Highly Selective Route for Producing Unsymmetrically Substituted Monomers toward Synthesis of Conjugated Polymers Derived from Poly(p-phenylene vinylene)

Article abstract of DOI:10.1021/jo9821022

A new convenient route for producing unsymmetrically substituted sulfinyl monomers of precursor polymers toward poly(p-phenylene vinylene) is described. Upon treating a symmetrical bissulfonium salt with a thiolate anion, an unexpected high selectivity for the monosubstituted thioethers (90%) is obtained. Optimization of the reaction conditions showed that the stoichiometry of the reactants in this reaction is important to ensure the high selectivity and to prevent unwanted side reactions. Reaction of equimolar amounts of reagents at ambient temperature gave the best results. A mechanism consistent with these results, supported by UV-vis experiments, is presented. Selective oxidation of the thioethers yielded the sulfinyl monomers. By using this new route, it was possible to increase the overall yield by a factor of 2, as compared to the route previously used to obtain these compounds.

Full text of DOI:10.1021/jo9821022

3106
J . Org. Chem. 1999, 64, 3106-3112
High ly Selective Rou te for P r od u cin g Un sym m etr ica lly
Su bstitu ted Mon om er s tow a r d Syn th esis of Con ju ga ted P olym er s
Der ived fr om P oly(p-p h en ylen e vin ylen e)
Albert J . J . M. van Breemen, Dirk J . M. Vanderzande,* Peter J . Adriaensens, and
J an M. J . V. Gelan
Institute for Materials Research, Universitaire Campus Gebouw D, Department SBG,
Chemistry Division, Limburg University, B-3590 Diepenbeek, Belgium
Received October 19, 1998
A new convenient route for producing unsymmetrically substituted sulfinyl monomers of precursor
polymers toward poly(p-phenylene vinylene) is described. Upon treating a symmetrical bissulfonium
salt with a thiolate anion, an unexpected high selectivity for the monosubstituted thioethers (90%)
is obtained. Optimization of the reaction conditions showed that the stoichiometry of the reactants
in this reaction is important to ensure the high selectivity and to prevent unwanted side reactions.
Reaction of equimolar amounts of reagents at ambient temperature gave the best results. A
mechanism consistent with these results, supported by UV-vis experiments, is presented. Selective
oxidation of the thioethers yielded the sulfinyl monomers. By using this new route, it was possible
to increase the overall yield by a factor of 2, as compared to the route previously used to obtain
these compounds.
In tr od u ction
steps of the process: formation of the actual monomer,
viz., p-xylylene derivative 2, polymerization to precursor
polymer 3, and thermal conversion11 to the conjugated
polymer 4 (Scheme 1).
Light-emitting diodes (LEDs), in which thin films of
conjugated polymers constitute the active layer, were first
reported in 1990 by Friend et al.1 They succeeded in
fabricating a LED with poly(p-phenylene vinylene), PPV,
as the emission layer. Interest in this field then grew
rapidly, and extensive research was performed in order
to improve the synthesis of the active materials and the
performance of these devices.2
Precursor routes for conjugated materials are of major
importance for the development of optical and electronic
applications for organic semiconductors. They introduce
processability, which makes the incorporation of these
materials into devices feasible. A precursor route that
has shown to be very versatile is the one introduced by
Wessling and Zimmerman.3,4 Their sulfonium precursor
polymer leads, after thermal conversion, to PPV deriva-
tives with good mechanical properties, high thermal
stability, and large conductivities. Still there are some
drawbacks, which are inherent to this route, e.g., insta-
bility of the precursor polymer and gel formation. Fur-
thermore, it is difficult to polymerize monomers with
extended aromatic systems such as 4,4′-biphenylene5 or
2,6-naphthalene.6
To have control over the polymerization process7,12 and
the stability of the precursor polymers,13 a chemical
differentiation of the polarizer (S(O)R) and leaving group
(Cl) is needed. A consequence of this approach is the use
of an unsymmetrically substituted monomer like 1.
For a convenient, large-scale synthesis of these un-
symmetrically monosubstituted monomers starting from
symmetrical starting products, a high selectivity of the
monosubstituted product is desired. This high selectivity
can be achieved in several ways. Precipitation of a
monosubstituted derivative from a reaction medium can
give good results. However, this method is often only
applicable for a small number of well-defined starting
products.14 Another possibility is the use of an excess of
symmetrical starting product to shift the product distri-
bution to the side of the unsymmetrically monosubsti-
tuted product. The disadvantage of this approach is often
a cumbersome recuperation of (expensive) starting prod-
uct. The drawbacks mentioned above demand for a new
synthesis route in which, starting from a commercially
available symmetrical starting product, unsymmetrically
substituted monomers can be made using equimolar
amounts of reagents.
To solve these problems we have evaluated a general
scheme,7-10 in which a clear distinction is made in three
In this paper we present such a simple process for
producing unsymmetrically substituted sulfinyl mono-
mers toward PPV with an unexpected high selectivity.
* To whom correspondence should be addressed. Tel: ++32/
11268321. Fax: ++32/11268301. E-mail: dvanderz@luc.ac.be.
(1) Burroughes, J . H.; Bradley, D. D. C.; Brown, A. R.; Marks, R.
N.; Mackay, K.; Friend, R. H.; Burn, P. L.; Holmes, A. B. Nature 1990,
347, 539.
(2) Kraft, A.; Grimsdale, A. C.; Holmes, A. B. Angew. Chem., Int.
Ed. 1998, 37, 402.
(3) Wessling, R. A.; Zimmerman, R. G. U.S. Patent 3401152, 1968.
(4) Wessling, R. A. J . Polym. Sci., Polym. Symp. 1985, 72, 55.
(5) Garay, R.; Lenz, R. W. Makromol. Chem., Suppl. 1989, 15, 1.
(6) Rempfler, H.; Bosshard, H.; Weber, K. U.S. Patent 4016203A,
1977.
(9) Louwet, F.; Vanderzande, D.; Gelan, J . Synth. Met. 1995, 69,
509.
(10) Issaris, A.; Vanderzande, D.; Gelan, J . Polymer 1997, 38, 2571.
(11) de Kok, M. M.; van Breemen, A. J . J . M.; Carleer, R. A. A.;
Adriaensens, P. J .; Gelan, J . M.; Vanderzande, D. J . Acta Polym.,
accepted for publication.
