JPH0445508B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing 4-amino-2,2,6,6-tetramethylpiperidine.

4-Amino-2,2,6,6-tetramethylpiperidine has wide application as a starting material in the synthesis of non-staining light stabilizers for polymeric materials.

[Conventional technology]

It is known that polymeric materials are destroyed under the influence of ultraviolet light, resulting in impaired operational properties and shortened service life of articles made from polymeric materials. To prevent destruction, special additives, namely light stabilizers, are introduced into the polymeric material.

Conventional types of light stabilizers are derivatives of P-hydroxybenzophenone and P-hydroxybenzotriazole. The most promising class of light stabilizers are sterically hindered amines, especially 4-amino-2,2,6,
It is a derivative of 6-tetramethylpiperidine. Stabilizers of this type exhibit relatively high effectiveness, several times better than conventional light stabilizers of the class of P-hydroxybenzophenones and P-hydroxybenzotriazoles. They also do not have any dyeing effect on the polymer and in some cases have both light and heat stabilizing properties.

Known in the art are 1, 1,
This is a method for producing 4-amino-2,2,6,6-tetramethylpiperidine by reacting 5,5-tetramethyl-1,4-dipentadien-3-one with ammonia and hydrogen (West Germany). (See Application Publication No. 2412750). This method uses these reagents at temperatures of 80-200°C (preferably 110-150°C),
At a pressure of 80 to 250 atm (preferably 100 to 180 atm),
It consists of reacting with an 8- to 10-fold excess of ammonia, calculated on 1,1,5,5-tetramethyl-1,4-dipentadien-3-one. The process is carried out in a solvent (mainly ethanol) in the presence of a hydrogenation catalyst. Used as a catalyst in the process for metals of group 8 of the periodic table and their compounds (mainly nickel, cobalt, iron and platinum).
The desired product is recovered by rectification.

However, in this prior art process,
The desired product is 1,1,5,5-tetramethyl-
A low yield of not more than 71% calculated for 1,4-dipentadien-3-one is obtained. Furthermore, the starting material namely 1,1,5,5-tetramethyl-
The process of producing 1,4-dipentadien-3-one is quite complex, which has a negative impact on the process of making the desired product from an economic efficiency point of view.

Also known in the art are 2, 2,
4- by reacting 6,6-tetramethyl-4-oxopiperidine (triacetonamine) with hydrogen and ammonia (reductive amination).
Another method for making amino-2,2,6,6-tetramethyl-piperidine (German Patent No. 3003843)
(see issue). This step can be carried out continuously or intermittently. The reaction is carried out at elevated temperatures up to 220° C. and under pressure from 150 to 500 bar in the presence of a hydrogenation catalyst in the medium of an organic solvent such as methanol. As a catalyst, metals of Group 8 of the periodic system such as nickel, cobalt, iron, platinum, etc. and their compounds are used. The desired product is isolated by rectification.

This prior art process is superior to the process described above in that it uses the less expensive 2,2,6,6-tetramethyl-4-oxopiperidine as a starting material in the process. In this step the desired product yield is 95% calculated for 2,2,6,6-tetramethyl-4-oxopiperidine.
It is. However, this process is carried out under rather harsh conditions, ie requires the use of high temperatures and pressures, and is therefore energy consuming and dangerous.

[Problem that the invention seeks to solve]

The present invention provides an economically efficient process for making 4-amino-2,2,6,6-tetramethylpiperidine, making it possible to obtain the desired product in sufficiently high yields following a simple procedure. This is what we are trying to provide.

[Means for solving problems]

The above purpose is to provide 2,2,6,6-
This is accomplished by providing a method for making 4-amino-2,2,6,6-tetramethylpiperidine by reacting tetramethyl-4-oxopiperidine with ammonia and hydrogen. According to the invention, this process involves the addition of 1 to 2% by weight of an alkali metal compound or alkaline earth metal hydroxide of a hydrogenation catalyst in an aqueous medium at a temperature in the range 100 to 135 °C and a pressure of 10 to 25 bar. Bring things into existence and do them.

The temperature and pressure range selected according to the invention ensures maximum yield of the desired product and high economic parameters of the process. Lowering the lower temperature and pressure limits increases the reaction time, thus producing significant amounts of reaction by-products and reducing the desired product yield. Expanding the upper limits of these parameters is economically inefficient.

Conventional hydrogenation catalysts can be used as hydrogenation catalysts, such as metals from group 8 of the periodic table (iron, cobalt, nickel, palladium, etc.), which can be used independently or supported on a carrier. It's okay.
Carbon, silicates, aluminum oxide, etc. can be used as carriers. The catalyst is used in an amount normally tolerated for the reaction of reductive amination, i.e. 2,
1 to 30% by weight, preferably 10% by weight, calculated on 2,6,6-tetramethyl-4-oxopiperidine
Use within the range of ~20% by weight.

The presence of alkali and alkaline earth metal hydroxides in the process according to the invention increases its selectivity and minimizes the formation of reaction by-products.
Sodium hydroxide, lithium hydroxide, potassium hydroxide, calcium hydroxide, etc. are used as hydroxides of alkali and alkaline earth metals. The use of a synthetic catalyst to carry out the process makes it possible to reduce the ammonia consumption rate, reduce the working pressure and shorten the process time.

〔Effect of the invention〕

The method for making 4-amino-2,2,6,6-tetramethylpiperidine makes it possible to obtain the desired product in sufficiently high yields of about 90-95% following a simple procedure. By using water as a solvent and adding an alkali metal hydroxide or an alkaline earth metal hydroxide, the following becomes possible. That is, the process pressure can be reduced by a factor of 15 to 20, which improves process safety and reduces energy consumption characteristics; Ammonia consumption rate can be reduced by a factor of 3 to 10. This allows for a very simple ammonia capture system; the process time can be reduced by more than half, which considerably increases the production of the desired product per unit of time. This increases equipment productivity.

