JPS6035996B2 - Electrochemical preparation of diphenyl ester - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrochemical method for producing alkanoic acid esters of diphenyl or its derivatives (hereinafter abbreviated as diphenyls).

Alkanoic acid esters of diphenyls are usually produced by converting hydroxy compounds of diphenyls, but obtaining the hydroxy compounds requires a long and complicated process.

The fact that alkanoic acid esters of diphenyls can be directly produced electrochemically by anodic acyloxylation of diphenyls has been reported, for example, in J. Am. Chem. Soc. 88'
8}1686 (1966), ibid89(18)44
69 (1967). A specific example is the anodic acetoxylation of diphenyl. In these methods, a substantially non-aqueous state is achieved by using an alkanoic acid or a mixture of an alkanoic acid and an organic co-solvent as a solvent during electrolysis. For this reason, in order to obtain sufficient conductivity in industrial implementation, it is necessary to add a relatively large amount of supporting salt to the system, which has the disadvantage of requiring a troublesome and expensive separation operation of the supporting salt. The present inventors investigated a practical and economical method for producing alkanoic acid esters of diphenyls, and found that good conductivity could be obtained by adding an appropriate amount of water to the reaction system. It has been found that electrolysis can be advantageously carried out simply by adding salt.

That is, the present invention relates to the anodic acyloxylation of diphenyl or its derivatives, as well as alkanoic acids, alkanoates,
The present invention provides a method for efficiently obtaining alkanoic acid esters of diphenyls by carrying out the process in the presence of water.

The present invention is particularly suitable for producing a 4-position acyloxyl compound, particularly 4-acyloxydiphenyl and/or 4,4'-acyloxydiphenyl, using diphenyl as a starting material. The acyloxylated substance targeted by the method of the present invention is diphenyl or a derivative thereof.

Diphenyl transfer derivatives include an alkyl group, an alkoxyl group, an acyloxyl group, an acylamino group, or an acylamino group in the diphenyl skeleton.
It has a substituent such as an aryl group. Among these diphenyl derivatives, Ashi. Those substituted with xyl groups are preferred. Among the acyloxyl groups, acetoxyl groups are particularly preferred. In the present invention, the alkanoic acid used as an acyloxyl group donor and solvent is a lower fatty acid, and particularly preferred examples include acetic acid and propionic acid. Acetic acid is preferred for industrial implementation. Further, as the supporting salt, alkali metal salts and ammonium salts of alkanoic acids are used, and among them, sodium salts and potassium salts of alkanoic acids, particularly potassium salts are preferable.

These supporting salts can be added to the system in the form of salts, but the brewing and base components can also be added separately, for example acetic acid and sodium hydroxide. By adding an appropriate amount of water to a system consisting of diphenyls, alkanoic acids, and alkanoic acid salts, the conductivity of the solution can be significantly improved.

As a result, the following effects can be obtained: (1) a reduction in the amount of alkanoate added and (2) a reduction in the applied interelectrode voltage. Here, the appropriate amount of water is 1% to 3% by weight based on the alkanoic acid,
Preferably, it is in the range of 2% by weight to 2% by weight. In the present invention, the concentrations of diphenyls, alkanoic acids, and supporting salts in the electrolytic solution are determined in relation to each other depending on their types, but for diphenyls, the concentrations are 1% by weight and 7% by weight.
, preferably from 5 to 60% by weight, for alkanoic acids from 20 to 9% by weight, and for supporting salts of up to 1% by weight.

In particular, for sodium acetate and potassium acetate, a concentration of 5% by weight or less is sufficient. As the anode used in the method of the present invention, platinum, gold, rhodium, ruthenium, lead peroxide or a metal electrode coated with these, graphite, ferrite electrode, etc. are used.

Among these, platinum is particularly preferred. As the cathode, noble metals, graphite, ferrite, iron, copper, SUS, lead electrodes, etc. can be used. Anode reed according to the present invention.

Xylation can be carried out both in cells divided by a diaphragm and in cells that are not divided. When performing the above electrolysis in such a cell, the anode potential is determined mainly depending on the type of diphenyl, but is generally in the range of 1.0 to 3.0 V with respect to SCE. In addition, the current density on the anode surface that allows efficient electrolysis is 0.5 and 5.
Although it is in the range of 0 A/d, 1 to 2 M/d is particularly preferable. The temperature of the electrolytic solution is limited by the boiling point of the alkanoic acid used, but generally a range of 0 to 10 pi is appropriate.

The concentration of diphenyls can be increased by increasing the temperature. In order to carry out the method of the invention more effectively, it is necessary to vigorously stir the anolyte, which can be satisfactorily achieved by means such as washing with a conventional stirring rod or high-speed circulation of the anolyte with a pump. .

