U.S. patent application number 10/942409 was filed with the patent office on 2005-03-24 for process for the purification of thiophenes.
Invention is credited to Brassat, Lutz, Kirchmeyer, Stephan.
Application Number | 20050065352 10/942409 |
Document ID | / |
Family ID | 34177890 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050065352 |
Kind Code |
A1 |
Brassat, Lutz ; et
al. |
March 24, 2005 |
Process for the purification of thiophenes
Abstract
The invention relates to a process for the purification of
thiophenes by means of precipitation. The purified thiophenes are
liquid at room temperature, have a purity of at least 99.50 wt. %,
and are represented by the following general formula (I), 1 wherein
R.sup.1 and R.sup.2 independently of each other are, for example, a
linear or branched C.sub.1-C.sub.20-alkyl group, or together form a
fused C.sub.1-C.sub.20-dioxyalylene ring. The process involves: (I)
precipitating the thiophene by cooling a solution of the thiophene
and at least one solvent; or (II) precipitating the thiophene by
adding the thiophene to a cooled solution of solvent and optionally
the thiophene. The solutions are cooled to a temperature below the
melting point of the thiophene.
Inventors: |
Brassat, Lutz; (Leverkusen,
DE) ; Kirchmeyer, Stephan; (Leverkusen, DE) |
Correspondence
Address: |
BAYER MATERIAL SCIENCE LLC
100 BAYER ROAD
PITTSBURGH
PA
15205
US
|
Family ID: |
34177890 |
Appl. No.: |
10/942409 |
Filed: |
September 16, 2004 |
Current U.S.
Class: |
549/13 |
Current CPC
Class: |
H01G 11/48 20130101;
C07D 333/32 20130101; H05K 3/424 20130101; Y02E 60/13 20130101;
C08G 61/126 20130101; C07D 495/04 20130101 |
Class at
Publication: |
549/013 |
International
Class: |
C07D 335/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 23, 2003 |
DE |
10343873.4 |
Claims
What is claimed is:
1. A process for purifying a thiophene represented by general
formula (I), 6wherein, R.sup.1 and R.sup.2 are each selected
independently from the group consisting of hydrogen, linear or
branched C.sub.1-C.sub.20-alkyl groups, linear or branched
C.sub.1-C.sub.20-oxyalkyl groups, linear or branched
C.sub.1-C.sub.20-oxyalkyl groups which are interrupted by 1 to 5
oxygen atoms, linear or branched C.sub.1-C.sub.20-oxyalkyl groups
which are interrupted by 1 to 5 sulphur atoms, a fused ring of
linear or branched C.sub.1-C.sub.20-dioxyalkylene formed by R.sup.1
and R.sup.2 together, and a fused ring of linear or branched
C.sub.1-C.sub.20-dioxyar- ylene formed by R.sup.1 and R.sup.2
together, and said thiophene being liquid at room temperature, said
method being selected from the group consisting of, a method (I)
comprising, (a) providing a first solution comprising said
thiophene and at least one solvent, and (b) cooling said first
solution to a temperature below the melting temperature of said
thiophene, thereby precipitating said thiophene as a solid from
said first solution, and a method (II) comprising, (a) providing a
second solution comprising at least one solvent and optionally said
thiophene, (b) cooling said second solution to a temperature below
the melting temperature of said thiophene, to form a cooled second
solution, and (c) adding said thiophene to said cooled second
solution, thereby precipitating said thiophene as a solid from said
cooled second solution.
2. The process of claim 1 wherein said thiophene is a compound
represented by general formula (II) 7wherein, A is selected from
the group consisting of a C.sub.1-C.sub.5-alkylene radical, a
substituted C.sub.1-C.sub.5-alkylene radical, a
C.sub.1-C.sub.12-arylene radical and a substituted
C.sub.1-C.sub.12-arylene radical, the substituted groups of said
substituted C.sub.1-C.sub.5-alkylene radical and said substituted
C.sub.1-C.sub.12-arylene radical being selected independently from
the group consisting of halogen, ether, thioether, disulfide,
sulfoxide, sulfone, sulfonate, amino, aldehyde, keto, carboxylic
acid ester, carboxylic acid, carbonate, carboxylate, cyano,
alkylsilane, alkoxysilane and carboxylamide groups, R is selected,
independently for each x, from the group consisting of a linear or
branched C.sub.1-C.sub.18-alkyl radical, a
C.sub.5-C.sub.12-cycloalkyl radical, a C.sub.6-C.sub.14-aryl
radical, a C.sub.7-C.sub.18-aralkyl radical, a
C.sub.1-C.sub.4-hydroxyalk- yl radical and a hydroxyl radical, x
represents an integer from 0 to 8.
