JPH0456811B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in a method for producing 2,3,5-trimethyl-hydroquinone (hereinafter abbreviated as TMHQ), and more specifically,
2,3,5-trimethyl-para-benzoquinone (hereinafter abbreviated as TMBQ), a precursor of TMHQ
The present invention relates to a method for producing high-quality TMHQ by first refining TMHQ to a state that facilitates catalytic hydrogen reduction, and then subjecting it to hydrogen reduction in the presence of an inexpensive Raney-Nickel catalyst. As the demand for vitamin E increases, the importance of TMHQ, one of its raw materials, is increasing.
There is a strong demand for the development of a method that can produce high-quality TMHQ at low cost. TMHQ can be produced by reducing TMBQ, but the reduction methods include methods using reducing agents such as hydrosulfite and acidic sodium sulfite, and catalytic methods using noble metal catalysts such as platinum and palladium. A method of hydrogen reduction is known. Of these, focusing on the hydrogen reduction method, this method depends on the solvent used and even the material of the reactor, such as the difficulty of reduction, the life of the catalyst, and the quality of the desired product TMHQ.
In consideration of this, the prior art has made numerous proposals regarding the solvent used in the hydrogen reduction method. For example, German Published Patent No. 1940386 proposes a method using a platinum catalyst or palladium catalyst and a _C3-5 branched aliphatic alcohol as a solvent, and Japanese Patent Publication No. 51-26425 proposes a method using a palladium catalyst. In Japanese Patent Publication No. 54-42964, a method using an aliphatic ketone as a solvent has been proposed. Regarding the material of the reactor, the above-mentioned German published patent No. 194086
In a steel reactor containing iron and nickel or chromium, using ethanol or methanol as a solvent.
It has been pointed out that when TMBQ is reduced with catalytic hydrogen, part of the reaction equipment is eluted, and quinhydrone is produced as a by-product due to the strong oxidation catalytic action of the eluted material, resulting in the inconvenience that the desired product becomes dark in color. As mentioned above, various reaction solvents have been proposed for the hydrogen reduction method of TMBQ using a noble metal catalyst. This shows that it is by no means easy to obtain TMHQ that is satisfactory as a raw material for vitamin E in terms of , melting point, stability, etc. Another method of hydrogen reduction is to use an inexpensive Raney-nickel catalyst instead of a precious metal catalyst.
JP-A No. 48-49732, JP-A No. 51-26424, JP-A No. 51-
It has been introduced in issues such as No. 26425 and No. 57-20285.
However, this method requires the use of a large amount of Raney-nickel compared to the method using a precious metal catalyst. For example, in Japanese Patent Publication No. 57-20285, it is necessary to use approximately 10% by weight of Raney-nickel based on TMBQ. It teaches that there is. Furthermore, JP-A-48
In the method taught by the embodiments of No. 49732,
The amount of nickel used is as much as 20% by weight of TMBQ. Moreover, in the method of this example, after hydrogen reduction, auxiliary reduction is performed with an aqueous solution containing 40% by weight of hydrosulfite based on the charged TMBQ, so in the true sense it is not catalytic hydrogen reduction by Raney-nickel. It's hard to say. From these known facts, it is possible to obtain high-grade TMHQ by catalytic hydrogen reduction of TMBQ with Raney-nickel.
In reality, this is likely to be quite difficult. In view of these circumstances, it is easier to produce high-quality TMBQ using a smaller amount of Raney nickel than before.
