GB2176473A

GB2176473A - Method for preparing 4-amino-2,2,6,6-tetramethylpiperidine

Info

Publication number: GB2176473A
Application number: GB08514952A
Authority: GB
Inventors: Zinaida Grigorievna Popova; Vitaly Ivanovich Tatsitov; Vladimir Ivanovich Paramonov; Raisa Dmitrievna Filina; Vladimir Khristianovich Gents; Viktor Mikhailovich Bukatin; Tatyana Anatolievna Pankova
Original assignee: KHIM DLYA POLIMERNYKH MATERIAL
Current assignee: KHIM DLYA POLIMERNYKH MATERIAL
Priority date: 1985-06-13
Filing date: 1985-06-13
Publication date: 1986-12-31
Also published as: JPH0445508B2; CH664361A5; DE3525387C2; JPS61293969A; GB2176473B; GB8514952D0; NL8501735A; DE3525387A1

Abstract

4-amino-2,2,6,6-tetramethylpiperidine is prepared by reacting 2,2,6,6-tetramethyl-4-oxopiperidine with ammonia and hydrogen at a temperature of 100-135 DEG C under a pressure of 10-25 bar. The reaction is carried out in an aqueous medium in the presence of a hydrogenation catalyst and hydroxides of alkali metals or alkali-earth metals, the hydroxides being employed in an amount of 1-2% by weight of the hydrogenation catalyst.

Description

SPECIFICATION Method for preparing 4-amino-2,2,6,6-tetramethylpiperidine The present invention relates to methods for preparing 4-amino-2,2,6,6-tetramethylpiperidine.

4-Amino-2,2,6,6-tetramethylpiperidine finds an extensive use as the starting product in the synthesis of non-dyeing photostabilizersfor polymeric materials.

The present invention is directed to the provision of such a method for preparing 4-amino-2,2,6,6tetramethylpiperidinewhich would make it possible to obtain the desired product following a simplified procedure with a sufficiently high yield and would be economically efficient.

The present invention resides in a method for preparing 4-amino-2,2,6,6-tetramethylpiperidine by reacting 2,2,6,6-tetramethyl-4-oxopiperidinewith ammonia and hydrogen at an elevated temperature and under an overatmospheric pressure in the presence of a hydrogenation catalyst, wherein according to the present invention the process is conducted at a temperature within the range offrom 100 to 1 35"C under a pressure of from 10to 25 bar in an aqueous medium in the presence of an alkali-metal hydroxide oran alkali-earth metal hydroxide in an amount offrom 1 to 2% by weight of the hydrogenation catalyst.

The range of temperatures and pressures selected according to the present invention ensures a maximum yield ofthe desired product and high economic parameters of the process. Lowering the lower limit of temperatures and pressures results in an extended duration ofthe reaction, whereby a considerable amount ofthe reaction by-products is formed and the desired product yield is reduced. Increasing the upper limit of these parameters is economically inefficient.

As the hydrogenation catalysts conventional hydrogenation catalysts can be used, for example metals of Group VIII of the periodic system (iron, cobalt, nickel, palladium and the like) which can be used both individually and supported on a carrier. As the carrier use can be made of carbon, silicates, aluminium oxide and the like. The catalyst is used in amounts generally accepted for reactions of reducing amination, i.e., within the range offrom 1 to 30% by weight, preferably from 10 to 20% by weight as calculated for2,2,6,6-tetramethyl- 4-oxopiperidine.

The presence of hydroxides of alkali and alkali-earth metals in the process according to the present invention enhances its selectivity, minimizes the formation of the reaction by-products. As hydroxides of alkali and alkali-earth metals sodium hydroxide, lithium hydroxide, potassium hydroxide, calcium hydroxide and the like are used. The use of an aqueous medium for carrying out the process makes it possible to lower the rate of ammonia consumption, to reduce the employed pressure and shorten the process duration.

The method for preparing 4-amino-2,2,6,6-tetramethylpiperidine makes it possible to obtain the desired product with a sufficiently high yield of about 90-95% following a simple procedure. The use of water as a solventandthe addition ofalkali metal hydroxide or an alkali-earth metal hydroxide makes it possibleto: - reduce by 15-20 times the process pressure which improves the process safety and lowers its energyconsumption characteristics; - reduce by 3-lOtimes the rate of ammonia consumption which enables a very simple system forcatching thereof; - shorten by more than 2 times the process duration which considerably increases the desired product output per time unit and increases the plant productivity.

The method for preparing 4-amino-2,2,6,6-tetramethylpiperidine is simple as to the equipment employed and can be performed in the following manner.

Into a standard-type autoclave provided with a stirrer 2,2,6,6-tetra,nethyl-4-oxopiperidine is charged along with an aqueous solution of ammonia, a hydrogenation catalyst and an alkali metal hydroxide or an alkaliearth metal hydroxide.