(12) Van Der Borght, M.; Vanderzande, D.; Gelan, J . Polymer 1998,
39, 4171.
(7) Louwet, F.; Vanderzande, D.; Gelan, J . Synth. Met. 1992, 52,
125.
(8) Louwet, F.; Vanderzande, D.; Gelan, J .; Mullens, J . Macromol-
ecules 1995, 28, 1330.
(13) Vanderzande, D. J .; Issaris, A. C.; Van Der Borght, M. J .; van
Breemen, A. J .; de Kok, M. M.; Gelan, J . M. Macromol. Symp. 1997,
125, 189.
(14) Costello, A. T.; Milner, D. J . Synth. Commun. 1987, 17, 219.
10.1021/jo9821022 CCC: $18.00 © 1999 American Chemical Society
Published on Web 04/02/1999

Unsymmetrically Substituted Monomers
J . Org. Chem., Vol. 64, No. 9, 1999 3107
Sch em e 1
of the sulfonium group by chlorine, an unwanted side
reaction of sulfonium precursor polymers,22 could be
exploited to yield thioethers such as 6.
The first step in this new route is synthesis of a bis-
sulfonium salt like 8. This reaction is very well docu-
mented in literature.22,23 Starting from 5 reaction with
tetrahydrothiophene gives the corresponding bissulfo-
nium salt 8 in a yield of 91%. Bissulfonium salts are very
hygroscopic and therefore contain a certain amount of
1
water. This amount of water can be determined by H
NMR in D2O (see Experimental Section). Different batches
of 8 contained 2-5 wt % H2O.
In a first experiment via route B, reaction of equimolar
amounts of 8, n-octanethiol, and NaOtBu gave, after
azeotropic distillation of tetrahydrothiophene,24 again a
mixture of three products, R,R′-dichloro-p-xylene (5) (5%),
R-chloro,R′-n-octylthio-p-xylene (6f) (90%), and R,R′-n-
Resu lts
Many synthetic routes to obtain sulfoxides are known
from literature.15-17 The most versatile one is the oxida-
tion of thioethers. In this approach the first step to these
sulfoxides is synthesis of thioethers.
1
octylthio-p-xylene (7f) (5%) according to H NMR. Re-
markably we obtained a very high selectivity for mono-
substituted thioether 6f. It should be emphasized that
precipitation of monosubstituted thioethers 6 or 9 from
the reaction medium was not observed. As a counter
example, the reaction was repeated in the same manner
via route C, starting from 5. In this way a statistical
distribution (25% 5, 50% 6f, 25% 7f) of products was
obtained.
Tu n in g of Rea ction Con d ition s. To tune the reac-
tion conditions, the influence of the amount of NaOtBu,
amount and type of thiol, and temperature on the product
distribution was investigated.
Syn th esis of Th ioeth er s. The reaction of alkyl ha-
lides with various nucleophilic sulfur species is one of
the classic methods of thioether synthesis.16 In Scheme
2 such a method using phase-transfer conditions18 (route
A) is applied for producing monosubstituted thio-
ethers 6a -g, which can be later converted to sulfinyl
monomers 1.
After workup the reaction mixture consists of three
products, R,R′-dichloro-p-xylene 5, R-chloro,R′-alkylthio-
p-xylene 6a -g, and R,R′-dialkylthio-p-xylene 7a -g. The
product distribution of the crude reaction mixture was
1
determined with 1H NMR. The aromatic part of the H
Op tim iza tion of Rela tive Am ou n t of Na OtBu . All
reactions were carried out with 1 equiv of n-octanethiol
and equimolar amounts of 8 and NaOtBu at 20 °C. The
results are collected in Table 2.
NMR spectra of the pure compounds 5 and 7f and the
1H NMR spectrum of a reaction mixture resulting from
method A (starting from equimolar amounts of reagents)
are presented in Figure 1a-c. The aromatic signals of 5,
6a -g, and 7a -g are sufficiently separated to allow a
reliable determination of the product distribution.
To avoid the unwanted disubstituted products 7a -g,
a large excess (2.2 equiv) of 5 has to be used. The results
are collected in Table 1. In all cases the amount of
disubstituted product is in the range 2-6%. Thus via this
route it is possible to minimize the amount of disubsti-
tuted product by using a large excess of 5, but the
selectivity for the monosubstituted product is poor.
To obtain a higher selectivity for the monosubstituted
product, a new route (Scheme 2, route B) using equimolar
amounts of reagents was explored starting from R,R′-
bissulfonium-p-xylene (8). Bissulfonium salts such as 8
give upon reaction with base a very reactive unsymmetric
compound, viz., a p-xylylene derivative.19-21 If these
p-xylylene derivatives can be trapped by, for example, a
thiol, this would lead to the unsymmetric substituted
compound 9. Moreover, the easily occurring substitution
Reaction conditions for route B resemble those of the
polymerization of bissulfonium salts to Wessling precur-
sor polymers.3 Hence this could be an important, un-
wanted side reaction of route B. If polymerization and
subsequent elimination to PPV occurs during the reac-
tion, it can be detected by the appearance of a charac-
teristic yellow fluorescent color caused by the conjugated
system of PPV. No efforts were made to determine the
exact amount of polymer, because we were only inter-
ested in avoiding this side reaction. As can be deduced
from Table 2, polymerization and subsequent elimination
to PPV becomes a side reaction if an excess of NaOtBu
and bissulfonium salt is used relative to the amount of
thiol. From these experiments it became clear that the
ratio of thiol and NaOtBu should be higher than 1 to
avoid polymerization.
Op tim iza tion of Rela tive Am ou n t of Th iol. All
reactions were carried out at 20 °C with a ratio n-
octanethiol:NaOtBu of 1:1 in order to prevent polymer-
ization. The results are collected in Table 3.
The experiments showed that no polymerization oc-
curred using equimolar amounts of thiol and NaOtBu.
In addition, the amount of R,R′-dichloro-p-xylene (5) in-
creased at the expense of monosubstituted R-chloro,R′-
n-octylthio-p-xylene (6f) when less than 1 equiv of thiol
was used. Combining these data with those of Table 2,
(15) Drabowicz, J .; Kielbasinski, P.; Mikolajczyk, M. In The Chem-
istry of Sulfones and Sulfoxides; Patai, S., Rappoport, Z., Stirling, C.,
Ed.; J ohn Wiley & Sons Ltd.: Chichester, U.K., 1988; pp 233-378.
