GB2117768A - Fungicidal pyridine and pyrazine derivatives - Google Patents

Abstract

Novel compounds of the formula <IMAGE> wherein R<1> signifies 2-halo-, 4-halo- or 2,4-dihalo-phenyl, R<2> signifies 3-pyridyl 1-oxide, 2-pyrazinyl 1-oxide, 2-pyrazinyl 4-oxide or 2-pyrazinyl 1,4-dioxide, R<3> signifies hydrogen or straight-chain C1-4-alkyl and R<4> signifies C1-6-alkyl, C3-6- cycloalkyl, C3-6-alkenyl or C3-6-alkynyl, and acid addition salts of these compounds have fungicidal properties, and are of use in agriculture and horticulture.

Description

SPECIFICATION Pyridine and pyrazine derivatives The invention is concerned with compounds of the general formula

wherein R1 signifies 2-halo-, 4-halo- or 2,4-dihalo-phenyl, R2 signifies 3-pyridyl 1-oxide, 2-pyrazinyl 1-oxide, 2-pyrazinyl 4-oxide or 2-pyrazinyl 1,4-dioxide, R3 signifies hydrogen or straight-chain C14-alkyl and R4 signifies C, C1.6-al kyl, C3.6-cycloal kyl, C3 6-alkenyl or C3.6-alkynyl, and acid addition salts of these compounds.

The compounds of formula I and their acid addition salts have fungicidal properties and are suitable as fungicidal active substances, especially for use in agriculture and in horticulture.

The invention is also concerned with a process for the manufacture of the compounds of formula I and their acid addition salts, compounds of formula I and acid addition salts thereof as fungicidal active substances, fugicidal compositions which contain compounds of formula I or acid addition salts thereof as the active substance as well as the use of such compounds, acid addition salts and compositions for the control of fungi in agriculture and in horticulture.

The term "halo" in the definition of formula I embraces fluorine, chlorine, bromine and iodine, with chlorine being preferred.

The halogen atoms in a 2,4-diahalophenyl group denoted by R1 can be the same or different.

The terms "Cls-alkyl", "CBg-alkenyl" and "C3 6-aikynyl" embrace not only straight-chain but also branched-chain hydrocarbon groups. Under alkyl there are to be understood, depending on the number of carbon atoms, for example the following groups: methyl, ethyl, n-propyl, isopropyl, n-butyl, tert.butyl, isoamyl and n-hexyl.

When R4 signifies C1.6-alkyl, C36-alkenyl or C3 6-alkynyl, this is preferably C1.4-alkyl, C3- or C4-alkenyl or C3 or C4-alkynyl. The allyl group is an especially preferred alkenyl group and the propargyl group is an especially preferred alkynyl group.

R1 preferably signifies 4-chlorophenyl or 2,4-dichlorophenyl, especially the latter group.

R3 preferably signifies hydrogen, methyl or ethyl, especially hydrogen.

2',4'-Dichloro-2-(3"-pyridyl)-acetophenone O-methyl oxime 1"-oxide is an especially preferred compound offormula I.

