WO1993004039A1

WO1993004039A1 - Purification of diphenylsulfone-4,4'-dicarboxylic acid

Info

Publication number: WO1993004039A1
Application number: PCT/EP1992/001828
Authority: WO
Inventors: Rudolf Frank De Block; Age Ruurd Waaksma
Original assignee: Akzo N.V.
Priority date: 1991-08-19
Filing date: 1992-08-11
Publication date: 1993-03-04

Abstract

Crude diphenylsulfone-4,4'-dicarboxylic acid (44 DDA) is purified by dissolving the crude 44 DDA in boiling acetic anhydride. This results in the formation of acetic acid/44 DDA mono-anhydride, which is separated, recovered and reconverted to 44 DDA.

Description

Puri fi cation of Diphenyl sul fone-4,4 ' -Di carboxyl i c Acid

Background of the Invention

The present i nventi on rel ates to di phenyl sul fone-4,4 ' -di carboxyl i c aci d (herei nafter referred to as 44DDA) , whi ch has the fol lowi ng general formul a (I) :

44DDA is normally produced via the liquid phase air oxidation of 4,4'-dimethyl diphenylsulfones. This process, in general, is well- known in the art and similar in most respects to the production of other aromatic polyacids. See, for example, JP-A-63310846, EP-A-0414062, US2673218, US3574727 and US3692828, all of which are hereby incorporated by reference for all purposes.

Yields from the oxidation process can vary significantly depending upon a number of factors such as, for example, raw materials, process conditions and catalyst choice. A yield of 96%, as disclosed in previously incorporated JP-A-63310846, is considered high.

The result is a "crude" product which comprises primarily 44DDA but also normally includes significant amounts (5-15 wt%) of unreacted starting materials and unwanted intermediate products such as onoacids, aldehyde acids, dialdehydes and alcohols.

44DDA potentially finds use, for example, in the production of aromatic polyesters, polyamides, polyara ides, polyarylates and other heterocyclic condensation polymers for application as engineering resins, fibers and films. These uses require a highly pure product (greater than 99% purity). The crude 44DDA resulting from the production process cannot, therefore, be utilized as such but must be purified. Described purification techniques for 44DDA and similar compound generally involve recrystallization in a solvent such as acetic acid, often under high pressure and temperature conditions. A variation on this technique is to first esterify the acid groups under high ^••• pressure conditions, recrystallize the ester, then saponify the so- recrystallized product.

Use of these purification techniques, however, has not resulted in a product of sufficient purity for significant commercial use. Product ¹⁰ loss (low yield) is also a drawback.

It would, therefore, be highly desirable to find a process which can be readily, effectively and efficiently utilized to purify crude 44DDA. 15

Summary of the Invention

The present inventors have found such a purification process which not -^ only results in highly pure 44DDA, but surprisingly also produces an exceptionally high yield of pure 44DDA based upon the amount of 44DDA contained in the crude product.

In accordance with the present invention, a purification process for -*^■•-^• crude 44DDA has been found which process comprises, in its overall concept, the steps of:

(1) dissolving the crude 44DDA in boiling acetic anhydride to thereby produce a solution comprising an acetic acid/44DDA monoanhydride; 0 (2) separating the acetic acid/44DDA monoanhydride from the so- produced solution, e.g., by cooling the solution in order to precipitate the acetic acid/44DDA monoanhydride; (3) recovering the separated acetic acid/44DDA monoanhydride e.g., by filtration; (4) reconverting the so-recovered monoanhydride back into 44DDA, e.g., by hydrolysis; and

(5) recovering the so-reconverted 44DDA in substantially pure form.

Analysis indicates that the intermediate formed during step (1) in accordance with the above-described process is acetic acid/44DDA monoanhydride, which has the following general formula (II):

0 0 0

H0-C- -S0₂- >-C-0-C-CH₃ (II)

It should be noted that previously incorporated US3574727 discloses a somewhat similar purification process except applied to terephthalic acid. While many of the steps disclosed in US3574727 may appear to be the same as those set forth above, it is believed that what actually occurs in the process with terephthalic acid is significantly different than what occurs with 44DDA.

