Efficient selective oxidation of organic substrates using pyridinum sulfonate halochromate under solvent-free conditions and microwave irradiation: Experimental and theoretical study

Article abstract of DOI:10.1080/15533174.2011.615045

A convenient and rapid method has been developed for the selective oxidation of several types of alcohols to related carbonyl compounds under solvent-free conditions. In this study, the authors report the microwave-assisted selective oxidation of alcohols and a number of organic compounds with pyridinum sulfonate chlorochromate (PSCC) and pyridinum sulfonate fluorochromate (PSFC). The density functional theory calculations were made at B3LYP/6-31G* levels of theory and thermodynamic data supported the proposed mechanism involving formation of a halochromate ester, which showed that PSFC should be a more capable oxidant than PSCC. The oxidation products are easily obtained in short reaction time with good yields.

Full text of DOI:10.1080/15533174.2011.615045

This article was downloaded by: [McGill University Library]
On: 14 October 2014, At: 09:36
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,
37-41 Mortimer Street, London W1T 3JH, UK
Synthesis and Reactivity in Inorganic, Metal-Organic,
and Nano-Metal Chemistry
Publication details, including instructions for authors and subscription information:
http://www.tandfonline.com/loi/lsrt20
Efficient Selective Oxidation of Organic Substrates
Using Pyridinum Sulfonate Halochromate Under
Solvent-Free Conditions and Microwave Irradiation:
Experimental and Theoretical Study
Ahmad R. Bekhradnia a & Sattar Arshadi b
a Pharmaceutical Sciences Research Center, Department of Medicinal Chemistry ,
Mazandaran University of Medical Sciences , Sari , I. R. Iran
b Department of Chemistry , Payame Noor University of Iran , Sari , I. R. Iran
Accepted author version posted online: 27 Mar 2012.Published online: 04 Jun 2012.
To cite this article: Ahmad R. Bekhradnia & Sattar Arshadi (2012) Efficient Selective Oxidation of Organic Substrates Using
Pyridinum Sulfonate Halochromate Under Solvent-Free Conditions and Microwave Irradiation: Experimental and Theoretical
Study, Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:5, 705-710
To link to this article: http://dx.doi.org/10.1080/15533174.2011.615045
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained
in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the
Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and
should be independently verified with primary sources of information. Taylor and Francis shall not be liable for
any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever
or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of
the Content.
This article may be used for research, teaching, and private study purposes. Any substantial or systematic
reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any
form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://
www.tandfonline.com/page/terms-and-conditions

Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 42:705–710, 2012
Copyright ꢀ Taylor & Francis Group, LLC
C
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2011.615045
Efficient Selective Oxidation of Organic Substrates Using
Pyridinum Sulfonate Halochromate Under Solvent-Free
Conditions and Microwave Irradiation: Experimental and
Theoretical Study
Ahmad R. Bekhradnia1 and Sattar Arshadi2
1Pharmaceutical Sciences Research Center, Department of Medicinal Chemistry, Mazandaran University
of Medical Sciences, Sari, I. R. Iran
2Department of Chemistry, Payame Noor University of Iran, Sari, I. R. Iran
mate,[7] 2,2’-bipyridinium chlorochromate,[8] pyridinum fluo-
rochromate (VI),[9] and Collins reagent.[10]
A convenient and rapid method has been developed for the se-
lective oxidation of several types of alcohols to related carbonyl
compounds under solvent-free conditions. In this study, the au-
thors report the microwave-assisted selective oxidation of alcohols
and a number of organic compounds with pyridinum sulfonate
chlorochromate (PSCC) and pyridinum sulfonate fluorochromate
(PSFC). The density functional theory calculations were made
at B3LYP/6–31G∗ levels of theory and thermodynamic data sup-
ported the proposed mechanism involving formation of a halochro-
mate ester, which showed that PSFC should be a more capable
oxidant than PSCC. The oxidation products are easily obtained in
short reaction time with good yields.
