JP2007039737A - Method for producing chemical substance by electrochemical reaction using ac power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a chemical substance which gives a high yield and does not cause a side reaction since it has been cleared that, when a distance between a working electrode and a counter electrode is made close for reducing the electric resistance of a solution in electrochemical reaction, by-products considered as a reactant with a supporting electrolyte is produced. <P>SOLUTION: In an electrochemical reaction apparatus provided with a working electrode and a counter electrode along a flow passage, an alternating current is made to flow, and an electrochemical reaction is carried out to produce a chemical substance by the method. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a chemical substance by an electrochemical reaction using an alternating current. More specifically, the present invention relates to a production method useful as a reaction device for chemical synthesis, chemical analysis, and biochemistry, particularly in fields such as chemistry, biochemistry, agriculture, forestry, medicine, food industry, pharmaceutical industry, and environmental conservation.

  Electrochemical reactors with short interelectrode distances have been actively researched in the field of so-called microreactors in the field of so-called microreactors because the solution resistance is lowered, so the power consumption and the supporting electrolyte can be reduced. It was. A microreactor is a device having a minute flow path, and is used for chemical reaction, minute analysis, drug development, genome / DNA analysis tool, and the like. A microreactor is characterized by extremely high heat exchange efficiency and precise temperature control since the entire apparatus is smaller than a conventional reactor. Therefore, even with reactions that generate a large amount of heat, there is a risk of runaway or explosion, reactions that require precise temperature control, or reactions that require rapid heating or cooling, precise control can be easily performed using a microreactor. There is an advantage that it is possible. In addition, when a plurality of compatible liquids or gases are mixed by providing a branch in a minute flow path, they can be mixed instantaneously because the diffusion distance is short. Therefore, mixing at a more ideal mixing ratio is possible, and undesirable side reactions can be suppressed. In addition, since the reaction is performed in a minute space, the area per unit volume of the fluid, for example, the liquid / liquid interface between the water-insoluble solvent and water, or the area of the solid / liquid interface between the liquid and the vessel wall, Become very large. Therefore, the mass transfer through the interface and the contact area with the heterogeneous catalyst are increased, so that the reaction can be performed efficiently. Furthermore, since the volume of the reactor is very small, the amount and cost of the sample (reaction reagent, sample, etc.) used for the reaction can be suppressed, and the reaction scale can be reduced to the limit of the analytical ability of the product. Waste can be suppressed and the burden on the environment can be reduced.

  In the production of substances using microreactors, it has been studied to perform so-called numbering up, in which a large number of microreactors are produced in parallel, instead of scaling up to increase the size of the reactor as in the past. In the conventional scale-up, in order to mass-produce substances developed in laboratory flasks, after conducting a small test of several liters and a medium test of several hundred liters, an actual plant with a scale of several meters is designed. It takes a lot of cost, labor, and time, and it is not uncommon for yield to deteriorate due to scale-up. On the other hand, in the numbering up in the microreactor, it is considered that a large number of the same microreactors are produced in parallel, so that production can be easily increased and products of the same quality can be produced.

Electrochemical reaction microreactors have many reports for analytical applications (see, for example, Patent Documents 1 to 3). In particular, Japanese Patent Application Laid-Open No. 5-223772 reports a highly sensitive electrochemical chemical detection microelectrode cell using microband electrodes opposed to each other with a gap in the plane or comb-shaped microelectrodes meshed with each other. However, there are very few examples of using a microreactor for chemical substance production (see, for example, Patent Documents 4 to 6). Moreover, Japanese Patent Application Laid-Open No. 2003-172736 is substantially intended for DNA PCR reactions and electrophoresis, and is not intended for chemical substance production. In addition, US Pat. No. 6,607,655 discloses an example of chemical production using a microreactor, but a space formed by two electrodes and a slit by sandwiching an insulating film having a slit between the electrodes. The reaction solution is injected into the tank and the electrochemical reaction is carried out. Japanese Patent Application Laid-Open No. 2004-66169 reports a microchemical device that performs an electrochemical reaction in a minute space made of a carbon material obtained by carbonizing and baking a thermosetting resin molded product. However, all of these are only studies using a DC power source, and there is no description about the AC power source.
Japanese Patent Application Laid-Open No. 5-223772 JP 2004-239781 A JP 2003-4752 A Japanese Patent Laid-Open No. 2003-172736 US Pat. No. 6,607,655 JP 2004-66169 A

  In the electrochemical reaction, an oxidation reaction occurs at the anode and a reduction reaction occurs at the cathode, and the products are different. In general, a direct current power source is used in electrochemical reactions to avoid mixing of the anode and cathode products. However, it was found that when a distance between the working electrode and the counter electrode was reduced in order to reduce the electric resistance of the solution, a by-product thought to have reacted with the supporting electrolyte was generated. An object of the present invention is to find a method for producing a chemical substance having a good yield without causing such a side reaction.