(16) Drabowicz, J .; Kielbasinski, P.; Mikolajczyk, M. In Synthesis
of Sulfones, Sulfoxides and Cyclic Sulphides; Patai, S., Rappoport, Z.,
Ed.; J ohn Wiley & Sons Ltd.: Chichester, U.K., 1994; pp 255-388.
(17) Rayner, C. M. Contemp. Org. Synth. 1994, 1, 191. Rayner, C.
M. Contemp. Org. Synth. 1995, 2, 409. Rayner, C. M. Contemp. Org.
Synth. 1996, 2, 499.
(18) Herriot, A. W. Synthesis 1975, 447.
(19) Lahti, P. M.; Modarelli, D. A.; Denton, F. R., III; Lenz, R. W.;
Karasz, F. E. J . Am. Chem. Soc. 1988, 110, 7258.
(20) Denton, F. R., III; Lahti, P. M.; Karasz, F. E. J . Polym. Sci.
Part A: Polym. Chem. 1992, 30, 2223.
(21) Denton, F. R., III; Sarker, A.; Lahti, P. M.; Garay, R. O.; Karasz,
F. E. J . Polym. Sci. Part A: Polym. Chem. 1992, 30, 2233.
(22) Lenz, R. W.; Han, C.-C.; Stenger-Smith, J .; Karasz, F. E. J .
Polym. Sci. Part A: Polym. Chem. 1988, 26, 3241.
(23) Massardier, V. Ph.D. Dissertation, L’Universite´ Claude Ber-
nard-Lyon I, 1993.
(24) Desty, D. H.; Fidler, F. A. Ind. Eng. Chem. 1951, 43, 905.

3108 J . Org. Chem., Vol. 64, No. 9, 1999
van Breemen et al.
Sch em e 2
Ta ble 2. Tu n in g of Rela tive Am ou n t of Na OtBu
product distribution (%)a
entry
equiv of NaOtBu
5
6f
7f
1
2
3
4
0.95
14
5
7
78
90
87
89
8
5
6
5
1.00
1.05b
1.10b
6
a
b
Crude reaction mixture (determined by 1H NMR). Polymer-
ization could not be avoided; amount of polymer is not determined.
Ta ble 3. Tu n in g of Rela tive Am ou n t of n -Octa n eth iol
product distribution (%)b
F igu r e 1. 1H NMR spectra of (a) R,R′-dichloro-p-xylene 5, (b)
R,R′-dioctylthio-p-xylene 7f, (c) reaction mixture obtained from
route A (equimolar amounts of reagents). The resonance
marked with an asterisk results from chloroform.
entry
equiv of thiola
5
6f
7f
1
2
3
0.95
0.98
1.00
14
8
5
78
84
90
8
8
5
Ta ble 1. P r od u ct Distr ibu tion of Cr u d e Rea ction
Mixtu r es of Th ioeth er Syn th esis a n d Over a ll Yield s of 1
by Ap p lyin g Rou tes A a n d B
a
One equivalent of 8 is used; ratio thiol:NaOtBu was 1:1.
Crude reaction mixture (determined by 1H NMR).
b
route A
product
route B
product
Ta ble 4. Tu n in g of Rea ction Tem p er a tu r e
product distribution (%)a
distribution
yield distribution
yield
(%)b
(%)a
(%)b
(%)a
entry
temp (°C)
5
6f
7f
1
2
3
4
-20
0
20
40
8
6
5
6
84
87
90
87
8
7
5
7
entry
thiol (R)
5
6
7
1
5
6
7
1
1
2
3
4
5
6
7
a : n-butyl 58
40
38
39
35
38
39
33
2
3
3
5
3
2
6
33
30
30
29
32
31
27
5
6
7
8
6
5
7
90
89
87
85
89
90
86
5
5
6
7
5
5
7
68
66
65
64
67
68
64
b: i-butyl
c: s-butyl
d : t-butyl
e: i-pentyl 59
f: n-octyl
g:
59
58
60
Crude reaction mixture (determined by 1H NMR).
a
59
61
Op tim iza tion of Rea ction Tem p er a tu r e. Four dif-
ferent temperatures were examined, while the optimized
ratio of reagents was used (ratio of 8:n-octanethiol:
NaOtBu is 1:1:1). The results are collected in Table 4.
The data in Table 4 show that a change in reaction
temperature does not affect the product distribution in
a significant way. This means that the reaction can be
performed at ambient temperature.
a
b
Crude reaction mixture (determined by 1H NMR). Overall
yield after column chromatography.
it is clear that the stoichiometry in route B is important
to achieve a high selectivity and to suppress polymeri-
zation.

Unsymmetrically Substituted Monomers
J . Org. Chem., Vol. 64, No. 9, 1999 3109
Ta ble 5. P r od u ct Distr ibu tion Ap p lyin g Differ en t
Rou tes for Th ioeth er Syn th esis
goes polymerization either by an anionic or a free radical
mechanism.3,18-20,28 It is accepted that this p-xylylene
derivative is produced via the ylide intermediate. The
mechanism of this step was assessed by H-D exchange
experiments.29 Furthermore, the increase and decrease
of p-xylylene derivatives can be visualized by UV-vis
measurements.20 Control comparison studies on nonpo-
lymerizable monobenzylic sulfonium salts established
that the absorbances are not due to ylides formed by
simple deprotonation.21 To verify whether such a p-
xylylene intermediate plays a role in the mechanism of
thioether synthesis via route B, similar UV-vis experi-
ments were performed. The results are depicted in Figure
2a,b. Polymerization and thioether synthesis can also be
examined by monitoring the change in absorbance (at the
absorption maximum of 316 nm) with time (Figure 3),
as described in the Experimental Section.
product distribution (%)a
entry
routeb
equiv of thiol
5
6f
7f
1
2
3
4
A
A
B
C
0.45
1.00
1.00
1.00
59
19
5
39
63
90
50
2
18
5
25
25
a
b
Crude reaction mixture (determined by 1H NMR). See
Scheme 2.
Use of Differ en t Th iols. Different thiols were used
in order to investigate the scope of this route starting
from 8. The optimized conditions, ratio 8:thiol:NaOtBu
of 1:1:1, were used. The results are collected in Table 1.
It is evident that this route is applicable for other types
of thiols as well with a comparable selectivity.
