JP5747460B2 - Process for producing dialkoxythiophene - Google Patents

Description

  The present invention relates to a novel synthesis method of dialkoxythiophene.

  Conductive polymers are used in applications such as antistatic and capacitors due to differences in conductivity. In recent years, it has attracted attention as an alternative material for ITO, which is a transparent electrode for liquid crystal and electronic paper. Among them, poly (3,4-ethylenedioxythiophene) [commonly known as PEDOT] and poly (3,4-ethylenedioxythiophene): polystyrenesulfonic acid [commonly known as PEDOT: PSS] are used as a transparent electrode of a resistive touch panel. Research has become active in recent years.

PEDOT: PSS is generally synthesized by oxidative polymerization, and 3,4-ethylenedioxythiophene as a raw material can be synthesized in five stages using thiodiglycolic acid as a raw material (see, for example, Patent Document 1). .
In recent years, apart from the above method, a method of synthesizing from a thiophene raw material in four steps has been reported (for example, see Patent Document 2). Specifically, it is a method comprising tetrabromination, debromination at the 2,5-position (synthesis of 3,4-dibromothiophene), dimethoxylation using sodium methoxide, and ethylene dioxylation.

  In the dialkoxylation in the third step, Patent Document 2 describes that sodium methoxide is synthesized from 3,4-dibromothiophene at 30 ° C. to 90 ° C. under normal pressure. On the other hand, in Patent Document 3, a metal alkoxide in a specific concentration range (specifically, the concentration of the metal alkoxide with respect to the alcohol solvent is 30 to 36% by weight) at 40 to 200 ° C. under normal pressure conditions. It is reported to use.

Japanese Patent Laid-Open No. 01-313521 Chinese Publication No. 101220038 JP 2009-161457 A

However, the method of Patent Document 2 requires a very long reaction time of 48 hours as seen in Examples. In Patent Document 3, although the reaction time is short, it is necessary to prepare a metal alkoxide solution having a high concentration that needs to be prepared in advance, specifically, 30 wt% or more. Specifically, the commercially available metal alkoxide solution is less than 30% by weight, and when preparing a high concentration metal alkoxide solution of 30% by weight or more, it is necessary to prepare from an alkali metal and an alcohol raw material. However, due to the generation of hydrogen and high heat generation, there has been a problem that it takes a considerable time for the heat removal operation.

  The present invention has been made in view of the above problems, and its object is to solve the problems of the prior art and to produce 3,4-dialkoxythiophene economically, safely and in a high yield. It is to provide a method that can.

  In order to solve the above-mentioned problems, the inventors of the present application have made extensive studies, and as a result, when synthesizing dialkoxythiophene using 3,4-dibromothiophene and a metal alkoxide-containing alcohol solution as raw materials, a specific content in a sealed container is determined. The inventors have found that the target dialkoxythiophene can be synthesized in high yield in a short time by carrying out at a temperature, and the present invention has been completed.

  That is, the present invention provides a substitution reaction in the production of a dialkoxythiophene represented by the following general formula (1) using 3,4-dibromothiophene and a metal alkoxide-containing alcohol solution as raw materials in the presence of a copper catalyst. Is carried out at 100 to 150 ° C. in a closed container, and relates to a method for producing dialkoxythiophene.

(In the formula, R represents an ethyl group having 2 carbon atoms).

  The production method will be described in detail below.

  The production method of the present invention is a method for producing dialkoxythiophene represented by the general formula (1).

Here, R in the general formula (1) is Ru ethyl Motodea 2 carbon atoms.
A specific dialkoxythiophene represented by the general formula (1) is 3,4-diethoxythiophene (DET) .

  The copper catalyst is not particularly limited as long as it is a commercially available monovalent or divalent copper compound. For example, copper acetate (I or II), acetylacetonate copper (II), copper bromide (I Or II), copper carbonate (II), copper cyanide, copper 2-ethylhexanoate (II), copper hydroxide, copper iodide (I), copper nitrate (II), copper oxide (I or II), Examples thereof include copper sulfate. Of the copper catalysts, copper oxide (I or II) is more preferred because it is economically advantageous.

  In this substitution reaction, an iodide salt such as sodium iodide or potassium iodide may be used in combination with the copper catalyst, and it is particularly preferable to use a mixture of copper (II) oxide and iodide.

  The amount of the copper catalyst is preferably in the range of 1 to 100 mol%, particularly preferably 10 to 40 mol% with respect to 1 mol of 3,4-dibromothiophene.

