α-Naphthyltriphenylphosphonium peroxodisulfate: A selective and regenerable reagent for oxidation of organic compounds

Article abstract of DOI:10.1080/10426500701648051

Alcohols, hydroquinones, tetrahydropyranyl ethers, trimethylsilyl ethers, oximes, semicarbazones, and phenylhydrazones were efficiently converted to the corresponding carbonyl compounds using α-naphthyltriphenylphosphonium peroxodisulfate (NTPPPODS) in acetonitrile at reflux conditions. This reagent could be regenerated and reused, which represents significant advantages over the known reagents. Copyright Taylor & Francis Group, LLC.

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α-
Naphthyltriphenylphosphonium
Peroxodisulfate: A Selective
and Regenerable Reagent
for Oxidation of Organic
Compounds
Moslem Mansour Lakouraj a , Mahmood Tajbakhsh a &
Farhad Ramzanian-Lehmali a
a Department of Chemistry, Faculty of Basic
Sciences, University of Mazandaran, Babolsar, Iran
Version of record first published: 04 Jun 2008.
To cite this article: Moslem Mansour Lakouraj, Mahmood Tajbakhsh & Farhad
Ramzanian-Lehmali (2008): α-Naphthyltriphenylphosphonium Peroxodisulfate: A
Selective and Regenerable Reagent for Oxidation of Organic Compounds, Phosphorus,
Sulfur, and Silicon and the Related Elements, 183:6, 1388-1395
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Phosphorus, Sulfur, and Silicon, 183:1388–1395, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500701648051
α-Naphthyltriphenylphosphonium Peroxodisulfate: A
Selective and Regenerable Reagent for Oxidation of
Organic Compounds
Moslem Mansour Lakouraj, Mahmood Tajbakhsh,
and Farhad Ramzanian-Lehmali
Department of Chemistry, Faculty of Basic Sciences, University of
Mazandaran, Babolsar, Iran
Alcohols, hydroquinones, tetrahydropyranyl ethers, trimethylsilyl ethers, oximes,
semicarbazones, and phenylhydrazones were efficiently converted to the correspond-
ing carbonyl compounds using α-naphthyltriphenylphosphonium peroxodisulfate
(NTPPPODS) in acetonitrile at reflux conditions. This reagent could be regenerated
and reused, which represents significant advantages over the known reagents.
Keywords α-Naphthyltriphenylphosphonium peroxodisulfate; oximes; phenylhydra-
zones; semicarbazones; tetrahydropyranyl ethers; trimethylsilyl ethers
INTRODUCTION
The oxidation of organic compounds under mild conditions has found
valuable applications in modern organic synthesis. So far, significant
improvments have been achieved by the use of new oxidizing agents.1−8
Unfortunately, many of the reagents mentioned in literature suffer from
at least one of the following disadvantages: cost of preparation, hygro-
scopicity, photosensitivity, instability, lack of selectivity, and tedious
work-up procedure with accompanying reagent decomposition.
The peroxodisulfate ion is one of the strongest oxidizing agents and
its standard redox potential in aqueous solution is about 2.01V, but
there are only a few reports concerning the capability of peroxodisulfate
for oxidative transfomations.9−16
In connection with our ongoing work on the application of per-
oxodisulfate based oxidants to the selective oxidation of organic
Received 9 January 2007; accepted 20 August 2007.
We are thankful to the Mazandaran University Research Council for partial support
of this work.
Address correspondence to Moslem Mansour Lakouraj, Department of Chemistry,
Faculty of Sciences, University of Mazandaran, P.O. Box 47416, Babolsar, Iran. E-mail:
lakouraj@umz.ac.ir
1388

α-Naphthyltriphenylphosphonium Peroxodisulfate
1389
FIGURE 1
compounds,9,17 we report here the oxidation of structurally differ-
ent alcohols, hydroquinones, tetrahydropyranyl ethers, trimethylsi-
lyl ethers, oximes, semicarbazones, and phenylhydrazones using
α-naphthyltriphenylphosphonium peroxodisulfate in acetonitrile at
reflux conditions. α-Naphthyltriphenylphosphonium peroxodisulfate
(NTPPPODS, Figure 1) as an oxidant can overcome most of the above-
mentioned disadvantages for the oxidation of organic compounds.
RESULTS AND DISCUSSION
α-Naphthyltriphenylphosphonium peroxodisulfate was readily pre-
pared from an aqueous solution of α-naphthyltriphenylphosphonium
chloride and potassium peroxodisulfate at room temperature and char-
acterized spectroscopically, as well as by elemental analysis. The con-
tent of active oxidizing agent (S2O2−) was determined by titrimetric
8
method.18 This reagent is a stable white powder, which can be stored
for months without losing its activity.
The effect of solvent on the oxidation reaction was evaluated by car-
rying out the oxidation in different solvents. Oxidation of benzyl alco-
hol with α-naphthyltriphenylphosphonium peroxodisulfate was carried
out in dichloromethane, chloroform, tetrahydrofuran, n-hexane, ace-
tonitrile, and in a mixture of water and acetonitrile (70:30) at reflux
temperature. The results are presented in Table I.
As indicated in Table I, a 1:0.5 molar ratio of benzyl alcohol and α-
naphthyltriphenylphosphonium peroxodisulfate in acetonitrile or in a
mixture of water and acetonitrile gave excellent yield of benzaldehyde
within five minutes.
In addition, the effect of temperature on this reaction was studied
by carrying out the oxidation of benzyl alcohol at lower temperatures;
longer reaction time was necessary to achieve complete conversion to
benzaldehyde, however.
In order to evaluate the general applicability of this method
we have treated benzylic, allylic and aliphatic alcohols,

