CS260755B1 - Method of 4-substituted-2,2,6,6-tetramethyl piperidine-n-oxides preparation - Google Patents

Abstract

The present invention relates to a process for preparing 4-substituted-2,2,6,6-tetramethylpiperidine-N- -oxyl by oxidation of 4-substituted-2,2,6,6- tetramethylpiperidines with hydrogen peroxide ultrasound. The method can be used in the chemical industry

Description

The present invention relates to a process for the preparation of 4-substituted-2,2,6,6-tetramethylplperidine-N-oxyls of the general formula I when n = 1 represents a hydroxyl group, an amino group, a group of the formula -OCOR ¹ wherein R ¹ represents an alkyl group. from 10 to 18 carbon atoms, and in the case where n is 2, R represents a bifunctional group —OCO (CH2) _m COO — wherein m-8 by oxidation of the 4-substituted-2,2,6,6-tetramethylpiperidines of formula II

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(1) oxidizing 4-substituted-2,2,6,6-tetramethylpiperidines with hydrogen peroxide to effect ultrasound. Said compounds can be used as thermal stabilizers of polyolefins.

The use, properties and synthesis of nitroxyl radicals are described in several monographs. The synthesis of nitroxyl radicals is based on either hydroxylamines or secondary amines. The synthesis of nitroxyl radicals of the spherically hindered amines of the piperidine, pyrrolidine, isoindoline and, in particular, the piperazine type by oxidation with hydrogen peroxide under catalysis of sodium tungstate is important [Sosnovski G., Konieczky M .: Z. Naturforsch. 318, 1776 (1976)]. Sodium tungstate may also be used in place of sodium tungstate, the reaction being carried out; at higher temperature y methanol with 10% acetonitrile (USSR No. 391 137). It is also known to use hydrogen peroxide in the presence of acetic acid, trifluoroacetic acid, cerium salts, silver oxide and alkaline solutions.

Substituted perbenzoic acids, dibenzoyl peroxide, diterebutyl peroxide, ozone and lead oxide are described as oxidizing agents.

In the above methods of preparation I achieve! yields at a relatively long reaction time (up to several weeks). This is due to the low reactivity of the higher molecular weight starting amines.

It has been found that the above disadvantages are largely eliminated by the process for preparing the 4-substituted-2,2,6,6-tetramethylpiperidine-N-oxyls of formula I

in which n is an integer of 1 or 2 and R, in the case (li) in which

The wounds are as defined hereinbefore, hydrogen peroxide, optionally in a solvent environment or in an aqueous solution in the presence of a catalyst and Chelaton 3 according to the invention, which is based on ultrasonic treatment of the reaction mixture.

The tangible advantages of the process according to the invention are to reduce the reaction time and to increase the yields.

The following examples illustrate but do not limit the invention.

Example 1

Preparation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl (Compound A).

In a 100 ml flat-bottomed flask 1 g (2.4 mmol) of 2,2,6,6-tetramethyl-4-stearoyloxyplperidine was dissolved in 40 ml of solvent and 0.05 g (0.15 mmol) of tungstate was added. sodium (NaCl 2 H 2 O), 0.05 g (1.4 x ^{10 4} mol) of Chelatone 3 and 3 ml of 30% H 2 O 2 .The flask was immersed in an ultrasonic cleaning bath U COO 2 BM1 (20 kHz, 160 W). After about 20 minutes, the ultrasonic water temperature reached 50 DEG C. After the selected reaction time, the solvent was distilled off in vacuo, the organic material was extracted into benzene. the calibration curve (EPR) determined the 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl content (results are shown in Table 1).

The product 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl was purified by chromatography on Al 2 O 3, eluent benzene-petroleum ether. Crystallization (petroleum ether) gave the product with mp 49-52 ° C.

Analysis for:

C27H52NO3 (M 438.7)

200755 calculated:

N, 3.19; C, 73.97; 11, 11.87; N, 3.24.

Table 1

Results of N-oxylation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine (compound Ά)

Solvent Reaction time Bath temperature% N-oxyl

CH3OH ^c 20 h Deň: 32 ° C 44 % CH3OH 20 h Deň: 32 ° C 78 % CH3OH ^d 10 h Deň: 32 ° C 76 % CH3OH ^c 20 h Deň: 18 ° C 0 % CH3OH 20 h Deň: 18 ° C 25 % CHaCOOH® 20 h 50 C 28 % CH3CN 20 h 50 ^& C 42.5 % DMF ^b 20 h Deň: 32 ° C 57 % CH3CH2OH 20 h Deň: 32 ° C 84 % ^and - after the reaction is complete the mixture neutralized with K2CG3 and organic material is ex-

^b - after completion of the reaction, the mixture was poured into water and the organic material was extracted into ether;

^c - reaction without ultrasound with mechanical stirring, ^d - experiment made with 15 g of starting material.

Example 2

Preparation of 2,2,6,6-tetramethyl-4-hydroxypiperidine-N-Oxyl {comp. B) ..

