Poly(N-bromobenzene-1,3-disulfonylamide), N,N,N′,N′- tetrabromobenzene-1,3-disulfonylamide and DABCO-bromine complex: As novel reagents for the oxidative coupling of thiols to disulfides

Article abstract of DOI:10.1002/jccs.200700114

An efficient method for the oxidative coupling of thiols to their corresponding disulfides by new reagents poly(N-bromobenzene-1,3- disulfonylamide) PBBS, N,N,N′,N′-tetrabromobenzene-1,3- disulfonylamide TBBDA and DABCO-bromine complex is described. The reaction was applicable to a variety of thiols with high chemoselectivity.

Full text of DOI:10.1002/jccs.200700114

Journal of the Chinese Chemical Society, 2007, 54, 791-794
791
Note
Poly(N-bromobenzene-1,3-disulfonylamide),
N,N,N¢,N¢-Tetrabromobenzene-1,3-disulfonylamide and DABCO-bromine
Complex: As Novel Reagents for the Oxidative Coupling of Thiols to
Disulfides
Ramin Ghorbani-Vaghei,* Mohammad Ali Zolfigol,* Nasrin Moshfeghifar,
Nadiya Koukabi and Gholamabbas Chehardoli
Faculty of Chemistry, Bu-Ali Sina University, Hamadan, Iran
An efficient method for the oxidative coupling of thiols to their corresponding disulfides by new re-
agents poly(N-bromobenzene-1,3-disulfonylamide) PBBS, N,N,N¢,N¢-tetrabromobenzene-1,3-disulfo-
nylamide TBBDA and DABCO-bromine complex is described. The reaction was applicable to a variety
of thiols with high chemoselectivity.
Keywords: Oxidation; Thiols; Mercaptans; Disulfides; Oxidative coupling of thiols; PBBS;
TBBDA; DABCO-bromine complex.
INTRODUCTION
oxidation of thiols to disulfides using the new reagents
1
9
20
2
TBBDA, PBBS and DABCO-Br complex (Scheme
The oxidation of thiols to disulfides is an important
transformation in organic synthesis and from a biological
I).
Poly(N-bromobenzene-1,3-disulfonylamide) PBBS,
1
,2
viewpoint. Industrially, they find wide application as vul-
N,N,N¢,N¢-tetrabromobenzene-1,3-disulfonylamide
canizing agents for rubber and elastomers, imparting excel-
3
lent tensile strength. This conversion has been accom-
2
TBBDA and DABCO-Br are relatively inexpensive, sta-
ble and easily handled oxidizing agents in comparision to
most oxidants usually employed for this transformation.
They have also been used for the bromination of aromatic
plished using a variety of reagents such as: pyridinum chlo-
3
rochromate, ammonium persulfate, tetrabutylammonium
4
5
peroxydisulfate, DBDMH, Sm/BiCl
6
7
, FeCl
8
/NaI, and
19
3
3
compounds, but their general applicability in organic syn-
9
benzyltriphenyl phosphonium dichromate. Oxidative cou-
thesis has largely been unexplored.
pling of thiols to disulfides have been also reported via
+
nitrosothiol intermediates in the presence of NO sources
Oxidative coupling of different types of mercaptans
2
was investigated with TBBDA, PBBS and DABCO-Br in
such as: alkyl nitrites, nitrosyl salts, dinitrogen trioxide, di-
nitrogen tetroxide, trichloronitromethane, oxalic acid di-
hydrate, inorganic acidic salts, silica sulfuric acid, silica
chloride and sodium nitrite, metal nitrate, and ionic com-
dichloromethane under mild conditions (Scheme II). Both
aromatic and aliphatic thiols reacted efficiently and the cor-
responding disulfides were isolated in good to excellent
yields.
+
- 10-18
plex of [NO .18-crown-6.H(NO
3
)
2
].
However, most of
The results of oxidation of thiols to disulfides are pre-
sented in Table 1.
the existing methods involve toxic metal ions, high cost,
expensive and unstable reagents, and cumbersome work-
up procedures.
2
Since TBBDA, PBBS and DABCO-Br contain bro-
mine atoms which are attached to nitrogen atoms it is very
+
possible that these reagents release Br in situ which can act
1
9,20
as an electrophilic species.
Therefore, the following
RESULTS AND DISCUSSION
mechanism can be suggested for the conversion of thiols to
6
their corresponding disulfides (Scheme III).
,19-22
Herein, we now report an efficient procedure for the
The advantages of our reagents over common re-
*
Corresponding author. E-mail: ghorbani@basu.ac.ir and zolfi@basu.ac.ir