Oxid a t ion of Th ioet h er s. The oxidation of a thio-
ether can yield either the corresponding sulfoxide or the
corresponding sulfone or both, depending on the method
used.14-16,25 Overoxidation to sulfones can be avoided by
using a tellurium dioxide (TeO2)-catalyzed selective oxi-
dation with H2O2 as the oxidant.26 Oxidation of the crude
mixtures of 6a -g from routes A and B afforded the
corresponding sulfoxides 1a -g in a 90% yield. The overall
yields of synthesis of sulfinyl monomers 1a -g via routes
A and B are collected in Table 1. The data reveal that
the overall yield is increased by a factor of 2 using route
B instead of route A.
From Figure 2a,b it is evident that during thioether
synthesis via route B the same p-xylylene intermediate
is formed. Although in both experiments the same
concentrations were used, one can see that the maximum
of absorption is lower in thioether synthesis and the
decrease of absorption is faster than for polymerization
(curves a and b Figure 3). Upon reaction of 11 with a
thiol, the p-xylylene intermediate is consumed with
formation of thioether 9, thereby leading to a decrease
in absorption. The thiol addition to 11 thus inhibits
polyaddition of 11, viz., polymerization. However, if the
ratio of NaOtBu to thiol is higher than 1, polymerization
can of course still occur. Curve c represents thioether
synthesis by route C in which no p-xylylene intermediate
is involved. Curve d represents thioether synthesis
starting from R,R′-bis(triethylammonium)-p-xylene in-
stead of 8. Under the conditions used for route B the
ammonium derivative gives no reaction at all. From curve
d it is evident that no p-xylylene intermediate is formed,
probably because of the higher pKa of this compound or
the poor leaving group capacity of an ammonium group
compared to a sulfonium group.30
Discu ssion
The products obtained in the synthesis of thioethers
by the routes described above are the same. In all cases
a mixture of starting compound 5, monosubstituted
compound 6, and disubstituted compound 7 is obtained.
This allows a comparison of the mechanisms operating
in these different routes. A spectacular improvement in
selectivity for monosubstituted thioether 6 is obtained
when route B is compared with routes A and C (Table
5). Introduction of the thioether group in the latter two
routes occurs via a simple nucleophilic substitution of
chlorine by a thiolate anion. In this way there is no
selectivity at all (route C), or just a small preference for
compound 6 if phase transfer conditions are used (Table
5, entry 2).
Since a sulfonium group is also a good leaving group,
nucleophilic substitution by a thiolate anion can be
envisaged (pathway II, Scheme 3). However, this cannot
explain the high selectivity for 9 and 6, if no precipation
of 9 from the reaction medium occurs. In all experiments
via route B precipitation was never observed; therefore
another mechanism should be operative here.
Combining the above-mentioned observations, we pro-
pose that thioether synthesis via route B occurs by
pathway I of the mechanism depicted in Scheme 3.
The first two steps are similar to the mechanism
proposed for the polymerization reaction. The only dif-
ference is that deprotonation in thioether synthesis will
take place by a thiolate anion since a thiol has a lower
pKa value than an alcohol.31 Overall addition of a thiol
to the unsymmetrical p-xylylene 11 gives the unsym-
metrically substituted thioether 9. Substitution of the
sulfonium group by chlorine, induced by azeotropical
removal of tetrahydrothiophene, leads to monosubsti-
tuted thioether 6. Apparently, the rate of introduction
of a thioether via an elimination-addition reaction (path-
way I) exceeds the rate of introduction via a nucleophilic
substitution (pathway II). Since 9 will not give a p-
Recently, Pierce et al.27 described a high selectivity for
the synthesis of the unsymmetrically substituted com-
pound (4-(chloromethyl)phenyl)methan-1-ol starting from
the symmetrical (4-(hydroxymethyl)phenyl)methan-1-ol.
They proposed a mechanism in which the reaction pro-
ceeds via a p-xylylene oxide derivative. However, no
further evidence for the existence of this intermediate
was presented.
(27) Pierce, M. E.; Harris, G. D.; Islam, Q.; Radesca, L. A.; Storace,
L.; Waltermire, R. E.; Wat, E.; J adhav, P. K.; Emmett, G. C. J . Org.
Chem. 1996, 61, 444.
(28) Cho, B. R.; Han, M. S.; Suh, Y. S.; Oh, K. J .; J eon, S. J . J . Chem.
Soc., Chem. Commun. 1993, 564.
(29) Cho, B. R.; Kim, Y. K.; Han, M. S. Macromolecules 1998, 31,
2098.
(30) Ingold, C. K. In Structure and Mechanisms in Organic Chem-
istry; Bell: London, 1953; Chapter 7, p 24.
The polymerization reaction of bissulfonium salts pro-
ceeds via a p-xylylene intermediate like 11, which under-
(25) Madesclaire, M. Tetrahedron 1986, 42, 5459.
(26) Kim, K. S.; Hwang, H. J .; Cheong, C. S.; Hahn, C. S. Tetrahe-
dron Lett. 1990, 31, 2893.
(31) Crampton, M. R. In The Chemistry of the Thiol Group; Patai,
S., Ed.; J ohn Wiley & Sons Ltd.: Chichester, U.K., 1974; pp 379-
415.

3110 J . Org. Chem., Vol. 64, No. 9, 1999
van Breemen et al.
Sch em e 3
F igu r e 2. UV-vis spectra for QM 11: (a) polymerization of 8 at different time intervals, (b) thioether synthesis via route B at
different time intervals. Both spectra were obtained in MeOH at room temperature under the conditions described in the
Experimental Section.
place. Exploration of the scope and limitations of this
route starting from other bissulfonium salts is currently
under way. Results of UV-vis and product studies reveal
that thioether synthesis via this route proceed via the
unsymmetrical p-xylylene intermediate 11. Selective
oxidation of the thioethers obtained from this new route
affords sulfinyl monomers for PPV precursors, with a
2-fold increase in overall yield compared to route A, which
was used previously to synthesize these compounds.
Exp er im en ta l Section
Rea gen ts a n d Meth od s. Unless stated otherwise, all
reagents and chemicals were obtained from commercial sources
and used without further purification. All reactions were
conducted under an inert atmosphere of nitrogen.
