Electrochemical transformation of diazonium salts into diaryl disulfides

Article abstract of DOI:10.1016/j.tetlet.2009.09.102

Electrolyses of aryldiazonium tetrafluoroborates in CS₂/EtOH and Bu₄NClO₄, as the solvent-supporting electrolyte system, led to the corresponding diaryl disulfides in good yields.

Full text of DOI:10.1016/j.tetlet.2009.09.102

Tetrahedron Letters 50 (2009) 6798–6799
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Tetrahedron Letters
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Electrochemical transformation of diazonium salts into diaryl disulfides
*
*
Fructuoso Barba , Fernando Ranz, Belen Batanero
Department of Organic Chemistry, University of Alcalá, 28871 Alcalá de Henares (Madrid), Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Electrolyses of aryldiazonium tetrafluoroborates in CS /EtOH and Bu NClO , as the solvent-supporting
2
4
4
Received 26 August 2009
Revised 15 September 2009
Accepted 18 September 2009
Available online 24 September 2009
electrolyte system, led to the corresponding diaryl disulfides in good yields.
Ó 2009 Elsevier Ltd. All rights reserved.
Keywords:
Aryldiazonium tetrafluoroborates
Carbon disulfide
Electrosynthesis of diaryl disulfides
Diaryl disulfides are important intermediates in various organic
nium fluoroborates 1(a–k) at the potential of their first reduction
1
,2
+
transformations. These compounds can be employed in the prep-
aration of 4-arylthio-5-pyrazolone magenta photographic cou-
wave (À0.5 V vs Ag/Ag ). The reaction proceeds in good yield, as
summarized in Table 1.
3
plers. Diphenyl disulfide as a devulcanization agent increases
In previous papers, we have demonstrated that the aryldiazo-
nium salts are easily reduced to the corresponding aryl radicals
that can react with the solvent, acetonitrile, DMF, or 1,2-dichloro-
ethane to produce the dimethylaminocarbonyl, cyanomethyl, or
4
the effectivity during thermochemical devulcanization. Hydrothi-
olation of terminal alkynes with diaryl disulfides has been
5
developed.
2
7
The anodic oxidation of diphenyl disulfides allows the forma-
1,2-dichloroethyl radicals, respectively. Now, the electrogenerat-
ed aryl radicals react with carbon disulfide as indicated in
Scheme 1.
tion of PhS+ capable of in situ reaction with a large palette of
6
nucleophiles.
There are many reports involving the synthesis of diaryl disul-
It is well known that the attack of a radical on a substrate
should be favored when the substrate has vacant p or d orbitals
7
–9
fides;
however, most of these methods require unusual sub-
strates and relatively harsh reaction conditions. More recently, a
selective reduction of arenesulfonyl chlorides promoted by samar-
ium metal in DMF to the corresponding disulfides has been
Table 1
1
0
Obtained yields of diaryl disulfides 2
published.
The conversion of arylthiols to diaryl disulfides has been per-
1
1
formed by different oxidative procedures, from electrochemistry
+
-
cathodic
1
2
Ar
N
BF4 + CS2
Ar-S-S-Ar + N
2
2
to the oxidation with 1,3-dibromo-5,5-dimethylhydantoin or
reduction
using n-butyltriphenylphosphonium dichromate.13
2
1
In the literature, there are two papers concerning the conver-
sion of aryldiazonium fluoroborates to diaryl disulfides. In the first
case, the diazonium salts were treated with sodium iodide in ace-
Ar:
Yield of 2 (%)
Mp (°C)
16
a: C
6
H
5
61
65
73
82
72
78
96
60
72
70
65
61–63 [lit : 61–62]
1
4
17
tone/carbon disulfide, but the obtained yields were poor. In the
b: 4-MeO–C
c: 4-Et–C
d: 2-Me–C
e: 3-Me–C
f: 4-Cl–C
g: 4-Br–C H4
h: 4-MeCO–C
i: 4-MeOOC–C
6
H
4
44–45 [lit : 44–45]
8
6
H
4
22–24 [lit1 : 23.4–24.3]
second case, the diazonium salts react with benzyltriethylammo-
19
nium tetrathiomolybdate.15
6
H
4
36–38 [lit : 36]
43–45 [lt2 : 44–45]
0
6
H
4
In this Letter we present a very easy, clean, and good-yielded
synthesis of diaryl disulfides 2 by cathodic reduction of aryldiazo-
21
6
H
4
72–73 [lit : 72]
94–95 [lit2 : 94–95]
2
6
96–98 [lit23: 97–98]
6
H
4
24
6
H
4
126–127 [lit : 127]
83–85 [lit25: 85]
j: 2-MeS–C
k: 2,6-DiMe–C
6 4
H
*
Corresponding authors. Tel.: +34 91 8854617/2517; fax: +34 91 8854686.
bp (°C) (3 Torr): 173 [lit26: 173–174]
6
H
3
E-mail addresses: fructuoso.barba@uah.es (F. Barba), belen.batanero@uah.es
(
B. Batanero).
0
040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.09.102

