JPH0240053B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for obtaining a less colored glutaraldehyde aqueous solution.

A method for obtaining glutaraldehyde by hydrolyzing 2-alkoxy-3,4-dihydro-2H-pyran (simply referred to as 2-alkoxydihydropyran in this specification) is known (US Pat.
2546018). In this production method, high-concentration glutaraldehyde is obtained by fractionating a hydrolysis solution containing water, alcohol, and glutaraldehyde, but high-concentration glutaraldehyde is highly polymerizable and cannot be stored. Generally, it is diluted with water and treated as an aqueous solution with a concentration of, for example, 50% or less.

If glutaraldehyde, which is obtained as an aqueous solution, can be commercialized as it is or by simply removing the coexisting alcohol by hydrolyzing 2-alkoxydihydropyran, it would be advantageous because energy loss and polymerization loss associated with distillation would be eliminated. That is clear. However, in the prior art, the hydrolysis reaction solution was significantly colored and was not suitable as a product. As a countermeasure against coloring, decolorization using activated carbon (as described in the above-mentioned US patent) has only been attempted, and a hydrolysis method for obtaining an aqueous glutaraldehyde solution with little coloration has not been known at all.

In the prior art, the raw material 2-alkoxydihydropyran is colorless, and when it is hydrolyzed into an aqueous glutaraldehyde solution, significant coloring occurs. For this reason, all attempts to prevent the coloration due to hydrolysis have ended in failure.

As a result of further investigation into the prevention of coloration during hydrolysis, the inventor of the present invention unexpectedly discovered that the cause of coloration was hidden in the apparently colorless raw material, and that it was manifested during the hydrolysis process. ,
Furthermore, it was found that the coloring was caused by 2-alkoxydihydropyran and oxygen in the atmosphere, which were the substances that caused the coloring contained in the raw materials. Based on this new knowledge, we carried out all post-distillation handling of 2-alkoxydihydropyran, such as distillation purification, storage and hydrolysis, under oxidation-preventing conditions. It was confirmed that a colorless hydrolyzate was obtained, and the present invention was completed.

Handling of 2-alkoxydihydropyran under the antioxidant conditions that characterize the present invention typically includes the use of an inert, ie, non-oxidizing, atmosphere and the use of an antioxidant. Handling in a non-oxidizing atmosphere is the most preferred method since it is highly effective and does not introduce foreign matter into the glutaraldehyde product.

In the method of the present invention, crude 2-alkoxydihydropyran, usually produced by the reaction of acrolein and alkyl vinyl ether, is first distilled under an inert gas atmosphere to obtain purified 2-alkoxydihydropyran. This is stored if desired and then hydrolyzed, but both storage and hydrolysis are preferably carried out under an inert gas atmosphere. When an inert gas cannot be used, an antioxidant is added to the purified 2-alkoxydihydropyran before it is taken out into the atmosphere to prevent the 2-alkoxydihydropyran from deteriorating due to oxygen. Inert gases include nitrogen, argon, helium, carbon dioxide, etc., and antioxidants include BHT, hydroquinone, resorcinol, catechol, phenothiazine, diphenylamine, hydroquinone monomethyl ether, hydroquinone monoethyl ether, and t-butyl. Catechol etc. are used.

It is currently not clear what kind of reaction is involved in the alteration of 2-alkoxydihydropyran by oxygen, but 2-alkoxydihydropyran, which becomes colored when hydrolyzed as a result of contact with oxygen, is treated in a nitrogen atmosphere. When redistilled and hydrolyzed, uncolored glutaraldehyde is produced, and the denatured 2-alkoxydihydropyran itself shows no coloring, and when it is hydrolyzed, the reaction solution becomes colored. , the following mechanism is presumed. That is, the 2-alkoxydihydropyran reacts with oxygen to produce a higher boiling point compound, which converts into a colored substance when the 2-alkoxydihydropyran is hydrolyzed. The amount of antioxidant used depends on the effectiveness of the variety used.

The 2-alkoxydihydropyran used in the present invention is obtained by reacting acrolein with an alkyl vinyl ether to perform a Diels-Alder reaction.