However, many important problems can occur during the ox-
idation process. Avoiding overoxidation, we have reported the
reasonable and chemoselective oxidizing agents for the oxida-
tion of alcohols and bioorganic substrates.[11,12] Nevertheless,
the troublesome problem of oxidation with pyridinum sulfonate
chlorochromate (PSCC) and pyridinum sulfonate fluorochro-
mate (PSFC) was that organic solvent should be separated from
the related carbonyl compound after the oxidation. Moreover,
the high reaction time was attained when these reagents were
employed. Therefore, we are going to report the microwave-
assisted oxidation under solvent-free conditions with PSCC and
PSFC. The use of microwave ovens for carrying out organic
synthesis has attracted the attention of scientists over the last
decades, which is due to the shorter reaction time, pure reac-
tions, higher yields, superior selectivity, and lack of organic
solvents in the reaction processes.[13–16] Herein, we wish to re-
port an efficient procedure for the oxidation of the considered
substrates with microwave and propose a mechanism which
is supported by DFT calculation using the Gaussian 98 pack-
age.[17] Thermodynamic data were calculated at B3LYP/6–31G∗
levels of theory for PSFC and PSCC. These data included the
sum of electronic and thermal energies (E), bond angles, bond
distances, and Mulliken charges, which were obtained by the
frequency option of Gaussian 98 program (Table 1).
Keywords DFT calculations, oxidation mechanism, pyridinum sul-
fonate halochromate, selective oxidation, solvent-free
conditions
INTRODUCTION
Over recent years, it has been an essential and challeng-
ing issue to develop an efficient method for selective oxida-
tion of alcohols to the corresponding carbonyl compounds.
To date, several general oxidations of alcohols have been re-
ported, and the most classical oxidant among of them is hex-
avalent chromium.[1–5] Some of the most common oxidizing
reagents are pyridinium chlorochromate,[6] pyridinum dichro-
EXPERIMENTAL
Received 13 August 2011; accepted 13 August 2011.
The authors are pleased to acknowledge financial support from
the Mazandaran University of Medical Sciences, “Professor’s Project
Funds.” The authors wish to express their special thanks to Mrs. N.
Khaki (Mazandaran University of Medical Sciences) for her editorial
cooperation in completing this research.
Address correspondence to Ahmad R. Bekhradnia, Pharmaceuti-
cal Sciences Research Center, Department of Medicinal Chemistry,
Mazandaran University of Medical Sciences, Sari 48175-861, I. R.
Iran. E-mail: reza bnia@yahoo.com
Preparation of the PSFC and PSCC reagents were made with
pyridinium sulfonate fluoride and pyridinium sulfonate chloride
as the starting materials, respectively. These compounds were
prepared by adding fluorosulfonic acid as well as chlorosulfonic
acid to pyridine in chloroform. At the result, the obtained pyri-
dinium sulfonate halides were employed for synthesizing PSFC
and PSCC reagents through the addition of chromium trioxide.
The spectral data and elemental analysis are given subsequently:
705

706
A. R. BEKHRADNIA AND S. ARSHADI
TABLE 1
Energies (E) (kcal/mol) along with the bond lengths, bond angles, and Mulliken charges for PSCC and PSFC, calculated by the
DFT method
-
3
O
X
Cr
N
+
O
2
SO3H
O
1
Entry
X=F
Bond lengths
Å
Bond angles
Degree
Charges
0.802887
Energy (Kcal.mol-1)
1
2
3
4
5
6
7
8
9
Cr-X
1.792
1.614
1.614
1.614
O(3)-Cr-X
O(2)-Cr-X
O(1)-Cr-X
O(3)-Cr-O(2)
O(3)-Cr-O(1)
O(2)-Cr-O(1)
O(3)-Cr-X
O(2)-Cr-X
O(1)-Cr-X
108.23
108.24
108.20
110.68
110.68
110.69
107.76
107.73
107.76
111.11
111.11
111.14
Cr
−258.5
Cr-O(1)
Cr-O(2)
Cr-O(3)
O(1)
O(2)
O(3)
X
−0.443592
−0.444075
−0.444104
−0.471117
X=Cl
Cr-X
2.275
1.610
1.610
1.609
Cr
0.620281
−0.416549
−0.416539
−0.416556
−0.370637
−205.2
Cr-O(1)
Cr-O(2)
Cr-O(3)
O(1)
O(2)
O(3)
X
10
11
12
O(3)-Cr-O(2)
O(3)-Cr-O(1)
O(2)-Cr-O(1)
PSFC: 1H NMR (90 MHz, CH3CN): δ = 8.1 (m, 2H, m-CH), 8.7
(m, 1H, p-CH), 8.9 (m, 2H, o-CH), 13C NMR (22.5 MHz,
CH3CN): δ = 129.5 (2C, m-CH), 148.5 (1C, p-CH),
181.5 (2C, o-CH); IR ν(KBr): 953 (s, Cr-O), 916 (s, Cr-
O), 630 (m, Cr-F), 1150–1250 (s, SO3) 1450–1650 cm−1
(originating due to the pyridinium sulfonate cation);
UV(CH3CN): 329–428 (Cr-F), 255 and 288 nm (orig-
inating due to the pyridinium sulfonate cation). Ele-
mental analysis data for the PSFC is the following:
Cr, 17.93%; C, 21.53%; N, 5.07%; H, 1.93%. Anal.
