GB2207425A

GB2207425A - Diphenyl ether herbicides

Info

Publication number: GB2207425A
Application number: GB08718039A
Authority: GB
Inventors: Michael Thomas Clark; Ian James Gilmore
Original assignee: Shell Internationale Research Maatschappij BV
Current assignee: Shell Internationale Research Maatschappij BV
Priority date: 1987-07-30
Filing date: 1987-07-30
Publication date: 1989-02-01
Also published as: GB8718039D0

Abstract

Diphenyl ether derivatives having the general formula I: <IMAGE> wherein R1 represents a hydrogen or halogen atom or an alkyl or haloalkyl group, R2 and R3, which may be the same or different each independently represents a hydrogen or halogen atom or an alkyl, haloalkyl, nitro or cyano group, X represents an oxygen or sulphur atom and A, B and D are as defined in the text; the preparation of such compounds, herbicidal compositions containing them and their use as herbicides.

Description

DIPHENYL ETHER HERBICIDES This invention relates to certain diphenyl ether derivatives, their preparation, herbicidal compositions containing such compounds and to their use in controlling undesired plant growth.

Our European Patent Application No. 84201740.2 relates to herbicidal compositions containing certain diphenyl ethers, one of the phenyl groups having a fused 5-membered ring at the 3,4 position, the compounds being 5-phenoxy phthalic anhydrides, phthalides and phthalimides.

It has now been found that certain diphenyl ethers which bear a fused 6-membered ring substituent at the 3,4 position, show interesting herbicidal activity.

Accordingly, the present invention provides diphenyl ether derivatives having the general formula I:

wherein Rl represents a hydrogen or halogen, preferably chlorine, atom or an alkyl or haloalkyl, preferably trifluoromethyl, group; R2 and R3, which may be the same or different, each independently represents a hydrogen or halogen, preferably chlorine, atom or an alkyl, haloalkyl, nitro or cyano group; A, B, and D which may be the same or different, each independently represents a divalent group selected from

provided that when A, B or D represents -X-, then the adjacent group or groups A and/or B and/or D must be different from A;; each R4, which may be the same or different,. represents a hydrogen or halogen atom or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aryl, aralkyl, alkaryl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkoxycarbonylalkoxy, alkylthio, acyl, acyloxy, carboxyl, alkoxycarbonyl or heterocyclic group, an amino group of formula-NR6R7, or when one R4 represents a hydrogen atom, an alkoxy group or a hydrocarbon group, then the other may represent a hydroxyl group, or both groups R4 together may represent an imino group of formula =NR6, or, when each of A and B or each of B and D represents the group C(R4)2, two groups R4 on adjacent carbon atoms may together represent a bond giving a double bond linkage between A and B or B and D;; R5 represents a hydrogen atom, a carboxyl or hydroxyl group, or an optionally substituted alkyl, alkoxy, aralkyl, alkoxycarbonyl, acyl, carbamyl, cycloalkyl, alkenyl, alkynyl or alkoxycarbonylalkyl group, or an amino group of formula NR6R7; R6 and R7, which may be the same or different, each represents a hydrogen atom or an optionally substituted alkyl, aryl or acyl group; and X, both in formula I and in the definitions of the substituents therein, represents an oxygen or sulphur atom.

The term "acyl" is used herein to denote the radical derived from an organic acid by the removal of a hydroxyl group; the organic acid may be a carboxylic.acid (including carbamic acid derivatives) or a sulphonic acid, examples of suitable acyl groups being alkylcarbonyl, alkylcarbamoyl and alkylsulphonyl, e.g. acetyl, methylsulphonyl and dimethylcarbamoyl.

When any of the foregoing substituents represents or contains an alkyl, alkenyl or alkynyl substituent group, this may be linear or branched and may contain up to 10, preferably up to 6, carbon atoms, suitable examples being methyl, ethyl, propyl, allyl and propynyl. When they represent 'or contain a cycloalkyl substituent group this may contain from 3 to 10, preferably 5 to 8, carbon atoms, and is suitably .cyclohexyl.

