JPH0841671A - Method for electrolytic reduction of disulfide compound - Google Patents

Abstract

(57) [Summary] [Purpose] To carry out electrolytic reduction of disulfide compounds stably over a long period of time. [Structure] In a cathode chamber of an electrolytic cell divided into an anode chamber and a cathode chamber by a diaphragm, titanium, tantalum, niobium, zirconium, or titanium, tantalum, niobium, zirconium, silver, tin, aluminum, iron, molybdenum, gold, antimony , Bismuth, palladium, zinc 2
In addition to using a cathode having an electrode active surface composed of one or more alloys, the anode is insoluble in which an electrode active material containing iridium oxide is coated on a corrosion-resistant metal composed of titanium, tantalum, niobium, zirconium or an alloy thereof. Method for electrolytic reduction of disulfide compound using anode [Effect] High current efficiency enables stable operation for a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for electrolytic reduction of disulfide compounds, and more particularly to a method for electrolytically reducing cystine to stably produce cysteine for a long period in a high yield.

[0002]

2. Description of the Related Art Compounds containing an HS-group are
It is used in a wide range of fields as a raw material for agricultural chemicals, intermediates, stabilizers for resins, etc. Cysteine, which is an important HS-containing amino acid, is produced by electrolytically reducing cystine, which is a disulfide compound, into a solution of hydrochloric acid or sulfuric acid. HS from disulfide compounds by electrolytic reduction
A method for obtaining a group-containing compound has been used for a long time, and a method for synthesizing an acidic aqueous solution by electrolytic reduction is found in US Pat. No. 2,907,703. Further, it is recently found in JP-A-4-9486 "High yield method for electrochemical preparation of cysteine and its analogs".

Japanese Unexamined Patent Publication (Kokai) No. 4-9486 describes in detail electrolysis conditions for obtaining cysteine in a high yield by electrolytic reduction, anode and cathode materials, and selection of anode and cathode materials and The importance of choosing a diaphragm to prevent loss of cystine or cysteine from leakage. Further, it is disclosed that the use of a solution of aqueous ammonia, aqueous amine or the like as the electrolytic solution makes it possible to carry out the synthesis by electrolytic reduction of cysteine more economically. In these conventional techniques, tin, copper, silver, nickel, carbon, fluorinated carbon or glassy carbon is disclosed as a cathode, and a silver plate is industrially used.

However, the cathode material disclosed in the prior art is a cathode in which the electrolyte has a noble hydrogen generation potential even in an alkaline solution containing ammonium hydroxide, amine, etc. or an acidic solution such as hydrochloric acid or sulfuric acid. It is also disclosed that a porous body is used as a material for the purpose of further increasing reaction efficiency. However, for example, a carbonaceous material is fragile in material itself, and the porosity further progresses during electrolysis. Therefore, the overvoltage of hydrogen generation becomes noble and hydrogen generation becomes easy, so that the reaction efficiency decreases. As a result, there is a problem that a reduction product cannot be stably obtained. Further, as the anode, a platinum-plated titanium plate is generally used in order to prevent harmful heavy metals from being mixed. In addition, JP-A-4-
Japanese Patent No. 9486 discloses an electrode in which platinum and iridium are supported on titanium, a lead or lead dioxide electrode, an electrode of titanium oxide (trade name: Ebonex Ti ₄ O ₇ ) or the like as an anode. Lead or lead dioxide is harmful and not suitable for the purpose of avoiding heavy metal contamination. Lead or lead dioxide electrodes can be halogen ions, ammonium ions,
Avoids mixing heavy metal ions such as lead ions in the electrolytic solution that is dissolved or sludge is generated as lead ions, lead chloride, lead hydroxide, lead complex ions, etc. when electrolyzing in electrolytic solution containing amine etc. Can not. In addition, since the lead or lead dioxide electrode electrolytically oxidizes organic substances such as amines, it also has a problem of destabilizing the electrolytic solution.