3. The process of claim 2 wherein said thiophene is a compound
represented by the general formula (IIa), 8wherein R is,
independently for each y, as defined in claim 2 and y denotes 0, 1,
2, 3 or 4.
4. The process of claim 3 wherein y is 0 or 1.
5. The process of claim 1 wherein said solvent comprises at least
one alcohol.
6. The process of claim 1 wherein the said first solution and said
second solution are each cooled to a temperature that is at least
20.degree. C. below the melting point of said thiophene.
7. The process of claim 1 wherein said method (I) further comprises
separating the precipitated solid thiophene from said first
solution at a temperature that is at least 20.degree. C. below the
melting point of said thiophene, and said method (II) further
comprises separating the precipitated solid thiophene from said
cooled second solution at a temperature that is at least 20.degree.
C. below the melting point of said thiophene.
8. The process of claim 1 wherein said method (I) further comprises
removing residual solvent from the precipitated solid thiophene by
means of distillation, and said method (II) further comprises
removing residual solvent from the precipitated solid thiophene by
means of distillation.
9. The purified thiophene prepared by the process of claim 1
wherein the purified thiophene has a purity of at least 99.50 wt.
%.
10. A thiophene represented by general formula (I), 9wherein,
R.sup.1 and R.sup.2 are each selected independently from the group
consisting of hydrogen, linear or branched C.sub.1-C.sub.20-alkyl
groups, linear or branched C.sub.1-C.sub.20-oxyalkyl groups, linear
or branched C.sub.1-C.sub.20-oxyalkyl groups which are interrupted
by 1 to 5 oxygen atoms, linear or branched
C.sub.1-C.sub.20-oxyalkyl groups which are interrupted by 1 to 5
sulphur atoms, a fused ring of linear or branched
C.sub.1-C.sub.20-dioxyalkylene formed by R.sup.1 and R.sup.2
together, and a fused ring of linear or branched
C.sub.1-C.sub.20-dioxyarylene formed by R.sup.1 and R.sup.2
together, and said thiophene having a purity of at least 99.50 wt.
%.
11. The thiophene of claim 10 wherein the thiophene is
3,4-ethylenedioxythiophene.
12. The thiophene of claim 10 wherein the thiophene has a content
of dimethoxythiophene of less than 0.05 wt. %.
13. A conductive polymer comprising residues of the thiophene of
claim 10.
14. A semiconductor comprising the conductive polymer of claim
13.
15. An article of manufacture selected from the group consisting of
capacitors and printed circuit boards, wherein said article of
manufacture comprises the conductive polymer of claim 13.
Description
CROSS REFERENCE TO RELATED PATENT APPLICATION
[0001] The present patent application claims the right of priority
under 35 U.S.C. .sctn.119 (a)-(d) of German Patent Application No.
103 43 873.4, filed Sep. 23, 2003.
FIELD OF THE INVENTION
[0002] The invention relates to a process for the purification of
thiophenes which are liquid at room temperature, the thiophenes
purified by this process and their use.
BACKGROUND OF THE INVENTION
[0003] Thiophenes are used, for example, for the preparation of
conductive polymers. Poly(3,4-alkylenedioxythiophenes) such as are
described, for example, in EP-A 339 340, are of particular interest
in this context. These compounds are distinguished by particular
properties, such as high conductivity, high transparency and
outstanding long-term stability. They have therefore found
increasing use in industry as organic conductive polymers. Thus
e.g. through-plating of printed circuit boards, antistatic
treatment of photographic films and use as an electrode or solid
electrolyte in solid electrolyte capacitors are described as
important fields of use.
[0004] An important prerequisite in the preparation of organic
conductive polymers is high purity of the starting substances
needed for their preparation. Impurities contained in the starting
substance can adversely influence the polymerization in that the
polymerization does not take place, or takes-place only very slowly
or incompletely, or is accelerated to an uncontrolled extent. The
processing time of these monomers can consequently drop
drastically, so that these can no longer be employed in the
processing processes.
[0005] In addition, the properties of the resulting polymers may
also be adversely influenced in that the impurities, for example,
adversely change the intrinsic colour of the resulting polymer and
as a result the transparency, which is essential for the use of the
polymers e.g. as transparent conductive or antistatic coatings, is
impaired.
