JPS6040453B2 - Method for producing polyethylene glycolic acid - Google Patents

Description

Detailed Description of the Invention The present invention involves oxidizing the hydroxy groups at both ends of polyethylene glycol with oxygen or oxygen-containing gas in the presence of an improved platinum palladium catalyst to produce polyethylene glycol acid having carboxy groups at both ends. It's about how to do it.

Polyethylene glycolic acid is a surfactant, chelating agent,
It is a useful material as a raw material for modifiers for polymer compounds.

Conventionally, there are the following methods for obtaining polyethylene glycolic acid.

■According to Hakamakai Publication No. 51-128909, polyethylene glycol having 2 to 8 polyethylene glycol units is reacted with an alkaline substance and molecular oxygen in the presence of a platinum group catalyst to form a reaction solution. There is a method of producing polyglycolic acid salts by always maintaining the range of 5.0 to 9.0, but when using this method, polyethylene glycolic acid is obtained as an alkali salt, and to obtain it as an acid, it must be neutralized and decomposed. Salt needs to be purified.

In addition, when using this method, it is preferable to add a catalyst during the reaction, and the amount of catalyst used is large, resulting in high production costs. According to US Pat. No. 392-73, there is a method for obtaining the corresponding dicarboxylic acid by oxidizing polyethylene glycol containing 2 or 3 ethylene glycol units with oxygen or an oxygen-containing gas in the presence of a platinum catalyst. However, in this method, diethylene glycol is oxidized and the corresponding dicarboxylic acid is obtained at a yield of 5%, but in the case of triethylene glycol, cleavage of the ether bond and other decomposition occur to produce the corresponding dicarboxylic acid. The acid yield is stated to be 79.2%, which is a poor yield of the corresponding dicarboxylic acid.

These facts suggest that polyethylene glycol having three or more ethylene glycol units is susceptible to cleavage of ether bonds and other side reactions during its oxidation reaction. According to Tokusei No. 51-131824, there is a method for producing diglycolic acid by oxidizing diethylene glycol with oxygen-containing gas in a strongly acidic aqueous solution with a pH of 3 or less in the presence of a noble metal catalyst. You need to add acid.

Additionally, this publication states that when the reaction is carried out in a pH range of 3 to 7, the reaction products are decomposition products of formic acid, oxalic acid, acetic acid, glycolic acid, etc., and diglycolic acid is not produced at all or is not produced at all. However, it is said that there are only traces. It is extremely difficult to obtain the corresponding dicarboxylic acid by catalytic oxidation of polyethylene glycol having a large number of ethylene glycol units as described above, and requires advanced technology, and no such technology has been disclosed to date.

When oxidizing the terminal hydroxyl group of polyethylene glycol, which has a relatively large molecular weight, ether bond cleavage is likely to occur as a side reaction because the oxygen of the ether bond and the oxygen of the hydroxyl group competitively catalyze the process toward the end of the chain. This is thought to be due to adsorption on the surface, and in order to selectively oxidize only hydroxyl groups without breaking ether bonds, it is necessary to select a catalyst that has a weak adsorption power to the catalyst of ether bonds.

Furthermore, aldehydes are produced as intermediates during the oxidation of hydroxyl groups, and a catalyst having the ability to quickly and completely oxidize these aldehydes is an important factor in increasing the reaction time and the purity of the product. From this perspective, the present inventors determined that the average molecular weight was approximately 180 in a non-alkaline solution.
After intensive research into a method for obtaining polyethylene glycol having carboxyl groups at both ends with high purity and good yield by oxidizing about 20,000 polyethylene glycol with oxygen or an oxygen-containing gas, we found that the oxidation reaction The present invention was completed based on the discovery that this is greatly influenced by the catalyst used.

That is, the present invention uses an improved platinum-palladium carbon catalyst in which platinum is the main catalyst metal and palladium is added thereto as a catalyst metal as described below in a non-alkaline solution, and polyethylene glycol having an average molecular weight of about 180 to about 20,000 is used. There is a method for producing polyethylene glycolic acid having carboxy groups at both ends by oxidizing the polyethylene glycolic acid without cleavage of its ether bonds.

