CA2305282A1

CA2305282A1 - Method for purifying 4-amino-piperidines

Info

Publication number: CA2305282A1
Application number: CA002305282A
Authority: CA
Inventors: Manfred Julius; Hardo Siegel; Tom Witzel; Wolfgang Siegel
Original assignee: Individual
Current assignee: BASF SE
Priority date: 1997-10-01
Filing date: 1998-09-25
Publication date: 1999-04-08
Also published as: ID23897A; JP2001518465A; DE19743433C1; WO1999016749A1; CO4770994A1; SK4262000A3; TW377345B; PL339578A1; EP1025084A1; BR9812595A; KR20010030840A; HUP0004584A2; AU9746998A; CN1272843A; NZ503565A

Abstract

The invention relates to a method for purifying 2,2,6,6-tetrasubstituted 4-amino-piperidines produced from the corresponding piperidin-4-ones, and subsequent distillation. According to the invention, the distilled 2,2,6,6-tetrasubstituted 4-amino-piperidine is reacted with hydrogen in the presence of a hydrating or dehydrating catalyst and the 4-amino piperidine is then separated from the reaction mixture.

Description

The present invention relates to a process for purifying 2,2,6,6-tetrasubstituted 4-aminopiperidines which have been prepared from the corresponding piperidin-4-ones with subsequent distillation.
In particular, the invention relates to a process for purifying 4-aminopiperidines of the formula I

I, R1 N~ R3 where R1 to R4 are C1-C6-alkyl, R1 and R2 and/or R3 and R4 together form a CHZ chain having from 2 to 5 carbon atoms, which have been prepared from the corresponding piperidin-4-ones of the formula II

II, R1 N~ R3 where the radicals R are as defined above, with subsequent distillation.
The 4-aminopiperidines which, owing to 2,2,6,6-substitution, eg.
tetraalkyl substitution, are designated as sterically hindered, are used in a variety of applications. In particular, they serve as intermediates in the preparation of UV stabilizers for synthetic polymers (see, for example: R. Gachter, H. Miiller (editors): Taschenbuch der Kunststoffadditive, Carl Hanser Verlag, Munich, 1979; F. Gugumus, Polym. Degrad. Stabil. 44 (1994), 299 - 322) and as chain regulators and stabilizers in the 30 preparation of polyamides (cf., for example: w0 952 84 43, DE-A-4 413 177).

0050/48395 CA o23os2s2 2000-o3-2s _ 2 It is of particular importance that the sterically hindered 4-aminopiperidines have not only a high chemical purity but also no or very little intrinsic color and that no discoloration takes place over a storage time of a number of months. This applies particularly when the 4-aminopiperidine is used for the preparation of stabilizers or employed directly as additive, since the product quality of these and thus also the quality of the stabilized polymers depends decisively on the chemical purity and, in particular, the color quality.
The sterically hindered 4-aminopiperidines are generally prepared industrially from dialkyl ketones, eg. acetone or acetone derivatives. The piperidines I can be obtained in a single step from the compounds by a catalytic ring-closure reaction in the presence of ammonia and hydrogen (DE-A-2 412 750) or from piperidin-4-ones II
O
II, R1 N~ R3 by aminative hydrogenation in one or two stages, for example catalytically. (See, for example DE-A-35 25 387, DE-A-2 040 975, DE-A-2 349 962, DE-A-26 21 870, EP-A-33 529, EP-A-42 119, Ep-A-303 279, EP-A-410 970, EP-A-611 137, EP-A-623 585 and DE-A-42 10 311).
The sterically hindered 4-aminopiperidines produced industrially are generally purified by distillation. (See, for example EP-A-33 529).
However, troublesome amounts of substances which give a color are still present, or are formed after a short time, in the 4-amino-2,2,6,6-tetraalkylpiperidines which are prepared using conventional processes.

