JPS6353982B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to the purification of p-aminophenol, and more specifically, to a method for recovering and extracting and purifying p-aminophenol, which removes the main impurities involved, namely 4,4'-diaminodiphenyl ether. This is a more selective removal method. p-Aminophenol (PAP) is well known and is an important chemical intermediate used in the production of the analgesic drug acetaminophene (APAP). It is also used as an intermediate in the production of dyes and photographic chemicals. Particularly with respect to 4,4'-diaminodiphenyl ether, high purity is desirable for p-aminophenol, especially for use in acetaminophene production. An important chemical and widely used method for the production of PAP involves the catalytic hydrogenation of nitrobenzene in a strongly acidic medium. In the basic method, the hydrogenation of nitrobenzene is carried out in the presence of 10-13% sulfuric acid with a small amount of a surfactant such as dodecyltrimethylammonium chloride and using a carbon-supported platinum catalyst. The reaction is somewhat complex and, in addition to the desired PAP, contains significant amounts of aniline as well as small amounts of 4,
4'-diaminodiphenyl ether (also known as oxydianiline or ODA), o
- produces a number of by-products including aminophenol, p-aminodiphenylamine and p-hydroxydiphenylamine. These by-products are significant impurities in the PAP final product; however,
Generally soluble in acidic aqueous media. 4,
4'-Diaminodiphenyl ether is a major minor amine byproduct, with an abundance of 20 ppm for PAP applications in the manufacture of pharmaceutical compounds.
It should be less than 10 ppm, preferably less than 10 ppm. In a particularly advantageous process for the production of PAP by catalytic hydrogenation of nitrobenzene in aqueous sulfuric acid (U.S. Pat. No. 1, Benner, May 14, 1968)
3383416), the hydrogenation reaction is interrupted before all of the nitrobenzene charged to the reactor is consumed. The catalyst tends to be suspended in the nitrobenzene layer and the aqueous reaction mixture containing PAP, aniline and minor amine byproducts in the form of salts is easily separated by decantation. As mentioned above, used in the production of APAP
It is preferred that the PAP is completely pure, especially with regard to 4,4'-diaminodiphenyl ether. p-
Many methods directed to improving the purification of aminophenols have been described in the patent literature. In addition to Benner U.S. Pat. No. 3,383,416, the following patents are suitable for methods of producing p-aminophenol: U.S. Pat. No. 〃 No. 4139562 No. 4176138 British Patent No. 1028078 No. 1038005 No. 1228568 No. 1291642 No. 1516380 Japanese Patent No. 1979-73741 US Patent No. 3717680 of Baron et al. In this case, aniline is used as a basic It is added to the aqueous reaction product from the Benner process to raise the PH above 6.0, preferably to a value of 6.5-7.5, at which point the PAP is in the free amine form. The solution is then cooled and PAP crystallizes out,
and washed first with aniline and then with toluene.
The aniline phase containing 4,4'-diaminodiphenyl ether and other minor amine byproducts is then separated from the aqueous phase. In Japanese patent number: 1979-73741,
A process for producing purified p-aminophenol is disclosed in which the catalytic reduction reaction mixture resulting from the catalytic reduction of nitrobenzene is partially neutralized with an alkali to a pH of 3.5 to 5. An aromatic amine such as aniline is then added to selectively replace 4,4'-diaminodiphenyl ether and other impurities associated with sulfuric acid in the aqueous phase. The liberated impurities are removed by extraction with excess aromatic amine. The recovered aromatic amine phase is washed with an aqueous alkaline solution and recycled for partial neutralization of the catalytic reduction reaction mixture. Reid, U.S. Pat. No. 3,845,129, describes a purified p-
discloses a production process in which aminophenol is recovered and aniline and 4,4'-diaminodiphenyl ether are present as impurities; - just before the PH where the diaminodiphenyl ether is in its free base form, the PH is
p in aqueous media that is 4.8 to 5.5 especially 5.0 to 5.5
- contacting a solution of aminophenol and impurities with an extraction medium consisting essentially of a water-immiscible, non-oxidizing solvent such as methylene dichloride, chloroform, carbon tetrachloride, etc. The solvent selectively dissolves impurities and recovers purified p-aminophenol from the aqueous phase. Toluene has been shown to be a relatively poor solvent for 4,4'-diaminodiphenyl ether. Yamamoto's U.S. Pat.