1390
M. M. Lakouraj et al.
TABLE I Oxidation of Benzylalcohol in Different Solvents Using
NTPPPODSa
Solvent
Reaction time (min)
Yield (%)b
CH3CN
H2O/CH3CN (70/30)
CHCl3
CH2Cl2
n-C6H12
2
5
60
60
60
60
98
96
4
5
0
THF
0
aReactions were carried out at reflux conditions using substrate/oxidant (2:1).
bYields refer to isolated products or GC.
hydroquinones, tetrahydropyranyl and trimethylsilyl ethers with
α-naphthyltriphenylphosphonium peroxodisulfate in refluxing ace-
tonitrile. The results are shown in Table II.
It is evident from Table II, that aromatic substrates, including bezylic
alcohols as well as tetrahydropyranyl and trimethylsilyl ethers, were
rapidly oxidized to the corresponding carbonyl compounds in excel-
lent yields under the reaction conditions, whereas aliphatic compounds
needed longer reaction time for oxidation.
It is noteworthy that, unlike other hydrolytic oxidative methods, the
major drawback of overoxidation of the resulting aldehydes was not
observed under this reaction conditions. α,β-Unsaturated derivatives
are oxidized very efficiently without affecting the olefinic bond and the
reaction is essentially chemoselective (Table II).
It is interesting to mention that NTPPPODS can selectivly oxidize
hydroquinones in the presence of alcohols in refluxing chloroform. When
an equimolar mixture of hydroquinone and a benzylic or an aliphatic
alcohol was treated with NTPPPODS, only the hydroquinone was oxi-
dized, while the alcohol remained unaffected (Scheme 1).
SCHEME 1

α-Naphthyltriphenylphosphonium Peroxodisulfate
1391
TABLE II Oxidation of Alcohols and Hydroquinones and Oxidative
Deprotection of Trimethylsilyl and Tetrahydropyranyl Ethers with
NTPPPODSa
Reagent Time Yield
Substrate
Product
C6H5CHO
p-MeOC6H4CHO
o-ClC6H4CHO
p-ClC6H4CHO
p-BrC6H4CHO
p-NO2C6H4CHO
C6H5COCH3
/substrate (min) (%)b,c
C6H5CH2OH
p-MeOC6H4CH2OH
o-ClC6H4CH2OH
p-ClC6H4CH2OH
p-BrC6H4CH2OH
p-NO2C6H4CH2OH
C6H5CH(OH)CH3
C6H5CH(OH)CH2CH3
(C6H5)2CHOH
0.5
0.5
0.5
0.5
0.5
1
0.5
0.5
0.5
1
1
1
1
1
0.5
0.5
0.5
0.5
0.5
0.5
1
2
2
3
2
4
15
3
4
98
95
97
99
97
65
95
97
95
93
84
87
95
89
99
95
98
96
99
97
74
92
81
84
86
94
98
C6H5COCH2CH3
(C6H5)2CO
2
C6H5CH2CH2OH
C6H5CH2CHO
CH3(CH2)5CHO
CH3(CH2)6CHO
C6H5CH=CHCHO
Cyclohexanone
Quinone
tert-Butylquinone
C6H5CHO
(C6H5)2CO
p-ClC6H4CHO
p-BrC6H4CHO
p-NO2C6H4CHO
C6H5CH2CHO
CH3(CH2)5CHO
CH3(CH2)6CHO
C6H5CH=CHCHO
Quinone
20
20
20
10
15
2
2
3
5
4
CH3(CH2)5CH2OH
CH3(CH2)6CH2OH
C6H5CH=CHCH2OH
Cyclohexanol
Hydroquinone
tert-Butylhydroquinone
C6H5CH2OSiMe3
(C6H5)2CHOSiMe3
p-ClC6H4CH2OSiMe3
p-BrC6H4CH2OSiMe3
p-NO2C6H4CH2OSiMe3
C6H5CH2CH2OSiMe3
CH3(CH2)5CH2OSiMe3
CH3(CH2)6CH2OSiMe3
C6H5CH=CHCH2OSiMe3
Hydroquinone trimethylsilylether
tert-Butylhydroquinone
trimethylsilylether
C6H5CH2OTHP
3
40
30
40
45
5
1
1
1
0.5
0.5
0.5
3
2
tert-Butylquinone
C6H5CHO
(C6H5)2CO
0.5
0.5
0.5
0.5
0.5
1
10
12
8
10
8
30
17
25
96
95
95
94
93
87
91
90
(C6H5)2CHOTHP
o-ClC6H4CH2OTHP
p-MeC6H4CH2OTHP
p-BrC6H4CH2OTHP
CH3(CH2)5CH2OTHP
CH3CH=CHCH2OTHP
Cyclohexanol tetrahydropyranyl ether
o-ClC6H4CHO
p-MeC6H4CHO
p-BrC6H4CHO
CH3(CH2)5CHO
CH3CH=CHCHO
Cyclohexanone
0.5
1
aReactions were carried out in water and acetonitrile (70/30) at reflux temperature.
bAll products were characterized spectroscopically (1H NMR, IR) and showed
physical and spectral data in accordance with their structures and also in accord with
those of authentic samples.
cYields refer to pure isolated products; the eluent in column chromarography was
EtOAc/n-hexane (1:5) for alcohols, and EtOAc/n-hexane (1:10) for TMS and THP ethers.

