Synthesis and application of 2,6-dicarboxy pyridinium fluorochromate as a new solid-phase oxidant

Article abstract of DOI:10.1081/SCC-200058007

2,6-Dicarboxypyridinium fluorochromate (2,6-DCPFC) was prepared and used for oxidation of alcohols, phenols, and hydroquinones under solvent-free conditions. This new compound is more efficient and has certain advantages over similar oxidizing agents in terms of the amount of oxidant, lack of solvent, short reaction times, and high yields. Copyright Taylor & Francis, Inc.

Full text of DOI:10.1081/SCC-200058007

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Synthesis and Application
of 2,6‐Dicarboxy Pyridinium
Fluorochromate as a New
Solid‐Phase Oxidant
a
a
M. Tajbakhsh , R. Hosseinzadeh & M.
a
Sadatshahabi
a
Department of Chemistry , Mazandaran University ,
Babolsar, Iran
Published online: 17 Dec 2010.
To cite this article: M. Tajbakhsh , R. Hosseinzadeh & M. Sadatshahabi (2005)
Synthesis and Application of 2,6‐Dicarboxy Pyridinium Fluorochromate as a New
Solid‐Phase Oxidant, Synthetic Communications: An International Journal for Rapid
Communication of Synthetic Organic Chemistry, 35:11, 1547-1554, DOI: 10.1081/
SCC-200058007
To link to this article: http://dx.doi.org/10.1081/SCC-200058007
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Synthetic Communications , 35: 1547–1554, 2005
Copyright # Taylor & Francis, Inc.
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1081/SCC-200058007
Synthesis and Application of 2,6-Dicarboxy
Pyridinium Fluorochromate as a New
Solid-Phase Oxidant
M. Tajbakhsh, R. Hosseinzadeh, and M. Sadatshahabi
Department of Chemistry, Mazandaran University, Babolsar, Iran
Abstract: 2,6-Dicarboxypyridinium fluorochromate (2,6-DCPFC) was prepared and
used for oxidation of alcohols, phenols, and hydroquinones under solvent-free con-
ditions. This new compound is more efficient and has certain advantages over
similar oxidizing agents in terms of the amount of oxidant, lack of solvent, short
reaction times, and high yields.
Keywords: Alcohols, 2,6-dicarboxypyridinium fluorochromate, hydroquinones,
oxidation, phenols, solvent-free
Organic reactions were found to occur efficiently in the solid state. There is an
increasing interest in the use of environmentally benign reagents and
[1,2]
[3]
and particularly solvent-free procedures. Avoiding organic
conditions
solvents during the reactions in organic synthesis leads to a clean, efficient,
and economical technology. In solid-state reactions, workup is considerably
simplified, cost is reduced, increased amounts of reactants can be used in
the same equipment, and reactivities and sometimes selectivities are
[
4]
enhanced without dilution.
Organic solid-state reactions are usually
carried out by keeping a mixture of finely powdered reactant and reagent at
room temperature. In some cases, these reactions are accelerated by heating,
shaking, irradiation with ultrasound or microwave, and grinding of the
[
5]
reaction mixture using a mortar and pestle.
Received in the UK November 3, 2004
Address correspondence to M. Tajbakhsh, Department of Chemistry, Mazandaran
University, Babolsar, Iran. E-mail: tajbaksh@umz.ac.ir
1
547