0050/48395 Ca o23o52s2 2000-o3-2s According to DE-A-195 55 58, EP-A-28 555, US 3 819 710 and JP
01,160,947 CChem. Abstr. 111: 232081r), color-producing compounds in certain aminoalcohols, which compounds are formed in the preparation of the aminoalcohols from ethylene oxide and an appropriate amine, can be converted into less color-producing compounds by catalytic hydrogenation.
JP 06 25,410 CChem. Abstr. 12I: 56988n), JP-OS 48-52708 CChem.
Abstr. 80: 36697y), JP 05,345,821 CChem. Abstr. 120: 272327t), US
5 362 914 and EP-A-262 562 disclose that discolorations in certain polyamines can be reduced by treatment with hydrogen in the presence of hydrogenation catalysts.
DE-A-22 05 958 discloses a process for purifying tertiary amines which have been obtained by reacting primary alcohols with ammonia, by hydrogenation of the impurities before the final distillation of the tertiary amine.
The abovementioned compounds are different classes of substances from those of the sterically hindered 4-amino-piperidines of the present invention. Furthermore, the origin of the color producing impurities in the abovementioned compounds lies in the specific preparative processes and starting materials employed in each case.
Japanese Patent Application JP-OS 02-311 457 describes the purification of 2,2,6,6-tetraalkyl-4-piperidinones by treatment with hydrogen in the presence of a hydrogenation catalyst.
According to the examples given in this application, the process product (triacetoneamine, TAA) is so color-unstable that it has a much poorer color quality than the starting material after just one week's storage at 60°C.
The development of preparative methods for chemically pure sterically hindered 4-aminopiperidines having low discoloration has taken a completely different route:
DD-A-266 799 teaches reacting 4-amino-2,2,6,6-tetramethyl-piperidine in acetone/water solution with C02, separating off the precipitate, washing with acetone, subsequently decomposing thermally and purifying the product by distillation.
SU 18 11 527 describes a different purification process for sterically hindered 4-aminopiperidines I. In that process, the contaminated crude product is dissolved in an aprotic solvent, 0050/48395 CA o23os2s2 2000-o3-2s reacted with ethylene glycol, the reaction product is isolated, the 4-aminopiperidine is set free using aqueous alkali and is, after removal of the aqueous phase, fractionally distilled.
Both processes are extraordinarily complicated and costly.
Finally, the earlier German Application No. 19622269.9 describes a distillation process for purifying crude 4-amino-piperidines I
by' in a first step, removing high-boiling substances and possibly 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, for example sodium borohydride, and, in a third step, isolating the plperidines I by distillation.
It is an object of the present invention to provide an inexpensive process which is simple to carry out and by means of which colorless, color-stable and highly pure sterically hindered 4-aminopiperidines, eg. of the formula I, can be made available.
This means products whose very low intrinsic coloration is maintained for a prolonged period and which have, at the same time, a low by-product content and contain no stabilizing auxiliaries. The reference to the 4-aminopiperidines I as "colorless" includes a minimum discoloration, namely up to a color number of at most 40 APHA (measured in accordance with DIN-ISO 6271).
We have found that this object is achieved by a process for purifying 2,2,6,6-tetrasubstituted 4-aminopiperidines which have been prepared from the corresponding piperidin-4-ones with subsequent distillation, which comprises reacting the distilled 2,2,6,6-tetrasubstituted 4-aminopiperidine with hydrogen in the presence of a hydrogenation or dehydrogenation catalyst and then again separating the 4-aminopiperidine from the reaction mixture.
In the sterically hindered 4-aminopiperidines I, the radicals R1, RZ, R3 and R4, independently of one another, are preferably C1-C3-alkyl, for example ethyl or methyl, in particular methyl.
The pure but discolored and/or color-unstable 4-amino-piperidine, eg. of the formula I, which has been obtained according to known methods by reaction of the corresponding piperidin-4-one, for example by aminative hydrogenation, and subsequent fractional rectification, is, according to the present invention, reacted with hydrogen in the presence of a hydrogenation catalyst, for example at from 20 to 200~C. Higher temperatures are also 0050/48395 ca o23os2s2 2000-o3-2s possible. Preference is given to a reaction temperature in the range from 50 to 150~C.
The reaction of the 4-aminopiperidine with hydrogen can be 5 carried out at atmospheric pressure or preferably under superatmospheric pressure, for example from 0.1 to 50 MPa. Higher pressures are also possible. Preference is given to a reaction pressure of from 1 to 30 MPa, in particular from 1 to 20 MPa.
The reaction of the 4-aminopiperidine with hydrogen can be carried out in the presence of a solvent or a solvent mixture which is inert under the reaction conditions, or preferably in the absence of solvent. When using a solvent, for example tetrahydrofuran, dioxane, 1,2-dimethoxyethane, methanol or ethanol, the reaction conditions are selected such that the solvent is present in liquid form in the reaction mixture.
As regards the hydrogenation catalysts which can be used, there are no restrictions. Dehydrogenation catalysts can also be used.
Suitable hydrogenation catalysts are, for example, catalysts which comprise copper, silver, gold, iron, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, chromium, molybdenum or a mixture thereof.
The hydrogenation catalyst used can be homogeneously dissolved in the 4-aminopiperidine or in the mixture of 4-aminopiperidine and solvent, for example when using tris(triphenylphosphine)rhodium chloride, or, particularly preferably, be present in undissolved form, ie. heterogeneous.
Suitable heterogeneous catalysts are support-free catalysts such as Raney nickel or Raney cobalt, with the latter being present as a suspension in the reaction mixture, or supported catalysts which are preferably arranged as a fixed bed in the reactor. In the case of the supported catalysts, suitable support materials for the catalytically active metals or metal compounds are, for example, carbon, aluminum oxide, silicon dioxide, titanium dioxide, zirconium dioxide, zinc oxide, magnesium oxide, silicon carbide, zeolites or mixtures thereof.
Examples which may be mentioned are supported catalysts comprising copper and/or cobalt and/or nickel and aluminum oxide and/or zirconium dioxide.

