Synthesis of methyltriphenylphosphonium peroxydisulfate as a mild selective reagent for the oxidation of alcohols

Article abstract of DOI:10.1080/00397910500330155

Methyltriphenylphosphonium peroxydisulfate (MTPPP) was synthesized by treating methyltriphenyl bromide and potassium peroxydisulfate in aqueous solution. This was used as an efficient and selective reagent for oxidation of alcohols to their corresponding carbonyl compounds in good to high yields. Copyright Taylor & Francis LLC.

Full text of DOI:10.1080/00397910500330155

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Synthesis of Methyltriphenylphosphonium
Peroxydisulfate as a Mild Selective Reagent
for the Oxidation of Alcohols
a b
a
b
A. R. Hajipour
, Saeed Zahmatkesh & A. E. Ruoho
a
Pharmaceutical Research Laboratory, College of Chemistry , Isfahan
University of Technology , Isfahan, Iran
b
Department of Pharmacology , University of Wisconsin Medical School ,
Madison, Wisconsin, USA
Published online: 21 Aug 2006.
To cite this article: A. R. Hajipour , Saeed Zahmatkesh & A. E. Ruoho (2006) Synthesis of
Methyltriphenylphosphonium Peroxydisulfate as a Mild Selective Reagent for the Oxidation of Alcohols,
Synthetic Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
36:1, 71-76, DOI: 10.1080/00397910500330155
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Synthetic Communications , 36: 71–76, 2006
Copyright # Taylor & Francis LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910500330155
Synthesis of Methyltriphenylphosphonium
Peroxydisulfate as a Mild Selective Reagent
for the Oxidation of Alcohols
A. R. Hajipour
Pharmaceutical Research Laboratory, College of Chemistry, Isfahan
University of Technology, Isfahan, Iran and Department of
Pharmacology, University of Wisconsin Medical School, Madison,
Wisconsin, USA
Saeed Zahmatkesh
Pharmaceutical Research Laboratory, College of Chemistry, Isfahan
University of Technology, Isfahan, Iran
A. E. Ruoho
Department of Pharmacology, University of Wisconsin Medical School,
Madison, Wisconsin, USA
Abstract: Methyltriphenylphosphonium peroxydisulfate (MTPPP) was synthesized by
treating methyltriphenyl bromide and potassium peroxydisulfate in aqueous solution.
This was used as an efficient and selective reagent for oxidation of alcohols to their
corresponding carbonyl compounds in good to high yields.
Keywords: Alcohol, carbonyl compound, methyltriphenylphosphonium peroxy-
disulfate, oxidation
Received in the UK April 18, 2005
Address correspondence to A. R. Hajipour, Pharmaceutical Research Laboratory,
College of Chemistry, Isfahan University of Technology, Isfahan 84156, Iran.
E-mail: haji@cc.iut.ac.ir
71

72
A. R. Hajipour, S. Zahmatkesh, and A. E. Ruoho
INTRODUCTION
Oxidation in modern organic chemistry is one of the most important reactions.
Classic reagents such as manganese dioxide (MnO ), potassium permanganate
2
(
potassium dichromate have been introduced. Some new ones have also
KMnO ), chromium trioxide (CrO ), potassium chromate (K CrO ), and
4 3 2 4
[1]
[
2–11]
been prepared.
Although some of these methods have convenient
protocols with good to high yields, the majority of these methods suffer at
least from one of these disadvantages: using strong acid, long reaction
times, hygroscopisity, instability, no selectivity, dangerous procedure,
tedious workup, photosensitivity, low yields of products, overoxidation to
carboxylic acids, high cost, and/or toxicity.
RESULTS AND DISCUSSION
[
12]
In continuation of our study,
herein we introduce an efficient, mild, safe,
selective, and rapid method for oxidation of alcohols to their corresponding
aldehydes or ketones using MTPPP (1). This reagent was easily prepared by
adding an aqueous solution of K S O to a stirring aqueous solution of
2
2 8
þ
2
MePh P Br . After 30 min MTPPP (1) was obtained as a white precipitate
3
in high yield (Schemes 1 and 2).
This reagent is soluble in acetonitrile, DMF, DMSO, and NMP and
slightly soluble in ethyl acetate. By using this oxidant, various alcohols
were converted to their corresponding carbonyl compounds in good to high
yields and short reaction times (Table 1).
In comparison to benzylic alcohols, oxidation of aliphatic ones with this
reagent occurs with lower yields and longer reaction times. The electron-
donor functional groups on phenyl ring of benzylic alcohols accelerate the
reaction rate and the electron acceptor ones decrease it. The rates of
secondary alcohols as compared to the primary ones are higher and also the
reaction times are shorter (Scheme 3, Table 1).
It is notable to say that the reactions under an N atmosphere need more
2
time and give lower yields. The ability of this reagent for oxidation of other
oxidizable functional groups such as thiols, sufides, amines, imines, and so
forth is being studied in our group.
In conclusion, we have developed a simple, efficient (no need of excess
amount of oxidant), and good chemoselective process for oxidation of
different types of alcohols. The stability, easy preparation, mildness of the
Scheme 1.