One significant difference is that the dissolving of the crude 44DDA in boiling acetic anhydride surprisingly results in a highly selective and substantially quantitative reaction of 44DDA and acetic anhydride toward the formation of the above-mentioned acetic acid/44DDA monoanhydride. When terephthalic acid is utilized in place of 44DDA, however, it has been found that no significant monoanhydride formation occurs but instead only a portion of the terephthalic acid reacts and then only toward the formation of the dianhydride.

The so-formed monoanhydride in accordance with the present invention is readily separable from the remaining solution and, therefore, easily recovered and isolated. Because of the substantially selective and quantitative reaction of the 44DDA in the crude product, the so- recovered monoanhydride is not only quite pure, but also the yield (based upon the amount of 44DDA in the crude product) is quite high. In contrast, when terephathalic acid is utilized under the same conditions, it has been found that a substantial amount of the dianhydride intermediate remains in solution and is ultimately lost, resulting in much lower yields of pure terephthalic acid.

The monoanhydride in accordance with the present invention is then readily convertible back into 44DDA (with acetic acid as a by-product) by hydrolysis. The so-produced 44DDA can then be recovered in a highly pure form by removal from the remaining solution.

As a result it has been found that, when crude 44DDA is treated via the purification process of the present invention, purities of at least 99,5% can readily be reached with yields of at least 95% based upon the amount of 44DDA contained in the crude product.

These and other features and advantages of the present invention will be more readily understood by those skilled in the art from a reading of the following detailed description. Detailed Description of the Preferred Embodiments

As mentioned earlier, the crude 44DDA to be purified in accordance with the present invention primarily comprises 44DDA. When the crude 44DDA is the result of the oxidation of 4,4'-dimethyl diphenylsulfone, the crude 44DDA generally comprises from 85-95 wt% 44DDA, with the remainder comprising significant amounts of unreacted starting components and corresponding monoacid, as well as smaller amounts of other intermediate products such as the aldehyde acid, dialdehyde and alcohols.

The first step in the present process comprises dissolving the crude product in boiling acetic anhydride, preferably under atmospheric conditions for convenience. This may be accomplished, for example, by adding the crude 44DDA to acetic anhydride which is then heated to reflux temperature. At atmospheric pressure acetic anhydride boils at about 140°C. Sufficient acetic anhydride should be utilized in order to solve the crude 44DDA under reflux conditions, and reflux should continue at least until a clear solution is obtained.

It should be noted that the present process is not restricted to atmospheric pressure conditions but also can be operated under subatmospheric or superatmospheric pressures. These varying conditions, of course, will affect the boiling point of the acetic anhydride and resultant solubility of the crude product; however, one skilled in the art can readily adjust the operating conditions to take account of any such pressure variations.

In many respects, this first step is similar to the first step described in previously incorporated US3574727 (see column 2, line 47 through column 3, line 3), and reference may be had thereto for further details. One significant difference exists, as mentioned before, which is crucial to the effective operation of the present process - it has been found that the 44DDA in the crude product reacts substantially selectively and quantitatively to result in an acetic acid/44DDA monoanhydride of the general formula (II) detailed above. In contrast, under the same conditions it has been found that terephthalic acid only partially reacts and then only toward the production of the acetic acid dianhydride.

Subsequent to dissolution of the crude 44DDA, the resulting solution comprising the acetic acid/44DDA monoanhydride and impurities is then allowed to cool to a temperature sufficiently low enough so that the acetic acid/44DDA monoanhydride precipitates from solution. Preferably, the solution is allowed to cool to below 65°C, more preferably to below 50°C, and especially to ambient temperature for convenience.

The resulting precipitate can then be recovered by any normal means such as, for example, filtration. At this point, the recovered precipitate substantially comprises the monoanhydride intermediate, with only at most trace amounts of impurities remaining.

The so-recovered monoanhydride precipitate is then reconverted back into 44DDA preferably by hydrolysis. This may be accomplished, for example, by adding the precipitate (still in wet form) to a highly dilute aqueous acidic solution such as, for example, 0,005 N aqueous HC1 , then refluxing the mixture for several hours.