When they contain a haloalkyl substituent group, this suitably contains up to 6, preferably up to 4, carbon atoms and the halogen atom is suitably fluorine or chlorine, trifluoromethyl being particularly preferred. When they contain an aryl substituent group, this is preferably a phenyl group. When they contain a heterocyclic group, this may, for example, be a pyrrole, pyrrolidine, pyridine, piperidine, furan or pyran ring.

When any of the foregoing substituents are designated as being optionally substituted, the substituent groups which are optionally present may be any of those customarily employed in the development of pesticidal compounds, and/or the modification of such compounds to influence their structure/activity, persistence, penetration or other property. Specific examples of such substituents include halogen, especially chlorine, atoms and nitro, cyano, hydroxyl, alkoxy, e.g. methoxy, or ester, e.g.

alkoxycarbonyl, groups.

Preferred compound are those of general formula I wherein X represents an oxygen atom; A represents a carbonyl group, or the group

wherein each group R4, which may be the same or different, is a hydrogen atom, or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or an oxygen or sulphur atom; B represents an oxygen atom, a carbonyl group, the group

wherein each group R4, which may be the same or different, independently represents a hydrogen atom or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or the group NR5 wherein R5 represents a hydrogen atom or an alkyl group of up to 4 carbon atoms, especially methyl; or A and B together are linked by a double bond and together are represented by a group -C(R4)=C(R4)- where each R4 is a hydrogen atom or an alkyl group of up to 4 carbon atoms, especially methyl; and D represents an oxygen atom, the group

where in each group R4, which may be the same or different, independently represents a hydrogen atom or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or the group

wherein R5 represents a hydrogen atom or an alkyl group of up to 4 carbon atoms, especially methyl; or B and D together are linked by a double bond and together are represented by a group -C(R4)=C(R4)- where each R4 is a hydrogen atom or an alkyl group of up to 4 carbon atoms.

One preferred group of compounds of formula I is represented by the formula II

where R1, R2, R3 and R4 are as defined above with reference to formula I. Preferably each group R4, which may be the same or different, independently represents a hydrogen atom, a halogen atom, or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkylthio or acyl group. Preferably each R4 represents a hydrogen atom.

A further preferred group of compounds of formula I is represented by the formula III

where R1, R2, R3, R4 and R5.ae as defined above with reference to formula I. Preferably each group R4, which may be the same or different, independently represents a hydrogen.atom or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl or aralkyl group and R5 represents hydrogen or an optionally substituted alkyl, acyl, carbamyl, cycloalkyl, alkenyl, alkynyl or aralkyl group. Preferably both groups R4 and R5 each represent a hydrogen atom.

A further preferred group of compounds of formula I is represented by the formula IV

where R1, R2, R3 and R4 are as defined above with reference to formula I. Preferably each group R4, which may be the same or different, is independently represented by a hydrogen atom, a halogen atom, -CN or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkoxycarbonyl, alkylthio or acyl group, or two groups R4 on adjacent carbon atoms together represent a bond giving a double bond linkage between the adjacent carbons, each of the other two groups R4 being as defined above.

Preferably each R4 represents a hydrogen atom or two groups R4 on adjacent carbon atoms together represent a bond giving a double bond linkage between the adjacent carbons, the other two groups R4 being represented by hydrogen atoms.

A further preferred group of compounds of formula I is represented by the formula V

where R1, R2, R3, R4 and X are as defined above with reference to formula I. Preferably, each group R4, which may be the same or different, independently represents a hydrogen atom, a halogen atom or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkylthio or acyl group, or, when one R4 is hydrogen or optionally substituted alkyl, the other R4 on the same carbon atom may be alkoxycarbonyl, or two groups R4 on adjacent carbons together represent a bond giving a double bond linkage between the adjacent carbons, the other two groups R4 on those adjacent carbons being as defined above. Preferably X represents an oxygen atom and each R4 represents a hydrogen atom or a methyl group.

A further preferred group of compounds of formula I is represented by the formula VI

where R1, R2, R3 and R5 are as defined above with reference to formula I. Preferably each group R5, which may be the same or different, independently represents a hydrogen atom, or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl or acyl group. Preferably each group R5 is hydrogen or methyl.

