JPH0522700B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing 4-amino-2,2,6,6-tetramethylpiperidine.

4-Amino-2,2,6,6-tetramethylpiperidine (hereinafter abbreviated as TAM) is an important intermediate for hindered piperidine stabilizers used in plastics, rubber, etc.

An object of the present invention is to provide a method for manufacturing such TAM at low cost and industrially advantageously.

As a method for producing TAM, it is known that it is produced according to the following formula. i.e. Liebigs Ann.d.
Chemie, vol. 417, pp. 118-119 and Izv.Akad.
Nauk.SSSR Ser.Khim.1966, p. 1477 contains holon () and ammonia. to obtain triacetonamine (),
A method is described in which hydroxylamine is then reacted to form an oxime (), which is then reduced with zinc or sodium metal to obtain TAM () with a yield of about 80%.

Furthermore, JP-A-50-126674 discloses a method for obtaining TAM at a yield of 71% by reductive amination of holon.

However, all of the above methods use holon as a starting material, and the yield of holon itself is extremely low at about 30% from acetone, which poses a major problem in terms of raw materials from an industrial perspective.

In addition to these problems, the former method requires a three-step complicated process and has an extremely low yield, while the latter method is not satisfactory in terms of yield. Furthermore, there are problems in that it requires a large amount of catalyst (20wt% based on holon), and in addition, acetic acid is required to prevent the formation of alcohol, and furthermore, holon is sequentially pressurized into an autoclave at high temperature and high pressure. There were also problems in that it required special equipment.

On the other hand, a method using triacetonamine obtained in good yield from acetone and ammonia as a starting material is disclosed in JP-A-56-122352.

However, this method uses a special catalyst (RCH45/20) for triacetonamine.
10wt% is used, and 180-200℃, 300Kg/cm ²
This is a method called G, which is carried out at high temperature and high pressure, and is not industrially preferred in terms of catalysts and equipment. Further, as a result of conducting additional tests on this method, the reaction yield of TAM was at most 70%, and the method required improvement in this respect as well.

As mentioned above, all the known methods have drawbacks and cannot be said to be production methods on an industrial scale.

In view of this current situation, the present inventors have conducted intensive studies on an industrial method for producing TAM by reductive amination of triacetone amine, and have found that if reductive amination is carried out using a specific catalyst and under specific reaction conditions, The present invention was completed by discovering that TAM can be obtained almost quantitatively.

That is, the present invention is an industrial method characterized in that the reductive amination of triacetonamine is carried out in the presence of a cobalt-based catalyst at a reaction temperature of 80 to 200°C and a pressure of less than 150 kg/cm ² G. This provides an excellent method for manufacturing TAM.

The present invention is represented by the following reaction formula.

The amount of ammonia used in the present invention is stoichiometrically 1 times the mole of triacetone amine, but it is preferably used in excess, usually in the range of 1 to 30 times, particularly preferably 5 to 10 times by mole. .

Further, hydrogen may be used in a theoretical amount, but an excess amount does not adversely affect the reaction, and the amount of hydrogen is usually determined to match the pressure range selected for the reaction.

Furthermore, the reductive amination catalyst used in the present invention is limited to cobalt-based catalysts. Use of other catalysts, such as nickel, palladium, platinum, or rhodium catalysts, is not preferred because the yield of the target product will be extremely low.

The cobalt-based catalyst may be supported on a carrier such as diatomaceous earth, alumina, silica gel, or activated carbon, or may be one without a carrier. Among them, Raney cobalt is most preferred.

The amount of catalyst used is usually relative to triacetonamine.
0.2-10% by weight, preferably 0.5-2% by weight.

The reaction temperature is 80-200°C, preferably 100-150°C. The reaction pressure is selected to be less than 150 Kg/cm ² G, but is usually 50 to 130 Kg/cm ² G.

Temperature and pressure ranges other than these are undesirable because they require a long reaction time, the yield is low, or a large amount of by-products are produced.

As mentioned above, the method of the present invention uses a specific cobalt catalyst and is carried out under specific reaction conditions, but the reaction solvent may or may not be used.

If a solvent is used, cyclic or acyclic aliphatic hydrocarbons such as hexane, isooctane, cyclopentane, cyclohexane, cyclic or acyclic aliphatic ethers such as propyl ether, butyl ether, amyl ether, tetrahydrofuran, dioxane, benzene, toluene, etc. , aromatic hydrocarbons such as xylene and propylbenzene, and lower alcohols such as methanol, ethanol, propanol, isopropanol, butanol, and isobutanol, among which methanol is preferred.

