JPH0971555A - Production of 4-methoxy-2,2',6'-trimethyldiphenylamine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain 4-methoxy-2,2',6'-trimethyldiphenylamine useful as an intermediate of a color former using to thermosensitive recording paper, etc., at a high yield and high selectivity in an industrial scale by specifying stirring power. SOLUTION: The objective 4-methoxy-2,2',6'-trimethyldiphenylamine is obtained by heat-reacting 2,6-dimethylcyclohexanone with 2-methyl-4- methoxyaniline in the presence of a dehydrogenation catalyst such as Raney nickel at 2.1-10kw/m<3> stirring power per unit volume with discharging generated hydrogen and water outside the reaction system.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an industrially improved 4-methoxy-2,2 ′, 6′-trimethyldiphenylamine useful as an intermediate for producing a color former for heat-sensitive recording paper and pressure-sensitive recording paper. Manufacturing method.

[0002]

2. Description of the Related Art The inventors of the present invention have proposed a method for producing 4-methoxy-2,2 ', 6'-trimethyldiphenylamine (hereinafter abbreviated as DMDPA) as 2,6-dimethylcyclohexanone. And a method of reacting 2-methyl-4-methoxyaniline with each other (Japanese Patent Application Laid-Open No. 60-192949) to propose a method for selecting 4-methoxy-2,2 ′, 6′-trimethyldiphenylamine. Since there are drawbacks such as poor efficiency, we proposed an improved method in which the selectivity is improved by reacting while releasing the generated hydrogen and water to the outside of the reaction system (Japanese Patent Application No. H6-6
-27880).

However, when a scale-up study was conducted to industrialize this method, the expected DMDPA selectivity could not be obtained. The reduction in the selectivity not only lowers the yield of DMDPA, but also lowers the purity of DMDPA, which may lead to a reduction in the quality of the color developing agent for the final heat-sensitive recording paper and pressure-sensitive recording paper.

In particular, the major by-product 4-methoxy-2,
The boiling point of 2'-dimethyldiphenylaniline (hereinafter abbreviated as K form) is similar to that of DMDPA, and D
Since it is difficult to separate it from MDPA, the K-form is directly produced by DM.
This leads to a deterioration in the quality of DPA. Therefore, it is necessary to establish means for dealing with the expected reduction in selectivity when industrialized.

[0005]

Means for Solving the Problems The inventors of the present invention studied the scale-up of the method of Japanese Patent Application No. 6-27880 previously proposed, found that the effect of stirring was great, and completed the present invention. .

That is, according to the present invention, in the presence of a dehydrogenation catalyst,
In the method for producing DMDPA, which is carried out by heating while releasing hydrogen and water generating 6-dimethylcyclohexanone and 2-methyl-4-methoxyaniline to the outside of the reaction system,
The method is characterized in that the reaction is carried out at a stirring power of 2.1 to 10 kw / m ³ per unit volume.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The method of the present invention is carried out in the presence of an acid catalyst, 2
-Methyl-4-methoxyaniline and 2,6-dimethylcyclohexanone were dehydrated to produce an intermediate Schiff base, which was subsequently catalytically dehydrogenated with a dehydrogenation catalyst to produce it. The target product, 4-methoxy-2,2 ', 6'-trimethyldiphenylamine, is obtained by releasing hydrogen together with water, which is a by-product during the formation of the Schiff base, out of the reaction system.

The 2,6-dimethylcyclohexanone used in the process of the present invention is 2,6-dimethylcyclohexanone using a known hydrogenation catalyst.
It can be easily produced by hydrogenating dimethylphenol.

The 2-methyl-4-methoxyaniline used in the present invention can be easily produced by hydrogenating o-nitrotoluene under acidic conditions with methanol as a solvent using a known hydrogenation catalyst.

