JPH0354935B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for purifying indole. (Prior Art) Indole is used not only as a raw material for dyes and medicines, but also as a raw material for essential amino acids. Indole is obtained not only by synthesis but also by separating and recovering indole present in coal tar. Methods for separating and purifying indole from coal tar fractions include (a) a distillation (rectification) method, (b) a method in which indole is separated as an alkali metal salt such as sodium and then recovered by hydrolysis; iii) A method of extracting indole using a polar solvent such as monoethanolamine, dimethyl sulfoxide, or triethylene glycol is known. (Problems to be Solved by the Invention) However, since the indole obtained by the method (a) contains many components whose boiling points are close to that of indole, it is difficult to separate high-purity indole. is difficult. Additionally, methods (b) and (c) are excellent methods for separating and recovering indole, but the indole fraction concentrated in this way cannot be distilled to produce high-purity indole. It is difficult to manufacture. This is because acidic components such as alkylphenols, which have boiling points close to indole, and basic components such as alkylpyridine, quinoline, isoquinoline, etc. contained in coal tar become concentrated in the indole fraction. It has been found. Therefore, it is conceivable to apply the method (b) or (c) after treating the indole-containing coal tar fraction with acid and alkali in advance. In this case, the basic components can be almost completely removed by acid treatment and each treatment in the indole separation step, but the acidic components cannot be sufficiently removed even by alkali treatment, and the indole solution remains in the indole solution. It was observed that the concentration of The reason why acidic components cannot be removed sufficiently by alkali treatment is thought to be that alkaline salts of alkylphenols exhibit oil solubility. Moreover, the treatment effect is very small in the low concentration range of alkylphenols. (Means for Solving the Problems) The present inventors have determined that alkylphenols having retention times between dimethylnaphthalene and indole are the main components by gas chromatographic analysis using polyethylene glycol as a stationary liquid phase. As a result of extensive research into methods for reducing the multiple components (referred to as indole pre-distillates), the present invention was completed. The present invention converts an indole fraction obtained from a coal tar fraction having an indole concentration of 50% by weight or more and an indole pre-distillation concentration of 1% by weight or more into alkali metal hydroxide, alkaline earth metal oxide and alkaline earth metal hydroxide. This is a method for purifying indole, which comprises distilling it after or while contacting it with at least one alkaline substance selected from the group consisting of substances at a temperature of 270° C. or lower. The indole fraction used in the method of the present invention is obtained from a coal tar fraction by distillation, extraction, etc., and has an indole concentration of 50% by weight or more, preferably 55 to 50% by weight.
It is an indole fraction with a concentration of 80% by weight and an indole pre-distillate concentration of 1% by weight or more. Usually, indole fraction contains, in addition to indole, a fraction whose main components are methylindole, methylnaphthalenes, dimethylnaphthalenes (hereinafter referred to as methylnaphthalenes fraction), and alkylphenols. Contains indole pre-distillate. The indole fraction can be obtained by the following method. (1) Boiling point 200~ obtained by distilling coal tar
The fraction in the range of 300℃ is treated with an aqueous sodium hydroxide solution to remove most of the acidic components mainly composed of phenols, and then treated with an aqueous sulfuric acid solution to remove quinoline, isoquinoline and alkylquinoline as the main components. Remove basic components. When the deacidified and debased fraction is reacted with potassium hydroxide under dehydration conditions at a temperature of about 200°C, the indole and methyl indole contained in the fraction become potassium salts. It separates from the oil phase. After separating this potassium salt, adding water and hydrolyzing it at a temperature of 70 to 80°C, sulfuric acid is further added to completely decompose the potassium salt, thereby obtaining an indole fraction. (2) Extract the deacidified and debased coal tar fraction in the same manner as in (1) using a polar solvent such as monoethanolamine and/or a non-polar solvent such as alkanes and cycloalkanes as an extractant. After extracting indole and methyl indole into a polar solvent phase, or hydrocarbons such as methylnaphthalenes into a non-polar solvent phase, removing the polar solvent and/or a small amount of non-polar solvent by distillation results in indole. A fraction is obtained. Examples of the alkali metal hydroxide used in the present invention include sodium hydroxide and potassium hydroxide; examples of the alkaline earth metal oxide include calcium oxide and magnesium oxide; and examples of the alkaline earth metal hydroxide include hydroxide. These include potassium, magnesium hydroxide, barium hydroxide, etc., and these may be used alone or as a mixture of two or more. Distillation is carried out after or while bringing these alkaline substances into contact with the indole fraction. In the method of the first invention in which the alkaline substances are brought into contact and then distilled, the alkaline substance can be used in the form of a solid such as powder or granules, or as an aqueous solution. When using an alkaline substance as a solid such as powder or granules, there are two methods: (1) passing the indole fraction through a column filled with the alkaline substance, (2) mixing the alkaline substance with the indole fraction and keeping it constant. There is a method of solid-liquid separation by filtration, centrifugation, etc. after stirring for a period of time. In addition, when using an alkaline substance as an aqueous solution, there are two methods: (1) mixing the aqueous solution of the alkaline substance and the indole fraction, stirring for a certain period of time, and then allowing it to stand for phase separation; (2) mixing the aqueous solution of the alkaline substance and the indole fraction; There are methods such as bringing the indole fraction into countercurrent contact. In these cases, the alkaline substance is preferably sodium hydroxide, and the concentration of the alkaline substance is preferably 10 to 30% by weight. The amount of the alkaline substance used is at least equivalent to the indole pre-distillate or phenols in the indole fraction, but it is preferably used in large excess.
For example, the alkaline substance is 1% by weight or more, preferably 5% by weight in anhydrous form, based on the indole fraction.
As mentioned above, it is more preferable to use 10% by weight or more. Further, the treatment temperature is 270°C or lower, preferably 100°C or lower, more preferably 80-300°C. Higher processing temperatures increase the amount of alkaline material required to provide a given indole pre-cut removal rate. For example, an example in which the indole pre-distillation removal rate was measured using a 20% by weight aqueous sodium hydroxide solution and varying the amount used and the treatment temperature is as follows.

