SK284691B6 - Process for preparing 4-amino-2,2,6,6-tetramethylpiperidine - Google Patents

Abstract

Described is a process for preparing of 4-amino-2,2,6,6- tetramethylpiperidine (TAD) wherein, in the first step, 2,2,6,6-tetramethyl-4-piperidinone (TAA) is reacted with ammonia in the presence of solid acid catalysts a), which are virtually insoluble in the reaction mixture, to give the TAA imine and, in the second step, the TAA imine is hydrogenated in the presence of a hydrogenation catalyst b).

Description

Technical field

The present invention relates to a process for the preparation of 4-amino-2,2,6,6-tetramethylpyridine (triacetonediamine, TAD) from triacetonamine (TAA).

TAD is a major intermediate for the synthesis of HALS (HALS = Hindered Amine Light Stabilizer), which are important as additives for stabilizing synthetic polymers (e. G. Polyolefins).

BACKGROUND OF THE INVENTION

EP-B 0 033 529 describes the reductive amination of 2,2,6,6-tetramethyl-4-piperidone (triacetonamine, TAA) to solvent-free TAD, with an excess of ammonia of from 10 to 50 moles (per mole of TAA), under pressure in the range of 50 to 500 bar and in the temperature range of 120 - 220 ° C, m. j. a one-step process, as shown in the following equation:

TAA TAD

EP-B 042 119 describes the synthesis of TAD from TAA in which the present initial step consists in reacting the TAA ketone with ammonia in the presence of inorganic and organic ion exchangers in ammonia form as imine-providing catalysts to give the TAA imine

NH

Imine TAA

The imine TAA is then hydrogenated in the presence of a hydrogenation catalyst to provide TAD (two step process). A disadvantage of this process for the preparation of TAD is that the ion exchanger used as the catalyst for the formation of the imine is expensive and has low low mechanical and thermal stability.

EP-A 0 611 137 describes a process for the preparation of amines from cyclic ketones. This process involves firstly converting the ketone (e.g., TAA) with ammonia in the presence of activated carbon to the corresponding imine, which is subsequently hydrogenated to give the amine (TAD) (two-component process).

EP-A 0 623 585 describes the reductive amination of a cyclic ketone (e.g. TAA) or the hydrogenation of the corresponding imine (imine TAA) in the presence of a specific cobalt catalyst.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process for the preparation of TAD from TAA which, in terms of cost and catalyst, represents an alternative to a conventional process that is superior to the industrial one.

It has been found that the present invention can be filled by a process for the preparation of 4-amino-2,2,6,6-tetramethylpyridine (TAD) of formula (I)

(D wherein, in the first step, 2,2,6,6-tetramethyl-4-piperidinone (TAA) of formula (II) is reacted

ABOUT

with ammonia in the presence of solid acid catalysts a) which are substantially insoluble in the reaction mixture to give the imine TAA of formula (III)

and in a second step, the imine TAA is hydrogenated in the presence of a hydrogenation catalyst b), wherein the aluminum hydrosilicates of the bentonite or montmorillonite type or aluminum silicates of the zeolite, mordenite or erionite type are used as catalysts a).

The invention further provides a process for the preparation of 2,2,6,6-tetramethyl-4-piperidinimine (imine TAA) of formula (III)

in which 2,2,6,6-tetramethyl-4-piperidinone (TAA) of formula (II) is left

ABOUT

react with ammonia in the presence of solid acidic catalysts a) which are substantially insoluble in the reaction mixture, wherein the bentonite or montmorillonite type aluminum hydrosilicates or zeolite, mordenite or erionite type aluminum silicates are used as catalysts a).

A method has been found which proceeds through the intermediate by which the imine TAA is provided by the initial formation; this process is different by the synthesis of the imine TAA in the presence of the catalyst.

Preferred examples of catalysts a) are aluminum hydrosilicates of the bentonite or montmorillonite type or aluminum silicates of the zeolite, mordenite or erionite type.

