JP2000095742A - Production of acetamide - Google Patents

Abstract

PROBLEM TO BE SOLVED: To readily obtain a highly purified acetamide by treating an aqueous solution of acetamide obtained by hydrating acetonitrile with a cation exchange resin. SOLUTION: This anhydrous, highly purified acetamide is obtained by treating (B) an aqueous solution of acetamide obtained by hydrating (A) acetonitrile, preferably in the presence of a copper-based catalyst (e.g. Raney copper) by bringing into contact with (C) a cation exchange resin (e.g. a porous type and strong acidic or weak acidic cation exchange resin) Diaion PK-208(R)}, preferably in a continuous method and at a line velocity of 0.5-10 m/hr at 0-50 deg.C, and distilling the resultant acetonitrile preferably at 80-150 deg.C to separate from water.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for producing acetamide useful as a raw material for pharmaceuticals and organic synthesis by hydrating acetonitrile, and more particularly to a method for producing high-purity acetamide.

[0002]

2. Description of the Related Art There are known industrial methods for producing acetamide, such as a method in which acetic acid and ammonia are reacted to synthesize an ammonium acetate salt and dehydrated, and a method in which acetonitrile is hydrated for production. I have. In particular, the latter method is known to have high acetamide selectivity,
For example, JP-A-5-255214 discloses a method using a Raney copper catalyst, and JP-A-8-59583 discloses a method using a catalyst comprising a cluster complex of an organometallic compound containing a Group 8 metal element and vanadium oxide. Methods have been disclosed.

[0003] In recent years, however, there has been an increasing demand for higher purification of acetamide, and there has been a demand for a method of purifying acetamide that can remove by-products contained in the produced acetamide. As a method for purifying acetamide,
For example, a method using a tower-type continuous crystallizer as described in JP-A-9-227476, a method combining a distillation method and a recrystallization method, and the like are known. There is a problem that the method is very complicated, and there has been a demand for a method capable of producing higher-purity acetamide by a simple operation.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing high-purity acetamide by a simple operation without using a special crystallizer or complicated purification operations.

[0005]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, when producing acetamide from acetonitrile, an aqueous solution of acetamide obtained by hydrating acetonitrile is treated with a cation exchange resin. It has been found that high-purity acetamide can be produced by a simple operation by the treatment, and the present invention has been completed. That is, the present invention relates to a method for producing high-purity acetamide, comprising treating an aqueous solution of acetamide obtained by hydrating acetonitrile with a cation exchange resin.

Hereinafter, the present invention will be described in more detail. The high-purity acetamide produced by the production method of the present invention is an acetamide having a very small content of organic substances such as acetic acid and inorganic impurities such as copper and iron. As acetonitrile as a starting material of the present invention, acetonitrile by-produced by ammoxidation reaction of propane, propylene or isobutylene in the presence of a catalyst can be used. This acetonitrile can be used as it is for the hydration reaction, but this acetonitrile contains trace impurities such as acrylic acid, acetic acid, and hydrocyanic acid and unsaturated substances. Since it causes deterioration of the hydration catalyst, the acetonitrile is converted to an alkali metal oxide or hydroxide or an aqueous solution thereof,
It is preferable to use it for a hydration reaction after removing the acidic substance and the unsaturated substance by contacting with an alkaline earth metal oxide or hydroxide or an aqueous solution thereof or a base substance such as an anion exchange resin.

Further, oxygen is dissolved in acetonitrile and water used in the reaction, and this oxygen causes deterioration of the hydration catalyst of acetonitrile. Therefore, it is preferable that the dissolved oxygen in acetonitrile and water is made substantially zero by an operation such as blowing in an inert gas such as nitrogen, and then supplied to the reactor. The concentration of acetonitrile supplied to the reactor is not particularly limited, but is in the range of 5 to 70% by weight, preferably 10 to 50% by weight from the viewpoint of productivity and efficiency.