[Table] Furthermore, in the method of the first invention, the indole fraction and the alkaline substance are brought into contact with each other in the presence of a hydrocarbon solvent with a boiling point of 200°C or less that is not substantially soluble in water. is preferred.
Examples of such solvents include aliphatic hydrocarbons such as pentane, hexane, heptane and octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and aromatic hydrocarbons such as benzene, toluene and xylene. Among these, alicyclic hydrocarbons, aromatic hydrocarbons, or mixtures thereof are preferred. The use of the above solvent has the following effects. (1) It lowers the viscosity and specific gravity of the indole fraction, making it easier to separate it from the alkaline substance after contact and reducing the loss of indole. (2) When using an aqueous solution such as sodium hydroxide as the alkaline substance, , the boundary between the oil phase and the aqueous phase becomes clear, and the incorporation of alkaline substances into the oil phase and the incorporation of oil into the aqueous phase are greatly reduced. (3) After contact, the indole fraction can be easily distilled The solvent can be recovered and recycled. The indole fraction from which alkylphenols have been removed by the above method is distilled to obtain high-purity indole either as it is or after performing purification operations such as adsorption and extraction if necessary. The distillation conditions at this time are such that the maximum temperature is 270°C or lower, preferably 250°C or lower, since indole polymerizes at high temperatures. For this purpose, vacuum distillation is preferred. In the method of the second invention, in which the alkaline substance is distilled in the presence of an alkaline substance, the alkaline substance is used in the form of a solid such as a powder or granules. The alkaline substance is preferably added to the indole fraction charged into the distillation column, but it may also be added to the bottom of the distillation column. When adding an alkaline substance, it is not preferable to use an aqueous solution or an aqueous suspension because the amount of water removed during distillation increases. The amount of the alkaline substance used is at least equivalent to the indole pre-distillate or phenols in the indole fraction. For example, it is preferably about 1 to 20 times, particularly about 1.5 to 4 times, the weight ratio of the indole pre-distillate. If the amount used is small, it is difficult to reduce the indole pre-distillate content in indole to 1% by weight or less. Moreover, there is no special effect even if the amount added is too large. An example of a method for distilling an indole fraction is as follows. (1) A method in which the indole fraction and alkaline substances are directly put into the pot of a batch distillation apparatus and distilled as is. (2) A method in which the indole fraction and alkaline substances are heated and stirred in a tank equipped with a stirring and heating device, and then distilled using a batch or continuous distillation device without separating the alkaline substances. Since distillation is carried out in the presence of an alkaline substance, the parts of the distillation apparatus that come in contact with the alkaline substance must be made of a material that has sufficient corrosion resistance against the high-temperature alkaline substance. Corrosion-resistant materials include pure nickel or alloys with high nickel and/or chromium content. In addition, it is necessary to keep the maximum temperature during distillation, and in the case of batch distillation, the temperature of the pot as low as possible. Since indole polymerizes at high temperatures, the maximum temperature is 270°C or lower, preferably 250°C or lower. For this purpose, it is preferable to carry out the process under reduced pressure as much as possible. The purified indole obtained by the method of the present invention is
It can be made into a product as it is, or if necessary, it can be made into a highly purified indole by further distillation, recrystallization, or other methods. (Example) Hereinafter, the present invention will be explained in detail with reference to Examples. Reference example A coal tar fraction with a boiling point of 200 to 300°C obtained by distillation is treated with potassium hydroxide, the separated potassium salt is hydrolyzed, neutralized, and further washed with pentanes. An indole fraction, which is a starting material for the invention, was obtained. Its composition is shown in Table 1 (before treatment). 10 parts by weight of granular sodium hydroxide was added to 90 parts by weight of this indole fraction, and the mixture was stirred at 70°C for 3 or 5 hours, and the composition was analyzed by gas chromatography after each hour. Using the gas chromatograph, the methylnaphthalene fraction, indole pre-distillation, indole, methylindoles, and others were distilled in this order. Here, the methylnaphthalene fraction is a distillate consisting of a plurality of components, each of which has methylnaphthalene and dimethylnaphthalene as main components, the indole pre-distillate contains alkylphenols, and the methylindoles mainly contain methylindoles. Furthermore, granular potassium hydroxide,
The same procedure as above was carried out for powdered calcium hydroxide and powdered calcium oxide. The results are shown in Table 1.

