JPS5921389B2 - Production method of quinones - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an advantageous process for the production of alkylbenzoquinones and alkylhydroquinones from alkylphenols.

Conventionally, quinones have been produced through complicated chemical reaction steps, but attempts have been made to produce quinones from corresponding phenols by electrolytic reactions, and several techniques have already been proposed.

For example, in Chem.
No. 540 gives an example of electrolyzing alkyl-substituted phenols using lead dioxide or a noble metal as an anode. However, the reaction results achieved by these methods are still not industrially satisfactory in terms of yield, current efficiency, etc. Furthermore, according to these conventional techniques, lead dioxide or noble metals are preferable as the anode for producing quinones by electrolysis of phenols, and carbon is not preferable. For example, the aforementioned special public service in 1974-3
No. 9928 shows results using a carbon electrode as an example of an unfavorable electrode as a comparative example. Therefore, the present inventors have intensively investigated a method for electrolyzing phenols with a high yield and current efficiency that is industrially satisfactory.As a result, we have unexpectedly discovered that alkyl-substituted phenols can be electrolyzed using carbon as an anode. The present invention has been completed by discovering that alkylbenzoquinones and alkylhydroquinones can be obtained with good results that could not be expected from conventional knowledge.

That is, the present invention produces an alkylbenzoquinone represented by the following general formula () and/or an alkylbenzoquinone represented by the following general formula () by electrolyzing an alkylphenol represented by the following general formula (1).
! ) is a method for producing alkylbenzoquinone and/or alkylhydroquinone from alkylphenol, which is characterized by using a carbon electrode as an anode.

General formula (1) General formula () General formula (] [In the formula, R represents an alkyl group having 1 to 4 carbon atoms,
n means an integer of 1 to 3.

However, in general formula (1), the para position relative to the hydroxyl group is not substituted. ] Conventionally, in the method for producing quinones by oxidizing phenols using reagents such as copper halides and manganese, there is a risk that the reagents used may remain in the product.On the other hand, even in the electrolytic synthesis method, the cathode is Although there is no problem with the use of lead on the anode, there are problems with the use of heavy metals such as lead in the anode, such as the possibility of contamination of the electrolyte due to dissolution or shedding of these substances.

However, according to the method of the present invention, since carbon is used for the anode, it is harmless, there is no need to worry about contaminating the electrolyte, and furthermore, the yield of the desired product is high, so it is possible to achieve high purity that could not be obtained conventionally. This makes it possible to produce products and obtain alkylquinones and/or alkylhydroquinones from alkylphenols with high current efficiency, providing an industrially extremely advantageous production method.

Examples of the alkylphenol represented by the general formula (1) which is the starting material of the present invention include 2-methylphenol,
3-methylphenol, 2,6-dimethylphenol,
Examples include 2,3,6-trimethylphenol and 2,3,5-trimethylphenol.

Among these, 2,3,5-trimethylbenzoquinone and 2,3,5-trimethylhydroquinone, which are useful as tocopherol raw materials, can be advantageously produced from 2,3,6-trimethylphenol, and are industrially important. It is.

Electrolysis is performed by dissolving an electrolyte and an alkylphenol in a solvent and installing an anode and a cathode.

As the solvent, water or a mixed solvent of water and an organic solvent added to promote dissolution of the alkylphenol is used.

Examples of the organic solvent include alcohols such as methanol and ethanol, and ketones such as acetone, methyl ethyl ketone, and diethyl ketone. The concentration of these organic solvents in the solvent is 10 to 80% by weight. Especially from 40~
60% by weight is preferred. Inorganic acids, organic acids, or salts thereof are used as the electrolyte.

Examples of inorganic acids include sulfuric acid or phosphoric acid, examples of organic acids include acetic acid, and examples of salts include potassium sulfate, lithium sulfate, sodium phosphate, sodium acetate, potassium acetate, and lithium acetate. These electrolytes readily ionize in water at a pH of 4 or less and do not harm the alkylphenols. When salts are used, they are used in combination with a sufficient amount of the above inorganic or organic acids to maintain a pH of 4 or less. The concentration of the electrolyte is preferably in the range of about 1 to 5% by weight, particularly 2 to 5% by weight, based on the solvent.

As the carbon electrode as the anode, which is a feature of the present invention, in addition to the usual carbon electrode for electrolysis, a glassy carbon electrode, a resin-impregnated graphite electrode, etc. can be used.