Other representative compounds of formula I are: 2',4'-Dichloro-2-(3"-pyridyl)-acetophenone O-ethyl oxime 1"-oxide, 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-methyl oxime 1"-oxide, 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-methyl oxime 4-oxide, 4'-chloro-2-(3"-pyridyl)-acetophenone O-methyl oxime 1 "-oxide, 4'-chloro-2-(2"-pyrazinyl)-acetophenone O-methyl oxime 1",4"-dioxide, 4'-chloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 1",4"-dioxide, 4'-chloro-2-(2"-pyrazinyl)-acetophenone O-allyl oxime 4"-oxide, 2',4'-dichloro-2-(3"-pyridyl)-acetophenone O-allyl oxime 1"-oxide, 2'-chloro-2-(2"-pyrazinyl )-acetophenone 0-methyl oxime 4-oxide, 4'-fluoro-2-(2"-pyrazinyl)-acetophenone O-methyl oxime 1"-oxide, 4'-bromo-2-(2"-pyrazinyl)-acetophenone O-methyl oxime 1",4"-dioxide, 4'-chloro-2-(2"-pyrazinyl)-propiophenone O-methyl oxime 4-oxide, 2',4'-dichloro-2-(2"-pyrazinyl)-butyrophenone O-methyl oxime 1",4"-dioxide, 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-allyl oxime 1 "-oxide, 2',4'-dichloro-2-(2"-pyrazinyl)-propiophenone O-methyl oxime 1",4"-dioxide, 2',4'-dichloro-2-(3"-pyridyl)-acetophenone O-cyclopropyl oxime 1"-oxide, 2',4'-dichloro-2-(3"-pyridyl)-acetophenone O-isopropyl oxime 1"-oxide, 2',4',dichloro-2-(3"-pyridyl)-acetophenone O-propargyl oxime 1 "-oxide, 4'-chloro-2-(2"-pyrazinyl)-acetophenone O-propargyl oxime 4"-oxide, 2',4'-dichloro-2-(2"-pyrazi nyl)-acetophenone O-propargyl oxime l"-oxide and 4'-iodo-2-(3"-pyridyl)-propiophenone O-cyclohexyl oxime 1"-oxide.

Geometric isomerism (E- and Z-isomers) occurs by virtue of the presence of the C=N double bond in the compounds of formula I. In addition, asymmetric carbon atoms can be present, so that the compounds can exist as optical antipodes. Formula I is accordingly intended to embrace all of these possible isomeric forms.

As acid addition salts of the compounds of formula I there come into consideration physiologically compatible salts with strong acids. Hereto there preferably belong salts of the compounds I with inorganic acids such as hydrochloric acid, nitric acid and phosphoric acid and with sulphonic acids such as 1,5-naphthalene-disulphonic acid.

The process in accordance with the invention for the manufacture of the compounds of formula land of their salts comprises (a) N-oxidizing a pyridine or pyrazine derivative of the general formula

wherein R1, R3 and R4 have the significances given above and R2 signifies 3-pyridyl or 2-pyrazinyl, or (b) reacting a ketone of the general formula

wherein R', R2 and R3 have the significances given above, with an O-substituted hydroxylamine of the general formula R410NH2 IV wherein R41 signifies Cl.galkyl, C3.6-cycloalkyl or C3.6-alkenyl, and, if desired, converting a compound of general formula I obtained into an acid addition salt.

Process variant (a) can conveniently be carried out by oxidizing the starting material of formula II by means of hydrogen peroxide or a peracid in the presence of an inert diluent.

When hydrogen peroxide is used as the oxidizing agent there come into consideration as diluents especially lower alkanols such as methanol, ethanol and isopropanol, and the oxidation is preferably carried out in a temperature range between 0" and 60 between 20 and 40"C.

As peracids there come into consideration preferably peracetic acid, perbenzoic acid and mchloroperbenzoic acid, the oxidation being preferably carried out in a halogenated hydrocarbon (e.g.

methylene chloride or chloroform) as the diluent. The oxidation with a peracid is preferably carried out in a temperature range between 0 C and the reflux temperature of the reaction mixture, especially between 0 C and room temperature. An especially preferred embodiment of this process comprises carrying out the oxidation with m-chloroperbenzoic acid in chloroform in a temperature range between 0 C and room temperature.

In accordance with process variant (b), which leads to compounds of formula I in which R4 signifies C, 6-alkyl, C3.6-cycloalkyl or C3 6-alkenyl, the reaction is conveniently carried out in an organic solvent, for example an alcohol such as methanol or ethanol, a dialkylamide such as dimethyl-formamide or a tertiary amine such as pyridine. The reaction is preferably carried out in a temperature range between room temperature and the reflux temperature of the reaction mixture. Since the starting material of formula IV is preferably used in the form of an acid addition salt (e.g. the hydrochloride or hydrosulphate), a base such as sodium or potassium carbonate, triethylamine or pyridine is conveniently added to the reaction mixture.

For the manufacture of acid addition salts, the compounds of formula I can, if desired, be reacted with the desired acids such as, for example, hydrochloric acid, nitric acid, phosphoric acid or a sulphonic acid.

The isolation and purification of the thus-manufactured compounds of formula I and their acid addition salts are carried out according to methods known per se.