1548
M. Tajbakhsh, R. Hosseinzadeh, and M. Sadatshahabi
The oxidation of organic substrates is important in modern organic
synthesis. The oxidation of primary and secondary alcohols to the correspond-
ing aldehydes and ketones is a fundamental area that is encountered at all
levels of organic synthesis. Therefore, the search for oxidizing agents is of
[
6]
interest to synthetic organic chemists. Numerous reagents and methods
have been developed to carry out this important reaction. In particular, there
is continued interest in the development of new chromium(VI) reagents for
the effective oxidation of alcohols under mild conditions. Of the large
number of mild chromium-based oxidizing agents available, many prove
[7]
impractical when the reactions are performed on a large (mol) scale,
although in recent years significant improvements have been achieved by
[8]
the use of new oxidizing agents, such as pyridinium chlorochromate, pyri-
[
9]
0
[10]
dinium dichromate,
11]
2,2 -bipyridinium chlorochromate,
[12]
pyridinium
quinolinium fluoro-
[
fluorochromate,
buthylaminium fluorochromate,
[14]
piperidinium chlorochromate,
[13]
chromate,
fluorochromate,
tetramethylammonium
[16]
[
15]
and 2,6-dicarboxypyridinium chlorochromate.
In general, most of the reactions described in the literature are carried out
in aliphatic or aromatic hydrocarbons, chlorinated hydrocarbons, diethyl
ether, THF, ethyl acetate, acetone, and acetonitrile.
Recently, we have noticed that 2,6-dicarboxypyridinium moiety in chro-
[16]
mium(VI) reagents is very important in the oxidation of organic substrates.
So, as a part of our program related to developing new oxidation methods, we
report here a new, simple, and general procedure that can be used for the
oxidative transformation of primary and secondary alcohols, phenols, and
hydroquinones into the corresponding carbonyl compounds under solvent-
free conditions.
2
,6-Dicarboxy pyridinium fluorochromate (2,6-DCPFC) is easily
prepared by the reaction of pyridine-2,6-dicarboxylic acid with chromium
trioxide in HF. The chromium content of the reagent was determined by
atomic absorption. Also, elemental analysis (C, H, N) were performed and
the experimental and calculated results are in very good agreement. This
reagent is soluble in polar solvents such as acetonitrile and acetone; slightly
soluble in THF, chloroform, and dichloromethane; and insoluble in
benzene, n-hexane, and carbon tetrachloride.
A wide variety of alcohols such as benzylic, allylic, aliphatic, phenols,
and hydroquinones have been converted to their corresponding carbonyl
compounds using this reagent, in solid phase at room temperature (Scheme 1).
In this method, the oxidant was carefully added to the substrate and the
mixture in a mortar was ground at room temperature until TLC analysis
Scheme 1.

2
,6-Dicarboxy Pyridinium Fluorochromate
1549
indicated a completed reaction. The oxidations were completed within 4–
5 min. The residue was then washed with a minimum amount of solvent
2
such as dichloromethane or diethyl ether. Distillation of the solvent gave a
product that is of acceptable purity for most purposes. During the reactions,
the color of the oxidant changed from orange to violet, providing visual
means for ascertaining the progress of reaction. The results, which are
shown in Table 1, indicate that the method is generally applicable to a
range of alcohols, phenols, and hydroquinones and gives the corresponding
oxidized compounds in excellent yields. Although most of the reactions
were carried out on a 1–5 mmol scale, to show the applicability of this
method in large scale, we have examined the oxidation of benzyl alcohol in
3
0-mmol scale and obtained the same result.
As shown in Table 1, in the case of secondary alcohols, the oxidation
requires longer reaction times (entries 11–14). Under the same reaction con-
ditions, primary and secondary allylic alcohols are oxidized to their a, b-unsa-
turated carbonyl compounds without the cleavage of carbon–carbon double
bonds (entries 15–17). Furthermore, hydroquinones (entries 18–19) and
Table 1. Oxidation of alcohols, phenols, and hydroquinones using 2,6-DCPFC under
a
solvent-free conditions at room temperature
b
Time
(min)
Yield
(%)
Entry
1
Substrate
Product
4
92
2
3
4
6
90
6
6
90
91
5
6
5
5
90
90
(
continued)

1550
M. Tajbakhsh, R. Hosseinzadeh, and M. Sadatshahabi
Table 1. Continued
b
Time
(min)
Yield
(%)
Entry
7
Substrate
Product
7
89
8
9
7
87
10
88
1
1
0
1
10
10
95
92
1
2
10
13
90
1
1
3
4
98
90
c
25
15
15
89
1
1
6
7
15
10
87
88
(
continued)

2
,6-Dicarboxy Pyridinium Fluorochromate
1551
Table 1. Continued
b
Time
(min)
Yield
(%)
Entry
Substrate
Product
18
19
20
21
22
23
4
95
7
93
94
89
86
90
4
5
10
8
2
4
5
15
20
85
89
2
2
6
Borneol
Camphor
18
85
a
b
c
1
Products were confirmed by comparison with authentic samples (IR, H NMR, GC).
Yield of isolated pure carbonyl compound.
This reaction was carried out with 2,6-DCPFC/alcohol: (3/1) molar ratio.

