Process for the preparation of 4-amino-2,2,6,6-tetramethylpiperidine

1. A process for the preparation of 4-amino-2,2,6,6-tetramethylpiperidine, comprising:

(1) reacting, in a main reaction, 2,2,6,6-tetramethylpiperidine-4-one with ammonia and hydrogen in the presence of a nickel and/or cobalt catalyst, and water,

at a pressure of at most 50 bar and a temperature of at most 120° C. up to a conversion of the 2,2,6,6-tetramethylpiperidine-4-one of at least 80%, to obtain a reaction mixture, and

(2) then after-reacting said reaction mixture at a higher temperature and at a higher pressure compared to the pressure and temperature of the main reaction.

2. The process according to claim 1 , wherein water and 2,2,6,6-tetramethylpiperidine-4-one are used in a molar ratio of from 2.5:1 to 9:1.

3. The process according to claim 1 , wherein water and 2,2,6,6-tetramethylpiperidine-4-one are used in a molar ratio of from 3:1 to 7:1.

4. The process according to claim 1 , wherein said catalyst is a skeletal metal catalyst in which an active metal is cobalt and/or nickel.

5. The process according to claim 4 , wherein from 0.5 to 15% by weight of the skeletal metal catalyst are used, based on a total amount of 2,2,6,6-tetramethylpiperidine-4-one.

6. The process according to claim 1 , wherein the main reaction is carried out at a temperature of from 40 to 110° C.

7. The process according to claim 1 , wherein the main reaction is carried out at a pressure of from 5 to 50 bar.

8. The process according to claim 1 , wherein the after-reaction is carried out at a temperature of from 130 to 200° C.

9. The process according to claim 1 , wherein the after-reaction is carried out at a pressure of from 35 to 150 bar.

10. The process according to claim 1 , wherein the after-reaction is carried out in the same reactor as the main reaction.

11. The process according to claim 1 , wherein no work-up of the reaction mixture after the main reaction and before the after-reaction takes place.

12. The process according to claim 1 , wherein ammonia and 2,2,6,6-tetramethylpiperidine-4-one are used in a molar ratio of from 1.5:1 to 4:1.

13. The process according to claim 1 , wherein the catalyst is separated off from a liquid phase of said reaction mixture by decantation, an agglomeration auxiliary being added beforehand to the reaction mixture.

14. The process according to claim 13 , wherein the separated off catalyst is fed as suspension to a second reductive amination of 2,2,6,6-tetramethylpiperidine-4-one with ammonia and hydrogen in the presence of a nickel and/or cobalt catalyst, and water,

wherein a main reaction is carried out at a pressure of at most 50 bar and a temperature of at most 120° C. up to a conversion of the 2,2,6,6-tetramethylpiperidine-4-one of at least 80%, and then an after-reaction takes place at a higher temperature and at a higher pressure compared to the pressure and temperature of the main reaction.

15. The process according to claim 13 , wherein an entrainer is added to the liquid phase after the catalyst has been separated off and then an azeotrope distillation is carried out to separate off the water which has been used in the reaction as a solvent.

16. The process according to claim 15 , followed by distillation of the 4-amino-2,2,6,6-tetramethylpiperidine.

17. The process according to claim 1 , wherein said 4-amino-2,2,6,6-tetramethylpiperidine has a APHA color number of <20 for a storage time of 6 month.

18. A process for the preparation of 4-amino-2,2,6,6-tetramethylpiperidine, comprising:

(1) reacting, in a main reaction, 2,2,6,6-tetramethylpiperidine-4-one with ammonia and hydrogen in the presence of a nickel and/or cobalt catalyst, and water,

at a pressure of at most 50 bar and a temperature of at most 120° C. up to a conversion of the 2,2,6,6-tetramethylpiperidine-4-one of at least 80%, to obtain a reaction mixture, and

(2) then after-reacting said reaction mixture at a higher temperature and at a higher pressure compared to the pressure and temperature of the main reaction,

wherein water and 2,2,6,6-tetramethylpiperidine-4-one are used in a molar ratio of from 2.5:1 to 9:1, and

wherein said 4-amino-2,2,6,6-tetramethylpiperidine has a APHA color number of <20 for a storage time of 6 month.

19. A process for the preparation of 4-amino-2,2,6,6-tetramethylpiperidine, comprising:

(1) reacting, in a main reaction, 2,2,6,6-tetramethylpiperidine-4-one with ammonia and hydrogen in the presence of a nickel and/or cobalt catalyst, and water,

at a pressure of at most 50 bar and a temperature of at most 120° C. up to a conversion of the 2,2,6,6-tetramethylpiperidine-4-one of at least 80%, to obtain a reaction mixture, and

(2) then after-reacting said reaction mixture at a higher temperature and at a higher pressure compared to the pressure and temperature of the main reaction,

wherein water and 2,2,6,6-tetramethylpiperidine-4-one are used in a molar ratio of from 2.5:1 to 9:1.

20. A process for the preparation of 4-amino-2,2,6,6-tetramethylpiperidine, comprising:

(1) reacting, in a main reaction, 2,2,6,6-tetramethylpiperidine-4-one with ammonia and hydrogen in the presence of a nickel and/or cobalt catalyst, and water,

at a pressure of at most 50 bar and a temperature of at most 120° C. up to a conversion of the 2,2,6,6-tetramethylpiperidine-4-one of at least 80%, to obtain a reaction mixture, and

(2) then after-reacting said reaction mixture at a higher temperature and at a higher pressure compared to the pressure and temperature of the main reaction;

wherein the after-reaction is carried out at a temperature of from 130 to 200° C. and at a pressure of from 35 to 150 bar.