The starting materials of formula II can be prepared by reacting an oxime of the general formula

wherein R1, R2 and R3 have the significances given above, with a compound of the general formula R4U VI wherein R4 has the significance given above and U signifies a leaving group (e.g. chlorine, bromine, iodine, mesyloxy, tosyloxy or an alkyl sulphate group), or reacting a ketone of the general formula

wherein R1, R2 and R3 have the significances given above, with an O-substituted hydroxylamine of the general formula R410NH2 IV wherein R41 signifies C1.6-alkyl, C3 6-cycloalkyl or C3 6-alkenyl.

The reaction of an oxime of formula V with a compound of formula VI can be conveniently carried out by treating the oxime of formula V with the compound of formula VI in the presence of a base, in an organic solvent and in a temperature range between 0 C and the reflux temperature of the reaction mixture. The solvent can be protic or non-protic. When protic solvents such as alcohols, especially methanol or ethanol, are used, an alkali metal hydroxide (e.g. sodium or potassium hydroxide) or an alkali metal alcoholate is preferably used as the base. When non-protic solvents such as aliphatic or alicyclic ethers, especially tetrahydrofuran or dimethoxyethane, or dialkylamides, especially dimethylformamide, are used, an alkali metal hydride (e.g. sodium hydride) is preferably used as the base.In a preferred embodiment of this process sodium hydride is used as the base and an aliphatic or alicyclic ether, especially tetrahydrofuran or dimethoxyethane, or a dialkylamide, especially dimethylformamide, is used as the solvent.

The reaction of a ketone of formula VII with a hydroxylamine of formula IV, which leads to compounds of formula II in which R4 signifies Cls-alkyl, Css-cycloalkyl or C3galkenyl, is conveniently carried out in an analogous manner to process variant (b) described above.

The starting materials of formula III can be prepared by N-oxidizing an above-mentioned ketone of general formula VII in an analogous manner to process variant (a) described above.

The compounds of formulae IV, V, VI and VII usable as starting materials are either known or can be prepared according to methods known per se. For example, the oximes of formula V can be prepared from the corresponding ketones of formula VII by reaction wkith hydroxylamine, and the ketones themselves can be prepared in accordance with the processes described in DOS 2 221 546, DOS 2800 010 and British Patent Specification No. 2 015 524, namely, for example, by condensing the corresponding methylated heterocyclic compound with a halogenated benzoic acid ester.

The compounds in accordance with the invention (i.e. the compounds of formula I and their acid addition salts) have fungicidal activity and can accordingly be used for the control of fungi in agriculture and in horticulture. They are especially suitable for checking the growth or for the eradication of phytopathogenic fungi on parts of plants (e.g. leaves, stems, roots, tubers, fruits or flowers) and on seeds as well as in the soil and are especially effective in the control of Botrytis cinerea (grey mould); of powdery mildew fungi such as, for example, Uncinula necator (powdery mildew of vines), Erysiphe cichoracearum (powdery mildew of curcubits), Podosphaera leucotricha (powdery mildew of apples) and Erysiphe graminis (powdery mildew of cereals); of Venturia inaequalis (apple scab); of Helminthosporium oryzae (brown spot disease of rice); and of harmful fungi of the genera Puccinia, Uromyces, Rhizoctonia, Penicillium, Septoria and Cercospora.

Individual representatives of the compounds in accordance with the invention have, moreover, a pronounced activity against wood-destroying fungi such as, for example, Coniophora puteana and Gloeophyllum trabeum.

The compounds in accordance with the invention are distinguished by local and/or systemic activity.

The compounds in accordance with the invention are active under greenhouse conditions even at a concentration of 10 mg to 500 mg of active substance per litre of spray liquor. In the open, concentrations of 50 g to 2000 g of active substance of formula I per hectare and treatment are advantageously used.

The compounds in accordance with the invention, namely the fungicidal active substances, can be converted using formulation adjuvants into the usual formulations such as dusts, powders, granulates, solutions, emulsions, suspensions, emulsifiable concentrates, pastes and the like. The fungicidal composition in accordance with the invention contains an effective amount of at least one compound of general formula I, as defined above, or of an acid addition salt of such a compound as well as formulation adjuvants.