1H NMR spectra were obtained in a deuterated solvent
F igu r e 3. Change of absorbance (316 nm) of 11 with time:
(CDCl3 or D2O) at 400 MHz. Chemical shifts (δ) in ppm were
(a) polymerization, (b) thioether synthesis via route B, (c)
determined relative to the residual nondeuterated solvent
thioether synthesis via route C, (d): thioether synthesis
absorption (7.24 ppm for CHCl3, 4.72 ppm for H2O). The 13C
starting from bisammonium-p-xylene.
NMR experiments were recorded at 100 MHz on the same
spectrometer. Chemical shifts were defined relative to the 13C
resonance shift of CHCl3 (77.0 ppm). Resonance assignments
were achieved by the use of one- and two-dimensional NMR
techniques such as 1H, 13C, attached proton test (APT), 2D
HETCOR (J ) 8 Hz, J ) 140 Hz), 2D COSY, and 2D
INADEQUATE and will be desribed elsewhere.32 For direct
insert probe mass spectra electron impact (EI) was used as
ionization mode. Ionization energy was 70 eV. Melting points
are uncorrected.
xylylene derivative under the reaction conditions used,
disubstitution is suppressed if 1 equiv of thiol is used.
Con clu sion s
The novel route described herein is a highly selective
one in which, starting from a symmetrical bissulfonium
salt 8, unsymmetrically substituted thioethers 6a -g are
obtained with selectivities of 90%. Stoichiometry of the
reactants used is very important to ensure this high
selectivity and to prevent side reactions from taking
(32) van Breemen, A. J . J . M.; Issaris, A. C. J .; de Kok, M. M.;
Adriaensens, P. J .; Vanderzande, D. J . M.; Gelan, J . M. J . V. Magn.
Reson. Chem., submitted for publication.

Unsymmetrically Substituted Monomers
J . Org. Chem., Vol. 64, No. 9, 1999 3111
1
Wa ter Deter m in a tion by H NMR. A blank sample of D2O
if necessary, and concentrated in vacuo. The crude product was
diluted with CHCl3 (200 mL), and the precipitate was filtered
off. The filtrate was concentrated in vacuo. The oil thus
obtained was diluted with n-octane or petroleum ether (boiling
range 100-130 °C) and concentrated to remove tetrahy-
drothiophene. This sequence was repeated three times.
1-(Ch lor om e t h yl)-4-[(n -b u t ylsu lfa n yl)m e t h yl]b e n -
zen e (6a ). This compound was synthesized according to the
general procedure for route A or route B, starting from
n-butanethiol (9.02 g, 0.1 mol (route A); 1.71 g, 19 mmol (route
B)) to give a crude mixture of 5, 6a , and 7a as a light yellow
solid (yield 44.24 g; 4.30 g).
1-(Ch lor om e t h yl)-4-[(isob u t ylsu lfa n yl)m e t h yl]b e n -
zen e (6b). This compound was synthesized according to the
general procedure for route A or route B, starting from
isobutanethiol (9.02 g, 0.1 mol (route A); 1.71 g, 19 mmol (route
B)) to give a crude mixture of 5, 6b, and 7b as a light yellow
solid (yield 44.00 g; 4.25 g).
1-(Ch lor om et h yl)-4-[(sec-b u t ylsu lfa n yl)m et h yl]b en -
zen e (6c). This compound was synthesized according to the
general procedure for route A or route B, starting from sec-
butanethiol (9.02 g, 0.1 mol (route A); 1.71 g, 19 mmol (route
B)) to give a crude mixture of 5, 6c, and 7c as a light yellow
solid (yield 44.32 g; 4.32 g).
1-(Ch lor om et h yl)-4-[(ter t-b u t ylsu lfa n yl)m et h yl]b en -
zen e (6d ). This compound was synthesized according to the
general procedure for route A or route B, starting from tert-
butanethiol (9.02 g, 0.1 mol (route A); 1.71 g, 19 mmol (route
B)) to give a crude mixture of 5, 6d , and 7d as a light yellow
solid (yield 43.79 g; 4.22 g).
1-(Ch lor om et h yl)-4-[(isop en t ylsu lfa n yl)m et h yl]b en -
zen e (6e). This compound was synthesized according to the
general procedure for route A or route B, starting from
isopentanethiol (10.42 g, 0.1 mol (route A); 1.98 g, 19 mmol
(route B)) to give a crude mixture of 5, 6e, and 7e as a light
yellow solid (yield 44.95 g; 4.51 g).
1-(C h lor o m e t h yl)-4-[(n -oc t y lsu lfa n yl)m e t h y l]b e n -
zen e (6f). This compound was synthesized according to the
general procedure for route A or route B, starting from
n-octanethiol (14.63 g, 0.1 mol (route A); 2.78 g, 19 mmol (route
B)) to give a crude mixture of 5, 6f, and 7f as a light yellow
solid (yield 49.21 g; 5.30 g).
1-(Ch lor om eth yl)-4-[({2-[2-(2-m eth oxyeth oxy)eth oxy]-
eth yl}su lfa n yl)m eth yl]ben zen e (6g). This compound was
synthesized according to the general procedure for route A or
route B, starting from 2-[2-(2-methoxyethoxy)ethoxy]ethylthiol
(18.03 g, 0.1 mol (route A); 3.42 g, 19 mmol (route B)) to give
a crude mixture of 5, 6g, and 7g as a light yellow solid (yield
52.30 g; 5.90 g).
1-(C h lor o m e t h y l)-4-[(n -oc t y lsu lfa n yl)m e t h y l]b e n -
zen e (6f) via Rou te C. A mixture of NaOtBu (1.83 g, 19
mmol) and n-octanethiol (2.78 g, 19 mmol) in MeOH (40 g)
was stirred for 30 min at 20 °C. The clear solution was added
dropwise to a stirred solution of 5 (3.33 g, 19 mmol) in MeOH
(100 g). After 1 h the reaction mixture was neutralized with
aqueous HCl (1 M), diluted with CHCl3 (250 mL), washed with
H2O (2 × 100 mL), dried over MgSO4, and concentrated in
vacuo to give a yellow oil (yield 5.29 g).
(750 µL) was recorded quantitatively using a delay time of 60
s, and the H2O signal was integrated (A). A 15 mg sample of
product was introduced in the same tube, and the sample was
recorded under the same conditions. The H2O signal was again
integrated (B), after which subtraction of B from A gave the
integration (C) corresponding to the amount of water from the
product. C can be correlated to another known proton signal
of the product leading to a formula of the type: product‚xH2O.