In one embodiment of the method of the present invention, a polyethylene glycol solution and a platinum-palladium carbon catalyst are charged into a reaction vessel equipped with a reaction gas inlet, a thermometer, a pressure gauge, and a condenser. Gas is blown into the mixture and the reaction is carried out under normal pressure or increased pressure at a reaction temperature of 40° C. and 120 qC under constant pressure.

As the reaction progresses, the absorption of oxygen progresses, and when the absorption of oxygen stops, the reaction is terminated, and after cooling, the reaction product is taken out and the catalyst is placed in the furnace to obtain a colorless and transparent reaction liquid. Through this reaction, polyethylene glycolic acid having carboxy groups at both ends can be obtained quantitatively with good purity. In the present invention, the term "in a non-alkaline solution" means that the reaction proceeds without adding an acid or alkali at the beginning of the reaction, and without adding an alkali during the reaction.

That is, when carrying out the method of the present invention, the raw material polyethylene glycol solution is directly subjected to the reaction without any need to adjust the pH before or during the reaction. As the reaction progresses, carboxylic acid is produced and p
H gradually decreases, but at the completion of the reaction, its p
H varies depending on the molecular weight, but is approximately in the range of 2 to 4. The reaction time varies depending on the raw materials and reaction conditions, but is usually about 5 to 1 hour. In the present invention, the polyethylene glycol is a commercially available polyethylene glycol selected from the group consisting of those having an average molecular weight of about 180 to about 20,000.

Polyethylene glycols having an average molecular weight of between about 180 and about 20,000 have ethylene glycol units of about 4 to about 460. Such polyethylene glycol is preferably used in the reaction as an aqueous solution, and the concentration of the aqueous solution can be any concentration as long as it is below the saturated solubility at the reaction temperature, but it is usually preferably 1.
0 and 5 weight percent. The platinum-palladium-carbon bran soot used in the method of the present invention contains platinum and palladium as essential components as catalyst metals, and palladium is contained in a proportion of 5 to 10 weight percent, preferably 1 percent by weight, based on platinum.
0 to 4 weight percent. On the other hand, the carbon used as a loss body has a pongee hole volume of 1.0,
Activated carbon having a diameter of 1.6 cc is used. The amount of catalyst metal supported on the carrier is approximately 1
The amount supported is not particularly limited. The method for preparing the catalyst used in the present invention is, for example, by suspending activated carbon in water and
Adjust H to 8 or higher, drop a mixed aqueous solution of chloroplatinic acid and palladium chloride into the solution, and if the pH drops to 8 or lower midway through, add alkali as necessary to completely adsorb platinum and palladium onto activated carbon. .

Next, a reducing agent such as formalin, formic acid, or sodium borohydride is added to reduce the chloroplatinic acid and palladium chloride on the activated carbon, which is then thoroughly washed with water and subjected to an oxidation reaction as it is or after drying. The catalyst thus obtained is amorphous according to X-ray diffraction.

The amount of the catalyst to be used in the method of the present invention may be determined by considering the desired reaction rate, economic efficiency, etc., but a range of 5% to 1% by weight based on the usual raw materials is appropriate.

The oxidizing agent used in the method of the present invention is oxygen or an oxygen-containing gas, and the pressure is normal pressure to increased pressure.When only oxygen is used, the reaction is sufficient, but when air is used, the reaction is sufficient.
It is preferable to carry out the reaction under pressure of k9/base.

In the method of the present invention, the reaction temperature greatly influences not only the reaction rate but also the selectivity of the oxidation reaction.
20 qC, preferably 50 to 100 qC; when the temperature is lower than this, the reaction rate is slow, and when it is higher, the ether bonds are likely to be cleaved.

The method of the present invention using an improved platinum-palladium-carbon catalyst has a shorter reaction time and improved selectivity of the oxidation reaction than when using a conventional platinum-carbon catalyst, resulting in less cleavage of ether bonds and less carboxyl groups. Since no decomposition occurs and no aldehyde, which is a reaction intermediate, remains, no coloring occurs in the reaction solution or during its concentration, thereby reducing the quality of the product.

