Organic compounds -- part of the class 532-570 series – Organic compounds – Heterocyclic carbon compounds containing a hetero ring...
Patent
1998-11-12
2000-01-04
Chang, Ceila
Organic compounds -- part of the class 532-570 series
Organic compounds
Heterocyclic carbon compounds containing a hetero ring...
546187, C07D21158, C07D22120
Patent
active
060111577
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a process for purifying crude piperidines of the formula I ##STR2## where R.sup.1 to R.sup.4 are C.sub.1 -C.sub.6 -alkyl or R.sup.1 and R.sup.2 and/or R.sup.3 and R.sup.4 together are a CH.sub.2 -chain of 2 to 5 carbons.
Sterically hindered 4-aminopiperidines of the formula I are widely employed. They are used in particular as intermediates in the preparation of UV stabilizers for synthetic polymers. It is therefore of great importance that the piperidines I possess as little inherent coloration as possible and retain this quality over a long period despite even the slightest content of by-product.
The industrial preparation of the sterically hindered 4-aminopiperidines generally starts from acetone or acetone derivatives. Compounds I can be obtained in one stage, in a catalytic ring closure reaction in the presence of ammonia and hydrogen, from the compounds ##STR3## (DE 2 412 750), or from triacetoneamines II ##STR4## by aminative hydrogenation in one or two stages, for example under catalysis (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). These industrially prepared sterically hindered 4-aminopiperidines are generally purified by distillation.
However, the piperidines I prepared by customary techniques usually still contain disruptive amounts of coloring substances, or else such substances are formed after a short time.
Against the background of this state of affairs it was known, for example from EP 477 593, that crude N-alkyldialkanolamines can be improved in terms of color by adding a metal borohydride and carrying out distillation in the presence of water under defined conditions. However, the N-alkyldialkanolamines are a totally different class of substance from the sterically hindered 4-aminopiperidines of the present invention. Furthermore, it was known from Spec. Chem. 4(2), (1984) 38-41 and from U.S. Pat. No. 3,159,276, U.S. Pat. No. 3,207,790 and U.S. Pat. No. 3,222,310 that it is possible to improve the color of the products by adding sodium borohydride to ethanolamines, ethyleneamines or aromatic amines before or after distillation. This document too makes no mention of the piperidines I. No particular distillation technique is suggested.
In contrast, the development of methods for high purification of the sterically hindered 4-aminopiperidines took a very different path.
From DD 266 799 it was known to react piperidines I in solution in acetone/water with CO.sub.2, to separate off the precipitate and wash it with acetone, and then to subject it to thermal decomposition and to purify the product by distillation. SU 18 11 527 describes another purification technique for sterically hindered 4-aminopiperidine I: the contaminated, crude product is dissolved in an aprotic solvent and reacted with ethylene glycol, and the reaction product is distilled and purified over a number of steps. Both techniques are extremely laborious and costly.
It is an object of the present invention, therefore, to provide a cost-effective process by which highly pure color-stable sterically hindered 4-aminopiperidines I can be made available, ie. products whose low degree of inherent coloration is retained over long periods and coupled with a low content of by-products, such as stabilizing auxiliaries.
We have found that this object is achieved by the abovementioned process, which comprises, in a first step, removing high-boiling substances and, if present, water from the crude piperidines by distillation; in a second step, adding from 0.01 to 5% by weight, based on the product of the first step, of a reducing agent; and, in a third step, isolating the piperidines by distillation.
Other features of the invention are evident from the subclaims.
In the sterically hindered 4-aminopiperidines I, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 independently are preferably C.sub.1 -C.sub.3 -alkyl, especially ethyl or methyl, for example methyl.
The reducing agents used are generally substances which are solid u
REFERENCES:
patent: 3159276 (1964-12-01), Moore
patent: 3222310 (1965-12-01), Hinckley
patent: 3922306 (1975-11-01), Takaku et al.
patent: 5208377 (1993-05-01), Overgaard et al.
Ohtawara et al. "Method of manufacturing acylated amines and slats and quaternary ammonium saltsthereof as fabric softeners" CA 130:209434, 1997.
Speciality Chem. 4 (2), pp. 38, 40, 41 (1984).
Julius Manfred
Krause Alfred
Rust Harald
Siegel Hardo
Siegel Wolfgang
BASF - Aktiengesellschaft
Chang Ceila
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