanol is required to facilitate the oxygenation of sulfide to give the corresponding
sulfoxide in excellent yield.
To explore the oxidation ability of the in situ–generated, polymer-supported hy-
droperoxide reagent (IV), the oxidation of a variety of aromatic and aliphatic aldehydes

2396
M. M. LAKOURAJ ET AL.
Table I Effect of PVPP-POCl3 on oxidation of p-methoxybenzaldehyde and methylphenyl sulfidea
Entry
Substrate (1 mmol)
H2O2 (mmol)
PVPP-POCl3 (g)
Yield (%)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
p-MeO-C6H4CHOa
1
2
3
3
3
3
4
1
2
3
2
2
2
2
0.5
0.5
0.0
0.25
0.35
0.5
38
62
15
26
38
82
88
96
98
98
20
90
95
96
”
”
”
”
”
”
0.5
b
Ph-S-Me
0.25
0.25
0.25
0.0
0.13
0.2
”
”
”
”
”
”
1
1
1
1
1
0.25
a
◦
Reactions were performed three runs in acetonitrile at 45 C in 12 h.
b
Reactions were performed three runs in methanol at room temperature in 10 min.
was examined by treating the substrate with polyvinylpyrrolidone-supported Vilsmeier
◦
reagent in the presence of 35% hydrogen peroxide in acetonitrile at 45 C (Scheme 2).
Scheme 2
These results are presented in Table III. As is evident, all the aliphatic aldehydes
were selectively and easily converted to the corresponding acids in excellent yields. Aro-
matic aldehydes were converted to the corresponding acids in moderate to good yields at
longer periods. The presence of other functional groups such as hydroxyl and double bond
Table II Oxidation of methyl phenyl sulfide and p-methoxybenzaldehyde in different solvents
Entry
Substrate (1 mmol)
Solvent
Reaction time
Yield (%)
1
2
3
4
5
6
7
8
PhSMea
CH3OH
CH3CN
Dioxane
CH2Cl2
CH3OH
CH3CN
Dioxane
CH2Cl2
10 min
25 min
45 min
25 min
12 h
12 h
12 h
12 h
98
92
75
65
65
75
68
55
”
”
”
b
p-MeOC6H4-CHO
”
”
”
a
Reactions were carried out using 0.25 g of the polymeric reagent and 2 mmol of H2O2.
Reactions were carried out using 0.5 g of the polymeric reagent and 3 mmol of H2O2.
b

POLYVINYLPYRROLIDONE-SUPPORTED HYDROPEROXIDE
2397
Table III Oxidation of aldehydes to carboxylic acids using (PVPP-POCl3)/H2O2a
Entry
Aldehyde
Time (h)
Yield%b
Ref.
1
2
CH3CH2CH2CH2 CH2CHO
1
1
98
98
32,33
32,33
CHO
3
1
98
32
CHO
4
5
Ph-CHO
12
12
75
72
32,33
32,33
Cl
CHO
6
7
8
PhCH = CH CHO
PhCH = C(Me)-CHO
12
12
12
85
87
78
33
33
33
HO
CHO
9
12
82
33
CHO
HO
OH
1
1
0
1
12
1
82
76
32,33
33
MeO
CHO
CHO
PhO
1
2
1
78
33
a
b
◦
Reaction conditions: substrate (1 mmol), PVPP-POCl3 (0.5 g), H2O2 (3 mmol), MeCN (45 C).
Isolated yields.
(Table III, entries 6–9) was found to be inert, and aldehydes were selectively oxidized to
the acids without affecting these groups.
Finally, we examined the oxidation reaction of structurally different sulfides with a
Vilsmeier reagent/H2O2 system in methanol at room temperature (Scheme 2). All reactions
were carried out under the optimized conditions, and the results are summarized in Table IV.
Reaction times are very short, and the sulfoxides are obtained in excellent yields. It is clear
that sulfides bearing sensitive functional groups such as hydroxy, methoxy, carbaldehyde,
and carbon–carbon double bonds are completely unaffected under the reaction conditions.
As shown in Scheme 1, after completion of the reactions and workup, the combined
spent resin was filtered off, and the phosphate species are removed from the reagent. Upon