The compositions conveniently contain at least one of the following formulation adjuvants: Solid carrier substances; solvents or dispersion media; tensides (wetting and emulsifying agents); dispersing agents (withouttenside action); and stabilizers.

As solid carrier substances there essentially come into consideration: natural mineral substances such as kaolin, aluminas, siliceous earth, talc, bentonite, chalk, (e.g. whiting), magnesium carbonate, limestone, quartz, dolomite, attapulgite, montmorillonite and diatomaceous earth; synthetic mineral substances such as highly dispersible silicic acid, aluminium oxide and silicates; organic substances such as cellulose, starch, urea and synthetic resins; and fertilizers such as phosphates and nitrates, whereby such carrier substances can be present, for example, in the form of granulates or powders.

As solvents or dispersion media there essentially come into consideration: aromatics such as benzene, toluene, xylenes and alkylnaphthalenes; chlorinated aromatics and chlorinated aliphatic hydrocarbons such as chlorobenzenes, chloroethylenes and methylene chloride; aliphatic hydrocarbons such as cyclohexane and paraffins (e.g. petroleum fractions); alcohols such as butanol and glycol as well as their ethers and esters; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; and strongly polar solvents or dispersion media such as dimethylformamide, N-methylpyrrolidone and dimethyl sulphoxide, such solvents or dispersion media preferably having flash points of at least 30"C and boiling points of at least 50"C, and water.Amongst the solvents or dispersion media there also come into consideration so-called liquified gaseous extenders or carrier substances, which are those products which are gaseous at room temperature and under normal pressure. Examples of such products are especially aerosol propellants such as halogenated hydrocarbons (e.g. dichlorodifluoromethane). When water is used as the solvent, organic solvents can, for example, also be used as auxiliary solvents.

The tensides (wetting and emulsifying agents) can be non-ionic compounds such as condensation products of fatty acids, fatty alcohols or fatty-substituted phenols with ethylene oxide; fatty acid esters and ethers of sugars or polyvalent alcohols; the products which are obtained from sugars or polyvalent alcohols by condensation with ethylene oxide; block polymers of ethylene oxide and propylene oxide; or alkyldimethylamine oxides.

The tensides can also be anionic compounds such as soaps; fatty sulphate esters (e.g. dodecyl sodium sulphate, octadecyl sodium sulphate and cetyl sodium sulphate); alkyl sulphonates, aryl sulphonates and fatty-aromatic sulphonates such as alkylbenzene sulphonates (e.g. calcium dodecyl-benzene sulphonate) and butylnaphthalene sulphonates; and more complex fatty sulphonates (e.g. the amide condensation products of oleic acid and N-methyltaurine and the sodium sulphonate of dioctyl succinate).

Finally, the tensides can be cationic compounds such as alkyldimethylbenzylammonium chlorides, dialkyldimethylammonium chlorides, alkyltrimethylammonium chlorides and ethoxylated quaternary ammonium chlorides.

As dispersing agents (withouttenside action) there essentially come into consideration: lignin, sodium and ammonium salts of lignin sulphonic acids, sodium salts of maleic anhydride-diisobutylene copolymers, sodium and ammonium salts of sulphonated polycondensation products of naphthalene and formaldehyde, and sulphite Iyes.

As dispersing agents, which are especially suitable as thickening or anti-settling agents, there can be used, for example, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, polyvinyl alcohol, alginates, caseinates and blood albumin.

Examples of suitable stabilizers are acid-binding agents (e.g. epichlorohydrin, phenyl glycidyl ether and soya epoxides); antioxidants (e.g. gallic acid esters and butylhydroxytoluene); UV-absorbers (e.g.

substituted benzophenones, diphenylacrylonitrile acid esters and cinnamic acid esters); and deactivators (e.g. salts of ethylenediaminotetraacetic acid and polyglycols).

The fungicidal compositions in accordance with the invention can contain, in addition to the active substances of formula I, other active substances (e.g. other fungicidal agents, insecticidal and acaricidal agents, bactericides, plant growth regulators and fertilizers). Such combination compositions are suitable for broadening the spectrum of activity or for specifically influencing the plant growth.

