KMnO4/guanidinium-based sulfonic acid: as an efficient Br?nsted acid organocatalyst for the selective oxidation of organic compounds

Article abstract of DOI:10.1080/17415993.2017.1359270

KMnO₄/guanidinium-based sulfonic acid as a green organocatalytic oxidative system can be used effectively for the selective oxidation of organic compounds in n-hexane as a nonpolar and inert solvent at room temperature in good yields. The use of this approach is described for the oxidation of alkyl arenes, alcohols, and sulfides.

Full text of DOI:10.1080/17415993.2017.1359270

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
KMnO /guanidinium-based sulfonic acid: as an
4
efficient Brønsted acid organocatalyst for the
selective oxidation of organic compounds
Ahmad Shaabani, Azadeh Tavousi Tabatabaei, Fatemeh Hajishaabanha,
Shabnam Shaabani, Mozhdeh Seyyedhamzeh & Mina Keramati nejad
To cite this article: Ahmad Shaabani, Azadeh Tavousi Tabatabaei, Fatemeh Hajishaabanha,
Shabnam Shaabani, Mozhdeh Seyyedhamzeh & Mina Keramati nejad (2018): KMnO /guanidinium-
4
based sulfonic acid: as an efficient Brønsted acid organocatalyst for the selective oxidation of
organic compounds, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2017.1359270
To link to this article: https://doi.org/10.1080/17415993.2017.1359270
Published online: 30 May 2018.
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JOURNAL OF SULFUR CHEMISTRY, 2017
https://doi.org/10.1080/17415993.2017.1359270
KMnO /guanidinium-based sulfonic acid: as an efficient
4
Brønsted acid organocatalyst for the selective oxidation
of organic compounds
Ahmad Shaabani, Azadeh Tavousi Tabatabaei, Fatemeh Hajishaabanha, Shabnam
Shaabani, Mozhdeh Seyyedhamzeh and Mina Keramati nejad
Faculty of Chemistry, Shahid Beheshti University, Tehran, Iran
ABSTRACT
ARTICLE HISTORY
KMnO4/guanidinium-based sulfonic acid as a green organocatalytic
oxidative system can be used effectively for the selective oxidation
of organic compounds in n-hexane as a nonpolar and inert solvent
at room temperature in good yields. The use of this approach is
described for the oxidation of alkyl arenes, alcohols, and sulfides.
Received 10 March 2017
Accepted 20 July 2017
KEYWORDS
1
,1,3,3-Tetramethylguanidine
sulfonic acid; organocatalyst;
oxidation reaction;
potassium permanganate
CONTACT Ahmad Shaabani
a-shaabani@sbu.ac.ir
Faculty of Chemistry, Shahid Beheshti University, G. C., P. O.
Box 19396-4716, Tehran, Iran
©
2017 Informa UK Limited, trading as Taylor & Francis Group

2
A. SHAABANI ET AL.
1. Introduction
Oxidation reactions are among the most important and widely used reactions for the syn-
thesis of complex organic compounds. The selective oxidation of organic substrates is one
of the most challenging reactions on both the laboratory and industry scale. As a con-
sequence, a large number of oxidants have been developed by researchers for specific
purposes. Among them, permanganate, as a green, versatile and commercially available
reagent, is widely used for the oxidation of organic compounds. The use of permanganate as
an effective and well-known oxidant in organic chemistry has a long and extensive history.
Industrial applications that consume thousands of tons of potassium permanganate annu-
ally are now being carried out without adverse environmental effect. The use of recycling
technology has made these processes environmentally friendly and sustainable because
manganese dioxide, as a co-product, is produced by the reduction of permanganate, can
be easily recycled [1–4].
Guanidines and their corresponding guanidinium salts, due to the widespread use
as strong and weak Brønsted base catalysts in useful chemical transformations, have
been known to chemists for over 150 years [5]. Recently, a number of excellent reviews
have been published on guanidine organocatalysis because of their excellent thermal and
chemical stabilities owing to their special structures [6–12]. Due to the wealth of func-
tionality present in the guanidine, very recently, we synthesized, characterized and applied
guanidinium-based sulfonic acid (GSA) as a Brønsted acid organocatalyst for the first time
in the synthesis of organic compounds in aqueous medium [13].
Accordingly, the incorporation of potassium permanganate with GSA as a Brøn-
sted acid organocatalyst can create an efficient organocatalytic oxidative system that can
have sufficient properties. As a part of our ongoing research program related to devel-
oping new methods for the oxidation of organic compounds [3,14,15], and based on
our previous investigations on KMnO as a green oxidant [16–19], herein we report
4
KMnO /guanidinium-based sulfonic acid as an efficient, green, and recyclable acidic
4
organocatalyst oxidant system for selective oxidative transformations of alkyl arenes, alco-
hols, and sulfides into the corresponding carbonyl compounds and sulfoxides in n-hexane
at room temperature.
2. Materials and methods
2.1. General
All reagents were obtained from Aldrich or Merck and used without further purifica-
tion. Melting points were measured on an Electrothermal 9200 apparatus. FT-IR spectra
were recorded on a Shimadzu IR-470 spectrometer. Products were analyzed using a Varian
3900 GC.
3. Results and discussion
In order to find the best reaction conditions, optimization studies were performed with
the oxidation of indane (3), as a model substrate, in the presence of various amounts of
GSA in various solvents at room temperature. As indicated in Table 1–I, based on these
experiments n-hexane was chosen as a suitable solvent in the presence of 0.02 g of GSA

