JPS626549B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a novel pyrazine derivative, and more particularly to a 2,3-dicyanopyrazine derivative, a method for producing the same, and a herbicide containing the compound as an active ingredient. According to the invention, the general formula [In the formula, R ₁ represents a halogen atom or a lower alkyl group, and R ₂ represents the formula when R ₁ is a halogen atom.

represents a group of [formula], and when R ₁ is a lower alkyl group, it represents -CH ₂ -CH ₂ -R ₅ , where n is 0 or 1, R ₃ is a halogen atom, -CN, the formula -COOR ₄ represents a group of the formula _-OR4 , _R4 represents a hydrogen atom or a lower alkyl group, and _R5 represents a halogen atom, -CN, or a lower alkyloxy group. ] A 2,3-dicyanopyrazine derivative represented by the following is provided. A group of 2,3-dicyanopyrazine derivatives represented by the above general formula () are new compounds that have not been described in any literature, and the present inventors have now demonstrated that these compounds have excellent herbicidal activity as active ingredients of herbicides. was discovered. In particular, in the treatment of flooded paddy soil, the compound of formula () above generally tends to form a solid chemical treatment layer on the surface layer of flooded paddy fields, although it depends on the type of substituent. It was found to be harmless to humans, and to have the ability to successfully control annual weeds such as field weeds. The "halogen atom" used in the above general formula () and the following description is preferably a fluorine atom, a chlorine atom, or a bromine atom. In addition, "lower alkyl group" has 1 to 6 carbon atoms.
, preferably 1 to 4 linear or branched saturated aliphatic hydrocarbon groups, such as methyl,
Included are ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl, tert-butyl, n-pentyl, iso-amyl, n-hexyl groups, and most preferably methyl or ethyl groups. It is. Thus, as representative examples of the compound represented by the formula () provided by the present invention, the following compounds can be exemplified, but the present invention is not limited thereto. 2,3-dicyano-5-(2-methoxyethylamino)-6-(p-methylphenyl)pyrazine2,3-dicyano-5-(2-chloroethylamino)-6-(p-methylphenyl)pyrazine2. 3-dicyano-5-(2-cyanoethylamino)-6-(p-chlorophenyl)pyrazine 2,3-dicyano-5-(2-methoxyethylamino)-6-(p-chlorophenyl)pyrazine 2,3-dicyano -5-(2-hydroxyethylamino)-6-(p-chlorophenyl)pyrazine2,3-dicyano-5-(2hydroxy-n-propylamino)-6-(p-chlorophenyl)pyrazine2,3-dicyano -5-(1-carboxyethylamino)-6-(p-chlorophenyl)pyrazine2,3-dicyano-5-(1-carboxyethylamino)-6-(m-methylphenyl)pyrazine2,3-dicyano-5 -(2-chloroethylamino)-6-(m-methylphenyl)pyrazine2,3-dicyano-5-(2-cyanoethylamino)-6-(m-methylphenyl)pyrazine2,3-dicyano-5-(2 -methoxyethylamino)-6-(m-methylphenyl)pyrazine2,3-dicyano-5-(2-cyanoethylamino)-6-(m-chlorophenyl)pyrazine2,3-dicyano-5-(2-methoxyethyl amino)-6-(m-chlorophenyl)pyrazine 2,3-dicyano-5-(2-chloroethylamino)-6-(m-chlorophenyl)pyrazine 2,3-dicyano-5-(2-bromoethylamino) -6-(m-chlorophenyl)pyrazine 2,3-dicyano-5-(ethoxycarbonylmethylamino)-6-(m-chlorophenyl)pyrazine 2,3-dicyano-5-(1-carboxy-n-
propylamino)-6-(m-chlorophenyl)pyrazine2,3-dicyano-5-(1-carboxyethylamino)-6-(m-bromphenyl)pyrazine2,3-dicyano-5-(1-carboxy-n −
propylamino)-6-(m-promphenyl)pyrazine 2,3-dicyano-5-(2-chloroethylamino)-6-(m-fluorophenyl)pyrazine 2,3-dicyano-5-(2-bromo ethylamino)-6-(m-fluorophenyl)pyrazine 2,3-dicyano-5-(1-carboxyethylamino)-6-(m-fluorophenyl)pyrazine 2,3-dicyanopyrazine derivatives of the present invention teeth,
2,3-dicyano-5- represented by the following formula ()
Halo-6-substituted phenylpyrazine and the following formula ()
It can be produced by reacting with the amine represented by the following reaction formula. [In the formula, R ₁ and R ₂ have the above-mentioned meanings, and X represents a halogen atom] The 2,3-dicyano-5-halo-6-substituted phenylpyrazine of formula () used as a starting material has the general formula 2,3-dicyano-5-hydroxy- represented by [wherein R ₁ has the above-mentioned meaning]
It can be prepared by treating a 6-substituted phenylpyrazine with a halogenating agent in the absence of a solvent or in an inert solvent. Examples of inert solvents that can be used include methylene chloride, chloroform,