In this way, the catalyst used in the method of the present invention has a The reason why it is a good droplet for the oxidation of reethylene glycol is not clear, but it is thought that it is because the adsorption of ether bonds to the catalyst surface is weak and the oxidation of aldehyde to carboxylic acid progresses rapidly. Furthermore, surprisingly, in addition to the above-mentioned characteristics, in the method of the present invention, the duration of the catalyst activity is long and almost semi-permanent.

That is, when the product is used repeatedly as shown in the Examples described later, no decrease in activity is observed even if the product is used repeatedly as it is without performing any operation such as activating the activity. Therefore, the cost of the catalyst relative to the product can be reduced despite the use of an expensive noble metal catalyst with very high catalytic productivity. Since the method of the present invention is carried out in a non-alkaline solution, the free carboxylic acid is directly obtained as a reaction product, so when the catalyst is separated from the reaction solution, a colorless and transparent solution is obtained, and the product can be used as it is or without any concentration or purification. It can be done.

Therefore, the method of the present invention is easy to implement industrially and is recognized as a very excellent method. Examples will be described in detail below.

Example 1 5.0 mm of platinum and 1.5 mm of palladium were dissolved in 20 mm of aqua regia, and the remaining acid was evaporated to dryness.The obtained chloroplatinic acid and palladium chloride were dissolved in 100 mm of a 5% aqueous hydrochloric acid solution. did.

Commercially available activated carbon (pongee hole volume 1.5cc/night) 1/4 of 95mm
It was suspended in a normal sodium carbonate aqueous solution IZ (the pH of this suspension was about 11.0), and the above-mentioned chloroplatinic acid and palladium chloride aqueous solution was added dropwise into the solution over a period of 10 minutes, and the temperature was then lowered to room temperature. The mixture was further humidified at 80.degree. C. for 1 hour and heated for 2 hours to completely adsorb chloroplatinic acid and palladium chloride onto the activated carbon. Next, 10% aqueous formalin solution was added thereto and the mixture was reduced by keeping at 80±5° C. for 1 hour, followed by washing with water in a furnace and drying to obtain a platinum-palladium carbon catalyst.
The X-ray diffraction pattern of this catalyst was amorphous. This catalyst was mixed with commercially available polyethylene glycol (PEG6).
500 volumes of an aqueous solution containing 200 volumes (manufactured by Sanyo Chemical Co., Ltd., Cape 00) were added to an electromagnetic transfer rope Azusa type 1.5 autoclave equipped with a gas inlet and outlet, a thermometer, and a pressure gauge. Pressurized air is introduced into this autoclave to increase the pressure to 10k.
9/ The reaction was carried out while maintaining the temperature at 90±5°C while worshiping the enemy. As the reaction progressed, absorption of oxygen gas was observed, and the reaction was completed 8 hours after the start of the reaction. After the autoclave was quenched, the reaction product was taken out and the catalyst was separated from the furnace to obtain a colorless and transparent reaction solution.The entire amount was concentrated and dried to obtain 200 g of solid platinum. A portion of this material was sampled and measured for acid value, hydroxyl value, melting point, and molecular weight using a Uberod viscometer. As a result, the acid value was 13.4, the hydroxyl value was 0,
A melting point of 57-60°C and a molecular weight of 7,500 were obtained. When the raw material PEG000O was analyzed using the same machine, it had a hydroxyl value of 137, a melting point of 57-60°C, and a molecular weight of 7,300.The conversion rate to dicarboxylic acid of the raw material was 100%, and the selectivity was almost 100%, indicating that it was polyethylene glycol. It was observed that the ether bond of was not broken and the hydroxyl groups at both ends were converted to carboxylic acid. Example 2 Using 500 g of an aqueous solution containing 20 g of the platinum palladium carbon catalyst obtained in Example 1 and 200 g of commercially available polyethylene glycol (PEG300 manufactured by Sanyo Chemical), pressurized air was introduced from the reaction gas inlet. 10k9 inside the autoclave
The reaction was carried out in the same manner as in Example 1, except that air was allowed to flow out from the reaction gas outlet at 0.3 m/h while maintaining the temperature at 0.3 m/m, and the reaction was completed within a short time.

