JP5194692B2 - Process for producing N, N-dimethylcyclohexylamine - Google Patents

Description

  The present invention relates to a method for producing N, N-dimethylcyclohexylamine.

  N, N-dimethylcyclohexylamine is a useful compound as a catalyst for polyurethane foam production, an epoxy curing agent, a resist remover, a corrosion inhibitor for steel, and the like.

  Conventionally, as a method for producing N, N-dimethylcyclohexylamine using aniline as a raw material, aniline is first hydrogenated to form cyclohexylamine (see, for example, Patent Documents 1 and 2), and then the obtained cyclohexylamine is used. A production method by reductive methylation is generally known (see, for example, Patent Documents 3 and 4).

  However, in order to obtain cyclohexylamine as an intermediate, nuclear hydrogenation of aniline under high-temperature and high-pressure conditions is required, and advanced techniques and equipment are required. Therefore, a simpler industrial production method is required. It has been.

  On the other hand, it is known that an aromatic amine compound can be reductively methylated under mild conditions with a palladium catalyst (see, for example, Non-Patent Document 1). It is also known that N, N-dimethylaniline can be nuclear hydrogenated to N, N-dimethylcyclohexylamine under mild conditions (see, for example, Patent Document 5).

  In this case, N, N-dimethylaniline is prepared by reductive methylation of aniline with formaldehyde derivatives such as formaldehyde or paraformaldehyde, a reduction catalyst and hydrogen, but the resulting crude N, N-dimethylaniline is isolated. There is no known example of performing a nuclear hydrogenation reaction without purification, that is, with a reductive methylation reaction solution of aniline. For example, also in the method described in Patent Document 5, isolated and purified N, N-dimethylaniline is used in the actual nuclear hydrogenation reaction.

  As a factor that makes it difficult to carry out the nuclear hydrogenation reaction continuously from the crude N, N-dimethylaniline, it is considered that unreacted formaldehyde remains in the crude N, N-dimethylaniline. In general, it is known that excessive formaldehyde reduces the activity of the catalyst even during the reductive methylation reaction (see, for example, Patent Document 6 and Non-Patent Document 1).

Japanese Patent Laid-Open No. 10-72377 JP-A-10-101484 Japanese Patent No. 60-130551 JP-A-62-10047 German Patent No. 297399 JP 52-71424 A A. P. Bonds, H.M. Greenfield, W.M. E. Pascoe (Ed) "Catalysis of Organic Reactions" Dekker, New York, 1992, p. 65

  The present invention has been made in view of the above-mentioned background art, and the object thereof is to continuously carry out a nuclear hydrogenation reaction without isolating and purifying crude N, N-dimethylaniline containing formaldehyde. It is to provide a process for the production of N, N-dimethylcyclohexylamine under mild conditions which is economically advantageous.

  As a result of intensive studies to solve the above-mentioned problems, the present inventors have heated the resulting reaction liquid at a temperature of 180 ° C. or higher when carrying out a nuclear hydrogenation reaction of crude N, N-dimethylaniline containing formaldehyde. By the treatment, it was found that the crude hydrogenation reaction can be carried out continuously without isolating and purifying crude N, N-dimethylaniline, and the present invention has been completed.

  That is, the present invention is a method for producing N, N-dimethylcyclohexylamine as shown below.

  [1] Crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities is heated at a temperature of 180 ° C. or higher, and then subjected to a nuclear hydrogenation reaction in the presence of a reduction catalyst and hydrogen. To produce N, N-dimethylcyclohexylamine.

  [2] The above-mentioned [1], wherein crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities is a reaction liquid obtained by reacting a formaldehyde derivative and aniline in the presence of a reduction catalyst and hydrogen. ] The manufacturing method of N, N- dimethylcyclohexylamine as described in any one of.

  The term “reductive methylation (reaction)” used in the present invention means a method of condensing a carbonyl compound with ammonia or an amine and reducing the resulting imine or iminium ion with a reducing agent to obtain amines. (Refer to “4th edition Experimental Chemistry Lecture 20 Organic Synthesis II” p. 302-303 (edited by the Chemical Society of Japan, Maruzen, 1992)), specifically, reducing formaldehyde and aniline such as formaldehyde and paraformaldehyde. The reaction is carried out in the presence of a catalyst and hydrogen and the amino group of aniline is reductively methylated to give N, N-dimethylaniline.

  According to the present invention, when a crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities obtained by reductive methylation reaction of aniline is subjected to a nuclear hydrogenation reaction, a temperature of 180 ° C. or higher. By carrying out the heat treatment with, a nuclear hydrogenation reaction can be carried out continuously without isolating and purifying crude N, N-dimethylaniline.

  The method of the present invention is extremely useful industrially because it can be carried out under mild conditions which are economically advantageous without a problem of a decrease in catalyst activity.

  The present invention is described in detail below.

  In the present invention, crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities is heated at a temperature of 180 ° C. or higher, and then subjected to nuclear hydrogenation in the presence of a reduction catalyst and hydrogen. It is characterized by reacting.