Halogenated hydrocarbons such as carbon tetrachloride; aromatic hydrocarbons such as benzene, toluene and xylene are suitable. As the halogenating agent, any of those often used to convert a hydroxyl group into a halogen atom can be used, such as phosphorus pentahalides such as phosphorus pentachloride and phosphorus pentabromide; Phosphorus oxyhalides such as phosphorus chloride; thionyl halides such as thionyl chloride, etc. are advantageously used. The amount of these halogenating agents used is not critical, but generally at least an equivalent amount per mole of the compound of formula (), preferably
It is advantageous to use an excess of 1.5 to 20 equivalents. In particular, a halogenating agent that is liquid at room temperature, such as phosphorus oxychloride, may be used in large excess so that it simultaneously functions as a solvent. Although the reaction temperature is not critical, the reaction can generally be carried out at a temperature ranging from room temperature to the reflux temperature of the reaction mixture. Further, the halogenation reaction can be carried out in the presence of a tertiary amine such as pyridine, triethylamine or N.N-dimethylaniline, if necessary, thereby promoting the reaction. The amount of such tertiary amine used is not critical, but it is usually used in an amount of several weight % to approximately equimolar amount relative to the compound of formula (). Under such conditions, the halogenation reaction can usually be completed in about 1 to 5 hours. The compound of formula () thus obtained can be separated and/or purified, if necessary, by means known per se, such as filtration, distillation, extraction, recrystallization, chromatography, etc., or a combination thereof. can. Next, 2,3-dicyano-5-halo- of formula ()
The reaction of a 6-substituted phenylpyrazine with an amine of formula () is generally carried out in an inert solvent such as acetone,
The reaction can be carried out in ketones such as methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; and hydrocarbons such as benzene, toluene and xylene. The reaction temperature is not critical and can vary widely depending on the type of reactants used, but it is generally preferred to use relatively low temperatures of about 50°C or less, especially cooling conditions at or below room temperature. Use is advantageous. The amount of the compound of formula () to be used is also not particularly restricted and can be varied over a wide range, but it is generally used in an approximately equimolar to a slight excess molar amount relative to 1 mole of the compound of formula (). can. The reaction can be carried out in the presence of an acid binder, for example the amine of formula () itself, an inorganic or organic base such as sodium hydroxide, sodium carbonate, triethylamine. The compound represented by the formula () obtained in this way can be prepared by a method known per se, such as percolation,
Distillation, extraction, recrystallization, chromatography, etc.
Alternatively, it can be separated and/or purified by a combination thereof. Next, reference examples and examples are given and the above formula ()
The method for producing the compound () and () will be explained in more detail. Reference example 1 2,3-dicyano-5-hydroxy-6-(m
- 14.5 g (0.056 mol) of pyrazine (chlorphenyl) was dissolved in 173 g (1.12 mol) of phosphorus oxychloride, and the mixture was heated to 5 to 10°C with stirring under ice cooling.
4.9 g (0.062 mol) was added dropwise over 10 minutes. Thereafter, the mixture was stirred and refluxed for 2.5 hours. After the reaction, excess phosphorus oxychloride was distilled off under reduced pressure, the resulting black and colored residue was extracted with 150 ml of chloroform, insoluble materials were removed separately, and the chloroform solution was washed twice with 80 ml of water. After drying over anhydrous calcium chloride, the solvent was distilled off to obtain a yellowish white solid. This solid was recrystallized from carbon tetrachloride to obtain 14.4 g of 2,3-dicyano-5-chloro-6-(m-chlorophenyl)pyrazine. Melting point 87-88℃ Elemental analysis value C ₁₂ H ₄ N ₄ Cl ₂ Calculated value C 52.39 H 1.47 N 20.37 Actual measurement C 52.38 H 1.61 N 20.24 Reference examples 2 to 6 The following was prepared in the same manner as described in Reference example 1. The compounds listed in Table 1 were obtained.

