PROCESS FOR THE PREPARATION OF 3-SUBSTITUTED THIOPHENES

Abstract: The invention relates to a process for the preparation of 3-substituted thiophenes in which the substituent is a C4-C18-alkyl group. According to the invention, the preparation is carried out by allowing an alkali metal salt of a C4-C18-alkyl-succinic acid to react with a compound of sulfur and phosphorus, e.g. tetraphosphorus decasulfide, in an organic solvent at a temperature of 100-180 DEG C, the product obtained being 3-(C4-C18-alkyl)thiophene. The said reaction may be the last step in a process in which the initial material is maleic acid anhydride with which alpha -C4-C18-alkene is combined so that C4-C18-alkenylsuccinic acid anhydride is obtained, whereafter this is hydrogenated catalytically to produce C4-C18-alkylsuccinic acid anhydride. This is thereafter reacted with an alkali metal hydroxide so that an alkali salt of the C4-C18-alkylsuccinic acid is obtained, which salt is reacted with a compound of sulfur and phosphorus to produce 3-(C4-C18-alkyl)thiophene, which constitutes the final product.

Description: Process for the preparation of 3-substituted thiophenes The invention relates to a process for the preparation of 3- substituted thiophenes in which the substituent consists of a C 4 -C 18 alkyl group. It is known that the preparation of 3-substituted thiophene is more difficult than the preparation of 2-substituted thiophene However, 3-substituted thiophene is a desirable intermediate o final product in various applications, for example as an herbi cide or a fungicide. Certain 3-substituted thiophenes can also be used as monomers in the preparation of, for example, elec¬ trically conductive polymers. 3-substituted thiophene can in principle be prepared in two different ways: by using as the initial material a thiophene o a thiophene provided with a modifiable 3-substituent, or by using as the initial material an acyclic compound. Substituted thiophenes can, of course, also be prepared by other methods, but in that case the products are usually 2-substituted. The best known way of using thiophene as the initial material is the bromination of thiophene. 3-Bromothiophene can be pre¬ pared, for example according to EP publication 299 586, cata- lytically from 2,5-dibromothiophene and thiophene. 3-Bromothio phene is one of the most important intermediates from which a wide variety of 3-substituted thiophenes are obtained, for example by means of Grignard reactions, by lithiation, or by oxidation. The use of 3-bromothiophene as the initial material in a production process is, however, hampered by the undesir¬ able bromides formed as byproducts and by the difficult reac¬ tion conditions, such as an unsuitable temperature and an iner atmosphere. The preparation of 3-substituted thiophenes by using an acycl compound as the initial material has been studied extensively. These processes often have the disadvantage that they produce large amounts of 2-substituted thiophenes as byproducts. Some examples of these processes are the use of various mercaptans or thioethers as the initial material (Butler, A.R., Henry, J.B., J. Chem. Soc, B, 1970, or Campaigne, E., Monroe, P.A., J. Am. Chem. Soc, 76 (1954), 2445). 3-substituted thiophene can also be prepared from other compounds which contain either double bonds or other functional groups (Veal, .T., Grinter, T.J., EP 38121, or Duus, F. , Tetrahedron, 32 (1976), 2817). As mentioned above, many of these processes known to an expert in the art produce large amounts of undesirable 2-substituted thiophene compounds and isomers, the separating of which cause difficulties. Furthermore, the undesirable byproducts are de¬ rived from the same initial material, and thus the yield will remain very low in the state-of-the-art processes. The object the present invention is to provide a maximally selective process for the preparation of a 3-substituted C 4 - C 18 -alkylthiophene, the yield and the degree of purity being maximally high. The said objectives have now been achieved by process which is characterized in that the preparation is car¬ ried out by allowing an alkali metal salt of a C -C 18 -alkylsuc- cinic acid to react with a compound of sulfur and phosphorus in an organic solvent at a temperature of 100-180 °C, the result¬ ing product being 3- (C 4 -C 18 -alkyl)thiophene. A yield of nearly 75% is achieved by the process according to the invention, the degree of purity being approx. 