Sterically hindered 4-amino-piperidine with a low dimer content,

Details Sterically hindered 4-amino-piperidine with a low dimer content, Sterically hindered 4-amino-piperidine with a low dimer content,

1998-11-12

2000-01-11

Chang, Ceila

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

546244, C07D21158, C07B 6306

Patent

active

060138033

DESCRIPTION:

BRIEF SUMMARY
The present invention relates to a process for reducing the dimerization of piperidines of the formula I ##STR2## where R.sup.1 to R.sup.4 are C.sub.1 - to C.sub.6 -alkyl, R.sup.1 and R.sup.2 and/or R.sup.3 and R.sup.4 together are a CH.sub.2 chain having 2 to 5 carbon atoms. The present invention furthermore relates to a mixture comprising piperidines of the formula I, from 1 to 1000 ppm of dimers of the formula II and from 0.001 to 0.2% by weight of a reducing agent, and to the use thereof for the preparation of HALS compounds.
Sterically hindered 4-aminopiperidines of the formula I are generally prepared on an industrial scale from acetone or acetone derivatives. I can be obtained in one step in a catalytic ring-closure reaction in the presence of ammonia and hydrogen from the compounds ##STR3## (DE 2 412 750) or from triacetoneamines of the formula III ##STR4## by reductive amination in one or two steps, for example catalytically (see, for example, DE 2 040 975, DE 2 349 962, DE 26 21 870, EP 33 529, EP 42 119, EP 303 279, EP 410 970, EP 611 137, EP 623 585 and DE 42 10 311). The sterically hindered 4-aminopiperidines prepared industrially are generally purified by distillation.
The sterically hindered 4-aminopiperidines of the formula I have a variety of applications. In particular, they are used as intermediates in the preparation of UV stabilizers for synthetic polymers. The present invention furthermore relates to a mixture comprising piperidine of the formula I, from 1 to 1000 ppm of a dimer of the formula II and from 0.001 to 0.2% by weight of a reducing agent, and to the use thereof for the preparation of HALS (hindered amine light stabilizer) compounds. These are usually piperidines of the formula I in which the nitrogen atom of the 4-amino group has been alkylated or acylated (see R. Gachter, H. Muller (editors), Taschenbuch der Kunststoff-additive, Carl Hanser Verlag, Munich, 1979; F. Gugumus, Polym. Degrad. Stabil. 44 (1994), 299-322).
For many applications, it is important that the piperidine of the formula I has high chemical purity. This is particularly true if the piperidine of the formula I is employed for the preparation of HALS compounds, since their product quality, and thus also the quality of the stabilized polymers, is crucially dependent on chemical purity. In particular, the dimer of the piperidine of the formula I, which is colorless, is an interfering by-product which forms in unacceptable amounts from the piperidine of the formula I even on storage under a protective gas in the dark at room temperature.
No processes are known for preventing dimerization of the piperidine.
U.S. Pat. No. 4,316,837 discloses the reduction of 4-aminopiperidyl groups in branched aliphatic alcohols to the corresponding 4-aminopiperidyl-containing branched alcohols. The dimer II of the piperidine I is not disclosed.
DD 266 799 describes purifying piperidines of the formula I by a process in which they are reacted in acetone/water solution with CO.sub.2, the precipitate is separated off, washed with acetone and then pyrolyzed, and the product is purified by distillation. SU 18 11 527 describes another purification method for sterically hindered 4-aminopiperidines of the formula I, in which the unpurified crude product is dissolved in an aprotic solvent and reacted with ethylene glycol, and the reaction product is distilled and purified in a number of steps. Both processes are extremely complex and expensive. They do nothing to prevent the interfering subsequent formation of the dimer.
EP 477 593 discloses that the inherent color of crude N-alkyldialkanolamines can be improved by adding a metal borohydride and distilling the mixture under certain conditions in the presence of water. However, the N-alkyldialkanolamines are a completely different class of substances to the sterically hindered 4-aminopiperidines of the present invention. Furthermore, Spec. Chem. 4(2) (1984), 38-41, and U.S. Pat. No. 3,159,276, U.S. Pat. No. 3,207,790 and U.S. Pat. No. 3,222,310 disclose that the product color can be impr

REFERENCES:
patent: 3159276 (1964-12-01), Moore
patent: 3207790 (1965-09-01), Glew
patent: 4316837 (1982-02-01), Molt et al.
Manfred, J. "Preparation of 4-amino-2,2,6,6-tetramethylpiperidine (TAD) via . . . " 128:309121, 1997.
Controlling Colour Degradation . . . , Maffucci et al., Speciality Chem. 4 (2), pp. 38, 40, 41 (1984).

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