1552
M. Tajbakhsh, R. Hosseinzadeh, and M. Sadatshahabi
phenols (entries 20–23) are oxidized to give excellent yields of the corre-
sponding benzoquinones. Another noteworthy advantage of this reagent is
the exclusive oxidation of aliphatic alcohols (entries 24–26).
It is interesting to mention that in the oxidation of alcohols, the overoxida-
tion of products to the corresponding carboxylic acids was not observed at all.
To compare the reactivity of this reagent with and without solvent, the
oxidation of benzyl alcohol and hydroquinone as a model substrate was
carried out in solvents such as CH Cl , CHCl , hexane, THF, and acetonitrile.
2
2
3
In most cases, the reaction proceeded slowly and was not completed except in
acetonitrile, which gave nearly same reactivity as in solid-phase conditions.
It has also been found that this reagent has certain advantages over similar
oxidizing agents in terms of amounts of oxidant, short reaction times required,
higher product yields, and especially milder conditions (Table 2).
In conclusion, we have developed an efficient, solvent-free method for the
oxidation of alcohols, phenols, and hydroquinones that possesses significant
advantages over the existing methods such as simple procedure, easy
[11,17]
reaction workup, efficiency, high yields, and lack of solvent.
These
advantages make this reagent a useful addition to the category of reagents
used for the oxidation of organic substrates.
Table 2. Oxidation of alcohols by 2,6-DCPFC in comparison with other oxidants
Ratio of
oxidant–
Reagent substrate
Yield
(%)
Substrate
Time
Conditions
Ref.
—
PhCH OH 2,6-
Cyclohexanol DCPFC
1:1
1:1
4 min
20 min
2 h
Solvent-free, rt
92
89
97
85
91
72
77
67
90
89
91
90
82
—
2
a
b
PhCH
Cyclohexanol
PhCH OH
2
OH
4-APCC 1.5:1
1.5:1
Support on
silicagel
[18]
[13]
[19]
[11]
[17]
[20]
6 h
2 h
c
2
QFC
1.5:1
1.5:1
12.2:1
12.2:1
1:1
Support on
alumina
Solvent-free, rt
Cyclohexanol
PhCH OH
6 h
48 h
MnO2
2
Cyclohexanol
PhCH OH
72 h
d
2
PFC
45 min
210 min
60 min
240 min
1 h
CH
2 2
Cl , rt
Cyclohexanol
PhCH OH
1:1
1:1
e
IQFC
CH Cl , rt
2
2
2
Cyclohexanol
PhCH OH
Cyclohexanol
1:1
7.5:5
Not reported
f
2
PCC
Support on
alumina
—
a
2
4
,6-Dicarboxy pyridinium fluorochromate.
-Aminopyridinium chlorochromate.
b
c
Quinolinium fluorochromate.
d
Pyridinium fluorochromate.
Isoquinolinium fluorochromate.
e
f
Pyridinium chlorochromate.

2
,6-Dicarboxy Pyridinium Fluorochromate
1553
EXPERIMENTAL
Preparation of 2,6-Dicarboxypyridinium Fluorochromate
(
2,6-DCPFC)
To a solution of 2 g (0.02 mol) CrO in 1.0 ml of water in a polyethylene beaker,
3
1
.5 ml (0.03 mol) 40% of hydrofluoric acid was added with stirring. An orange-
red solution was obtained. The reaction mixture was then cooled in an ice bath
258C) and 3.342 g (0.02 mol) of pyridine-2,6-dicarboxylic acid was added por-
(
tionwise, with stirring. When an orange crystalline compound separated out, this
was filtered under vacuum, using a polyethylene funnel, washed with petroleum
ether (3 ꢀ 10ml), rapidly dried in a vacuum desicator, and finally stored in a
polyethylene bag. The yield of 2,6-DCPFC was found to be 5.28g (92%).
Analysis: C H NO [CrO F] calculated: Cr, 18.11%; C, 29.28%; N, 4.88%; H,
7
6
4
3
2
.10%. Found: Cr, 18.09%; C, 29.25%; N, 4.86%; H, 2.03%.
General Procedure for the Conversion of Alcohols, Phenols, and
Hydroquinones to the Corresponding Carbonyl Compounds
A mixture of substrate (1 mmol) and oxidizing agent (1 mmol, 0.287 g) in a
mortar was ground for the time specified in Table 1. When TLC showed
complete disappearance of substrate (alcohol, phenol, or hydroquinone), the
residue was then washed with a minimum amount of solvent such as dichlo-
romethane or diethyl ether. Distillation of the solvent gave a product that is of
acceptable purity for most purposes. If necessary, products were purified
by column chromatography (eluent: hexane–EtOAc). The products were
1
identified by IR, H NMR, and GC.
ACKNOWLEDGMENTS
Financial support from research council of Mazandaran University is
gratefully acknowledged.
REFERENCES
1
2
3
. Clark, J. H.; Cullen, S. R.; Barlow, S. J.; Bastock, T. W. Environmentally friendly
chemisry using supported reagent catalysts: Structure–property relationships for
clayzic. J. Chem. Soc., Perkin Trans. 2 1994, 1117.
. Varma, R. S.; Dahiya, R.; Saini, R. K. Iodobenzene diacetate on alumina: Rapid
oxidation of alcohols to carbonyl compounds in solventless system using micro-
waves. Tetrahedron Lett. 1997, 38, 7029.
. Loupy, A.; Bram, G.; Sansoulet, J. Anionic activation in solvent-free hetero-
geneous media, utilization of microwaves ovens. New J. Chem. 1992, 16, 233.