95-98%. It is a further advantage of the invention that the separating of the final product is easy. s regards the state of the art, it should further be pointed that US patent publication 2,658,903 discloses a process for the preparation of 3-alkylated thiophene from the correspondin alkali metal salt of an alkylsuccinic acid. According to the publication, however, only 3-methylthiophene and 3-ethylthio¬ phene have been prepared, i.e. the alkyl substituents are dif¬ ferent from those in the present invention, in addition to which the reaction has been carried out within a temperature range of 225-300 °C, preferably at 250 °C, i.e. at a tempera¬ ture substantially higher than in the present invention. According to the present invention, the preparation of 3-sub¬ stituted thiophene is carried out preferably by reacting first a C 4 -C 18 -alkylsuccinic acid anhydride with an alkali metal hydroxide to give the alkali metal salt of C 4 -C 18 -alkylsuccinic acid, and by reacting thereafter the said salt with a compound of sulfur and phosphorus so that the final product obtained will be a 3- (C 4 -C 18 -alkyl)thiophene. According to the present invention, the initial material in th preparation of 3-substituted thiophene may be maleic acid an¬ hydride, the process consisting of the following steps: a) ce-C 4 -C 18 -alkene is combined with the maleic acid anhydride so that C 4 -C 18 -alkenylsuccinic acid anhydride is obtained, b) the C 4 -C 18 -alkenylsuccinic acid anhydride is hydrogenated catalytically to form C 4 -C 18 -alkylsuccinic acid anhydride, c) the C 4 -C 18 -alkylsuccinic acid anhydride is reacted with an alkali metal hydroxide so that the alkali metal salt of C 4 -C 18 - alkylsuccinic acid is formed, and d) the alkali metal salt of C 4 -C 18 -alkylsuccinic acid is react¬ ed with a compound of sulfur and phosphorus so that 3- (C 4 -C 18 - alkyl)thiophene is obtained as the final product. The present process differs substantially from that disclosed in US publication 2,658,903, in which the preparation of 3- methylthiophene is started with the hydrogenation of the di- sodium salt of itaconic acid. The process is described by the following reaction formula, wherein R = C^-C^- lkyl and MOH = alkali metal hydroxide. Tetraphosphorus decasulfide is indi¬ cated as the compound of sulfur and phosphorus. The compound of sulfur and phosphorus used in the process ac¬ cording to the invention is preferably tetraphosphorus deca¬ sulfide, P 4 S 10 . A high yield has been achieved with a mixture of tetraphosphorus decasulfide and red phosphorus, the molar ratio of the components in the mixture being 1:4-1:6, suitably 1:5.3. The molar ratio of the active compound of sulfur and phosphorus to the alkali salt of alkylsuccinic acid is suitabl 0.5:1-2:1, most preferably approx. 0.5:1. In the process according to the invention it is possible to us as the said organic solvent aliphatic or aromatic hydrocarbons or their mixtures, e.g. xylene, halogenated hydrocarbons, e.g. chloro- or dichlorobenzene, ethers, e.g. 2-ethoxyethyl ether, of mixtures of these. For example, o-dichlorobenzene is especially suitable. In the process of the invention, the reaction temperature is preferably within the range 130-180 °C. The reaction time may vary between 1 and 20 hours. The reaction may occur in a norma atmosphere or under slight overpressure in an argon or nitroge blanket. After the reaction between the alkali salt of alkylsuccinic acid and the compound of sulfur and phosphorus has occurred, the solid precipitate is first removed, for example, by filtra¬ tion or centrifugation. Thereafter the solvent is removed by distillation, and ultimately the 3- (C 4 -C 18 -alkyl)thiophene obtained as the product is recovered by vacuum distillation. A washing or neutralization of the organic phase before the vacuum distillation is not necessary in the process of the invention. The invention is illustrated below with the following embodi¬ ment examples. Example 1 Alkenylsuccinic acid anhydride Maleic acid anhydride (14g, 0.14 mol) and 1-octene (50ml, 0.32 mol) were loaded into an autoclave. The mixture was purged wit nitrogen. The reaction mixture was heated at 210 °C for 4 hours. After cooling the mixture was filtered, and excess octene was evaporated out at reduced pressure. The yield of octenylsuccinic acid anhydride was 25g (85% of the theoretical amount) . Example 2 Alkenylsuccinic acid anhydride The procedure was as in Example 1, but the amount of octene wa 30ml (0.19 mol) , whereupon the yield was 80% of the theoretica amoun . Example 3 