- Adjusting the pH to 7-8 by adding alkali to the aminophenol in an atmosphere of inert gas such as nitrogen and in the presence of a reducing agent such as sodium dithionite or sodium sulfite, the resulting crude separating the p-aminophenol precipitate from the liquid phase;
A method for purifying crude p-aminophenol is disclosed. The separated p-aminophenol is then redissolved in an aqueous alkali metal solution to form an aqueous solution of the alkali metal salt of crude p-aminophenol, which is brought into contact with an inert organic solvent that is immiscible with water to reduce the amount present in the system. This allows impurities to be selectively extracted in this organic solvent. A preferred organic solvent is aniline. U.S. Pat. No. 4,176,138 to Sathe discloses a process for producing p-aminophenol by catalytic hydrogenation of nitrobenzene in an acidic reaction medium, in which dimethyldodecylamine sulfate is Replaced with trimethyldodecyl ammonium chloride to remove impurities. U.S. Pat. No. 3,876,703 to Harmetsu et al.
A method for purifying crude aminophenol is disclosed, comprising preparing a mixture of an aqueous aminophenol solution and nitrobenzene, adjusting the mixture to a pH between 4.5 and 7.5, and separating the nitrobenzene phase. Although these purification methods, as well as others disclosed in the patent literature mentioned above, have some utility, they are more selective in removing 4,4'-diaminodiphenyl ether from PAP and require a larger general overview. Provides PAP with improved purity in yield,
There continues to be a need for a purification method that avoids the loss of PAP inherent in prior art methods. One object of the present invention is to reduce the content of 4,4'-diaminodiphenyl ether, preferably
It is an object of the present invention to provide an improved method for the recovery and extraction purification of p-aminophenol below 20 ppm or even below 10 ppm. Yet another purpose is p
- lower overall loss of aminophenols;
The objective is to provide a higher degree of purification of p-aminophenol that maximizes the removal of 4,4'-diaminodiphenyl ether and minimizes the loss of p-aminophenol. According to the invention, recovery and extraction of p-aminophenol produced by catalytic reduction of nitrobenzene in an acidic medium, whereby 4,4'-diaminodiphenyl ether and aniline are present as impurities. The purification method involves neutralizing an aqueous raw material solution containing p-aminophenol and the above impurities with a base, adjusting the pH of the solution to between 4.0 and 5.0, and adding 1 part by volume of toluene to the resulting aqueous raw material solution. 4 parts of aniline to 1 part of aniline per 4 parts of toluene with an organic solvent consisting of a mixture of aniline and toluene, thereby extracting the 4,4'-diaminodiphenyl ether in the organic solvent. selectively extracted into an aqueous phase containing primarily p-aminophenol and aniline containing p-aminophenol, 4,4'-diaminodiphenyl ether as well as other minor amine by-products.
A toluene organic phase is formed and p-aminophenol of improved purity is then recovered from the aqueous phase. Preferably, the organic phase containing aniline, p-aminophenol, and 4,4'-diaminodiphenyl ether is back-extracted with a basic solution of potassium hydroxide or sodium hydroxide, and the basic solution and an aqueous layer containing p-aminophenol, which was previously included in all of the above organic phases, and a 4,4'-
A residual organic phase containing diaminodiphenyl ether is formed and the aqueous phase is recycled as part of the base used to adjust the pH of the initial aqueous feed solution to between about 4.0 and 5.0. The method is such that it can be carried out using conventional equipment. Instead of potassium hydroxide or sodium hydroxide, the organic phase can be back extracted by treating with ammonium sulfate solution whose pH is adjusted to between about 4.8 and 5.0. In another embodiment of the invention, the advantages of increased overall yield and higher purity p-aminophenol production are both p-
Contains aminophenol and the above-mentioned impurities, and has a pH of approximately
This can be achieved by fractional countercurrent extraction of an aqueous raw material solution between 4.0 and 5.0 with an aniline-toluene mixture and an ammonium sulfate solution or aniline sulfate or sulfuric acid, whereby 4.