That is, the present invention provides a method for producing a chemical substance characterized in that an electrochemical reaction is performed by passing an alternating current between electrodes using an electrochemical reaction device in which a working electrode and a counter electrode are provided along a flow path. It is.

  By using the electrochemical reaction method of the present invention, side reactions are less likely to occur, and the yield of electrochemical reactions can be improved.

  Hereinafter, the present invention will be described in detail.

  The electrochemical reaction device used in the present invention includes a working electrode and a counter electrode along the flow path. In the present invention, the distance between the working electrode and the counter electrode is preferably 1000 μm or less, and more preferably 500 μm or less. If the distance between the electrodes becomes too large, there may be a problem that the electric resistance of the reaction solution increases and the power consumption increases.

  The shape of the electrode used in the present invention is not particularly limited. Further, the arrangement of the electrodes used in the present invention is not particularly limited.

  Although the electrode installation form of the electrochemical reaction apparatus used in the present invention is not particularly limited, it may be installed on the wall surface of the flow path, or may be installed with an insulating spacer interposed between the electrodes.

  The method for producing the electrode used in the present invention is not particularly limited. As a preferable method, there is a method in which a thin plate mask cut into an electrode shape is covered or a photoresist is used, and then a metal is used as an electrode by vapor deposition or sputtering technique. When a thin film electrode is used, it may be provided on a part of the flow path wall, may be provided so as to surround the flow path, or may be connected in a double spiral shape. In addition, a film made of a conductive material to be an electrode and a film made of an insulating material are alternately stacked, a through hole is formed in the overlapping direction as a flow path, and the electrode film You may utilize what made the insulation film come alternately.

  The electrode material of the microreactor used in the present invention is not particularly limited as long as power is supplied. For example, metals such as palladium, platinum, rhodium, iridium, nickel, gold, tungsten, niobium, cadmium, manganese, thallium, lead, mercury, and carbon materials such as glassy carbon, spectroscopic grade graphite, pyrolytic graphite, and carbon cloth And those powders dispersed in xylene wax, epoxy resin, silicone rubber, Nujol or the like can be used. In addition, when the metal is deposited by vapor deposition or sputtering, a thin film such as chromium or titanium may be deposited as a base in order to improve adhesion to the substrate. Carbon may be coated with a paste in which carbon powder is dispersed in an adhesive material on the surface of the metal electrode. Similarly, a hydrocarbon compound is coated on the surface of the metal electrode and thermally decomposed under reduced pressure. Pyrolytic graphite may also be used.

  A method such as metal plating may be applied to the electrode surface of the microreactor used in the present invention so as to widen the electrode surface, and platinum black or palladium black having particularly high catalytic activity may be adhered.

  In the electrochemical reaction of the present invention, it is necessary to pass an alternating current between the electrodes. Although the reason for this is not clarified, when a direct current is used, the potential gradient increases as the distance between the electrodes decreases, and charged molecules are strongly attracted to the electrodes and react. Guessed. When alternating current in which the poles are switched at a constant period is used, an unexpected side reaction does not occur and the yield of the target product is improved.

  In order to pass an alternating current between the electrodes, it is preferable to use an alternating current power source. The frequency of the alternating current is not particularly limited, but is preferably 1 Hz to 100 kHz, and more preferably 10 Hz to 2 kHz. By using a frequency within this range, it is possible to obtain the effect of using an alternating current under the condition that the reactive current does not increase.

  The material used for producing the electrochemical reaction device used in the present invention is not particularly limited. Insulating materials such as glass, quartz, polyimide, fluororesin and acrylic are preferred. Even a conductive material such as silicon or metal can be used as long as the surface is insulated.

  Examples of a method for producing an electrochemical reaction apparatus used in the present invention include a method in which an electrode is provided on an insulating substrate, and a plate on which a groove is formed by etching or machining on the insulating substrate is adhered. It is done. Here, the shape of the flow path is not particularly limited, and may be linear or curved. The bonding method is not particularly limited, but an adhesive may be used as long as the method does not affect the reaction, such as thermocompression bonding or heat fusion.