[Table] Example 1 0.76 g (0.003 mol) of 2,3-dicyano-5-chloro-6-(p-methylphenyl)pyrazine was dissolved in 40 ml of acetone, cooled to 1 to 2°C, and mixed with stirring. -Methoxyethylamine 0.45g
(0.006 mol) dissolved in 10 ml of Ascent,
It was added dropwise over 5 minutes. After stirring for 45 minutes at 1-2°C, the precipitated solid was removed separately and the liquid was concentrated under reduced pressure to give a colored oil. Mix this oil with water.
The precipitate that precipitated was collected and recrystallized from benzene to give 0.54 g of 2,3-dicyano-5.
-(2-methoxyethylamino)-6-(p-methylphenyl)pyrazine was obtained. Melting point 196-200℃ Elemental analysis value C ₁₆ H ₁₅ N ₅ Calculated value as O C 65.52 H 5.15 N 23.88 Actual value C 65.37 H 5.30 N 23.78 Example 2 2,3-dicyano-5-chloro-6-(m- 0.76 g (0.003 mol) of pyrazine (methylphenyl) was dissolved in 40 ml of tetradrofuran, cooled to 1-5°C, and while stirring, 0.43 g of 2-cyanoethylamine was dissolved.
A solution of 0.006 mol of g (0.006 mol) dissolved in 20 ml of tetrahydrofuran was added dropwise over 5 minutes. 1~5℃
After stirring for 30 minutes, the mixture was treated in the same manner as in Example 1.
Recrystallization from ethanol yielded 0.54 g of 2,3-dicyano-5-(2-cyanoethylamino)-6-(m
-methylphenyl)pyrazine was obtained. Melting point 182-184℃ Elemental analysis value C ₁₆ H ₁₂ N ₆ Calculated value C 66.66 H 4.20 N 29.15 Actual value C 66.76 H 4.23 N 29.01 Example 3 2,3-dicyano-5-chloro-6-(m-chlorophenyl ) Dissolve 0.82 g (0.003 mol) of pyrazine in 30 ml of tetrahydrofuran, cool to 5°C, and add 2-chloroethylamine hydrochloride while stirring.
0.70g (0.006mol), sodium hydroxide 0.24g
(0.006 mol) water 10 ml and tetrahydrofuran 10
A solution prepared from ml was added dropwise over 5 minutes.
Thereafter, the reaction solution was stirred at 5° C. for 30 minutes, and then concentrated under reduced pressure to obtain a yellowish white solid. This solid was washed with water, dried, and then recrystallized from ethanol to obtain 0.34 g of 2,3-dicyano-5-(2-chloroethylamino)-6-(m-chlorophenyl)pyrazine. Melting point 137-140℃ Elemental analysis value C ₁₄ H ₉ N ₅ Calculated value as Cl ₂ C 52.85 H 2.85 N 22.01 Actual value C 52.62 H 2.85 N 21.84 Example 4 2,3-dicyano-5-chloro-6-(m - 0.82 g (0.003 mol) of pyrazine (chlorophenyl) was dissolved in 30 ml of benzene, cooled to 10°C, and while stirring, a solution of 0.31 g (0.003 mol) of glycine ethyl ester dissolved in 10 ml of benzene was added dropwise over 5 minutes. Continued Sodium hydroxide 0.12g
A solution of (0.003 mol) dissolved in 10 ml of water was added dropwise over 5 minutes, and the mixture was further stirred at 10°C for 30 minutes. After the reaction,
After separating the two layers and washing the benzene layer twice with 20 ml of water, the solvent was distilled off to obtain a yellowish white solid. This solid was recrystallized from toluene to give 0.42 g of 2.3-
Dicyano-5-(ethoxycarbonylmethylamino)-6-(m-chlorophenyl)pyrazine was obtained. Melting point 98-101℃ Elemental analysis value C ₁₆ H ₁₂ N ₂ O ₂ Calculated value C 56.23 H 3.54 N 20.49 Actual value C 56.45 H 3.50 N 20.45 Example 5 2,3-dicyano-5-chloro-6-( Dissolve 1.00 g (0.0039 mol) of m-methylphenyl)pyrazine in 20 ml of acetone, cool to 5-10°C, and while stirring, add 0.35 g (0.0039 mol) of DL-α-alanine, 5 ml of water, and 0.32 g of sodium hydroxide.
