Microwave-assisted synthesis of disulfides

Article abstract of DOI:10.1080/10426507.2010.520174

A new microwave-assisted synthesis methodology for the preparation of substituted disulfide derivatives is presented. 4-Substituted sulfenimides were reacted with 4-substituted thiols under neat (to right doughy consistency) conditions in chloroform, with both microwave heating and conventional methods. The resulting 4-substituted disulfide derivatives were obtained at higher yields and in shorter reaction times with microwave heating. Their chemistry was confirmed by ¹H-NMR, ¹³C-NMR, infrared (IR), and elemental analysis.

Full text of DOI:10.1080/10426507.2010.520174

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Microwave-Assisted Synthesis of
Disulfides
Halil Kutuk a & Nalan Turkoz a
a Ondokuz Mayıs Üniversitesi, Fen-Edebiyat Fakültesi, Kimya Bölümü
, Samsun , Atakum , Turkey
Published online: 04 Aug 2011.
To cite this article: Halil Kutuk & Nalan Turkoz (2011) Microwave-Assisted Synthesis of
Disulfides, Phosphorus, Sulfur, and Silicon and the Related Elements, 186:7, 1515-1522, DOI:
10.1080/10426507.2010.520174
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Phosphorus, Sulfur, and Silicon, 186:1515–1522, 2011
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2010.520174
MICROWAVE-ASSISTED SYNTHESIS OF DISULFIDES
Halil Kutuk and Nalan Turkoz
¨
Ondokuz Mayıs Universitesi, Fen-Edebiyat Faku¨ltesi, Kimya Bo¨lu¨mu¨, Samsun,
Atakum, Turkey
GRAPHICAL ABSTRACT
Abstract A new microwave-assisted synthesis methodology for the preparation of substituted
disulfide derivatives is presented. 4-Substituted sulfenimides were reacted with 4-substituted
thiols under neat (to right doughy consistency) conditions in chloroform, with both microwave
heating and conventional methods. The resulting 4-substituted disulfide derivatives were ob-
tained at higher yields and in shorter reaction times with microwave heating. Their chemistry
was confirmed by 1H-NMR, 13C-NMR, infrared (IR), and elemental analysis.
Keywords Disulfides; microwave; microwave effect; synthesis
INTRODUCTION
The high-speed synthesis of many organic compounds with the assistance of mi-
crowave irradiation has attracted a considerable amount of attention in recent years.1
Microwave-promoted organic reactions, as well as environmentally benign methods, can
accelerate a great number of chemical processes. In particular, reaction times and energy
inputs are reduced in normally long running reactions at high temperatures when com-
pared to conventional conditions,2 which is a comparatively slow and inefficient method
Received 25 June 2010; accepted 23 August 2010.
We thank the Ondokuz Mayis University (Grant No. F-391) for financial support of this work.
¨
Address correspondence to H. Kutuk, Ondokuz Mayıs Universitesi, Fen-Edebiyat Faku¨ltesi, Kimya Bo¨lu¨mu¨,
Samsun, Atakum 55139, Turkey. E-mail: hkutuk@omu.edu.tr
1515

1516
H. KUTUK AND N. TURKOZ
for transferring energy into the system. In contrast, microwave irradiation produces efficient
internal heating by direct coupling of microwave energy with molecules that are present
in the reaction mixture, so the microwave heating technique is slowly moving from labo-
ratory curiosity to an established technique that is widely used in both the academic and
industrial environments. Microwave irradiation frequently leads to dramatically reduced
reaction times, from days and hours down to minutes and seconds; higher yields; and
cleaner reaction profiles and improved reproducibility.3
Recently, manystudies havebeenreportedintheliteratureonmicrowave-assistedsyn-
thesis of N-arylsulfonyl imines,4 N,N-dialkyl-p-alkylphosphonamidic anhydrides,5 bicyclic
thiazolo-pyrimidine and pyrimido-thiazine derivatives,6 and alkyl and arenesulfonamides,7
quinolines using N-bromosulfonamides.8
The previously stated benefits of microwave irradiation have direct application, be-
cause disulfides are important organic sulfide compounds possessing a unique and rich
chemistry in the synthetic and biochemical areas. For example, large disulfide-linked ag-
gregates are prevalent in proteins and many other bioactive molecules.9 Industrially, disul-
fides find wide application as vulcanizing agents for rubbers and elastomers, giving them
excellent tensile strength.10 In the field of human health they have exciting potential. Di-
allyl sulfide (DAS), diallyl disulfide (DADS), and diallyl trisulfide (DATS), which are the
major organosulfide compounds (OSCs) of garlic, have been shown to inhibit chemically
induced cancers of the skin, fore-stomach, lung, breast, colon, and esophagus,11 as well as
to suppress the proliferation of cancer cells in culture and inhibit the growth of transplanted
tumor xenographs in vivo.12
RESULTS AND DISCUSSION
Substituted disulfide derivatives 2 were synthesized by treating 4-substituted thiols
with 4-substituted sulfenimides 1 by using microwave irradiation, as described in Scheme 1.
4-Substituted sulfenimides were prepared according to the literature.13 Microwave reactions
were carried out using chloroform as a neat solvent.
O
O
MW
R
1
+
R
S
N
S
H
R
+
R1
S
S
H
N
O
O
2
1
R and R1
-H
a
-CH3
-NO2
-OCH3
-Cl
b
c
d
e
f
-Br
Scheme 1