There is no particular limitation on its shape, and a shape suitable for the device, such as a plate or column, can be selected. As the cathode, metals having a high hydrogen overvoltage such as lead, mercury, cadmium, etc. are preferred, and lead is particularly preferred. Considering the solubility in the solvent and the electrolytic efficiency, the concentration of the raw material alkylphenols in the solvent is 1 to 30% by weight, especially 1 to 30% by weight.
10% by weight is preferred.

It is preferable to electrolyze the alkylphenol while optionally supplying raw materials in a batch method or a continuous method so that the concentration falls within this range. Other important factors influencing reaction performance include both anodic potential and current density.

The anode potential must be set within a range that does not cause side reactions such as water electrolysis and at the same time allows the desired product to be obtained in good yield. Therefore, it is desirable to set the value as close as possible to the lowest value at which electrolysis of alkylphenol can occur.
1.0-3.0V especially 1.0 for saturated calomel electrode
~2.0 is preferred. The higher the current density, the better the conversion rate per unit area of the electrode surface, so the current density is 3/dm2.
It is necessary to maintain it at A or higher. However, if it becomes too high, the anode will be contaminated with organic matter, so 3 to 20 A per 1 dm2 is preferable. The temperature of electrolysis is preferably 10 to 80°C, particularly 20 to 60°C.

In the case of a mixed solvent, it goes without saying that the boiling temperature of the organic solvent used together should not be exceeded. Electrolysis can be carried out either in a separated tank in which the anode and cathode are partitioned by a diaphragm, or in a non-separated tank without partitions. If electrolysis is carried out in a separation tank, virtually only alkylbenzoquinone can be produced,
In addition, if the process is carried out in a non-separated tank, both anokylbenzoquinone and alkylhydroquinone can be produced in different proportions depending on the electrolytic conditions. In the latter case, the alkylquinone that is oxidized at the anode is reduced to alkylhydroquinone at the cathode, which increases the efficiency of electricity use, and makes it possible to produce alkylhydroquinone, a more useful compound, in a single electrolysis process, making it very industrially viable. This can be said to be an advantageous method. The resulting electrolytic solution containing the reaction products, alkylhydroquinone and/or alkylbenzoquinone, is subjected to conventional solvent removal methods, such as evaporation or extraction using a water-immiscible solvent such as ether, followed by precipitation. Alternatively, the target alkylhydroquinone and/or alkylbenzoquinone can be obtained by fractional crystallization.

The present invention will be explained in more detail by giving experimental examples below, but the present invention is not limited by the examples. Example 1 A carbon flat plate anode was placed in the center of a beaker having a capacity of about 12, and two lead plate cathodes were symmetrically placed on both sides of the anode at a distance of about 3c1rL from the anode.

Add sodium sulfate 259 as an electrolyte, then preliminarily
300ml of water adjusted to pH 3 with sulfuric acid, 20ml of methanol
An electrolytic solution prepared by dissolving 2,3,6-trimethylphenol 59 as a raw material in a mixed solvent of 0 ml was added. Electrolysis was carried out while maintaining the temperature of the solution at approximately 30° C. while continuing magnetic stirring, and the electrolysis was stopped when the amount of electricity reached 10,000 coulombs. The anode potential measured by a saturated calomel electrode placed near the anode is 1 during electrolysis.
．． It was in the range of 4 to 1.8V. After the completion of electrolysis, the red-yellow electrolyte was extracted with ether and quantified by gas chromatography. It was found that 62,3,5-trimethylbenzoquinone and 2,3,5-trimethyl were detected relative to the raw material 2,3,6-trimethylphenol. The total yield of hydroquinone was 51.2 (:fl), and the current efficiency was 72.6 (:fl). Comparative Example 1 Electrolysis was carried out using the same equipment and experimental conditions as in Example 1, except that a lead dioxide flat plate electrode was used instead of the carbon electrode serving as the anode, and the electrolysis product was quantified by gas chromatography. , 3,5-trimethylbenzoquinone and 2,3,5-trimethylphenol total yield is 32
(fl), and the current efficiency was 46%.

Claims (1)

[Claims] 1. An alkylphenol represented by the following general formula (I) is electrolyzed to produce an alkylbenzoquinone represented by the following general formula (II) and/or an alkylhydroquinone represented by the following general formula (III). 1. A method for producing alkylbenzoquinone and/or alkylhydroquinone from alkylphenol, which method comprises using a carbon electrode as an anode. General formula (I) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ General formula (II) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ General formula (III) ▲There are mathematical formulas, chemical formulas, tables, etc.▼ [In the formula, R is an alkyl group having 1 to 4 carbon atoms,
n means an integer from 1 to 3. However, in general formula (I), the para position relative to the hydroxyl group is not substituted]