JP2003238471A - Method for purifying methylal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove little amounts of peroxides and other impurities existing in methylal used as a raw material for fine chemicals such as medicines eliminating reactions caused by the peroxides and the impurities. <P>SOLUTION: This method for purifying methylal comprises reducing the methylal containing the peroxides as the impurities and then subjecting the reduced product to an adsorption treatment. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying methylal, and more particularly to a method for purifying methylal in which peroxide contained as an impurity is removed from methylal.

[0002]

BACKGROUND OF THE INVENTION Methylal (also called formal or dimethoxymethane) is a compound useful as a raw material for the synthesis of fine chemicals such as medicines and as a molecular weight regulator of polyacetal resin, and is produced by the condensation reaction of methanol and formaldehyde. ing.

Since this methylal has an ether bond, autoxidation is likely to occur, and a peroxide is generated during the process of transportation, transportation, storage and the like, which causes coloring and various impurities. And, as mentioned above, since methylal is used as a raw material for the synthesis of fine chemicals such as pharmaceuticals, even very small amounts of highly reactive impurities such as peroxides pose a problem, and it is necessary to remove peroxides from methylal. Becomes

By the way, as a method of removing the peroxide in the organic compound, a reductive purification method is known, and a method of hydrogenating using reduced nickel, Pt, Pd or the like as a catalyst is known. For example, JP-A-57-57013 discloses a method for purifying ethyl ether using a reduced nickel catalyst. Further, JP-A-8-9555 discloses a method for removing an organic peroxide in an olefin using a Pt catalyst.

However, even if the methylal is simply reduced by the above method to remove the peroxide, the reactivity is not completely lost, which is a problem in its utilization.

[0006]

SUMMARY OF THE INVENTION It is therefore an object of the present invention to remove traces of peroxides and other impurities present in methylal to substantially eliminate reactivity.
To provide methylal that can be safely used as a synthetic raw material for fine chemicals such as medicines.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to achieve the above object, and as a result, the reason why the reactivity is not completely lost even if the peroxide is removed by hydrogenolysis in methylal is as follows. We have found that this reaction produces formic acid, which is as highly reactive as peroxide.
Then, after removing the peroxide in the methylal by a reduction treatment, if the formic acid is further removed by an adsorption treatment, it is found that a methylal can be obtained substantially free of a reactive substance, and the present invention completed.

That is, the present invention is a method for purifying methylal, which comprises subjecting methylal containing peroxide as an impurity to a reduction treatment, and then subjecting the reduced product to an adsorption treatment.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a methylal compound containing a peroxide as an impurity is first subjected to a reduction treatment to remove the peroxide, and then a formic acid produced in this step is removed by an adsorption treatment.

Methylal containing peroxide (hereinafter,
The reduction treatment of "crude methylal") is carried out by a method of hydrocracking in a liquid phase or a gas phase in the presence of hydrogen and a hydrogenation catalyst, or a method of contacting with a reducing agent such as sodium borohydride. Be implemented.

The above-mentioned hydrotreatment is conducted by Raney nickel,
Pd / activated carbon, Pd / alumina, Pt / activated carbon, Ru /
It is carried out using a general hydrogenation catalyst such as activated carbon. The shape of this catalyst is not particularly limited, but pellets, spheres, rings, granules, powders and the like can be used. The catalyst particle size is not particularly limited as long as the optimum value can be selected depending on the inner diameter of the reaction tube and the like.

The amount of the solid catalyst used in the hydrotreatment is not particularly limited and may be determined in consideration of the reaction rate, heat removal, catalyst cost, etc., but it should be an amount effective for catalytic activity and as small as possible. Is desirable. The hydrogen used for the hydrotreatment may be pure hydrogen, or may be diluted with a gas inert to the reaction such as nitrogen and methane.

The above-mentioned hydrogenation reaction may be carried out in a liquid phase or a gas phase, and can be carried out continuously, semi-continuously or batchwise by a slurry method or a fixed bed method. The reaction conditions are appropriately selected depending on the catalyst used, and generally, the temperature is 20 to 15
It can be carried out under conditions of 0 ° C. and a reaction pressure of 0.1 to 5 MPa.