[0006] Impurities which are also capable of polymerization can be
co-incorporated into the polymer and thereby significantly lower
the conductivity thereof. Further adverse effects of impurities can
be that the order of the conductive layers may be lowered by
impurities, whereby poorer conductivities result, that impurities
become concentrated on the surface of the polymer after the
polymerization and undesirable transition resistances thereby
result, so that the function of the conductive layer is restricted,
or that the long-term stability of the conductive polymers is
adversely influenced in that the impurities, for example, initiate
reaction of the conductive polymer with oxygen and thus
significantly impair the properties of the polymer.
[0007] The starting substances which are needed for the preparation
of organic conductive polymers and are as a rule prepared from raw
materials by chemical reactions, are therefore purified before
their use.
[0008] A number of purification operations which are in principle
suitable for purification of the monomers for the polymerization to
give organic conductive polymers are known to the expert. Such
purification methods are, for example, distillation, sublimation,
extraction, crystallization, chromatography and adsorption. These
purification methods have been known to the expert for a long time
and are described in the usual textbooks.
[0009] Thiophenes which are liquid at room temperature and are
suitable for the preparation of electrically conductive polymers
are of particular importance because of their easy processability
in the liquid form. For the purification of these thiophenes the
expert has available the purification methods which can be used on
liquid substances, preferably distillation, which is also carried
out on a large industrial scale, extraction and chromatography.
[0010] Distillative purification of thiophenes as monomers for use
for the preparation of electrically conductive polymers is known,
for example, from EP-A 1 142 888. The doctrine of EP-A 1 142 888 is
that the number and amount of by-products can be reduced by
optimized reaction conditions and e.g. 3,4-ethylenedioxythiophene
is obtainable in a purity of up to 97.7%. However, the doctrine of
EP-A 1 142 888 furthermore is that for further purification an
additional extraction is necessary in order to remove water-soluble
by-products and to achieve a purity of more than 99%.
3,4-Dimethoxythiophene predominantly occurs as a secondary
component, i.e. impurity, in this synthesis of
3,4-ethylenedioxythiophene- .
[0011] Furthermore, separating off of compounds by distillation is
only possible if the components to be separated differ
significantly, i.e. by more than 1.degree. C., in their boiling
points. The less the boiling points differ, the greater the
expenditure on apparatus for the separation, so that such
separations are no longer to be carried out economically. Since
substituted thiophenes, such as, for example,
alkylenedioxythiophenes, are preferably distilled under reduced
pressure, the difference in the boiling points is reduced further,
which further increases the expenditure on separation.
[0012] The purification of 3,4-alkylenedioxythiophenes, in
particular of 3,4-ethylenedioxythiophene, which are contaminated
with 3,4-dimethoxythiophene represents a particular difficulty.
Thus, for example, 3,4-dimethoxythiophene produced during the
synthesis of 3,4-ethylenedioxythiophene can be separated off only
with a high expenditure because of the molecular weight differing
by only two units and the very similar structure, which makes
purification via distillation no longer economical beyond a certain
degree of purity. 3,4-Dimethoxythiophene as an impurity has the
disadvantage, however, that it is co-incorporated into the polymer
during polymerization and can thus adversely influence properties
of the polymer, such as, for example, the conductivity.
[0013] Chromatographic purification of thiophenes as monomers for
use for the preparation of electrically conductive polymers is also
known. WO-A 02/79295 describes the preparation of liquid and solid
chiral alkylenedioxythiophenes and mentions in examples the
purification by chromatography on silicon dioxide. The compounds
prepared according to WO-A 02/79295 have purities of up to 99.7%
after purification. However, chromatographic separation also has
disadvantages. Thus, large amount of solvents are needed to carry
it out, since the compounds to be separated must be in a very
dilute form in order to achieve the desired separation effect.
Furthermore, the chromatographic separation cannot be operated
continuously with the aid of simple apparatuses, so that in each
case only small amounts of the desired purified thiophene are
obtained. A continuous separation of large amounts would therefore
be associated with an extremely high expenditure on apparatus, so
that such a purification of thiophenes can no longer be carried out
economically.
[0014] Conventional recrystallization in which thiophenes which are
solid at room temperature are dissolved at elevated temperature,
usually under reflux of the solvent, and are then crystallized out
again by cooling is also known for the purification of thiophenes
as monomers for use for the preparation of electrically conductive
polymers and is described in WO-A 02/79295, but is limited to
thiophenes which are solid at room tm.
