JPS607619B2 - Method for producing indoles - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing indoles with simple operations and high yield.

Indoles are important compounds as raw materials for fragrances, pharmaceuticals, pesticides, polymer stabilizers, etc. Regarding their production, for example, Dai Organic Chemical (Supervised by Fujio Kotake, Asakura Shoten)
As described in Section 14, a number of methods have been proposed.

However, many of them have drawbacks such as the use of expensive raw materials or large amounts of auxiliary raw materials, and the need to carry out the reaction under harsh conditions in some cases. Special Public Service 1977-20
The method disclosed in the specification of Japanese Patent No. 778, that is, the method for obtaining indole by the gas phase reaction of 2-(o-nitrophenyl)ethanol, uses easily available raw materials, and produces indole with a relatively simple operation and in good yield. However, according to the study of the present invention, the catalyst deteriorates quickly and the indole yield decreases as the amount of reaction increases, making it necessary to frequently replace the catalyst. I couldn't say it had any value. The present invention provides a method for producing indoles from 2-(o-nitrophenyl)ethyl/ol by a liquid phase method, and according to this method, compared to the conventional gas phase method, The present inventors have discovered a method that can produce indoles in high yields with little loss of catalyst activity even when a large amount of 2-(o-nitrophenyl)ethanol, which is a raw material per unit amount of catalyst, is reacted.

That is, the present invention is characterized in that a nitrobenzene derivative represented by the general formula (wherein x and Y represent hydrogen or a hydrocarbon residue) is heated and reacted in the presence of hydrogen and a reduction catalyst while being kept in a liquid state. This is a method for producing indoles represented by the general formula:

The nitrobenzene derivative represented by the above general formula used as the raw material of the present invention is not limited to one in which both X and Y are hydrogen, and either or both of X and Y may be a hydrocarbon residue. The hydrocarbon residue may be aliphatic, alicyclic or aromatic, but usually has 1 carbon atom.
10 to 10 will be selected. In the present invention, hydrogen is an essential component along with the nitrobenzene derivative.

Hydrogen is required in an amount of 2 moles or more per mole of the nitrobenzene derivative, preferably about 2.5 to 10 moles. Hydrogen does not need to be of high purity; nitrogen,
It may be used in combination with an inert gas such as helium. Further, the reduction catalyst in the present invention refers to a general catalyst used for catalytic reduction of a nitro group to an amino group, such as copper, nickel, cobalt, palladium, rhodium, ruthenium, iridium, osmium, platinum, rhenium, etc. metals or their compounds. These may be used alone, or may be supported on a solid surface such as silica, alumina, silica alumina, or activated carbon. The amount of reduction catalyst used is from 0.01 to 20% by weight, preferably from 0.05 to 1% by weight, based on the nitrobenzene derivative. These reduction catalysts can be used alone or in combination of two or more.
The reaction is carried out in a closed system under pressure of hydrogen or a hydrogen-containing gas mixture while maintaining the nitrobenzene derivative in a liquid state.

Although a solvent is not particularly required in the reaction, it is preferable to use an inert solvent in the reaction, such as water, hydrocarbons such as hexane, heptane, and cyclohexane, and ethers such as tetrahydrofuran and dioxane, in order to increase the life of the catalyst. . When a solvent is used, it is generally appropriate to use it in an amount of about 1 to 2 times the weight of the nitrobenzene derivative. The reaction pressure is usually 1 to 50 atm, preferably 5 to 50 atm, and the reaction temperature is usually 150 to 35,000, preferably 200 to 300 oo.
Reaction time is usually 0.5 no, 2 feeding time, preferably 1
None, it takes 1 field time. The indoles produced by the method of the present invention can be separated and purified from the reaction system by common operations such as distillation, recrystallization, and extraction.

The method of the present invention will be specifically explained below using Examples.

Examples 1 to 13 A 2-(o-nitrophenyl)ethanol 3 night autoclave, 10 volumes of dioxane, and the reduction catalyst listed in Table 1 were charged into an autoclave with a capacity of no. The lamp was lit for 1 hour at the temperature described in 1.

The produced indole was analyzed by gas chromatography and is shown in Table 1. Table 1 Examples 14-20 20 mmol of the nitrobenzene derivatives listed in Table 2, 10% of the solvent and 5%
Charge 0.38 m of Pd-carbon and 20k9' of hydrogen.
After pressurizing the ground, we lit a lantern at 250 oo for 2 hours.

The product was analyzed by gas chromatography to determine the yield of the indole derivative. The results are shown in Table 2. table
2 Example 21 In an autoclave with a capacity of 100, 2-(o-nitrophenyl)ethanol was added for 3 days, dioxane was added for 10 days, and 0
．． 5% Pd-carbon catalyst (manufactured by Nippon Engelhard Co., Ltd.,
Particle size: 10-30 mesh) in a bag and 20k with hydrogen.
9/ After pressurizing the enemy, I prayed for an hour at 25 pi.

After the reaction mixture was cooled, the catalyst was heated in a furnace for 8U, and the furnace liquid was analyzed by gas chromatography, and the yield of indole was 85%. After washing the separated catalyst with dioxane, 2-(o-nitrophenyl)ethanol was added for 3 nights.
Charged into an autoclave with 10% dioxane,
Hydrogen was again pressurized and the lamp was lit at 250 oo for 1 hour. The same operation was repeated 10 times, and the indole yield was 84% when 2-(o-nitrophenyl)ethanol was reacted for a total of 10 nights per night of catalyst. Example 22 Example 21 except that the catalyst separated from the furnace was used again in the next reaction without washing with dioxane.
did the same thing.

In this case, the 10th reaction result is an indole yield of 80
%, and the cumulative amount of 2-(o-nitrophenyl)ethanol reacted per night of catalyst use at this time was 1 female. Comparative Example A quartz glass tube with an inner diameter of 2 arcs and a length of 30 mm had 40 pieces of quartz glass fragments placed at the bottom, and a 0.5% Pd-carbon catalyst (manufactured by Nippon Engelhard Co., Ltd., particle size 10 to 30 mesh) on the top.
It was filled with 10 ml of water and heated to 250°C in an electric furnace.

From the top of the glass tube, 2-(o-nitrophenyl) ethanol vapor was added at 1.2 t/hr, and dioxane vapor was added at 10/hr.
．． 8 min/hr and hydrogen at a rate of 120 min/min, and the resulting crabmeat was subjected to gas chromatography.
- was analyzed. The results are shown in Table 3. Table 3 Reaction amount of catalyst per night

Claims (1)

[Claims] 1. A nitrobenzene derivative represented by the general formula ▲ includes mathematical formulas, chemical formulas, tables, etc. A method for producing indoles represented by the general formula ▲There are mathematical formulas, chemical formulas, tables, etc.▼, which is characterized by carrying out a heating reaction in the presence of a reduction catalyst.