To a 50 mL round-bottomed flask were placed 0.5 g (0.3 mmol) of 2,2,6,6 tetramethyl-4-hydroxypiperidine, 0.05 g ^(-t 1,5.10 mole) of sodium tungstate, 0, 05 g (1.4. 10 ^-4 mol) of Chelatone 3, 3 ml of H2O and 1 ml of 30% H2O2. The flask was immersed in an ultrasonic cleaning bath U COO 2BM1 (20 kHz, 160 W) and the reaction mixture was subjected to sonication. After completion of the reaction, the reaction mixture was saturated with K 2 CO 3 and the product was shipped into ether. After evaporation of the ether, the residue was determined for N-oxyl content by UV (calibration curve), the results are shown in Table 2.

Crystallization (ether / hexene) gave the product with m.p. 70-72 ° C.

Table 2

Results of N-oxylation of Compounds B

Compound Reaction Time

The bath temperature was% N-oxyl

B ^c 30 minutes

B 30 mins ° C 50% ° C 89%

Example 3

Preparation of 2,2,6,6-tetraimethyl-4-aminopiperidine-N-oxyl (comp.

In a 50 ml flat-bottomed flask was added 0.5 g (3 mmol) of 2,2,6,6-tetramethylaminopiperidine, 0.02 g (6.10 ^-5 moles of sodium tungstate), 0.02 g (5.4.10 ^{- 5} mol) Chelatone 3, 1 ml of 30% H 2 O 2 and 5 ml of H 2 O. Further procedure as in Example 2.

Crystallization (hexane) gave the product with m.p. 37 ° C.

Example 1 4

Preparation of 4-lauryloxy-2,2,6,6-tetramethylpiperidine-N-oxyl (Compound D)

0.5 g (1.47.10 ^-3 mol) of 4-lauryloxy-2,2,6,6-tetramethylpiperidine, 0.02 g (6.10 ^-5 mol) of sodium tungstate, 0.02 g (5, 4.10 ^-5 mol) Chelatone 3, 2 ml of 30% H2O2 in 40 ml of ethanol.

Procedure as in Example 1.

Example 5

Preparation of di- (2,2,6,6-tetramethyl-4-piperidyl) sebacate-N-oxyl (Compound E)

To the reaction were taken, 0.5 g (10.01 ^-3 mol) of bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, 0.04 g (1,2.10 ^-4 mol) of sodium tungstate, 0.04 g (1.10 ^-4 mol) of Chelatone 3, 1 ml of 30% H2O2 in 20 ml of ethanol. Procedure as in Example 1.

Crystallization (hexane / CCl4) gave the product at 1.1.120-124 ° C.

The results of Examples 4 and 5 are shown in the hunting was determined by the calibration curve of the Diver 3. Percentage of N-oxydimetry EPR.

Table 3

Results of N-oxylation of compounds D and E

Compound Solvent Reaction time Bath temperature % N-oxyl D CH3CH2OH 20 h Deň: 32 ° C 68% D CH3CH2OH 8 h Deň: 32 ° C 60% E CH3CH2OH 12 h Deň: 32 ° C 37%

Note:

In all cases except c, ultrasound as in Example 1 was used.

Example 6

Preparation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl (Compound A)

1 g (2.4 mmol) of 2,2,6,6-tetramethyl-4-stearoylxypiperidine, 0.05 g (0.15 mmol) of sodium tungstate was reacted. 3 ml of 30% H2O2 in 40 ml of ethanol.

Procedure as in Example 1.

Example 7

Preparation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl (Compound A)

1 g (2.4 mmol) of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine, 0.05 g (1.4. 10 ^-4 moles) of Chelatone 3 and 3 ml of 30% H2O2 in 40 ml were taken into the reaction. ethanol.

Procedure as in Example 1.

Example

Preparation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl (Compound A).

1 g (2.4 mmol) of 2,2,6,6-tetramethyl-4-stearyl-oxypiperidine and 3 ml of 30% H2O2 in 30 ml of ethanol were reacted.

Procedure as in Example 1.

Example 9

Preparation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine-N-oxyl (Compound A)

0.5 g (1.2 mmol) of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine, 0.1 g (0.94 mmol) of Na2CO3 and 3 ml of 30% or H2O2 in 10 ml of ethanol were reacted.

Table 4

Results of N-oxidation of 2,2,6,6-tetramethyl-4-stearoyloxypiperidine under the conditions set forth in Examples 6-9.

Example Catalyst Reaction time Bath temperature % N-oxyl 6. NažWOá. 2 H2O 20 h Deň: 32 ° C 75 7. Chelatón 3 20 h Deň: 32 ° C 50 8. ₍ -. 20 h Deň: 32 ° C 50 9. Na (2CO3 20 h Deň: 32 ° C 20 May

Claims (1)

SUBJECT Process for the preparation of 4-substituted 2,2,6,6-tetramethylpiperidine-N-oxyls of the formula I INVENTION oxidation of 4-substituted-2,2,6,6-tetramethylpiperidines of formula II wherein n is an integer of 1 or 2 and R, when n = 1, represents a hydroxyl group, an amino group, a group of the formula —OCOR ¹ wherein R ¹ represents an alkyl of 10 to 18 carbon atoms and, when n is 2, R represents a bifunctional group -OCO (CH 2) _m COO-, where m = 8 in which The wounds have already been mentioned with hydrogen peroxide, optionally in a solvent medium or in an aqueous solution, in the presence of a catalyst and Chelatone 3, characterized in that the reaction mixture is sonicated.