The method for producing 4-amino-2,2,6,6-tetramethylpiperidine is simple in terms of the equipment used and can be carried out in the following manner.

In a standard autoclave equipped with a stirrer,
2,2,6,6-tetramethyl-14-oxopiperidine is charged together with aqueous ammonia, hydrogenation catalyst and alkali metal hydroxide or alkaline earth metal hydroxide.

The autoclave is flushed with nitrogen and then with hydrogen and heated with continuous stirring to a temperature within the range of 100-135°C. The pressure in the autoclave initially increases to 10-17 bar and then begins to fall with the beginning of the reductive amination step. The pressure in the autoclave is maintained in the range 10-25 bar by means of a hydrogen pressure valve. Completion of the reaction is controlled by cessation of hydrogen uptake. The process time is 20-30 minutes. Once the reaction is complete, cool the contents of the autoclave for 20 min by supplying water into the cooling jacket.
Cool to ~25 °C and release pressure. The reactants are decanted from the catalyst and subjected to fractional distillation at 78-79℃ (7 mm
Hg) and collect the boiling fraction. The yield of desired product is 90-95%.

〔Example〕

Preferred embodiments are described below for a better understanding of the invention.

Example 1 In an autoclave equipped with a stirrer, a pressure gauge and a thermometer, 310 g of 2,2,6,6-tetramethyl-4-oxopiperidine, 410 ml of a 25% aqueous solution of ammonia, 31 g of Raney nickel and 0.62
g of sodium hydroxide. The autoclave is sealed and purged twice with nitrogen and then with water to maintain a hydrogen pressure within it at 10 bar. The temperature in the autoclave is brought to 100° C. by operating the stirrer and supplying steam into the autoclave jacket. The pressure in the autoclave initially rises to 15 bar and then begins to fall due to the onset of the reductive amination reaction.
The hydrogen pressure in the autoclave is controlled by the hydrogen pressure valve.
Hold at 15 bar. The course of the reaction is controlled by the pressure drop in the reactor with temporary interruption of the hydrogen supply into the reactor. Completion of the reaction is determined by the cessation of hydrogen uptake. The time for reductive amination is 30 minutes. When the reaction is complete, the contents of the autoclave are cooled to a temperature of 25°C by supplying water into the autoclave jacket and the pressure is released. The reactants are decanted from the catalyst and subjected to fractional distillation.
Collect the fraction boiling at 78-79°C/7mmHg.
The desired product yield is 294 g (94.0% of theory calculated for 2,2,6,6 _{-tetramethyl-4-oxopiperidine), n20D} ⁼ _1.4700 , ^d204 =
It is 0.8963.

Example 2 The desired product is obtained under the conditions described in Example 1 above, except that the process is carried out using 64 g of nickel supported on diatomaceous earth as catalyst at a temperature of 120° C. and a pressure of 25 bar. .

The desired product yield is 294 g (94.0% of theory calculated for 2,2,6,6 _{-tetramethyl-4-oxopiperidine), n20D} ⁼ _1.4710 , ^d204 =
It is 0.8966.

Example 3 Using Raney cobalt in an amount of 46.5 g as a hydrogenation catalyst at a temperature of 135° C. and a pressure of 10 bar, 2.
The desired product is obtained under the conditions of Example 1 above, except that the process is carried out using a 2.5-fold excess of ammonia per mole of 2,6,6-tetramethyl-4-oxopiperidine. The desired product yield is
291.7g (2,2,6,6-tetramethyl-4-
93.2 of theory calculated for oxopiperidine
%), n ²⁰ _D = 1.4699, d ²⁰ ₄ = 0.8950.

Example 4 In the presence of 0.31 g of calcium hydroxide 2,
The desired product is obtained under the conditions of Example 1, except that the process is carried out using a 2.5-fold excess of ammonia per mole of 2,6,6-tetramethyl-4-oxopiperidine. Desired product yield is 290.1g
(93% of theory calculated for 2,2,6,6-tetramethyl-4-oxopiperidine),
n ²⁰ _D = 1.4699, d ²⁰ ₄ = 0.8961.

Example 5 2, in the presence of 0.54 g of calcium hydroxide
The desired product is obtained under the conditions of Example 1, except that the process is carried out using a 3.5-fold excess of ammonia per mole of 2,6,6-tetramethyl-4-oxopiperidine. Desired product yield was 297.4 g (2,
95.0% of theory calculated for 2,6,6-tetramethyl-4-oxopiperidine) and n ²⁰ _D
= 1.4718, d ²⁰ ₄ = 0.8965.

Example 6 3.5 per mole of 2,2,6,6-tetramethyl-4-oxopiperidine in the presence of lithium hydroxide in an amount of 0.46 g at a temperature of 125° C. and a pressure of 10 bar.
The desired product is obtained under the conditions of Example 1 above, except that the process is carried out with a two-fold excess of ammonia. The desired product yield was 296.7 g (2,2,6,
94.8% of theory calculated for 6-tetramethyl-4-oxopiperidine), n ²⁰ _D = 1.4691,
d ²⁰ ₄ =0.8967.

Claims (1)

[Claims] 1 4-Amino-2,2,6,6-tetra In a process for making methylpiperidine, an alkali or alkaline earth metal hydroxide is present in an amount of 1 to 2% by weight of the hydrogenation catalyst in an aqueous medium at a temperature of 100 to 135 °C and a pressure of 10 to 25 bar. The above-mentioned method is characterized in that the step is carried out.