A still further group of compounds of formula I is represented by the formula VII

where R1, R2, R3, R4 and X are as defined above with reference to formula I. Preferably, each group R4, which may be the same or different, independently represents a hydrogen atom, a halogen atom, or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aralkyl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkylthio or acyl group, or two groups R4 on adjacent carbon atoms together represent a bond giving a double bond linkage between the adjacent carbons, the other two groups R4 being as defined above.

Particularly preferred compounds are those of formulae I to VII in which R1 represents a trifluoromethyl group, R2 represents a halogen, especially chlorine, atom and R3 represents a hydrogen atom.

It will be appreciated that when the nature of the substituents is such as to introduce an asymmetric carbon atom, then the resulting compound will exist in stereoisomeric forms Also, some substitutent combinations permit the existence of tautomeric forms. The scope of the present invention includes these different forms of the compounds and their mixtures, and herbicidal compositions containing the active ingredient in such isomeric forms and mixtures.

The invention further provides a process for the preparation of the novel diphenyl ethers as defined above which comprises reacting a compound of formula:

with a compound of the formula:

wherein A, B, D, X, R1, R2 and R3 have the meanings given above for formula I; one of Z and Q represents a.halogen, suitably chlorine, atom or nitro group, and the other represents a group of formula -OM wherein M represents a hydrogen or alkali metal atom. Conveniently the reaction is carried out by reacting a compound of formula VIII wherein Q is hydroxy with an alkali metal hydroxide in an alkanol, e.g.. ethanol, solvent, thereby forming the corresponding alkali metal salt which is then reacted with a compound of formula IX wherein Z represents a chlorine atom.The reaction of the said salt with the chlorocompound is preferably carried out in a suitable organic solvent, eg dimethyl sulphoxide, sulpholane, dimethyl formamide, or dimethyl acetamide at elevated temperature, e.g. above 25"C and in particular between 40"C and reflux, conveniently under reflux, and also under an inert atmosphere such as nitrogen.

An alternative process for the preparation of the diphenyl ethers df formula I comprises reacting a compound of formula X or XI

where R1, R2, R3, X, A, B and D are as defined above with reference to formula I, under conditions effecting cyclisation where E and K, or J, are groups capable of cyclisation to form a six membered ring resulting in a compound of formula I, or with a compound of formula G-B-D-H, where B and D are as defined with reference to formula I and G and H are leaving groups and E and K are groups capable of condensation with the compound of formula G-B-D-H resulting in a compound of formula I, and, optionally, reducing and/or halogenating and/or akylating the compound of formula I to yield further compounds of formula I.

Compounds wherein X in formula I represents sulphur may be obtained from the corresponding oxygen analogues by reaction with phosphorus pentasulphide. Compounds wherein A, B or D represents. a halomethylene group may suitably be obtained by reacting the corresponding methylene compound with an appropriate halogenating agent. Thus, a compound wherein A, B or D represents / CHBr may be obtained by reacting the corresponding / CH2 compound with N-bromo-succinimide, suitably in the presence of a peroxide such as benzoyl peroxide and in a solvent such as carbon tetrachloride. Compounds wherein A, B or D represents a hydroxymethylene group may be obtained by hydrolysis of the corresponding halomethylene compound.

Compounds of formula II above may conveniently be prepared by cyclisation of a dicarboxylic acid of formula X above when E is -COOH, X is oxygen and K is -OH. Cyclisation may be effected for example under reflux in a solvent such as xylene. The dicarboxylic acid may be prepared by conventional preparative techniques such as the bromination of a 2-alkyl-4-phenoxybenzoic acid ester, followed by conversion to the corresponding cyanide (for example with methanolic sodium cyanide) and alkaline hydrolysis thereof.

Compounds of formula III above may conveniently be prepared by condensation, for example in the presence of alcoholic potassium hydroxide, of a compound of formula X above where E is a halogen (suitably bromine) and K is an alkyl group with a compound of formula HO-N(R5)-COOR (where R is an alkyl group) in accordance with the procedure described in Tetrahedron, 22, (1966), 2107.