Calcd.: Cr, 17.65%; F, 6.81%; C, 21.50%; N, 5.01%;
H, 2.15%.
1.88%. Anal. Calcd.: Cr, 17.65%; C, 20.38%; N, 4.75%;
H, 1.83%.
General Procedure for the Application of PSFC and PSCC
in Solvent-Free Conditions as the Oxidizing Agents
The solid organic substrates were added in a mortar until
they became homogeneous by the addition of oxidant with the
molar ratios of 1:1.1 (entries 1–19) to 1:5 (entries 20–21). The
reaction mixture was placed in a 100 mL, three-necked, round-
bottomed flask, completed with Teflon-coated magnetic stirring
bar and fiber-optic temperature sensor; the magnetic stirrer was
set at 80% of the maximum speed, and the reaction mixture
was treated for the time indicated in Table 2 at 300/500 W.
The completion of the reaction oxidations was scrutinized by
UV-vis spectrometer. After the completion of the reaction, the
extent of the oxidation was determined with proton nuclear
magnetic resonance (1H NMR) (Table 2). The spectral data of
products, 1H-NMR (90 MHz, CDCl3, δ/ppm); 13C NMR (22.5
MHz, CDCl3, δ/ppm) are the following:
1
PSCC: H NMR (90 MHz, CH3CN): δ = 7.9 (m, 2H, m-CH),
8.4 (m, 1H, p-CH), 8.6 (m, 2H, o-CH), 13C NMR (22.5
MHz, CH3CN): δ = 125.3 (2C, m-CH), 139.2 (1C,
p-CH), 176.9 (2C, o-CH); IR ν(KBr): 958 (s, Cr-O),
924 (s, Cr-O), 610 (m, Cr-Cl), 1120–1250 (s, SO3)
1420–1630 cm−1 (originating due to the pyridinium
sulfonate cation); UV(CH3CN): 350–400 (Cr-Cl), 256
and 260 nm (originating due to the pyridinium sul-
fonate cation). Elemental analysis data for the PSCC
is the following: Cr, 17.60%; C, 20.46%; N, 4.80%; H,
Product (1): 1H-NMR: 7.6 (m, 2H, m-CH), 7.8 (m, 2H, o-CH),
9.8 (s, 1H, -CHO); 13C-NMR: 130.1 (C-Br), 132.1 (2C,

SELECTIVE OXIDATION OF ORGANIC SUBSTRATES
707
TABLE 2
Oxidation of organic substrates with PSFC and PSCC under microwave irradiation conditions
Time (sec)
Entry
Compound
PSFC PSCC Substrate: oxidant
Product
Yield
1
2
3
4
5
6
7
8
4-Bromobenzyl alcohol
4-Methylbenzyl alcohol
Ethyl alcohol
4-Methoxybenzyl alcohol
Benzyl alcohol
1-Pentanol
2,6-Dimethylcyclohexanol
Methanol
2-Methyl-1-propanol
Cyclohexanol
1-Butanol
Allyl alcohol
3-Chloro-2-butene-1-ol
Furfuryl alcohol
30
15
30
10
15
35
40
35
35
35
45
25
40
35
35
30
20
100
80
400
400
40
15