  In the present invention, as crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities, reduced methyl aniline obtained by reacting a formaldehyde derivative and aniline in the presence of a reduction catalyst and hydrogen. The reaction solution can be used.

  In the present invention, the amount of formaldehyde used in the reductive methylation reaction of aniline is generally a theoretical amount (see, for example, Patent Document 6). However, even when an approximately equivalent amount of formaldehyde is used, the reaction is performed after the reductive methylation reaction. A small amount of formaldehyde may remain in the liquid. In the present invention, the content of formaldehyde in the reductive methylation reaction solution of aniline is not particularly limited. However, if it is too much, a formalin-derived polymerization impurity is produced as a by-product by heat treatment, and the target product is isolated. Since it is considered that a great burden is required, it is preferably 1000 ppm or less, and more preferably 350 ppm or less.

  In the present invention, crude N, N-dimethylaniline containing formaldehyde and N, N-dimethylcyclohexylamine as impurities is heat-treated at a temperature of 180 ° C. or higher. The upper limit of the heat treatment temperature is not particularly limited, but the effect of the present invention can be sufficiently achieved if it is carried out in a range of 250 ° C. or lower where steam heating is industrially possible. Further, the heat treatment time is not particularly limited, but if it is carried out for 30 minutes or longer, the effect of the present invention is sufficiently achieved, and a long-time heat treatment is not necessary.

  In the present invention, the nuclear hydrogenation reaction of N, N-dimethylaniline can be carried out using the reaction solution as it is after the reductive methylation reaction solution of aniline is heated at a temperature of 180 ° C. or higher. As the solvent used for the above, the solvent for the reductive methylation reaction can be used as it is. Specific examples of such a solvent include aliphatic alcohols such as methanol, ethanol, 1-propyl alcohol, isopropyl alcohol, 1-butanol, 2-butanol and tert-butanol, ethers such as tetrahydrofuran and dioxane, Aprotic polar solvents such as N, N-dimethylformaldehyde, N, N-dimethylacetaldehyde, dimethyl sulfoxide, 1,3-dimethyl-2-imidazolidinone and the like can be used. These solvents may be used alone or in combination. Of these, aliphatic alcohols are particularly preferable as a reaction solvent from the viewpoint of economy and operability.

  In the present invention, examples of the reduction catalyst used in the nuclear hydrogenation reaction include a catalyst for nuclear hydrogenation of aromatic compounds such as rhodium, ruthenium, platinum, palladium, nickel, and the like. A palladium catalyst supported on activated carbon, which can be used for the reaction and is economical, is particularly preferred.

  The amount of the reduction catalyst used is preferably 0.5% by weight or more, more preferably 5% by weight or more, based on the amount of N, N-dimethylaniline which is a substrate. However, even if the catalyst exceeds 10% by weight, no special effect is observed, which is disadvantageous economically.

  The hydrogenation reaction temperature is in the range of 60 ° C to 180 ° C, preferably 120 ° C to 160 ° C. The reaction pressure is 0.4 MPa or more, preferably 0.8 MPa or more.

  In the present invention, a crude N, N-dimethylaniline reaction liquid containing formaldehyde and N, N-dimethylcyclohexylamine as impurities is heat-treated at a temperature of 180 ° C. or higher, and then a new reduction catalyst is added. Then, the nuclear hydrogenation reaction can be carried out under hydrogen pressure conditions without any special treatment. Alternatively, the crude N, N-dimethylaniline reaction solution heat-treated at a temperature of 180 ° C. or higher is transferred to a container containing a new reduction catalyst, so that it can continue to be nucleated under hydrogen pressure conditions without any special treatment. Hydrogenation reaction can be performed.

  The details of the present invention will be described below with reference to examples, but they do not limit the present invention. The product and the yield in this example were confirmed by gas chromatography. The concentration of formaldehyde contained in the reductive methylation reaction solution of aniline was measured by quantitative analysis using a gas chromatograph mass spectrometer-selected ion monitor method (GCMS-SIM).

  Gas chromatography: (GC-17A manufactured by Shimadzu Corporation, measurement condition capillary column (DB-5 manufactured by J & WS Science), temperature rise, detector FID).

  GCMS-SIM: (GC-MSJMS-K9, manufactured by JEOL Ltd., measurement conditions, capillary column (DB-5, manufactured by J & WS Science), temperature increase).

  First, an example of a reductive methylation reaction from aniline of N, N-dimethylaniline as a reaction raw material will be shown.

Preparation Example 1:
A 1000 mL autoclave equipped with a stirrer was charged with 130.0 g (1.40 mol) of aniline, 226.2 g of methanol, and 13.0 g of a palladium catalyst in which 5 wt% of palladium was supported on activated carbon (manufactured by Degussa, 57% water-containing product). The autoclave was sealed, and after nitrogen substitution and hydrogen substitution, the hydrogen pressure was increased to 0.5 MPa, and the temperature was increased to 150 ° C. under stirring conditions. Under the condition of hydrogen pressure of about 0.9 MPa, 226.2 g of 37 wt% formaldehyde aqueous solution (2.79 mol, industrial chemical JIS K 1502 standard product, product containing 6.0 wt% of methanol is considered to contain methanol adduct in the autoclave. ) Was fed with a pump over 10 hours, and further heated and stirred for 3 hours. As a result, hydrogen absorption disappeared, and the reaction was terminated. After cooling and depressurization, the reaction solution was filtered to remove the palladium catalyst.