The fungicidal compositions in accordance with the invention generally contain, according to type, between 0.0001 and 95 weight percent of a compound in accordance with the invention or compounds in accordance with the invention as the active substance(s). They can be present in a form which is suitable for storage and transport. In such forms (e.g. emuslifiable concentrates) the active substance concentration is normally in the higher region of the above concentration range. These forms can be diluted with the same or different formulation adjuvants to give active substance concentrations which are suitable for practical use, and such concentrations normally lie in the lower region of the above concentration range. Emulsifiable concentrates generally contain 5 to 95 weight percent, preferably 25 to 75 weight percent, of a compound or compounds of formula I.As forms of use there come into consideration, inter alia, ready-for-use solutions, emulsions or suspensions which are suitable, for example, as spray liquors. In such spray liquors there can be present, for example, concentrations between 0.0001 and 20 weight percent. In the Ultra-Low-Volume process there can be formulated spray liquors in which the active substance concentration is preferably from 0.5 to 20 weight percent, while the spray liquors formulated in the Low-Volume process and in the High-Volume process preferably have an active substance concentration of 0.02 to 1.0 weight percent and 0.002 to 0.1 weight percent, respectively.

The fungicidal compositions in accordance with the invention can be manufactured by mixing at least one compound of general formula I or an acid addition salt of such a compound with formulation adjuvants.

The manufacture of the compositions can be carried out in a known manner; for example, by mixing the active substance with solid carrier substances, by dissolution or suspension in suitable solvents or dispersion media, if necessary with the use of tensides as wetting or emulsifying agents or of dispersing agents, by diluting pre-prepared emulsifiable concentrates with solvents or dispersion media etc.

In the case of pulverous compositions the active substance can be mixed with a solid carrier substance (e.g. by grinding them together) or the solid carrier substance can be impregnated with a solution or suspension of the active substance and then the solvent or dispersion medium can be removed by evaporation, heating or sucking-off under reduced pressure. By adding tensides or dispersing agents such pulverous compositions can be made readily wettable with water, so that they can be converted into aqueous suspensions which are suitable, for example, as spray compositions.

The compounds in accordance with the invention can also be mixed with a tensile and a solid carrier substance to form a wettable powder which is dispersible in water or they can be mixed with a solid pre-granulated carrier substance to give a product in the form of a granulate.

When desired, a compound in accordance with the invention can be dissolved in a water-immiscible solvent such as, for example, an alicyclic ketone, which conveniently contains dissolved emulsifying agent, so that the solution becomes self-emulsifying upon addition to water. Alternatively, the active substance can be mixed with an emulsifying agent and the mixture can then be diluted with water to give the desired concentration. Moreover, the active substance can be dissolved in a solvent and thereafter the solution can be mixed with an emulsifying agent. Such a mixture can likewise be diluted with water to give the desired concentration. In this manner there are obtained emulsifiable concentrates and ready-for-use emulsions.

The use of the compositions in accordance with the invention can be carried out according to application methods which are usual in plant protection or in agriculture such as sprinkling, spraying, dusting, pouring or scattering. The method in accordance with the invention for the control of fungi comprises treating the locus to be protected (e.g. plants, parts of plants or seeds) with an effective amount of a compound in accordance with the invention or of a composition in accordance with the invention.

The following Examples illustrate the invention.

I Manufacture of the active substances of formula 1: Example 1 Asolution of 10 g of 2',4'-dichloro-2-(3-pyridyl)-acetophenone O-methyl oxime in 100 ml of chloroform is treated at 0 C with 7.2 g of m-chloroperbenzoic acid and the mixture is subsequently stored at about 4"C in a refrigerator for 24 hours. The mixture is then diluted with 200 ml of chloroform and extracted with 250 ml of 10% potassium carbonate solution. The organic phase is dried over anhydrous sodium sulphate and concentrated. As the residue there is obtained 2',4'-dichloro-2-(3"-pyridyl)-acetophenone O-methyl oxime 1"-oxide as the E,Z-isomer mixture in the form of a yellowish paste.