If the above-mentioned hydrotreating is carried out at an unnecessarily high reaction temperature, the performance of the catalyst may be deteriorated and the methylal itself may be hydrolyzed. The decomposition rate of the substance becomes slow, and the reaction time must be lengthened. Further, increasing the reaction pressure more than necessary leads to an increase in cost due to the need for special equipment, and conversely, at a low reaction pressure of less than 0.1 MPa, the decomposition rate is significantly reduced, and the present invention It cannot be implemented effectively.

On the other hand, as the reducing agent used in the above-mentioned method, borohydride salts such as sodium borohydride, cyanohydroborate salts such as sodium cyanohydroborate, and trimethoxyborohydride such as sodium trimethoxyborohydride. Elementary salts, lithium aluminum hydride and the like can be used. The amount of these reducing agents used is generally from 0.1 ppm to 10% by weight based on the crude methylal.
It is 00 ppm, preferably 1 ppm to 200 ppm.

The above-mentioned reaction with the reducing agent is preferably carried out by a batch system in which the reducing agent is dissolved or dispersed in crude methylal and the reaction is carried out in a stirring tank. The reaction conditions may be appropriately selected depending on the reducing agent used, and generally, the temperature is 0 to 10
0 ° C., preferably 10 to 40 ° C., reaction time 1 to 3
6 hours, preferably 2 to 10 hours. The reducing agent after the reaction can be separated from methylal by a method such as distillation or filtration.

Since the removal of impurities generated during transportation is usually a one-time process, it is simpler to use a reducing agent that does not require equipment such as high temperature and high pressure and can be processed at around room temperature. It is also economical and preferable.

In the methylal which has been subjected to the reduction treatment as described above, about several to several hundred tens ppm of formic acid generated by the reduction treatment remains, but this is removed by the adsorption treatment. An adsorbent is used for this adsorption treatment.

As the adsorbent used for the adsorption treatment, polar adsorbents such as zeolite, layered compounds and activated alumina are preferable. Of these, specific examples of zeolites include molecular sieves 3A, 4A, 5A, 13X, ZSM.
-5 etc. are mentioned. Examples of the layered compound include montmorillonite. Among these, especially the molecular sieve 4A has a high adsorption capacity for formic acid,
It is preferable because it is inexpensive and easy to handle.

The shape and particle size of the adsorbent are not particularly limited, but pellets, spheres, granules, flakes, powders and the like can be used. The amount of the adsorbent used in the adsorption treatment is not particularly limited, and may be determined in consideration of the residual amount of formic acid, the removal rate, the heat removal, the cost and the like. For example, when a molecular sieve 4A type zeolite is used, a sufficient effect can be obtained by using 1 g or more of zeolite for 0.2 mg of formic acid to be removed.

The adsorption treatment may be carried out by bringing the adsorbent and the methylal subjected to the reduction treatment into contact with each other at room temperature. The time of this adsorption treatment is about 2 to 20 hours, and the adsorbent after the adsorption treatment is removed from the methylal by filtration, centrifugation, decantation, or the like. The used adsorbent can be reused by being regenerated by a general regeneration method such as washing with a solvent, heating in air, and heating under reduced pressure. Further, as the adsorption treatment, a method of continuously passing the reduced methylal through a column filled with an adsorbent may be adopted.

The method of the present invention is effectively applied to crude methylal having a relatively small amount of peroxide. For example, the reduction and adsorption treatments according to the present invention can be effectively carried out for the removal of peroxides which are usually contained in an amount of 1000 ppm or less, especially several hundreds ppm or less in terms of active oxygen.

[0023]

The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto. In the examples shown below, the peroxide concentration was analyzed by the small reflection photometer method, and the formic acid concentration was analyzed by the capillary electrophoresis method. All units are by weight.

Example 1 50 g of methylal containing 180 ppm of peroxide and 1 g of Raney nickel were placed in a stainless steel autoclave, and hydrogen was supplied to adjust the pressure to 0.6 MPa, followed by stirring at 50 ° C. for 1 hour. After the reaction was completed, the amount of residual peroxide was less than the lower limit of quantification (<0.2 ppm), and that of formic acid was 60 ppm.

Then, hydrotreated methylal 10
and 3 g of molecular sieve 4A were placed in a glass container and left at room temperature for 20 hours. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

Example 2 50 g of methylal containing 180 ppm of peroxide and 5%
1 g of Pd / activated carbon was put into a stainless steel autoclave, hydrogen was supplied to 3.8 MPa, and the mixture was stirred at 120 ° C. for 1 hour. After the reaction was completed, the amount of residual peroxide was less than the lower limit of quantification (<0.2 ppm), and that of formic acid was 61 ppm.