  The metal alkoxide-containing alcohol solution is an alcohol solution containing a metal alkoxide, preferably containing 5 to less than 30% by weight of metal alkoxide, more preferably containing 15% to 28% by weight of metal alkoxide, particularly preferably. 20 wt% sodium ethoxide / ethanol solution, 28 wt% sodium methoxide / methanol solution, commercially available from Wako Pure Chemical, 24 wt% potassium ethoxide / ethanol solution, 25 wt% potassium methoxy, manufactured by Sigma-Aldridge And methanol solution.

  The amount of the metal alkoxide is preferably in the range of 2.0 to 10 times mol per mol of 3,4-dibromothiophene, and particularly preferably 3 to 6 times mol from the viewpoint of yield and economy.

  The reaction temperature is 100 to 150 ° C, particularly preferably 110 to 140 ° C.

  In the present invention, 3,4-dibromothiophene, a copper catalyst, and a metal alkoxide-containing alcohol solution are charged into an airtight container and are performed in an inert gas. As a result of being carried out in a closed vessel, pressure is applied by the vapor pressure of the alcohol used. If necessary, an inert gas may be enclosed and the reaction may be carried out under further pressure. The reaction pressure after pressurization is sufficient if the gauge pressure is 0.1 MPa or more, and even if the reaction is carried out at a high pressure exceeding the gauge pressure of 1 MPa, the improvement in yield is particularly small. Usually, a natural pressure increase in the solvent used by heating is sufficient.

  Examples of the sealed container here include a SUS or glass autoclave.

  After completion of the reaction, dialkoxythiophene can be isolated as crystals or oily matter by a known method such as distillation and chromatography.

  As described above, according to the present invention, the problems of the prior art can be overcome, and dialkoxythiophene can be produced economically and with high yield.

The present invention will be described in more detail with reference to the following examples, but the present invention should not be construed as being limited thereto. The purity of the compounds obtained in the examples was measured by gas chromatography using cyclododecane as an internal standard. ¹ H, ¹³ C-NMR was measured using Gemini 200 manufactured by Varian.
[Gas chromatography measurement]
Device: GC-17A manufactured by Shimadzu Corporation
Column: capillary column (GL Science NB-5)
Carrier gas: Helium column temperature: 50 ° C. (5 minutes hold) → 10 ° C./min→300° C.
Injection: 280 ° C
Detector: FID
Example 1 (Synthesis of DET)
In a 30 ml SUS autoclave, 1.81 g (7.55 mmol) of 3,4-dibromothiophene, 0.15 g (1.88 mmol) of copper (II) oxide, 0.08 g (0.48 mmol) of potassium iodide, 20% sodium ethoxy After adding 12.9 g (37.9 mmol, commercially available product) in order, a vacuum treatment and nitrogen substitution were repeated three times in order to make the inside of the system an inert atmosphere. Thereafter, the autoclave was heated and stirred in a sealed container at 130 ° C. for 6 hours. The pressure at that time was a gauge pressure of 0.4 MPa. After cooling to room temperature, 15 ml of water and 30 ml of ethyl acetate were added. When the obtained reaction solution was filtered and the organic phase was analyzed by gas chromatography, 3,4-dibromothiophene as a raw material disappeared (dibromothiophene conversion rate of 100%), and 3,4-diethoxythiophene was recovered. The rate was 74.7%.

  The organic layer was purified by silica gel chromatography (eluent: hexane / ethyl acetate = 100/1 volume ratio) to obtain 3,4-diethoxythiophene as pale yellow crystals in a yield of 65%.

The compound was identified by ¹ H-NMR and ¹³ C-NMR (CDCl ₃ ).
¹ H-NMR (CDCl ₃ ) δ ppm; 6.16 (s, 2H), 4.07 (4H, q, J = 7.0 Hz), 1.45 (6H, t, J = 7.0 Hz),
¹³ C-NMR (CDCl ₃ ) δ ppm; 14.79, 66.00, 96.69, 147.12.

  There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Examples 2-3
3,4-Diethoxythiophene was synthesized in the same manner as in Example 1 except that the reaction temperature was 140 ° C or 120 ° C. The results are shown in Table 1.