As a result of repeated research to develop a catalytic hydrogen reduction method that can reduce hydrogen to TMHQ and is not affected by the solvent used or the material of the reactor, unlike conventional methods that use precious metal catalysts, The present inventors have discovered that the success or failure of the catalytic hydrogen reduction method depends solely on the quality of the raw material TMBQ. To explain this point in more detail, the method for producing TMBQ described in Japanese Patent Publication No. 58-23858 previously proposed by the applicant is that 2,3,6-trimethylphenol (hereinafter abbreviated as TMP) is mixed with nitric acid and hydrochloric acid. According to the method of oxidation with mixed acid, TMBQ with a purity of 99% or more
However, despite the high purity of this TMBQ, hydrogen reduction using a Raney-nickel catalyst slows down the reaction, requires a relatively large amount of catalyst, and is difficult to obtain. The quality of TMHQ is also inadequate. From this, the above-mentioned special public service
We surmised that TMBQ obtained by the method disclosed in Publication No. 23858 contained some substance that inhibited the reduction reaction, and we investigated its properties in detail. and the above
TMBQ is apparently nearly neutral, but when it is heated, acidic substances are gradually released. Although it is unknown in what form this acidic substance exists in TMBQ, hydrogen reduction of TMBQ is Therefore, prior to the hydrogen reduction of TMBQ, it is possible to remove latent acidic substances without using expensive precious metal catalysts, and with the use of solvents and reactor materials. It has been found that high-quality TMHQ with excellent whiteness can be easily obtained by a hydrogen reduction method using a Raney-nickel catalyst without any limitations. Furthermore, the presence of acidic substances that inhibit hydrogen reduction can be obtained by the method disclosed in Japanese Patent Publication No. 58-23858.
There is nothing specific to TMBQ, but similar methods are used, for example, chlorinating TMP and then oxidizing it with nitric acid or hydrogen peroxide.
It was confirmed that the same effect was observed in TMBQ obtained by the method of No. Therefore, in the method for producing high-quality TMHQ according to the present invention, before subjecting TMBQ to catalytic hydrogen reduction,
TMBQ is mixed with an aqueous solution of an alkali metal salt of carbon or heavy carbon acid, the mixture is stirred while being heated to a temperature below 60°C, and its pH is stabilized within the range of 8 to 11, and then this mixture is The method is characterized in that TMBQ separated and recovered from is subjected to hydrogen ring formation in an organic solvent in the presence of a Raney-Nickel catalyst. In the present invention, acidic substances contained in TMBQ are removed by neutralizing TMBQ.
In this case, it is easy to remove latent acidic substances by harshening the neutralization conditions, but since TMBQ is extremely unstable to heat and alkali, especially to alkalis, simply strengthen the neutralization conditions. This has the disadvantage of significantly impairing TMBQ. However, the alkali metal carbonate or bicarbonate salts used in the present invention, typically sodium or potassium salts, can be used in excess without seriously impairing TMBQ. Incidentally, when sodium or potassium hydroxide is used in excess, there is a disadvantage that most of TMBQ turns into tar. The appropriate concentration of the aqueous alkali metal salt solution of carbonic acid or bicarbonate is 1 to 10% by weight, but considering volumetric efficiency, TMBQ loss due to dissolution in the aqueous layer, etc.
Particularly preferred is about 5 to 6% by weight. The treatment temperature can be room temperature as long as sufficient time is given; in short, crude TMBQ containing latent acidic substances can be treated at
mixed with an aqueous solution of the carbonate or bicarbonate described above;
The purpose is to stabilize the pH of this mixture within the range of 8 to 11, thereby making it possible to refine crude TMBQ to TMBQ that can be easily subjected to catalytic hydrogen reduction.

[Table] Table 1 shows the experimental results when crude TMBQ was purified by treating it with an aqueous sodium carbonate solution, and the resulting refined TMBQ was reduced with hydrogen in the presence of a Raney-nickel catalyst. As expected,
At a temperature of 30℃, it takes a long time to process crude TMBQ.