Compounds of formula IV above where the fused ring is saturated (isochromanones) may conveniently be prepared by reduction of compounds of formula II, for example using sodium borohydride in a solvent such as tetrahydrofuran. Those compounds of formula IV containing unsaturation (isocoumarins) may be obtained from the saturated compounds by conventional techniques such as treatment with N-bromosuccinimide followed by treatment with a tertiary amine. Such procedures are described in J. Org. Chem. 35, (1970), 3514. Alternatively isochromanone compounds of formula IV may be obtained by oxidation (for example using selenium oxide) of the corresponding isochromone, the latter having been prepared by cyclisation of a precursor dihydroxy derivative of a diphenyl ether. The isochromanones may be prepared more directly by cyclisation of a precursor diester derivative of a diphenyl ether.They may also be prepared by ring cleavage of compounds of formula II followed by reductive cyclisation in accordance with the method described in Tetrahedron 20, (1964), 49. The isocoumarins of formula IV, where the fused ring is unsaturated and where one R4 is alkoxycarbonyl, may be obtained by cyclisation of corresponding precursor diester diphenyl ethers, for example in the presence of a sodium alkoxide followed by acidification, optionally followed by hydrolysis to the free acid. The isocoumarins may alternatively be prepared by condensation of the precursor diester with an oxalic diester (for example in the presence of sodium) or treatment of a carboxy substituted diphenyl ether monoester with an acid anhydride, such procedures being described in J. Chem. Soc. (1954), 3617. Such preparative methods are generally reviewed in Chem. Rev. 64, (1964), 229.

Saturated compounds of formula V may conveniently be prepared by reaction of the appropriate compounds of formulae VIII and IV), followed by desired by reactions such as alkylation to give further compounds of formula V. They may also be prepared by cyclisation of the corresponding optionally substituted carboxypropyl- or propenyl- substituted diphenyl ethers of formula XI (where A, B and D are C(R4)2 and X is O for example in the presence of polyphosphoric acid or aluminium chloride, optionally followed by introduction of further groups such as alkoxycarbonyl, alkyl and dialkyl by conventional procedures such as those described in Chem. Bey.'108, (1975), 203 and J. Chem. Soc., C, (1969), 217.

Compounds of formula VI may be prepared by reacting a compound of formula X, where E and K are hydroxy, halogen or alkoxy, with a compound of formula RN(R5)-N(R5)R where each R is alkyl and R5 is as previously defined. Alternatively the compounds of formula VI may be derived from the corresponding phthalimides described in our copending European Application No.

84201740.2 by reaction with a hydrazine.

Finally, chromanone and chromone compounds of formula VII may be prepared by cyclisation of a compound of formula XI, where A is O or S, B and D are each ) C(R4)2 and J is hydrogen, for example in the presence of polyphosphoric acid or condensation of a compound of formula X, where E is hydrogen and K is alkyl, with an ester or diester in accordance with the teachings of The Chemistry of Heterocyclic compounds", Vol. 31 (John Wiley) p 220 and 496.

The compounds of the general formula I have been found to show interesting activity as herbicides. Accordingly the invention also provides a herbicidal composition comprising a compound of formula I as defined above in association with at least one carrier. The invention also provides the use as a herbicide of such a compound or composition according to the invention. 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 post-emergence. The dosage of active ingredient used may, for example, be from 0.05 to 4 kg/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 Pr 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, montomorillonites 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 ndnionic or ionic. Examples of suitable surface-active agents include the sodium or calcium salts of polyacrylic acids andllignin 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, sorbitan, sucrose or pentaerythritol; condensates of these with ethylene oxide and/or propylene oxide; condensation products of fatty alcohol or alkyl phenols, for example p-octylphenol or E-octylcresol, 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, 3-108 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 dust 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 h-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 w 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 conentrates are usually compounded so as to obtain a stable, non-sedimenting flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-108 w of suspending agents such as protective colloids and thixotropic agents, 0-108 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 anti-freeze 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 following Examples illustrate the invention.

Example 1 6-(2'-Chloro-4'-trifluoromethylphenoxy)-l-totralone 6-Hydroxy-l-tetralone (4.9g) and potassium hydroxide (2.0g) in dry dimethyl sulphoxide (50ml) were stirred together for 15 minutes with warming. 3,4-Dichlorobenzotri- fluoride (6.5g) was added and the mixture heated at 1600C under dry nitrogen for 5 hours. After cooling and removal of the solvent,! a saline solution was added and the mixture extracted with methylene chloride, dried over sodium sulphate, the solvent removed and the residue chromatographed on silica with methylene chloride eluant. The main fraction was a colourless oil which solidified to a white solid (m.p. 47-480C).

