GB2192879A - Phenoxybenzisoxazole herbicides - Google Patents

Abstract

The invention provides phenoxy benzisoxazole compounds having the general formula I: <IMAGE> wherein R1 represents a hydrogen or halogen atom or a C1-4 alkyl or haloalkyl group; R2 and R3 which may be the same or different, each independently represents a hydrogen or halogen atom or C1-4 alkyl or haloalkyl, nitro or cyano group; characterized in that R represents an ethyl group; together with a process for the preparation of such compounds, herbicidal compositions containing them, and their herbicidal use.

Description

SPECIFICATION Phenoxybenzisoxazole herbicides This invention relates to a class of phenoxybenzisoxazole compounds, the preparation of such compounds, herbicidal compositions containing them, and to their use in combating undesired plant growth.

US patent 4571255 discloses 5- and 6-(2-chloro-4-trifluoromethylphenoxy)-3-methylbenzisoxazole as herbicidally active compounds and claims a broad class of the formula:

wherein: A is a benzisoxazole radical selected from:

wherein: X and Y are hydrogen, halogen, C1 to C4 haloalkyl, nitro or cyano; Z is halogen C1 to C4 alkylsulfonyl, aminosulfonyl or C, or C4 haloalkyl; R is hydrogen, halogen, cyano, amino, mono- or dialkylamino, hydroxy C1 to C4 alkyl or haloalkyl, C1 to C4 alkoxy, haloalkoxy or alkylthio, phenyl or substituted phenyl, phenoxy or substituted phenoxy, carboxy or alkoxycarbonyl; Q is halogen, nitro, cyano or C1 to C4 haloalkyl; and n=0-2.

It has now been found, unexpectedly, that a compound of a narrow class of compounds from those generically proposed in US 4571255 possesses substantially higher herbicidal activity in field applications than the corresponding compound actually disclosed in that patent.

Accordingly, the present invention provides a phenoxybenzisoxazole compound having the general formula I:

wherein R1 represents a hydrogen or halogen atom or a C14 alkyl or haloalkyl group; R2 and R3, which may be the same or different, each independently represents a hydrogen or halogen atom or C14 alkyl or haloalkyl, nitro or cyano group; characterized in that R represents an ethyl group.

When any compounds of the invention contain a haloalkyl substituent group, this is preferably a halomethyl group. Chlorine and/or fluorine atoms are preferred halogen atoms in any haloalkyl group. Trifluoromethyl is particularly preferred.

Preferred compounds are those wherein R1 represents a halogen, especially chlorine, atom or, more particularly, a trifluoromethyl group; R2 represents a nitro, cyano, trifluoromethyl or, more particularly, a halogen, especially chlorine, atom; and R3 represents a halogen, especially chlorine, or, more particularly, a hydrogen atom.

The invention also provides a process for the preparation of the compounds of which comprises cyclising, in the presence of a base, a compound of formula II

where R is an ethyl group, L represents a leaving group and M represents a hydrogen or metal atom or a group of formula Ill

where R1, R2 and R3 are as defined above, followed, when M in the resulting compound is other than a group of formula Ill, by reacting said compound with a compound of formula IV

where X represents a halogen atom or nitro group.

The leaving group L is suitably a halogen atom or an acyloxy, (e.g. acetoxy), arylsulphonate (e.g. tosyl), or nitro group. Suitable bases for the cyciising reaction include alkali hydroxides and carbonates such as sodium and potassium hydroxide and carbonate, and hydrides such as sodium and potassium hydride.

An organic solvent is preferably present for the cyclising reaction. Suitable are hydrocarbons, for example benzene, toluene and xylene, halogenated hydrocarbons, for example carbon tetrachloride and dichloromethane, alcohols, for example methanol, ethanol and ethane-1, 2-diol, ethers, for example dimethylether, diethylether, and cyclic ethers such as tetrahydrofuran, sulphoxides such as dimethylsulphoxide, amides, such as N, N-dimethylformamide, and amines, for example pyridine, piperidine and triethylamine. Alcohols and ethers are especially suitable.

The cyclising reaction is preferably effected under an inert atmosphere, suitably nitrogen. It preferably takes place at an elevated temperature, such as 50-150"C, and suitably at the reflux temperature.

When it is desired to cyclise compounds of formula II in which M is other than a group

that is to say, compounds in which M represents a hydrogen atom or metal atom, M is preferably an alkali metal atom. The reaction is preferably carried out in a suitable solvent, for example, dimethyl sulphoxide, sulpholane, dimethyl formamide, or dimethyl acetamide at elevated temperature such as 50-150"C, conveniently under reflux, and also under an inert atmosphere such as nitrogen.