In an analogous manner, by oxidizing 2',4'-dichloro-2-(2-pyrazinyl)-acetophenone O-ethyl oxime using m-chloroperbenzoic acid as the oxidizing agent there is obtained a product which can be separated by chromatography on silica gel with ethyl acetate into a mixture of 2',4'-dichloro-2-(2"-pyrazinyl)- acetophenone O-ethyl oxime 1"-oxide and 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 4-oxide (viscous oil) as well as 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 1",4"-dioxide, m.p. 164-168 C.

Example 2 1.41 g of 2',4'-dichloro-2-(3"-pyridyl)-acetophenone 1 "-oxide are dissolved in 5 ml of ethanol, the solution is treated with 1 g of sodium carbonate and 0.83 g of O-methyl-hydroxylamine hydrochloride and the mixture is subsequently heated under reflux for 3 hours. The mixture is then poured on to ice and extracted with ethyl acetate. The organic phase is dried over anhydrous sodium sulphate and subsequently concentrated. The residue consists of 2',4'-dich Ioro-2-(3"-pyridyl)-acetophenone O-methyl oxime 1 "-oxide.

II Preparation of the starting materials: Example 3 A solution of 13.3 g of 2',4'-dichloro-2-(3-pyridyl)-acetophenone in 40 ml of ethanol is treated with 10g of sodium carbonate and 8.3 g of O-methylhydroxylamine hydrochloride and the mixture is subsequently heated to reflux temperature while stirring. After 4 hours the mixture is poured on to ice and extracted with ethyl acetate. The organic phase is washed, dried over an hydros sodium sulphate and concentrated under reduced pressure. There is obtained 2',4'-dichloro-2-(3-pyridyl)-acetophenone O-methyl oxime as the E,Z-isomer mixture in the form of a yellowish oil.

In an analogous manner, from 2',4'-dichloro-2-(2-pyrazinyl)-acetophenone and O-ethylhydroxylamine hydrochloride there is obtained 2',4'-dichloro-2-(2-pyrazinyl)-acetophenone O-ethyl oxime in the form of an oil.

Example 4 A solution of 5 g of 2',4'-dichloro-2-(3-pyridyl)-acetophenone in 20 ml of chloroform is treated at 0 C with 3.6 g of m-chloroperbenzoic acid and the mixture is subsequently stored at about 4"C in a refrigerator for 24 hours. The mixture is then diluted with 100 ml of chloroform and extracted with 100 ml of 10% potassium carbonate solution. The organic phase is dried over anhydrous sodium sulphate and concentrated. There is obtained 2',4'-dichloro-2-(3"-pyridyl)-acetophenone 1"-oxide, m.p. 137-140"C.

Example 5 A mixture of 27.6 g of ethyl 2,4-dichlorobenzoate and 20.81 g of ethyl 3-pyridylacetate at 20-25"C is treated portionwise with 10.59 g of sodium methylate. The mixture is subsequently heated to 65-700C and resulting readily volatile products are blow off with dry nitrogen. After 20 hours the mixture is treated with 40 ml of concentrated hydrochloric acid and heated at reflux temperature for 18 hours. The mixture is washed with diethyl ether and the aqueous phase is basified by adding concentrated ammonia and then extracted with methylene chloride. The organic phase is concentrated and the crude product is chromatographed on silica gel with methylene chloride/methanol (98:2). The product, 2',4'-dichloro-2-(3-pyridyl)-acetophenone, can be crystallized from diethyl ether/n-pentane and melts at 55-56"C.

III Formulation examples Example 6 1. Spray powder (for active substances which are liquid or which melt below 75"C) Parts by weight Active substance of formula 1 50 Hydrated silicic acid 37 Kaolin 5 Alkylphenol ethoxylate 4 Sodium polynaphthalenesulphonate 4 100 The liquid or molten active substance is taken up on the silicic acid, the remaining components are admixed and the mixture is finely ground in a suitable mill.

2. Spray powder (for solid active substances which melt above 75"C) Parts by weight Active substance of formula 1 50 Hydrated silicic acid 5 Kaolin 42 Sodium lauryl sulphate 1 Sodium lignosulphonate 2 100 The components are mixed with one another and the mixture is finely ground in a suitable mill.