The hydration catalyst for converting acetonitrile to acetamide used in this reaction includes a copper catalyst,
Examples of the catalyst include a ruthenium catalyst, a platinum catalyst, and a catalyst comprising a cluster complex of an organometallic compound containing a Group 8 metal element and vanadium oxide described in JP-A-8-59583, and a copper-based catalyst is preferable. As a copper-based catalyst,
Reduced copper, copper oxide, and copper hydroxide obtained by reducing metallic copper such as copper powder and copper wire, copper oxide, copper hydroxide, and copper compounds such as copper salts at 100 to 400 ° C. with hydrogen, carbon monoxide, and the like. Copper, copper oxide, copper hydroxide or copper obtained by reducing a copper compound such as copper or copper salt in a liquid phase using a reducing agent such as hydrazine, an alkali metal or alkaline earth metal borohydride, formalin, acetaldehyde, etc. Zinc, aluminum, copper compounds such as salts in the liquid phase
Reduced copper obtained by treating with a metal having a greater ionization tendency than copper such as iron and tin, Raney copper formed by developing a Raney alloy composed of copper with aluminum, zinc, magnesium and the like in an alkaline aqueous solution, copper formate and oxalic acid Organic compounds such as copper
Metallic copper obtained by thermal decomposition at 00 to 400 ° C. is exemplified.

These copper-based catalysts may contain metals such as silver, iron, nickel, chromium and vanadium, and can also be used by being supported on a carrier such as silica, alumina and activated carbon. Among these copper catalysts, Raney copper is preferably used. The hydration reaction of acetonitrile can be carried out in a continuous or batch mode with a suspension bed or a fixed bed. Preferably, Raney copper is suspended and reacted in a tank reactor with a stirrer.

The amount of the catalyst is 0.00
1-0.7 kg / L, preferably 0.01-0.5 kg
/ L. The contact time or residence time between the catalyst and acetonitrile as a raw material and water is in the range of 0.1 to 10 Hr, preferably 0.3 to 5 Hr. If the contact time or residence time is less than 0.1 Hr, the conversion of the reaction is not sufficient, and if the contact time or residence time is greater than 10 Hr, the amount of by-products increases, which is not preferable from the viewpoint of economic efficiency.

The conversion of acetonitrile to acetamide is preferably from 10 to 98%, more preferably from 30 to 95%. If the conversion is less than 10%, the production efficiency is not preferable, and if it is 98% or more, the amount of by-products increases. The reaction temperature is in the range of 50 to 200C, preferably 70 to 150C. If the reaction temperature is lower than 50 ° C., the reaction rate decreases, which is not practical. On the other hand, if the reaction temperature is higher than 200 ° C., the deterioration of the catalyst becomes large, and the amount of by-products increases. Separation of the catalyst and the reaction solution can be performed by a separation method such as filtration, sedimentation, or centrifugation using a wire mesh, nylon mesh, sintered metal, or a combination of these methods.

An acetamide aqueous solution containing acetonitrile obtained by this hydration reaction is brought into contact with a cation exchange resin for purification. The function of the cation exchange resin in the present invention is considered as follows. The cation exchange resin is mainly intended to remove cations such as copper ions, iron ions, and ammonium ions. However, in fact, the purity of acetamide is improved as apparent from the examples described below, and the quality is affected. It is considered that a very small amount of impurities such as acetic acid are also removed.

As the cation exchange resin used in the present invention, a commercially available porous or gel type strongly acidic or weakly acidic cation exchange resin can be used. A strongly acidic or weakly acidic cation exchange resin is preferred. For example, Diaion PK-208
And Diaion WK-10 (manufactured by Mitsubishi Kasei), Levatit SP-112 and Levatit CNP-80 (manufactured by Bayer), Amberlite IR-120B, Amberlite IRC-50, and Amberlyst 15 (Roam and Haar).
And the like). These cation exchange resins are preferably used after converting the exchange groups into H-type.

The contacting of the aqueous solution of acetamide can be carried out by a continuous method or a batch method, but is preferably a continuous method. In the continuous method, the space velocity (SV) is 1 to
60 Hr ^-1 , preferably in the range of 3 to 20 Hr ^-1 ,
The linear velocity (LV) is in the range of 0.1 to 20 m / Hr, preferably 0.5 to 10 m / Hr. The temperature at which the acetamide aqueous solution is brought into contact with the cation exchange resin is 0 to 50 ° C.
And more preferably in the range of 10 to 40 ° C.