UV-Vis Sp ectr oscop y. All MeOH used in preparation of
the solutions was thoroughly purged with nitrogen before use.
A magnetic stirrer was incorporated in the sample holder of
the UV-vis spectrometer to achieve efficient mixing of the
reagents.
A stock solution of 8 was made by dissolving 18.3 mg (52.1
µmol) in MeOH (100 mL) to generate a 0.52 mM solution. The
same concentration range was used for all other compounds.
Stock solution NaOtBu: 12.5 mg (130.3 µmol) in MeOH (250
mL). Stock solution NaOtBu + n-octanethiol: 12.5 mg of
NaOtBu (130.3 µmol) + 19.1 mg of n-octanethiol (130.3 µmol)
in MeOH (250 mL). Stock solution R,R′-bis(triethylammonium)-
p-xylene: 25.5 mg (52.1 µmol) in MeOH (100 mL). Stock
solution 5: 18.2 mg (104.0 µmol) in MeOH (200 mL).
Mon itor in g P olym er iza tion . Stock solution of 8 (100 µL)
was transferred by syringe to a quartz cuvette and diluted with
MeOH (1.5 mL). A blank spectrum was recorded at ambient
temperature against a MeOH reference. Next, NaOtBu solu-
tion (100 µL) was injected in the cuvette, and spectra were
acquired from 200 to 400 nm (scan rate “fast”) at different
programmed time intervals, or the change in absorbance at
λmax (316 nm) was monitored in time (sampling interval 0.2
nm).
Mon itor in g Mon om er Syn th esis via Rou te B. The same
procedure was followed as for polymerization starting from 8
now using the NaOtBu/n-octanethiol stock solution.
Mon itor in g Mon om er Syn th esis via Rou te C. The same
procedure was followed as for route B now starting from 5.
Mon itor in g Mon om er Syn th esis Sta r tin g fr om r,r′-
Bis(tr ieth yla m m on iu m )-p-xylen e. The same procedure was
followed as for route B now starting from R,R′-bis(triethylam-
monium)-p-xylene.
Syn th esis. 1,4-Bis(tetr ah ydr oth ioph en iom eth yl)xylen e
Dich lor id e (8). A solution of 5 (52.5 g, 0.3 mol) and tetrahy-
drothiophene (105 mL, 1.19 mol) in MeOH (105 mL) was
stirred for 60 h at ambient temperature. The reaction mixture
was precipitated in acetone (420 mL) at -10 °C. The precipi-
tate was collected and washed with cold acetone (600 mL).
Evaporation of the solvent gave a white hygroscopic solid (95.9
g, 91%): 1H NMR (D2O, 400 MHz) δ 2.12-2.30 (m, 8H), 3.31-
3.50 (m, 8H), 4.48 (s, 4H), 7.53 (s, 4H) ppm.
r,r′-Bis(t r iet h yla m m on iu m )-p -xylen e. A well-stirred
amount of dibromo-p-xylene (11.8 g, 45 mmol), Et3N (25 mL,
180 mmol), and EtOH (250 mL) was refluxed for 72 h. After
cooling the reaction mixture, the precipitate was filtered off,
washed with Et2O (2 × 100 mL), and dried under vacuum to
give a white solid (19.9 g, 95%): 1H NMR (D2O, 400 MHz) δ
1.32 (t, J ) 9.6 Hz, 18H), 3.17 (q, J ) 9.6 Hz, 12H), 4.39 (s,
4H), 7.56 (s, 4H) ppm.
1-(Ch lor om et h yl)-4-[(a lk ylsu lfa n yl)m et h yl]b en zen es
(6a -g) via Rou te A. Gen er a l P r oced u r e. To a stirred
mixture of 5 (39.4 g, 0.225 mol) in toluene (400 mL), NaOH
(23.7 g, 0.59 mol) in H2O (400 mL) and Aliquat 336 (1 g) was
added a solution of thiol (0.10 mol, 0.45 equiv) in toluene (100
mL) dropwise over a period of 24 h at room temperature. The
organic layer was washed with H2O (3 × 200 mL), dried over
MgSO4, and concentrated in vacuo.
1-(Ch lor om et h yl)-4-[(a lk ylsu lfa n yl)m et h yl]b en zen es
(6a -g) via Rou te B. Gen er a l P r oced u r e. A mixture of
NaOtBu (1.83 g, 19 mmol) and thiol (19 mmol) in MeOH (40
g) was stirred for 30 min at the temperatures indicated in the
text. The temperature was maintained by a thermostated
experimental setup. The clear solution was added in one
portion to a stirred solution of 8 (6.68 g, 19 mmol) in MeOH
(100 g) at the temperatures indicated in the text. After 1 h
the reaction mixture was neutralized with aqueous HCl (1 M),
1-(Br om om e t h yl)-4-[(n -b u t ylsu lfa n yl)m e t h yl]b e n -
zen e. A mixture of NaOtBu (0.97 g, 10 mmol) and n-
butanethiol (0.88 g, 9.8 mmol) in MeOH (20 g) was stirred for
30 min at 20 °C. The clear solution was added in one portion
to a stirred solution of R,R′-bis(triethylammonium)-p-xylene
(4.66 g, 10 mmol) in MeOH (50 g). After 1 h the reaction
mixture was neutralized with aqueous HCl (1 M) and concen-
trated in vacuo to give a white solid identified as R,R′-bis-
(triethylammonium)-p-xylene (yield 4.60 g, 99%).
Gen er a l P r oced u r e for th e Oxid a tion of Th ioeth er s
fr om Rou te A; Rou te B. An aqueous (35 wt %) solution of
H2O2 (11.7 g, 0.12 mol; 3.4 g, 35 mmol) was added dropwise to
a solution of crude thioether (∼0.06 mol; ∼17 mmol) in MeOH
(400 mL; 125 mL) and TeO2 (1.44 g, 5 mol %; 0.28 g). After 6
h the reaction was quenched by adding a saturated aqueous
NaCl solution (200 mL; 75 mL). The reaction mixture was
extracted with CHCl3 (3 × 150 mL; 3 × 50 mL), and the

3112 J . Org. Chem., Vol. 64, No. 9, 1999
van Breemen et al.
combined organic layers were dried over MgSO4 and concen-
trated in vacuo. The reaction mixture was purified by column
chromatography (SiO2, eluent CHCl3) and subsequent crystal-
lization from CH2Cl2/hexane. The yields given below (route A;
route B) are referred to starting compound 5.
and 7e from route A to give 1e as a white solid (18.63 g, 32%,
3.61 g, 67%): mp 90.0-91.0 °C. Rf ) 0.47 (CHCl3/MeOH 99:
1). 1H NMR (CDCl3, 400 MHz): δ 0.88 (d, J ) 6.4 Hz, 3H),
0.90 (d, J ) 6.4 Hz, 3H), 1.50-1.70 (m, 1H), 1.50-1.70 (m,
2H), 2.56 (m, 2H), 3.93 + 3.94 (dd, J AB ) 13.2 Hz, 2H), 4.56
(s, 2H), 7.27 (d, J ) 8.4 Hz, 2H), 7.38 (d, J ) 8.4 Hz, 2H) ppm.