Although in one embodiment the imine intermediate can be isolated as a pure substance, it is preferred to carry out hydrogenation directly under conventional conditions (e.g., 130 ° C, 250 bar H ₂ ) in the presence of excess ammonia (preferred procedure) in the preparation of TAD. It is also possible to use commercially available noble metal hydrogenation catalysts as catalyst b) for this second step.

This process is preferably carried out in the absence of an additional solvent, but it is possible, where appropriate, to use organic solvents which are inert to the reactants and products, such as e.g. tetrahydrofuran or alkanols (e.g. methanol). The reaction with excess ammonia is carried out especially in the temperature range of 20 to 150 ° C, preferably the pressures used are in the range of 15 to 500 bar.

The two reaction processes can be carried out in batches in autoclaves or elsewhere, preferably in continuously stirred reactors or in cascades of pressure vessels.

DETAILED DESCRIPTION OF THE INVENTION

Synthesis of 4-amino-2,2,6,6-tetramethylpiperidine (TAD)

Example 1

The liquid mixture consisting of 40.0 g / h (GC purity: 97.3%) and 792 ml / h ammonia and which was preheated to 80 ° C was pumped up through a vertical pressure reactor (volume = 50 ml) ), which was charged with 37 g of titanium dioxide (1.5 mm tablets). The reactor temperature was maintained at 120 ° C by means of an oil-heated jacket. The reactor effluent was passed along with 43 L / h of hydrogen through another tubular reactor (volume = 200 mL) filled with 307 g of hydrogenation catalyst containing 90% CoO, 1% Mn ₃ O ₄ , 2% P ₂ O ₅ and 2% Na ₂ O (4 mm tablets) at 250 bar at 130 ° C. The reactor effluent was then passed through a high-pressure separator to remove excess hydrogen, pressurized to atmospheric pressure and distilled to remove excess ammonia. According to gas chromatography, the effluent contained 95% TAD and 1.9% triacetone amino alcohol (TTA-ol), corresponding to a yield of 98%.

Example 2

The process of Example 1 was repeated, but with the change that 41.0 g / h of TTA and 1097 ml / h of NH ₃ were pumped into the first reactor and 59 L / h of hydrogen were passed through the second reactor to provide a effluent containing 94% TAD a

1.8% TAA-ol. This corresponded to a yield of 97% TAD.

Example 3

The method of Example 1 was repeated, but with the change that 77.2 g / h of TAA and 1217 ml / h of NH ₃ were pumped into the first reactor and 59 ml / h of hydrogen was passed through the second reactor to provide a effluent containing 92% TAD a

3.2% TAA-ol. This corresponded to a yield of 95% TAD.

Claims (5)

PATENT CLAIMS A process for the preparation of 4-amino-2,2,6,6-tetramethylpyridine C) characterized in that in the first step, 2,2,6,6-tetramethyl-4-piperidinone (TAA) of formula (II) is reacted With ammonia in the presence of solid acid catalysts a) which are substantially insoluble in the reaction mixture to form the imine TAA of formula (III) and in the second step the imine TAA is hydrogenated in the presence of hydrogenation catalyst b) where aluminum is used as catalyst a) bentonite or montmorillonite type hydrosilicates or zeolite, mordenite or erionite type aluminum silicates. A process for the preparation of 2,2,6,6-tetramethyl-4-piperidinimine (imine TAA) of formula (III), characterized in that 2,2,6,6-tetramethyl-4-piperidinone (TAA) of formula (II) Reacting with ammonia in the presence of solid acidic catalysts a) which are substantially insoluble in the reaction mixture, wherein the bentonite or montmorillonite type aluminum hydrosilicates or zeolite, mordenite or erionite type aluminum silicates are used as catalysts a). Process according to claim 1 or 2, characterized in that the TAA, when dissolved in an organic solvent, is reacted with an excess of ammonia at 20 to 150 ° C. The process according to claim 1 or 2, characterized in that the TAA is dissolved in an organic solvent, where appropriate, with an excess of ammonia at a pressure of 15 to 500 bar. Process according to claim 1, 3 or 4, characterized in that the reaction of TAA with ammonia takes place in a reactor comprising catalysts a) and b).