Method for purifying sulfonated aromatic monomer

Abstract

The present invention relates to an improved method for purifying a sulfonated aromatic monomer. The method is an economical method capable of providing a highly pure sulfonated aromatic monomer, in which a salt precipitation step and a recrystallization step are simplified while maintaining the reaction conditions used in a conventional method for synthesizing the sulfonated aromatic monomer, and a purification process is carried out using an easily available and stable chemical substance. The sulfonated aromatic monomer obtained by the purification method will be useful for the preparation of a polymer for a polymer electrolyte membrane and will be advantageous to synthesize polymer with high molecular weight.

Claims

1. A method for purifying a sulfonated aromatic monomer represented by formula 1 as shown in the following reaction scheme 2, the method comprising the steps of: allowing an aromatic monomer 3 to react with fuming sulfuric acid 4 to prepare a sulfonated aromatic compound 2; adding a salt to the compound 2 to precipitate a crude compound 1-1; dissolving the crude compound 1-1 in water, wherein the step of dissolving the crude compound is carried out after washing the crude compound with alcohol selected from among methanol, ethanol or a mixture thereof to remove sulfuric acid remaining in the crude compound 1-1; neutralizing the aqueous solution containing the crude compound, wherein the step of neutralizing the aqueous solution containing the crude compound is carried out using any one weak base selected from the group consisting of sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, ammonia, sodium phosphate and sodium sulfate; and concentrating the neutralized aqueous solution and recrystallizing the concentrate from water, wherein alcohol is not added during the steps of neutralizing and recrystallizing: ##STR00004## wherein X is a halogen group element, and Y is any one selected from the group consisting of S, CO, P(O)(C.sub.6H.sub.5) and SO.sub.2.

2. A method for a sulfonated aromatic monomer represented by formula 1 as shown in the following reaction scheme 2, the method comprising the steps of: allowing an aromatic monomer 3 to react with fuming sulfuric acid 4 to prepare a sulfonated aromatic compound 2; adding a salt to the compound 2 to precipitate a crude compound 1-1; dissolving the crude compound 1-1 in water; neutralizing the aqueous solution containing the crude compound, wherein the step of neutralizing the aqueous solution containing the crude compound is carried out by neutralizing the aqueous solution with anion exchange resin, followed by a washing step; and concentrating the neutralized aqueous solution and recrystallizing the concentrate from water, wherein alcohol is not added during the steps of neutralizing and recrystallizing: ##STR00005## wherein X is a halogen group element, and Y is any one selected from the group consisting of S, CO, P(O)(C.sub.6H.sub.5) and SO.sub.2.

3. The method of claim 2, wherein the washing step is carried out by washing the anion exchange resin with the same amount of a base as that of the anion exchange resin.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a flowchart showing a conventional process for purifying a sulfonated aromatic monomer;

(2) FIG. 2 is a flowchart showing a process for purifying a sulfonated aromatic monomer according to a first preferred embodiment of the present invention;

(3) FIG. 3 is a flowchart showing a process for purifying a sulfonated aromatic monomer according to a second preferred embodiment of the present invention; and

(4) FIG. 4 shows the .sup.1H NMR spectrum of the sulfonated aromatic monomer purified according to the first and second embodiments of the present invention.

BEST MODE

(5) Hereinafter, the present invention will be described in further detail.

(6) The present invention provides a method for purifying a sulfonated aromatic monomer 1 as shown in the following reaction scheme 2, the method comprising the steps of: allowing an aromatic monomer 3 to react with fuming sulfuric acid 4 to prepare a sulfonated aromatic compound 2; adding a salt to the compound 2 to precipitate a crude compound 1-1; dissolving the crude compound 1-1 in water; neutralizing the aqueous solution containing the crude compound; and concentrating the neutralized aqueous solution and recrystallizing the concentrate from water:

(7) ##STR00003##

(8) The improved method for purifying the sulfonated aromatic monomer 1 according to the present invention is characterized in that the salt precipitation step and the recrystallization step are simplified while maintaining the reaction conditions used in a conventional method for purifying the sulfonated aromatic monomer.

