JPH01157957A - Production of indole - Google Patents

Abstract

PURPOSE:To obtain the aimed substance, by distilling an indolecontaining fraction obtained by distillation of coal tar and diethylene glycol to obtain an azeotropic fraction of indole and diethylene glycol and removing diethylene glycol from the azeotropic fraction. CONSTITUTION:A coal tar fraction at 220-280 deg.C is mixed with 0.6-0.8 as much diethylene glycol as the coal tar fraction by weight and distilled to distill an azeotropic mixture of methylnaphthalenes and quinoline and other organic compounds which are not the aimed substance and diethylene glycol in a raw temperature range. Then indole and diethylene glycol concentrated in a high concentration in an oil at the bottom are subjected to azeotropic distillation. The distillate is mixed with water to extract and remove diethylene glycol, the indole concentrated fraction is recovered and cooled to give indole crystal. Indole can be purified to >=99.5% by recrystallization with hexane, cyclohexane, etc.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention involves recovering a concentrated indole fraction by azeotropic distillation from an indole-containing fraction obtained by distilling coal tar, and crystallizing and recrystallizing the concentrated indole fraction. The present invention relates to a method for producing high purity indole.

[Prior Art] Indole is a compound useful as a raw material for fragrances, agricultural chemicals, medicines, etc., or as a raw material for tryptophan, which is one of the essential amino acids.

Conventionally, as a method for obtaining indole, in addition to synthesis, a method of separating and recovering indole present in coal tar has generally been adopted.

The method for recovering indole from coal tar is as follows:
Coal tar is distilled to collect an indole-containing fraction at around 250°C, and this indole-containing fraction is recovered by various methods. However, the indole-containing fraction contains neutral components such as 1-methylnaphthalene, 2-methylnaphthalene, biphenyl, ethylnaphthalene, dimethylnaphthalenes, and acenaphthenes, and basic components such as quinoline and inquinoline-methylquinolines. It contains various components with boiling points and/or melting points close to indole. For this reason, it is extremely difficult to recover indole with high purity from an indole-containing fraction.

For this reason, various methods have been proposed. For example, strong bases and phenols are removed from the 220 to 270°C fraction obtained by distilling coal tar, heated to 100 to 125°C with sodium or sodium amide to form indole sodium, and then decomposed with water. A method of purifying by recrystallization, a method of extracting indole from the indole fraction of coal tar using pentane and a polar solvent (monoethanolamine, dimethyl sulfoxide, pyrrolidone, etc.) (USSR Patent No. 598889), a method of distilling coal tar The fraction with a boiling point range of 220 to 270°C obtained by Alternatively, a method of desorption and separation using a developing agent (Special Publication Publication No. 60-21
No. 587), a mixture containing nonpolar or slightly polar compounds present in coal tar is brought into contact with a solvent such as alkanes and naphthenes, and the solvent is removed from the raffinate phase rich in indoles to obtain indoles. (Japanese Unexamined Patent Publication No. 58-135862), crude indole from a coal tar fraction is distilled to obtain an indole fraction consisting of indole and methyl indoles at a specific concentration, and then this is heated to a boiling point of 50 to 150°C. There is a method of recrystallizing using a paraffinic or naphthenic hydrocarbon solvent to obtain high purity indole (Japanese Patent Application Laid-Open No. 134462/1983).

However, the method using sodium or sodium amide is not only expensive and dangerous, but also has problems with the material of the equipment and requires complicated operations, so it is not efficient.

Furthermore, the method of Soviet Patent No. 598889 has disadvantages in that it is not easy to separate and recover the solvent, and that separation and recovery requires a large amount of energy.

In the method disclosed in Japanese Patent Publication No. 60-21587, the zeolite used as an adsorbent has a decreased adsorption performance due to basic substances, acidic substances, or water, and a shortened service life for continuous use. For this reason, the boiling point range is 220 to 270°C, which contains basic substances such as quinoline and isoquinoline, or acidic substances such as phenol, cresols, and xylenol.
When using a coal tar fraction as a raw material, basic substances and acidic substances must be removed by pretreatment. In particular, by the inorganic acids used to remove basic substances,
Polymerization of indole may occur, leading to a decrease in yield, and complicated operations must be added to the pretreatment of raw materials, such as the need for dehydration to completely remove water after washing. .

The method disclosed in JP-A-58-135862 limits the raw materials to a mixture containing indoles and non-polar and/or slightly polar compounds present in coal tar, such as quinoline, isoquinoline, methylquinoline, etc. Difficult to apply to mixtures containing polar compounds.

