7
608
J . Org. Chem. 1996, 61, 7608-7610
P r ep a r a tion of Oligo(th io-2,5-th ien ylen es)
the dibromide 3′ in 61% yield. The reaction of 3′ with 2
equiv of 2-thiophenethiolate in refluxing DMF in the
presence of the foregoing copper(I) oxide gave the ex-
pected pentamer 5 in 54% yield. Treatment of 5 with 2
equiv of NBS also brought about regioselective bromi-
nation to give the dibromide 5′ in 79% yield. The reaction
of 5′ with 2 equiv of 2-thiophenethiolate produced the
expected heptamer 7 in 58% yield.
J uzo Nakayama,* Naoki Katano, Yoshiaki Shimura,
Yoshiaki Sugihara, and Akihiko Ishii
Department of Chemistry, Faculty of Science,
Saitama University, Urawa, Saitama 338, J apan
Received May 20, 1996
Oligomers containing an even number of thiophene
Poly(thio-1,4-phenylene) [poly(p-phenylene sulfide)] is
ring were prepared starting from 2,2′-thiobis(thiophene)
a useful high-performance polymer because of its high
temperature resistance, dimensional stability, solvent
resistance, and high conductivity.1 In this connection,
there have also appeared a large number of patents and
papers on syntheses, chemical properties, and industrial
use of oligo(thio-1,4-phenylenes). On the other hand,
although thiophene has played a very important role in
constructing many electronic devices, their thiophene
analogs, poly(thio-2,5-thienylene) and oligo(thio-2,5-thi-
enylene), have never attracted keen interest. In 1967,
J ones and Moodie synthesized poly(thio-2,5-thienylene)
by condensation of thiophene with sulfur dichloride and
by self-condensation of 5-chloro-2-thiophenethiol.2 There-
after, several reports have appeared on the preparation
and properties of poly(thio-2,5-thienylene).3 As for oligo-
5
(
2) (Scheme 2). Treatment of 2 with 2 equiv of NBS gave
the dibromide 2′ in 81% yield. The reaction of 2′ with 2
equiv of 2-thiophenethiolate gave the expected tetramer
in 54% yield. Bromination of 4 with 2 equiv of NBS
also took place regioselectively to give the dibromide 4′
in 71% yield. The reaction of 4′ with 2 equiv of
4
2
-thiophenethiolate produced the hexamer 6 in 43% yield.
Dibromination of 6 with NBS gave a mixture containing
several products, from which the desired dibromide was
isolated in a low yield after repeated purification by silica
gel column chromatography and crystallization. Unfor-
tunatley, however, no expected octamer could be obtained
in pure form by reaction of the above dibromide with
2
-thiophenethiol.
Structures of new oligomers 4-7 and their dibromo
(
thio-2,5-thienylenes), J ones and Moodie reported the
1
13
derivatives were determined by H and C NMR spec-
trometry, mass spectrometry, and elemental analyses;
preparation of 2,5-bis[(2-thienyl)thio]thiophene (3) by
reaction of 2,5-dibromothiophene with 2-thiophenethiol.4
These authors also synthesized the other three consti-
13
particularly useful was C NMR spectrometry because
of their symmetrical structure. Oligomers 4-7 are all
crystalline compounds, and their melting points tend to
rise as the molecules become larger. Figure 1 shows the
UV-vis spectra of oligomers 2-7 which were determined
4
tutional isomers of 3. We report here the preparation
of a higher series of oligo(thio-2,5-thienylenes).
The method reported by J ones and Moodie4,5 was
applied with slight modification to the preparation of
oligo(thio-2,5-thienylenes). Thus, oligomers consisting of
an odd number of thiophene ring were prepared in the
following manner starting from reaction of 2,5-dibro-
mothiophene with 2 equiv of 2-thiophenethiol (1) (Scheme
with chloroform as the solvent in the same concentration
-5
(
5.0 × 10 M). Molar absorption coefficients (ꢀ) increase
progressively with an increasing number of thiophene
ring. The longest absorption maxima (λmax) also increase
with an increasing number of thiophene ring, but it is
not so much marked as observed with R-thiophene
7
1
). The reaction of 2,5-dibromothiophene with 2 equiv
of potassium 2-thiophenethiolate in refluxing N,N-di-
methylformamide (DMF) gave 2,5-bis[(2-thienyl)thio]-
thiophene (3) in a better yield (72%) than previously
6
oligomers and (thiophene-2,5-diyl)vinylene oligomers.