[0015] A particular form of crystallization can also be used for
the crystallization of liquid thiophenes. This specific form of
crystallization, melt crystallization, is described, for example,
in N. Wynn, Chem. Engineering (1986), 93(8), 26-27 and in J. Ulrich
and H, C. Bulau, Editor(s): Myerson, Allan S. "Handbook of
Industrial Crystallization (2nd Edition)" (2002), 161-179. Melt
crystallization is substantially based on cooling a liquid
substance until a melt is formed, from which only the substance to
be purified crystallizes out. After crystallization, the mother
liquid, which in the ideal case contains all the impurities, is
separated off. Where appropriate, the crystallized substance is
heated gently so that impurities adhering to the product can be
removed together with some of the substance which is then melting.
However, this process is limited to substances or substance
mixtures which contain relatively large amounts of impurities which
can be separated off in liquid form. Small amounts of impurities
can be removed only uneconomically via this process, since large
amounts of the desired compound have to be separated off at the
same time in order to wash out the small amount of impurity.
Moreover, melt crystallization is critical in respect of the
temperature programme and therefore expensive on apparatus.
SUMMARY OF THE INVENTION
[0016] There was therefore still a need for a process for the
purification of thiophenes which are liquid at room temperature in
which an extremely high purity, preferably of more than 99.9%, is
achieved and which does not have the disadvantages described
above.
[0017] The present invention was therefore based on the object of
discovering a less expensive process for the purification of
thiophenes with which highly pure 3,4-alkylenedioxythiophenes,
preferably with a purity of more than 99.9%, can be prepared.
[0018] In accordance with the present invention, there is provided
a process for purifying a thiophene represented by general formula
(I), 2
[0019] wherein,
[0020] R.sup.1 and R.sup.2 are each selected independently from the
group consisting of hydrogen,
[0021] linear or branched, optionally substituted
C.sub.1-C.sub.20-alkyl groups, linear or branched
C.sub.1-C.sub.20-oxyalkyl groups, linear or branched
C.sub.1-C.sub.20-oxyalkyl groups which are interrupted by 1 to 5
oxygen atoms, linear or branched C.sub.1-C.sub.20-oxyalkyl groups
which are interrupted by 1 to 5 sulphur atoms, a fused ring of
linear or branched, optionally substituted
C.sub.1-C.sub.20-dioxyalkylene formed by R.sup.1 and R.sup.2
together, and a fused ring of linear or branched, optionally
substituted C.sub.1-C.sub.20-dioxyarylene formed by R.sup.1 and
R.sup.2 together, and
[0022] said thiophene being liquid at room temperature,
[0023] said method being selected from the group consisting of,
[0024] a method (I) comprising,
[0025] (a) providing a first solution comprising said thiophene and
at least one solvent, and
[0026] (b) cooling said first solution to a temperature below the
melting temperature of said thiophene, thereby precipitating said
thiophene as a solid from said first solution, and
[0027] a method (II) comprising,
[0028] (a) providing a second solution comprising at least one
solvent and optionally said thiophene,
[0029] (b) cooling said second solution to a temperature below the
melting temperature of said thiophene, to form a cooled second
solution, and
[0030] (c) adding said thiophene to said cooled second solution,
thereby precipitating said thiophene as a solid from said cooled
second solution.
[0031] Unless otherwise indicated, all numbers or expressions, such
as those expressing process conditions, etc., used in the
specification and claims are understood as modified in all
instances by the term "about."
DETAILED DESCRIPTION OF THE INVENTION
[0032] In the context of the invention, thiophenes which are liquid
at room temperature are to be understood as those thiophenes which
have their melting point below +40.degree. C., preferably below
+30.degree. C.
[0033] In the context of the invention, room temperature can be a
temperature of 10 to 40.degree. C., preferably 15 to 30.degree. C.,
particularly preferably 18 to 25.degree. C.
[0034] Thiophenes of the general formula (I) which are preferably
purified with the process according to the invention are compounds
of the general formula (II) 3
[0035] wherein
[0036] A represents an optionally substituted
C.sub.1-C.sub.5-alkylene radical or a C.sub.1-C.sub.12-arylene
radical, preferably an optionally substituted
C.sub.2-C.sub.3-alkylene radical,
[0037] R represents a linear or branched, optionally substituted
C.sub.1-C.sub.18-alkyl radical, preferably linear or branched,
optionally substituted C.sub.1-C.sub.14-alkyl radical, an
optionally substituted C.sub.5-C.sub.12-cycloalkyl radical, an
optionally substituted C.sub.6-C.sub.14-aryl radical, an optionally
substituted C.sub.7-C.sub.18-aralkyl radical, an optionally
substituted C.sub.1-C.sub.4-hydroxyalkyl radical, preferably
optionally substituted C.sub.1-C.sub.2-hydroxyalkyl radical, or a
hydroxyl radical,
[0038] x represents an integer from 0 to 8, preferably from 0 to 6,
particularly preferably 0 or 1 and
[0039] in the case where several radicals R are bonded to A, these
can be identical or different.