1392
M. M. Lakouraj et al.
As summarized in Table III, our experiments show, that oximes,
phenylhydrazones and semicarbazones can be deprotected to the cor-
responding aldehydes and ketones in water and acetonitrile (70/30) at
reflux temperature.
TABLE III Deprotection of Phenylhydrazones, Oximes and
Semicarbazones to the Corresponding Carbonyl Compounds Using
NTPPPODSa
Reagent
/substrate
Time
(min)
Yield
(%)b,c
Substrate
Product
C6H5CHO
4C6H5CHNNHC6H5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
2
2
2
2
2
2
2
2
2
15
15
12
12
12
45
18
40
30
25
20
18
15
20
18
60
20
40
45
20
20
20
20
20
15
18
55
20
30
25
96
95
94
96
94
78
95
83
85
91
96
93
97
93
94
81
97
87
85
91
96
91
95
93
95
92
78
96
92
92
o-ClC6H4CHNNHC6H5
p-ClC6H4CHNNHC6H5
p-MeOC6H4CHNNHC6H5
p-MeC6H4CHNNHC6H5
p-NO2C6H4CHNNHC6H5
(C6H5)2CNNHC6H5
C6H5CH2CH2CHNNHC6H5
Cyclohexanone Phenylhydrazone
C6H5CH=CHCHNNHC6H5
C6H5CHNOH
o-ClC6H4CHO
p-ClC6H4CHO
p-MeOC6H4CHO
p-MeC6H4CHO
p-NO2C6H4CHO
(C6H5)2CO
C6H5CH2CH2CHO
Cyclohexanone
C6H5CH=CHCHO
C6H5CHO
p-MeC6H4CHO
p-MeOC6H4CHO
m-ClC6H4COCH3
o-ClC6H4COCH3
p-NO2C6H4COCH3
(C6H5)2CO
C6H5CH2CH2CHO
Cyclohexanone
C6H5CH=CHCHO
C6H5CHO
p-MeC6H4CHNOH
p-MeOC6H4CHNOH
m-ClC6H4C(CH3)NOH
o-ClC6H4C(CH3)NOH
p-NO2C6H4C(CH3)NOH
(C6H5)2CNOH
C6H5CH2CH2CHNOH
Cyclohexanone Oxime
C6H5CH=CHCHNOH
C6H5CHNNHCONH2
p-ClC6H4CHNNHCONH2
o-ClC6H4CHNNHCONH2
p-BrC6H4CHNNHCONH2
m-MeOC6H4CHNNHCONH2
p-MeOC6H4CHNNHCONH2
o-NO2C6H4CHNNHCONH2
(C6H5)2CNNHCONH2
C6H5CH2CH2CHNNHCONH2
C6H5CH=CHCHNNHCONH2
2
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
1.5
p-ClC6H4CHO
o-ClC6H4CHO
p-BrC6H4CHO
m-MeOC6H4CHO
p-MeOC6H4CHO
o-NO2C6H4CHO
(C6H5)2CO
C6H5CH2CH2CHO
C6H5CH=CHCHO
aReactions were carried out in water and acetonitril (70/30) at reflux temperature.
bAll products were characterized spectroscopically (1H NMR, IR) and showed
physical and spectral data in accordance with their structures and also in accord with
those of authentic samples.
cYields refer to pure isolated products; the eluent in column chromarography was
EtOAc/n-hexane (1:4).