A solution prepared from (0.0078 mol) was added dropwise over 10 minutes. After further stirring for 30 minutes at 5-10°C, 0.6 ml of concentrated hydrochloric acid was added to make the reaction solution acidic, and the mixture was extracted with 180 ml of benzene. The extracted benzene layer was washed twice with 50 ml of saturated sodium chloride aqueous solution,
After drying over magnesium sulfate, the solvent was distilled off and a colored extract was obtained. 20 ml of toluene was added to this oil, the precipitated solid was collected, recrystallized from ethanol, and 0.26 g of 2,3-dicyano-5-(1-
Carboxyethylamino)-6-(m-methylphenyl)pyrazine was obtained. Melting point 177.5-179.0 (decomposition) Elemental analysis value C ₁₆ H ₁₃ N ₅ O ₂ Calculated value C 62.53 H 4.26 N 22.79 Actual value C 62.32 H 4.24 N 27.56 Examples 6-18 Same as described in Examples 1-5 The compounds listed in Table 2 below were obtained by the method.

【table】

[Table] The herbicide of the present invention has the ability to suppress the germination of weed seeds and/or kill the foliage of weeds, and can be used as a pre-emergence herbicide and/or a post-emergence herbicide in paddy field flooding soil treatment, It exhibits outstanding herbicidal effects in foliage treatment during the weed growing season, field soil treatment, etc. In particular, the herbicide of the present invention exhibits excellent herbicidal activity in flooded paddy fields that can withstand abundant water, and can be advantageously used as a herbicide for paddy fields.
This is thought to be because the active compound of the present invention dissolves in water and is easily absorbed from the seeds, roots, and leaves of weeds in water, and directly acts on the germination inhibition, growth inhibition, withering, etc. of the weeds. The herbicidal activity of the compound of the present invention varies depending on the types of substituents at the 5- and 6-positions of the 2,3-dicyanopyrazines represented by the general formula (), but especially in the treatment of paddy flooded soil, Compound Nos. 13, 14, 15, 16 and 18 shown in Table 2 of Examples exhibit outstanding herbicidal effects. Moreover, herbicides containing this compound as an active ingredient have the effect of selectively bleaching and killing weeds that germinate from the surface layer of paddy soil, and when used for foliage treatment in fields, they can also be used to treat important economic crops such as rice. It is substantially harmless to humans and can selectively control weeds that occur in cultivated areas such as rice by bleaching. Examples of weeds that can be controlled by the herbicide of the present invention include the following, but the following list is merely an example, and the herbicide of the present invention is effective against other weeds. It should be understood that it also exhibits excellent herbicidal effects as well. (1) Paddy field weeds, such as Asteraceae (e.g. Asteraceae), Asperaceae (e.g. Capsicum spp.
Lythraceae (e.g., Lythrum, Lythrum, Lythrum), Lythraceae (e.g., Lythrum), Lythraceae (e.g., Lythrum), Polygonaceae (e.g., Polygonum), Polygonaceae (e.g., Polygonum) , Chrysophyllaceae (e.g., Asperaceae), Lemnaceae (e.g., Lemnaceae, Poaceae), Lemnaceae (e.g., Duckweed, Hinjimo, Lemnaeus), Cyperaceae (e.g., Hyderico, Firefly, Cyperus japonica, Poaceae), Poaceae (e.g.: Phyllidae (e.g., P. elegans), Aceridae (e.g., P. spp., A. spp.), Omodacidae (e.g., P. elegans), Amanidae (e.g., A. elegans), P. elegans (e.g., P. elegans), etc. (2) Upland weeds include, for example, Chenopodiaceae (e.g., Coaxiaceae), Brassicaceae (e.g., shepherd's purse, Japanese radish, wild mustard), Amaranthaceae (e.g., Amaranthaceae),
Polygonaceae (e.g., Kishigigi, Hurtaceae), Rubiaceae (e.g., Caryophyllaceae), Caryophyllaceae (e.g., Caryophyllaceae, Chrysanthemum chinensis, Caryophyllaceae), Phosphoraceae (e.g., Prunus japonicus), Asteraceae (e.g., Harjiyon, Mugwort, Porphyra), Convolvulaceae (e.g. Convolvulaceae), Oxalis (e.g. Oxalis), Poaceae (e.g. Poaceae, Poaceae), Euphorbiaceae (e.g. Convolvulus), Solanaceae (e.g. Cyperaceae), Cyperaceae (e.g. Cyperaceae) )Such. When the compound of the present invention is used as an active ingredient of a herbicide, one or a combination of two or more of the active compounds represented by the above formula () may be used in an inert liquid or an inert liquid commonly used in the herbicide field. It can be mixed with a solid carrier material or diluent and, if necessary, additives such as a surfactant, and formulated into a suitable dosage form. As the carrier material or diluent that can be used in the herbicide of the present invention, any carrier material or diluent commonly used in the field can be used. Examples of the solid carrier material or diluent include kaolin, diatomaceous earth, talc, and bentonite. , montmorillonite,