Analysis: Calc. for C17H1202C1F3 C 59.9% H 3.5% Found C 59.8% H 3.4% Example 2 2,2-Dimethyl-6-(2'-chloro-4'-trifluoromethylphenoxy)-1-terralone 6-(2' -Chloro-4'-trifluoromethylphenoxy)-l-tetralone (1.7g) in dry dimethylformamide (lOml) was added dropwise to a 50% dispersion of sodium hydride (0:5g) in dry dimethyl formamide (5ml). After stirring for half an hour iodomethane (2.0g) was added and the mixture stirred overnight at room temperature under nitrogen. After solvent removal, the product was partitioned with methylene chloride and dilute hydrochloric acid, extracted with methylene chloride, washed with water, dried with sodium sulphate and the solvent removed.

Chromatographic purification on silica with methylene chloride eluant yielded a pale yellow oil.

Analysis: Calc. for C19H1602C1F3 C 61.9% H 4.3% Found C 61.5% H 4.3% Example 3 6- (2' -Chloro-4' -trifluoromethylphenoxy)homophthalic anhydride a) 2-Bromomethyl-4-(2'-chloro-4s-trifluoromethylphenoxy benzoic acid methyl ester.

2-Methyl-4-(2'-chloro-4'-trifluoromethylphenoxy benzoic acid methyl ester (27.5g) in dry carbon tetrachloride (120ml) was mixed with N-bromosuccinimide (14.25g) and a small quantity (about O.lg) of benzoyl peroxide.. The mixture was refluxed with stirring for 2 hours under bright light. After cooling and filtering the filtrate was extracted with carbon tetrachloride, washed with water and dried over sodium sulpahte. The residue was chromatographically purified on silica with hexane/methylene chloride (75:25v/v) eluant. The major fraction was collected as a clear oil.

Analysis: Calc. for C16H11O3ClF3Br C 45:3% H 2.6% Found C 45..3% H 2.8% b) 2-Cyanomethyl-4- (2 -chloro-4' -trifluoromethylphenoxy) - benzoic acid methyl ester.

The product from a) above (19.8g) in methanol (30ml) was mixed with potassium cyanide (3.9g) in water (30ml) and refluxed with stirring for 5 hours. After cooling the mixture was diluted with water, extracted with ether, washed with water and dried over sodium sulphate. After removal of solvent the residue was chromatographed on silica with methylene chloride eluant. The second major fraction was recovered as a colourless solid (m.p.

74-750C).

Analysis: Calc. for C17H11ClF303N C 55.2% H 3.0% N 3.8% Found C 55.2% H 3.2% N 3.7% c) 6- (2' -Chloro-4' -trifluoromethylphenoxy)homophthalic acid.

The product from b) above (3.6g) in 10%v/v sodium hydroxide (lOOml) was refluxed for 5 hours. After cooling and neutralisation with concentrated hydrochloric acid, the mixture was extracted with ethyl acetate, washed with water, dried with sodium sulphate and solvent removed to yield a clear gum which recrystallised as white needles from ethyl acetate/hexane (m.p. 152-50C).

Analysis: Calc. for C16H10C1F3O5 C 51.3% H 2.7% Found C 51.4% H 2.9% d) 6 - (2' -Chloro-4' -trifluoromethylphenoxy)homophthalic anhydride.

The product from c) above (l.Og) in xylene (25ml) was heated under reflux for 6 hours. After solvent removal, the residue was dried in vacuo to yield a colourless solid (m.p. 1120C) Analysis: Calc. for C16H8ClF304 C 53.9% g 2.2% Found C 54.1% H 2.4% Example 4 6-(2'-Chloro-4'-trifluoromethylphenoxy)-3,4-dihydroisocoumarin 6-(2'-Chloro-4'-trifluoromethylphenoxy)homophthalic anhydride (2.7g) (prepared as in Example 3) in dry tetrahydrofuran (40ml) was added dropwise to sodium borohydride (0.3g) in dry tetrahydrofuran (5ml) cooled at 0 C. Cooling was discontinued and the mixture stirred for 2 hours at room temperature. After solvent removal, dilute hydrochloric acid was added and the resulting gum heated on a steam bath for half an hour.After cooling, the product was extracted with methylene chloride, washed with water, dried over sodium sulphate and chromatographed on silica with methylene chloride eluant. The first fraction yielded a colourless oil which solidified to a white solid (m.p. 78-81 C).