(9) Specifically, the steps of obtaining the sulfonated aromatic compound 2 by sulfonation and adding the salt (NaCl) to the sulfonated aromatic compound 2 to obtain the compound 1-1 are the same as those of the conventional method.

(10) However, in the salt precipitation step of the conventional process, the sulfonated aromatic compound 2 obtained by reacting the aromatic monomer with 20-60%; fuming sulfuric acid for 4-12 hours is added to the salt (NaCl) in an ice/waster (50%) solution to precipitate the compound (1-1).

(11) In comparison with this, in the purification of the present invention, the sulfonated aromatic compound 2 is added to the salt (NaCl) on ice alone and stirred to obtain the compound 1-1.

(12) When the sulfonated aromatic compound 2 is added to ice to precipitate the salt, the generation of heat can be prevented, and thus a reaction time of 6 hours or longer in the conventional method can be shortened to 1 hour or shorter in the method of the present invention.

(13) The dissolution step in the purification method of the present invention is a step of dissolving the crude compound 1-1 in water, like that of the conventional method. However, the dissolution step of the present invention is characterized in that the crude compound 1-1 is dissolved in water after washing with alcohol. Herein, the alcohol that is used in the dissolution step is preferably methanol, ethanol or a mixture thereof. More preferably, the alcohol is any one selected from among methanol and ethanol.

(14) When the crude compound 1-1 is washed with alcohol, a sulfuric acid component remaining in the crude compound 1-1 can be removed by washing, and thus the purity of the target compound can be increased.

(15) Next, the neutralization step is carried out. In a preferred embodiment of the present invention, the neutralization step is carried out using a weak base. More preferably, it is carried out using any one weak base selected from the group consisting of sodium carbonate, sodium hydrogen carbonate, ammonium hydroxide, ammonia, sodium phosphate, and sodium sulfate.

(16) Sodium carbonate (NaCO.sub.3) is used in the neutralization step in the most preferred embodiment of the present invention, but any conventional weak base may be used without limitation in the present invention, as long as it can neutralize the compound to a pH of 6-7. Also, in the neutralization step of the present invention, if the range of the pH to be adjusted is broad, the pH may be first adjusted with 10% NaOH solution, and then adjusted with a weak base solution.

(17) Thus, according to the present invention, the neutralization step can be easily performed without causing a change in pH that result from the use of a strong base (NaOH) in the conventional method.

(18) In another embodiment of the present invention, the neutralization step is carried out using anion exchange resin. Specifically, the crude compound 1-1 dissolved in water in the dissolution step is neutralized by passage through anion exchange resin. The neutralization step employing anion exchange resin may be repeated 1-3 times.

(19) When the anion exchange resin is used, a large amount of NaCl dissolved in the aqueous solution of the crude compound 1-1 can be removed by washing. After the neutralization step employing the anion exchange resin, washing with a base is carried out to detach the compound 1-1 attached to the anion exchange resin, and the detached compound 1-1 is neutralized in the next neutralization step. Herein, the base is used in the same amount as the anion exchange resin.

(20) The recrystallization step in the purification method of the present invention is carried out by concentrating the aqueous solution resulting from the neutralization step and recrystallizing the concentrate from water.

(21) However, the recrystallization step in the conventional purification method is carried out in a mixed solvent of alcohol and water (50:50 v/v). Because the compound 1-1 does not easily dissolve in the mixed solvent of water and alcohol, the alcohol/water mixture should be used in an amount corresponding to 30-40 times that of the compound 1 in order to recrystallize the compound 1. In comparison with this, in the method of the present invention, a crystal can be recovered by removing a slight amount of water from the aqueous solution, and thus the recrystallization step can be simplified compared to the conventional method.

