JPS5853075B2 - Method for producing chlorohydroquinone monomethyl ethers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing chlorohydroquinone monomethyl ethers, and more particularly to a method for producing corresponding chlorohydroquinone monomethyl ethers in one step by electrolytic oxidation reaction of ortho- or metachlorophenols.

Chlorhydroquinone dimethyl ethers have a wide range of uses as synthetic intermediates for dyes and pigments, pharmaceuticals, fragrances, etc.;
As described in No. 854, it is produced using hydroquinone or its methyl ether as a raw material, or it is produced by substituting nuclear chlorine with chlorine.

However, hydroquinone and its methyl ether are expensive, and their nuclear chlorination reactions are complicated.
Since various products are produced as by-products, it is difficult to obtain the desired chlorohydroquinone dimethyl ether in high yield.

On the other hand, a method for producing hydroquinone through the electrolytic reaction of phenol in water has been known for a long time, but according to this method, it is first separated by anodization using an electrolytic cell equipped with a diaphragm such as an ion exchange membrane or an unglazed plate. Not only does a two-stage electrolytic reaction of obtaining benzoquinone and then cathodic reduction of this to obtain hydroquinone require two steps, but also the equipment costs are high due to the use of an electrolytic cell equipped with a diaphragm, and the electricity consumption is high. Energy consumption is also large.

It is already known that when phenols are electrolytically oxidized in an electrolytic cell without a diaphragm, a large amount of benzoquinones are produced in addition to hydroquinones, and undesirable UILJ reactions such as coupling reactions also occur. (e.g., J. Nilsson et al., J. O.
hem, Soc,, Perkin I, 23
77 (197:3)).

The present inventors have conducted intensive research to solve the various problems described above in the production of chlorohydroquinone dimethyl ethers and the related electrolytic reactions of phenols. When ortho- or metha-chlorophenols are electrolytically oxidized in the presence of a supporting electrolyte using methanol, which may contain a The present invention was achieved by discovering that it can be obtained with high yield and high selectivity.

On the other hand, as is easily understood, chlorohydroquinone monomethyl ethers easily give chlorohydroquinone dimethyl ethers by methylation of the hydroxyl group.

Therefore, the present invention provides a method for easily and inexpensively producing precursors of chlorohydroquinone dimethyl ethers, which were conventionally expensive and complicated to produce, from lorphenols by a single electrolytic reaction. .

The method for producing chlorohydroquinone monomethyl ether according to the present invention is characterized by electrolytically oxidizing ortho- or metha-chlorophenols in methanol containing a supporting electrolyte in an electrolytic cell without a diaphragm.

The starting materials used for the process of the present invention are orthochlorophenol, methachlorophenol, and have nuclear substituents that do not deleteriously affect the reaction under the electrooxidation conditions of the present invention and do not produce significant amounts of undesirable by-products. These are ortho- and metachlorophenols, and such nuclear substituents include halogens such as chlorine, bromine, and iodine, alkyl groups such as methyl and ethyl groups, and carbalkoxy groups such as phenyl and carbomethoxy groups. I can do it.

Methanol is used as the reaction solvent, and methanol may contain water or acetic acid.

If methanol contains water or acetic acid, the content is 1
Less than 0% by weight is desirable.

If it exceeds 10% by weight, undesirable side reactions will occur,
This is because it becomes difficult to obtain the desired chlorohydroquinone monomethyl ethers in high yield and high selectivity.

Furthermore, a conventionally known supporting electrolyte may be used as appropriate.

For example, sulfuric acid, nitric acid, perchloric acid and its salts such as lithium perchlorate, sodium perchlorate, hydroborofluoric acid and its salts such as sodium borofluoride, ammonium borofluoride, potassium fluoride, sodium fluoride, One or a mixture of two or more of potassium hydroxide, sodium hydroxide, para-toluene sulfonic acid, tetraethylamine para-toluene sulfonate and the like can be used, but the desired chlorhydroquinone monomethyl ether and its salts are preferably used.