Apparently, the rate of increase becomes smaller as the
number of thiophene ring becomes larger, and finally the
max value converges around 300 nm. These observations
4
reported, when copper(I) oxide that was freshly prepared
λ
by reduction of copper(II) acetate with hydrazine was
used as the catalyst. Bromination of 3 with 2 equiv of
N-bromosuccinimide (NBS) in a mixture of acetic acid
and dichloromethane took place regioselectively to give
lead to the conclusion that, although the conjugation
between thiophene rings takes place through the lone
pair electrons on sulfur atom,4 it attenuates when
4 2
thiophene rings are separated by several -C H S-S-
units, and therefore the conjugation in the present
system is less effective than in the case where thiophene
rings are connected by carbon-carbon double bond.
(
1) (a) Brady, D, G. J . Appl. Polym. Sci. 1976, 20, 2541. (b) Hill, H.
W., J r.; Brady, D. G. J . Coat. Technol. 1977, 49, 33. (c) Brady, D. G. J .
Appl. Polym. Sci., Appl. Polym. Symp. 1981, 36, 231. (d) Vives, V. C.;
Dix, J . S.; Brady, D. G. ACS Symp. Ser. (Am. Chem. Soc.) 1983, 229,
7
6
5. (e) Dix, J . S. Chem. Eng. Prog. 1985, 81(1), 42. (f) Kreja, L.;
Exp er im en ta l Section
Warszawski, A.; Czerwinski, W. Angew. Makromol. Chem. 1986, 141,
7
2
7. (g) Cheng, S. Z. D.; Wu, Z. Q.; Wunderlich, B. Macromolecules 1987,
0, 2802. (h) Bourbon, D.; Kamiya, Y.; Mizoguchi, K. J . Polym. Sci.,
Melting points are uncorrected. Elemental analyses were
performed by the Chemical Analysis Center of Saitama Univer-
sity. Column chromatography was performed with Merck
Kieselgel 60 (70-230 mesh).
Part B: Polym. Phys. 1990, 28, 2056.
(
2) J ones, E.; Moodie, I. M. J . Polym. Sci. (C) 1967, 2281.
(3) (a) Voronkov, M. G.; Khaliullin, A. K.; Annenkova, V. Z.; Antonik,
L. M.; Kamkina, L. M.; Deryagina, E. N.; Vakul’skaya, T. I. Dokl. Akad.
Nauk SSSR 1976, 228, 1341. (b) J en, K.-Y.; Benfaremo, N.; Cava, M.
P.; Huang, W.-S.; MacDiarmid, A. G. J . Chem. Soc., Chem. Commun.
2
-Thiophenethiol was prepared from 2-thienyllithium (pur-
8
chased from Aldrich) and elemental sulfur. Copper(I) oxide,
freshly prepared in the following manner, was used throughout
this work. A 20% aqueous solution of hydrazine (55 mL, 0.34
mol) was added to a stirred solution of copper(II) acetate
monohydrate (40 g, 0.20 mol) in water (650 mL) over a period
of 1 h. The resulting very fine precipitate was subjected to
1
983, 633. (c) Cava, M. P.; Lakshmikantham, M. V.; J en, K.-Y.;
Benfaremo, N.; Huang, W.-S.; MacDiarmid, A. G. Polym. Prepr. (Am.
Chem. Soc., Div. Polym. Chem.) 1983, 24, 251. (d) Ford, W. T.;
Gutierrez, M.; Pohl, H. A. Polym. Prepr. (Am. Chem. Soc., Div. Polym.
Chem.) 1983, 24, 332. (e) Giuffre, L.; Tempesti, E.; Montoneri, E.;
Bonfanti, C.; Modica, G. Int. J . Hydrogen Energy 1984, 9, 907.
(
4) (a) J ones, E.; Moodie, I. M. J . Chem. Soc. 1965, 7018. See also
b) Fedorov, B. P.; Stoyanovich, F. M. Zh. Obshch. Khim. 1963, 33,
251.
5) (a) J ones, E.; Moodie, I. M. Tetrahedron 1965, 21, 2413. (b) J ones,
E.; Moodie, I. M. Organic Syntheses; Wiley: New York, 1988; Coll. Vol.
,p 558.
(
2
(6) Nakayama, J .; Konishi, T.; Hoshino, M. Heterocycles 1990, 27,
1731.
(7) Nakayama, J .; Fujimori, T. Heterocycles 1991, 32, 991.
(8) J ones, E.; Moodie, I. M. Organic Syntheses; Wiley: New York,
1988; Coll. Vol. 6, p 979.
(
6
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