Regarding the molar ratio of 2,6-dimethylcyclohexanone and 2-methyl-4-methoxyaniline used in the method of the present invention, the molar ratio of 2,6-dimethylcyclohexanone and 2-methyl-4-methoxyaniline is 2:
It may be between 1 and 1: 2, but is preferably between 2: 1 and
The ratio is preferably 1: 1, more preferably 1.1: 1 to 1.5: 1, and a ratio lower than 1: 1 or higher is not preferable because the selectivity is lowered.

The catalyst used in the process of the invention is
Usually, suitable hydrogenation reduction reaction catalysts are also suitable for the dehydrogenation reaction, and thus these hydrogenation reduction reaction catalysts are used. Specifically, Raney nickel, reduced nickel or nickel-supported catalyst, Raney cobalt, reduced cobalt or cobalt-supported catalyst, Raney copper, reduced copper or copper-supported catalyst, noble metal catalyst of Group 8 of the Periodic Table or its noble metal as a carrier, Examples include catalysts supported on carbon, alumina, barium carbonate, rhenium catalysts such as rhenium-carbon, and copper-chromium oxide catalysts. Of these catalysts, palladium is preferable, and a palladium-supported catalyst supported on a carrier such as carbon, alumina and magnesia is particularly preferable. The amount used is 2-methyl-4-methoxyaniline 1
It is usually 0.001 to 0.
2 grams atom, preferably 0.004 to 0.1 grams atom.

In the method of the present invention, it is preferable to add an organic amine compound, an alkali metal compound or an alkaline earth metal compound as a cocatalyst. As the organic amine compound,
Examples include diethylenetriamine, pentamethyldiethylenetriamine, tributylamine, diamylamine, triamylamine, tetraethylenepentamine, triethanolamine, aminoethylethanolamine, and among them, pentamethyldiethylenetriamine is preferable. As the alkali metal compound and the alkaline earth metal compound, alkali metal, hydroxides, carbonates, bicarbonates and the like of the alkaline earth metal can be used. Specific examples include lithium hydroxide, sodium hydroxide, sodium hydroxide, calcium hydroxide, magnesium hydroxide, sodium carbonate, potassium carbonate, sodium hydrogen carbonate, and the like, among which sodium hydroxide and potassium hydroxide are preferred. .
These cocatalysts are used alone or in combination of two or more. These cocatalysts may be added to the reaction system separately from the dehydrogenation catalyst, or a catalyst prepared by additionally supporting from a solution after producing a noble metal-supported catalyst may be used.
The amount of the co-catalyst used may be 2% by weight or more, preferably 5 to 150% by weight, based on the catalyst metal. If it is more than this, the reaction rate tends to decrease, and conversely, if it is less, the yield tends to deteriorate. In particular, these bases are 2
-The effect of suppressing the deammonification reaction of methyl-4-methoxyaniline is recognized.

In the method of the present invention, the charging method of 2-methyl-4-methoxyaniline may be either batch charging or drop charging, but there is no particular problem, but drop charging is preferable, and high charging is possible by dropping. Selectivity, high yield of 4-methoxy-2,
2 ', 6'-Trimethyldiphenylamine is obtained.
In that case, it is advantageous to add dropwise as a mixed solution with 2,6-dimethylcyclohexanone from the viewpoint of yield and operability.

The reaction temperature is usually 150 to 300 ° C., preferably 180 to 250 ° C. If it is less than this, the reaction rate becomes slow, and if it is more than this, the selectivity becomes poor, which is not preferable.

In the method of the present invention, the reaction pressure is not particularly limited, but it is preferably atmospheric pressure to 4.0 kg / cm ² G. When the reaction pressure is higher than this, the selectivity of the product decreases,
Not preferred. Under pressure, the reaction pressure may be a gas that is inert to the reaction, or may be the vapor pressure of the substrate or solvent.

The reaction solvent used in the method of the present invention is not particularly limited as long as it is a solvent known in the art, but if 2,6-dimethylphenol is used, a part thereof is converted to 2,6-dimethylcyclohexanone. It is particularly preferable because it can be used as it is in the method of the present invention as a 2,6-dimethylphenol solution of 2,6-dimethylcyclohexanone after conversion.