MICROWAVE-ASSISTED SYNTHESIS OF DISULFIDES
1517
Table 1 IR, 1H-NMR, and 13C-NMR data for the synthesized compounds
13C-NMR (DMSO-d6, δ,
Compound no.
IR (υ, cm−1
)
1H-NMR (DMSO-d6, δ, ppm)
ppm)
2aa
3080 (C H); 1600–1446
(C C); 476 (S S)
7.62–7.52 (4H, dd, J = 8.0
Hz); 7.43–7.37 (4H, dd, J =
8.0 Hz); 7.33–7.24 (2H, dd,
J = 8.0 Hz)
136.22, 129.93, 128.04,
127.63
2ab
3050 (C H); 2948–2821
7.80–7.70 (2H, dd, J = 8.0
Hz); 7.68–7.65 (2H, d);
7.62–7.53 (2H, dd, J = 8.5
Hz); 7.25–7.20 (H, dd, J =
8.2 Hz); 7.15–7.10 (2H, d);
2.35 (3H, s, CH3)
, 134.68, 134.26, 131.88,
130.85, 129.28, 124.03,
123.54, 25.00
(
CH3); 1628–1439
(C C); 523 (S S)
2ac
2ad
3100 (C H); 1618–1456
(C C); 1550–1345
8.90–8.20 (2H, d); 7.88–7.80
(2H, d); 7.70–7.63 (2H, dd,
J = 8.0 Hz); 7.55–7.51 (2H,
dd, J = 8.2 Hz); 7.40–7.35
(H, dd, J = 8.6 Hz)
146.57, 143.63, 129.74,
127.79, 126.75, 126.28,
124.61, 123.00
(
NO2); 1048 (C N);
540 (S S)
3050 (C H); 2945–2833
7.90–7.85 (2H, dd, J =
7.8 Hz); 7.80–7.77 (2H, d);
7.50–7.41 (2H, dd, J = 8.2
Hz); 7.33–7.27 (H, dd, J =
8.1 Hz); 6.10–5.84 (2H, d);
3.79 (3H, s, OCH3)
134.33, 132.66, 131.72,
128.97, 128.14, 123.60,
114.56, 55.34
(
OCH3); 1613–1412
(C C); 1197–1062
(C C); 550 (S S)
O
2ae
3070 (C H); 1618–1432
(C C); 1054 (C Cl);
542 (S S)
7.50–7.48 (2H, dd, J = 8.0
Hz); 7.44–7.42 (2H, dd, J =
8.1 Hz); 7.28–7.26 (2H, dd,
J = 8.1 Hz); 7.24–7.20 (H,
dd, J = 8.0 Hz); 7.31–7.29
(2H, d)
139.64, 134.20, 132.60,
129.36, 127.59, 127.04,
126.09, 122.81
2bb
2bc
3056 (C H); 2921–2868
(C H); 1601–1466
(C C); 520 (S S)
3083 (C H); 2920–2841
(C H); 1574–1530
(C C); 1460–1330
(Ar-NO2); 1085 (C N);
496 (S S)
7.38–7.34 (4H, d); 7.17–7.13
(4H, d); 2.24 (6H, s, CH3)
137.63, 132.72, 130.15,
128.22, 20.68
8.22–8.16 (2H, d); 7.77–7.58
(2H, d); 7.43–7.33 (2H, d);
7.18–7.12 (2H, d); 2.43 (3H,
s, CH3)
146.29, 145.27, 137.87,
130.26, 128.70, 128.11,
126.25, 124.36, 20.58
2bd
3110 (C H); 2956–2863
(C H); 1513–1460
(C C); 1180–1053
7.37–7.35 (2H, d); 7.32–7.20
(2H, d); 7.10–7.01 (2H, d);
6.83–6.76 (2H, d); 3.76 (3H,
s, OCH3); 2.30 (3H, s,
CH3)
159.83, 134.25, 132.64,
132.56, 129.71, 129.30,
127.36, 114.55, 55.30,
21.02
(C
O C); 496 (S S)
2be
2bf
2cd
3057 (C H); 2921–2868
(C H); 1655–1574
(C C); 1089 (C Cl);
496 (S S)
3057 (C H); 2921–2868
(C H); 1655–1574
(C C); 654 (C Br); 496
(S S)
3101 (C H); 2968–2840
(C H); 1655–1593
(C C); 1520–1350
(Ar-NO2); 1114–1038
7.63–7.58 (2H, d); 7.48–7.44
(2H, d); 7.42–7.37 (2H, d);
7.21–7.12 (2H, d); 2.26 (3H,
s, CH3)
7.37–7.36 (2H, d); 7.35–7.24
(2H, d); 7.12–7.08 (2H, d);
6.90–6.73 (2H, d); 2.31 (3H,
s, CH3)
8.24–8.20 (2H, d); 7.83–7.80
(2H, d); 7.60–7.50 (2H, d);
6.98–6.96 (2H, d); 3.50 (3H,
s, OCH3)
137.80, 135.09, 134.48,
132.53, 131.95, 130.11,
129.16, 128.27, 20.54
137.87, 134.55, 132.71,
132.03, 130.04, 129.35,
128.62, 121.06, 21.00
158.17, 145.80, 145.01,
131.16, 130.07, 127.60,
121.50, 115.30, 55.50
(Continued on next page)