[Table] Example 1 To 100 parts by weight of the indole fraction obtained in the reference example
Add 100 parts by weight of 30% sodium hydroxide solution
The mixture was stirred at 70°C for 1 hour. The aqueous phase was then removed and 10 parts by weight of granular sodium hydroxide was added to
The mixture was stirred at ℃ for 2 hours. 200 parts by weight of isopropyl ether was added to the resulting paste-like mixture, and centrifugal sedimentation was performed. After removing the liquid phase by distillation with isopropyl ether, distillation was carried out at a column top pressure of 50 mmHg. The results are shown in Table 2.

[Table] Comparative Example 1 The indole fraction was distilled under the same conditions as in Example 1 without being treated with sodium hydroxide. The results are shown in Table 3.

[Table] Example 2 A coal tar fraction with a boiling point of 200 to 300°C obtained by distillation was extracted with monoethanolamine to obtain an indole fraction as a starting material. Its composition is shown in Table 4. After adding 100 parts by weight of toluene to 100 parts by weight of the indole fraction and dissolving it, 100 parts by weight of 20% by weight sodium hydroxide solution was added and stirred at 40°C for 1 hour.
Thereafter, the aqueous phase was separated and removed, and toluene was distilled off from the liquid phase, followed by distillation at normal pressure. The results are shown in Table 4.

[Table] Example 3 100 parts by weight of an indole fraction (2.9 parts by weight of an indole pre-distillate) produced by treating a distilled coal tar fraction with a boiling point of 200 to 300°C with potassium hydroxide and hydrolyzing it. Add 5 parts by weight of granular sodium hydroxide to a pot (made by Nickel) and add 100%
The mixture was kept at 0.degree. C. and stirred for 1 hour. Thereafter, simple distillation was performed under reduced pressure of 300 mmHg. The purified indole obtained was 78 parts by weight. The results are shown in Table 5.

[Table] The obtained purified indole was further rectified (packed column with approximately 50 theoretical plates, reflux ratio 10), and then recrystallized using cyclohexane to obtain 47 parts by weight of indole with a purity of 99% by weight. Comparative Example 2 100 parts by weight of the raw indole fraction obtained in Example 3 was rectified in the same manner as in Example without granular sodium hydroxide treatment and simple distillation, and recrystallized with cyclohexane, resulting in a purity of 98.5 weight parts. % indole was obtained in an amount of 28 parts by weight. (Effects of the Invention) According to the method of the present invention, high purity indole can be obtained in high yield. In particular, it is possible to significantly reduce the indole pre-distillate whose main components are alkylphenols, which are difficult to separate using conventional methods.

Claims (1)

[Claims] 1. Indole concentration obtained from coal tar fraction 50% by weight or more, indole pre-distillate concentration 1% by weight
The above indole fraction is converted into alkali metal hydroxide,
A method for purifying indole, which comprises bringing it into contact with at least one alkaline substance selected from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides at a temperature of 270°C or lower, and then distilling it. . 2. The method for purifying indole according to claim 1, wherein the contact between the indole fraction and the alkaline substance is carried out in the presence of a solvent that is substantially insoluble in water. 3. The method for purifying indole according to claim 1 or 2, in which an aqueous sodium hydroxide solution having a concentration of 10 to 30% by weight is used as the alkali metal hydroxide. 4. The indole according to claim 2, wherein the solvent is at least one hydrocarbon selected from the group consisting of aliphatic hydrocarbons, alicyclic hydrocarbons, and aromatic hydrocarbons with a boiling point of 200°C or less. Purification method. 5 Indole concentration obtained from coal tar fraction 50% by weight or more, indole pre-distillate concentration 1% by weight
The above indole fraction is converted into alkali metal hydroxide,
A method for purifying indole, which comprises distilling in the presence of at least one alkaline substance selected from the group consisting of alkaline earth metal oxides and alkaline earth metal hydroxides. 6. The method for purifying indole according to claim 5, wherein the alkaline substance is at least one selected from the group consisting of sodium hydroxide, potassium hydroxide, calcium hydroxide, and magnesium hydroxide. 7. The method for purifying indole according to claim 5, wherein the maximum temperature is 270°C or less when distilling the indole fraction in the presence of an alkaline substance.