The alkanoic acid ester of diphenyls produced by the above-mentioned anodic acyloxylation is obtained by separating and purifying it by a conventional process combining distillation, extraction, crystallization, etc.

Unreacted diphenyls and alkanoic acids can be separated and recovered and then subjected to electrolysis again. The process according to the invention can be carried out either continuously or batchwise.

Furthermore, switching the electrode gutter properties during electrolysis is effective in preventing tar from adhering to the electrode surface. The diphenyl alkanoate ester produced by the method of the present invention is
Not only is it a useful chemical substance as a raw material for heat-resistant resins, but it can also be used as an intermediate raw material for agricultural chemicals and medicines.

Hereinafter, specific methods of the present invention will be explained using Examples.

All percentages in the text are based on moles.

Identification and quantification of the product was done by IR, NMR and liquid chromatography methods. Example 1 Two platinum plates with a surface area of 50 mm were inserted into a glass container with an internal volume of 300 cc and equipped with a cooling pipe, an N2 gas supply port, and an outlet at the top, and were fixed while maintaining the distance between the two poles on the 4th side.

After adding 180 hours of acetic acid, 5 hours of potassium acetate, 40 hours of diphenyl, and 20 hours of water to this electrolytic cell, magnetic
Constant current electrolysis was performed for 6 hours while stirring the liquid vigorously with a stirrer.

During this time, N2 gas was flowed into the gas phase within the cell at a rate of 20 cc per minute. Voltage between electrodes was 6 to 7 V, liquid temperature was 60 pm, and current density was 5.0 A/d. After the reaction solution was allowed to cool to room temperature, it was subjected to fractionation, and the following results were obtained.

Diphenyl reaction rate 64.1%, 2-acetoxydiphenyl selectivity 6.1%, 4-acetoxydiphenyl selectivity 4
3.2%, 4.4-diacetoxydiphenyl selectivity 12
．． 8% Example 2 In the same electrolytic cell as used in Example 1, 180 ml of acetic acid, 5 ml of potassium acetate, 80 ml of 4-acetoxydiphenyl, and 2 ml of water were added.
After 0 pm, constant current electrolysis was performed for 1 hr under N2 flow while vigorously stirring with a magnetic stirrer.

Liquid temperature 60o0 Voltage between electrodes 5~6V Current density 3.0A/d〆 The reaction results were as follows.

4-acetoxydiphenyl reaction rate 59.8%, 4,4-
The diacetoxydiphenyl selectivity was 67.1%, and a small amount of 4,4'-dihydroxydiphenyl was also observed to be produced.

Comparative Example 1 After adding 180 ml of acetic acid, 20 ml of potassium acetate, and 80 ml of 4-acetoxydiphenyl to the same electrolytic cell used in Example 1, the mixture was heated for 1 lull while vigorously using a magnetic stirrer under a N2 stream. Time constant current electrolysis was performed.

Liquid temperature 6000 Voltage between electrodes 10.0V Current density 5.0A/d〆 The reaction results were as follows.

4-acetoxydiphenyl reaction rate 61.3%, 4,4-
Diacetoxydiphenylene selectivity 48.9% Example 3
Into a glass container having an internal volume of 200 cc, a magnetite plate having a copper wire in the center as an anode and a platinum plate as a cathode were inserted at a distance of 4 cc.

The current-carrying surface area of both the anode and cathode is 30 mm. After adding 80 parts of acetic acid, 3 parts of potassium acetate, 3 parts of 4-acetoxydiphenyl, and 10 parts of water to the above electrolytic cell, constant current electrolysis was performed for 5 hours while vigorously stirring with a magnetic stirrer. Liquid temperature 30oo Voltage between electrodes 3 to 3.5V Current density 1. The M/d reaction results were as follows.

4-acetoxydiphenyl reaction rate 56.8%, 4,4-diacetoxydiphenyl selectivity 53.5% Example 4 Into the same electrolytic cell used in Example 1, 180% propionic acid and 85% by weight potassium hydroxide 5. 4th evening, diphenyl 10
In the evening, after adding 20 hours of water, magnetic
Constant current electrolysis was performed for 5 hours while stirring vigorously with a stirrer.

Liquid temperature 3000 Voltage between electrodes 5~6V At a current density of 1.7A/d The reaction results were as follows.

Claims (1)

[Claims] 1. An electrochemical method for producing alkanoic acid esters of diphenyl, which is characterized in that anodic acyloxylation of diphenyl or its derivatives is carried out in the coexistence of an alkanoic acid, an alkanoate, and water.