1518
H. KUTUK AND N. TURKOZ
Table 1 IR, 1H-NMR, and 13C-NMR data for the synthesized compounds (Continued)
13C-NMR (DMSO-d6, δ,
Compound no.
IR (υ, cm−1
)
1H-NMR (DMSO-d6, δ, ppm)
ppm)
(C
O
C); 1078 (C N);
519 (S S)
2ce
2de
3188 (C H); 1650–1599
(C C);1538–1320
(Ar-NO2); 1111 (C N);
1090 (C Cl); 510 (S S)
3029 (C H); 2953–2840
(C H); 1450–1375
8.20–8.18 (2H, d); 7.79–7.74
(2H, d); 7.52–7.48 (2H, d);
7.42–7.21 (2H, d)
146.97, 144.99, 144.03,
134.14, 133.00, 130.02,
127.17, 124.88
8.23–8.21 (2H, d); 7.77–7.72
(2H, d); 7.43–7.41 (2H, d);
7.20–7.18 (2H, d); 3.61 (3H,
s, -OCH3)
159.80, 136.04, 135.06,
132.50, 132.00, 129.66,
129.20, 114.70, 55.24
(C C); 502 (S S);
1114–1050 (C
1038 (C Cl)
O C);
2df
3029 (C H); 2953–2840
(C H); 1450–1375
(C C);1114–1038
7.54–7.46 (2H, d); 7.40–7.37
(4H, d); 7.10–6.90 (2H, d);
3.73 (3H, s, -OCH3)
159.82, 135.89, 135.00,
132.03, 129.20, 126.97,
120.89, 115.08, 55.27
(C
O C); 818 (C Br);
502 (S S)
2ee
2ef
2ff
3130 (C H); 1548–1395
(C C); 1012 (C Cl);
476 (S S)
3130 (C H); 1550–1450
(C C); 1012 (C Cl);
757 (C Br); 476 (S S)
3106 (C H); 1548–1395
(C C); 757 (C Br); 476
(S S)
7.54–7.51 (4H, d); 7.46–7.43
(4H, d)
134.76, 133.01, 130.10,
129.93
7.48–7.45 (2H, d); 7.43–7.41
(2H, d); 7.39–7.37 (2H, d);
7.33–7.30 (2H, d)
7.54–7.51 (4H, d); 7.43–7.41
(4H, d)
136.00, 133.20, 132.50,
131.20, 130.72, 129.20,
120.30
134.92, 133.20, 132.50,
131.20, 130.72, 129.20,
120.30
By using 360-W (2450 MHz, a wavelength of 12.2 cm, and an energy of 0.23
cal/mol) microwave irradiation, 2a–f were obtained at higher yields and with lower re-
action times than by classical heating methods. For example, under classical conditions,
4-bromodiphenyldisulfide af was produced with 25% yield in 1920 min; under microwave
conditions, the reaction proceeded 640 times faster and reaction yield increased to 69%
in just 3 min. 4-Chlorodiphenyldisulfide ae, under the conventional method, was obtained
with 40% yield in 1440 min, whereas under microwave conditions it was synthesized with
77% yield in 2 min, an approximately 720 times shorter period.
Spectral investigations of the newly synthesized intermediates and sulfenimides were
in accordance with the proposed structures. Comparison of the infrared (IR) spectra at each
step clearly indicated the formation of disulfides, generally by the disappearance of the
C O band at about 1748 cm−1, the S-N band at about 1079 cm−1 in sulfenimides, and the
1
appearance of a new S S band at about 520 cm−1 in disulfides. The IR, H-NMR, and
13C-NMR values in Table 1 are in agreement with the structures of synthesized disulfides.
The current experimental results are summarized in Table 2. All of the products
were produced in a very short time, and their yields were very high. The experimental
procedure is simple and there were no undesirable by-products. Finally, some advantages
of microwaves over traditional heating (hot plates, Bunsen burner, etc.) for performing
an organic reaction are better yields, shorter reaction time (usually 1/1000), reduction of
by-products, and no thermal decomposition of products.3