13C NMR (CDCl3, 100 MHz): δ 22.0, 22.2, 27.5, 30.8, 45.6, 49.0,
57.4, 129.0, 130.1, 130.3, 137.5 ppm. IR (KBr): ν 2959, 2912,
2872, 1025 cm-1. MS (EI, m/z, rel int (%)): 258 ([M]+, 20), 223
([C13H19OS]+, 32), 139 ([C8H8Cl]+, 100), 104 ([C8H8]+, 20), 77
([C6H5]+, 7). Anal. Calcd for C13H19ClOS: C, 60.33; H, 7.40;S,
12.39. Found: C, 60.65; H, 7.67; S, 12.13.
1-(C h lo r o m e t h y l)-4-[(n -b u t y ls u lfin y l)m e t h y l]b e n -
zen e (1a ). This compound was synthesized according to the
general procedure starting from the crude mixture of 5, 6a ,
and 7a to give 1a as a white solid (18.16 g, 33%; 3.46 g, 68%):
1
mp 111.5-112.5 °C. Rf ) 0.43 (CHCl3/MeOH 99:1). H NMR
(CDCl3, 400 MHz): δ 0.90 (t, J ) 7.2 Hz, 3H), 1.41 (m, 2H),
1.70 (m, 2H), 2.56 (t, J ) 8.0 Hz, 2H), 3.92 + 3.95 (dd, J AB
)
13.2 Hz, 2H), 4.55 (s, 2H), 7.27 (d, J ) 8.0 Hz, 2H), 7.38 (d, J
) 8.0 Hz, 2H) ppm. 13C NMR (CDCl3, 100 MHz): δ 13.1, 21.3,
23.8, 45.1, 50.2, 56.9, 128.4, 129.8, 129.9, 136.8 ppm. IR
(KBr): ν 2965, 2902, 2870, 1025 cm-1. MS (EI, m/z, rel int
(%)): 244 ([M]+, 9), 209 ([C12H17OS]+, 5), 139 ([C8H8Cl]+, 100),
104 ([C8H8]+, 19), 77 ([C6H5]+, 5). Anal. Calcd for C12H17ClOS:
C, 58.88; H, 7.00; S, 13.10. Found: C, 59.26; H, 7.09; S, 12.89.
1-(Ch lor om e t h yl)-4-[(isob u t ylsu lfin yl)m e t h yl]b e n -
zen e (1b). This compound was synthesized according to the
general procedure starting from the crude mixture of 5, 6b,
and 7b to give 1b as a white solid (16.45 g, 30%, 3.39 g, 66%):
1-(Ch lor om eth yl)-4-[(n -octylsu lfin yl)m eth yl]ben zen e
(1f). This compound was synthesized according to the general
procedure starting from the crude mixture of 5, 6f, and 7f to
give 1f as a white solid (20.99 g, 31%, 4.25 g, 68%): mp 109.5-
110.5 °C. Rf ) 0.52 (CHCl3/MeOH 99:1). 1H NMR (CDCl3, 400
MHz): δ 0.84 (t, J ) 6.8 Hz, 3H), 1.23 (m, 8H), 1.36 (m, 2H),
1.70 (m, 2H), 2.53 (t, J ) 7.8 Hz, 2H), 3.91 + 3.93 (dd, J AB
)
13.0 Hz, 2H), 4.55 (s, 2H), 7.26 (d, J ) 8.0 Hz, 2H), 7.37 (d, J
) 8.0 Hz, 2H) ppm. 13C NMR (CDCl3, 100 MHz): δ 14.0, 22.4,
22.5, 28.7, 28.9, 29.1, 31.6, 45.6, 51.0, 57.6, 129.1, 130.2, 130.3,
137.5 ppm. IR (KBr): ν 2959, 2918, 2847, 1024 cm-1. MS (EI,
m/z, rel int (%)): 300 ([M]+, 5), 265 ([C16H25OS]+, 82), 139
([C8H8Cl]+, 100), 104 ([C8H8]+, 45), 77 ([C6H5]+, 5). Anal. Calcd
for C16H25ClOS: C, 63.87; H, 8.37; S, 10.66. Found: C, 64.15;
H, 8.69; S, 10.32.
1
mp 116.0-117.0 °C. Rf ) 0.41 (CHCl3/MeOH 99:1). H NMR
(CDCl3, 400 MHz): δ 1.02 (d, J ) 6.8 Hz, 3H), 1.02 (d, J ) 6.8
Hz, 3H), 2.17 (m, 1H), 2.29 + 2.32 (d, J ) 12.4 Hz, 1H), 2.54
+ 2.57 (d, J ) 12.4 Hz, 1H), 3.92 + 3.95 (dd, J AB ) 12.8 Hz,
2H), 4.57 (s, 2H), 7.27 (d, J ) 8.4 Hz, 2H), 7.38 (d, J ) 8.4 Hz,
2H) ppm. 13C NMR (CDCl3, 100 MHz): δ 21.4, 22.8, 23.6, 45.6,
58.2, 60.4, 129.0, 130.1, 130.3, 137.4 ppm. IR (KBr): ν 2964,
2911, 2894, 2870, 1019 cm-1. MS (EI, m/z, rel int (%)): 244
([M]+, 16), 209 ([C12H17OS]+, 39), 139 ([C8H8Cl]+, 100), 104
([C8H8]+, 21), 77 ([C6H5]+, 7). Anal. Calcd for C12H17ClOS: C,
58.88; H, 7.00; S, 13.10. Found: C, 59.41; H, 7.15; S, 12.82.