The amount of supporting electrolyte in the reaction solvent is not particularly limited, but is usually 0.5 to 10 g, preferably 1 to 5 L per 1 solvent.
If.

In the method of the present invention, the target chlorohydroquinone monomethyl ethers can be obtained in high yield and with high selectivity by electrolytically oxidizing chlorophenols in an electrolytic cell that does not have a diaphragm separating the anode and cathode. be able to.

Although the reason is not clear, when an electrolytic cell is equipped with a diaphragm,
A large amount of undesirable by-products are produced, making it impossible to obtain the desired chlorohydroquinone monomethyl ethers with high selectivity.

In addition, almost no chlorobenzoquinone monoacecule, which is normally expected, is produced.

Next, platinum is generally preferred as the anode material because of its high yield and reaction selectivity, as well as the high reaction rate of chlorophenols, but platinum is not limited to this. , platinum-coated metal, carbon, etc. are also used.

Various cathode materials can be used, such as carbon, copper, zinc, nickel, and stainless steel, but carbon is preferably used.

It is economically advantageous to use carbon for both electrodes.

In the method of the present invention, the concentration of chlorophenols in the solvent is not particularly limited, but is usually 0.05 to 5 mol/l, preferably 0.1 to 1 mol/l.

The reaction temperature is also not particularly limited, but is usually 0 to 50°C, preferably 5 to 40°C.

Regarding the conditions of electrolytic oxidation, the current density of the anode is usually 0
05-5A/dm2, preferably 01-IA
/dm2.

Further, although the voltage between the electrodes depends on the distance between the negative and positive electrodes and the surface area of the electrodes, a relatively low voltage of 1 to 20 V is usually sufficient.

It should be noted that as the reaction progresses, the interelectrode voltage tends to decrease, so it is highly economical.

According to the method of the present invention, almost the entire amount of the raw material chlorophenols reacts with a current flow of 1 mole of 8 to 10 F (faraday) (theoretical current flow is 1 mole of 2F), but as the current flow increases, chlorohydroquinone monomethyl ether reacts at the same time. Since the amount of secondary oxidation products and high boiling point by-products tends to increase, in practice, only a part of the raw material chlorophenols is electrolytically oxidized with an electric current of 1 mole of 2 to 6F, and the unused chlorophenols are electrolytically oxidized. It is preferable to use a method of separating and recovering the reaction raw materials and reusing them as raw materials.

The raw material chlorophenol can usually be easily separated from the corresponding product chlorohydroquinone monomethyl ether by vacuum distillation.

According to the present invention, corresponding chlorohydroquinone monomethyl ethers having methoxy substitution at the para-position of the hydroxyl group can be obtained with high selectivity from raw material ortho- or metha-chlorophenols, but in some cases, the ortho-position of the hydroxyl group may be substituted with methoxy. A small amount of 2- or 3-chloro-6-methoxyphenol is produced as a by-product.

Separation of the two is possible, for example, by precision distillation or column chromatography.

According to the method of the present invention, as described above, by electrolytically oxidizing ortho- or metha-chlorophenols using methanol as a reaction solvent in an electrolytic cell without a diaphragm, the corresponding chlorohydroquinone monomethyl Ethers are obtained in high yields and with high selectivity, which readily give chlorohydroquinone dimethyl ethers by methylation of the hydroxyl group.

That is, the method itself of the present invention has an important feature of providing chlorohydroquinone monomethyl ethers without complicated side reactions by using an electrolytic cell that does not have a diaphragm, and also that the electrolytic cell does not have a diaphragm. for,
To simplify the device configuration, reduce the device cost, and further save the required power energy.

Furthermore, according to the method of the present invention, the precursor of chlorohydroquinone dimethyl ethers, which conventionally required multiple steps and complicated reactions, can be obtained easily from lorphenols at low cost. can.

In particular, orthochlorophenol and methachlorophenol give 2-chloro-4-methoxyphenol and 3-chloro-4-methoxyphenol, respectively, but when their hydroxyl groups are methylated, both give chlorohydroquinone dimethyl ether, so the final When the objective is chlorohydroquinone dimethyl ether, there is an advantage that a mixture of ortho and metachlorophenol can be used as the raw material for electrolytic oxidation.