(22) In addition, the method of the present invention can eliminate the problem of the conventional method in which an excessive amount of the solvent is used to increase the purification cost or the salt (NaCl) is recrystallized in an excessive amount of the solvent.

(23) FIG. 2 is a flowchart showing a process for purifying a sulfonated aromatic monomer according to a first preferred embodiment of the present invention, and FIG. 3 is a flowchart showing a process for purifying a sulfonated aromatic monomer according to a second preferred embodiment of the present invention. As shown therein, in the method for purifying the sulfonated aromatic monomer according to the present invention, while the reaction conditions used in the conventional method for purifying the sulfonated aromatic monomer are maintained, the number of the salt precipitation steps is reduced, the recrystallization step is simplified, and the purification step is carried out using an easily available, stable substance under economical and mild conditions.

(24) FIG. 4 shows the 1H NMR spectrum of the sulfonated aromatic monomer obtained by the purification method of the present invention. As can be seen therein, the sulfonated aromatic monomer was synthesized with high purity.

(25) Further, the sulfonated aromatic monomer purified by the purification method of the present invention can be used for the preparation of a polymer for a polymer electrolyte membrane, and the polymer has an intrinsic viscosity of 1.0-3.0 dl/g, suggesting that the sulfonated aromatic monomer will be advantageous to synthesize polymer with high molecular weight.

MODE FOR INVENTION

(26) Hereinafter, the present invention will be described in further detail with reference to examples. It is to be understood, however, that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention.

Example 1

Prepare of Pure Disulfonated Dichlorodiphenyl Sulfone (SDCDPS)

(27) In a 3-neck flask, 28.7 g (99 mmol) of 4,4-dichlorodiphenyl sulfone (DCDPS) was dissolved in 35 ml of 65% fuming sulfuric acid. The solution was completely dissolved by heating at 110 for 6 hours. Then, the solution was cooled to room temperature and poured onto 400 ml of ice, and 180 g of sodium chloride (NaCl) was added thereto to precipitate a disulfonated dichlorodiphenyl sulfone (SDCDPS) salt substituted with sodium ion. The precipitate was filtered under reduced pressure, and the resulting salt was washed 1-3 times with 50 ml of ethanol to remove the remaining sulfuric acid. The material resulting from the ethanol washing process was dissolved in 100 ml of distilled water, and an aqueous solution of 2N Na.sub.2CO.sub.3 was slowly added dropwise thereto to adjust the pH to 6-7. Then, the resulting aqueous solution was distilled under reduced pressure to remove a slight amount of water and allowed to stand in a cold place (refrigerator) for about one day, thereby obtaining a white pure crystal. The obtained crystal was dried in a vacuum oven at 100 for about 2 days, thereby obtaining pure disulfonated dichlorodiphenyl sulfone (SDCDPS).

Example 2

Preparation of Pure Disulfonated Dichlorodiphenyl Sulfone

(28) In a 3-neck flask, 28.7 g (99 mmol) of 4,4-dichlorodiphenyl sulfone (DCDPS) was dissolved in 0.35 ml of 65% fuming sulfuric acid. The solution was completely dissolved by heating at 110 C. for 6 hours. Then, the solution was cooled to room temperature and poured onto 400 ml of ice, and 180 g of sodium chloride (NaCl) was added thereto to precipitate a disulfonated dichlorodiphenyl sulfone (SDCDPS) salt substituted with sodium ion. The precipitate was filtered under reduced pressure, and the resulting salt was washed 1-3 times with 50 ml of ethanol to remove the remaining sulfuric acid. The material resulting from the ethanol washing process was dissolved in 100 ml of distilled water, and then passed through 50 g of an anion exchange resin comprised of NH.sub.3.sup.+Cl.sup. coupled to a polystyrene structure in a filter funnel. The SDCDPS received in an Erlenmeyer flask was passed again through the anion exchange resin, and this process of passing the SDCDPS through the anion exchange resin was repeated 1-3 times. Then, the disulfonated dichlorodiphenyl sulfone (SDCDPS) attached to the anion exchange resin was detached using the same amount of a base as that of the anion exchange resin. The resulting solution was distilled under reduced pressure to remove water, and then allowed to stand in a cold place (refrigerator) for one day, thereby obtaining a white pure crystal. The obtained crystal was dried in a vacuum oven at 100 C. for about 2 days, thereby obtaining pure disulfonated dichlorodiphenyl sulfone (SDCDPS).