2398
M. M. LAKOURAJ ET AL.
Table IV Oxidation of sulfides to sulfoxides using (PVPP-POCl3)/H2O2a
Entry
Sulfide
Time (min)
Yield%b
Ref.
1
2
3
4
5
Ph-S-Me
10
15
25
40
35
99
98
97
94
92
34
34
35
32,33
33
Ph-CH2-S-CH2-Ph
PhCH2-S-Ph
Ph-S-Ph
PhCH2
S
Cl
6
7
8
9
0
1
Ph-S-CH2CH2OH
Me-S-CH2CH2-CHO
(CH3CH2CH2)2S
(CH3CH2CH2CH2)2S
(CH2 = CH CH2)2S
25
5
5
5
5
95
98
99
99
98
98
36,47
47
37
38
39,47
40
1
1
5
S
1
2
20
95
29
PhCH2
S
OMe
a
Reaction conditions: sulfide (1 mmol), PVPP-POCl3 (0.25 g), H2O2 (2 mmol), MeOH, r.t.
Isolated yields.
b
treatment of the recycled PVPP with a fresh POCl3 solution, the Vilsmeier reagent was
regenerated and reused for the new oxidation reactions.
Investigation about the use of the polyvinylpyrrolidone-supported Vilsmeier reagent
and hydrogen peroxide for oxygenation of alkenes to corresponding epoxides is underway.
In order to show the advantages and disadvantages of our method, some of our re-
sults in oxidation of sulfides and aldehydes were compared with some of those reported
26–41
in literature
(Table V). It is evident that the PVPP-POCl3/H2O2 system allows these
transformations to proceed with excellent selectivity, good yield, shorter times, and milder
conditions. Furthermore, the recyclability of the polymer support together with its biocom-
patibility makes the method environmentally safe and friendly.
In summary, we demonstrated poly(vinylpyrrolidone)-phosphorous oxychloride as a
versatile polymeric Vilsmeier reagent that exhibits excellent selectivity toward oxygenation
of sulfides to sulfoxides, and oxidation of aldehydes to carboxylic acids in the presence of
hydrogen peroxide under mild reaction conditions. This polymeric Vilsmeier reagent was
found to retain its activity after months and is stable in a glass bottle at room temperature. In
addition, this method is suitable both for preparative and industrial usage because of its low
cost, biocompatibility, and recyclability of the poly(vinylpyrrolidone) as a safe polymer
support.
EXPERIMENTAL
Melting points were recorded on an electrothermal melting point apparatus and are
uncorrected. The NMR spectra were recorded in CDCl3 with TMS as an internal standard