F. Barba et al. / Tetrahedron Letters 50 (2009) 6798–6799
6799
+
+ e
-
References and notes
Ar-N=N
Ar
.
Ar
.
+ N2
Ar N2
S
1. Standfest-Hauser, C. M.; Mereiter, K.; Schmidt, R.; Kirchner, K. Organometallics.
004, 23, 2194–2196.
2. Mitin, Y.; Zapevalova, N. P. Zh. Obshch. Khim. 1974, 44, 2074–2075.
2
.
Ar-S + CS
.
Ar
.
+ CS2
S
3
4
.
.
Canuti, A.M.; Coraluppi, E. EP763774. 1997. CAN 126: 299644.
Verbruggen, M. A. L.; Van der Does, L.; Noordermeer, J. W. M.; Van Duin, M. J.
Appl. Polym. Sci. 2008, 109, 976–986.
dimerization
S
Ar
5. Wang, Z.-L.; Tang, R.-Y.; Luo, P.-S.; Deng, Ch.-L.; Zhong, P.; Li, J.-H. Tetrahedron
008, 64, 10670–10675; . Tetrahedron 2009, 65, 579.
S
Ar
2
6
.
Simonet, J.; Pilard, J.-F. In Organic Electrochemistry; Lund, H., Hammerich, O.,
Eds., 4th ed.; Marcel Dekker: NY, 2001; p 1214. Chapter 9.
Wohlfahrt, T. J. Prakt. Chem 1902, 66, 551–557.
Dhar, P.; Ranjan, R.; Chandrasekaran, S. J. Org. Chem 1990, 55, 3728–3729. and
references cited therein.
Scheme 1. Proposed pathway formation of diaryl disulfides.
7
8
.
.
CH
3
S
S
CH
3
S
S
9. Guo, H.; Wang, J. Q.; Zhang, Y. Synth. Commun. 1997, 27, 85–87.
10. Liu, Y.; Zhang, Y. Tetrahedron Lett. 2003, 44, 4291–4294.
.
S
11. Leite, S. L. S.; Pardini, V. L.; Viertler, H. Synth. Commun. 1990, 20, 393–
.
397.
-
3
CH .
S
12. Khazaei, A.; Zolfigol, M. A.; Rostmai, A. Synthesis 2004, 2959–2961.
(
b)
(
a)
13. Mohammadpoor-Baltork, I.; Memarian, H. R.; Bahrami, K. Phosphorus, Sulfur,
Silicon 2004, 179, 2315–2321.
-
CS
S
S
14. Benati, L.; Montevecchi, P. C. J. Org. Chem. 1976, 41, 2639–2640.
S
S
CH
3
15. Bhar, D.; Chandrasekaran, S. Synthesis 1994, 785–786.
16. Pinnick, H. W. J. Org. Chem. 1980, 45, 930–932.
17. Campaigne, E. E. J. Org. Chem. 1961, 26, 2486–2491.
1
8. Overberger, C. G. J. Am. Chem. Soc. 1956, 78, 4792–4797.
dimerization
3
j
S
S
S
CH
3
19. Fujihara, H. Bull. Chem. Soc. Jpn. 1989, 62, 616–617.
2j
20. Tajbakhsh, M. J. Chem. Res. 2007, 486–489.
21. Olah, G. A. J. Org. Chem. 1981, 46, 2408–2410.
22. Banfield, S. C. J. Org. Chem. 2007, 72, 4989–4992.
S
.
3
H C S
Scheme 2. Common intermediate (b) in the formation of 2j and 1,3-benzodithiole-
-thione (3j).
23. Walker, D. J. Org. Chem. 1963, 28, 3077–3082.
24. Meier, H. Chem. Ber. 1984, 117, 107–126.
2
2
2
2
2
5. Paquer, D. Recl. Trav. Chim. Pays-Bas 1978, 97, 88.
6. Goldfarb, Y. Izvestiya Akad. Nauk SSSR, Ser. Khim. 1966, 1426–1432.
7. Batanero, B.; Saez, R.; Barba, F. Electrochim. Acta 2009, 54, 4872–4879.
8. Nonhebel, D.C.; Walteu. Free radical Chemistry. Structure and Mechanism;
Cambridge at the University Press, 1974, p 546.
´
.
.
CH -S + CS
3
CH3
.
+
S=C=S
CH
3
-S-C=S
29.
Mp: 164–166 °C [lit. 164–165 °C (Nakayama, J. Chem. Lett. 1977, 127–
1
30)].
+
+
+
3
0. GC–MS (EI): m/z (%) = 204 (M +2, 5), 202 (M , 36), 187 (M À15, 17), 172
+
+
+
S CH
3
S CH
3
(M À15–15, 10), 156 (M ÀCH
S (McLafferty), 93), 153(78), 141 (M ÀCH
2
S-15,
2
.
10), 91(100).
CH -S
+
3
3
1. The electroactive diazonium tetrafluoroborates were prepared according to
conventional methods (Organic Reactions; Krieger, R.E., Ed.; Publishing
Company: Huntington, NY, 1977; Vol. V, pp 198–228).The electrochemical
reductions were performed under potentiostatic conditions in a concentric cell
with two compartments separated by a low porosity (D4) glass frit diaphragm
and equipped with a magnetic stirrer. The temperature was maintained
constant at 0 °C with a cryostat. A graphite electrode was used as the cathode, a
S.
S
S-CH
3
Scheme 3. Radical coupling formation of methyl 2-(methyl thio)phenyl disulfide.
available for coordination with the radical, since a bond between