On the other hand, platinum-plated electrodes and platinum-iridium electrodes are electrodes in which a titanium plate is coated with platinum or a metal of platinum and iridium by plating or the like, and the coated precious metal has poor durability and the precious metal dissolves as a precious metal ion or complex ion. It is not preferable because it is consumed and expensive precious metal is consumed in a short period of time. Further, when an electrode made of titanium oxide (trade name: Evonex) is used as an anode for the purpose of reducing a disulfide compound, the surface of the electrode is oxidized due to the generation of oxygen at the anode to form a non-conductive oxide film. Moreover, there is a drawback that the voltage rises in a short period of time and electrolysis becomes impossible.

[0006]

DISCLOSURE OF THE INVENTION The present invention provides a highly efficient and long-term stable operation in electrolytic reduction of a disulfide compound by using a cathode having a high reduction yield and an anode having a long life. It is an object to provide an electrolysis method capable of

[0007]

The present invention relates to a method for electrolytically reducing a disulfide compound in a cathode chamber of an electrolytic cell divided by a diaphragm into an anode chamber and a cathode chamber, wherein titanium, tantalum, niobium, zirconium, or titanium is used as a cathode. ,
Tantalum, niobium, zirconium, silver, tin, copper, aluminum, iron, molybdenum, gold, antimony, bismuth,
An electrode having an electrode active surface composed of two or more alloys selected from palladium and zinc, and an anode having an electrode active material containing iridium oxide on a corrosion-resistant metal composed of titanium, tantalum, niobium, zirconium or alloys thereof. This is a method for electrolytic reduction of disulfide compounds using an insoluble anode coated with.

Further, the coating of the electrode active material of the anode is a metal selected from titanium, tantalum, niobium, zirconium, tin, copper, antimony, ruthenium, platinum, cobalt, indium, molybdenum, and tungsten together with iridium oxide, or an oxide thereof. Is a method of electrolytically reducing the above disulfide compound containing at least one of the above.

That is, the method of electrolytic reduction of a disulfide compound of the present invention is performed by using titanium, tantalum, niobium, zirconium, titanium, tantalum, niobium, zirconium, silver, tin, aluminum, iron, molybdenum, gold, antimony as a cathode. An electrode made of an alloy of two or more kinds selected from bismuth, palladium and zinc is used, and the disulfide compound is electrolytically reduced as compared with the conventionally disclosed materials such as lead, tin, copper, silver, nickel and carbon. The generation potential of hydrogen gas at the time of carrying out is equal to or shows a base potential, which is advantageous for the electrolytic reduction reaction of the disulfide compound. Further, by alloying these materials, the hydrogen gas generation potential can be made more advantageous. Further, the cathode material of the present invention is excellent in corrosion resistance and rarely elutes in the electrolytic solution. Further, it is possible to further improve the corrosion resistance by alloying, and it is possible to prevent harmful heavy metals from mixing into the electrolytic solution.

Alloys that can be used as the cathode include Ti-5% Al-2.5% Sn (aluminium 5%).
% By weight, 2.5% by weight of tin and the balance titanium. The same applies to the following. ), Ti-5% Mo, Ti-4
5% Au, Ti-5% Nb, Zr-42% Zn, Ti-
34-65% Zn, Zr-2.5% Sn, Ta-25%
Pd, Sn-23% Pd, Au-42% Zr, Sn-1
0% Sb, Mo-10% Sn, Sn-33 to 56% T
i, Cu-20% Sn, Cu-10% Au, Ti-5%
Cu-20% Sn, Zr-32% Ag, Ti-65% A
g, Fe-65% Al, Sn-13% Bi, Ti-25
% Bi can be mentioned.

The cathode can be selected in consideration of the hydrogen generation potential and the corrosion resistance depending on the type of electrolyte used.
When cystine is electrolytically reduced to produce cysteine stably for a long time in a high yield, it is preferable to use particularly inexpensive titanium, zirconium or an alloy thereof. The cathode may have any shape such as plate, mesh, rod, and porous pair. From the viewpoint of reaction yield, a net-like shape having an expanded actual surface area, a shape such as a porous body is preferable, and a porous body such as an expanded metal, a punched metal or a porous sintered body is preferable. Since the generation potential of the by-product hydrogen is low in the porous body of the material that has been conventionally used, the production amount of the by-product hydrogen increases when the porous body is used for the purpose of improving the reaction yield. Since the cathode material of the present invention has a high hydrogen gas generation potential, the reaction yield does not decrease even if a porous body is used as the cathode. Therefore, the reaction time can be shortened and the electrolysis apparatus can be downsized, which is economical.

