JPH10120653A - Production of 4-hydroxy-1,2,2,6,6-pentamethylpiperidine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a process for producing 4-hydroxy-1,2,2,6,6- pentamethylpiperidine in high yield and selectivity like prior arts even without using formic acid. SOLUTION: This production process comprises the methylation of 4- hydroxy-2,2,6,6-tatramethyl-piperidine by the addition of one or more compounds selected form the group consisting of formaldehyde, paraformaldehyde and trioxane and the addition of formic acid in the zero to less than equimolar amount per 4-hydroxy-2,2,6,6-tatramethyl-piperidine.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to 4-hydroxy-
Methylation of 2,2,6,6-tetramethylpiperidine (also known as triacetone alkamine; hereinafter may be abbreviated as TAAM) to give 4-hydroxy-1,
The present invention relates to a method for producing 2,2,6,6-pentamethylpiperidine (hereinafter sometimes abbreviated as N-methyl-TAAM).

[0002]

BACKGROUND OF THE INVENTION N-methyl-TAAM is useful as a raw material for synthesizing sterically hindered piperidine compounds used as a plastic light stabilizer. N-methyl-TAAM is produced by methylation of TAAM. For example, N-methylation using formaldehyde / formic acid is known as Eschweiler-Clark reaction. This reaction is thought to proceed by the following mechanism, and formic acid is considered to have a role of reducing the enamine intermediate.

[0003]

Embedded image

[0004] USP 3,364,220, JP-A-2-2-2
12479 describes the synthesis of N-methyl-TAAM by the Eschweiler-Clark reaction. U
SP3,364,220 contains 4 g of formic acid containing 18 g of 37% formalin and 1% of water for 18 g of TAAM.
It describes that an N-methylation reaction is carried out by adding l.

[0005] JP-A-2-212479 describes the use of at least a 20 mol% excess of formaldehyde or paraformaldehyde based on TAAM and a nearly stoichiometric amount of formic acid based on TAAM. However, formic acid is a highly corrosive substance and is difficult to handle for safety. Further, it is necessary to make the formic acid feed device resistant to corrosion, which is a factor of cost increase.

[0006]

The present inventors have found that when the amount of formic acid used is reduced, the desired N-methyl-TAAM can be obtained in a surprisingly high yield.
The present invention has been completed. From the above reaction mechanism, it would be necessary to use 1 mol or more of formic acid with respect to TAAM. However, even when the amount of formic acid used is smaller than conventionally thought or not used at all, N-methyl-T
The AAM was unexpected.

That is, the present invention relates to 4-hydroxy-2,2,2
At least one compound selected from the group consisting of formaldehyde, paraformaldehyde, and trioxane is added to 6,6-tetramethylpiperidine, and 0 to 1 mole times 4-hydroxy-2,2,6,6-tetramethylpiperidine. 4-hydroxy-1,1, wherein the methylation reaction is carried out by adding a smaller amount of formic acid.
Provided is a method for producing 2,2,6,6-pentamethylpiperidine.

[0008] TAAM used as a raw material is produced by hydrogenating 4-oxo-2,2,6,6-tetramethylpiperidine in, for example, an aqueous solvent in the presence of a catalyst such as Raney nickel or ruthenium. . In the present invention, the solution obtained after hydrogenation may be used as it is, or may be used after concentration or isolation and purification.

Next, the methylation reaction of TAAM will be described. Formaldehyde, paraformaldehyde and trioxane may be used alone or in combination.
The addition amount of at least one compound selected from the group consisting of formaldehyde, paraformaldehyde and trioxane is generally 1 to 4 moles, preferably 1.5 to 3.0 mole times as much as TAAM in terms of formaldehyde. It is preferable because the yield of the target product is high and the amount of the base used in the subsequent neutralization step is reduced.

At least one compound selected from the group consisting of formaldehyde, paraformaldehyde and trioxane may be added in its entirety to TAAM at the start of the reaction, or may be partially mixed with TAAM and melted by heating. After that, the reaction may be performed by feeding the remainder. Formaldehyde is preferably 35-
Used as 37% formalin.

The amount of formic acid to be added is generally 0 to 1 mol times, preferably 0 to 0.5 mol times, relative to TAAM. The addition amount of 0 means an embodiment in which formic acid is not added, and this embodiment is most preferable. When formic acid is added, the entire amount of formic acid may be added to TAAM at the start of the reaction, or a part of the formic acid may be added to at least one compound selected from the group consisting of TAAM, formaldehyde, paraformaldehyde and trioxane. After mixing and melting or melting by heating, the reaction may be carried out by feeding the remainder.

The reaction temperature is usually from 60 to 160 ° C, preferably from 90 to 160 ° C. The reaction time is usually 1 to 10
Hours, preferably 1-2 hours. A solvent can be used for the reaction. As the solvent, water, methanol or the like, preferably water may be used. Before the end of the reaction, the reaction mixture is brought to 120-160 ° C., preferably 130-16 ° C.
It is preferable to raise the temperature to 0 ° C., because unreacted formaldehyde, formic acid, carbon dioxide by-produced in the reaction, and the like are removed from the reaction mixture in addition to water, and N-methyl-TAAM is concentrated. The reaction pressure is usually at atmospheric pressure.