In the method of the present invention, the water produced during the dehydration reaction has a high dehydration rate when the produced water is removed from the reaction system using a non-aqueous azeotropic dehydrating agent such as benzene or toluene, and the water yield is high. The desired product can be obtained at a rate, which is preferable. At that time, the water content in the system may be set to 1% or less, but it is possible to obtain the target product in a high yield by performing the reaction while keeping it at 0.3% or less, particularly preferably 0.1% or less. it can.

In the method of the present invention, the present invention exerts its effect even if an acid is not used as a catalyst for the dehydration reaction, so that there is no particular problem. However, use of an acid is preferable because the dehydration rate increases. Specific examples of the acid catalyst include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid and phosphoric acid, acetic acid, phenylacetic acid, trifluoroacetic acid, propionic acid, butyric acid, octylic acid, lauric acid, formic acid, benzoic acid and their nuclear substitution products. , Phenylsulfonic acid and its nuclear substitutes, oxalic acid, phthalic acid (o
-, M-, p-), trimellitic acid, pyromellitic acid, and other organic acids are mentioned, but not limited thereto. Organic acids such as benzoic acid, octylic acid, trifluoroacetic acid, phthalic acid and pyromellitic acid are preferred.
The amount used is 0.5 to 20% by weight, preferably 1 to 10% by weight, based on 4-methoxy-2-methylaniline.

The produced 4-methoxy-2,2 ', 6'-
Trimethyldiphenylamine can be obtained by treating the mixture after the reaction according to a conventional method such as distillation, crystallization and extraction. For example, the reaction completed liquid is filtered to separate and recover the catalyst. This recovered catalyst can be reused. The filtrate is concentrated and the solvent is recovered. The solvent is returned to the reaction system as it is. 4-Methoxy-2,2 ', 6'-trimethyldiphenylamine in the kettle is purified and separated by distillation, crystallization and the like.

In the present invention, the stirring power is 2.1 to 10.
kw / m ³ may be used, but preferably 3.1 to 10 kw
/ M ³ , more preferably 6.0 to 10 kw / m ³ to obtain the desired product in a high yield.

The influence of stirring in the present invention is presumed as follows. When the stirring power is less than 2.1 kw / m ³ , the release rate of hydrogen and water generated during the reaction to the outside of the system becomes slow, and the generated hydrogen is retained in the reaction system. This hydrogen catalytically hydrogenates the Schiff bases of the intermediate 2,6-dimethylcyclohexanone and 2-methyl-4-methoxyaniline to form a by-product other than the intended product, and as a result, DMDPA selection The rate will decrease. That is, the stirring power is 2.1 kw / so that the produced hydrogen and water are quickly released to the outside of the reaction system.
It was necessary to raise it to m ³ or more. The larger the stirring power is, the higher the effect is. However, if it exceeds 10 kw / m ³ , the difference in the effect is small and it is not preferable from the economical aspect.

[0022]