The autoclave is sealed, purged with nitrogen, then with hydrogen and heated to a temperature within the range of from 100 to 1 35"C still under agitation. In doing so, the pressure in the autoclave first increases to 10-17 bar andthen starts to drop with the beginning of the reducing amination process. The pressure in the autoclave is maintained within the range of from lotto 25 bar by means of a hydrogen pressure valve. The reaction completion is controlled by discontinuation of hydrogen absorption. The process duration is 20-30 minutes. On completion of the reaction the autoclave contents are cooled to 20-25"C by supplying water into the cooling jacket and the pressure is released.The reaction mass is decanted from the catalyst and subjected to fractionation; the fraction boiling at 78-790C (7 mm Hg) is collected. The yield ofthe desired product is 90-95%.

For a better understanding of the present invention some specific examples are given hereinbelow byway of illustration.

Example 1 Into an autoclave provided with a stirrer, pressure gauge and a thermometer 310 g of 2,2,6,6-tetramethyl-4 oxopiperidine,410 ml of a 25% aqueous solution ofammonia, 31 g of Raney nickel and 0.62 g sodium hydroxide are charged. The autoclave is sealed, twice purged with nitrogen, then with hydrogen and the pressure of hydrogen therein is maintained at 10 bar. With operating stirrerthe temperature in the autoclave is brought to 1 00'C by supplying steam into the autoclave's jacket. In doing so, the pressure in the autoclave is first raised to 15 barandthen it starts to drop owing to the beginning ofthe reaction of reducing amination. By means of hydrogen pressure valve the pressure of hydrogen in the autoclave is maintained at 15 bar.The course ofthe reaction is controlled by pressure drop in the reactor at a temporary discontinuation of hydrogen supplythereinto. The completion of the reaction is determined by stopping of hydrogen absorption. The duration of the reducing amination is 30 minutes. On completion of the reaction the autoclave contents are cooled to thetemperature of 25"C by supplying water into the autoclave jacket and the pressure is released.

The reaction mass is decanted from the catalyst and subjected tofractionation; the fraction boiling at78-79 C/7 mm Hg is collected. The yield ofthe desired product is 294 g (94.0% ofthe theory as calculated for 2,2,6,6tetramethyl-4-oxopiperidine); n20, = 1.4700; d20 = 0.8963.

Example 2 The desired product is obtained under the conditions described in the foregoing Example 1, exceptthatthe process is conducted at the temperature of 120"C, underthe pressure of 25 bar using nickel supported on kieselguhr as the catalyst in the amount of 64 9.

The desired productyield is 294 g (94.0% of the theory as calculated for2,2,6,64etramethyl-4- OxOpipOridine);n20 = 1.4710; d20 = 0.8966.

Example 3 The desired product is obtained under the conditions of Example 1 hereinbefore, exceptthatthe process is conducted atthe temperature of 1 35"C underthe pressure of 10 bar using Raney cobalt as the hydrogenation catalyst in the amount of 46.5 g and with a 2.S4ime excess of ammonia per mole of 2,2,6,6-tetramethyl-4oxopiperidine. The yield ofthe desired product is 291.7 g (93.2% ofthetheory as calculated for 2,2,6,6- tetramethyl-4-oxopiperidine); n200 = 1.4699; d24 = 0.8950.

Example 4 The desired product is obtained underthe conditions of Example 1, except that the process is conducted in the presence of calcium hydroxide in the amount of 0.31 g and with a 2.5-time excess of ammonia per moleof 2,2,6,6-tetra methyl-4-oxopi peridi ne. The desired product yield is 290.1 g (93% ofthetheory as calculated for 2,2,6,6-tetramethyl-4-oxopiperidine); n20 = 1.4699; d24= 0.8961.

Example 5 The desired product is obtained underthe conditions of Example 1, exceptthatthe process is conducted in the presence of potassium hydroxide in the amount of 0.54 g and with a 3.5-time excess of ammonia per mole of 2,2,6,6-tetramethyl-4-oxopiperidine. The desired product yield is 297.4 g (95.0% of the theory as calculated for 2,2,6,6-tetramethyl-4-oxopiperidine). n20, = 1.4718; d20 = 0.8965.

Example 6 The desired product is obtained underthe conditions of Example 1 hereinbefore, with the exception thatthe process is conducted at the temperature of 1 25"C under the pressure of 10 bar in the presence of lithium hydroxide in the amount of 0.46 g and a 3.5-time excess of ammonia per mole of 2,2,6,6-tetramethyl-4oxopiperidine. The desired product yield is 296.7 g (94.8% ofthe theory as calculated for2,2,6,6-tetramethyl-4- oxopiperidine) n2g = 1.4691; d20 = 0.8967.

Claims

1. A method for preparing 4-amino-2,2,6,6-tetramethylpiperidine comprising reacting 2,2,6,6-tetramethyl4-oxopiperidine with ammonia and hydrogen at a temperature of 100 to 1 35"C under a pressure of from 1 Oto 25 bar in an aqueous medium in the presence of a hydrogenation catalyst and hydroxides of alkali metals our alkali-earth metals in an amount offrom 1 to 2% by weight ofthe hydrogenation catalyst.

2. A method according to the foregoing claim 1, substantially as described in the Specification and in any of Examples 1 to 6 herein.

3. A method for preparing 4-amino-2,2,6,6-tetramethylpiperidine, substantially as described herein with reference to any one ofthe Examples 1 to 6.

4. 4-amino-2,2,6,64etramethylpiperidine whenever produced by the method according to any ofthe foregoing claims 1 to 3.