JPH0552825B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for producing indole, and more particularly to a method for economically producing highly pure indole by crystallizing indole.

<Prior art> Indole is a white crystal with a boiling point of 253°C and a melting point of 53°C, and many of its derivatives exhibit physiological activity and are useful compounds that are important raw materials for medicines and agricultural chemicals. A crystallization method is one of the methods for producing indole from separated indole oil (hereinafter referred to as crude indole oil) separated from coal tar or the like. The crystallization methods applied to indole are roughly divided into two types: methods in which crude indole oil is cooled as it is to obtain indole crystals, and methods in which crude indole oil is dissolved or dispersed in a recrystallization solvent such as methanol or n-hexane. There is a method of obtaining indole crystals by cooling. (U.S. Patent No. 2916497; Polish Patent No.
No. 45667; Published by Japan Society of Chemical Engineers, Chemical Engineering Symposium Series 7, Current Status and Challenges of Crystallization Engineering, No. 79
page).

<Problems to be Solved by the Invention> However, with only the above-mentioned crystallization method, when crude indole oil with a concentration of 90% or less is used as a raw material,
The purity of the obtained indole crystals is low, and it is necessary to further increase the purity by repeating the crystallization method, resulting in a problem that the recovery rate of high-purity indole decreases. Further, in the recrystallization method, the amount of recrystallization solvent used is about 3 to 1 times the amount of crude indole oil, and the processing equipment becomes large, so there is a problem that the equipment cost is high and the running cost is also high.

<Means for Solving the Problems> The present invention solves the problems of the prior art and provides a method for economically producing high-purity indole with a high recovery rate regardless of the concentration of crude indole oil used as a raw material. This is what we provide.

The present inventors have demonstrated that indole can be easily purified to high purity by cooling and crystallizing crude indole oil from coal tar and washing the obtained crude indole crystals with an aliphatic hydrocarbon solvent or an alicyclic hydrocarbon solvent. The present inventors have discovered that the indole can be converted into a polyurethane compound with low dissolution loss, and as a result of various experiments, the present invention has been achieved.

In the method for producing indole of the present invention, crude indole oil is cooled to crystallize crude indole crystals, and the obtained crude indole crystals are washed with an aliphatic hydrocarbon and/or alicyclic hydrocarbon solvent and then dried. It is characterized by this.

According to the method of the present invention, even if the indole concentration in crude indole oil from coal tar is 90% or less, high purity indole can be economically produced with a high recovery rate.

In the present invention, the indole concentration in the indole oil used as a raw material may be 50% or more. The crystal precipitation temperature of raw materials varies depending on the concentration of indole; for example, in the case of 83% indole oil, it is 33℃.
Crystals precipitate. Although general solid-liquid separation methods can be used to separate the precipitated crystals from the mother liquor, filtration separation is particularly preferred.

The cleaning solvent used in the method of the present invention must have low solubility for indole and high solubility for other aromatic hydrocarbons, which are impurities, and is selected from aliphatic hydrocarbons and alicyclic hydrocarbons. A solvent containing one or more components. In addition, since the cleaning solvent adheres to the washed indole crystals, it is necessary to evaporate and remove the cleaning solvent after cleaning. Therefore, the boiling point of the cleaning solvent should be low, and a solvent having a boiling point range of 30 to 200°C is preferable.

Specific aliphatic hydrocarbons include, for example, pentane, hexane, heptane, octane, nonane,
Decane etc. are used. Examples of alicyclic hydrocarbons include cyclopentane, cyclohexane,
Methylcyclopentane, methylcyclohexane,
Ethylcyclohexane or the like is used.

There are no particular restrictions on the cleaning method, but specific examples include the following method. (1) Pour the washing solvent over the filter cake and wash it through the cake. (2) The filter cake is slurried with a washing solvent and then filtered. The amount of the cleaning solvent to be used is not particularly limited, but is preferably 0.1 to 10 times the amount by weight of indole, and more preferably 0.5 to 3 times by weight.
The temperature at which the cleaning solvent is used is preferably low in order to reduce the solubility of indole, and is preferably 30°C or lower.

If the crystallization method of the present invention is carried out, for example, in a batch-type crystallization tank, the crystallization tank capacity will be 1/4 to 1/1 that of the recrystallization method.
It is about 1. Furthermore, since the indole crystals can be easily washed within the filter, the equipment cost can be considerably reduced compared to the recrystallization method. Furthermore, the energy for recovering the solvent can be reduced to about 1/5 to 2/3.

<Example> Next, the present invention will be explained in detail with reference to Examples.

Example 1 The indole concentration in the crude indole oil obtained by contacting the distilled coal tar fraction at 200 to 300°C with hydrochloric acid, deoxidizing the separated indole oligomer salt, and then thermally decomposing it was 83.2. It was %. 3℃/160g of this crude indole oil from 40℃ to 5℃
The mixture was cooled and crystallized at a cooling rate of 10 minutes, followed by suction filtration to obtain 92.2 g of crude indole crystals. The indole concentration is
It was 95.9%. 200 g of cyclohexane at 0° C. was poured into the indole crude crystal cake, and the mixture was filtered with suction.

The washed indole crystals were vacuum dried for 2 hours to obtain 81.0 g of indole crystals. The purity of indole crystals is 98.8%, and the recovery rate of indole at this time is
It was 60%.

Example 2 The same procedure as in Example 1 was carried out except that cyclohexane was changed to n-hexane. The purity of the indole crystals was 98.5%, and the recovery rate of indole was 62%.

Comparative example Indole crude crystals obtained in the same manner as in Example 1
After heating and dissolving 160 g with 1600 g of n-heptane at 50°C, cooling to 15°C allowed crystallization, filtration to obtain indole crystals, and vacuum drying for 2 hours. The purity of the dried indole crystals was 98.4%, and the recovery rate of indole was 58%. Although a large amount of n-heptane was consumed, the recovery rate of indole was as low as 58%.

<Effects of the invention> According to the method of the invention, the raw material indole concentration is 83
Despite being as low as 98% to 99%, high purity indole can be recovered with a high recovery rate of over 60%. Furthermore, the amount of solvent used is extremely small, about 1.3 times the amount of raw materials, making it possible to achieve an economical indole production method with low running costs.

Claims (1)

[Claims] 1. An indole crystallization method characterized by cooling crude indole oil to crystallize crude indole crystals, washing the obtained crude indole crystals with an aliphatic hydrocarbon and/or alicyclic hydrocarbon solvent, and then drying them. Production method.