Particularly preferred reaction conditions are, for example, as follows. First, TAAM and formaldehyde in an amount of 0.5 to 1.5 mole times the formaldehyde conversion to TAAM,
At least one compound selected from the group consisting of paraformaldehyde and trioxane is mixed, heated and melted or dissolved. The TAA was then stirred while the mixture was stirred.
At least one compound selected from the group consisting of formaldehyde, paraformaldehyde and trioxane in an amount of 1.0 to 2.0 mole times as much as formaldehyde with respect to M is additionally fed, and the reaction mixture is heated to 95 to 100 ° C. Perform the reaction for 0.5-2 hours. Thereafter, the reaction mixture is heated to about 140 ° C. to 160 ° C. to concentrate the N-methyl-TAAM in the mixture.

The target N-methyl-TAAM can be isolated and purified from the reaction mixture or the concentrated reaction mixture (hereinafter referred to as a crude product) by distillation, crystallization, or the like. Prior to an operation such as distillation or crystallization, an organic solvent that is hardly miscible with water may be added to the crude product to transfer N-methyl TAAM to the organic solvent phase. Such organic solvents include benzene, toluene,
Aromatic hydrocarbon solvents such as xylene, n-hexane, n-
Examples thereof include aliphatic or alicyclic hydrocarbons such as heptane, cyclohexane and cycloheptane, and ethers.

Further, after the crude product, preferably the crude product, is transferred to an organic solvent phase, a base is added thereto to form an excess of formaldehyde and formic acid (including formate of N-methyl-TAAM produced by the reaction. ) Is neutralized and the aqueous layer is separated and removed, followed by distillation or crystallization. The neutralized aqueous layer may be recycled to the neutralization step again. Examples of the base include sodium hydroxide, potassium hydroxide, ammonia and the like.

The distillation is carried out, for example, at atmospheric pressure to a pressure of 2.7 Kpa and at a temperature of 100 to 150 ° C. Examples of the crystallization solvent include aromatic hydrocarbon solvents such as benzene, toluene, and xylene; aliphatic and alicyclic hydrocarbons such as n-hexane, n-heptane, cyclohexane, and cycloheptane; and ethers.

After crystallization, the crystals are filtered and dried to obtain the desired N-methyl-TAAM crystals. It is also possible to recycle the crystallization mother liquor and add it to the crude product.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION

[0019]

【Example】

Example 1 An 80% aqueous solution of TAAM and 37% formalin were charged in a reaction vessel. The mixture was heated to 100 ° C. and reacted under the conditions shown in Table 1 below. Table 1 shows the results.

[0020]

[Table 1]

Example 2 80% TAAM aqueous solution and 3%
7% formalin was charged into a reaction vessel equipped with a packed tower (10 × 1 cmφ). After heating and dissolving the mixture at 90 ° C., 9
The temperature was raised to 8 ° C. (reflux temperature), and the reaction was carried out at atmospheric pressure for 1 hour. Then, in 2 hours, the reaction mixture was heated to 140 ° C. and concentrated. Table 2 shows the results.

[0022]

[Table 2]

Example 3 An 80% aqueous solution of TAAM (T
AAM 1.0 mol) and 37% formalin HCHO
1.0 mol) in a reaction vessel equipped with a packed tower (10 × 1 cmφ), and the mixture was heated and dissolved at 70 ° C. 98 ℃
(Reflux temperature) and then 37% formalin (HC
(HO 1.3 mol) was fed over 1 hour, and the reaction was further performed at atmospheric pressure for 2 hours. Then, in 1 hour, the reaction mixture was heated to 140 ° C. and concentrated. N-methyl-TAAM
The yield was 99 mol%. Reference Example 1 An 80% aqueous solution of TAAM, 37% formalin, and formic acid were combined with TAAM: HCHO: HCOOH = 1:
The mixture was charged into a reaction vessel at 2: 1 (molar ratio), and the mixture was heated and reacted at 100 ° C. and atmospheric pressure for 8 hours. T
The AAM conversion was 99 mol%, the N-methyl-TAAM selectivity was 99 mol%, and the N-methyl-TAAM yield was 98 mol%.

[0024]

According to the present invention, TAAM is converted to N- with formaldehyde.
Conventionally, it has been considered that the reaction for synthesizing N-methyl-TAAM by methylation requires the use of formic acid in an equivalent amount or more. The desired product can be obtained with high yield and high selectivity.

Claims (4)

[Claims] 1. A method according to claim 1, wherein 4-hydroxy-2,2,6,6-tetramethylpiperidine is combined with at least one compound selected from the group consisting of formaldehyde, paraformaldehyde and trioxane, and 4-hydroxy-2,2,2.
4-hydroxy-1,2,2,6,6, wherein methylation reaction is carried out by adding formic acid in an amount of 0 to less than 1 mole relative to 6,6-tetramethylpiperidine.
-A method for producing pentamethylpiperidine. 2. The amount of formic acid added is 4-hydroxy-2,
0 to 0,2 with respect to 2,6,6-tetramethylpiperidine.
The method according to claim 1, wherein the molar ratio is 5 times. 3. The amount of at least one compound selected from the group consisting of formaldehyde, paraformaldehyde and trioxane is 4-hydroxy-2,2,2
2. The method according to claim 1, wherein the amount is 1 to 4 mol times as much as 6,6-tetramethylpiperidine in terms of formaldehyde. 4. The method according to claim 1, wherein no formic acid is added.