Methyltriphenylphosphonium Peroxydisulfate
73
Scheme 2.
reagent (no overoxidation to corresponding carboxylic acids), easy workup,
mild reaction conditions, high yields of the products, and nonaqueous
condition make this reagent useful for oxidation of alcohols to their corre-
sponding carbonyl compounds.
EXPERIMENTAL
All reagents were purchased from Merck and Aldrich and used without further
purification. All yields refer to isolated products. Products were characterized
1
by comparison with authentic samples ( H NMR, IR, and GC spectra; melting
1
or boiling points; and TLC). H NMR spectra were recorded on a 250-MHz
Bruker Advanced DPX-250 spectrometer. IR spectra were recorded on
FT-IR-680 plus and GC spectra on a GC-14A Shimadzu.
Preparation of Methyltriphenylphosphonium
Peroxydisulfate (MTPPP)
A solution of potassium peroxydisulfate (5 mmol, 1.35 g) in water (40 mL)
was added to a solution of methylriphenylphosphonium bromide (10 mmol,
3
.57 g) in water (25 mL) under stirring at room temperature. After 30 min of
stirring, a white precipitate was formed. The mixture was filtered, washed
with water (2 ꢀ 15 mL), and dried at room temperature (3.78 g, 96% yield),
which decomposed at 210–2128C to a dark brown material. IR (KBr) 3100,
2
1 1
2
980, 1600, 1495, 1480, 1260, 1190, 1050, 860, 750, 690 cm . H NMR
(
DMSO-d ) d, ppm: 7.9–7.7 (m, 15H), 3.19 (d, J ¼ 14.6, P-CH ).
6
3
1
3
C NMR: d 134.5, 134.4, 132.5, 132.3, 129.7, 129.3, 116.4. Anal. calcd.
for C H O P S : C, 61.13%; H, 4.83%; N, 0.00%. Found C, 61.18%; H,
3
8 36 8 2 2
4
.90%; N, 0.01%.
Oxidation of Benzyl Alcohol with MTPPP to Benzaldehyde
In a round-bottomed flask (25 mL) equipped with a reflux condenser and a
magnetic stirrer, a solution of benzyl alcohol (1 mmol, 0.108 g) and MTPPP
(0.5 mmol, 0.363 g) in acetonitrile was added and then refluxed for 15 min
until TLC [EtOAC/n-hexane (10 : 90)] showed the complete disappearance

a,b,c
Table 1. Oxidation of alcohols by (MePh P) S O (1) in refluxing acetonitrile
3 2 2 8
Time
(min)
Yield
(%)
[
Lit]
[
Entry
Substrate
OH
3-MeOC H CH OH
Product
PhCHO
3-MeOC H CHO
Mp (8C) or bp (8C)/Torr
13]
1
2
3
4
5
6
7
8
9
PhCH
2
15
15
93
95
95
97
95
95
95
90
75
97
55
55
56
56
60
62
176–177/760 (178–179/760)
[
14]
228–230/760 (230/760)
246–247/760 (248/760)
6
4
2
6
4
[
13]
4-MeOC
3,4-(MeO)
6
H
4
CH
2
OH
CH
4-MeOC
6
H
4
CHO
CHO
15
15
[
13]
2
6
C H
3
2
OH
3,4-(MeO)
2-OHC H CHO
2
C
6
H
3
42–45 (42–45)
194–195/760 (197/760)
[
13]
2-OHC H CH OH
6
15
4
2
6
4
[
13]
2-ClC
4-ClC
4-BrC
6
H
4
CH
2
OH
2-ClC
4-ClC
4-BrC
6
H
4
CHO
15
15
11–12 (10–11.5)
210–211/760 (213–214/760)
[
13]
6
H
4
CH
2
OH
6
H
4
CHO
[
13]
6
H
4
CH
2
OH
6
H
4
CHO
25
57–58 (55–58)
107–109 (105–108)
[
13]
4-NO C H CH OH
4
4-NO C H CHO
2 6 4
120
10
2
6
2
[
13]
1
1
1
1
1
1
1
0
1
2
3
4
5
6
PhCHOHPh
PhCOPh
50–52 (49–51)
95–97 (94–95)
[
13]
PhCHOHCOPh
1-Hexanol
1-Octanol
PhCOCOPh
1-Hexanal
1-Octanal
150
150
150
150
100
100
[
[
[
[
13]
13]
15]
13]
128–129/760 (131/760)
168–169/760 (171/760)
158–159/760 (160/760)
152–154/760 (155/760)
2-Ethyl-1-hexanol
Cyclohexanol
Cyclododecanol
2-Ethyl-1-hexanal
Cyclohexanone
Cyclododecanone
[
13]
60–62 (59–61)
a
b
c
Substrate/oxidant (2 : 1).
Yields based on the isolated pure products after chromatography.
The products were characterized by comparison of their physical and spectral data with authentic samples.

Methyltriphenylphosphonium Peroxydisulfate
75
Scheme 3.
of benzyl alcohol. The reaction mixture was cooled to room temperature, and
the solid was separated through a short pad of silica gel and washed with
acetonitrile (5 mL). The filtrate was evaporated, and the resulting crude
material was purified by column chromatography on silica gel using a
mixture of ethyl acetate and n-hexane as eluent (10 : 90). Pure benzaldehyde
1
was obtained in 93% yield (0.095 g). IR and H NMR data were in good
agreement with the spectral data published.
ACKNOWLEDGMENTS
We gratefully acknowledge the funding support received for this project from
the Isfahan University of Technology (IUT), IR Iran (A. R. H.) and Grant
GM 33138 (A. E. R.) from the National Institutes of Health, USA. Further
financial support from Center of Excellency in Chemistry Research (IUT) is
gratefully acknowledged.
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1
1
1