If the temperature is lower than 0 ° C., there are problems such as blockage of the apparatus due to precipitation of crystals. On the other hand, when the temperature is higher than 50 ° C., impurities such as acetic acid increase due to side reactions such as hydrolysis of acetamide, which causes deterioration of the quality of acetamide. When an aqueous acetamide solution is brought into contact with a cation exchange resin, since unreacted acetonitrile is present, coloring components may be eluted from the cation exchange resin and the quality of acetamide may be reduced. Is preferred.

As a method for separating acetonitrile and water from an aqueous solution of acetamide that has been brought into contact with a cation exchange resin, separation by distillation, separation by stripping using an inert gas such as nitrogen or carbon dioxide, air or the like can be mentioned. However, separation by distillation is preferred. By distillation,
An acetamide aqueous solution from which acetonitrile has been separated can be produced, and anhydrous acetamide from which acetonitrile and water have been removed can also be produced.

When acetonitrile is separated by distillation to obtain an acetamide aqueous solution, the temperature at the bottom of the distillation column is adjusted to 30.
To 200 ° C, preferably 50 to 150 ° C.
When the bottom temperature of the distillation column is lower than 30 ° C., there is a problem that the operation pressure becomes unnecessarily low and the apparatus becomes large. On the other hand, when the bottom temperature of the distillation column is higher than 200 ° C., hydrolysis is remarkable, and acetic acid is generated, which is a quality problem.

Acetonitrile and water are separated by distillation,
In the case of obtaining anhydrous high-purity acetamide, it is preferable to perform the reaction at a temperature in the range of 80 ° C to 150 ° C in order to maintain a liquid state.
Distillation towers include towers having trays such as bubble bell trays, perforated plate trays, valve trays, and Raschig rings, lessing rings, berl saddles, interlock saddles, teralet packings, polling, McMahon packings, Dixon rings, etc. A column packed with packing can be used. In the present invention, the packing of the distillation column is not necessarily required, and simple distillation without packing is also included in the distillation column.

In the case of producing acetamide crystal grains, it can be produced by a method of crystallization and granulation while cooling the dehydrated molten acetamide after distillation. As described above, in summary, the method of the present invention can provide high-purity acetamide by a simple operation by treating an acetamide aqueous solution obtained by hydrating acetonitrile with a cation exchange resin. it can.

It has not been known until now that high-quality acetamide can be obtained by a simple operation of contact without contacting with a cation exchange resin, without a complicated crystallization operation. Further, by performing distillation after the cation exchange treatment, higher quality acetamide can be obtained.
On the other hand, when the cation exchange resin treatment is not performed,
High-purity acetamide could not be obtained.
No. 76 requires complicated crystallization.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to examples, but these do not limit the scope of the present invention. The obtained acetamide is analyzed by the following method. The purity is a percentage obtained by analyzing acetamide, acetic acid, acetonitrile and the like by gas chromatography and excluding water and acetonitrile. Copper was analyzed by ICP emission spectroscopy.

[0022]

EXAMPLE 1 The inside of a 1000 ml autoclave made of SUS304 was replaced with nitrogen, and Raney copper (R) manufactured by Nikko Rica Co., Ltd. was used.
-300C) 180 g of acetonitrile and 35 g of water, in which 35 g were charged and nitrogen was blown in advance to remove dissolved oxygen.
0 g was charged. The reaction was performed at a rotation speed of 300 rpm and a temperature of 120 ° C. for 2 hours. The conversion of acetonitrile to acetamide is 85% and the selectivity for acetamide is 99.4%.
And the selectivity for acetic acid was 0.6%. Copper is 5pp
m. The reaction solution was withdrawn from the autoclave through a 2μ sintered metal filter.

A glass double tube having an inner diameter of 15 mm and a length of 500 mm was prepared, and 70 ml of Diaion PK208 (exchange group H type) manufactured by Mitsubishi Kasei Corporation was filled as a cation exchange resin. Before use, a 30% aqueous solution of acetonitrile was passed through at 350 ° C. and a space velocity (SV) of 5 Hr ⁻¹ at 30 ° C. for pretreatment. A reaction solution taken out of the autoclave into this cation exchange resin at a temperature of 30 ° C. and 140 ml
/ Hr. About 36% by weight of acetamide and 5% by weight of acetonitrile aqueous solution were obtained. The purity of acetamide was 99.6% and the acetic acid was 0.4%.