JOURNAL OF SULFUR CHEMISTRY
3
Table 1. To investigate the effect of solvent (I) and the amount of acidic catalyst (GSA) (II) and KMnO4
III) on the oxidation of indane.
(
(
I)a
d
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
n-Hexane
H2O
CH2Cl2
MeOH
CH3CN
7
24
10
24
24
24
95
Trace
67
Trace
Trace
Trace
Solvent free
aReaction conditions: indane (0.12 g, 1.00 mmol), GSA (0.02 g, 8.6 mol%), KMnO4 (1.00 g, 6.33 mmol), solvent (10 mL), at
room temperature.
d
Yield determined by GC analysis.
(
II)b
d
Entry
GSA (mol%)
Yield (%)
1
2
3
4
–
–
2
11
45
95
4.30
8.60
bReaction conditions: indane (0.12 g, 1.00 mmol), GSA, KMnO4 (1.00 g, 6.33 mmol),
n-hexane (10 mL), at room temperature, time (7 h).
Yield determined by GC analysis.
d
(
III)c
KMnO4
Number of equivalent
d
Entry
(g)
Yield (%)
1
2
3
4
5
6
0.30
0.60
0.70
0.80
0.90
1.0
4.74
9.48
11.06
12.64
14.22
15.80
3
20
67
79
88
95
cReaction conditions: indane (0.12 g, 1.0 mmol), GSA (0.02 g, 8.6 mol%), KMnO4, n-hexane (10 mL), at
room temperature, time (7 h).
Yield determined by GC analysis.
d
(
8.6 mol%). Also, different amounts of potassium permanganate were investigated in order
to obtain proper amounts (Table 1, III). As it is clear from Table 1–II, III (Entries 4 and
), the 0.02 g of GSA (8.6 mol%) and 1.0 g of KMnO in n-hexane at room temperature
6
4
provided the best result.
It is important to note that the presence of GSA plays an essential role in oxidation
reaction because the oxidation of indane did not proceed in the absence of GSA after 7 h
(
Table 1–II, Entry 1).

Table 2. Oxidation of various alkyl arenes to corresponding aldehydes and ketonesa
Mp or Bp (°C)
found (reported)
b
Entry
1
Reactant
Product
Time (h)
Yield (%)
Ref.
[22]
7
95
40–42
(42)
2
10
8
90
91
81–83
84)
[18]
[18]
(
2,4-DNP derivative
37–238
239)
2
(
4
9
92
171–173
174)
[18]
(
(
continued)

Table 2. Continued.
Mp or Bp (°C)
found (reported)
b
Entry
Reactant
Product
Time (h)
Yield (%)
Ref.
5
6
7
9
8
87
86
92
174–176
[18]
[23]
[18]
(176)
5–7
(2-7)
10
2,4-DNP derivative
97–199
200)
1
(
8
9
10
3
91
88
23–24
–
2,4-DNP derivative
35–237
[24]
2
(237)vn
10
5
92
212–215
–
a
Reaction conditions: alkyl arene (1.00 mmol), GSA (0.02 g, 8.6 mol%), KMnO4 (1.00 g, 6.33 mmol), n-hexane (10 mL), room temperature.
Yield determined by GC analysis.
b

