Process for preparing monovinyl thioethers

Abstract

1. A process for producing monovinyl thioethers by reacting acetylene with a compound containing one thiol group and one hydroxy group, hereinafter referred to as a thiol-hydroxy compound, wherein the reaction is carried out at a pressure of less than 2 bar.

Description

[Technical field]

[0001] The present invention relates to a process for the preparation of monovinyl thioethers by reacting acetylene with a compound containing one thiol group and one hydroxy group, hereinafter referred to as a thiol-hydroxy compound, wherein the reaction is carried out at a pressure of less than 2 bar. [Background technology]

[0002] A well-known method for the synthesis of vinyl ethers is the Reppe method. According to the Reppe method, vinyl ethers or vinyl thioethers are obtained by reacting a compound containing at least one hydroxy group or at least one thiol group with acetylene in the presence of a basic catalyst. Such a method is described, for example, in US2003 / 0105354. According to US2003 / 0105354, the reaction is carried out at a preferred pressure range of 0.2 MPa to 2 MPa, which corresponds to 2 to 20 bar. In the example, the pressure is maintained at 20 bar.

[0003] A.S. Atvin et al., Journal of Organic Chemistry of the USSR, volume 4, number 5 (May 1968), pages 765-768, disclose a process for the preparation of 2-(vinylthio)ethanol, which is carried out at a pressure of 12 atm absolute, 11 gauge atm, which corresponds to about 12 bar.

[0004] In the case of compounds containing both hydroxy and thiol groups, mixtures of various vinyl compounds are usually obtained, including thiol vinyl ethers, hydroxyvinyl thioethers and divinyl compounds.

[0005] Such mixtures are less compatible with the technical applications of vinyl compounds. Certain technical applications, such as polymerization processes, require pure compounds.

[0006] For various technical applications, vinyl compounds having thioether groups and free hydroxy groups are in demand. Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention was to provide a simple and economical process for the preparation of vinyl compounds having thioether groups and free hydroxy groups, which can be obtained in high yields and with high selectivity by such a process. [Means for solving the problem]

[0008] Thus, the method defined above has been found. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Thiol-hydroxy compounds are preferably compounds having a molecular weight of less than 1000 g / mol, more preferably less than 500 g / mol, and most preferably less than 200 g / mol.

[0010] In a particularly preferred embodiment, the thiol-hydroxy compound is liquid at 20° C. and 1 bar.

[0011] A preferred thiol-hydroxy compound is a compound of formula I HS-R-OH wherein R is a linear or branched aliphatic hydrocarbon group which may contain oxygen in the form of an ether group. Preferably, the linear or branched aliphatic hydrocarbon group contains 1 to 10, more preferably 2 to 6, especially 2 to 4 carbon atoms.

[0012] In particularly preferred embodiments, R is ethylene, n-propylene or n-butylene.

[0013] In a most preferred embodiment, the compound of formula I has the formula HS-CH2 -CH 2 -OH and the method comprises the steps of: H 2 C=CH-S-CH 2 -CH 2 -OH The present invention relates to a process for producing vinylthioethanol.

[0014] The reaction is preferably carried out in the presence of a catalyst, which is preferably an alkali salt of a thiol-hydroxy compound.

[0015] Preferably, the alkali salt is prepared by adding a metal hydroxide, preferably an alkali metal hydroxide, most preferably sodium hydroxide or potassium hydroxide, to the thiol-hydroxy compound and reacting the metal hydroxide with the thiol-hydroxy compound at elevated temperature, for example 50-150° C.

[0016] Preferably, the catalyst or alkali salt is used in an amount of 0.1 to 10 parts by weight, more preferably 0.5 to 7 parts by weight, and most preferably 1 to 5 parts by weight, per 100 parts by weight of the thiol-hydroxy compound.

[0017] The alkali salt can be prepared separately or in situ. In the case of separate preparation, the desired amount of alkali salt is prepared separately and then added to the reaction mixture. In the case of in situ preparation, an alkali metal hydroxide is added to the reaction mixture in an amount to obtain the desired amount of alkali salt in situ under the reaction conditions.

[0018] The reaction can be carried out in the presence of a solvent. The thiol-hydroxy compound used and the resulting monovinyl thioether are preferably liquid themselves under the reaction conditions, so that a solvent is usually not required. More preferably, the thiol-hydroxy compound used and the resulting monovinyl thioether are liquid at 20° C. and 1 bar.