0050/48395 ca o23os2s2 2000-o3-2s For example, the two supported catalysts having the following compositions can be employed:
76% by weight of A1, calculated as A1203, 4% by weight of Cu, calculated as CuO, 10% by weight of Co, calculated as CoO, and 10% by weight of Ni, calculated as Ni0 (as described in DE-A-1 953 263) °r 31.5% by weight of Zr, calculated as Zr02, 50% by weight of Ni, calculated as NiO, 17% by weight of Cu, calculated as CuO, and 1.5% of Mo, calculated as Mo03 (as described in EP-A-696 572).
The necessary residence time of the 4-aminopiperidine over the catalyst is determined, inter alia, by the degree of discoloration of the distilled 4-aminopiperidine and by the desired decolorization and/or color stability of the piperidine.
As a rule, the residence time is longer, the higher the degree of discoloration of the 4-aminopiperidine used in the process step of the present invention and the higher the color quality requirements for the product.
Depending on the reaction conditions selected, residence times of from 10 minutes to a few hours are generally sufficient.
The process step of the present invention can be carried out either continuously, for example in tube reactors, stirred vessels or cascades of stirred vessels, or batchwise, for example in stirred vessels.
After carrying out the process step of the present invention, the 4-aminopiperidine is separated from the hydrogenation catalyst and from any solvent used.
Hydrogenation catalysts dissolved in the reaction product are separated off by distillation, with any solvent used and the 4-aminopiperidine being taken off in succession at the top in a customary manner.
Hydrogenation catalysts used in suspension are separated off by decantation and/or filtration. The reaction product can subsequently be distilled, which is in any case necessary if a solvent is used.

0050/48395 Ca o23o52s2 2000-o3-2s When using a hydrogenation catalyst arranged as a fixed bed, the reaction product is advantageously filtered in order to remove any abraded catalyst present. The reaction product can subsequently be distilled, which is in any case necessary if a solvent is used.
The process of the present invention gives, in a simple, inexpensive manner, pure sterically hindered 4-aminopiperidines which have virtually no intrinsic color and remain color-stable on storage, so that the addition of stabilizers is superfluous.
Examples The color of the sterically hindered 4-aminopiperidines was determined by measuring the APHA color number in accordance with DIN-ISO 6271.
In all examples, the storage of the TAD samples was carried out under comparable conditions (room temperature, in the dark).
Example 1 (Comparative Example):
1.632 kg of crude synthetic product having the composition (in %
by weight) 85.6% of 4-amino-2,2,6,6-tetramethylpiperidine (triacetonediamine, TAD) 9.0% of Hz0 about 0.7% of NH3 1.4% of 4-hydroxy-2,2,6,6-tetramethylpiperidine (triacetoneaminoalcohol,TAA-ol) 3.3% of by-products including high boilers, which had been obtained by aminative hydrogenation of 2,2,6,6-tetramethylpiperidin-4-one (triacetoneamine, TAA) [GC
purity: 99%; APHA color number: about 370 (measured as a 1%
strength solution in ethanol)] at 165°C, 12 MPa HZ, in the presence of a heterogeneous catalyst comprising 76% by weight of A1, calculated as A1203, 4% by weight of Cu, calculated as CuO, 10% by weight of Co, calculated as CoO, and 10% by weight of Ni, calculated as Ni0 (as described in DE-A-1 953 263), was rectified in a distillation apparatus comprising a 2.0 1 still pot with double-wall heating, a 70 cm mirrored glass column filled with 3 mm V2A wire helices (3.5 cm internal column diameter) and a column head with liquid splitter.