Comparative Example 1

Preparation of Disulfonated Dichlorodiphenyl Sulfone

(29) In a 3-neck flask, 28.7 g (99 mmol) of 4,4-dichlorodiphenyl sulfone (DCDPS) was dissolved in 60 ml of 30% fuming sulfuric acid (more than 3 equivalents). The solution was completely dissolved by heating at 110 C. for 6 hours. Then, the solution was cooled to room temperature and poured added to 400 ml of ice water, and 180 g of sodium chloride (NaCl) was added thereto to precipitate a disulfonated dichlorodiphenyl sulfone (SDCDPS) salt substituted with sodium ion. The precipitate was filtered under reduced pressure, and the filtrate was dissolved in 400 ml of distilled water and then adjusted to a pH of 6-7 by adding 2N NaOH thereto in small amounts.

(30) After the neutralization step, 180 g of sodium chloride (NaCl) was added to the solution to precipitate a disulfonated dichlorodiphenyl sulfone (SDCDPS) salt again. The precipitated material was filtered under reduced pressure and recrystallized from a 5:5 mixture of isopropanol and water. The resulting material was allowed to stand in a cold place for about one day, thereby obtaining a needle-like white crystal. The crystal was dried in a vacuum oven at 100 for about 2 days.

Test Example 1

(31) The disulfonated dichlorodiphenyl sulfone (SDCDPS), prepared and purified in each of Examples 1 and 2, was analyzed by an NMR spectrophotometer (Bruker AMX-300 MHz).

(32) As a result, as can be seen in the .sup.1H NMR spectrum in FIG. 4, the disulfonated dichlorodiphenyl sulfone compound was synthesized with high purity.

Test Example 2

(33) The kind and content of element in the disulfonated dichlorodiphenyl sulfone (SDCDPS), prepared and purified in each of Examples 1 and 2, were analyzed by an ICP (inductively coupled plasma-atomic emission) analyzer. Table 1 below shows the results of analyzing the content of sodium (Na) element in the compound obtained in each of Examples 1 and 2. As can be seen therein, the measured content of sodium was similar to the theoretical value, suggesting that the disulfonated dichlorodiphenyl sulfone as the target compound was synthesized with high purity.

(34) TABLE-US-00001 TABLE 1 Results of analysis of sodium content Theoretical value (%) Measured value (%) Example 1 9.35 9.25 Example 2 9.35 9.30

INDUSTRIAL APPLICABILITY

(35) As described above, the present invention provides an improved method for purifying a sulfonated aromatic monomer. Specifically, the improved purification method of the present invention is an economical method capable of providing a highly pure sulfonated aromatic monomer, in which the salt precipitation step and the recrystallization step are simplified while maintaining the reaction conditions used in the conventional method for synthesizing the sulfonated aromatic monomer, and the purification process is carried out using an easily available and safe-to-handle chemical substance.

(36) Further, the sulfonated aromatic monomer purified by the purification method of the present invention will be useful for the preparation of a polymer for a polymer electrolyte membrane. When a polymer is synthesized using the sulfonated aromatic monomer purified by the purification method of the present invention, the polymer has an intrinsic viscosity of 1.0-3.0 dl/g, suggesting that the sulfonated aromatic monomer will be advantageous to synthesize polymer with high molecular weight.

(37) Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.