[0019] The vinylation of a thiol-hydroxy compound with acetylene is preferably carried out at 50 to 200°C, particularly 80 to 150°C, and more preferably 90 to 120°C.

[0020] The reaction is carried out at a pressure of less than 2 bar, preferably less than 1.5 bar, more preferably less than 1.3 bar. In a preferred embodiment, the pressure is at least 0.5 bar, more preferably at least 0.8 bar.

[0021] In the most preferred embodiment, the reaction is carried out at a pressure of 0.8 to 1.3 bar, in particular at a pressure of 0.9 to 1.1 bar, most preferably at 1 bar. The pressure can be the pressure of acetylene itself or a mixture of acetylene and an inert gas, such as nitrogen. Preferably, acetylene is not used in combination with an inert gas and the aforementioned pressure is the acetylene pressure.

[0022] Preferably, acetylene is fed directly into the liquid phase containing the thiol-hydroxy compound and any products already formed. In particular, acetylene can be introduced into the liquid phase via a stirrer (in the case of a stirred tank reactor) or directly via a nozzle.

[0023] The process can be carried out as a batch process, a semi-continuous process, or a continuous process, in which all starting materials are added to the reactor before the reaction is started, in which at least one of the starting materials is fed continuously during the reaction, and in which all starting materials are fed continuously to the reactor and all product is continuously withdrawn from the reactor.

[0024] In a preferred embodiment, the method is carried out semi-continuously or continuously.

[0025] In a preferred semi-continuous process, the entire amount of thiol-hydroxy compound is added to the reactor, while acetylene is continuously fed to the reactor during the reaction, and the pressure is maintained below 2 bar, or below the preferred values, or in the preferred ranges listed above, while unreacted acetylene and any other gaseous compounds are continuously withdrawn from the reactor.

[0026] The process can be carried out in a single reactor or in several reactors in series, for example a reactor battery. Suitable reactors include stirred tank reactors, a series of stirred tank reactors, flow tubes, bubble columns and loop reactors.

[0027] The reaction can be terminated, for example, by lowering the temperature and / or stopping the acetylene supply.

[0028] The resulting product mixture contains the monovinyl thioether.

[0029] The product mixture may contain, as a by-product, a divinyl compound resulting from vinylation of the thiol and hydroxy groups of the thiol-hydroxy compound. When the thiol-hydroxy compound is 2-hydroxy-ethane-1-thiol, the product mixture may be represented by the formula H 2 C=CH-S-CH 2 -CH 2 -O-CH=CH 2 can be obtained as a by-product.

[0030] The resulting product mixture may further contain unreacted thiol-hydroxy compound.

[0031] Preferably, more than 90% by weight, especially more than 95% by weight, more preferably more than 98% by weight of the thiol-hydroxy compound is consumed in the case of a batch or semi-continuous process. Continuous processes may preferably be operated with a steady-state concentration of 10-80% by weight of the thiol-hydroxy compound in the reaction mixture.

[0032] An advantage of the present invention is the low formation of divinyl compounds. Preferably, the content of divinyl compounds is less than 5% by weight, in particular less than 2% by weight, more preferably less than 1% by weight, based on 100% by weight of monovinyl thioether and divinyl compounds.

[0033] The catalyst, which is preferably an alkali salt, can be separated from the product mixture obtained by conventional methods.Due to the high conversion rate and high selectivity to thiol-hydroxy compounds, further work-up of the product mixture obtained in batch or semi-continuous methods and removal of unconsumed thiol-hydroxy compounds is usually not required.In continuous methods, unconsumed thiol-hydroxy compounds can be separated from the product mixture and recycled to the reaction.

[0034] The resulting monovinyl thioether can be purified, for example, by distillation.