Not very practical. The higher the treatment temperature, the faster the disappearance of acidic substances, but the more tar formation of TMBQ will occur, so a treatment temperature of 50 to 60°C is appropriate. When TMBQ is treated with an aqueous solution of carbonate or bicarbonate, the
TMBQ can be isolated from the oxidation reaction mixture and mixed with an aqueous solution of carbonate or bicarbonate; however, if TMBQ is obtained, for example, as a solution in benzene, the benzene solution can be The treatment of the present invention can be carried out by mixing it with an aqueous solution. Incidentally, according to the method of Japanese Patent Publication No. 58-23858 introduced earlier, TMBQ is obtained as a benzene solution, but by treating this benzene solution as it is by the method of the present invention, the crude TMBQ contained in it can be obtained. can be purified. In any case, after mixing crude TMBQ with an aqueous solution of carbonate or bicarbonate and stabilizing the pH of the mixture within the range of 8 to 11, TMBQ is unstable to heat and alkali. Taking this into consideration, it is preferable to return the PH of the mixture to neutral, and if benzene coexists in this mixture, distill it off, then statically separate the oil layer, collect the oil layer, and collect the obtained oil layer components. Purified TMBQ can be recovered by subjecting it to distillation. As mentioned above, catalytic hydrogen reduction of TMBQ is troublesome in conventional techniques, but it is extremely easy when TMBQ purified by the method of the present invention is used as a raw material, and when a precious metal catalyst such as platinum or palladium is used. Of course, only 2% by weight compared to TMBQ
The hydrogen reduction reaction can be completed in a short period of time by using only Raney-nickel (the amount before development). Furthermore, from the second time onwards, if 1% by weight (relative to TMBQ) of Raney-nickel is newly added, the catalyst can be used repeatedly, and in effect, TMBQ can be made by adding 1% by weight of Raney-nickel to TMBQ. It can be returned. Regarding the material of the reactor used for catalytic hydrogen reduction, we compared stainless steel (SUS 304) and iron (SB 42) autoclaves, but as long as TMBQ purified by the method of the present invention is used as a raw material, No difference was observed in the reduction rate or the quality of TMBQ obtained. Regarding solvents, ethanol, t-butanol, methyl-
Isobutyl-carbinol, dioxane, t-butyl ether, methyl-t-butyl ether, n-butyl acetate, tetrahydrofuran, and the like can all be used in the present invention. Among these, ethanol, dioxane, and tetrahydrofuran have conventionally been considered unsuitable as solvents for producing highly colored TMHQ, but if refined TMBQ produced by the method of the present invention is used as a raw material, these solvents can be used as raw materials. Even when using this method, TMHQ with high whiteness can be obtained. For the reaction pressure and reaction temperature in the catalytic hydrogen reduction reaction of the present invention, pressures and temperatures conventionally used in similar reactions can be used as they are. After the reduction reaction, the reaction solution is cooled, the catalyst is filtered off, water is added to the filtrate, the solvent is distilled off, the remaining solution is cooled and filtered, and the resulting filter cake is washed with water. shiny white
TMHQ crystals are obtained. A more specific explanation will be given below using examples. Example 1-a 70g of TMP (purity 97.3%, 0.5 mol) was dissolved in the same amount of benzene, and while stirring while maintaining the temperature at 30°C,
A mixed acid having a composition of 30% HNO ₃ , 10% HCl, and 60% H ₂ O was added dropwise to this. NOx generation begins at the same time as the dripping starts. Thereafter, the mixed acid was added dropwise while maintaining the temperature at 30°C until the generation of NOx stopped. The required amount of mixed acid is 13.4g (0.64 mol as _HNO3 ). The reaction solution was allowed to stand still at 30° C. for liquid separation to obtain 142.5 g of an oxidized oil layer (upper layer). For this oil layer,
71.5 g of 5% aqueous sodium carbonate solution was added, and the mixture was stirred at 50°C for 4 hours to stabilize the pH in the range of 8 to 11. Next, the pH was returned to 7 by neutralization with sulfuric acid, and benzene was distilled off. The residual liquid was separated by standing, and the oil layer was distilled to obtain 65 g of purified TMBQ. Purity 99.6%, theoretical yield 86