6
A. SHAABANI ET AL.
Table 3. Toinvestigatetheeffectofsolvent(I)andtheamountofacidiccatalyst
(GSA) (II) and KMnO4 (III) on the oxidation of indanol.
(
I)a
b
Entry
Solvent
Time (h)
Yield (%)
1
2
3
4
5
6
n-Hexane
H2O
CH2Cl2
MeOH
CH3CN
–
3
96
Trace
69
Trace
Trace
Trace
24
10
24
24
24
aReaction conditions: indanol (0.134 g, 1 mmol), GSA (0.02 g, 8.6 mol%), KMnO4 (1.00 g,
.33 mmol), solvent (10 mL), at room temperature.
6
b
Yield determined by GC analysis.
(
II)c
d
Entry
GSA (mol%)
Yield (%)
1
2
3
4
–
–
2.00
4.30
8.60
23
54
96
cReaction conditions: indanol (0.134 g, 1 mmol), GSA, KMnO4
(
1.00 g, 6.33 mmol), n-hexane (10 mL), at room temperature, time
(3 h).
d
Yield determined by GC analysis.
(
III)e
KMnO4
f
Entry
(g)
Number of equivalent
Yield (%)
1
2
3
4
5
6
0.30
0.60
0.70
0.80
0.90
1.00
4.74
9.48
11.06
12.64
14.22
15.80
14
45
60
71
90
96
eReactionconditions:indanol(0.134 g,1 mmol),GSA(0.02 g,8.6 mol%),KMnO4,n-hexane
10 mL), at room temperature, time (3 h).
(
f
Yield determined by GC analysis.
Then, the efficiency of the catalytic system was studied for the oxidation of various alkyl
arenes to the corresponding aldehydes and ketones using GSA and KMnO in n-hexane at
4
room temperature. The obtained results are presented in Table 2.
The oxidation of the alcohols to related carbonyl compounds was studied. In order to
obtain the optimum reaction conditions, indanol (7) has been oxidized in the presence of
various amounts of GSA and KMnO in different organic solvents and water at room tem-
4
perature (Tables 3). As indicated in Table 4, various primary and secondary aliphatic and

Table 4. Selective oxidation of various alcohols to corresponding aldehydes and ketones.a
M. p. or B. p. (°C)
Found (Reported)
b
Entry
1
Reactant
Product
Time (h)
3
Yield (%)
Ref
97
93
2,4-DNP derivative
[18]
235–237 (237)
2
3
4
5
5
4
4
4
2,4-DNP derivative
53–255 (255)
[18]
[18]
–
2
98
94
2,4-DNP derivative
90–191 (191)
1
178–180
100
45–49
[22]
(45–50)
6
4
100
55–56
–
(
continued).

Table 4. Continued.
M. p. or B. p. (°C)
Found (Reported)
b
Entry
Reactant
Product
Time (h)
2
Yield (%)
Ref
7
8
100
98
105–106 (106)
[18]
3
4
2,4-DNP derivative
[18]
[18]
247–249 (250)
9
99
2,4-DNP derivative
86–188
187–189)
1
(
1
0
1
3
4
96
2,4-DNP derivative
55–257 (258)
[18]
[18]
2
1
100
2,4-DNP derivative
38–239 (239)
2
1
2
3
5
5
96
81–83
84)
[18]
(
1
100
95–96
94–96)
[22]
(
(
continued).