Then, hydrotreated methylal 10
g and montmorillonite 3 g were put in a glass container and left at room temperature for 20 hours. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

Example 3 Methylal containing 180 ppm of peroxide 50 g and 5%
1 g of Pt / activated carbon was placed in a stainless steel autoclave, hydrogen was supplied to 3.8 MPa, and the mixture was stirred at 120 ° C. for 1 hour. After the reaction was completed, the amount of residual peroxide was less than the lower limit of quantification (<0.2 ppm), and that of formic acid was 39 ppm.

Then, hydrotreated methylal 10
and 3 g of molecular sieve 4A were placed in a glass container and left at room temperature for 20 hours. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

Example 4 A stainless steel reaction tube filled with 35 ml of 0.3% Pd / alumina was charged with methylal containing 180 ppm of peroxide at a feed rate of 35 ml / hr and with hydrogen at 15 ml / m.
at a reaction rate of 100
A hydrogenation treatment was carried out at a reaction temperature of 0.3 MPa and a pressure of 0.3 MPa. Peroxide in methylal spilled out was below the lower limit of quantification (<0.2 pp
m) and formic acid was 3.0 ppm.

Next, hydrotreated methylal 20
and 1 g of molecular sieve 4A were placed in a glass container and left at room temperature for 20 hours. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

Also, about 44 mL of molecular sieve 4A
(30 g) was packed in a glass column, and at room temperature, hydrotreated methylal was fed downward by a pump at a rate of 60 ml / h. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

Example 5 47 g of methylal containing 180 ppm of peroxide and 5 mg of sodium borohydride were placed in a glass flask equipped with a condenser and stirred at room temperature for 8 hours. After the reaction was completed, the reaction solution was distilled, and 90% thereof was distilled. Peroxide in the distillate was below the lower limit of quantification (<0.2 ppm), and formic acid was 12 ppm.

Then, 20 g of the obtained methylal and 1 g of molecular sieve 4A were placed in a glass container and left at room temperature for 20 hours. The amount of formic acid remaining in the treated methylal was less than the lower limit of quantification (<1.0 ppm).

[0035]

As described above, according to the present invention, purified methylal substantially free of peroxide and formic acid can be obtained. In particular, the method of performing the adsorption treatment after the reduction treatment using a reducing agent does not require equipment such as high temperature and high pressure, can be treated at around room temperature, and can easily and economically remove peroxide and formic acid. It can be removed.

Therefore, according to the method of the present invention, it is possible to easily obtain methylal which does not substantially contain reactive impurities and can be safely used as a raw material for the synthesis of fine chemicals such as pharmaceuticals. that's all

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Claims (10)

[Claims] 1. A method for purifying methylal, which comprises subjecting methylal containing peroxide as an impurity to a reduction treatment, and then subjecting the reduced product to an adsorption treatment. 2. The method for purifying methylal according to claim 1, wherein the reduction treatment is carried out by a method of hydrocracking in a liquid phase or a gas phase in the presence of hydrogen and a hydrogenation catalyst. 3. The hydrogenation catalyst is Raney nickel, Pd /
The method for purifying methylal according to claim 2, which is activated carbon, Pd / alumina, Pt / activated carbon or Ru / activated carbon. 4. The method for purifying methylal according to claim 2 or 3, wherein the reduction treatment is carried out under the conditions of a temperature of 20 to 150 ° C. and a reaction pressure of 0.1 to 5 MPa. 5. The method for purifying methylal according to claim 1, wherein the reduction treatment is carried out by a method of contacting with a reducing agent. 6. The method for purifying methylal according to claim 5, wherein the reducing agent is a borohydride, a cyanohydroborate, a trimethoxyborohydride or lithium aluminum hydride. 7. The method for purifying methylal according to claim 5 or 6, wherein the amount of the reducing agent used is 0.1 ppm to 1000 ppm by weight relative to methylal. 8. The reduction treatment is carried out under atmospheric pressure at a temperature of 0 to 100.
The method for purifying methylal according to any one of claims 5 to 7, which is carried out at a temperature of ° C. 9. The method for purifying methylal according to claim 1, wherein the adsorption treatment is performed using a polar adsorbent. 10. The method for purifying methylal according to claim 9, wherein the polar adsorbent is zeolite, a layered compound or activated alumina.