JPS621933B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high purity 2,5-xylenol, and more specifically, from the middle distillate of the reaction mixture obtained by dimethylating the ortho position of m-cresol with methanol, high purity 2,5-xylenol is produced.
The present invention relates to a method for separating and recovering 5-xylenol. 2,5-xylenol is known to be useful as a raw material for PH indicators or as a raw material for pharmaceuticals such as antilipidemic drugs. Conventionally,
To synthesize 2,5-xylenol, p-xylene is sulfonated with concentrated sulfuric acid or fuming sulfur, and the resulting 2,5-xylenol sulfonic acid is alkaline fused to produce 2,5-xylenol sodium salt. Then, a method was adopted in which this sodium salt was neutralized to form 2,5-xylenol. However, this conventional method not only produces large amounts of gypsum and sodium sulfite as by-products, but also generates a large amount of wastewater, which poses problems for industrial implementation. The present invention proposes a method for producing highly pure 2,5-xylenol by orthomethylation reaction using m-cresol as a starting material, unlike the conventional method using p-xylene as a starting material. Both Yura and Abe, who are also the inventors of this invention,
As taught in No. 36738 (registered as Patent No. 862905), we have previously proposed a method for orthoalkylating phenols, and using this method to diorthomethylate m-cresol with methanol, vitamin E can be obtained. 2, 3, and 6 are important raw materials for
-A method for synthesizing trimethylphenol was established. It was also recognized that in this synthesis method, 2,5-xylenol and its isomer 2,3-xylenol are inevitably produced as by-products. However, as shown in Table 1, 2,5-xylenol and 2,3-xylenol have very similar boiling points and melting points, so normal distillation operations or simple recrystallization methods cannot separate them from 2,5-xylenol. High purity 2,5-xylenol cannot be separated and recovered from a mixture of 2,3-xylenol isomers.

[Table] However, according to the research conducted by the present inventors, from the middle distillate of the reaction mixture produced by diorthomethylating m-cresol with methanol, it was found that although the distillate mainly contains the above-mentioned isomer mixture, Nevertheless, it has been found that highly pure 2,5-xylenol can be separated and recovered, unlike the case where 2,5-xylenol is separated and recovered from a mixture of 2,5-xylenol and 2,3-xylenol. . The method for producing high-purity 2,5-xylenol according to the present invention involves producing a reaction mixture containing 2,3,6-trimethylphenol through an orthomethylation reaction of m-cresol with methanol.
From this reaction mixture, an unreacted methanol fraction and a by-product water fraction were collected as an initial distillate, and then a mixture of unreacted m-cresol and xylenols, which are intermediate products of the reaction, was collected as a middle distillate. Finally, the above middle distillate obtained when the 2,3,6-trimethylphenol fraction is obtained as the main fraction is cooled to precipitate crystals, and the crystals are recovered. In the present invention, the orthomethylation of m-cresol with methanol can be carried out under conditions that produce 2,3,6-trimethylphenol. -36738, methanol and m-cresol are mixed in the gas phase in the presence of a mixed catalyst consisting of magnesium oxide and iron oxide.
It is preferable to adopt a method of reacting at a temperature of 400 to 470°C. According to this method, 2,3,6-
Contains trimethylphenol, as well as xylenol isomers such as 2,5-xylenol and 2,3
- A reaction mixture containing xylenol can be obtained, the composition of which varies depending on the reaction conditions as shown in Table 2.