Furthermore, the method of JP-A-57-134462 uses an indole fraction with an indole concentration of 80 to 98% by weight and a methylindole concentration of 4% by weight or less as a raw material, and only distills from coal tar. Obtaining the high-concentration indole fraction by this method is disadvantageous in terms of recovery yield. For this reason, 23
The crude indole obtained by heat-treating the 0-260'C fraction with caustic alkali and hydrolyzing the resulting reaction product is used, and the fraction satisfying the above composition is used. It is necessary to prepare raw materials through a process,
It's not an efficient method.

[Problems to be Solved] This invention enables easy, high-yield, and high-purity production of indole-containing fractions obtained by distilling coal tar by azeotropic distillation and crystallization without requiring complicated steps. The present invention provides a method for producing indole that can be recovered using

[Means for Solving the Problems] As a result of intensive research into the production of indole from an indole-containing fraction obtained by distilling coal tar, the present inventors discovered that diethylene glycol was added to the indole-containing fraction and distillation was performed. By doing so, methylnaphthalenes,
Neutral components such as biphenyl, dimethylnaphthalenes, and acenaphthene, and basic components such as quinoline, isoquinoline, and methylquinoline are azeotroped with diethylene glycol,
It was discovered that almost all of the indole was distilled out in a temperature range lower than that at which indole was distilled, indole was concentrated to a high concentration, and that high-purity indole could be recovered in high yield by precision distillation. The application has been filed as

Further research was conducted using an Osmer equilibrium distillation apparatus to examine the two components coexisting in the indole-containing fraction and diethylene glycol. As shown in Table 1, methylnaphthalenes in the indole-containing fraction , biphenyl, dimethylnaphthalenes, acenaphthenes, and basic components such as quinoline, isoquinoline, and methylquinoline, azeotropes with diethylene glycol and distills out at a temperature below the distillation temperature of indole. It has been found that there is a temperature range in which it is azeotropic and does not azeotrope with most impurities other than indole. Incidentally, the azeotropic temperature of indole and diethylene glycol is 244.6°C under normal pressure.

The inventors discovered that indole could be easily recovered in high yield and purity by removing diethylene glycol from the azeotropic indole and diethylene glycol fraction and crystallizing it, and came up with the present invention.

That is, this invention subjects an indole-containing fraction obtained by distilling coal tar and diethylene glycol to distillation,
This method for producing indole is characterized by distilling an azeotropic fraction of indole and diethylene glycol, removing diethylene glycol from the fraction, and then cooling to separate precipitated crystals.

The indole-containing fraction of the raw material in this invention is as follows:
Coal tar fractions with a boiling point of 220 to 280°C, that is, naphthalene oils obtained by distilling coal tar, washing oils, etc., can be mentioned, but distillations obtained by distilling these by batch distillation, continuous distillation, or a combination thereof. is suitable.

When diethylene glycol is added to the indole-containing fraction and distilled, the non-target substances methylnaphthalenes, biphenyl, dimethylnaphthalenes,
Neutral components such as acenaphthene, basic components such as quinoline, isoquinoline, methylquinoline, and other organic compounds are azeotropically distilled with diethylene glycol, and most of the indole is concentrated to a high concentration and remains in the bottom oil. do. Next, the bottom oil and diethylene glycol from which non-target substances have been almost completely removed are subjected to distillation to azeotropically distill indole with diethylene glycol, and after removing diethylene glycol from the fraction, crystallization is performed on cooling to obtain high-purity indole. Crystalline substances can be easily recovered in high yield.

According to the experimental results conducted by the present inventors, the amount of diethylene glycol added to the indole-containing fraction obtained by distilling coal tar varies depending on the cutting temperature during coal tar distillation. 0.5 to 1.2 times by weight, preferably 0.6 to 0.8 times by weight.

Furthermore, diethylene glycol may be added to the indole-containing fraction before it is charged into the distillation column, or it may be separately charged into the distillation column and mixed within the column.

Since the azeotropic fraction of diethylene glycol and indole is difficult to dissolve indole, a solvent that dissolves diethylene glycol, mainly water, is added to extract and remove diethylene glycol, and an indole concentrated fraction is recovered.

The amount of water added to the azeotropic fraction of diethylene glycol and indole may be 0.3 to 0.7 times by weight, preferably about 0.5 times the amount of diethylene glycol in the azeotropic fraction.

The collected indole concentrated fraction is cooled to precipitate indole crystals, and then centrifugally filtered to separate indole.

The temperature at which the crystals are precipitated is 0 to 20'C1, preferably 5
~10°C is appropriate.

Further, the cooling/crystallization operation may be performed either batchwise or continuously.