The 4'-diaminodiphenyl ether is extracted into an aniline-toluene mixture, and the aqueous phase containing primarily p-aminophenol and p-aminophenol, 4,4'-diaminodiphenyl ether, as well as other by-product amines are separated. An organic aniline phase containing This aqueous phase is then separated from the organic phase and p-aminophenol of improved purity is recovered from the aqueous phase as before. Using the present invention, an aqueous stock solution containing p-aminophenol and aniline and 4,4'-diaminodiphenyl ether as impurities, obtained in a conventional manner from a nitrobenzene catalytic reaction in an acidic medium, is first treated with a base. The pH of this raw material solution upon contact
p-aminophenol with improved purity can be produced through a recovery and extractive purification process in which the p-aminophenol is adjusted to between about 4.0 and 5.0 and then extracted with an organic solvent consisting of a mixture of aniline and toluene. Under these specific PH conditions and with such organic solvents, the main impurity of interest, i.e. 4,4'-
The diaminodiphenyl ether is more selectively extracted into the organic solvent phase to improve the purity of p-aminophenol, i.e. less than 20 ppm of 4,4'-diaminodiphenyl ether, more preferably in the experimental examples described below. As dismantled by 4,
An additional 10 ppm of 4′-diaminodiphenyl ether
It becomes possible to produce less p-aminophenol. As mentioned above, the starting materials for the process of the present invention are p-aminophenol and aniline, 4, resulting from the catalytic reduction of nitrobenzene in a sulfuric acidic medium as described in Benner U.S. Pat. No. 3,383,416. An aqueous feed solution containing 4'-diaminodiphenyl ether and other minor amine byproducts. This aqueous feed solution may also contain small amounts of unreacted nitrobenzene or may be treated to remove substantially all nitrobenzene before commencing the practice of the invention. This raw aqueous solution is first contacted with a base to adjust the pH of the solution to about 4.0-5.0. This is one important feature of the present invention, because this PH
In the region 4,4'-diaminodiphenyl ether, aniline and minor amine byproducts are
- Aminophenol, which is a weaker base, is liberated in the form of the free amine, while p-aminophenol remains mainly in its sulfate form. Thus, the difference in basicity of these compounds allows the undesired components to be present in the free amine form and the desired components to be present as the p-aminophenol sulfate salt. As can be seen from the experimental results described later, 4.0 to 4.5
A PH in the range of 4.5 to 5.0 is more favorable for the reaction of p-aminophenol in the aqueous phase, while a PH in the range 4.5 to 5.0 is more favorable for the removal of 4,4'-diaminodiphenyl ether. However, within the scope of the present invention, both of these objectives can be met over the entire range of 4.0 to 5.0 by utilizing a sufficient number of extraction stages. The use of a base such as ammonia (which includes ammonium hydroxide) or potassium hydroxide is highly preferred in order to achieve the adjustment of the pH of the raw aqueous solution to 4.0-5.0. However, any alkali metal hydroxide or alkali metal salt of p-aminophenol may also be used for this purpose.
Furthermore, a basic solution containing potassium hydroxide or sodium hydroxide and p-aminophenol generated from the back extraction step described below is added to the pH of the raw material aqueous solution.