α-Naphthyltriphenylphosphonium Peroxodisulfate
1393
Similarly, this reagent can selectively deprotect oximes,
semicarbazones, and phenylhydrazones in the presence of 2,4-
dinitrophenylhydrazones to the coreesponding carbonyl compounds
in refluxing acetonitrile. When an equimolar mixture of an oxime, a
semicarbazone, or a phenylhydrazone and 2,4-dinitrophenylhydrazone
was treated with NTPPPODS, the oxime, semicarbazone or phenylhy-
drazone were deprotected but 2,4-dinitrophenylhydrazone remained
unchanged (Scheme2).
SCHEME 2
Another interesting feature of this method is, that the α-naphthyl-
triphenylphosphonium cation could be recycled and reused for regen-
eration of the reagent. On completion of the reaction, the residual solid
materials were collected, dissolved in DMSO, and treated with freshly
prepared aqueous K2S2O8 to give α-naphthyltriphenylphosphonium
peroxodisulfate quantitatively (Scheme 3).
SCHEME 3
In conclusion, we have developed a convenient and efficient method
for oxidation of structurally different alcohols, hydroquinones, tetrahy-
dropyranyl ethers and trimethylsilyl ethers to the corresponding car-
bonyl compounds and the regeneration of carbonyl compounds from
oximes, phenylhydrazones and semicarbazones. Our new method has
significant advantages over the existing methods such as selective and
recyclable procedure, high yields and mild reaction conditions.

1394
M. M. Lakouraj et al.
EXPERIMENTAL
All the alcohols and hydroquinones were purchased from Fluka and
Merck. The reactions were monitored by TLC using silica gel plates.
The products were purified by flash column chromatography on silica
gel (Merck; 230–400 mesh) and were identified by comparison of their
IR and 1H NMR spectra and physical data with those of authentic sam-
1
ples. H NMR spectra were measured at 90 MHz with a JEOL JNM-
EX 90 spectrometer with tetramethylsilane as an internal reference
and DMSO-d6 as solvent. IR spectra were recorded with a Pye-unicam
SP 1100 spectrophotometer. Elemental analyses were performed on a
LECO 250 instrument.
Preparation of α-Naphthyltriphenylphosphonium
Peroxodisulfate (NTPPPODS)
To an aqueous solution of α-naphthyltriphenylphosphonium chloride
(0.878 g, 2 mmol, 10 mL) was added an aqueous solution of potassium
peroxodisulfate (0.32 g, 1.2 mmol). The mixture was stirred at room
temperature for 20 min. The resulting white solid product was filtered,
washed with cooled distilled water (10 mL) and dried in vacuum des-
iccators. Yield 0.969 g, 97%; m.p. = 221–223◦C.1H NMR (DMSO): δ =
5.61 (d, J = 16.3 Hz, 4H, CH2), 7.02–8.27 (m, 44H, arom. H). IR (KBr)
ν(cm−1): 1290, 1260, 1092, 1058, 700, 685, 590, 554; Elemental analy-
sis: Calcd for C58H48P2S2O8: C, 69.72%; H, 4.84%; S, 6.41%, Found: C,
69.75%; H, 4.79%; S, 6.38%.
General Procedure for Oxidation of Alcohols, Hydroquinones
Tetrahydropyranyl and Trimethylsilyl Ethers, and
Deprotection of Oximes, Phenylhydrazones
and Semicarbazones
A mixture of the substrate (1 mmol), acetonitrile (10 mL) and NTPP-
PODS (0.5-2 mmol), were placed in a round bottomed flask and stirred
for the specified time (Tables II and III) at reflux conditions. After com-
pletion of the reaction (monitored by TLC), the reaction mixture was
cooled to room temperature and filtered. The solid material was washed
with acetonitrile (10 mL). From the combined filtrates the solvent was
evaporated under reduced pressure and the resulting crude material
was purified on a silica-gel column with an appropriate eluent. The
pure carbonyl compounds were obtained in 65–99% yield.
Regeneration of α-Naphthyltriphenylphosphonium
Peroxodisulfate
The used reagent was washed with diethyl ether (2 × 10 mL). The filter
cake was dissolved in DMSO (5 mL) and added dropwise to a freshly

α-Naphthyltriphenylphosphonium Peroxodisulfate
1395
prepared aqueous solution of potassium peroxodisulfate. The mixture
was stirred at room temperature for 20 min. Then, the solid material
was separated by filtration, repeatedly washed with water to remove
the free peroxodisulfate, and dried in a vacuum desiccator over calcium
chloride to obtain the regenerated reagent.
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