To remove acetonitrile and water from the resulting acetonitrile-containing acetamide aqueous solution, SUS was placed in a glass double tube having an inner diameter of 20 mm and a length of 200 mm.
Distillation was performed using an apparatus equipped with a 1000 ml round bottom flask at the bottom of a packed column made of 316 and filled with 3 mmφ Dixon packing. While maintaining the liquid temperature at the bottom of the tower at 80 to 83 ° C, the pressure of the packed tower was set to 200 to 50 mmHg,
The round bottom flask at the bottom was immersed in an oil bath at about 100 ° C. and distilled. Acetonitrile and water were withdrawn from the top with steam and condensed with a condenser. The bottom liquid after distillation is
Acetamide was 99.1% by weight, and the purity of acetamide was 99.97% and acetic acid was 0.03%. Further, the content of copper was 0.1 ppm or less.

[0025]

Example 2 In Example 1, the charge to the autoclave was changed to 25 g of Raney copper (R-300A), 150 g of acetonitrile and 450 g of water, manufactured by Nikko Rica Co., Ltd.
The same operation was performed except that the reaction was carried out at a temperature of 3 ° C. for 3 hours. The conversion of acetonitrile to acetamide was 82%, the selectivity for acetamide was 99.6%, and the selectivity for acetic acid was 0.4%. 6 ppm of copper ions were eluted.
The obtained reaction solution was converted to the cation exchange resin of Example 1 using Amberlyst 15 (exchange group H type) manufactured by Rohm and Haas.
The same operation was performed except that the temperature was changed to 20 ° C. An aqueous solution of about 39% by weight of acetamide, about 6% by weight of acetonitrile was obtained. Acetamide purity is 9
9.7% and acetic acid 0.3%. The obtained acetamide aqueous solution was distilled in the same manner as the distillation apparatus of Example 1 except that the packing was not filled in the distillation column. The bottom liquid after distillation was 99.5% by weight of acetamide, the purity of acetamide was 99.98%, and the concentration of acetic acid was 0.02%. Moreover, copper was 0.1 ppm.

[0026]

Example 3 The same operation as in Example 1 was carried out except that the autoclave was charged with 240 g of acetonitrile and 360 g of water and reacted at a temperature of 120 ° C. for 3 hours. 84% conversion of acetonitrile to acetamide
The selectivity for acetamide was 99.5%, and the selectivity for acetic acid was 0.5%. Copper was eluted at 6 ppm. The obtained reaction solution was treated with a cation exchange resin in the same manner as in Example 1. About 48% by weight of acetamide,
An aqueous solution of about 6% by weight of acetonitrile was obtained, the purity of acetamide was 99.7% and the acetic acid was 0.3%. The obtained acetamide aqueous solution was distilled by the distillation apparatus of Example 1. The liquid temperature at the bottom was 70 ° C., the pressure in the distillation column was 200 to 50 mmHg, acetonitrile was taken out from the top of the column, and the bottom liquid was subjected to gas chromatography analysis during distillation, and the distillation was stopped when the acetonitrile concentration became 10 ppm. The bottom solution after the distillation is a 55% by weight aqueous solution of acetamide, and the purity of the acetamide is 99.9%.
Acetic acid was 0.1%. Further, the content of copper was 0.15 ppm.

[0027]

Comparative Example 1 The same operation was performed as in Example 1, except that the reaction solution was not passed through the cation exchange resin. The obtained bottom liquid after distillation was 99.0% by weight of acetamide, the purity of acetamide was 99.7%, the acetic acid was 0.3%, and the content of copper was 10 ppm.

[0028]

According to the method of the present invention, a simple operation of bringing an aqueous solution of acetamide obtained by hydrating acetonitrile into contact with a cation exchange resin without using a conventional special crystallizer or complicated operations, Since high quality acetamide can be produced, it is an economical process and has high industrial value.

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Claims (3)

[Claims] 1. A method for producing high-purity acetamide, comprising treating an acetamide aqueous solution obtained by hydrating acetonitrile with a cation exchange resin. 2. The method for producing high-purity acetamide according to claim 1, wherein an aqueous solution of acetamide obtained by subjecting acetonitrile to a hydration reaction in the presence of a copper-based catalyst is used. 3. The method for producing high-purity acetamide according to claim 2, wherein Raney copper is used as the copper-based catalyst.