EXAMPLES The method of the present invention will be specifically described below with reference to Examples and Comparative Examples. Example 1 Dewatering rectification column 2, condenser 3, liquid separating tank 4, and pressure adjusting valve 5
A 200 liter reactor 1 made of stainless steel equipped with was prepared as a reactor. The vapor generated in the reactor 1 is condensed in the condenser 3 via the dehydration rectification column 2 and received in the liquid separation tank 4, and then a part of the separated upper layer is returned to the reactor 1. There is. Further, in order to keep the pressure in the reaction system constant, a pressure adjusting valve 5 is attached to the upper part of the liquid separation tank. 2,6-dimethylphenol 44.0k was previously added to this reactor 1.
g, 0.48 kg of isophthalic acid, 5% Pd / C (water content 50% by weight) made by Japan NE Chemcat Ltd. 5.2
7 kg and 8.0 kg of toluene were charged, and the separating tank (50 liters) 4 was charged up to a pipe 7 for returning toluene to the reactor. The gas phase in the system was replaced with nitrogen and the internal pressure was 1.0 kg /
After setting to cm ² G, stirring 350 rpm (stirring power 2.1.
kw / m ³ ) and the temperature was gradually raised. Pressure 1.0kg
/ Cm ² G, the boiling point of the reaction solution was 200 ° C. 20
Raise the temperature of the reaction solution to 0 ° C and increase the pressure to 1.0 kg / cm ^2.
While keeping the temperature at G, 4-methoxy-2-
Methylaniline 32.9 kg (0.24 mol), 2,
6-Dimethylcyclohexanone 37.0 kg (0.26
(mol) mixed solution was added dropwise over 15 hours. The steam generated when 4-methoxy-2-methylaniline is added dropwise starts to distill with toluene from the dehydration rectification column 2,
After being cooled in the condenser 3, the toluene and water were separated in the separation tank 4. In the liquid separation tank 4, water is stored in the lower layer side and toluene is stored in the upper layer side, and part of the upper layer toluene overflows from the liquid separation tank 4 and returns to the reactor 1. The hydrogen generated at the same time was continuously discharged to the outside of the reaction system using the pressure control valve 5 so that the internal pressure was maintained at 1.0 kg / cm ² G. After completion of dropping, stirring was continued for 2 hours while maintaining this temperature and internal pressure. Next, the reactor 1 is cooled, and the reaction mixture is 5%
Pd / C was filtered off. A part of the filtrate was collected and analyzed by gas chromatography to find that 4-methoxy-2-
The conversion of methylaniline was 100%, the selectivity of DMDPA was 90.0%, and the selectivity of K-form was 1.7%.

Example 2 Reaction and treatment were carried out in the same manner as in Example 1 with stirring at 400 rpm (stirring power 3.1 kw / m ³ ). When analyzed in the same manner as in Example 1, the selectivity of DMDPA was 93.0% and the selectivity of K-form was a trace amount.

Example 3 The reaction and treatment were carried out in the same manner as in Example 1 with stirring at 500 rpm (stirring power 6.0 kw / m ³ ). When analyzed in the same manner as in Example 1, the selectivity of DMDPA was 95.0%, and the selectivity of K-form was a trace amount.

Comparative Example 1 Reaction and treatment were carried out in the same manner as in Example 1 with stirring at 300 rpm (stirring power 1.3 kw / m ³ ). When analyzed in the same manner as in Example 1, the selectivity of DMDPA was 85.0% and the selectivity of K-form was 6.8%.

Comparative Example 2 Reaction and treatment were carried out in the same manner as in Example 1 with stirring at 250 rpm (stirring power 0.8 kw / m ³ ). When analyzed in the same manner as in Example 1, the selectivity of DMDPA was 79.0% and the selectivity of K-form was 11.6%. The results of these Examples and Comparative Examples are shown in Table 1.

[0027]

[Table 1]

[0028]

According to the present invention, 4-methoxy-2, on an industrial scale, which was not achieved by the prior art,
The production of 2 ', 6'-trimethyldiphenylamine in a high yield and a high selectivity can be carried out, and the significance of the present invention is great.

[Brief description of drawings]

FIG. 1 is a schematic view of equipment for carrying out the present invention.

[Explanation of symbols]

 1. Reactor 2. Dewatering rectification tower 3. Condenser 4. Separation tank 5. Pressure control valve 6. Drip tank 7. Toluene return pipe

Claims (1)

[Claims] 1. 4-methoxy which reacts with heating in the presence of a dehydrogenation catalyst while releasing hydrogen and water generating 2,6-dimethylcyclohexanone and 2-methyl-4-methoxyaniline to the outside of the reaction system. In the method for producing -2,2 ', 6'-trimethyldiphenylamine, 4-methoxy-2,2', 6 is characterized in that the reaction is carried out at a stirring power per unit volume of 2.1 to 10 kw / m ^3. Method for producing'-trimethyldiphenylamine.