Silica, clay, vermiculite, Zeeklite (product name: Zeeklite Chemical Co., Ltd.), white carbon, mica, gypsum, calcium carbonate,
Starch, vegetable flour, etc., and liquid carrier materials or diluents include, for example, water, ethanol, cyclohexane, xylene, toluene, benzene, methylnaphthalene, kerosene, acetone,
Examples include methyl ethyl ketone, cyclohexanone, isophorone, N.N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, dioxane, ethylene glycol ethyl ether, and liquefied tetrafluoroethane. The herbicide of the present invention may contain a surfactant in a conventional amount depending on its dosage form, and examples of such surfactants include, for example, alkylbenzene sulfonate, lignin sulfonate, naphthalene sulfonate, formalin Condensates, dialkyl sulfosuccinic acid esters, sodium acids, fatty acid salts, alkyl sulfates, higher alcohol sulfates, sorbitan fatty acid esters, polyalkylene glycols, polyoxyalkylene monoalkyl ethers, polyoxyalkylene alkylaryl ethers, polyoxyalkylene fatty acid esters, Polyoxyalkylene alkyl mercaptan ethers, quaternary ammonium salts, and the like can be used alone or in combination of two or more. Therefore, the herbicide of the present invention generally contains the active compound of the formula (), although it depends on its dosage form.
At least 0.5% by weight, preferably 1 to 99%, more preferably 2% by weight, based on the weight of the herbicide.
It can be included in concentrations of ~80% by weight. Furthermore, the herbicide of the present invention can be formulated into any conventional dosage forms such as powders, granules, wettable powders, solutions, emulsions, and sprays, depending on the method of application. The formulation can be carried out by methods known per se in the art. For example, powders, granules and wettable powders can be prepared by mixing and grinding at least one active compound of formula () with at least one of the solid carrier materials or diluents mentioned above, adding an appropriate amount of surfactant; They can be mixed uniformly and formulated into a formulation. Solutions or emulsions can also be prepared by dissolving or dispersing at least one active compound of formula () in at least one of the above liquid carrier materials or diluents, and optionally adding a surfactant. can be converted into Thus, in the case of powders and granules, from 2 to 80% by weight of active compound, based on the weight of the herbicide.
5 for wettable powders, solutions and emulsions.
It can be included at a concentration of ~60% by weight. Furthermore, the herbicide of the present invention can contain fungicides, insecticides, nematicides, fertilizers, plant growth regulators, etc. commonly used in the agricultural field, and can also be used in combination with other herbicides. can. As mentioned above, the herbicide of the present invention can be applied as a pre- and/or post-emergence herbicide directly to the soil as a paddy flooded soil treatment or upland soil treatment, or directly sprayed on weeds as a foliar treatment. be able to. The amount applied is not critical and can vary widely depending on the type of active compound, time of application, method of application, etc.
It is generally advantageous to apply at least 25 g, preferably 50 to 2000 g, more preferably 100 to 1000 g of active compound per 10 are.
However, the above application amount is just a standard, and it is of course possible to use less or more than the above amount depending on the condition of the crop, the infestation of weeds, etc. In addition, any conventional method can be used for its application, such as applying it from the ground or in the air to the area to be controlled before or after sowing or transplanting the crop, or spraying it with the seeds at the time of sowing the crop. A method such as spraying is used. Alternatively, the germination of weed seeds contained in the crop seeds can be suppressed by soaking the crop seeds in an aqueous solution containing the active compound of the present invention before sowing the crop seeds. is also possible. Next, specific examples of herbicide formulations and herbicidal activity provided by the present invention will be further explained using the following formulation examples. In the formulation examples, "parts" are parts by weight. Formulation Example 1 (Water Dispersible) 40 parts of the active compound of the present invention was mixed with Sieglite (trade name: Sieglite Chemical Co., Ltd.) as a carrier material.