[Table] However, as can be seen from column 6 of Table 2, 2,5
-The xylenol content is almost unaffected by the reaction conditions and maintains a value of around 80% over an extremely wide range of m-cresol conversion rates. Therefore, in the orthomethylation reaction of the present invention, 2,
The reaction rate of m-cresol can be arbitrarily selected as long as the production of 3,6-trimethylphenol is guaranteed. However, if the reaction rate is low, the distillation load will increase when obtaining a middle distillate containing xylenol isomers from the reaction mixture produced, which is not a good idea. Therefore, the reaction rate of m-cresol in the present invention is 2. , 3,6-trimethylphenol is generally preferred. The reaction mixture produced by the orthomethylation reaction of the present invention includes 2,3,6-trimethylphenol and xylenol (2,5-xylenol +
2,3-xylenol), and usually contains unreacted m-cresol and methanol as well as by-produced water. According to the present invention, this reaction mixture is subjected to a distillation operation to extract an unreacted methanol fraction, a by-produced water fraction, and 2,3,
By separating the 6-trimethylphenol fraction from the reaction mixture, a middle distillate containing xylenol isomers and unreacted m-cresol is obtained. According to the knowledge obtained by the present inventors, in order to separate and recover high-purity 2,5-xylenol from this middle distillate, it is necessary to maintain the amount of m-cresol in the middle distillate at about 10 to 45%. It is possible to do so. The middle distillate is then cooled, whereby crystals of 2,5-xylenol precipitate. These crystals can be recovered by filtration means such as nutsie filter or centrifugation, but to facilitate the filtration operation, aromatic solvents such as benzene, toluene, xylene, n-pentane, n-hexane, etc. , n-heptane, cyclohexane, ligrolein, petroleum ether and other aliphatic solvents, as well as methanol, ethanol, isopropanol, t-
An alcoholic solvent such as butanol can be appropriately selected and used. Moreover, if the crystals recovered from the middle distillate are washed with the above-mentioned organic solvent, even higher purity 2,5-xylenol can be obtained. In order to obtain high-purity 2,5-xylenol according to the method of the present invention, it is essential to maintain the content of m-cresol in the middle distillate at about 10 to 45%, as described above. However, it is further desirable to appropriately select the temperature at which the middle distillate is cooled and filtered depending on the content of m-cresol in the middle distillate.
That is, the m-cresol content in the middle distillate is 10%.
Select a cooling filtration temperature of 30-37℃ if the content is about 20%, 23-30℃ if the content is about 20%, 18-25℃ if the content is 30%, and 15-22℃ if the content is 40%. is desirable. When the temperature is lower than the above temperature range, 2,5-
The purity of xylenol decreases, and when the temperature increases, the amount of 2,5-xylenol recovered decreases. As is clear from the detailed explanation above, the method for producing 2,5-xylenol according to the present invention is as follows:
Not only does it have the advantage that it can be carried out as part of the method for synthesizing 2,3,6-trimethylphenol, but it also has the advantage that it can be carried out as part of the method for synthesizing 2,3,6-trimethylphenol.
- There is no disadvantage of producing a large amount of by-products or waste water, as in the xylenol manufacturing method. Incidentally, in the method of the present invention, the filtrate obtained by filtering off unreacted methanol and 2,5-xylenol crystals separated from the orthomethylation reaction mixture can be recycled to the orthomethylation reaction system. Example 1 m-cresol was orthomethylated with methanol according to the method taught in Japanese Patent Publication No. 51-36738 to obtain a reaction mixture containing 2,3,6-trimethylphenol. From this reaction mixture, unreacted methanol and water were used as initial fractions, and 2,3,6-
Trimethylphenol is separated by rectification as the main distillate, and the middle distillate between the first distillate and the main distillate is m-cresol 43.9%, 2,5-xylenol 37.6%,
A middle distillate having a composition of 7.6% 2,3-xylenol, 4.7% 2,3,6-trimethylphenol, and 6.2% others was obtained. When 100 g of the above middle distillate was cooled while stirring in a 200 ml glass flask, acicular 2,5-xylenol crystals were precipitated at 15°C. The mixture was further cooled down to 10°C, and the precipitated crystals were filtered using a centrifuge. The crystals were then washed in a centrifuge with 23.6 g of cyclohexane, yielding 17 g of 2,5-xylenol as an almost white needle-like crystalline powder. The melting point of this product was 74-75°C, and the purity by gas chromatography was 99.5%. Example 2 100 g (m
-Cresol 30.7%, 2,5-xylenol 50.4
%, 2,3-xylenol 5.4%, 2,3,6-
Trimethylphenol 1.4%, other 12.1%)
When the mixture was cooled while stirring in a 200 ml glass flask, needle-shaped crystals were precipitated at 37°C. After further cooling to 25° C., the crystals were filtered using a centrifuge and washed with 26 g of cyclohexane to obtain 24 g of 2,5-xylenol as an almost white needle-like crystalline powder. The melting point of this product was 74-75°C, and the purity as determined by gas chromatography was 99.8%. Example 3 100 g (m
- 10% cresol, 72% 2,5-xylenol,
When 2,3-xylenol (18%) was cooled while stirring in a 200 ml glass flask, the temperature reached 40°C.
Needle-shaped crystals were precipitated. After further cooling to 30℃,
Filter the crystals with a centrifuge and add 70g of cyclohexane.
As a result of washing with water, 39 g of 2,5-xylenol was obtained as an almost white acicular crystalline powder. The melting point of this product was 73.8-75°C, and the purity by gas chromatography was 99.2%. Example 4 Distillate with the same composition as the middle distillate used in Example 2
When 20g of cyclohexane was added to 100g and cooled while stirring in a 200ml glass flask,
Needle crystals precipitated at 27°C. After further cooling to 15° C., the crystals were filtered using a centrifuge and washed with 34 g of cyclohexane to obtain 31.6 g of white needle-shaped crystalline powder of 2,5-xylenol. The melting point of this product was 73.8-75°C, and the purity by gas chromatography was 99.2%. Example 5 The same operation as in Example 2 was performed except that the cyclohexane used for washing the crystals in Example 2 was replaced with n-pentane, and 2,5-xylenol with a purity of 99.5% was used.
Obtained 25g. Comparative Example After heating and dissolving 30 g of a mixture of 80% 2,5-xylenol and 20% 2,3-xylenol in 80 g of cyclohexane, the solution was cooled while stirring in a 200 ml glass flask, and crystals precipitated at 30°C. After further cooling to 15° C., the crystals were filtered using a centrifuge and washed with 30 g of cyclohexane to obtain 22.5 g of white needle-like crystalline powder. The purity of this product by gas chromatography was 89.2%, and the presence of 2,3-xylenol was observed.

Claims (1)

[Claims] 1. A reaction mixture containing 2,3,6-trimethylphenol is produced by the orthomethylation reaction of m-cresol with methanol, and from this reaction mixture, an unreacted methanol fraction and a by-produced water fraction are extracted by rectification. is taken as the first distillate, then a mixture of unreacted m-cresol and xylenol, which is an intermediate product of the reaction, is taken as the middle distillate, and finally 2,3,6-trimethylphenol is taken as the main distillate. A method for producing high-purity 2,5-xylenol, which comprises cooling the middle distillate obtained during the production to precipitate crystals, and collecting the crystals.