40
15
15
45
55
50
55
45
60
30
50
50
55
30
40
100
80
400
400
1:1.1
1:1.1
1:1.4
1:1.1
1:1.1
1:1.4
1:1.3
1:1.4
1:1.4
1:1.4
1:1.4
1:1.1
1:1.2
1:1.2
1:1.3
1:1.2
1:1.3
1:1.2
1:1.5
1:5
4-Bromobenzaldehyde
4-Methylbenzaldehyde
Acetaldehyde
4-Methoxybenzaldehyde
Benzaldehyde
1-Pentanal
2,6-Dimethylcyclohexanone
Formaldehyde
2-Methylpropanal
Cyclohexanone
1-Butanal
Acrolein
3-Chloro-2-butenal
Furfural
80%
86%
89%
96%
95%
86%
77%
84%
89%
80%
89%
95%
76%
81%
80%
84%
80%
81%
9
10
11
12
13
14
15
16
17
18
19
20
21
Ethylene glycol
Cinnamyl alcohol
Anthracene
Glyoxal
Cinnamaldehyde
Anthraquinone
9,10-Phenanthrenequinone
1, 8-Dihydroxy- 9, 10-antracenedione 88%
Phenanthrene
1,8-Dihyroxy-9(10H) anthracenones
Cholest-5-en-3-ol benzoate
Cholest-5-en-3-ol acetate
7-Keto-cholest-5-en-3-ol benzoate
7-Keto-cholest-5-en-3-ol acetate
82%
87%
1:5
Product (9): 1H-NMR: 1.0 (d, 6H, -CH3), 2.3 (m, 1H, -CH), 9.2
(s, 1H, CHO); 13C-NMR: 13.4 (2C,-CH3), 39.4(1C,-
CH), 199.2 (1C, -CHO).
m-CH), 131.2 (2C, o-CH), 134.8 (1C,C-CHO), 185.7
(-CHO).
1
Product (2): H-NMR: 2.4 (s, 3H, -OCH3), 7.5 (m, 2H, m-
CH), 7.8 (m, 2H, 0-CH), 9.8 (s, 1H, -CHO); 13C-NMR:
22.9 (-CH3) 128.1 (4C, -CH), 134.9 (1C,C-CHO), 145.1
(1C CH3), 189.2 (-CHO).
Product (10): 1H-NMR: 1.5–1.8 (10H, CH2); 13C-NMR: 21.3
(1C, CH2), 26.1(2C, CH2), 39.6 (2C,-CH), 201.5
(1C, C O).
Product (3): 1H-NMR: 2.3 (s, 3H, -CH3), 9.4
(s, 1H, -CHO); 13C-NMR: 32.1 (1C CH3)
197.2 (1C–CHO).
Product (11): 1H-NMR: 1.0 (t, 3H, CH3), 1.5 (m, 2H, CH2),
2.2 (t, 2H, CH2), 9.2 (s,1H,-CHO); 13C-NMR: 13.4
(1C, CH3), 14.5(1C, CH2), 43.7(1C, CH2), 196.4
(1C, -CHO).
Product (4): 1H-NMR: 3.8 (s, 3H, -OCH3), 6.8 (m, 2H, m-CH),
7.8 (m, 2H, 0-CH), 9.8 (s, 1H, -CHO); 13C-NMR: 58.9
(-OCH3) 116.1 (2C, m-CH), 129.2 (1C,C-CHO), 131.2
(2C, o-CH), 165.1 (C-O CH3), 186.2 (-CHO).
1
Product (12): H-NMR: 5.9 (dd, 1H, CH2), 6.2 (m, 1H,
CH2), 6.3 (dd, 1H, -CH), 9.1 (s,-CHO); 13C-NMR:
23.8 (1C, CH3), 129.5 (1C, CH2), 133.6 (1C,-CH),
190.5 (1C, C O).
Product (5): 1H-NMR: 7.4–7.9 (m, 5H, -ph), 9.8 (s, 1H, -CHO);
13C-NMR: 128.5–137.5 (5c-ph), 189.9 (-CHO).
Product (13): 1H-NMR: 2.3 (s, 3H, CH3), 6.0 (s, 1H, -CHCl),
9.3 (s, 1H, -CHO); 13C-NMR: 24.3 (1C, CH3), 128.5
(1C, = CH), 149.2 (1C, = CCl), 181.2 (1C, -CHO).