Further, the method of the present invention can be carried out in either a batch method or a continuous method. In the case of a batch method, triacetone amine, catalyst, ammonia, and in some cases a solvent are added to the autoclave, and finally hydrogen is pressurized to a predetermined pressure, and then heated to a predetermined temperature. The reaction is usually complete in 1 to 5 hours, with the end point indicated by the absence of hydrogen absorption. In the case of a continuous method, raw materials are introduced into a reactor filled with a catalyst in advance and adjusted to a predetermined reaction temperature and pressure, and reacted. The catalyst bed in this case may be either a fixed bed or a fluidized bed.

Thus, according to the method of the present invention, TAM can be obtained under much milder conditions than in known methods and with a high reaction yield of 98% or more.

The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these in any way.

Example 1 In a 300ml autoclave, add triacetonamine.
46.7 (g), methanol 93.1 (g), 50% hydrated Raney cobalt 1.0 (g), liquid ammonia 40.9
Enclose (g). Thereafter, hydrogen was pressurized to 80 kg/cm ² G, the temperature was raised to 130° C., and this temperature was maintained. The pressure rose to a maximum of 130 Kg/cm ² G, but decreased with time and reached a constant value of 35 Kg/cm ² G about 2 hours after the temperature was raised, so it was cooled.

After cooling, the solution in the pot was bubbled with N ₂ to remove excess ammonia, and then filtered to remove the reaction catalyst and obtain a reaction mass.

Analysis of the reaction mass by gas chromatography showed that the triacetonamine conversion rate was 100 (%) and the TAM selectivity was 99.
(%).

To remove TAM from the reaction mass, the solvent was recovered by simple distillation and then rectified, yielding 45.4 g of 98% TAM.
was obtained (yield 95%). BP 114℃/50Torr Example 2 In an autoclave, add triacetonamine 46.7
(g), methanol 74 (g), 50% hydrated Raney cobalt 0.93 (g), liquid ammonia 40.9 (g)
Enclose. Thereafter, hydrogen was injected to a pressure of 80 kg/cm ² G, and the temperature was raised to 130°C. The reaction was completed in 2 hours. Removal was carried out in the same manner as in Experimental Example 1, and analysis of the reaction mass revealed that the triacetone amine conversion rate was
The TAM selection rate was 100% and 98%.

Comparative Example 1 Using the same charging composition as Example 1, the reaction temperature was changed to
The temperature was raised to 190℃. The pressure at this time was 180Kg/cm ² G, and even though the temperature was maintained at 190℃, the pressure gradually increased to 200Kg/cm ² G after 4 hours of keeping it warm.
It became. At this point, it was cooled and the reaction mass was taken out and analyzed in the same manner as in Example 1. The triacetone amine conversion rate was 100 (%) and the TAM selectivity was 60 (%).

Comparative example 2 Triacetonamine 49.7 (g), methanol 74.5
(g), 50% water content pt-c0.5 (g), ammonia 40.9
Charge (g) into an autoclave and add 80 kg/h of hydrogen.
It was press-fitted up to cm ² G. When the mixture was heated to 130 (°C) and reacted, a maximum pressure of 150 Kg/cm ² G was exhibited, and hydrogen absorption was completed within 4 hours.

After cooling, the reaction mass was taken out and analyzed in the same manner as in Example 1, and the triacetone conversion rate was 100 (%).
The TAM selectivity was 44 (%), and many side reaction products were produced.

Comparative Example 3 In an autoclave, triacetonamine 49.7
(g), commercial name RCH45/20 catalyst (manufactured by Hoechst)
5 (g) and liquid ammonia (109 g) were charged, and hydrogen was pressurized to 100 Kg/cm ² G. The reactor was heated to 190 (°C), hydrogen was then pressurized to 300 Kg/cm ² G, and the reaction was continued until no more H ₂ was absorbed. When the reaction mass was taken out and analyzed in the same manner as in Example 1, it was found that the triacetone amine conversion rate was 100 (%) and the TAM selectivity was 70 (%).

Claims (1)

[Claims] 1 In reductively aminating triacetonamine with ammonia and hydrogen, in the presence of a cobalt-based catalyst, the reaction temperature was 80 to 200°C, and the pressure was 150 kg/kg.
4 characterized in that it is carried out under conditions of less than cm ² G.
-A method for producing amino-2,2,6,6-tetramethylpiperidine.