It may be recycled as part of the base used to adjust to 4.0-5.0. After making the desired pH adjustment, this raw aqueous solution is then extracted with a mixture of aniline and toluene to selectively dissolve the 4,4'-diaminodiphenyl ether and extract the aqueous solution containing primarily p-teminophenol. A phase and an aniline-toluene organic phase containing p-aminophenol, substantially all of the 4,4'-diaminodiphenyl ether originally present in the feed aqueous solution, as well as other aniline-toluene soluble impurities are formed. In accordance with the present invention, it has been found that the desired results are achieved when the ratio of aniline to toluene ranges between about 4 parts aniline per 1 part toluene and about 1 part aniline per 4 parts toluene by volume. Ta. Preferably a ratio of 1 part aniline to 1 part toluene by volume reduces dissolution losses of PAP in the organic solvent phase while reducing the 4,4'-
It is used to allow equivalent removal of diaminodiphenyl ether. In such organic solvent mixtures, aniline functions as an extractant, while toluene functions as an antisolvent and diluent. Thus, while toluene is inherently a poor solvent for p-aminophenol and 4,4'-diaminodiphenyl ether, the resulting mixture when combined with aniline in the above ratios provides the desired solvent properties for this system as well as the desired It was found that it exhibits the physical properties of The extraction of 4,4'-diaminodiphenyl ether from the aqueous raw material solution described above can be carried out either batchwise or continuously. Preferably, it is carried out in a countercurrent extraction column, such as a reciprocating plate countercurrent extraction column of Cull or other similar columns known by those skilled in the art. Equipment such as centrifugal countercurrent extractors, pumper-decanter pulsating extraction columns or mixer-settler equipment may also be used. Thus, for example, using a Cal countercurrent extraction column, the 4,4'-diaminodiphenyl ether content of the p-aminophenol aqueous phase can be reduced from 50% to 50% aniline-toluene with a number of 3-4 theoretical extraction plates. At a pH of 4.8 with the mixture
to less than 50 ppm and typically less than 10 ppm, while attempting to achieve similarly low 4,4'-diaminodiphenyl ether content at a constant organic-to-aqueous ratio requires a single bed of aniline. In this case, it was found that about 5 stages are required, and 16-20 cross-flow extractions are required for a single batch of aniline. It has also been found that the volume ratio of aniline-toluene to raw aqueous solution is an important factor in the formation of the extraction stage. Generally, lower ratios are preferred because less p-aminophenol is extracted into the organic phase and therefore p-
This is because more aminophenols are found in the aqueous phase. Overall, a volume ratio of aniline-toluene to raw aqueous solution of 0.05 to 1:1 can be used, with a ratio of 0.2:1 being preferred. Once the extraction is complete, some aniline and a very small amount (based on p-aminophenol)
The aqueous phase or raffinate containing the majority of p-aminophenol together with 4,4'-diaminodiphenyl ether (up to 50 ppm) is separated from the organic phase. This aqueous roughinate phase is then treated with 7-
Neutralization to a pH of 8 precipitates the partially purified p-aminophenol product. Precipitation of p-aminophenol occurs at pH between 5 and 8, but the minimum solubility of p-aminophenol is between 7 and 8.
The majority of the product precipitates in this range. The precipitated p-aminophenol is then collected by filtration, washed with toluene and sodium bisulfate solution, and dried in vacuo. Toluene removes attached aniline and sodium bisulfate acts as an antioxidant. The dry p-aminophenol product thus obtained is typically
It contains less than 10 ppm of 4,4'-diaminodiphenyl ether and has an acceptable purity for use in the production of acetaminophene. aniline, p-aminophenol, and 4,
The organic phase or extract from the extraction step containing 4'-diaminodiphenyl ether is subjected to distillation to recover the aniline for reuse, or preferably to additional addition to improve the overall yield of p-aminophenol. It is further subjected to treatment as described below for the recovery of p-aminophenol. Thus, preferably the organic phase is subjected to back extraction by addition of a solution of potassium or sodium hydroxide, preferably potassium hydroxide, thereby removing the potassium or sodium hydroxide originally contained in the organic phase. an aqueous layer containing substantially all of the p-aminophenol;
A residual organic phase is formed which contains substantially all of the 4,4'-diaminodiphenyl ether originally contained in the organic phase. The concentration of the potassium hydroxide or sodium hydroxide solution should be in excess of the amount necessary to convert the p-aminophenol to its phenolate salt form. Generally, for example 10
A concentration of potassium hydroxide of −50% by weight should be used. The pH of the aqueous layer obtained from back extraction is above 12. The pH of this aqueous layer can be adjusted to 7-8, such as by the addition of concentrated sulfuric acid, to produce a solid containing technical grade p-aminophenol. but,
According to the present invention, the aqueous phase is recycled as part of the base used to adjust the pH of the starting aqueous feedstock solution, thereby passing unrecovered p-aminophenol from this aqueous phase into the main process stream. By reintroducing
p with increased purity through the basic extraction method described above.