Product (14): 1H-NMR: 6.2 (dd, 1H, = CH), 6.8 (d, 1H, = CH),
7.2 (d, 1H, = CH), 9.2 (s, CHO); 13C-NMR: 109.3 (1C,
= CH), 118.1 (1C, = CH), 141.1 (1C, = CH), 149.4
(1C, = C-O), 171.2 (1C, -CHO).
1
Product (6): H-NMR: 0.9 (t, 3H, -CH3), 1.3–1.5 (m, 4H,
CH2), 2.3 (t, 2H, CH2), 9.0 (s, 1H, -CHO); 13C-
NMR:14.9 (1C-CH3), 23.1 (1C-CH2), 24.2 (1C-CH2),
44.1 (1C-CH2), 199.6 (-CHO).
Product (7): 1H-NMR: 1.2 (d, 6H, -CH3), 1.6 (m, 6H, CH2),
2.2 (m, 2H, CH); 13C-NMR: 17.8 (6C-CH3), 21.1 (1C-
CH2), 33.3 (2C-CH2), 42.1 (2C-CH), 209.9 ( C O).
Product (8): 1H-NMR: 9.2; 13C-NMR: 182.1.
1
Product (15): H-NMR: 9.6 (s, 2H, -CHO); 13C-NMR: 180.5
(2C,-CHO).

708
A. R. BEKHRADNIA AND S. ARSHADI
1
C
Product (16): H-NMR: 6.3 (d, 1H, = CH), 7.0–7.2 (5H, Ar-
H), 7.4 (d, 1H, = CH), 9.1 (s, 1H, -CHO); 13C-NMR:
123.9–130.1 (Ar-CH), 128.9 (1C, = CH), 149.1 (1C, =
CH), 189.2 (1C, CHO).
50
1) CHCl3
2) CrO3
,
X-SO3H
+
I)
N+
[XCrO3]
N
SO3H
(i)
Product (17): 1H-NMR: 7.7–8.1 (Ar = CH); 13C-NMR: 122.9
and 132.1 (Ar-CH), 131.1 (Ar-C), 181.1 (2C, C O).
X= Cl, F
1
Product (18): H-NMR: 7.1 (m, 2H, Ar-H), 7.3 (m,2H, Ar-
H), 7.6 (m, 2H, Ar-H), 7.9 (m, 2H, Ar-H); 13C-NMR:
121.2 (2C, Ar-CH), 124.9 (2C, Ar-C), 126.1 (2C, Ar-
CH), 129.2 (2C, Ar-CH), 130.3 (2C, Ar-C), 133.1 (2C,
Ar-CH), 178.1 (2C, C O).
R
R
(i),
OH
O
II)
Microwave irradiation
'
'
R
R
1
Product (19): H-NMR: 7.1 (dd, 2H, Ar-H), 7.5 (dd,2H, Ar-
H), 7.6 (dd, 2H, Ar-H), 11.5 (2H, Ar-OH); 13C-NMR:
114.2 (2C, Ar-C), 117.6 (2C, Ar-CH), 121.3 (2C, Ar-
CH), 130.8 (2C, Ar-C), 134.9 (2C,Ar-CH), 157.8 (2C,
Ar-CHOH), 177.1 (Ar-CO), 186.3 (Ar-CO).
R, R'=H or alkyl
SCH. 1.
1
Product (20): H-NMR: 1.8 (dd, 1H, HC-CO-), 2.1 (m, 2H,
The synthesis of reagents PSFC and PSCC were accom-
CH2), 2.3 (d, 2H, CH2), 3.9(m, 1H, CH O ), 5.3
(s, CH = C), 7.5–8.1 (5H, Ar-H); 13C-NMR: 32.1 (1C,
CH2), 43.2 (1C, CH2), 73.4 (1C, CH O), 126.7
(1C, = CH-), 162.3 (1C, C ), 200.4 ( O CO ben-
zoate), 167.9 (C O).
plished, as before.[11,12] First, pyridinium sulfonate fluoride and
pyridinium sulfonate chloride were prepared by adding fluoro-
sulfonic acid and chlorosulfonic acid to pyridine in chloroform,
respectively. Consequently, these prepared compounds were
employed for synthesizing PSFC and PSCC reagents through
addition of chrome trioxide (CrO3) (Scheme 1).