[0040] The general formula (II) is to be understood such that the
substituent R can be bonded to the alkylene or arylene radical A x
times.
[0041] Preferred compounds of the general formula (II) are those of
the general formula (IIa) 4
[0042] wherein
[0043] R has the meaning given in the general formula (II) and y
represents 0, 1, 2, 3 or 4.
[0044] In the context of the invention, C.sub.1-C.sub.5-alkylene
radicals A are methylene, ethylene, n-propylene, n-butylene or
n-pentylene. In the context of the invention,
C.sub.1-C.sub.12-arylene radicals can be, for example, phenylene,
naphthylene, benzylidene or anthracenylidene. In the context of the
invention, C.sub.1-C.sub.18-represents linear or branched
C.sub.1-C.sub.18-alkyl radicals, such as, for example, methyl,
ethyl, n- or isopropyl, n-, iso-, sec- or tert-butyl, n-pentyl,
1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-ethylpropyl,
1,1-dimethylpropyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl,
n-hexyl, n-heptyl, n-octyl, 2-ethylhexyl, n-nonyl, n-decyl,
n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, n-hexadecyl or
n-octadecyl. C.sub.1-C.sub.20-alkyl groups moreover include, for
example, n-nonadecyl and n-eicosyl. In the context of the
invention, C.sub.5-C.sub.12-cycloalkyl represents
C.sub.5-C.sub.12-cycloalkyl radicals, such as, for example,
cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, cyclononyl or
cyclodecyl, C.sub.5-C.sub.14-aryl represents C.sub.5-C.sub.14-aryl
radicals, such as, for example, phenyl or naphthyl, and
C.sub.7-C.sub.8-aralkyl represents C.sub.7-C.sub.18-aralkyl
radicals, such as, for example, benzyl, o-, m- or p-tolyl, 2,3-,
2,4-, 2,5-, 2,6-, 3,4- or 3,5-xylyl or mesityl. In the context of
the invention, C.sub.1-C.sub.20-oxyalkyl represents
C.sub.1-C.sub.20-oxyalkyl radicals, such as, for example, methoxy,
ethoxy, n- or iso-propoxy, n-, iso-, sec- or tert-butoxy,
n-pentyloxy, 1-methylbutyloxy, 2-methylbutyloxy, 3-methylbutyloxy,
1-ethylpropyloxy, 1,1-dimethylpropyloxy, 1,2-dimethylpropyloxy,
2,2-dimethylpropyloxy, n-hexyloxy, n-heptyloxy, n-octyloxy,
2-ethylhexyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy,
n-dodecyloxy, n-tridecyloxy, n-tetradecyloxy, n-hexadecyloxy,
n-octadecyloxy, n-nonadecyloxy or n-eicosyloxy. The preceding list
serves to explain the invention by way of example and is not to be
regarded as conclusive. Further substituents of the alkylene or
arylene radicals A which are optionally possible are numerous
organic groups, for example alkyl, cycloalkyl, aryl, halogen,
ether, thioether, disulfide, sulfoxide, sulfone, sulfonate, amino,
aldehyde, keto, carboxylic acid ester, carboxylic acid, carbonate,
carboxylate, cyano, alkylsilane and alkoxysilane groups, as well as
carboxylamide groups.
[0045] If the thiophene to be purified has one or more
stereocentres, the thiophene can be a racemate, an enantiomerically
pure or diastereomerically pure compound or an enantiomerically
enriched or diastereomerically enriched compound. An
enantiomerically enriched compound is to be understood as meaning a
compound having an enantiomer excess (ee) of more than 50%. A
diastereomerically enriched compound is to be understood as meaning
a compound having a diastereomer excess (de) of more than 30%.
According to the invention, however, the compound can also be any
desired mixture of diastereomers.
[0046] Before purification with the process according to the
invention, the thiophene to be purified preferably has a purity of
greater than 70%, particularly preferably a purity of greater than
90%.
[0047] The thiophenes of the general formulae (I), (II) or (IIa) to
be purified can be prepared by processes known to the expert. Such
a preparation process is described, for example, in EP-A 1 142
888.
[0048] Solvents which are employed are those in which the thiophene
to be purified dissolves and which have a sufficiently low melting
point, preferably below -40.degree. C. Examples of suitable
solvents which may be mentioned are isobutyl methyl ketone,
chloroform, methylene chloride, toluene, methanol, propanol,
ethanol, acetone, iso-propanol, n-butanol, sec-butanol,
dimethylformamide, methyl tert-butyl ether, tetrahydrofuran,
diethyl ether, hexane or pentane.