Table 4. Continued.
M. p. or B. p. (°C)
Found (Reported)
b
Entry
Reactant
Product
Time (h)
18
Yield (%)
Ref
14
91
2,4-DNP derivative
[18]
160–162 (162)
15
18
87
2,4-DNP derivative
60–163 (163)
[24]
1
1
6
7
17
17
85
86
208–209
–
1
2,4-DNP derivative
[18]
1
1
03–105 (lit.
06)
18
17
83
172–174
–
a
Reaction conditions: alcohol (1.00 mmol), GSA (0.02 g, 8.6 mol%), KMnO4 (1.0 g, 6.33 mmol), n-hexane (10 mL), room temperature.
Yield determined by GC analysis.
b

10
A. SHAABANI ET AL.
Table 5. Selectively oxidation of various sulfides to corresponding sulfoxides.a
Mp or Bp (°C)
Found
(Reported)
b
Entry
Reactant
Product
Time (h) Yield (%)
Ref.
[24]
[25]
1
2
5
2
95
90
32–34
(33–34)
104–102
103–106)
(
3
4
87
25–23
[26,27]
(24.5–25.5)
4
5
5
6
88
85
121–124
[28]
[29]
(123–124)
132–134
133–135)
(
6
7
16
4
93
90
70–74
[24]
[30]
(70.5)
234–236
235–237)
(
aReaction conditions: sulfide (1.00 mmol), GSA (0.02 g, 8.6 mol%), KMnO4 (1.00 g, 6.33 mmol), n-hexane (10 mL), room
temperature.
Yield determined by GC analysis.
b
aromatic alcohols were oxidized selectively to the corresponding aldehydes and ketones in
good to high yields without further oxidation to carboxylic acid product.
To extend the scope of the prepared organocatalytic oxidative system, the oxidation
of the sulfides to the corresponding sulfoxides has been studied under the previous-
mentioned optimized conditions. As indicated in Table 5, the reaction proceeded smoothly
in good to high yields. This procedure was used for the oxidation of sulfides to sulfoxides
without any over oxidation to sulfones.
Recyclability of KMnO /TMG-SO H was examined in the oxidation reaction of
4
3
diphenylmethanol. After carrying out the oxidation reaction of diphenylmethanol, the
reaction mixture was filtered off and KMnO /TMG-SO H was washed with n-hexane, and
4
3
by adding 6.33 mmol KMnO it was reused for subsequent reactions. This procedure was
4

JOURNAL OF SULFUR CHEMISTRY
11
Figure 1. Successive runs by using recoverable KMnO4/TMG-SO3H for oxidation of diphenylmethanol.
Scheme 1. Preparation of catalyst.
performed for four repetitive cycles and no decrease in the reaction yield was observed
(
Figure 1).
Summarizing, the purpose of this protocol was to introduce KMnO /guanidinium-
4
based sulfonic acid as a green organocatalytic oxidative system for the selective oxidation
of a variety of arenes, alcohols, and sulfides in n-hexane as an inert solvent at room tem-
perature. Using KMnO /GSA in the selective oxidation of various primary and secondary
4
alcohols, alkyl arenes, and sulfides has several advantages such as satisfactory yields of
products, easy and quick separation of the products from the oxidant and catalyst, recy-
clability of the catalyst with no loss in its activity, use of an inexpensive and green oxidant,
fast reactions, and mild reaction conditions. The prepared organocatalytic oxidative system
showed high selectivity in the oxidation of the alcohols to the related aldehydes or ketones
and no carboxylic acid was produced. Similar selectivity for the oxidation of alkyl arenes
was also observable, which increases the utility of the organocatalytic oxidative system in
complex systems. In addition, KMnO /guanidinium-based sulfonic acid can be used for
4
the oxidation of sulfides to sulfoxides without any overoxidation to sulfones.
3.1. Experimental
3.1.1. Catalyst preparation
GSA was prepared according to our previously reported method (Scheme 1) [13,20,21].

12
A. SHAABANI ET AL.
3.1.2. Oxidation of alkyl arenes, alcohols, and sulfides; a general procedure
An alkyl arene, alcohol, or sulfide (1.00 mmol) was added to a round-bottomed flask
containing potassium permanganate (6.33 mmol, 1.00 g) and GSA (0.02 g, 8.6 mol%) in
n-hexane (10 mL) with a magnetic stirrer. The reaction mixture was stirred at room tem-
perature for indicated times as given in Tables 2, 4 and 5, respectively, while the progress
of the reaction was followed by thin layer chromatography (TLC). Upon completion, the
reaction mixture was filtered and the filtrate was analyzed by the GC method.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
We gratefully acknowledge financial support from the Iran National Science Foundation (INSF), the
Research Council of Shahid Beheshti University and Catalyst Center of Excellence (CCE) at Shahid
Beheshti University.
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