Example 7 Emulsifiable concentrate (for active substances which are liquid at 20-25"C) Parts by weight Active substance of formula 1 500 Castor oil ethoxylate 100 Calcium dodecylbenzene sulphonate 25 Mixture of C10-alkylbenzenes ad 1000 parts by volume The components are mixed with one another until a clear solution is obtained.

Claims (13)

1. Compounds of the general formula

wherein R1 signifies 2-halo-, 4-halo- or 2,4-dihalo-phenyl, R2 signifies 3-pyridyl 1-oxide, 2-pyrazinyl 1-oxide, 2-pyrazinyl 4-oxide or 2-pyrazinyl 1,4-dioxide, R3 signifies hydrogen or straight-chain C14-alkyl and R4 signifies Cl.e-alkyl, C3.6-cycloalkyl, C36-alkenyl or C36-alkynyl, and acid addition salts of these compounds.

2. Compounds according to claim 1, wherein R1 signifies 4-chlorophenyl or 2,4-dichlorophenyl.

3. Compounds according to claim 1 or claim 2, wherein R3 signifies hydrogen.

4. 2',4'-Dichloro-2-(3"-pyridyl)-acetophenone O-methyl oxime 1"-oxide.

5. A compound according to claim 1, selected from: 2',4'-Dichloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 1"-oxide, 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 4"-oxide and 2',4'-dichloro-2-(2"-pyrazinyl)-acetophenone O-ethyl oxime 1",4"-dioxide.

6. A compound or an acid addition salt according to any one of claims 1 to 5 as a fungicidal active substance.

7. A fungicidal composition which contains an effective amount of at least one compound of the general formula

wherein R7 signifies 2-halo-, 4-halo- or 2,4-dihalo-phenyl, R2 signifies 3-pyridyl 1-oxide, 2-pyrazinyl 1-oxide, 2-pyrazinyl 4-oxide or 2-pyrazinyl 1,4-dioxide, R3 signifies hydrogen or straight-chain C1.4-alkyl and R4 signifies C16-alkyI, C36-cycioalkyl, C36-alkenyl or C36-alkynyl, or an acid addition salt of such a compound, as well as formulation adjuvants.

8. A fungicidal composition according to claim 7 which contains an effective amount of 2',4'-dichloro-2 (3"-pyridyl)-acetophenone O-methyl oxime 1"-oxide as well as formulation adjuvants.

9. A process for the manufacture of compounds of the general formula

wherein R signifies 2-halo-, 4-halo- or 2,4-dihalo-phenyl, R signifies 3-pyridyl 1 -oxide,2-pyrazinyl 1-oxide, 2-pyrazinyl 1-oxide or 2-pyrazinyl 1,4-dioxide, R signifies hydrogen or straight-chain C1-4-alkyl and R4 signifies C1.6-alkyl, C36-cycI oalkyl C3.6-alkenyl or C36-alkynyl, and of their acid addition salts, which process comprises (a) N-oxidizing a pyridine or pyrazine derivative of the general formula

wherein R1, R3 and R4 have the significances given earlier in this claims and R2 signifies 3-pyridyl or 2-pyrazinyl, b) reacting a ketone of the general formula

wherein R1, R2 and R3 have the significances given earlier in this claim, with an O-substituted hydroxylamine of the general formula R410NH2 IV wherein R41 signifies C1 6-alkyl, C3.6-cycloalkyl or C3.6-alkenyl, and, if desired, converting a compound of general formula I obtained into an acid addition salt.

10. A method for the control of fungi in agriculture and in horticulture, which method comprises treating the locus to be protected with an effective amount of at least one of the compounds set forth in claims 1 to 5 or of a composition set forth in claim 7 or claim 8.

11. The use of one of the compounds set forth in claims 1 to 5 or of a composition set forth in claim 7 or claim 8 for the control of fungi in agriculture and in horticulture.

12. Afungicidal composition according to claim 7, substantially as described herein with reference to Example 6 or 7.

13. A process according to claim 9, substantially as described herein with reference to Example 1 or 2.