[manufactured by Kunimine Kogyo Co., Ltd.] and Kunilite [product name: manufactured by Kunimine Kogyo Co., Ltd.]
and 55 parts of a 2:1 mixture of Solpol 800A [trade name: manufactured by Toho Chemical Industry Co., Ltd.] as a surfactant.
40% wettable powder is obtained. Formulation example 2 (emulsion) 15 parts of active compound of the invention, tetrahydrofuran
Mix and dissolve 80 parts and 5 parts of a surfactant (Solpol 800A) to obtain a 15% emulsion. Formulation example 8 (granules) 10 parts of the active compound of the present invention, 50 parts of bentonite,
35 parts of Kunilite and surfactant (Solpol
After mixing and pulverizing 5 parts of 800A), add 10 parts of water, stir evenly, extrude through a sieve hole with a diameter of 0.7 mm, dry, and cut into appropriate lengths to obtain 10% granules. Next, plant test results of the herbicide according to the present invention will be shown to clarify the method of use of the present invention and its effects. Test example (paddy field flooded soil treatment method) Fill a 1/5000 are polyethylene pot with paddy soil (on top of the soil), sow seeds of wild grass, broad-leaved weeds, and scallops in a 2cm layer on the surface, and
The stock was transplanted. At the same time, two 3-leaf stage paddy rice plants were planted, transplanted to a depth of 2 cm, and flooded to a depth of 3 cm. At the same time as weed germination, a predetermined amount of a wettable powder containing the active compound of the present invention was weighed out, diluted to 10 ml of water per pot, and dropped onto the water surface. Thereafter, the plants were grown in a glass room, and three weeks after the treatment, the herbicidal effect and the effect on paddy rice were investigated. The results are shown in Table 3 below. In addition, the test compound numbers in the test examples correspond to the above-mentioned example numbers, and the numerical values in the table indicate the degree of rice damage and herbicidal effect, and are specifically as follows.

【table】

【table】

【table】

Claims (1)

[Claims] 1. General formula [In the formula, R ₁ represents a halogen atom or a lower alkyl group, R ₂ represents a group of the formula [formula] when R ₁ is a halogen atom, and -CH ₂ -CH ₂ when R ₁ is a lower alkyl group _-R5 , where n is 0 or 1, _R3 is a halogen atom, -CN, a group of formula _-COOR4 , a group of formula _-OR4 , and _R4 is a hydrogen atom or a lower alkyl group. , and R ₅ represents a halogen atom, -CN, or a lower alkyloxy group. ] A 2,3-dicyanopyrazine derivative represented by the following. 2 General formula [In the formula, R ₁ represents a halogen atom or a lower alkyl group, and X represents a halogen atom. ] 2,3-dicyano-5-halo-6-substituted phenylpyrazine represented by the general formula R ₂ -NH ₂ () [wherein, R ₂ is _the formula [ When R ₁ in the general formula () is a lower alkyl group, it represents -CH ₂ -CH ₂ -R ₅ , where n is 0 or 1, and R ₃ is a halogen atom, -CN , expression −
A COOR ₄ group represents a group of the formula -OR ₄ , R ₄ represents a hydrogen atom or a lower alkyl group, and R ₅ represents a halogen atom, -CN, or a lower alkyloxy group. ] A general formula characterized by reacting with an amine represented by [In the formula, R ₁ represents a halogen atom or a lower alkyl group, R ₂ represents a group of the formula [formula] when R ₁ is a halogen atom, and -CH ₂ -CH ₂ when R ₁ is a lower alkyl group _-R5 , where n is 0 or 1, _R3 is a halogen atom, -CN, a group of formula _-COOR4 , a group of formula _-OR4 , and _R4 is a hydrogen atom or a lower alkyl group. , and R ₅ represents a halogen atom, -CN, or a lower alkyloxy group. ] A method for producing a 2,3-dicyanopyrazine derivative represented by the following. 3 General formula [In the formula, R ₁ represents a halogen atom or a lower alkyl group, R ₂ represents a group of the formula [formula] when R ₁ is a halogen atom, and -CH ₂ -CH ₂ when R ₁ is a lower alkyl group _-R5 , where n is 0 or 1, _R3 represents a halogen atom group of the formula _-COOR4 , a group of the formula _-OR4 , _R4 represents a hydrogen atom or a lower alkyl group, and R ₅ represents a halogen atom, -CN, or a lower alkyloxy group. ] A herbicide containing a 2,3-dicyanopyrazine derivative as an active ingredient.