[0035] The process of the present invention is a simple and economical method for producing monovinyl thioethers. The monovinyl thioethers are obtained in high yields. The selectivity is very high. Only small amounts of by-products, such as divinyl compounds, are formed. Separation of small amounts of divinyl compounds from the resulting product mixture is usually not necessary. Some embodiments are given below. Item 1 1. A process for producing monovinyl thioethers by reacting acetylene with a compound containing one thiol group and one hydroxy group, hereinafter referred to as a thiol-hydroxy compound, wherein the reaction is carried out at a pressure of less than 2 bar. Section 2 The thiol-hydroxy compound is a compound of formula I HS-R-OH wherein R is a linear or branched aliphatic hydrocarbon group which may contain oxygen in the form of an ether group. The method according to item 1, Section 3 Item 3. The method according to item 1 or 2, wherein the thiol-hydroxy compound is 2-hydroxy-ethane-1-thiol. Section 4 formula H 2 C=CH-S-CH 2 -CH2 -OH The method according to any one of items 1 to 3, which is a method for producing vinylthioethanol of the formula: Section 5 5. The method according to any one of items 1 to 4, wherein the reaction is carried out in the presence of a catalyst. Section 6 Item 6. The method of item 5, wherein the catalyst is an alkali salt of a thiol-hydroxy compound. Section 7 Item 7. The method according to item 5 or 6, wherein the catalyst is used in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the thiol-hydroxy compound. Section 8 8. The method of any one of paragraphs 1 to 7, wherein the reaction is carried out at a pressure of less than 1.5 bar. Section 9 9. The method according to any one of paragraphs 1 to 8, wherein acetylene is fed directly into the liquid phase containing the thiol-hydroxy compound and any products already formed. Section 10 10. The method of any one of paragraphs 1 to 9, wherein the pressure is maintained below 2 bar, or below 1.5 bar according to paragraph 8, while acetylene is continuously fed to the reactor and unreacted acetylene and any other gaseous compounds are withdrawn from the reactor. EXAMPLES

[0036] [Examples 1-4] Vinylation at various acetylene pressures A 0.3 liter autoclave was charged with 100 g of 2-mercaptoethanol (molecular weight: 78.13 g / mol) and 5 g of KOH pellets. The reactor was closed and heated to 100° C., and acetylene was passed through at 6 normal-liters / hour for a reaction time of 10 hours under the pressures listed in Table 1. 1 normal-liter is 1 liter of gas at 0° C. and 1013 mbar. The composition of the mixture obtained in the reactor after 10 hours of reaction was analyzed by gas chromatography. The percentages listed in Table 1 are the area percentages of the corresponding peaks. The area percentages correspond substantially to the respective weight percentages. The residual percentages up to 100% correspond to unreacted starting materials.

[0037] [Table 1]

Claims

1. Acetylene is reacted with a compound of formula I HS-R-OH wherein R is a linear or branched aliphatic hydrocarbon group which may contain oxygen in the form of an ether group.

1. A process for producing monovinyl thioethers by reacting a compound, hereinafter referred to as a thiol-hydroxy compound, with A process wherein the reaction is carried out at a pressure of less than 2 bar in the presence of a catalyst which is an alkali salt of said thiol-hydroxy compound.

2. The method of claim 1, wherein the linear or branched aliphatic hydrocarbon group contains 1 to 10 carbon atoms.

3. 2. The method of claim 1, wherein the linear or branched aliphatic hydrocarbon group contains from 2 to 6 carbon atoms.

4. 2. The method of claim 1, wherein the thiol-hydroxy compound is 2-hydroxy-ethane-1-thiol.

5. formula H 2 C=CH-S-CH 2 -CH 2 -OH 5. The method according to claim 4, which is a method for producing vinylthioethanol of formula

6. 6. The method according to claim 1, wherein the catalyst is used in an amount of 0.1 to 10 parts by weight per 100 parts by weight of the thiol-hydroxy compound.

7. The method of claim 1, further comprising the step of preparing the alkali salt of the thiol-hydroxy compound by adding an alkali metal hydroxide to the thiol-hydroxy compound and reacting the alkali metal hydroxide with the thiol-hydroxy compound at 50 to 150°C.

8. The method of claim 1, further comprising the step of preparing the alkali salt of the thiol-hydroxy compound by adding an alkali metal hydroxide to the thiol-hydroxy compound and reacting the alkali metal hydroxide with the thiol-hydroxy compound at 50 to 150° C., wherein the alkali metal hydroxide is sodium hydroxide or potassium hydroxide.

9. 9. The process according to claim 1, wherein the reaction is carried out at a pressure of less than 1.5 bar.

10. 10. The process according to any one of claims 1 to 9, wherein acetylene is fed directly to the liquid phase containing the thiol-hydroxy compound and any products already formed.

11. 11. The process according to any one of claims 1 to 10, wherein the pressure is maintained below 2 bar, or according to claim 9 below 1.5 bar, while acetylene is continuously fed to the reactor and unreacted acetylene and any other gaseous compounds are recovered from the reactor.

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