The resulting slurry is then allowed to cool, preferably to ambient temperature, and the precipitate (substantially pure 44DDA) recovered by any normal means, such as filtration, washing and drying.

The so-recovered 44DDA is substantially pure, with purities of at least 99,5% readily obtainable and greater than 99,9% achievable. In addition, the yield of substantially pure 44DDA is a surprisingly high at least 95% based upon the amount of 44DDA in the crude product.

The following general discussion of the present invention will be exemplified by the following examples offered by way of illustration and not limitation on the scope thereof.

Example 1

Crude 44DDA containing 10wt% of the methyl monoacid was purified as follows:

753 g of the crude 44DDA was added to 9 liters of acetic anhydride and the mixture heated to reflux (± 141°C). The mixture was maintained at reflux until a clear solution was obtained, which solution was then allowed to cool slowly to room temperature.

Upon cooling, a precipitate was formed which was removed by filtration then washed with 400 ml acetic anhydride. The wet precipitate was then added to 4 liters of a 0,005 N aqueous HCl solution, and the mixture heated to reflux. After refluxing for several hours, the resulting slurry was cooled to room temperature. The precipitate was removed by filtration then dried at 150°C under vacuum.

644 g of product were recovered. NMR spectroscopy revealed that the product was substantially pure 44DDA containing less than 0,1 wt% of impurities. The yield of the purification process, therefore, was 95%.

Example 2

This example sustantiates that a monoanhydride intermediate is indeed formed during the purification process involving 44DDA, while the same behavior is not experienced with terephthalic acid.

15 g of 44DDA (>99% purity) was added to 165 ml of acetic anhydride and the mixture heated to reflux (140°C). The mixture was maintained at reflux until a clear solution was obtained, which solution was then allowed to cool slowly to room temperature.

Upon cooling, a precipitate was formed which was removed by filtration then dried. The precipitate and remaining solution were then analyzed by NMR spectroscopy, with the results set forth below in Table I.

This procedure was then repeated in its entirety, except that the 44DDA was replaced with 15 g of terephthalic acid (>99% purity). The results are also set forth below in Table I. TABLE I

44DDA Terephthal i c Acid

15 165

9,4 0

1,6

0 0

5,9

Only a limited number of preferred embodiments of the present invention have been specifically described above. One skilled in the art, however, will recognize numerous substitutions, modifications and alterations which can be made without departing from the spirit and scope of the invention as limited by the following claims.

Claims

Cl aims

1. A purification process for crude diphenylsulfone-4,4'-dicarboxylic acid (44DDA), characterized in that the process comprises the steps of:

(1) dissolving the crude 44DDA in boiling acetic anhydride to thereby produce a solution comprising an acetic acid/44DDA monoanhydride;

(2) separating the acetic acid/44DDA monoanhydride from the so- produced solution; (3) recovering the separated acetic acid/44DDA monoanhydride;

(4) reconverting the so-recovered acetic acid/44DDA monoanhydride back into 44DDA; and

(5) recovering the so-reconverted 44DDA in substantially pure form.

2. The purification process of claim 1, characterized in that the crude 44DDA is dissolved by adding the crude 44DDA to acetic anhydride to form a mixture, then heating the mixture to reflux.

3. The purification process of claim 1, characterized in that the acetic acid/44DDA monoanhydride is separated from the solution by cooling the solution in order to precipitate the acetic acid/44DDA monoanhydride.

4. The purification process of claim 1, characterized in that the separated acetic acid/44DDA monoanhydride is recovered by filtration.

5. The purification process of claim 1, characterized in that the recovered acetic acid/44DDA monoanhydride is reconverted back into 44DDA by hydrolysis.

6. The purification process of claim 1, characterized in that the reconverted 44DDA is recovered in substantially pure form by washing then drying.

7. The process of any one of cl aims 1-6, characteri zed i n that the so-reconverted 44DDA i s recovered in a purity of at least 99,5%.

8. An aceti c acid/44DDA monoanhydri de of the general formul a:

9. A process of producing the acetic acid/44DDA monoanhydride of claim 8 by dissolving 44DDA in boiling acetic anhydride.