Alkylsuccinic acid anhydride The octenylsuccinic acid anhydride was dissolved in ethyl acetate and was hydrogenated using a palladium/carbon catalyst (5% by weight of the initial material) . The catalyst was filtered out, and the solvent was evaporated. The obtained yield of octylsuccinic acid was 24g (95% of the theoretical amount) . Example 4 Alkylsuccinic acid anhydride The procedure was as in Example 3, but dodecylsuccinic acid anhydride was used, which had been prepared by substantially the same procedure as used in Examples 1 and 2, and a palladium/carbon catalyst at 1% by weight. The yield was the same as in Example 3, i.e. 95% of the theoretical amount. Example 5 Potassium salt of alkylsuccinic acid 254g (1.2 mol) of octylsuccinic acid anhydride was mixed with 500ml of ethanol, and the mixture was heated until the an¬ hydride had dissolved. A solution of 134.6g (2.4 mol) of potassium hydroxide in 1200ml of ethanol was added to the solution. The solution was cooled slowly for several hours, whereafter the produced precipitate was filtered. The precipi¬ tate was dried in an oven at 40 °C. The yield of the potassium salt of octylsuccinic acid was 275g, which was 75% of the theoretical amount. Example 6 Disodium salt of alkylsuccinic acid 143.lg (0.675 mol) of octylsuccinic acid anhydride was mixed with 250ml of ethanol, and the mixture was heated until the anhydride had dissolved. A solution of 54g (1.35 mol) of sodiu hydroxide in 675ml of ethanol was added to the solution. The solution was cooled slowly for several hours, whereafter the produced precipitate was filtered. The precipitate was dried i an oven at 40 °C. The yield of the disodium salt of octylsuccinic acid was 168.3g, which was 91% of the theoretica amount. Example 7 2-Octylthiophene 22.9g (0.075 mol) of the dipotassium salt of octylsuccinic acid, 16.6g (0.0375 mol) of tetraphosphorus decasulfide, 9.3g (0.3 mol) of red phosphorus and 100ml of o-dichlorobenzene wer charged into a 300ml pressure reactor. Nitrogen was blown through the reactor for 1 hour, whereafter the reactor was closed. The reactor temperature was raised to 180 °C, which w maintained for 3.5 hours. Thereafter the temperature was lowered to 40 °C, and overpressure was removed from the reactor. Thereafter 150ml of ether was added to the reaction mixture, and the inorganic precipitate was filtered out by suction. The filtrate was first washed with 50ml of water, the neutralized with a 10% NaOH solution, and ultimately washed with water several times, until the ether solution was neutral The organic solution was then dried with Na 2 S0 4 , whereafter th ether and the o-dichlorobenzene were distilled out at a slightly reduced pressure. Ultimately the product was distille by means of a vacuum pump at a temperature of approx. 90 °C an a pressure of 1 mbar. The yield was 45%. Example 8 3-Dodecylthiophene The reaction was carried out in substantially the same manner as in Example 7, by using 27.2g (0.075 mol) of the dipotassium salt of dodecylsuccinic acid as the initial materials (the sal was prepared in the manner described in Example 5) , 33.3g (0.075 mol) of tetraphosphorus decasulfide, and 9.3g (0.3 mol) of red phosphorus, as well as 100ml of dichlorobenzene as a solvent. The yield of dodecylthiophene was 48% (b.p. 196 °C/20 mbar) . Example 9 3-Octyl hiophene 160.3g (0.525 mol) of the dipotassium salt of octylsuccinic acid, 116.9g (0.263 mol) of tetraphosphorus decasulfide, 43. g (1.4 mol) of red phosphorus, and 600ml of o-dichlorobenzene were charged into a 2000ml Parr pressure reactor which was equipped with a mechanical stirrer and with inlet and outlet connections for the trough-flow of nitrogen. The reactor was closed, the stirrer was started, and nitrogen was blown throug the reactor for l hour. Thereafter the flow of nitrogen was cu off, and the reactor temperature was raised to approx. 150 °C, at which it was kept for 4.5 hours. After cooling to 40 °C the overpressure was released. The reaction mixture was treated by removing the inorganic precipitate by filtration. The precipitate was washed upon a filter with 600ml of MTBE, which was used in four 150ml portions. The filtrate was combined with the organic phase. The combined organic phase was subjected to fractional distillation (a 15 cm VIGREAUX column) . Most of the MTBE was distilled out at normal pressure, and the remainder, as well a the o-dichlorobenzene, at a reduced pressure of 40-70mbar. The crude product was thereafter subjected to fractional dis¬ tillation at a pressure of approx. 