[0049] Preferred solvents are polar solvents, and alcohols are
particularly preferred in this context. Methanol or ethanol are
very particularly preferred.
[0050] The solvent can also be a mixture of two or more
solvents.
[0051] Mixtures of one or more alcohol(s) optionally with one or
more further solvent(s) are preferred in this context. For this
purpose it is not absolutely necessary for each individual solvent
to dissolve the thiophene and to have a correspondingly low melting
point, merely the mixture must have these properties. A mixture of
two alcohols is particularly preferred, and a mixture of methanol
and ethanol is very particularly preferred.
[0052] The solvent is mixed with the thiophene in a ratio of 0.01:1
to 10:1, preferably in a ratio of 0.3:1 to 3:1 and very
particularly preferably in a ratio of 1:1.
[0053] The new process is carried out e.g. by a procedure in which
the thiophenes to be purified and at least one solvent are brought
together in any desired sequence, the solvent or solvents, before
being brought together with the thiophene, or the solution obtained
during or after bringing them together, is or are cooled down to a
temperature at which a mixture of a solid and a liquid forms, the
mixture of a solid and a liquid is optionally subsequently stirred
and the solid is then separated off.
[0054] Preferably, the solvent or solvents before being brought
together with the thiophenes, or the solution obtained during or
after bringing them together is or are cooled down to a temperature
which is at least 10.degree. C., preferably at least 20.degree. C.
below the melting temperature of the pure thiophene to be purified.
Cooling particularly preferably takes place to 0.degree. C. or
lower, very particularly preferably to -15.degree. C. or lower.
[0055] The new process can be carried out, for example, by
dissolving the thiophenes in the solvent(s) and then cooling this
solution down at least to the extent that the purified thiophene
precipitates out or crystallizes out.
[0056] In this procedure, the thiophene can be dissolved in the
solvent(s) at a temperature above the melting point of the
thiophene. In this context a temperature of between 0.degree. C.
and +40.degree. C. is preferred. A temperature of between
+15.degree. C. and +25.degree. C. is particularly preferred.
[0057] The solution obtained from the solvent and the thiophene is
then cooled. The solution is cooled here until the thiophene
separates out or crystallizes out of the solution in the form of a
solid. Preferably, the solution is cooled to a temperature of at
least 20.degree. C. below the melting temperature of the pure
thiophene. Cooling to -15.degree. C. or to a temperature of lower
than -15.degree. C. is particularly preferred.
[0058] The solution is preferably cooled down at a rate such that
the thiophene crystallizes out within a period of a few minutes to
several hours. Cooling down to the desired temperature over a
period of approx. one hour is preferred here.
[0059] The cooling down can be effected by external cooling or by
introduction of an inert cooling medium. The cooling down is
preferably achieved by external cooling.
[0060] During the cooling phase, the thiophene separates out of the
solution as a solid, for example in the form of crystals. In this
context, the solid obtained can contain the thiophene as the pure
substance or can consist of a mixture of the solvent(s) and the
thiophene.
[0061] Alternatively, the new process can be carried out by a
procedure in which the liquid thiophene is metered into the already
cooled solvent. Solvent mixture or cooled thiophene solution.
[0062] In this case the solvent is cooled to a temperature of at
least 20.degree. C. below the melting temperature of the pure
thiophene. Cooling to -15.degree. C. or a temperature of lower than
-15.degree. C. is particularly preferred.
[0063] The liquid thiophene is then metered into the cooled
solvent--preferably over a period of a few minutes to several
hours. The metering rate is to be chosen here such that the
thiophene does not precipitate out or crystallize out too rapidly
and impurities are thereby also included in the solid. A metering
time of at least 1 hour is preferred. However, metering times of
less than one hour may also be sufficient, depending on the amount
of thiophene which must be metered in. The solid obtained can also
contain the thiophene as the pure substance or consist of a mixture
of the solvent(s) and the thiophene.
[0064] Preferably, the suspension obtained is then subsequently
stirred for a period of 1 minute up to 5 hours. A subsequent
stirring time of approx. three hours is particularly preferred
here.
[0065] The subsequent stirring is carried out at a temperature of
at least 20.degree. C. below the melting temperature of the pure
thiophene. A temperature of -15.degree. C. or a temperature of
lower than -15.degree. C. is preferred here.