MICROWAVE-ASSISTED SYNTHESIS OF DISULFIDES
1519
The products’ structures were confirmed by IR, 1H-NMR, 13C-NMR, and elemental
analysis and are given in Tables 1 and 3, respectively.
In comparing the microwave-assisted synthesis method with the classical method
from the literature,14 it is clear that the synthesized compounds were obtained in a much
shorter time and at higher yields under microwave irradiation than by classical heating.
Related experimental results are collated in Table 4.
The conventional mechanism for the synthesis of disulfides is shown in Scheme 2.15
O
O
δ
..
N
+δ
N
S
R
R1
+
S
−δ
H
R
S
H
O
O
S
−δ
R1
(1)
O
O
H
+
H
N
N
+δ
_
:
..
R1
S
S
R
+
R
S
S
..
O
O
−δ
R1
(2)
O
R
S
..
N
S
R1
+
H
O
Scheme 2
EXPERIMENTAL
The substituted disulfide derivatives 2a–f were synthesized under microwave irradi-
ation (360 W) by using a domestic microwave (Bosch HMT 812 C) oven that was modified
by fitting a reflux system, and an internal camera was used for all syntheses. Microwaves

1520
Table 2 Physical data and reaction times for the synthesized disulfides under microwave irradiation (360 W)
Microwave Conditions Classical Heating
H. KUTUK AND N. TURKOZ
Compound
no.
m.p.
(◦C)
Reaction
time (min)
Yield
(%)
m.p.
◦C (Lit.17
Reaction
time (h)
Yield
(%)
Reaction
cond.
Rf
TLC
)
2aa
2ab
2ac
2ad
2ae
2af
2ba
2bb
2bc
2bd
2be
2bf
2ca
2cb
2cc
2cd
2ce
2cf
2da
2db
2dc
2dd
2de
2df
2ea
2eb
2ec
2ed
2ee
2ef
56–58
153–155
170–173
226–228
150–153
219–223
154–156
41–43
46–49
Liquid
48–50
61–64
169–172
47–50
155–158
64–66
117–121
145–148
227–229
Liquid
63–66
Liquid
Liquid
Liquid
151–155
48–50
117–120
Liquid
60–62
75–78
220–223
61–63
146–150
Liquid
76–78
90–93
7
12
10
15
2
72
88
98
83
77
69
73
93
55
75
94
91
55
46
70
58
82
78
71
67
54
58
78
83
73
72
55
54
85
80
70
65
60
67
84
92
62
19
70
a
0.28
0.31
0.36
0.41
0.22
0.25
0.31
0.32
0.33
0.26
0.29
0.30
0.36
0.33
0.27
0.38
0.35
0.29
0.41
0.26
0.38
0.35
0.25
0.24
0.22
0.29
0.34
0.25
0.34
0.33
0.25
0.30
0.28
0.24
0.34
0.29
3
15
17
14
20
5
47.5
19
73
59
a
46–47
0.5
b
8
27
38
20
33
16
19
16
18
15
21
7
10
6
15
13
18
3
0.5
19
58
70
b
a
19
1
80
35
a
c
72.8
4
9
16
14
20
4
2fa
2fb
2fc
2fd
2fe
2ff
3
aReflux in CH2Cl2.18
b
−20 ◦C in CH2Cl2.19
cCatalytic amount of nitric oxide in air and CD3CN.20
at 2450 MHz were used in the microwave oven. This frequency corresponds to a wave-
length of 12.2 cm and an energy of 0.23 cal/mol (=0.94 J/mol). This frequency can only
cause rotation of molecules.16 All raw materials and solvents were purchased from Aldrich
Chemical Company and were used without further purification. IR spectra were recorded
on a Bruker Vertex 80v spectrophotometer. 1H- and 13C-NMR spectra were determined in
DMSO-d6 at 400 MHz in an Avance II NMR spectrometer using tetramethylsilane (TMS)
as the internal standard. Elemental analyses were performed by the Central Laboratory