Specifically, 2-methoxydihydropyran, 2
-ethoxydihydropyran, 2-n-propoxydihydropyran, 2-isopropoxydihydropyran and the like. In order to prevent the polymerization of acrolein in the above Diels-Alder reaction, a polymerization inhibitor is added as a polymerization inhibitor such as hydroquinone, hydroquinone monomethyl ether, etc. depending on the effect of the type used.
It is common to add ~50,000 ppm. The reaction temperature is appropriately selected from the range of 30° to 250° depending on the reaction process, and the reaction time is appropriately selected depending on the amount of the alkyl vinyl ether used and the reaction temperature. Furthermore, a catalyst such as a Lewis acid may be used to promote the reaction.

Next, the reaction crude liquid containing the generated 2-alkoxydihydropyran is distilled under an inert gas atmosphere to remove 2-alkoxy from unreacted raw materials and coloring substances that may have been generated in the previous step. Separate and purify dihydropyran. The action of oxygen and 2-alkoxydihydropyran is suppressed by handling the process from separation and purification to hydrolysis under oxidation-preventing conditions such as an inert gas atmosphere. The usage rate of water in the hydrolysis step is 2 to 1000 times the mole of 2-alkoxydihydropyran, preferably 5 to 20 times, and the temperature is adjusted between 20° and 200° to satisfy the desired treatment time.゜、
Preferably, the angle is selected from the range of 60° to 90°. Furthermore, by adding an acid as a catalyst, the reaction temperature can be lowered and the reaction time can be shortened. As the acid, choose from phosphoric acid, hydrochloric acid, sulfuric acid, etc.
It is added at a concentration of 50,000 ppm, preferably 100-10,000 ppm.

As described in detail above, deterioration of 2-alkoxydihydropyran due to oxygen in the steps after distillation purification according to the present invention can be prevented by handling in an inert gas atmosphere or under anti-oxidation conditions by using an antioxidant. By this method, a color-free hydrolyzate can be obtained, and products of these aqueous glutaraldehyde solutions can be advantageously obtained.

In this way, high-grade glutaraldehyde can be obtained in a shortened process without using the distillation process or powdered activated carbon decolorization process required in the prior art. The distillation process has a large loss (for example, 17% due to flash evaporation), and activated carbon treatment increases the cost of auxiliary materials, so the savings of the present invention extend to all aspects of equipment, operation, and raw materials. The value above is great.

In the Examples and Comparative Examples specifically illustrating the present invention, % used for concentration means % by weight.

Example 1 Acrolein 41.4%, ethyl vinyl ether
A mixture of 57.6% hydroquinone and 1.0% hydroquinone was continuously charged into an autoclave equipped with a stirrer maintained at 180° so that the residence time was 8 hours. Once steady state was reached, the 2-ethoxydihydropyran concentration in the distillate was determined by gas chromatography.
It was analyzed as 84.2%.

This crude 2-ethoxydihydropyran was distilled using a 30-stage Olderschau column under nitrogen atmosphere at normal pressure at a reflux ratio of 1, and the fractions with a boiling point of 142° were collected to obtain a purity of 98.5.
% pure 2-ethoxydihydropyran was obtained. The distillate was led to a tank also sealed with nitrogen through a pipe sealed with nitrogen so as not to come into contact with the outside air, and stored.

Two days after distillation, 150 g of distilled water, 180 g of distilled water, were introduced into the reactor, which was also insulated from outside air by nitrogen.
Hydrolysis was carried out by adding 0.35 g of 85% phosphoric acid and stirring at 80°.

After 70 minutes, when the conversion of 2-ethoxydihydropyran exceeded 99% by gas chromatography, it was cooled.
The APHA of the hydrolysis solution containing glutaraldehyde, ethanol and water was 10 or less. The ethanol and excess water are distilled off and the concentration is adjusted.
A 50% aqueous glutaraldehyde solution of APHA15 was obtained.

In addition, distillation purification of 2-alkoxydihydropyran can also be carried out by vacuum distillation. In this case, it is necessary to prevent air from leaking into the parts of the distillation equipment below atmospheric pressure, and to avoid atmospheric pressure parts such as distillation lines and distillation tanks. By keeping it under a nitrogen atmosphere, 2-alkoxydihydropyran, which is less colored and can be used as a raw material for an aqueous gluta solution, can be similarly obtained.