% (vs. TMP). Example 1-b 50 g of refined TMBQ obtained in Example 1-a, 500 g of methyl t-butyl ether (MTBE), and 1 g of developed Raney nickel (JGC N152D) (in terms of alloy before development) were placed in a SUS304 autoclave. After nitrogen substitution, temperature 100-120℃, pressure 10-16
Hydrogen reduction was performed at Kg/cm ² . It takes 30 minutes. After cooling the reducing solution, filter out the catalyst, add 150 g of water to the filtrate, and
MTBE was distilled off by heating. The residual liquid after MTBE distillation (TMHQ slurry liquid) is cooled, filtered at 30℃,
White TMHQ crystals were obtained by washing with water. Weight after drying: 48.6g, theoretical yield: 96% (to charged TMBQ), acetone solution (TMHQ1g/acetone 10ml)
APHA30, UVT ₃₉₀ 90%, UVT ₄₅₀ 94%, melting point 172
~173℃, purity 99.77%. Comparative Example 1-a Half the amount of water was added to the oxidized oil layer obtained by performing the oxidation reaction using the same method and the same preparation as in Example 1-a, and the pH was simply neutralized to 7 with 5% sodium carbonate aqueous solution while stirring vigorously. do. Immediately after the neutralized solution was allowed to stand still, it was separated and the oil layer was distilled to obtain 66.9 g of a TMBQ fraction following a benzene fraction. Purity 99%, theoretical yield 88.5%. Comparative Example 1-b The TMBQ obtained in Comparative Example 1-a was used in Example 1-
Hydrogen reduction was attempted using the same method and preparation as in b, but almost no hydrogen was absorbed, so a Raney-nickel catalyst was added. Hydrogen absorption became smooth for the first time when the amount of catalyst was increased to four times that of Example 1-b, and hydrogen absorption was completed in 30 minutes. Thereafter, 48.1 g of TMHQ obtained by the same post-treatment as in Example 1-b was light brown in color.
Theoretical yield 95%, APHA450 in acetone solution (TMHQ1g/acetone 10ml), melting point 171.8-172.5℃,
Purity 99.2%. Example 2 The catalyst filtered through a G-4 glass filter in Example 1-b was quickly washed back into the autoclave with a small amount of MTBE. Next, purified TMBQ (Example 1-b) was added to this autoclave in the same manner as in Example 1-b.
a) and TMBE were added, and 1/2 the amount of developed Raney nickel (1% of TMBQ) of Example 1-b was added, and the reaction and post-treatment were carried out in the same manner as in Example 1-b. . The reaction time was 40 minutes, and hydrogen absorption was rapid. The obtained TMHQ crystals have high whiteness, the theoretical yield is 96%, and APHA in acetone solution (TMHQ1g/acetone 10ml),
UVT ₃₉₀ and UVT ₄₅₀ were the same as in Example 1-b. Example 3 The catalyst was repeated four more times in the same manner as in Example 2, but the hydrogen absorption rate was improved and the obtained
No deterioration in the quality of TMHQ was observed, and TMBQ subjected to the purification treatment of the present invention had a substantially 1%
It was confirmed that TMBQ's Raney-nickel ring element is possible. Examples 4 to 10 Table 2 shows the results of hydrogen reduction performed in the same manner as in Example 1-b, except for the solvent.

[Table] Solvents marked with * in the above table give a large coloring TMHQ,
Although this solvent is considered unsuitable for catalytic hydrogen reduction of TMBQ, there is no problem and it has good whiteness.
Gave TMHQ. Example 11 Except for using an iron autoclave (SB42),
The reaction and work-up were carried out exactly as in Examples 1--b. The reduction rate and the quality of the obtained TMHQ were completely unchanged from Example 1-b, and no influence of the reactor material was observed.

Claims (1)

[Claims] 1. Production of 2,3,5-trimethyl-hydroquinone by catalytic hydrogen reduction of 2,3,5-trimethyl-para-benzoquinone obtained by oxidizing 2,3,6-trimethyl-phenol. In the method of
Prior to catalytic hydrogen reduction, 2,3,5-trimethyl-para-benzoquinone is mixed with an aqueous alkali metal salt solution of carbonate or bicarbonate, and the mixture is stirred while being heated to a temperature below 60°C to reduce its pH. 8-11
2,3,5-Trimethyl-para-benzoquinone separated and recovered from this mixture is hydrogen-reduced in the presence of a Raney-nickel catalyst in an organic solvent. , 5-trimethyl-hydroquinone manufacturing method. 2 Claim 1 in which the alkali metal salt of carbonic acid or bicarbonate is a sodium salt or a potassium salt
The method described in section.