[0066] The product which has precipitated out or crystallized out
is then separated off by known methods. This separating off is
preferably carried out by a filtration. The filtration can be
carried out under normal pressure or under pressure.
[0067] The filtration is preferably carried out with the aid of a
filter unit which can be temperature-controlled, and is preferably
carried out such that the product to be filtered is present as a
solid during the filtration. The filtration is preferably carried
out at a temperature of between 0.degree. C. and -20.degree. C.
Preferably, the filtration is carried out at -15.degree. C. or a
temperature of lower than -15.degree. C.
[0068] Thereafter, the solid obtained can be washed with one or
more solvent(s) in order to remove residues of impurities from the
filter cake. Polar solvents are preferably used for this purpose.
Alcohols, optionally in a mixture with one another and/or with
further solvents, are particularly preferably used. The solid is
particularly preferably washed with ethanol or methanol or a
mixture of these.
[0069] In the case where the filter cake is washed to remove
impurities adhering to the filter cake, it is appropriate to cool
the washing agent, i.e. the solvent used for the washing, in order
to prevent relatively large amounts of purified thiophene from
dissolving in the washing agent. The washing agent has a
temperature below 0.degree. C. during the washing. Preferably, the
washing agent is cooled down to -15.degree. C. or lower for the
washing.
[0070] The solid then obtained is warmed to a temperature above the
melting point of the thiophene over a period of between 5 minutes
and 5 hours. Preferably, the solid is allowed to melt over a period
of 1 hour.
[0071] After the melting, the molten solid may still contain
residues of the solvent added before the crystallization or
residues of the washing agent. These residues can be removed by
methods known to the expert, e.g. by simple distillation. The
solvent is distilled over during the distillation. The distillation
can be carried out under normal pressure or under reduced pressure.
Preferably, it is carried out under reduced pressure at
temperatures of between 30.degree. C. and 150.degree. C.,
preferably between 50.degree. C. and 100.degree. C.
[0072] The thiophene obtained in this way, which remains as the
bottom product, preferably has a purity of at least 99.50%,
preferably at least 99.9%, after the solvent has been distilled off
completely. For example, thiophenes which have been synthesized
using 3,4-dimethoxythiophene or during the synthesis of which
3,4-dimethoxythiophene is produced as a by-product contain less
than 0.05 wt. % of 3,4-dimethoxythiophene after purification with
the process according to the invention. Such a low content of
3,4-dimethoxythiophene cannot be achieved or can be achieved only
with a very high loss in the yield of the desired thiophene with
conventional purification processes, such as e.g. simple
distillation.
[0073] Thiophenes of such purity are not known. Therefore another
subject matter of the invention is a thiophene of the general
formula (I), 5
[0074] wherein
[0075] R.sup.1 and R.sup.2 independently of one another represent
hydrogen, optionally substituted C.sub.1-C.sub.20-alkyl groups or
C.sub.1-C.sub.20-oxyalkyl groups which are optionally interrupted
by 1 to 5 oxygen and/or sulfur atoms, or together represent an
optionally substituted C.sub.1-C.sub.20-dioxyalkylene or
C.sub.1-C.sub.20-dioxyaryle- ne group,
[0076] characterized in that it has a purity of at least 99.50 wt.
%, in particular of the least 99.9 wt. %.
[0077] Particular preferred is a 3,4-ethylene-dioxythiophene with
such purity.
[0078] Unless mentioned otherwise--all the purity data are data in
percent by weight.
[0079] The thiophene remaining as the bottom product after the
distillation can also be distilled over to separate off traces of
colouring substances. As a rule, a thiophene which is colourless to
the eye is obtained by this means. The distillation of the
thiophene is also preferably carried out under reduced
pressure.
[0080] By way of example, up to 70%, preferably up to 90%,
particularly preferably up to 95% and very particularly preferably
virtually 100% of the thiophene employed is obtained in the
purified form, depending on the amount of solvent used in relation
to the amount of thiophene employed and depending on the
temperature during the precipitation and, where appropriate, during
the washing. Any remaining portion of the thiophene employed
remains dissolved in the mother liquor, i.e. e.g. in the filtrate
separated off during the filtration, or, where appropriate, in the
washing agent. Since a recovery, in the purified form, of virtually
100% of the thiophene employed is desirable, in a preferred
embodiment the purification process can also be carried out by a
procedure in which the mother liquor of a preceding precipitation
or crystallization and/or the washing agent is or are employed
again as solvent or together with the solvent in the process for
the purification of further thiophene.
[0081] The process according to the invention renders possible the
purification of thiophenes in a simple procedure. The products are
moreover obtained in good yields.