MICROWAVE-ASSISTED SYNTHESIS OF DISULFIDES
1521
Table 3 Analytical data for some of the synthesized disulfides
Analytical data found/(calcd.) (%)
Comp. no.
Formula (m.wt)
C12H10S2 (218)
C
H
N
S
2aa
2bb
2bc
2be
2bf
2cc
2cf
2ec
2ee
2ff
65.83 (66.05)
68.71 (68.29)
56.97 (56.31)
59.25 (58.54)
50.47 (50.16)
46.85 (46.75)
41.89 (42.10)
48.87 (48.40)
50.73 (50.17)
37.28 (38.29)
4.69 (4.58)
5.76 (5.69)
4.22 (3.97)
4.58 (4.13)
3.88 (3.53)
3.04 (2.59)
2.64 (2.33)
2.88 (2.68)
2.98 (2.78)
2.70 (2.12)
29.16 (29.35)
25.84 (26.01)
22.76 (23.10)
23.32 (24.01)
20.10 (20.57)
20.45 (20.78)
17.75 (18.71)
21.19 (21.51)
21.40 (22.29)
17.47 (17.02)
C
14H14S2 (246)
13H11NO2S2 (277)
13H11S2Cl (266.5)
13H11S2Br (311)
12H8N2O4S2 (308)
12H8NO2S2Br (342)
C12H8NO2S2Cl (297.5)
C
C
5.29 (5.05)
C
C
C
9.20 (9.09)
4.58 (4.09)
4.80 (4.70)
C
C
12H8S2Cl2 (287)
12H8S2Br2 (376)
of the Middle East Technical University (METU) in Ankara, Turkey. Melting points were
measured with a Gallenkamp electrothermal apparatus and are uncorrected. Reactions were
monitored by thin-layer chromatography (TLC) on Merck plates.
Synthesis of Substituted Disulfides
General Process—Conventional Method. A mixture of 4-substituted sulfen-
imide (5.00 mmol) and 4-substituted thiol (5.00 mmol) was ground thoroughly and then
transferred to a round-base flask. The mixture was refluxed in ethanol (50 mL). The reaction
mixture was controlled by TLC at regular intervals on silica gel with a mixture of hexane
and ethyl acetate (5:1) as the eluent. When the reaction was finished, hot water was added,
and it was stirred and filtered. Because phthalimide dissolves in hot water, the disulfide
was separated from the phthalimide. Then the disulfide was recrystallized using ethanol or
acetone.
General Process—Microwave Method. A mixture of 4-substituted sulfenimide
(5.00 mmol) and 4-substituted thiol (5.00 mmol) was ground thoroughly and then trans-
ferred to a flask and chloroform was added. The mixture was irradiated in a microwave
oven at 360 W. The reaction mixture was monitored throughout the experiment with TLC
Table 4 Comparison of microwave and classical heating for production of some disulfides
Classical heating
Microwave conditions
Yield
Reaction
time (min)
Yield
(%)
Reaction
cond.
Reaction
Reaction
cond.
Comp. no.
time (min)
(%)
1aa
1ab
1ac
1ad
1ae
1af
2700
3600
3180
5760
1440
1920
23
35
40
30
40
25
a
a
a
a
a
a
7
12
10
15
2
72
88
98
83
77
69
b
b
b
b
b
b
3
aReflux in EtOH.
bWith chloroform under microwave irradiation (360 W).

1522
H. KUTUK AND N. TURKOZ
on silica gel with a mixture of hexane and ethyl acetate (5:1) as the eluent, to determine
whether the reaction had terminated. When the reaction was finished, the product was
purified as mentioned above.
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