0050/48395 ca o23os2s2 2000-o3-2s As main fraction, 1.191 kg of slightly yellowish TAD having a purity of 99.9 (according to GC) were obtained at a pressure of 40-42 hPa and a temperature at the top of 99-102~C.
The TAD obtained became increasingly yellow during the following days, ie. it was not color-stable.
Storage time in days APHA color number Example 2:
In a 300 ml autoclave with stirrer and basket insert, about 70 g (0.45 mol) of yellowish TAD (purity according to GC:> 99.9%; APHA
color number: 72), which had been obtained as described in Example 1, was treated with hydrogen at a pressure of 10 MPa for 6 hours at 90~C in the presence of a heterogeneous catalyst comprising 76% by weight of A1, calculated as A1z03, 4% by weight of Cu, calculated as CuO, 10% by weight of Co, calculated as Co0 and 10% by weight of Ni, calculated as Ni0 (4 mm extrudates), which was present as a fixed bed in the basket insert.
The reaction product was then filtered. The purity of the colorless TAD obtained was 99.9% according to GC.
The APHA color number of the TAD was < 1 after a storage time of 50 days. Even after a storage time of 147 days, the TAD appeared colorless to the eye, ie. the APHA color number was < 10.
Example 3:
Carrying out the experiment as in Example 2 but using 5 g of Raney nickel as heterogeneous catalyst (suspended) gave, after filtration, colorless TAD having a purity of 99.9% according to GC and an APHA color number of 17 after a storage time of 50 days. After a storage time of 148 days, the APHA color number was 23.

Claims

We claim:

1. A process for purifying 2,2,6,6-tetrasubstituted 4-amino-piperidines which have been prepared from the corresponding piperidin-4-ones with subsequent distillation, which comprises reacting the distilled 2,2,6,6-tetrasubstituted 4-aminopiperidine with hydrogen in the presence of a hydrogenation or dehydrogenation catalyst and separating the 4-aminopiperidine from the reaction mixture.

2. A process as claimed in claim 1 for purifying 4-amino-piperidines of the formula I
where R1 to R4 are C1-C6-alkyl, R1 and R2 and/or R3 and R4 together form a CH2 chain having from 2 to 5 carbon atoms, which have been prepared from the corresponding piperidin-4-ones of the formula II
where R1 to R4 are as defined above.

3. A process as claimed in claim 1 for purifying 4-amino-piperidines of the formula I as defined in claim 2 in which R1, R2, R3 and R4 are methyl.

4. A process as claimed in any of claims 1 to 3, wherein the reaction with hydrogen is carried out at from 20 to 200°C.

5. A process as claimed in any of claims 1 to 4, wherein the reaction is carried out at pressures of from 1 to 30 MPa.

6. A process as claimed in any of claims 1 to 5, wherein the reaction is carried out in the absence of a solvent.

7. A process as claimed in any of claims 1 to 6, wherein the hydrogenation catalyst comprises copper, silver, gold, iron, cobalt, nickel, ruthenium, rhodium, palladium, rhenium, osmium, iridium, platinum, chromium, molybdenum or a mixture thereof.

8. A process as claimed in any of claims 1 to 7, wherein the hydrogenation catalyst used is a supported catalyst.

9. A process as claimed in any of claims 1 to 8, wherein the hydrogenation catalyst used is a supported catalyst comprising nickel and/or copper and/or cobalt and aluminum oxide and/or zirconium dioxide.