Example 2 The same 2-ethoxydihydropyran as in Example 1 was distilled at normal pressure and a reflux ratio of 1 using a 30-stage Olderschau column maintained under a nitrogen atmosphere, and the fraction with a boiling point of 142 was distilled into a receiver charged with BHT. It was distilled to
BHT is 10ppm in 2-ethoxydihydropyran
This 2-ethoxydihydropyran was transferred to a sample bottle and stored in contact with air for 2 days without replacing with nitrogen. First, when hydrolysis was carried out in an air atmosphere, the resulting hydrolyzate was
APHA was 30.

Comparative Example 1 A glutaraldehyde aqueous solution had an APHA of 400 in the same manner as in Example 1, except that 2-ethoxydihydropyran was purified, stored, and hydrolyzed in an air atmosphere without a nitrogen seal.

Comparative Example 2 2-Ethoxydihydropyran, which was obtained in the same manner as in Example 2 without using BHT, was stored in a sample bottle without nitrogen substitution. Two days later, the solution obtained by hydrolysis under an air atmosphere was colored with APHA300.

Example 3 Acrolein 46.7%, methyl vinyl ether
A mixture of 52.3% and 1.0% hydroquinone.
The concentration of 2-methoxydihydropyran in the distillate was 86.2% (as determined by gas chromatography). ).

This crude 2-methoxydihydropyran was distilled using a 30-stage Olderschau column at a reflux ratio of 1 under a nitrogen atmosphere at normal pressure, and the fractions with a boiling point of 127° were collected to determine the purity.
99.3% pure 2-methoxydihydropyran was obtained.
The distillate was introduced into a nitrogen-sealed tank and stored so as not to be exposed to the outside air.

Two days after distillation, 141 g of distilled water, 189 g of distilled water, were introduced into the reactor, which was also insulated from outside air by nitrogen.
Hydrolysis was carried out by adding 0.35 g of 85% phosphoric acid and stirring at 80°.

After 60 minutes, when the conversion of 2-methoxydihydropyran exceeded 99%, it was cooled, and the APHA of the resulting glutaraldehyde-methanol aqueous system was 10 or less. Excess water was distilled off from the methanol and the concentration was adjusted to obtain a 50% glutaraldehyde aqueous solution of APHA15.

Example 4 The same crude 2-methoxydihydropyran as in Example 3 was distilled at normal pressure and a reflux ratio of 1 using a 30-stage Olderschau column maintained under a nitrogen atmosphere, and the fraction with a boiling point of 127 was distilled into a receiver charged with BHT. It was distilled to

BHT is 10ppm in 2-methoxydihydropyran
This 2-methoxydihydropyran was transferred to a sample bottle and stored in contact with air without replacing with nitrogen. After 2 days, it was distilled using the same equipment as in Example 3, but under an air atmosphere. When hydrolysis was carried out, the APHA of the glutaraldehyde-methanol-water system produced was 25.

Comparative Example 3 A glutaraldehyde aqueous solution was prepared in the same manner as in Example 3, except that 2-methoxydihydropyran was purified, stored, and hydrolyzed without a nitrogen seal.
APHA was 350.

Comparative Example 4 2-methoxydihydropyran obtained in the same manner as in Example 4 without using BHT was stored in a sample bottle without nitrogen substitution. Two days later, the solution obtained by hydrolysis under an air atmosphere was colored with APHA400.

Claims (1)

[Claims] 1 In a method for producing an aqueous glutaraldehyde solution by hydrolysis of 2-alkoxydihydropyran, crude 2-alkoxydihydropyran obtained by the reaction of acrolein and alkyl vinyl ether is distilled under an inert gas atmosphere to obtain purified 2-alkoxydihydropyran. pyran, and the purified 2-alkoxydihydropyran is stored under an inert gas atmosphere or with the addition of an antioxidant and then handled under antioxidant conditions to obtain a hydrolyzed solution with little coloration. Method for producing glutaraldehyde.