It is preferred, however, to cyclise compounds of formula Il in which M represents a group

so that a further step to produce compounds of formula I is not required.

The compounds of general formula I have been found to show interesting activity as herbicides. Accordingly, the invention further provides a herbicidal composition comprising a compound of formula I as defined above in association with at least one carrier, and a method of making such a composition which comprises bringing a compound of formula I into association with at least one carrier.

The invention also provides the use of such a compound or composition according to the invention as a herbicide. Further, in accordance with the invention there is provided a method of combating undesired plant growth at a locus by treating the locus with a compound or composition according to the invention. Application to the locus may be pre-emergence or postemergence. The dosage of active ingredient used may, for example, be from 0.05 to 4kg/ha. A carrier in a composition according to the invention is any material with which the active ingredient is formulated to facilitate application to the locus to be treated, which may for example be a plant, seed or soil, or to facilitate storage, transport or handling.A carrier may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, and any of the carriers normally used in formulating herbicidal compositions may be used.

Preferably compositions according to the invention contain 0.5 to 95% by weight of active ingredient.

Suitable solid carriers include natural and synthetic clays and silicates, for example natural silicas such as diatomaceous earths; magnesium silicates, for example talcs; magnesium aluminium silicates, for example attapulgites and vermiculites; aluminium silicates, for example kaolinites, montmorillonites and micas; calcium carbonate; calcium sulphate; ammonium sulphate; synthetic hydrated silicon oxides and synthetic calcium or aluminium silicates; elements, for example carbon and sulphur; natural and synthetic resins, for example coumarone resins, polyvinyl chloride, and styrene polymers and copolymers; solid polychlorophenols; bitumen; waxes; and solid fertilisers, for example superphosphates.

Suitable liquid carriers include water; alcohols, for example isopropanol and glycols; ketones, for example acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers; aromatic or araliphatic hydrocarbons, for example benzene, toluene and xylene; petroleum fractions, for example kerosine and light mineral oils; chlorinated hydrocarbons, for example carbon tetrachloride, perchloroethylene and trichloroethane. Mixtures of different liquids are often suitable.

Agricultural compositions are often formulated and transported in a concentrated form which is subsequently diluted by the user before application. The presence of small amounts of a carrier which is a surface-active agent facilitates this process of dilution. Thus preferably at least one carrier in a composition according to the invention is a surface-active agent. For example the composition may contain at least two carriers, at least one of which is a surface-active agent.

A surface-active agent may be an emulsifying agent, a dispersing agent or a wetting agent; it may be nonionic or ionic. Examples of suitable surface-active agents include the sodium or calcium salts of polyacrylic acids and lignin sulphonic acids; the condensation of fatty acids or aliphatic amines or amides containing at least 12 carbon atoms in the molecule with ethylene oxide and/or propylene oxide; fatty acid esters of glycerol, sorbitol, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohol or alkyl phenols, for example Roctylphenoi or poctylcresol, with ethylene oxide and/or propylene oxide; sulphates or sulphonates of these condensation products; alkali or alkaline earth metal salts, preferably sodium salts, of sulphuric or sulphonic acid esters containing at least 10 carbon atoms in the molecule, for example sodium lauryl sulphate, sodium secondary alkyl sulphates, sodium salts of sulphonated castor oil, and sodium alkylaryl sulphonates such as dodecylbenzene sulphonate; and polymers of ethylene oxide and copolymers of ethylene oxide and propylene oxide.

The compositions of the invention may for example be formulated as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders usually contain 25, 50 or 75% w of active ingredient and usually contain in addition to solid inert carrier, 3-10% w of a dispersing agent and, where necessary, 0-10% w of stabiliser(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a duqt concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing --10% w of active ingredient. Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676 0.152 mm), and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain 2-75% w active ingredient and 0 10% w of additives such as stabilisers, surfactants, slow release modifiers and binding agents.

The so-called "dry flowable powders" consist of relatively small granules having a relatively high concentration of active ingredient. Emulsifiable concentrates usually contain, in addition to a solvent and, when necessary, co-solvent, 10-50% w/v active ingredient, 2-20% w/v-emulsifiers and 0-20% w/v of other additives such as stabilisers, penetrants and corrosion inhibitors.

Suspension concentrates are usually compounded so as to dbtain a stable, non-sedimenting flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 010% w of other additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids or inorganic salts may be present dissolved in the formulation to assist in preventing sedimentation or as antifreeze agents for water.

Aqueous dispersions and emulsions, for example compositions obtained by diluting a wettable powder or a concentrate according to the invention with water, also lie within the scope of the invention. The said emulsions may be of the water-in-oil or of the oil-in-water type, and may have a thick 'mayonnaise'-like consistency.