  As an example of the above-described method, an insulating substrate in which a pair of electrodes is provided on an insulating substrate such as glass or thermoplastic resin by vapor deposition or sputtering, and then grooves are formed by etching or machining. You may use what was covered and heat-sealed and adhere | attached.

  Also, a groove was formed on an insulating substrate such as glass using a thick film resist (eg, SU-8 MicroChem), and a pair of electrodes were provided in the groove using vapor deposition or sputtering techniques. After that, the substrate may be covered with an insulating substrate such as glass and bonded using a resist.

  In addition, a groove is formed on the silicon substrate whose surface has been oxidized to enhance the insulating property using an etching technique, and a pair or more electrodes are provided in the groove using an evaporation or sputtering technique. It is also possible to use what is covered with a conductive substrate and bonded by anodic bonding.

  The flow path of the electrochemical reaction apparatus used in the present invention is preferably formed using a photolithography technique. Photolithographic technology enables easy microfabrication, can be freely designed in two dimensions, and has established mass production technology, so it can supply electrochemical reactors at low cost. There are many advantages such as being able to do.

  The length of the channel of the electrochemical reaction apparatus used in the present invention is not particularly limited, and may be appropriately designed in consideration of the reaction solution concentration, the reaction solution flow rate, the current density, the current efficiency, and the like.

  The electrochemical reaction apparatus used in the present invention may be equipped with a temperature control device. Here, the temperature control device is not particularly limited as long as it has a heating and cooling function and can be controlled to a predetermined temperature. However, a pipe through which a heat medium or a refrigerant flows, an electric heater, a Peltier element, etc. Can be mentioned. It is preferable to install the thermal control device near the reaction flow path because the temperature response is quick.

  The electrochemical reaction performed in the present invention is not particularly limited. Electrochemical reactions are roughly classified into oxidation reactions and reduction reactions. Especially in the electrochemical reaction of organic compounds, functional group conversion type, addition type, insertion type, substitution type, exchange type, elimination type, dimerization type, cross dimerization type, cyclization type, multimerization type, cleavage type , Metallized type, asymmetric synthetic type, and the like, but any of them is not particularly limited. More specific reaction examples include carbon-carbon multiple bond reduction, aromatic ring reduction, carbon-halogen bond reduction, aldehyde and ketone reduction, carboxylic acid and its derivative reduction, and ketone or carboxylic acid. Reduction dimerization reaction of olefins, reduction of nitro group, reduction of nitrogen-nitrogen single bond, reduction of nitrogen-nitrogen double bond, reduction of carbon-nitrogen single bond, reduction of carbon-nitrogen double bond, carbon- Reduction of nitrogen triple bond, oxidation of carboxylic acid with decarboxylation, oxidation of aldehyde to carboxylic acid, oxidation of aromatic compounds, oxidation of olefins, oxidation of amines and hydrazine, oxidation of sulfides, oxidation of thiourea derivatives , Oxidation of a thiocarbonyl derivative, oxidation of an organometallic compound or carbanion, and the like are not particularly limited. In addition, active electrochemical species called ionic species and radical species are generated in organic electrochemical reactions. Reactions via these active intermediate species, such as methoxylation, acetoxylation, cyanation, etc. for cationic species. You may use for a nuclear substitution reaction.

  Electrochemical reactions are broadly divided into direct methods in which the substrate is oxidized and reduced by transferring electrons between the reaction substrate and the electrode, and indirect methods using an electron transfer carrier called a mediator. There is no particular limitation. Similarly, the reaction substrate used in the present invention is not limited to an organic compound and an inorganic compound, and is not particularly limited.

  The reaction substrate for the reduction dimerization reaction performed in the present invention is not particularly limited. Examples thereof include compounds having a carbon-carbon double bond such as maleic acid, succinic acid, dimethylmaleic acid, dimethyl succinic acid and acrylonitrile, and compounds having a carbon-oxygen double bond such as ketones and aldehydes. These reaction substrates may be reacted in the same kind or in different kinds.

  The reaction substrate for the methoxylation reaction performed in the present invention is not particularly limited.

  The solvent that can be used in the present invention is not particularly limited as long as it can supply protons. For example, water, methanol, ethanol, n-propanol, isopropanol, 1,2-ethanediol, acetic acid, hydrochloric acid and the like can be used. These may be used as a single solvent or as a mixed solvent. As the solvent to be mixed, the above-mentioned solvents may be used, and acetonitrile, dimethylformamide, propylene carbonate, dimethyl sulfoxide, formamide, 2-pyrrolidone, pyridine, tetramethylurea, ethylenediamine, nitromethane, nitrobenzene, hexane, dichloromethane, chloroform, etc. should be used. Can do.