7
92 J. Chin. Chem. Soc., Vol. 54, No. 3, 2007
Ghorbani-Vaghei et al.
Scheme I
Scheme II
EXPERIMENTAL
General Procedure for Oxidative Coupling of Thiols
with TBBDA (Method A)
2 2
To a solution of benzenethiol (1 mmol) in CH Cl (15
mL) was added N,N,N¢,N¢-tetrabromobenzene-1,3-disulfo-
nylamide (1 mmol). The mixture was stirred for 2 h at r.t.
while the progress of the reaction was monitored by TLC
agents in the oxidation of benzenethiol, 2-naphtalenethiol
and 4-chlorobenzenethiol are shown in Table 2.
It is noteworthy that electronic/or steric variation of
the thiols has no effect on the efficiency of yields. Other ox-
idizable functional groups such as chloro (Entries 7-9), car-
boxyl (Entries 13-15 and 19-21) and methyl group (Entry
(
n-hexane-EtOAc, 4:1). Once the reaction was complete,
the sulfonamide 1 was filtered off under vacuum filtration;
CH Cl was removed under reduced pressure. Recrystal-
2
2
lization (ethanol) afforded pure disulfide in 90% yield.
4
-6) were unchanged during the reaction. Also, oxidation
of aromatic thiols to their corresponding disulfides without
General Procedure for Oxidative Coupling of Thiols
with PBBS (Method B)
1
bromination of aromatic rings demonstrate the chemo-
9
selectivity of this method.
2 2
To a solution of benzenethiol (1 mmol) in CH Cl (15
In conclusion, the oxidation of thiols using PBBS,
mL) was added poly(N-bromobenzene-1,3-disulfonyl-
amide) (0.50 g). The mixture was stirred for 2 h at r.t. while
the progress of the reaction was monitored by TLC (n-hex-
ane-EtOAc, 4:1). Once the reaction was complete, the sul-
2
TBBDA and DABCO-Br under room temperature pro-
vides a simple, mild, general, and environmentally benign
procedure for the high-yielding preparation of disulfides.
Scheme III

Oxidative Coupling of Thiols to Disulfides
J. Chin. Chem. Soc., Vol. 54, No. 3, 2007 793
Table 1. Oxidation of thiols to disulfides with TBBDA (A),
Table 2. Comparison of the yields obtained by our methods with
previously published methods
PBBS (B), DABCO-Br (C)
2
a
Entry
Substrate
Benzenethiol
Method Time (h) Yield (%)
Substrate
Conditions
(n-Bu N )S O
Yields %
5
1
2
3
4
5
6
7
8
9
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
2
2
90
90
98
90
90
92
75
75
92
80
75
95
99
75
30
99
90
83
75
90
61
Benzenethiol
87
4
2
2
8
Benzenethiol
Benzenethiol
PBBS
TBBDA
90
90
98
Benzenethiol
1
Benzenethiol
4-Methylbenzenethiol
4-Methylbenzenethiol
4-Methylbenzenethiol
4-Chlorolbenzenethiol
4-Chlorolbenzenethiol
4-Chlorolbenzenethiol
Benzyl mercaptan
5
Benzenethiol
DABCO-Br2
2
4
3
6
2
6
3
3
48
0.7
7
Benzenethiol
VO(acac)2
92
79
97
93
87
90
99
90
83
82
90
80
90
93
75
75
92
Benzenethiol
Ammonium persulfate
Pyridinum chlorochromate
DBDMH
Benzenethiol
72
1
Benzenethiol
2-Naphtalenethiol
2-Naphtalenethiol
2-Naphtalenethiol
2-Naphtalenethiol
2-Naphtalenethiol
VO(acac)2
1
1
1
1
1
1
1
1
1
1
2
2
a
0
1
2
3
4
5
6
7
8
9
0
1
12
72
1.5
9
DBDMH
Benzyl mercaptan
PBBS
Benzyl mercaptan
TBBDA
3-Mercaptopropionic acid
3-Mercaptopropionic acid
3-Mercaptopropionic acid
2-Naphtalenethiol
DABCO-Br2
5
2
4
3
6
72
2
4-Chlorolbenzenethiol (n-Bu N )S O
4 2 2 8
3
4-Chlorolbenzenethiol VO(acac)2
12
72
1
4-Chlorolbenzenethiol Ammonium persulfate
4-Chlorolbenzenethiol Pyridinum chlorochromate
4-Chlorolbenzenethiol DBDMH
2-Naphtalenethiol
2-Naphtalenethiol
Thiosalicylic acid
18
72
1.2
4-Chlorolbenzenethiol PBBS
Thiosalicylic acid
4-Chlorolbenzenethiol TBBDA
Thiosalicylic acid
4-Chlorolbenzenethiol DABCO-Br2
The oxidation products were characterized by comparison of
their spectral and physical data with authentic samples.
2
. Li, K. W.; Wu, J.; Xing, W.; Simon, J. A. J. Am. Chem. Soc.
996, 118, 7237.
3. Salehi, P.; Farrokhi, A.; Gholizadeh, M. Synth. Commun.
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. Varma, R. S.; Meshram, H. M.; Dahiya, R. Synth. Commun.
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1
fonamide 3 was filtered off under vacuum filtration; CH
2
Cl
2
2
was removed under reduced pressure. Recrystallization
ethanol) afforded pure disulfide in 90% yield.
4
5
6
(
2
. Chen, F.-E.; Lu, Y.-W.; He, Y.-P.; Luo, Y.-F.; Yan, M.-G.
Synth. Commun. 2002, 32, 3487.
General Procedure for Oxidative Coupling of Thiols
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. Khazaei, A.; Zolfigol, M. A.; Rostami, A. Synthesis 2004,
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To a solution of benzenethiol (1 mmol) in CH
2 2
Cl (15
mL) was added DABCO-Br (0.166 mmol). The mixture
2
7. Firouzabadi, H.; Iranpoor, N.; Zolfigol, M. A. Synth.
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was stirred for 1 h at r.t. while the progress of the reaction
was monitored by TLC (n-hexane-EtOAc, 4:1). Once the
reaction was complete, the residue was filtered off under
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1
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