1
Product (21): H-NMR: 1.6 (dd, 1H, HC-CO-), 1.8 (m, 2H,
CH2), 2.0 (s, 3H, CO CH3), 2.2 (d, 2H, CH2),
4.5 (m, 1H, CH O ), 5.8 (s, CH = C); 13C-NMR:
21.2 (1C, O-CH3 Acetyl), 27.3 (1C, CH2), 37.3 (1C,
CH2), 70.8 (1C, CH O), 125.9 (1C, = CH-), 161.1
(1C, C ), 171.4 ( O CO Acetyl), 191.2 (C O).
To scrutinize reaction conditions, several alcohols and other
bio-organic compounds were employed and oxidized under mi-
crowave irradiation. The aptitude of a specific substance to con-
vert electromagnetic energy into heat is known as loss tangent,
tan δ. A reaction with a high tan δ is required for efficient absorp-
tion and consequently rapid heating. However, the compounds
with high dielectric constant cannot necessarily have high tan δ
values. Actually, alcohols and most of organic compounds have
a considerably lower dielectric constant, but heat much rapidly
in a microwave field due to their high tan δ. All used compounds
as substrates had high tan δ microwave-absorbing.[18]
Different alcohols and bioorganic compounds, with high tan
δ, in various conditions were investigated until we obtained good
isolated yields of related products (Table 2). The substrate: ox-
idant molar ratios of 1:1.1 to 1:1.5 for entries 1–19 as well
as 1:5 for entries 20–21 were employed. Microwave-assisted
Geometry optimizations were performed in Pharmaceutical
Sciences Research Center, Sari, using the Gaussian 98 system
of programs.[17] To assess the performance of this approach,
the compounds were computed at higher theoretical levels, in a
way that HF/STO-3G outputs were used as inputs for the HF/
6–31G∗. Also, HF/6–31G∗ outputs were used as inputs for the
B3LYP/6–31G∗. The latter method was preferred because it was
less common to find any significant spin contamination in DFT
calculations.
RESULTS AND DISCUSSION
All microwave irradiation reactions were carried out on a oxidation of primary, secondary, allylic, and benzylic alcohols
Milestone Micro-SYNTH apparatus (Mazandaran University resulted in a better yield compared with solvent conditions (en-
of Medical Sciences). Internal temperatures were measured tries 1–13 in Table 2). Microwave irradiation also permitted a
with fiber-optic sensor in conjunction with Milestone immer- shorter reaction time for both PSCC and PSFC. Moreover, vari-
sion well.
ous biological compounds can be prepared by this method. For
1H spectra and 13C NMR were recorded using a JEOL JNM- example, cholest-5-en-3-ol acetate and cholest-5-en-3-ol ben-
EX90A spectrometer (Tarbiat Modares University). Chemical zoate were chemoselectively oxidized at position 7 in solvent-
shifts (δ) are given in ppm relative to TMS. The UV-vis spectra free conditions (entries 20 and 21 in Table 2). For the mentioned
were obtained using a Perkin-Elmer lambda-EZ 201 spectrome- bioorganic compounds, the reaction time of microwave-assisted
ter (Mazandaran University of Medical Sciences). Melting point oxidation for both PSFC and PSCC was much shorter than that
was measured in open capillary tubes with an Electrothermal- of solvent conditions and also both led to good yields. These
9200 melting point apparatus (Mazandaran University of Med- derivatives are found in mammal tissues and are known in cell
ical Sciences).
replication process.[19,20]

SELECTIVE OXIDATION OF ORGANIC SUBSTRATES
709
(Cr–Cl) in PSCC reagents. These absorption bands are related to
ligand-to-metal charge transfer (LMCT) with highly intense and
lie in the ultraviolet or visible portion of the spectrum. LMCT
complex arises from transfer of electrons from molecular orbital
of oxygen, as ligand-like character, to that chromium as metal-
like character. This type of transfer is done if the chromium has
low-lying empty orbitals. The PSCC and PSFC reagents have
chromium in high oxidation state, Cr (VI). After the comple-
tion of the oxidation reaction, the chromium was reduced to
Cr (IV) as residue product, which was a complex compound
of Cr (IV), C5H5NSO3H [CrO2F].[11] Apparently, the transition
energies correlated with the order of oxidation number. There-
fore, the chromium molecular orbital energy increased with the
progress of oxidation reaction and LMCT spectral band position
in the absorption shifted to a shorter wavelength (hypsochromic
shift). Thus, the UV-vis spectroscopy is an efficient method
for evaluation of progress of oxidation reaction in solvent-free
conditions.