- It is highly preferred to obtain a greater overall yield of aminophenol. Aniline and toluene are recovered from the residual organic phase by distillation and reused. Instead of back-extracting the organic phase from the basic extraction step with a solution of potassium hydroxide or sodium hydroxide, the organic phase can also be back-extracted with an ammonium sulfate solution to obtain a greater overall yield of p-aminophenol. can. However, preferably, and according to another feature of the invention, p-aminophenol, aniline,
A raw aqueous solution containing 4,4'-diaminodiphenyl ether and other minor component by-products and having a pH of 4.0 to 5.0 is mixed with a mixture of aniline and toluene, an ammonium sulfate solution with a pH of 4.0 to 5.0, and aniline sulfate. We have discovered that higher yields of p-aminophenol with improved purity can be achieved by fractional extraction in a sulfur-oriented manner, such as in Cal's reciprocating plate extraction column, with sulfuric acid or with sulfuric acid. . For example, a 15% ammonium sulfate solution with a PH of 4.8 to 5.0 or a 1.5% ammonium sulfate solution with a PH of 4.0 may be used for this purpose. Instead of ammonium sulfate, either aniline sulfate or sulfuric acid can be used. When the latter is used, it forms aniline sulfate with the aniline present in the organic phase. The 4,4'-diaminodiphenyl ether is again selectively extracted into the aniline-toluene mixture. This extraction removes more p-aminophenol originally present in the raw aqueous solution than in the previously described extraction step, which uses an aniline-toluene mixture without an ammonium sulfate solution for the back extraction of p-aminophenol. An aqueous phase containing . The similarly formed organic phase contains substantially all of the 4,4'-diaminodiphenyl ether previously contained in the raw aqueous solution. The aqueous phase containing p-aminophenol is separated from the organic phase and treated as before to yield p-aminophenol of improved purity containing less than 10 ppm of 4,4'-diaminodiphenyl ether. The organic phase can be used for the recovery of aniline-toluene and also for the recovery of p-aminophenol, as described above. The following working examples further illustrate the practice of the invention. Example 1 Catalytic hydrogenation of nitrobenzene in the presence of platinum on a carbon support, 10-13% aqueous sulfuric acid, and a small amount of dodecyltrimethylammonium chloride (U.S. Pat. No. 3,383,416 to RG Benner, May 14, 1968). p-aminophenol hydrogenated solution (10) obtained by
was added to a 12 round bottom flask and the pH was adjusted to 4.8-5.0 by addition of concentrated ammonium hydroxide (1). Separately at this point, an aqueous phase containing potassium hydroxide and p-aminophenol (Example 2
may be used in place of a portion of the concentrated ammonium hydroxide. The aqueous p-aminophenol raw material solution whose pH has been adjusted to 4.8-5.0 in this way is usually treated as sulfate.
The main components are 100 mg/ml p-aminophenol, 20 mg/ml aniline, and 3 mg/ml 4,4'-diaminodiphenyl ether. The solution was heated to 85-90°C using a heating mantle and fed through an adiabatic metering pump at approximately 250 ml/min to the top section of a Kull reciprocating plate extraction column with a 1 inch diameter and 8 foot tall plate stack. do. at the same time,
50%-50% of aniline and toluene at a temperature of 85℃
The mixture (by volume) (approx. 1) is fed at 50 ml/min to the bottom of the column via the same metering pump, thus achieving the desired countercurrent flow pattern of droplet dispersion and coalescence according to the normal operation of the extraction column. was established. After reaching equilibrium, the aqueous ruffinate phase contains approximately 90 mg/ml p-
aminophenol, 35 mg/ml aniline, and
It contained less than 0.001 mg/ml of 4,4'-diaminodiphenyl ether. The organic phase, the aniline-toluene extract phase, contained approximately 50 mg/ml p-aminophenol, 15 mg/ml 4,4'-diaminodiphenyl ether, and other aniline-toluene soluble impurities. Aqueous roughinate phase (11)
is collected and treated with concentrated ammonium hydroxide.
Partially purified p- was further neutralized to a pH of 7.0-8.0.
The aminophenol product was precipitated. The product was collected by filtration, washed with toluene (750ml) and 10% sodium bisulfate solution (300ml) and then dried in vacuo. Approximately 950 g of dry diaminodiphenyl ether containing less than 10 ppm of 4,4'-diaminodiphenyl ether was obtained. This organic extract was utilized for recovery of aniline by distillation or for recovery of p-aminophenol as described in Example 2 below. Example 2 Example 1 was repeated and the resulting hot organic extraction phase (approximately
2.2) was isolated and placed in a 5 round bottom flask equipped with a stirrer. The organic phase was cooled to ambient temperature. An aqueous potassium hydroxide solution (900 ml, 10% by weight) was added to the organic extract phase and the heterogeneous mixture was stirred for 15 minutes and allowed to settle for 5 minutes. Each layer was then separated by decanting. The aqueous phase now contains approximately 97% of the p-aminophenol and approximately 97% of the diaminophenyl ether previously contained in the organic phase.