Analysis: Calc. for C16HloClF3 C 56.1% H 2.9% Found C 56.5% H 2.8% Example 5 2,3-Dimethyl-6-(2'-chloro-4'-trifluoromethylphenoxy) phthalazine1,4-dione 5- (2' -Chloro-4' -trifluoromethylphenoxy)phthalic acid (l.Og), 1,2-dimethylhydrazine dihydrochloride (0.5g) and anhydrous sodium acetate (0.7g) in 50%v/v aqueous acetic acid (lOml) were refluxed with stirring for 3 hours. After solvent removal, saturated sodium bicarbonate solution was added to the residue which was then extracted with ethyl acetate, washed with water, dried over sodium sulphate and chromatographed on silica with ethyl acetate eluant.After removal of solvent a hygroscopic white solid was obtained which after drying gave a solid (m.p. 73-740C).

Analysis: Calc. for C17H12N203ClF3 C 53.1% H 3:1% N 7.3% Found C 52.7% H 3.1% N 7.6% Example 6 7-(2'-Chloro-4'-trifluoromethylphenoxy)-3H-2,3-benzoxazine-4-one 2-Bromomethyl-4- (2' -Chloro-4' -trifluoromethylphenoxy) - benzoic acid methyl ester, (prepared as in a) of Example 3) (4.2g), potassium hydroxide (2.0g) and N-hydroxyurethane (3.15g) in ethanol (50ml) were refluxed for 6 hours. The ethanol was stripped off and the residue partitioned between dilute hydrochloric acid and ethyl acetate.The desired product was recovered by extraction with ethyl acetate, washing with water, drying with sodium sulphate, chromatography on silica with diethyl ether eluant and collection of the major fraction which, after solvent removal, yielded a white crystalline solid which crystallised from ethyl acetate/hexane as white needles (m.p..

144-80C) Analysis: Calc. for C15H9NO3ClF3 C 52.4% H 2.6% N 4.1% Found C 52.4% H 2.8% N 4.3% Example 7 6-(2' -Chloro-4'-trifluoromethylphenoxy)isocoumarin 6-(2'-Chloro-4'-trifluoromethylphenoxy)-3,4-dihydroisocoumarin (prepared as in Example 4) (0.7g) in dry carbon tetrachloride (15ml) was reacted with N-bromosuccinimide (0.65g) and benzoyl peroxide (about O.lg) under reflux fornl hour. A further O.lg of benzoyl peroxide was added and the mixture refluxed 1 hour further under bright light. After cooling and filtration and evaporation of solvent, a bromo compound was obtained which was refluxed overnight with triethylamine (30ml).

After removal of excess triethylamine a brown solid was obtained which was partitioned between dilute hydrochloric acid and methylene chloride, extracted with methylene chloride, washed with water and dried over sodium sulphate. After solvent removal and chromatographic purification on silica with methylene chloride eluant, the major fraction yielded a colourless brown oil which solidified to a cream solid (m.p.

136-70C).

Analysis: Calc. for C16H803C1F3 C 56.4% H 2.35% Found C 56.3% H 2.6% Example 8 Herbicidal Activity To evaluate their herbicidal activity, compounds according to the invention were tested using as representative range of plants: maize, Zea mays (Mz); rice, Oryza sativa (R); barnyard grass, Echinochloa crusgalli (BG); oat, Avena satiMa (0); linseed, Linum usitatissimum (L); mustard, Sinapsis alba (M); sugar beet, Beta vulgaris (SB) and soya bean, Glycine max (S).