  As a result of performing gas chromatography analysis on the obtained reaction solution, it was confirmed that N, N-dimethylaniline was obtained in a yield of 85% and N, N-dimethylcyclohexylamine was obtained in a yield of 5%. The formaldehyde concentration in the reaction solution was 350 ppm as a result of GCMS-SIM analysis.

  Next, an example of a nuclear hydrogenation reaction using the obtained crude N, N-dimethylaniline is shown.

Example 1:
In a 200 mL autoclave equipped with a stirrer, 80.0 g of a reaction solution obtained according to the method described in Preparation Example 1 (11.0 g of N, N-dimethylaniline, 0.6 g of N, N-dimethylcyclohexylamine, and formaldehyde) 28 mg each) was heat treated at 180 ° C. for 1 hour and then cooled to room temperature.

  Next, 3.0 g of palladium catalyst (57% water-containing product, manufactured by Degussa) in which 5 wt% of palladium was supported on activated carbon was charged into the obtained reaction solution. The autoclave was sealed, and after nitrogen substitution and hydrogen substitution, the hydrogen pressure was increased to 0.4 MPa, and the temperature was increased to 150 ° C. under stirring conditions. When the reaction was terminated by heating and stirring for 5 hours in a sealed state under hydrogen pressure, the reaction was terminated because hydrogen absorption disappeared. After cooling and depressurization, the reaction solution was filtered to remove the palladium catalyst.

  As a result of performing gas chromatography analysis on the obtained reaction solution, it was confirmed that N, N-dimethylaniline was 3% recovered and that N, N-dimethylcyclohexylamine was obtained in a yield of 80%.

Example 2:
In a 200 mL autoclave equipped with a stirrer, 80.0 g of a reaction solution obtained according to the method described in Preparation Example 1 (11.0 g of N, N-dimethylaniline, 0.6 g of N, N-dimethylcyclohexylamine, and formaldehyde) 28 mg each) was heat treated at 200 ° C. for 0.5 hour, and then cooled to room temperature.

  Next, 3.0 g of palladium catalyst (57% water-containing product, manufactured by Degussa) in which 5 wt% of palladium was supported on activated carbon was charged into the obtained reaction solution. The autoclave was sealed, and after nitrogen substitution and hydrogen substitution, the hydrogen pressure was increased to 0.4 MPa, and the temperature was increased to 150 ° C. under stirring conditions. When the reaction was terminated by heating and stirring for 5 hours in a sealed state under hydrogen pressure, the reaction was terminated because hydrogen absorption disappeared. After cooling and depressurization, the reaction solution was filtered to remove the palladium catalyst.

  As a result of conducting gas chromatography analysis on the obtained reaction liquid, it was confirmed that N, N-dimethylaniline was not observed and N, N-dimethylcyclohexylamine was obtained in a yield of 81%.

Comparative Example 1:
In a 200 mL autoclave equipped with a stirrer, in the same manner as in Example 1, 80.0 g of the reaction solution obtained according to the method described in Preparation Example 1 (11.0 g of N, N-dimethylaniline, N, N-dimethylcyclohexyl) Each of them was heated at 160 ° C. for 2 hours and then cooled to room temperature.

  Next, 3.0 g of palladium catalyst (57% water-containing product, manufactured by Degussa) in which 5 wt% of palladium was supported on activated carbon was charged into the obtained reaction solution. The autoclave was sealed, and after nitrogen substitution and hydrogen substitution, the hydrogen pressure was increased to 0.4 MPa, and the temperature was increased to 150 ° C. under stirring conditions. The reaction was carried out by heating and stirring for 3 hours under hydrogen pressure in a sealed state, but no hydrogen absorption was observed, so the reaction was terminated. After cooling and depressurization, the reaction solution was filtered to remove the palladium catalyst.

  As a result of performing gas chromatography analysis on the obtained reaction solution, 100% of N, N-dimethylaniline was recovered, and no increase in the amount of N, N-dimethylcyclohexylamine was observed.

Claims (2)

The reaction of the formaldehyde derivative and aniline in the presence of a reduction catalyst and hydrogen is removed from the reaction solution obtained in step (1) and step (1), and formaldehyde and N, N-dimethylcyclohexylamine are contained as impurities. Step (2) for obtaining crude N, N-dimethylaniline, and the heat treatment of crude N, N-dimethylaniline obtained in step (2) at a temperature of 180 ° C. or higher, followed by the presence of a reduction catalyst and hydrogen A process for producing N, N-dimethylcyclohexylamine, which comprises a step (3) of nuclear hydrogenation reaction below. The method for producing N, N-dimethylcyclohexylamine according to claim 1, wherein the reduction catalyst is a palladium catalyst supported on activated carbon.