It contained 1.5%. The remaining organic phase contained approximately 3% of the p-aminophenol and 98% of the 4,4'-diaminodiphenyl ether. The aqueous phase can be utilized in combination with ammonia or other bases in the initial neutralization step (adjusting the pH of the aqueous stock solution to 4.0-5.0) as described in Example 1, or p-
It is operated separately for the recovery of aminophenol. Addition of concentrated sulfuric acid (about 900 ml) to the aqueous phase with cooling precipitated a solid containing about 154 g of technical p-aminophenol. Example 3 Example 1 was repeated, except that the pH of the aqueous stock solution was
was adjusted to 4.5 by addition of concentrated ammonium hydroxide. After reaching equilibrium, the resulting aqueous ruffinate phase contains 97 mg/ml of p-aminophenol, 35
mg/ml of aniline and less than 0.001 mg/ml of 4,4'-diaminodiphenyl ether. The organic extract phase contained approximately 16 mg/ml p-aminophenol and 15 mg/ml 4,4'-diaminodiphenyl ether in addition to other minor impurities. Example 4 Example 1 was repeated, except that the aqueous stock solution was
PH to 4.0 by addition of concentrated ammonium hydroxide
I adjusted it to After reaching equilibrium, the aqueous ruffinate phase formed contained 98 mg/ml of p-aminophenol, 35
mg/ml of aniline and less than 0.001 mg/ml of 4,4'-diaminodiphenyl ether. The organic extract phase contained approximately 12 mg/ml p-aminophenol and 15 mg/ml 4,4'-diaminodiphenyl ether in addition to other minor impurities. Example 5 Example 1 was repeated except that the organic solvent feed was a 25% to 75% (by volume) mixture of aniline and toluene. After reaching equilibrium, the aqueous raffinate phase formed contains 94 mg/ml of p-aminophenol,
35 mg/ml aniline and 0.015 mg/ml 4,4'-
Contains diaminodiphenyl ether. The organic extract phase contains approximately 30 mg/ml of p-aminophenol.
It contained 15 mg/ml of 4,4'-diaminodiphenyl ether. Example 6 Example 1 was repeated except that the organic solvent feed was 75%:25% (by volume) of aniline and toluene.
It was a mixture. After reaching equilibrium, the aqueous raffinate phase formed contains 88 mg/ml of p-aminophenol,
It contained 35 mg/ml aniline and less than 0.001 mg/ml 4,4'-diaminodiphenyl ether. The organic extract phase contained 60 mg/ml p-aminophenol and 15 mg/ml 4,4'-diaminodiphenyl ether. Example 7 Example 1 was repeated except that the p-aminophenol hydrogenation solution and the aniline-toluene were made in the same manner to the Cal countercurrent extraction column, and the pH of the p-aminophenol hydrogenation solution was the same. 4.8 in a way
Adjusted to -5.0. In addition, the pH can be adjusted by adding sulfuric acid.
1 with 1.5% ammonium sulfate adjusted to 4.0. p-Aminophenol hydrogenation solution at 85℃
was fed to the center of the Cull tower at a rate of 250 ml/min. Aniline-toluene and ammonium sulfate feed solution
ml/min at 85°C to the bottom and top of the column, respectively. The operation of the column was carried out to provide four theoretical plates and clear phase separation in the lower half of the column.
After reaching equilibrium, the aqueous raffinate phase contained approximately 99 mg/ml p-aminophenol, 35 mg/ml aniline, and less than 0.001 mg/ml 4,4'-diaminodiphenyl ether. The organic extract phase is approximately 5
mg/ml p-aminophenol, 15 mg/ml 4,
Contained 4'-diaminodiphenyl ether and other aniline-toluene soluble impurities. Example 8 Example 7 was repeated, except that aniline sulfate, made by titrating 2% sulfuric acid with aniline to a pH of 3.8, was used in place of the 1.5% ammonium sulfate solution. After reaching equilibrium, the aqueous raffinate phase contains 99.9 mg/ml p-aminophenol, 45
mg/ml aniline and less than 0.001 mg/ml 4,
It contained 4'-diaminodiphenyl ether.