X
R
R
H
O
N
O
OH
+
Cr
O
SO3H
'
R
O
X
-H2O
O
+
N
O
-
N
+[CrO2X]
SO3H
R'
Cr
R
R'
H
SO3H
OH
O
X=F,Cl
SCH. 2. The proposed oxidation mechanism by PSCC and PSFC supported
by the DFT method.
In addition to what is mentioned, 1,8-dihyroxy-9(10H) an-
thracenones derivatives with blocked position 10 are known
as compounds having substantial therapeutic activity and
minimal inflammatory effect.[21] In solvent-free conditions,
1,8-dihydroxy-9,10-anthracenedione was afforded by PSFC and
PSCC oxidants (1:1.5, substrate:oxidant) in excellent yield and
short reaction time (entry 19, Table 2).
Analysis of brown residue remaining after the oxidation re-
action was accomplished by the procedure reported in a previ-
ous paper.[12] The magnetic susceptibility was measured to the
amount of 2.88 BM at room temperature. Thus, the oxidation
level of the metal was 3.8–4.1. This confirmed that the isolated
solid product was C5H5NSO3H [CrO2X], where X=F, Cl.
Based on the oxidation level of the residue, the proposed
mechanism can be involved in the formation of a halochromate
ester that leads to a conversion in the following step to the related
carbonyl compounds (Scheme 2).
The theoretical study of the PSFC and PSCC structures were
performed by DFT method (Table 1). The Mulliken charge of
chromium atom in PSFC (entry 1, Table 1) was more than that of
PSCC (entry 7, Table 1). Therefore, these calculations support
our proposed mechanism (Scheme 2) and show the chromium
atom of PSFC is more capable oxidant than that of PSCC.
Thus, the fluorine atom in PSFC contributes to oxygen
transfer oxidations more rapidly than chlorine atom in PSCC
reagent. Hence, the proposed intermediate halochromate an-
ion is easily converted to Cr(IV) species. Moreover, the reac-
tion time of oxidations with PSFC is much shorter than that
of PSCC oxidant for similar substrates and it results in better
yields.
Noticeably, due to reaction conditions, the completion of re-
action could not be evaluated with thin layer chromatography
(TLC). The application of TLC solvents may result in the com-
plication in oxidation products and circumstances. To avoid such
complications, the progress of the reaction was investigated by
UV-vis spectrometer. The maximum absorbance was found at λ
= 329–430 nm for (Cr–F) in PSFC and at λ = 250–400 nm for
CONCLUSIONS
The advantages in the use of this method are shorter reac-
tion time, higher yields, economical technology, lack of solvent
use, and waste generation. Moreover, the oxidation of these
compounds is performed devoid of overoxidation during the re-
action process. A variety of functionalities are investigated in
these solvent-free conditions and the selective products have
been obtained in excellent overall yields. This procedure pro-
vides an ideal synthetic approach for carbonyl and some biolog-
ical compounds. Furthermore, on the basis of our DFT calcu-
lations and proposed oxidation mechanism, PSFC is suggested
to be a more capable oxidant reagent than PSCC. However,
due to the limited capacity of our current microwave equip-
ment, these reactions have not been carried out on a larger
scale. However, it was supposed that the present method should
be simply extended to large-scale syntheses when appropri-
ate microwave apparatus and efficient separation method are
used.
REFERENCES
1. Freeman, F. In Organic Synthesis by Oxidation with Metal Compounds;
Plenum Press: New York, 1986; p. 68.