The reaction product is taken out and the catalyst is heated to a colorless and transparent pH 2.
．． A reaction solution of No. 4 was obtained. The entire amount was concentrated and dried to obtain a colorless and transparent viscous liquid. The chemical analysis values for this product were an acid value of 33, a hydroxyl value of 0, and a molecular weight of 335. Also, some of this material is esterified with diazomethane to produce gask. As a result of analysis by matography, glycolic acid and diglycolic acid, which are decomposition products, were not detected. The raw material has a hydroxyl value of 369 and a molecular weight of 31.
5 and the yield of the dicarboxylic acid having carboxyl groups at both ends was quantitative. From this result, it was confirmed that the method of the present invention can selectively convert the hydroxyl groups at both ends of polyethylene glycol into dicarboxylic acid without cutting the ether bonds of polyethylene glycol. Example 3 1,000 g of an aqueous solution containing 20.0 g of the platinum palladium carbon catalyst obtained in Example 1 and 200 g of polyethylene glycol (PEG 6.00) was heated using a strainer, thermometer, and oxygen-containing gas injection. The mixture was added to a 2.5 liter reaction vessel equipped with a cap and a pH electrode.

This aqueous solution was maintained at 90±5° C. while being stirred, and oxygen gas was introduced at a rate of 0.2 so/min. The pH at the start of the reaction is 6
．． As the reaction progressed, the pH decreased to 3.4 after 1 hour, and the reaction was completed. The catalyst was removed from the reaction solution to obtain a colorless and transparent reaction solution. The whole amount was concentrated and dried to obtain 199 g of white solid. This thing has an acid value of 13,
1. The hydroxyl value was 0.1, the melting point was 57-6 pi, the molecular weight was 7,400, and the conversion rate of the raw material was about 99%. Example 4 Chloroplatinic acid containing 50% platinum and 0% palladium.
A platinum-palladium carbon catalyst was obtained in accordance with Example 1 using a mixed aqueous solution of palladium chloride containing 50% chloride.

This material was found to be amorphous by X-ray diffraction. Using 20.0 mm of this catalyst, 200 mm of polyethylene glycol (PEG 6,00) was oxidized according to Example 1, and the reaction was completed in 8 hours. The catalyst was removed from the reaction solution to obtain a colorless and transparent reaction solution with a pH of 3.2. The entire amount was concentrated and dried to obtain 201 white solids. This product has an acid value of 12.8, a hydroxyl value of 0, a melting point of 57 to 5 pi○,
The molecular weight was 7,450, and the rolling b-axis of the raw material was 100%. Example 5 In preparing a platinum palladium carbon catalyst, a platinum palladium carbon catalyst was obtained by replacing formalin, the reducing agent in Example 1, with an aqueous solution 30% containing 3.0 g of sodium poronohydride.

The X-ray diffraction pattern of this catalyst was amorphous. Using 20 grams of this catalyst, 200 grams of polyethylene glycol (PEG 6,00 Misaki) was oxidized in the same manner as in Example 1, and the reaction was completed in 8 hours.

The catalyst was removed from the reaction solution in a furnace to obtain a colorless and transparent reaction solution with a pH of 3.1. When this whole amount was concentrated and dried, a white solid 19
I got 9 nights. This product had an acid value of 13.0, a hydroxyl value of 0.1, a melting point of 57 to 60 qo, a molecular weight of 7,450, and a conversion rate of polyethylene glycol of about 99%. Example 6 The catalyst obtained by separating the reaction product from the reaction product in Example 1 after completion of the reaction was used as it was in the second reaction according to Example 1.

Furthermore, in the third round, the 5M group was used repeatedly and the reaction was carried out to test the durability of the catalyst, and the results shown in Table 1 were obtained. Table 1 From the results, the method of the present invention allows the catalyst to be used repeatedly 50 times or more, and even after the 50th use, the reaction time does not increase, the catalyst has excellent durability, and the resulting dicarboxylic acid has high purity and is highly economical. It was recognized that this is a method.

Comparative Example 1 A reaction was carried out according to Example 1 using a commercially available 5% platinum carbon catalyst (the average particle diameter of platinum according to X-ray diffraction is 173 A) at 20.0 mm and polyethylene glycol (PEG6,000P) at 200 mm for 8 hours. The reaction was stopped.