1.5mbar using the same frac¬ tional distillation column. The product obtained was 77.5g of 3-octylthiophene having a purity of 94.4%, which corresponded to a yield of 71.1% as calculated from the theoretical yield. Examples 10-17 3-Octylthiophene The results from the reactions which were carried out substan¬ tially in accordance with the above Example 7 (Examples 10-13) and the above Example 9 (Examples 14-17) in pressure reactors of 300ml and 2000ml are presented in the following table. The initial material in Examples 10-12 and 14-16 was the dipotas¬ sium salt and in Examples 13 and 17 the disodium salt of octyl¬ succinic acid (HASA) . The solvent used was o-dichlorobenzene (o-DCB) , 2-ethoxyethyl ether, or products LI 200 and SOLVESSO 100. Table Ex- Initial material Time Tempera- Solvent Yield Pur- ample h ture % ity 10 HASA-K 0.075 mol 3.5 180 0-DCB+ 41.9 87 P 4 Λ S°10 .0375 mol Li200 0.15 mol (1:4) 11 HASA-K 0.075 mol 3.5 180 SOLVES¬ 51.3 94 P 4 S 10 0.0375 mol SO 100 P 4 0.15 mol 2 HASA-K 0.075 mol 3.5 180 2-ethoxy- 21.7 94 P 4 S 10 0.0375 mol ethyl- 0.225 mol ether 3 HASA-Na 0.075 mol 3.5 180 o-DCB 57.1 98 P Δ 4S°10 0.075 mol 0.225 mol 4 HASA-K 0.525 mol 17 130- 0-DCB 73.6 97 P 4 S 10 0.525 mol 150 2.1 mol 5 HASA-K 0.525 mol 160- SOLVES- 66.9 96 P 4 S 10 0.263 mol 170 SO 100 1.4 mol 6 HASA-K 0.525 mol 5.5 160- o-DCB+ 66.5 95 P 4 S 10 0.263 mol 170 SOLVES- 1.4 mol SO 100 (1:4) 7 HASA-Na 0.525 mol 4 160- o-DCB 67.1 95 P 4 S 10 0.263 mol 170 1.4 mol

Claims: Claims 1. A process for the preparation of 3-substituted thio¬ phenes in which the substituent is a C 4 -C 18 -alkyl group, char¬ acterized in that the preparation is carried out by reacting a alkali metal salt of C 4 -C 18 -alkylsuccinic acid with a compound of sulfur and phosphorus in an organic solvent at a temperatur of 100-180 °C, whereby a 3- (C 4 -C 18 -alkyl)thiophene is obtained as the product. 2. A process according to Claim l, characterized in that the compound of sulfur and phosphorus is tetraphosphorus deca¬ sulfide. 3. A process according to Claim 2, characterized in that a mixture of tetraphosphorus decasulfide and phosphorus is used in the process. 4. A process according to any of the above claims, charac¬ terized in that the solvent used is a chlorinated hydrocarbon, such as o-dichlorobenzene. 5. A process according to any of Claims 1-3, characterized in that an aromatic hydrocarbon mixture having a boiling point within the range 130-210 °C is used. 6. A process according to any of the above claims, charac¬ terized in that the reaction temperature is within the range 130-180 °C. 7. A process according to any of the above claims, charac¬ terized in that, after the reaction has occurred, the solid precipitate is removed, the solvent is removed by distillation, and ultimately the 3- (C 4 -C 18 -alkyl)thiophene obtained as the product is recovered by vacuum distillation. 8. A process according to any of the above claims, charac¬ terized in that 3-octylthiophene is produced by the process. 9. A process according to any of the above claims, charac¬ terized in that a C 4 -C 18 -alkylsuccinic acid anhydride is first reacted with an alkali metal hydroxide so that the alkali meta salt of the C 4 -C 18 -alkylsuccinic acid is produced, and that th said salt is thereafter reacted with a compound of sulfur and phosphorus so that the final product obtained is a 3-(C 4 -C 18 - alkyl)thiophene. 10. A process according to Claim 9, characterized in that the alkali metal hydroxide is potassium hydroxide or sodium hydroxide. 11. A process according to Claim 9 or 10, characterized in that it comprises the following steps: a) α-C 4 -C 18 -alkene is combined with maleic acid anhydride so that C 4 -C 18 -alkenylsuccinic acid anhydride is obtained, b) the C 4 -C 18 -alkenylsuccinic acid anhydride is hydrogenated catalytically to produce C 4 -C 18 -alkylsuccinic acid anhydride, c) the C 4 -C 18 -alkylsuccinic acid anhydride is reacted with an alkali metal hydroxide so that an alkali salt of the C 4 -C 18 - alkylsuccinic acid is formed, and d) the alkali salt of C 4 -C 18 -alkylsuccinic acid is reacted with a compound of sulfur and phosphorus so that the final product obtained is a 3- (C 4 -C 18 -alkyl)thiophene.

Inventors: HORMI OSMO, JAERVINEN HANNELE, LAHTINEN LEILA, NAESMAN JAN, TAMMI ANNA-LIISA, HORMI, OSMO, JAERVINEN, HANNELE, LAHTINEN, LEILA, NAESMAN, JAN, TAMMI, ANNA-LIISA
Applicants: NESTE OY
Application year: 1992
Main classification: C07D333
IPC codes: C07D333