Further, in the electrolytic reduction method of the present invention, titanium, tantalum, niobium, zirconium or an alloy thereof is used as an anode and iridium oxide or iridium oxide and titanium, tantalum, niobium, zirconium or tin is used as an electrode substrate. Since an insoluble electrode having a coating made of at least one kind of metal or oxide of antimony, ruthenium, platinum, cobalt, indium, molybdenum, and tungsten is used, it has excellent corrosion resistance and is conventionally used for platinum plating. It has a longer life than titanium electrodes, platinum-iridium electrodes, lead or lead alloy electrodes, lead dioxide electrodes, and titanium oxides (trade name Ebonex Ti ₄ O ₇ ) and has no elution of electrode components into the electrolyte. Stable operation is possible for a long time. The electrode substrate of the anode can be arbitrarily selected in consideration of the corrosion resistance to the electrolytic solution, but titanium is preferable because it has sufficient durability and is inexpensive among the thin film forming metals.

As an electrode material, an electrode in which only an iridium oxide is coated on an electrode substrate has sufficient durability, but iridium oxide and titanium, tantalum, niobium, zirconium, tin, antimony, ruthenium, platinum, cobalt, indium, molybdenum, By providing a coating made of at least one kind of metal or oxide of tungsten, it is possible to expect a longer electrode life. The metal or oxide to be coated with iridium oxide can be arbitrarily selected depending on the electrolytic solution and electrolytic conditions. If 20% or more of iridium oxide is contained, the potential becomes stable. For example, I
rO ₂ —Ta ₂ O ₅ and IrO ₂ —SnO ₂ are used in acidic to neutral solutions, and IrO ₂ —In ₂ O ₃ and IrO _{2 are used.
-Co 2 O 3, IrO 2 -SnO} 2 -In 2 O 3 can be used in alkaline solution in, it may be selected in consideration of the corrosion resistance of the coating components. Also, Japanese Patent No. 129642
No. 9 (Japanese Patent Publication No. 60-22074), Patent No. 129
Of the electrode base and the electrode active material found in Japanese Patent No. 6432 (Japanese Patent Publication No. 60-22075), Japanese Patent No. 1472759 (Japanese Patent Publication No. 63-20313) and Japanese Patent No. 1767891 (Japanese Patent Publication No. 4-43985). It is possible to further prolong the service life by providing an intermediate layer coating for prolonging the service life of the electrode.

As a coating method for these electrode substrates, any one of conventionally known electroplating methods, chemical plating methods, vapor deposition methods, thermal decomposition methods and the like or a combination thereof can be used for coating. The coating amount of iridium oxide on the anode substrate varies depending on the electrolysis conditions, etc., but the coating amount is set to a service life of several years in order to stabilize the anode potential and reduce the suspension of operation due to disassembly of the electrolytic cell due to electrode life. Should be 10 mg
/ M ^{2 to} 60 mg / m ² is preferable. Further, the shape of the anode can be any shape such as a plate shape, a net shape, and a rod shape, and like the cathode, it is selected in consideration of the current density, the current distribution, the heat generation, the flow rate of the electrolytic solution, and the like.

The diaphragm used in the present invention may be a cation exchange membrane, an anion exchange membrane, a neutral membrane, an amphoteric membrane, etc., and is a fluorine-based or hydrocarbon-based cation exchange membrane or anion exchange membrane. A neutral film or an amphoteric film is preferable in terms of handling and power consumption. Further, in order to prevent the disulfide as a raw material and the reaction product from leaking to the anode chamber through the diaphragm and being lost, the disulfide as the raw material, the dissolved state of the reaction product in the electrolytic solution, that is, the size of charges and ions, etc. The choice of septum should be made according to.