The tests fall into two categories, pre-emergence and post-emergence. The pre-emergence tests involved.spraying a liquid formulation of the compound onto the soil in which the seeds of the plant specied mentioned above had recently been sown. The post-emergence tests involved two types of test, viz., soil drench and foliar spray tests. In the soil drench tests the soil in which the seedling plants of the above species were growing was drenched with a liquid formulation containing a compound of the invention, and in the foliar spray tests the seedling plants were sprayed with such a formulation.

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

The formulatibns used in the tests were prepared from solutions of the test compounds in acetone containing 0.4% by weight of an alkylphenol/ethylene oxide condensate available under the trade mark TRITON X-155. These acetone solutions were diluted with water and the resulting formulations applied at dosage levels correponding to 5 kg or 1 kg of active material per hectare in a volume equivalent to 600 litres per hectare in the soil spray and foliar spray test, and at a dosage of level equivalent to 10 kilograms of active material per hectare in a volume equivalent to approximately 3,000 litres per hectare in the soil drench tests.

In the pre-emergence tests untreated sown soil and in the post-emergence tests untreated soil bearing seedling plants were used as controls.

The herbicidal effects of the test compounds were assessed visually twelve days after spraying the foliage and the soil, and thirteen days after drenching the soil and were recorded on a 0-9 scale. A rating 0 indicates growth as untreated control, a rating 9 indicates death. An increase of 1 unit on the linear scale approximates to a 10% increase in the level of effect.

The results of the tests are set out in Table I below, in which the compounds are identified by reference to the preceding examples.

TABLE I

Compound Soil drench 10/kg/ha Dosage Foliar spray Pre-emergence of Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 1 0 0 0 0 2 1 3 2 5 3 0 3 2 8 5 5 4 0 0 4 0 4 4 7 0 1 2 0 0 1 4 4 3 3 0 0 0 0 2 2 2 0 2 5 6 0 5 3 7 5 6 6 5 0 4 0 0 4 4 0 1 4 0 4 2 4 2 5 4 2 0 2 0 0 2 2 0 3 0 2 1 2 0 5 2 5 5 5 4 9 6 8 8 7 7 0 0 2 0 0 7 5 0 1 5 3 8 3 6 7 6 5 0 0 0 0 0 5 5 0 4 4 4 8 6 7 4 8 0 5 6 5 9 7 9 9 9 9 2 2 8 2 8 8 8 0 1 6 3 9 6 9 8 9 9 2 1 7 1 6 6 8 0 TABLE I (continued)

Compound Soil drench 10/kg/ha Foliar spray Pre-emergence of Dosage Ex. No. Mz R BG O L M SB S kg/ha Mz R BG O L M SB S Mz R BG O L M SB S 5 0 0 4 3 0 2 3 0 5 7 5 8 6 8 7 8 6 0 0 7 3 4 6 8 0 1 5 4 6 5 8 6 6 4 0 0 4 1 2 4 6 0 6 5 4 0 8 5 6 7 8 6 0 0 8 4 4 5 6 0 1 2 0 5 2 5 5 6 5 0 0 2 0 0 2 5 0 7 4 0 8 4 0 0 4 3 5 6 2 8 6 9 8 9 8 0 0 8 2 8 8 8 1 1 6 2 8 6 9 8 9 8 0 0 8 1 7 6 8 1

Claims

CLAIMS 1. Diphenyl ether derivatives having the general formula I:

wherein R1 represents a hydrogen or halogen chlorine, atom or an alkyl or haloalkyl group; R2 and R3, which may be the same or different, each independently represents a hydrogen or halogen atom or an alkyl, haloalkyl, nitro or cyano group; A, B, and D which may be the same or different, each independently represents a divalent group selseted from

provided that when A, B or D represents -X-, then the adjacent group or groups A and/or B and/or D must be different from A;; each R4, which may be the same or different, represents a hydrogen or halogen atom or an optionally substituted alkyl, cycloalkyl, alkenyl, alkynyl, aryl, aralkyl, alkaryl, alkoxy, cycloalkoxy, alkenyloxy, alkynyloxy, alkoxycarbonylalkoxy, alkylthio, acyl, acyloxy, carboxyl, alkoxycarbonyl or heterocyclic group, an amino group of formula NR6R7, or when one R4 represents a hydrogen atom, an alkoxy group or a hydrocarbon group, then the other may represent a hydroxyl group, or both groups R4 together may represent an imino group of formula =NR6, or, when each of A and B or each of B and D represents the group