The purity of indole obtained in this step is 97% or more, but it can be further increased to 99.5% or more by recrystallizing it using a solvent.

The recrystallization solvent used is preferably an aliphatic hydrocarbon having 5 to 10 carbon atoms such as hexane or heptane, or an alicyclic hydrocarbon having 6 to 7 carbon atoms such as cyclohexane or methylcyclohexane.

The higher the amount of recrystallization solvent used, the higher the purity, but the lower the recovery rate, so for aliphatic hydrocarbons it is appropriate to use an amount of 5 to 15 times, preferably 9 to 11 times by weight, relative to the indole crystal. For alicyclic hydrocarbons, the amount may be 0.2 to 2 times, preferably 0.4 to 0.8 times by weight.

This recrystallization is carried out by ordinary heating dissolution-cooling crystallization, and the temperature at which purified crystals are precipitated by cooling a homogeneous solution of dissolved indole and recrystallization solvent is 0 to 20 °C, preferably 5 to 15 °C. °C is suitable.

Note that it is economically advantageous to distill the aqueous diethylene glycol solution extracted from the azeotropic fraction of diethylene glycol and indole to remove water, and then recycle the recovered diethylene glycol to the azeotropic distillation process.

Further, the distillation operation in the present invention is carried out using a conventional distillation column under normal pressure or reduced pressure.

[Example] Example 1 Diethylene glycol 4
Added θOg, effective inner diameter 25 mm, effective column length 1
, 200 mm, and a Helipack packed distillation apparatus having approximately 50 theoretical plates. Distillation is carried out at a reflux ratio of 1 under normal pressure.
0 and the column top temperature to 235°C, the fraction of
7. 650 g of an azeotropic fraction with Seacoal was distilled off.

Then, the bottom oil was refluxed at a reflux ratio of 20 under a reduced pressure of 100 mmHg.
After distilling to a column top temperature of 172°C and distilling off 148g of an azeotropic fraction of non-target substances and diethylene glycol, the kettle temperature was raised and a co-distillation of indole and diethylene glycol was carried out at a column top temperature of 173°C. 145 g of boiling fraction was obtained.

Table 2 35 g of water was added to this azeotropic fraction, and the diethylene glycol aqueous solution was separated and removed to obtain 80 g of an indole concentrated fraction. This concentrated fraction was cooled to 5°C to precipitate crystals, and then centrifugally filtered to obtain 67.5 g of indole crystals. The purity of this indole crystal was 97.4%, and the recovery rate from the indole-containing fraction was 77.2%.

500 g of heptane was added to 50 g of this indole crystal, heated and dissolved at 55°C, cooled to 5°C to precipitate purified crystals, centrifugally filtered and collected crystals were vacuum dried, purified indole crystals 37 .1g was obtained. The purity of this purified indole was 99.5%, and the recovery rate in this step was 75.8%.

Example 2 Same indole-containing fraction used in Example 1 1.20
800 g of diethylene glycol was added to 0 g and distilled using the same distillation apparatus as in Example 1 to give 100 mm Hg.
Distilled under reduced pressure at a reflux ratio of 20 to a tower top temperature of 172°C,
Azeotropic distillate of non-target substance and diethylene glycol 1406
g was distilled off.

Further, 276 g of an azeotropic fraction of indole and diethylene glycol was obtained at a column bottom oil of 100 mmHg, a reflux ratio of 40, and a column top temperature of 173°C. 69 g of water was added to this azeotropic fraction, and the diethylene glycol aqueous solution was separated and removed to obtain 160 g of an indole concentrated fraction.

This concentrated indole fraction was cooled to 5°C to precipitate crystals, and then centrifugally filtered to obtain 136 g of indole crystals. This indole crystal had a purity of 97.1%, and a recovery rate from the indole-containing fraction was 77.5%.

52 g of cyclohexane was added to 130 g of this indole crystal, heated and dissolved at 55°C, cooled to 5°C to precipitate purified crystals, centrifugally filtered, separated purified crystals, vacuum dried, and purified indole 111.2 g. obtained. This purified indole had a purity of 99.6%, and the recovery rate in this step was 87.7%.

[Effects of the Invention] As described above, according to the method of this invention, high-purity indole can be recovered in high yield by combining azeotropic distillation and crystallization from an indole-containing fraction.

Claims (1)

[Claims] (1) The indole-containing fraction obtained by distilling coal tar and diethylene glycol are subjected to distillation to collect an azeotropic fraction of indole and diethylene glycol, and after removing diethylene glycol from the fraction, it is cooled and precipitated. A method for producing indole, which comprises separating crystals of indole.