In the present invention, a supporting electrolyte may be used. The kind and amount of use are not particularly limited as long as they can be dissolved in the reaction solution and have conductivity. Since the supporting electrolyte acts as an ion in the solvent, it is a salt combined with an anion and a cation that are easily ionized. Examples of the cation include alkali metal ions such as Li ⁺ , Na ⁺ , K ⁺ , Rb ⁺ , and Cs ⁺ , ammonium ions, tetramethylammonium ions, tetraethylammonium ions, tetra (n-propyl) ammonium ions, tetra (i−). And quaternary alkyl ammonium such as propyl) ammonium ion, tetra (n-butyl) ammonium ion, and tetra (n-hexyl) ammonium ion. Examples of anions include halogen ions such as Cl ⁻ , Br ⁻ and I ⁻ , acetate ions, sulfate ions, nitrate ions, perchlorate ions, BF ₄ ⁻ , PF ₆ ⁻ , bis (trifluoromethanesulfonyl) imide, bis ( 1,1,2,2,3,3,3-heptafluoro-1-propanesulfonyl) imide, bis (1,1,2,2,3,3,4,4,4-nonafluoro-1-butanesulfonyl) ) Imido and various sulfonate ions.

  The inlet of the channel of the electrochemical reaction device used in the present invention may be connected to a supply device for introducing a fluid into the channel from the outside, and a small pump may be built in the channel. . The supply means for introducing the fluid into the electrochemical reaction apparatus from the outside is not particularly limited. For example, various pumps, a method of pumping, a method of utilizing a difference in gravity, a container compressed to a high pressure The method of supplying from, etc. can be used. Specific examples of pumps include 1) a syringe pump that pushes fluid in a cylinder with a piston, and 2) a reciprocating pump that increases pressure using a reciprocating motion of a piston or plunger, such as a piston pump or a diaphragm pump, 3) Rotating pumps that rotate gears and rollers such as gear pumps and peristaltic pumps, confine the fluid in a gap and push it to transport, 4) Rotary fluids such as volute pumps and diffuser pumps, which rotate by rotating blades and pressurize by centrifugal force Centrifugal pumps that increase the pressure, and other generally known pumps.

  The hydraulic equivalent diameter of the flow path of the electrochemical reaction apparatus used in the present invention is preferably 1 μm or more and 2000 μm or less, more preferably 10 μm or more and 1000 μm or less, and particularly preferably 20 μm or more and 500 μm or less. If the hydraulic equivalent diameter of the flow path of the electrochemical reaction apparatus is 1 μm or less, the pressure loss is extremely large and the amount of treatment is remarkably reduced, which is not preferable, and if it is 2000 μm or more, temperature control becomes difficult and the by-product increases. Therefore, it is not preferable. The hydraulic equivalent diameter mentioned here can be expressed by (channel cross-sectional area × 4 ÷ wetting side length).

  The pre-treatment method and post-treatment method of the reaction solution used in the present invention are not particularly limited, but may be performed using a flow path having a hydraulic equivalent diameter similar to that of the electrochemical reaction device used in the present invention.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited at all by these Examples.

  In the following Examples and Comparative Examples, the selectivity is the mol% of the raw material converted into the target product with respect to the consumed raw material.

Example 1
The microreactor was made by bonding two acrylic plates with electrodes and grooves, respectively. Specifically, it was created according to the following procedure.
1) One acrylic plate was machined to form a groove having the shape shown in FIG. The dimensions of the groove were a width of 900 μm, a depth of 200 μm, and a length applied to the electrode of 100 mm. A through-hole for feeding liquid from the outside was opened at both ends of the groove.
2) The other acrylic plate was covered with a mask in which the electrode shape shown in FIG. 2 was cut, and chrome was deposited by 1000 liters, and then gold was deposited by 2,000 liters to provide an electrode. The dimensions of the electrode applied to the flow path were 300 μm wide, 10 mm long, and the gap between the electrodes was 300 μm.
3) The above two acrylic plates were superposed and adhered, placed in an inert oven set at 115 ° C. for 1 hour, and joined by thermocompression to complete a microreactor. A schematic plan view of the microreactor is shown in FIG.