  There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Example 4
In Example 1, after raising the temperature to 130 ° C., nitrogen was injected so that the gauge pressure was 1.0 MPa, and then the reaction was performed in the same manner as in Example 1. The results are shown in Table 1.
There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Comparative Example 1
In a 50 ml eggplant type flask, 2.41 g (10.0 mmol) of 3,4-dibromothiophene, 0.2 g (2.5 mmol) of copper (II) oxide, 0.1 g (0.60 mmol) of potassium iodide, 10 g of dimethylformamide After adding 17 g (50 mmol, commercially available) of a 20% sodium ethoxide / ethanol solution under a nitrogen atmosphere, the mixture was refluxed at 95 ° C. for 6 hours under normal pressure. After cooling the reaction solution, 20 g of water was added to complete the reaction. The reaction solution was filtered and then separated, and the obtained organic phase was analyzed. As a result, 3,4-diethoxythiophene as the target product was not detected. The results are shown in Table 1.

  The reaction temperature was low and the reaction did not proceed.

Comparative Example 2
In Example 1, 3,4-diethoxythiophene was synthesized in the same manner as in Example 1 except that the reaction temperature was set to 155 ° C. The reaction temperature was high, and the yield of 3,4-diethoxythiophene was as low as 56.1%. The results are shown in Table 1.

Reference example 1
In a 30 ml SUS autoclave, 2.91 g (12.1 mmol) of 3,4-dibromothiophene, 0.24 g (3.0 mmol) of copper (II) oxide, 0.12 g (0.72 mmol) of potassium iodide, 28% sodium methoxy After sequentially adding 11.7 g (60.7 mmol, commercially available) of a methanol / deuterium solution, the pressure reduction treatment and the nitrogen substitution were repeated three times to make the inside of the system an inert atmosphere. Thereafter, the autoclave was heated and stirred in a sealed container at 110 ° C. for 6 hours. The pressure at that time was a gauge pressure of 0.3 MPa. After cooling to room temperature, 15 ml of water and 30 ml of ethyl acetate were added. After filtering the reaction solution and separating the obtained mother liquor, the organic phase was analyzed by gas chromatography, and the raw material 3,4-dibromothiophene disappeared (dibromothiophene conversion rate 100%). The yield of 4-dimethoxythiophene was 90.4%. The results are shown in Table 1.

  There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Reference example 2
The reaction was conducted in the same manner as in Example 4 except that the reaction temperature and reaction time were 120 ° C. and 2 hours, respectively. The results are shown in Table 1.

  There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Reference example 3
In a glove box, 11.7 g (60.7 mmol, commercially available) of 28% sodium methoxide / methanol solution and 12 g of dehydrated methanol were added to prepare a 14 wt% sodium methoxide / methanol solution. The obtained solution, 3,4-dibromothiophene 2.91 g (12.1 mmol), copper (II) oxide 0.24 g (3.0 mmol), potassium iodide 0.12 g (0.72 mmol) under nitrogen atmosphere And added to a SUS 50 ml autoclave. Thereafter, as in Reference Example 1 , 3,4-dimethoxythiophene was synthesized. The results are shown in Table 1.

  There was no need to prepare a high concentration metal alkoxide-containing alcohol solution in advance, and 3,4-diethoxythiophene was obtained in high yield.

Reference example 4
In a 100 ml eggplant-shaped flask, 8.73 g (36.4 mmol) of 3,4-dibromothiophene, 1.31 g (9.07 mmol) of copper (I) bromide, 35.1 g (182 mmol, 28% sodium methoxide / methanol solution) (Commercial product) was added, and the system was purged with nitrogen, and then refluxed at 88 ° C. for 6 hours.

The reaction solution was filtered and then separated, and the obtained organic phase was analyzed. The conversion of dibromothiophene was 95%, and the yield of 3,4-dimethoxythiophene was 73.2%.
The reaction temperature was low, and the yield of 3,4-dimethoxythiophene was low compared to Reference Examples 1 to 3 .

Claims (3)

In a substitution reaction for producing a dialkoxythiophene represented by the following general formula (1) using 3,4-dibromothiophene and a metal alkoxide-containing alcohol solution as raw materials in the presence of a copper catalyst, the substitution reaction is carried out in a sealed vessel at 100 to 150. A process for producing dialkoxythiophene, which is carried out in an inert gas at a temperature of 0.1 ° C. and a gauge pressure of 0.1 MPa or more.

  The method for producing dialkoxythiophene according to claim 1, wherein the metal alkoxide content of the metal alkoxide-containing alcohol solution is 5 wt% or more and less than 30 wt%.   The method for producing dialkoxythiophene according to claim 1 or 2, wherein the copper catalyst comprises a mixture of copper (II) oxide and an iodide salt.