The composition of the invention may also contain other ingredients, for example other compounds possessing herbicidal, insecticidal or fungicidal properties.

The invention is illustrated by the following Example.

Preparation of 5-(2-chloro-4-trifluoromethylphenoxy)-3-ethylbenzisoxazole.

5-(2-Chloro-4-trifluoromethylphenoxy)-2-nitro-propiophenone oxime (2.09) (prepared by treatment of 5-(2-Chloro-4-trifluoromethylphenoxy)-2-nitro-propiophenone with hydroxylamine hydrochloride and sodium acetate in water and ethanol) was dissolved in dry tetrahydrofuran (20ml) and added to a suspension of oil-free sodium hydride (0.2g) in tetrahydrofuran (20ml) and stirred, under nitrogen, for 2 hours. Solvent was removed by evaporation and diethyl-water (50/50, v/v; 400ml) was added. The organic layer was separated, washed, dried and chromatographed to give the title compound as a colourless oil (1.39) b.p.: 1700C at 8mm Hg (1060Pa), which solidified, m.p. 65"C.

Analysis Calculated: 56.2%C 3.2%H 4.1%N Found: 56.4%C 3.3%H 4.2%i Herbicidal Activity A biological evaluation was carried out to demonstrate the activity of the compound of Example 1, and to compare that activity with that of the diphenyl ether compound (hereinafter designated as "A") specifically described in Example 1 of US Patent 4419122.

The test conducted was a spray test, in which seedling plants of a range of species were sprayed with the test compounds. The test plant species were wheat (WH), chickweed (ST), mayweed (MW), pale persicaria (PP), field forget-me-not (FF), speedwell (SW), field pansy (FP) and cleavers (GG). The plants were at the stage of 1-3 true leaves.

The soil used in the test was a prepared horticultural loam.

The compounds were tested as technical materials and formulated in a 1:1 acetone:water mix containing up to 0.2% of the alkylphenol/ethylene oxide wetting agent, Triton X155 (trade mark) and applied as single dose foliar sprays in a total volume of 600 litres/hectare. Application was at 4 different dosage ievels 0.3, 0.1, 0.03 and 0.01 kg/ha designed to produce a range of responses. At least two replicate pots were used for each treatment. Untreated seedling plants were used as controls.

Phytotoxicity compared with the untreated control was assessed visually approximately 2 weeks after treatment using the standard 0-9 scale, 0 indicating no effect and 9 indicating death.

The results were -subjected to a standard probit analysis by computer to calculate the dosage of each compound in g/ha; required to kill 50% of the plant species. This dosage is referred to as the GID50 dosage.

The GID50 values obtained are set out in Table I below.

Table I GIRD50 values expressed in glha rest gg?ound ~~ SW ST a FP PP E1! WH Example 1 10 5 43 12 1 7 6 42 22 28 843 75 4 3 6 164

Claims (10)

1. A phenoxybenzisoxazole compound having the general formula I:

wherein R, represents a hydrogen or halogen atom or a C14 alkyl or haloalkyl group; R2 and R3, which may be the same or different, each independently represents a hydrogen or halogen atom or C14 alkyl or haloalkyl, nitro or cyano group; characterized in that R represents an ethyl group.

2. A compound as claimed in claim 1 wherein R1 represents a halogen atom or trifluoromethyl group; R2 represents a halogen atom, or a nitro, cyano, or trifluoromethyl group; and R3 represents a hydrogen or halogen atom.

3. A compound as claimed in claim 2 wherein R1 represent a trifluoromethyl group; R2 represents a halogen atom; and R3 represents a hydrogen atom.

4. 5-(2-Chloro-4-trifluoromethylphenoxy)-3-ethylbenzisoxazole.

5. Process for the preparation of a compound of the general formula I as defined in any preceeding claim, which comprises cyclising, in the presence of a base, a compound of formula II

where R is an ethyl group, L represents a leaving group and M represents a hydrogen or metal atom or a group of formula Ill

where R1, R2 and R3 are as defined above, followed, when M in the resulting compound is other than a group of formula Ill, by reacting said compound with a compound of formula IV

where X represents a halogen atom or nitro group.

6. Process as claimed in claim 7 carried out substantially as hereinbefore described with particular reference to the accompanying Example.

7. Herbicidal composition, which comprises a compound as claimed in any of claims 1 to 4, together with a carrier.

8. A composition as claimed in claim 7, which comprises at least two carriers, at least one of which is a surface-active agent.

9. Method of combating undesired plant growth at a locus, which comprises treating the locus with a compound as claimed in any one of claims 1 to 4, or a composition as claimed in either of claims 7 and 8.

10. The use of a compound as claimed in any one of claims 1 to 4 as a herbicide.