For example, when cystine is dissolved in an acidic aqueous solution having an isoelectric point of pH = 5 or less and electrolytic reduction is carried out, a sulfonic acid is selected by selecting a membrane having a carboxylic acid group as an ion exchange group as the cation exchange membrane. It is possible to reduce loss due to leakage of cystine into the anode chamber compared to a membrane having a group as an ion exchange group. For example, selemion membrane (Asahi Glass Co., Ltd.), aciplex membrane (Asahi Kasei Co., Ltd.) ) And the like are preferably used. Furthermore, an amphoteric membrane having a cation exchange group and an anion exchange group can reduce loss due to leakage of disulfide and products into the anode chamber, and it is possible to use a neoceptor membrane (manufactured by Tokuyama Corp.) or the like. preferable.

[0017]

When the useful amino acid cysteine is produced by electrolytic reduction of a disulfide compound such as cystine, titanium is used as the cathode in the cathode chamber of the electrolytic cell divided into the anode chamber and the cathode chamber by the diaphragm. -Using an electrode with a high yield of cysteine formation, such as a tin alloy, the anode is coated with an electrode active material containing iridium oxide on a corrosion-resistant metal consisting of titanium, tantalum, niobium, zirconium or alloys thereof. Since the insoluble anode is used, it is possible to produce an amino acid with a high production efficiency and stably with a long period of time with little contamination of impurities.

[0018]

EXAMPLES The present invention will be described in more detail below with reference to examples. Example 1 100 mm in length and 1 in width, which have been pickled with a hot oxalic acid solution
An aqueous solution in which chloroplatinic acid and iridium chloride were dissolved was applied to a titanium plate having a thickness of 00 mm and a thickness of 3 mm, dried, and then baked in a muffle furnace at 550 ° C. for 15 minutes in air to form an iridium oxide-platinum coating by thermal decomposition. The steps of applying the solution, drying and firing were repeated 10 times to coat 15 g / m ^{2 of} iridium and 5 g / m ² of platinum to prepare an iridium oxide-platinum electrode. On the other hand, as the cathode, tin was plated to a thickness of 5 μm by electroplating on a titanium plate having a length of 100 mm, a width of 100 mm, and a thickness of 3 mm, and then an electron beam was irradiated under a reduced pressure of 10 ⁻⁴ torr to irradiate the titanium surface with titanium. A titanium-tin alloy consisting of 5% tin was formed.

The above-mentioned electrodes were used as the anode and cathode of the two-chamber electrolysis cell shown in FIG. 1, the sulfuric acid aqueous solution of 1 mol / l was used as the anolyte, and the L-cystine concentration was 0.5 mol / l as the catholyte.
1, an aqueous solution having a hydrochloric acid concentration of 2 mol / l, and an amphoteric membrane having a quaternary ammonium group as an anion exchange group and a sulfonic acid group as a cation exchange group on the opposite side (Neocepter manufactured by Tokuyama Corp.) Electrolysis was carried out using a membrane) while circulating an external electrolytic solution storage tank and electrolytic solution. Electrolysis was carried out at a cathode current density of 15 A / dm ² and an electrolysis temperature of 45 ° C. to produce L-cysteine. The cathodic current density was maintained, and the catholyte after being energized for 4 hours was analyzed by the iodometric titration method to determine the conversion amount to L-cysteine. Current efficiency is L
-Calculated from the amount of conversion of cysteine and the amount of electricity supplied, and the results are shown in Table 1.

Comparative Example 1 Electrolysis was conducted in the same manner as in Example 1 except that a silver plate, a graphite plate and a lead plate were used as the cathode, and the current efficiency was obtained. The results are shown in Table 1. Graphite collapse was observed on the graphite plate, and carbon was suspended in the catholyte. Although the current efficiency of the lead plate was good, lead was eluted during electrolysis and white sludge was suspended in the catholyte, so it could not be used.