1554
M. Tajbakhsh, R. Hosseinzadeh, and M. Sadatshahabi
4
5
6
7
. Loupy, A.; Petit, A.; Hamelin, J.; Texier-Boullet, F.; Jacquault, P.; Mathe, D. New
solvent-free organic synthesis using focused microwaves. Synthesis 1998, 1213.
. Toda, F. Solid-state organic chemistry: Efficient reactions, remarkable yields, and
stereoselectivity. Acc. Chem. Res. 1995, 28, 480.
. Fieser, L. F.; Fieser, M. Reagents for Organic Synthesis; Wiley: New York; Vols.
1
–11; 1967–1984.
. Corey, E. J.; Suggs, J. W. Pyridinium chlorochromate. An efficient reagent for
oxidation of primary and secondary alcohols to carbonyl compounds. Tetrahedron
Lett. 1975, 16, 2647.
8. Corey, E. J.; Boger, D. L. Oxidative cationic cyclization reactions effected by
pyridinium chlorochromate. Tetrahedron Lett. 1978, 19, 2461.
9
. Corey, E. J.; Schmidt, G. Useful procedures for the oxidation of alcohols involving
pyridinium dichromate in approtic media. Tetrahedron Lett. 1979, 20, 399.
0
1
1
0. Guziec, F. S.; Luzzio, F. A. The oxidation of alcohols using 2,2 -bipyridinium
chlorochromate. Synthesis 1980, 691.
1. Bhattacharjee, M. N.; Chaudhuri, M. K.; Dasgupta, H. S.; Roy, N.; Khathing, D. T.
Bipyridinium fluorochromate; a new and efficient oxidant for organic substrates.
Synthesis 1982, 588.
1
1
2. Santeniello, E.; Milani, F.; Casati, R. Tetrabutylamonium chlorochromate, a new,
mild and selective oxidizing agent. Synthesis 1983, 749.
3. Rajkumar, G. A.; Arabindoo, B.; Murugesan, V. Quinolinium fluorochromate
(
QFC) supported on alumina as a selective oxidant for alcohols. Synth.
Commun. 1999, 29, 2105.
1
4. Tajbakhsh, M.; Ghaemi, M.; Sarabi, M.; Ghassemzadeh, M.; Heravi, M. M.
N-methyl piperidinium chlorochromate adsorbed on alumina: A new and
selective reagent for the oxidation of benzylic alcohols to their corresponding
carbonyl compounds. Monatsh. Chem. 2000, 131, 1213.
1
1
5. Mahjoub, A. R.; Ghammami, Sh.; Kassaee, M. Z. Tetramethylammonium fluoro-
chromate(VI): A new and efficient oxidant for organic substrates. Tetrahedron
Lett. 2003, 44, 4555.
6. (a) Tajbakhsh, M.; Hosseinzadeh, R.; Yazdani-Niaki, M. Synthesis and application
of 2,6-dicarboxypyridinium chlorochromate as a new oxidizing reagent for
alcohols, silyl ethers, and THP ethers under mild and non-aqueous conditions.
J. Chem. Research, Synop. 2002, 10, 508; (b) Tajbakhsh, M.; Hosseinzadeh, R.;
Yazdani-Niaki, M. 2,6-Dicarboxypyridinium chlorochromate: A mild, efficient,
and selective reagent for oxidative deprotection of oximes to carbonyl
compounds. Tetrahedron Lett. 2002, 43, 9413.
17. Bora, U.; Chaudhuri, M. K.; Dey, D.; Kalita, D.; Kharmawphlang, W.;
Mandal, G. C. 3,5-Dimethylpyrazolium fluorochromate (VI), C
DmpzHFC): A convenient new reagent for oxidation of organic substrates. Tetra-
hedron 2001, 57, 2445.
8. Hashemi, M. M.; Ghazanfari, D.; Akhbari, M. Oxidation of alcohols with
5 8 2 3
H N H[CrO F],
(
1
4-aminopyridinium chlorochromate supported on silica gel. Monatsh. Chem.
2004, 135, 793.
1
2
9. Lou, J. D.; Xu, Z. N. Solvent free oxidation of alcohols with manganes dioxide.
Tetrahedron Lett. 2002, 43, 6149.
0. Bhar, S.; Chaudhuri, S. K. Remarkable reactivity of pyridinium chlorochromate
adsorbed on neutral alumina under solvent-free conditions. Tetrahedron 2003,
59, 3493.