2. Regen, S.; Koteel, C. J. Am. Chem. Soc. 1977, 99, 3837.
3. Tang, J.; Zhu, J.; Shen, Z.; Zhang, Y. Tetrahedron Lett. 2007, 48, 1919.
4. Ley, S. V.; Madin, A. In Comprehensive Organic Synthesis; eds. B. M.
Trost, I. Fleming; Pergamon Press: London, 1991; Vol. 7, pp. 251–289.
5. Meenakshisundaram, S.; Markkandan, R. Trans. Met. Chem. 2004, 29, 136.
6. Corey, E.; Suggs, J. Tetrahedron Lett. 1975, 16, 2647.
7. Corey, E.; Schmidt, G. Tetrahedron Lett. 1979, 20, 399.
8. Guziece, F.; Luzzio, F. Synthesis 1980, 691.
9. Bhattacherjee, M.; Chaudhuri, M.; Purkayastha, S. Tetrahedron 1987, 43,
538.
10. Collins, J.; Hes, W.; Frank, F. Tetrahedron Lett. 1968, 9, 3363.
11. Bekhradnia, A .R.; Zahir, F.; Arshadi, S. Monatsh Chem. 2008, 139, 521.
12. Kassaee, M. Z.; Bekhradnia, A. R. Phosphorus Sulfur 2004, 179, 2025.

710
A. R. BEKHRADNIA AND S. ARSHADI
Raghavachari, K.; Foresman, J.B.; Cioslawski, J.; Oritz, J.V.; Stlefanov,
13. Dallinger, D.; Kappe, C. Chem. Rev. 2007, 107, 2563.
14. Kappe, C. Angew. Chem. Int. Ed. 2004, 43, 6250.
15. Stadler, A.; Pichler, S.; Horeis, G.; Kappe, C. Tetrahedron 2002, 58, 3177.
16. Kidwai, M. Pure App. Chem. 2001, 73, 147.
B.B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Comperts, R.;
Martin, R.L.; Fox, P.J.; Keith, T.; Al-laham, M.A.; Peng, C.Y.; Akkara,
A.N.; Gonzales, C. G.; Combe, M.C.; Gill, P.M.W.; Johnson, B.; Chem,
W.; Wong, M.W.; Andres, J.L.; Gonzales, C.; Head-Gordon, M.; Replogle,
E.S.; Pople, J.A. Gaussian Inc.: Pittsburgh, PA, 1998.
17. (a) Bekhradnia, A. R.; Ebrahimzadeh, M. A.; Hejazi, V.; Gorji, R.; Vessally,
E. Asian J. Chem. 2009, 21, 2110; (b) Bekhradnia, A. R.; Arshadi, S. Chin.
J. Struct. Chem 2011, 30, 906; (c) Arshadi, S.; Bekhradnia, A. R.; Ahmadi,
S.; Karami, A. R.; Pourbeyram, S. Chin. J. Chem. 2011, 29 (7), 1347; (d)
Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.;
Cheeseman, J.R.; Znkrzewski,V.G.; Montgomery, G.A.; Startmann, R.E.;
Burant, J.C.; Dapprich, S.; Millam, J.M.; Daniels, A. D.; Kudin, K.N.;
Strain, M.C.; Farkas, O.; Tomasi, J.; Barone, V.; Cossi, M.; Cammi, R.;
Mennucci, B.; Pamelli, C.; Adamo, G.; Clifford, S.; Ochterski, J.; Petersson,
G.A.; Ayala, P.Y.; Cui, Q.; Morokoma, K.; Malick, D.K.; Rubuck, A. D.;
18. Hayes, B.L. Microwave Synthesis: Chemistry at the speed of light; CEM:
Matthews, NC, 2002.
19. Kassaee, M. Z.; Bekhradnia, A. R. J. Biosci. Bioeng,. 2003, 95, 526; (b)
Schroepfer, G. J. Ann. Rev. Biochem. 1981, 51, 585.
20. Taylor, F.R.; Saucier, S.E.; Shown, E.P.; Parish, E.J.; Kandutsch, A.A. J.
Biol. Chem. 1984, 259, 12382.
21. Wilson, C.O.; Gisvold, O. Textbook of Organic Medicinal and Pharmaceu-
tical Chemistry; New York: Lippincott-Raven, 1998.