1-(Ch lor om e t h yl)-4-[(sec-b u t ylsu lfin yl)m e t h yl]b e n -
zen e (1c). This compound was synthesized according to the
general procedure starting from the crude mixture of 5, 6c,
and 7c to give 1c as a white solid (16.52 g, 30%, 3.34 g, 65%):
1-(Ch lor om eth yl)-4-[({2-[2-(2-m eth oxyeth oxy)eth oxy]-
eth yl}su lfin yl)m eth yl]ben zen e (1g). This compound was
synthesized according to the general procedure starting from
the crude mixture of 5, 6g, and 7g to give 1g as a white solid
(20.34 g, 27%, 4.50 g, 64%): mp 51.0-53.0 °C. Rf ) 0.17
1
(CHCl3/MeOH 99:1). H NMR (CDCl3, 400 MHz): δ 2.70 (m,
1H), 2.90 (m, 1H), 3.33 (s, 3H), 3.51 (m, 2H), 3.61 (m, 2H),
3.64 (m, 4H), 3.84 + 3.92 (m, 2H), 3.98 + 4.11 (dd, J AB ) 12.8
Hz, 2H), 4.57 (s, 2H), 7.28 (d, J ) 8.0 Hz, 2H), 7.38 (d, J ) 8.0
Hz, 2H) ppm. 13C NMR (CDCl3, 100 MHz): δ 45.5, 50.3, 57.4,
58.7, 63.0, 70.1, 70.2, 70.2, 71.6, 128.7, 130.0, 130.4, 137.2 ppm.
IR (KBr): ν 2883, 1384, 1135, 1116, 1032 cm-1. MS (EI, m/z,
rel int (%)): 334 ([M]+, 8), 299 ([C15H23O4S]+, 8), 139 ([C8H8-
Cl]+, 100), 104 ([C8H8]+, 16), 77 ([C6H5]+, 5). Anal. Calcd for
1
mp 105.0-107.0 °C. Rf ) 0.40 (CHCl3/MeOH 99:1). H NMR
(CDCl3, 400 MHz): δ 0.99 + 1.02 (t, J ) 7.2 Hz, 3H), 1.24 +
1.29 (d, J ) 6.8 Hz, 3H), 1.56 (m, 1H), 1.81 + 1.92 (m, 1H),
2.41 + 2.58 (m, 1H), 3.78 + 3.95 (dd, J AB ) 12.8 Hz, 1H), 3.86
+ 3.92 (dd, J AB ) 12.8 Hz, 1H), 4.57 (s, 2H), 7.28 (d, J ) 8.0
Hz, 2H), 7.38 (d, J ) 8.0 Hz, 2H) ppm. 13C NMR (CDCl3, 100
MHz): δ 10.1, 10.5, 11.2, 12.2, 22.0, 24.1, 45.5, 45.6, 53.6, 54.3,
54.4, 55.5, 128.8, 128.9, 130.0, 130.2, 130.8, 137.2 ppm. IR
(KBr): ν 2966, 2917, 2876, 1020 cm-1; MS (EI, m/z, rel int
(%)): 244 ([M]+, 4), 209 ([C12H17OS]+, 5), 139 ([C8H8Cl]+, 100),
104 ([C8H8]+, 19), 77 ([C6H5]+, 5). Anal. Calcd for C12H17ClOS:
C, 58.88; H, 7.00; S, 13.10. Found: C, 59.08; H, 6.72; S, 12.86.
1-(Ch lor om et h yl)-4-[(ter t-b u t ylsu lfin yl)m et h yl]b en -
zen e (1d ). This compound was synthesized according to the
general procedure starting from the crude mixture of 5, 6d ,
and 7d from route A to give 1d as a white solid (15.97 g, 29%,
3.25 g, 64%): mp 101.0-103.0 °C. Rf ) 0.38 (CHCl3/MeOH
C
15H23ClO4S: C, 53.80; H, 6.92; S, 9.58. Found: C, 53.71; H,
7.05; S, 9.19.
Ack n ow led gm en t. One of us (A.v.B.) acknowledges
a grant supported within the framework of the BRITE/
EURAM project BE96-3510 LEDsplay. The Inter Uni-
versity Attraction Pole (IUAP, contract number P4/11)
supported by the Belgian Government and the Fonds
voor Wetenschappelijk Onderzoek (FWO) are acknowl-
edged for financial support. A.v.B. wishes to thank Dr.
H. Haitjema for carefully reading the manuscript. Dr.
J . Van Gronsveld is kindly acknowledged for allowing
A.v.B. the use of its UV-vis spectrophotometer. Fur-
thermore we would like to thank H. Amatdjais and Prof.
B. Zwanenburg of the University of Nijmegen, The
Netherlands, for performing the elemental analysis.
1
99:1). H NMR (CDCl3, 400 MHz): δ 1.30 (s, 9H), 3.59 + 3.79
(dd, J AB ) 12.4 Hz, 2H), 4.56 (s, 2H), 7.31 (d, J ) 8.4 Hz, 2H),
7.36 (d, J ) 8.4 Hz, 2H) ppm. 13C NMR (CDCl3, 100 MHz): δ
22.9, 45.8, 52.3, 53.7, 129.0, 130.4, 132.3, 137.1 ppm. IR
(KBr): ν 2962, 1384, 1037 cm-1. MS (EI, m/z, rel int (%)): 244
([M]+, 5), 209 ([C12H17OS]+, 27), 139 ([C8H8Cl]+, 100), 104
([C8H8]+, 34), 77 ([C6H5]+, 11), 57 ([C4H9]+, 80). Anal. Calcd
for C12H17ClOS: C, 58.88; H, 7.00; S, 13.10. Found: C, 58.97;
H, 6.85; S, 12.96.
Su p p or tin g In for m a tion Ava ila ble: Spectral character-
ization of sulfinyl monomers 1a -g (1H and 13C spectra),
1
analysis by means of H NMR of crude reaction mixtures of
1
routes A, B, and C using 1 equiv of n-octanethiol, and H NMR
spectra of 5 and 7f. This material is available free of charge
via the Internet at http://pubs.acs.org.
1-(Ch lor om et h yl)-4-[(isop en t ylsu lfin yl)m et h yl]b en -
zen e (1e). This compound was synthesized according to the
general procedure starting from the crude mixture of 5, 6e,
J O9821022