  The reaction solution (dimethyl maleate: 5 wt%, sodium acetate: 2 wt% / methanol) was fed from the inlet of the channel of the electrochemical reaction device at a total flow rate of 10 μL / min using a syringe pump. The electrochemical reaction apparatus was mounted on a Peltier device and the temperature was controlled at 15 ° C. Using an alternating current power source, an alternating current having a frequency of 10 Hz and an amplitude of 3.5 V was applied, and the discharged sample was quantitatively analyzed by gas chromatography. The conversion of dimethyl maleate was 29.8%, and the dimer tetrabutylbutanecarboxylic acid was not produced. The selectivity for methoxylated dimethyl methoxysuccinate (methoxy succinate over consumed dimethyl maleate) Mol% of dimethyl acid) was 80.3%.

(Example 2)
When an experiment was conducted in the same manner as in Example 1 except that the amplitude of the alternating current was changed to 5.0 V, the conversion of dimethyl maleate was 38.8%, and the selectivity for tetrabutylbutanecarboxylic acid was 6.6. %, The selectivity for dimethyl methoxysuccinate was 61.9%.

(Example 3)
An experiment was conducted in the same manner as in Example 1 except that the frequency of the alternating current was changed to 100 Hz and the amplitude was changed to 10 V. As a result, the conversion rate of dimethyl maleate was 62.8%, and the selectivity of tetrabutylbutanecarboxylic acid was The selectivity for 12.6% and dimethyl methoxysuccinate was 38.8%.

Example 4
An experiment was conducted in the same manner as in Example 1 except that the frequency of the alternating current was changed to 1 kHz and the amplitude was changed to 10 V. As a result, the conversion rate of dimethyl maleate was 44.8%, and the selectivity of tetrabutylbutanecarboxylic acid was The selectivity for 11.1% and dimethyl methoxysuccinate was 54.2%.

(Example 5)
When an experiment was conducted in the same manner as in Example 1 except that the frequency of the alternating current was changed to 10 kHz and the amplitude was changed to 10 V, the conversion rate of dimethyl maleate was 29.8%, and tetrabutylbutanecarboxylic acid was not produced. The selectivity for dimethyl methoxysuccinate was 80.0%.

(Example 6)
When the reaction solution was changed to dimethyl maleate: 20 wt%, sodium acetate: 2 wt% / methanol, the experiment was performed in the same manner as in Example 1 except that the frequency of the alternating current was changed to 100 Hz and the amplitude was changed to 10 V. The conversion of dimethyl maleate was 83.3%, the selectivity for tetrabutylbutanecarboxylic acid was 14.4%, and the selectivity for dimethyl methoxysuccinate was 49.0%.

(Example 7)
When the experiment was conducted in the same manner as in Example 6 except that the frequency of the alternating current was changed to 1.2 kHz and the amplitude was changed to 30 V, the conversion rate of dimethyl maleate was 50.2%, and tetrabutylbutanecarboxylic acid was produced. The selectivity for dimethyl methoxysuccinate was 79.4%.

(Comparative Example 1)
An experiment was conducted in the same manner as in Example 1 except that the DC voltage was changed to a constant voltage condition of 3.9 V. As a result, the conversion of dimethyl maleate was 51.7%, and the selectivity for tetrabutylbutanecarboxylic acid was Was 1.7%, and the selectivity for dimethyl methoxysuccinate was 8.8%. From this, it was found that the selectivity for dimethyl methoxysuccinate was lower than that in Examples.

(Comparative Example 2)
Experiment was conducted in the same manner as in Example 1 except that the reaction solution was changed to dimethyl maleate: 20 wt%, sodium acetate: 2 wt% / methanol and changed to a constant current condition of 3.9 V using a DC power source. As a result, the conversion rate of dimethyl maleate was 77.3%, the selectivity of tetrabutylbutanecarboxylic acid was 1.3%, and the selectivity of dimethyl methoxysuccinate was 20.8%. From this, it was found that the selectivity for dimethyl methoxysuccinate was lower than that in Examples.

It is a schematic plan view of the flow path part of the microreactor which concerns on one Embodiment of this invention. It is a schematic plan view of the electrode part of the microreactor which concerns on one Embodiment of this invention. 1 is a schematic plan view of a microreactor according to an embodiment of the present invention.

Explanation of symbols

1. 1. Electrode part flow path 2. A flow path from the electrode part to the inlet and outlet. Inlet and outlet

Claims (2)

A method for producing a chemical substance, wherein an electrochemical reaction is performed by passing an alternating current between electrodes using an electrochemical reaction device in which a working electrode and a counter electrode are provided along a flow path.
The method for producing a chemical substance according to claim 1, wherein the electrochemical reaction is a methoxylation reaction.