The organic extract phase contained approximately 2 mg/ml p-aminophenol, 15 mg/ml 4,4'-diaminodiphenyl ether and other minor impurities. The results are summarized in the table below.

【table】

[Table] Aqueous toluene 6.2/1 75/25 4.9−5.0 88
35 ＜.001 60 15 88

7.2/1.1 50/50 4.8−5.0 99
35 ＜.001 5 15 99

8.2/1.1 50/50 4.5
99.9 45 ＜.001 2 15 9
9

Claims (1)

[Claims] 1. A method for recovering and extracting and purifying p-aminophenol produced by catalytic reduction of nitrobenzene in an acidic medium containing 4,4'-diaminodiphenyl ether and aniline as impurities. First, the method involves neutralizing an aqueous raw material solution containing p-aminophenol and the above-mentioned impurities with a base, adjusting the pH of this solution between 4.0 and 5.0, and using the resulting aqueous raw material solution. , by volume, with an organic solvent consisting of a mixture of aniline and toluene ranging between 4 parts of aniline per 4 parts of toluene and 1 part of aniline per 4 parts of toluene, thereby extracting 4,4'-diaminodiphenyl ether. is selectively extracted into this organic solvent to form an aqueous phase containing primarily p-aminophenol and an aniline-toluene organic phase containing p-aminophenol, 4,4'-diaminodiphenyl ether, and other minor amine byproducts. give rise to a phase,
A process consisting of separating the aqueous phase from the organic phase and subsequently recovering purified p-aminophenol from the aqueous phase. 2. A process according to claim 1, wherein the base is ammonia, an alkali metal hydroxide, an alkali metal salt of p-aminophenol, or a mixture of ammonia and a potassium or sodium salt of p-aminophenol. 3. The method according to claim 1 or 2, wherein the pH of the aqueous raw material solution is about 4.0. 4 The above organic solvent is 50% aniline and 50% by volume.
Claims 1 to 3 consisting of toluene.
method. 5 Adjust the pH of the aqueous phase between 7.0 and 8.0 to
A method according to any of the preceding claims for precipitating aminophenols. 6 The volume ratio between the organic solvent and the aqueous raw material liquid is
A method according to any of the claims, between 0.05:1 and 1:1. 7. A method according to claim 6, wherein said volume ratio is about 0.2:1. 8. A method according to any of the preceding claims, wherein the extraction with the organic solvent is carried out in a countercurrent manner using approximately 5 theoretical extraction stages. 9. A method according to any of the preceding claims, wherein the recovered p-aminophenol is further washed with toluene and sodium bisulfate solution and dried. 10. A method according to any of the preceding claims, wherein aniline is recovered from the organic phase by distillation. 11 Treating the organic phase with a base consisting of a solution of potassium hydroxide or sodium hydroxide,
an aqueous phase containing the base and substantially all of the p-aminophenol previously contained in the organic phase; and a residual organic phase containing substantially all of the 4,4'-diaminodiphenyl ether previously contained in the organic phase. A method according to any of the preceding claims for producing a phase. 12. Process according to claim 11, characterized in that the organic phase is treated with a base consisting of a solution containing 10 to 50% by weight of potassium hydroxide. 13. Treating the organic phase with an agent selected from the group consisting of aqueous ammonium sulfate, aniline sulfate, and sulfuric acid to produce an aqueous phase containing the agent and substantially all of the p-aminophenol previously contained in the organic phase. and a residual organic phase comprising substantially all of the 4,4'-diaminodiphenyl ether previously contained in the organic phase. 14. Claim 1, wherein said agent is a 15% solution of ammonium sulfate with a PH between 4.8 and 5.0.
Method according to 3. 15. The method according to claim 13, wherein said agent is a 1.5% aqueous solution of ammonium sulfate with a PH of 4.0. 16. A method according to any of claims 1 to 12, wherein the aqueous phase is recycled and utilized as part of the base used to adjust the pH of the initial aqueous raw material solution between 4.0 and 5.0.