the radical and the substrate can then be formed before any bonds
are broken.
+
platinum plate as the anode, and a saturated Ag/Ag electrode as the reference.
2
8
The SSE (solvent-supporting-electrolyte) was CS /EtOH (20:50) containing
2
0.1 M tetrabutylammonium perchlorate.The aryldiazonium tetrafluoroborate
When the diazonium salt of 2-methylthioaniline (1j) was re-
duced, together with the corresponding disulfide 2j (70% yield),
(
2.0 mmol) was added, in small solid portions for 4 h, to the cathodic
compartment, to be electrolyzed at a constant potential of À0.5 V (vs Ag/
+
Ag ). The slow addition of the substrate was made in order to avoid the
1
,3-benzodithiole-2-thione29 (3j) (15%) was obtained. The forma-
dimerization of the aryl radical.The substrate can be reduced faster at a
mercury cathode; however, the electrogenerated aryl radicals evolve in the
presence of mercury to undesired organomercury compounds.Once the
reaction was finished the cathodic solution was removed under reduced
tion of this product can be explained as follows: the reaction starts,
as described above, with the formation of the radical a. But this
radical is able to intramolecularly attack the sulfur atom of the
methylthio group (again the vacant d orbitals at the sulfur are
available for coordination) giving the intermediate b, which
evolves to 2j after dimerization or to 3j through a methyl radical
evolution (see Scheme 2).
The methyl radical reacts with CS (solvent) to afford a methyl-
2
thio radical which can be coupled with any of the radicals present
in the solution to give, for instance, methyl 2-(methylthio)phenyl
pressure. The residue was then extracted with ether/H
2
O. The organic phase
was dried over MgSO and concentrated by evaporation. The resulting
4
disulfides were purified by flash chromatography on Silica Gel 60 (35–70
mesh) in a (12 Â 2.5 cm) column, using mixtures Tol/Hex (1:20) (2a–g, 2j and
2 2
2k) and CH Cl /EtOH (100:1) (2h, 2i) as eluents. The physical and
spectroscopical properties of the obtained diaryl disulfides were coincident
with those already described in the literature. However, IR or NMR is not very
resolutive in this case, and the experimental MS spectra of 2 are given:MS (EI):
+
+
m/z (%) (2a): 219 (M +1, 12), 218 (M , 84), 185(14), 154(16), 140(6), 109(100),
+
6
1
5(29). (2b): 278 (M , 11), 260(5), 200(33), 172(18), 171(28), 140(49),
39(100), 125(26), 108(35), 97(21), 95(26). (2c): 275 (M +1, 23), 274 (M ,
30
disulfide (Scheme 3) detected by GC–MS.
+
+
The presented methodology31 is clearly a convenient and useful
alternative that can be generalized to the obtention of diaryl disul-
fides from anilines.
100), 260(19), 210(23), 195(23), 181(24), 137(81), 135(38), 123(35), 91(44).
+
+
(
(
2d): 247 (M +1, 12), 246 (M , 64), 213(6), 211(8), 123(100), 121(41), 91(88).
+
+
2e): 247 (M +1, 19), 246 (M , 100), 213(36), 198(23), 182(69), 167(42),
23(37), 121(14), 91(75). (2f): 290 (M +4, 11), 288 (M +2, 50), 286 (M , 64),
45(40), 143(100), 108(60). (2g): 378 (M +4, 16), 376 (M +2, 28), 374 (M , 13),
97(9), 295(9), 216(17), 189(44), 187(44), 108(100), 82(16). (2h): 303 (M +1,
0), 302 (M , 100), 287(70), 136(74), 108(17). (2i): 335 (M +1, 12), 334 (M ,
7), 303(16), 270(5), 239(8), 198(8), 184(18), 167(37), 139(63), 136(100),
+ + +
1
1
2
2
5
+ + +
+
Acknowledgment
+
+
+
+
+
This study was financed by the Spanish Ministry of Science and
Education CTQ2007-62612/BQU.
108(38), 82(19). (2j): 311 (M +1, 12), 310 (M , 62), 155(32), 121(9), 91(100).
+
(2k): 274 (M , 91), 241 (4), 168(9), 138(75), 137(90), 105(100), 91(53).