POLYVINYLPYRROLIDONE-SUPPORTED HYDROPEROXIDE
2399
Table V Comparison of PVPP-POCl3/H2O2 with some other reagents for oxidation of sulfides and aldehydes
to corresponding sulfoxide and carboxylic acids, respectively
Substrate
Reagent
Conditions
Time
Yield (%)a
Ref.
Ph-S-Me
”
”
”
”
”
”
”
H2O2(35%), TiCl3
Caro s acid/SiO2
Oxone (3 eq.)
KMnO4/MnO2
NaIO4
H2O/MeOH, r.t.
MeCN, reflux
H2O/MeOH, 0 C
5 min
4.5 h
4 h
3 h
15 h
5 h
100
92
41
42
43
44
45
46
,
◦
a
95
93
a
CH2Cl2, r.t.
◦
H2O/0 C
91
80
98
91
70
75
84
94
96
78.6
99
95
98
97
◦
t-BuOOH, Ti(O-Pr)4
PVP-POCl3/H2O2
CH2Cl2, −20 C
MeOH, r.t.
10 min
1 h
b
NAHBP
THF/ H2O, r.t.
H20/CHCl3, r.t.
Petroleum ether/reflux
AcOH, r.t.
47
48
49
50
51
22
52
53
41
54
PhCHO
Oxone/H2SO4
MnO2
PhCH2NEt3MnO4
NiO2/NaOH
UHP (4eq)c
48 h
24 h
1.25 h
1.5 h
1.5 h
6 h
20 h
24 h
1.5 h
1 h
”
”
”
”
”
”
”
◦
H2O, 30 C
HCOOH(95%)/r.t.
◦
Ni(dmp)2/O2 (1atm)
PB-SiO2/KMnO4
H2O2/MeReO3
Acetone, 0 C
◦
Cyclohexane, 65 C
◦
[bmim]BF4, 50 C
d
◦
MPHT (10%)/H2O2
MeCN, 80 C
◦
”
PVP-POCl3/H2O2
MeCN, 45 C
a
Yield refers to the corresponding sulfone.
NAHBP = nicotinic acid hydrobromide perbromide.
b
c
UHP = urea hydrogen peroxide.
d
MPHT = methylpyridin-2-one hydrobromide.
on Bruker WM 250 and 400 MHz NMR spectrometers. IR spectra were determined on a SP-
100, P-UV-Com instrument. 20% cross-linked polyvinylpyrrolidone (PVPP) and linear
1
PVPP (Mw = 90000) were purchased from Fluka. Elemental analyses were performed by
a CHN-O rapid Heraeus elemental analyzer (Wellesley, MA). Purity determination of the
products was accomplished by TLC on silica gel polygram SIL G/UV 254 plates. Products
were identified by the comparison of their mp, IR, and NMR spectra with those reported
for authentic samples.
Preparation of Polyvinylpyrrolidone-Supported Phosphorus
Oxychloride (PVPP-POCl3)
To a suspension of cross-linked polyvinylpyrrolidone (PVPP, 4g) in CH2Cl2 (25 mL),
a solution of phosphorus oxychloride (5 mL) in CH2Cl2 (15 mL) was added dropwise, and
the mixture was stirred for 0.5 h at room temperature. The resulting resin was filtered and
washed with CH2Cl2 (2 × 10 mL), and was finally dried in desiccator to give stable and
non-hygroscopic powder. CHN: Anal. Calcd. C, 27.22; N, 5.65; H, 3.38. Found: C, 2734;
N, 5.41; H, 3.58. IR (KBr): 3399, 2952, 1644, 1543, 1516, 1474, 1293, 1224, 1027,750,
−
1
13
+
31
5
35cm . C NMR, (100.6 MHz, CDCl3): δ = 176 (-(Cl)C N -). P NMR (161.8MHz,
−
DMSO-d6): δ = −13.6 (PO2Cl2 ). Capacity of the reagent was determined by iodometric
−
titration and was found to be 3.7 mmol of PO2Cl2 per gram of polymeric reagent.

2400
M. M. LAKOURAJ ET AL.
General Procedure for Oxidation of Aldehydes to Carboxylic Acids
To a suspension of aldehyde (1 mmol) and PVPP-POCl3 (0.5 g) in acetonitrile (5 mL),
3
5% hydrogen peroxide (3 mmol) was added dropwise. The reaction mixture stirred for
◦
1–12 h at 45 C. After completion of the reaction (TLC), the mixture was filtered and
purified by silica gel column chromatography to afford the desired products in 72–98%
yields.
General Procedure for Oxidation of Sulfides
To a suspension of sulfide (1 mmol) and PVPP-POCl3 (0.25 g) in methanol (5 mL),
35% hydrogen peroxide (2 mmol) was added dropwise. The reaction mixture was stirred
for 10–45 min at room temperature. After completion of the reaction (TLC), the mixture
was filtered and washed with H2O (5 mL). The filtrates were extracted with diethyl ether
(20 mL), and the combined organic fraction was washed with 3% NaHSO3 and dried over
Na2SO4. Evaporation of the solvent gave the corresponding sulfoxide in 92–99% yields.
Benzyl (4-Methoxyphenyl) Sulfoxide
◦
−1
Mp = 105–107 C. IR(KBr)(νmax, cm ): 3090, 2992, 2832, 1442, 1305, 1147, 1037,
1
7
2
50, 660. H NMR (400MHz, DMSO-d6): δ = 7.8(d, 2H), 7.75(d, 2H), 7.47(m, 3H), 7.3(m,
H), 4.0(s, 3H), 3.8(d, 1H), 4.2(d, 1H).
Regeneration of Polyvinylpyrrolidone-Supported Phosphorus
Oxychloride (PVPP-POCl3)
The spent reagent collected from each oxidation reaction was washed thoroughly
with water and diethyl ether to remove any residual compounds. The resin was filtered
◦
and dried in vaccum at 50 C. The recycled polyvinylpyrrolidone was treated with POCl3
in dichloromethane and was stirred for 0.5 h at room temperature. Then, the mixture was
filtered and washed with dichloromethane and dried in a desiccator.
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