The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Attach a thermometer to a 100ml beaker and
As an anode, use 80 mesh platinum wire mesh (frame length: 30 m, width: 40 m).
mm ), three carbon rods as cathodes (cross-sectional area 50 m
, height 150 mm) was attached to form an electrolytic cell.

80 ml of methanol was added to this electrolytic cell. Orthochlorophenol 3.86f (0.03 mol) and 42 ml of borohydrofluoric acid aqueous solution 0.3'? While cooling the electrolytic cell with water solution and keeping the temperature at about 20°C with stirring, constant current electrolysis conditions (current value 0.2OA, current density 0.4-A) were carried out.
/dm", interelectrode voltage of 9 to 10 V), and an electrolytic oxidation reaction was carried out by passing a current of 1 mol of 2F for 8 hours.

After the reaction, methanol was distilled off from the reaction mixture under reduced pressure, water was added to the residue and extracted with methylene chloride, and the resulting extract was dried over magnesium sulfate overnight.

Next, methylene chloride was distilled off under reduced pressure, and a distillate was further obtained by coercive distillation.

As a result of quantitative analysis of this fraction by gas chromatography, the reaction rate of orthochlorophenol was 25%, and the yield of 2-chloro-4-methoxyphenol (
Yield based on reacted orthochlorophenol; the same applies hereinafter.

) was in charge of 54. The yield of the by-product 2chloro-6-methoxyphenol was 9%.

Similarly, electrolytic oxidation of orthochlorophenol was carried out in methanol using hydrofluoroboric acid, sodium fluoroboride, or perchloric acid as the supporting electrolyte as shown in Table 1, and with various amounts of current applied.

Together with the above, the results are shown in Table 1.

When using hydroborofluoric acid and sodium borofluoride as the supporting electrolyte, 2-chloro-4-methoxyphenol can be obtained with good selectivity.

Example 2 Using the same platinum wire mesh or three carbon rods (cross-sectional area 50-1 height 150 mm) as in Example 1 as the anode material, the same procedure as in Example 1 was carried out using the supporting electrolyte and the amount of current shown in Table 2. Orthochlorophenol was electrolytically oxidized in methanol.

The results are shown in Table 2. Example 3 A thermometer was attached to a beaker with a capacity of 100,772 g, and the same carbon rods 3 as in Example 1 were used as both positive and negative electrodes.
Attach a book and use it as an electrolytic cell.

80 ml of methanol and 2.58 L of methachlorophenol in the electrolytic cell? (0.02 mol) and 20 g of sodium borofluoride were cooled from the outside in a water bath to reduce the humidity to 1.
Electrolysis was carried out under constant current electrolysis conditions (current value 0.2 OA, current density 0.4 A/dm2, interelectrode voltage 9-10 V) with a current flow of 80 F1 mol while maintaining the temperature at 5-20°C with stirring. An oxidation reaction was carried out.

The reaction mixture was treated in the same manner as in Example 1 to obtain a distilled fraction.

As a result of quantitative analysis of this fraction by gas chromatography, the reaction rate of methachlorophenol was 88%, and the yield of 3-chloro-4-methoxyphenol was 6.
I was in charge 4.

The yield of by-product 3-chloro-6-methoxyphenol is 9
%Met.

In the above, when methachlorophenol was electrolytically oxidized in methanol in exactly the same manner except that 0.51% of 98% sulfuric acid was used instead of sodium borofluoride as the supporting electrolyte, the raw material conversion rate was 82%, and 3-chlorophenol was -4-
Methoxyphenol and 3-chloro-6-methoxyphenol were obtained with yields of 38 fO and 14, respectively.

Claims (1)

[Claims] 1. A method for producing chlorohydroquinone monomethyl ethers, which comprises electrolytically oxidizing ortho- or methachlorophenols in methanol containing a supporting electrolyte in an electrolytic cell without a diaphragm.