The catalyst was removed from the reaction solution to obtain a colorless and transparent reaction solution. When the whole amount was concentrated and dried, 200 g of a pale yellow solid was obtained. This product had an acid value of 18.0, a hydroxyl value of 6.2, a melting point of 53-5600, and a molecular weight of 5,800. It was found that this platinum-carbon catalyst easily breaks the ether bond of polyethylene glycol, and that a large amount of unreacted substances remained in the same period as in Example 1, requiring a long time for the reaction. Comparative example
2 Example 2 was prepared using 20.0 kg of the platinum carbon catalyst of Comparative Example 1 and 200 kg of polyethylene glycol (PEG300).
Polyethylene glycol was acidified according to the method, and the reaction was stopped after 1 hour.

The catalyst was removed from the reaction solution to obtain a colorless and transparent reaction solution. When the entire amount was concentrated and dried, a slightly yellowish brown colored viscous steel liquid 218 was obtained. This product had an acid value of 350, a hydroxyl value of 31.2, and a molecular weight of 210. As a result of quantifying the decomposition products glycolic acid and diglycolic acid by gas chromatography, they were 8.3% each.
It was 2.2%.

From this, it was determined that a catalyst consisting of platinum alone would easily cleave the ether bonds of polyethylene IJ col. Comparative Example 3 When obtaining a platinum palladium carbon catalyst, water 1
A catalyst was prepared in the same manner as in Example 1 except that the activated carbon used in Example 1 was suspended therein and no alkali was added.

At this time, the pH of the suspension was 1 or less when the dropwise addition of the mixed solution of chloroplatinic acid and palladium chloride was completed. The average particle diameter of this catalyst was 80A as determined by X-ray diffraction. This catalyst 20.0% and polyethylene glycol (6,000P
) The reaction was carried out according to Example 1 using 200 hours, and the reaction was stopped in 8 hours.

The catalyst was separated from the reaction solution by a furnace to obtain a colorless and transparent reaction solution, and the entire amount was concentrated and dried to obtain 200% of a pale yellow solid. This product has an acid value of 15.5, a hydroxyl value of 3.6, and a melting point of 56~
It was found that the polyethylene glycol had a molecular weight of 59 qo and a molecular weight of 6,500, and that the ether bond of polyethylene glycol had been broken. Example 4 To obtain a platinum-palladium carbon catalyst, a catalyst was prepared according to Example 1 using activated carbon having a pore volume of 0.7 cc/day.

This catalyst had an average particle diameter of 40△ as determined by X-ray diffraction. This catalyst 20.0% and polyethylene glycol (PE
According to Example 1, polyethylene glycol was oxidized using 200 g of 200 ml of polyethylene glycol, and the reaction was stopped in 8 hours.

The catalyst was separated from the reaction solution by a furnace to obtain a colorless and transparent reaction solution, and the entire amount was concentrated and dried to obtain 1 white solid sea bream. This product had an acid value of 9.5, a hydroxyl value of 3.8, a melting point of 57 to 60°C, a molecular weight of 7,350, and a conversion rate of the raw material of about 70%. Comparative Example 5 Polyethylene glycol (PEG 6,00 Misaki) was oxidized in the same manner as in Example 1 using 20.0 kg of a commercially available 5% palladium on carbon catalyst, and the reaction was stopped in 8 hours.

Claims (1)

[Scope of Claims] 1. When polyethylene glycol is catalytically oxidized with oxygen or oxygen-containing gas in the presence of a platinum metal catalyst in a non-alkaline solution to obtain polyethylene glycol having carboxyl groups at both ends, platinum and palladium are used as the platinum metal catalyst. The water-soluble salt is adsorbed on activated carbon having a pore volume of 1.0 to 1.6 cc/g in an aqueous solution with a pH of 8 or higher, and then reduced with a reducing agent selected from formalin, formic acid or sodium polyhydride. A method for producing polyethylene glycolic acid, characterized by using a platinum palladium carbon catalyst. 2. The manufacturing method according to claim 1, wherein the polyethylene glycol has an average molecular weight of about 180 to about 20,000. 3. The manufacturing method according to claim 1, wherein the ratio of platinum to palladium in the platinum palladium carbon catalyst is 5 to 100 weight percent of palladium to platinum. 4. The manufacturing method according to claim 1, wherein the reaction temperature is 40 to 120°C.