[0021]

[Table 1]

Example 2 As in Example 1, a titanium plate was coated with an aqueous solution of tin chloride and iridium chloride, dried, and then baked in a muffle furnace at 550 ° C. for 15 minutes in the air and pyrolyzed to produce iridium oxide. Formed a tin oxide coating. The steps of applying the solution, drying and firing are repeated 10 times to obtain 15 g / iridium.
m ^2, iridium oxide coated with 205g / m ² as tin - created tin oxide electrode. On the other hand, the cathode is 10
0 mm, width 100 mm, thickness 3 mm Zircaloy (Zr
-2.5% Sn), using the same electrolytic cell as in Example 1, using 1 mol / l ammonium chloride aqueous solution as the anolyte and 0.5 mol / l L-cystine 2 as the catholyte.
Mol / l ammonia water was used, and Nafion 324 (manufactured by DuPont) was used for the diaphragm, and the cathode current density was 10 A.
/ Dm < ² >, electrolysis temperature: 45 [deg.] C., the catholyte after being energized for 6 hours was analyzed by the iodometric titration method to determine the conversion amount to L-cysteine. The current efficiency was calculated from the conversion amount of L-cysteine and the amount of electricity supplied, and the results are shown in Table 2.
There was no change in both the anode and cathode.

Comparative Example 2 Electrolysis was conducted in the same manner as in Example 2 except that a silver plate, a graphite plate and a lead plate were used for the cathode, and the current efficiency was obtained. The results are shown in Table 1. Graphite collapse was observed on the graphite plate, and carbon was suspended in the catholyte. On the lead plate, white sludge was suspended in the catholyte.

[0024]

[Table 2]

Example 3 In the same manner as in Example 1, an anode containing iridium oxide containing another metal or oxide was prepared, and the anode was prepared in an aqueous solution containing 5% sulfuric acid and 3% ammonium chloride. A cathode prepared in the same manner was used as a counter electrode, and a long-term continuous durability test was conducted in a diaphragmless electrolytic cell with a current density of 10 A / dm ² and an electrolysis temperature of 45 ° C. and an electrode interval of 10 mm, and the electrolysis voltage increased by 5 V from the initial voltage. The time is the life of the anode,
Table 3 shows the life time together with the electrode composition.

Comparative Example 3 As the anode, a platinum-plated electrode, a platinum-iridium electrode,
Graphite electrodes, ferrite electrode, a lead - tin alloy electrodes, with the electrodes of the oxides of titanium (trade name Ebonekkusu Ti ₄ O _7), carried out in the same manner as in Example 3, Table 3 and the results
Shown in

[0027]

[Table 3]

[0028]

INDUSTRIAL APPLICABILITY The present invention uses a titanium-tin electrode, a zircaloy electrode or the like as the cathode in the method for electrolytically reducing a disulfide compound, so that cysteine or the like can be obtained in high yield, and iridium oxide as the anode. By using an insoluble electrode as an electrocatalyst containing, it is possible to perform stable operation for a long period of time.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an electrolytic cell used in the electrolysis method of the present invention.

Claims (2)

[Claims] 1. A method for electrolytically reducing a disulfide compound in a cathode chamber of an electrolytic cell, which is divided into an anode chamber and a cathode chamber by a diaphragm, wherein titanium, tantalum, niobium, zirconium, or titanium, tantalum, niobium, zirconium, silver is used as a cathode. , Tin, copper, aluminum, iron, molybdenum,
An electrode having an electrode active surface made of an alloy of two or more kinds selected from gold, antimony, bismuth, palladium and zinc is used, and an anode is made of titanium, tantalum, niobium, zirconium or iridium oxide on a corrosion resistant metal made of these alloys. Method for Electroreduction of Disulfide Compounds Using Insoluble Anode Coated with Electrode Active Substance Containing Phenol 2. A metal selected from titanium, tantalum, niobium, zirconium, tin, copper, antimony, ruthenium, platinum, cobalt, indium, molybdenum, and tungsten, or an oxide thereof, in which the coating of the electrode active material of the anode is iridium oxide. 2. The electrolytic reduction method of a disulfide compound according to claim 1, wherein the disulfide compound contains at least one of