[0082] Because of their high purity, the thiophenes purified by the
process according to the invention are outstandingly suitable for
the preparation of conductive polymers or for the preparation of
organic semiconductors which are suitable e.g. in the production of
capacitors, printed circuit boards, antistatic layers, transparent
conductive layers, displays, electrochromic glazing and integrated
semiconductor circuits. These uses are further subject matter of
the invention.
[0083] The following compounds may be mentioned by way of example
as compounds which can be purified with the process according to
the invention: 3,4-ethylenedioxythiophene,
3,4-methylenedioxythiophene;
R,S-3,4-(1'-hydroxymethyl)ethylenedioxythiophene,
S-3,4-(1'-hydroxymethyl- )ethylenedioxythiophene;
R-3,4-(1'-hydroxymethyl)ethylenedioxythiophene,
3,4-(2'-hydroxy)propylenedioxythiophene;
3,4-(1'-methyl)ethylenedioxythio- phene,
3,4-(3'-tert-butyl)benzodioxythiophene;
3,4-(1'-n-hexyl)ethylenedio- xythiophene;
3,4-(1'-ethyl)ethylenedioxythiophene; 3,4-(1'-n-propyl)ethyle-
nedioxythiophene; 3,4-(1'-butyl)ethylenedioxythiophene;
thieno[3,4-b]-1,4-oxathiine; 3,4-ethylenedioxythiophene-1-methyl
N-methylcarbamate; 3,4-ethylenedioxythiophene-1-methyl
N-ethylcarbamate; 3,4-ethylenedioxythiophene-1-methyl
N-hexylcarbamate; 3,4-ethylenedioxythiophene-1-methyl
N-phenylcarbamate; 3,4-ethylenedioxythiophene-1-methyl
N-tolylcarbamate; (3,4-ethylenedioxythiophene-1-methyl) methyl
ether; (3,4-ethylenedioxythiophene-1-methyl) ethyl ether;
(3,4-ethylenedioxythiophene-1-methyl) propyl ether;
(3,4-ethylenedioxythiophene-1-methyl) hexyl ether;
3-hexylthiophene; and 3-octylthiophene.
EXAMPLES
Example 1
Purification of 3,4-ethylenedioxythiophene
[0084] 1,800 g 3,4-ethylenedioxythiophene having a purity of 98.4%
and a content of 3,4-dimethoxythiophene of 0.3% and a slightly
yellowish colour were stirred with 2,400 ml ethanol in a
sulfonating beaker. The solution was cooled down to a temperature
of -15.degree. C. by external cooling and stirred at -15.degree. C.
for 3 h. The solid formed was separated off with the aid of a
suction filter and washed with ethanol precooled to -15.degree. C.
The filter cake was warmed to a temperature of +20.degree. C. In a
distillation apparatus comprising a reservoir flask, a distillation
bridge and a condensation flask, the solvent was first distilled
off under a pressure of 16 hPa at a temperature of 50.degree. C.
and 3,4-ethylenedioxythiophene was then distilled at a temperature
of 90.degree. C. under a pressure of 16 hPa. 1,374 g
3,4-ethylenedioxythioph- ene (76% of theory) were obtained in a
purity of 100%. The colourless product no longer contained
3,4-dimethoxythiophene.
Example 2
Purification of 3,4-ethylenedioxythiophene
[0085] 1,800 g 3,4-ethylenedioxythiophene having a purity of 70%
and a content of 3,4-dimethoxythiophene of 0.3% and a dark brown
colour were stirred with 1,800 ml ethanol in a sulfonating beaker.
The solution was cooled down to a temperature of -23.degree. C. by
external cooling and stirred at -23.degree. C. for 3 h. The solid
formed was separated off with the aid of a suction filter and
washed with ethanol precooled to -15.degree. C. The filter cake
separated off was warmed to a temperature of +20.degree. C. In a
distillation apparatus comprising a reservoir flask, a distillation
bridge and a condensation flask, the solvent was first distilled
off under a pressure of 12 hPa at a temperature of 50.degree. C.
and 3,4-ethylenedioxythiophene was then distilled at a temperature
of 90.degree. C. under a pressure of 12 hPa. 718 g
3,4-ethylenedioxy-thiophene (55% of theory) were obtained in a
purity of 99.2%. The product no longer contained
3,4-dimethoxythiophene.
[0086] Although the invention has been described in detail in the
foregoing for the purpose of illustration, it is to be understood
that such detail is solely for that purpose and that variations can
be made therein by those skilled in the art without departing from
the spirit and scope of the invention except as it may be limited
by the claims.
* * * * *