two groups R4 on adjacent carbon atoms may together represent a bond giving a double bosd linkage between A and B or B and D;; R5 represents a hydrogen atom, a carboxyl or hydroxyl group, or an optionally substituted alkyl, alkoxy, aralkyl, alkoxycarbonyl, acyl, carbamyl, cycloalkyl, walkenyl, alkynyl or alkoxycarbonylalkyl group, or an amino group of formula NR6R7; R6 and R7, which may be the same or different, each represents a hydrogen atom or an optionally substituted alkyl, aryl or acyl group; and X, both in formula I and in the definitions of the substituents therein, represents an oxygen or sulphur atom.
2. Compounds as claimed in claim 1, wherein X represents an oxygen atom; A represents a carbonyl group, or the group

wherein each group R4, which may be the same or different, is a hydrogen atom, or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or an oxygen or sulphur atom; B represents an oxygen atom, a carbonyl group, the group

wherein each group R4, which may be the same or different, independently represents a hydrogen atom or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or the group

wherein R5 represents a hydrogen atom or an alkyl group of up to 4 carbon atoms, especially methyl; or A and B together are linked by a double bond and together are represented by a group -C(R4)=C(R4)- where each R4 is a hydrogen atom or an alkyl group of up to 4 carbon atoms especially methyl; and D represents an oxygen atom, the group

wherein each group R4, which may be the same or different, independently represents a hydrogen atom or an alkyl, alkenyl, alkynyl or alkoxy group of up to 4 carbon atoms, especially methyl or methoxy, or the group

wherein R5 represents a hydrogen atom or an alkyl group of up to 4 carbon atoms, especially methyl; or B and D rtogether are linked by a double bond and together are represented by a group -C(R4)-C(R4)- where each R4 is a hydrogen atom or an alkyl group of up to 4 carbon atoms.
3. Compounds as claimed in claim 1 or 2 represented by the formula II

where R1, R2, R3 and R4 are as defined in claim 1.
4. Compounds as claimed in claim 1 or 2 represented by the formula III

where R1? R2, R3, R4 and R5 are as defined in claim 1.
5. Compounds as claimed in claim 1 or 2 represented by the formula IV

where R1, R2, R3 and R4 are as defined in claim 1.
6. Compounds as claimed in claim 1 or 2 represented by the formula V

where R R1, R2, R3, R4 and X are as defined in claim 1.
7. Compounds as claimed in claim 1 or 2 represented by the formula VI

where R1, R2, R3 and R5 are as defined in claim 1.
8. Compounds as claimed in claim 1 or 2 represented by the formula VII

where R1, R2, R3, R4 and X are as defined in claim 1.
9. A process for the preparation of a compound of the general formula I as defined in claim 1 which comprises reacting a compound of formula:

with a compound of the formula:

wherein A, B, D, X, R1, R2 and R3 have the meanings given in claim 1; one of Z and Q represents a halogen, suitably chlorine, atom or nitro group, and the other represents a group of formula -OM wherein M represents a hydrogen or alkali metal atom.
10. A process for the preparation of a compound of the general formula I as defined in claim 1 which comprises reacting a compound of formula X or XI

where R1, R2, R3, X, A, B and D are as defined in claim 1, under conditions effecting cyclisation where E and K, or J, are groups capable of cyclisation to form a six membered ring resulting in a compound of formula I, or with a compound of formula G-B-D-H, where B and D are as defined with reference to formula I and G and H are leaving groups and E and K are groups capable of condensation with the compound of formula G-B-D-H resulting in a compound of formula I, and, optionally, reducing and/or halogenating and/or alkylating the compound of formula I to yield further compounds of formula I.
11. A compound as defined in claim 1, whenever prepared by a process as claimed in claim 9 or 10.
12. A herbicidal composition, which comprises a compound as claimed in any one of claims 1 to 8 or 11, together with a carrier.
13. A herbicidal composition as claimed in claim'l2, which comprises at least two carriers, at least one of which is a surface-active agent.
14. A 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 8 or 11, or a composition as claimed in claim 12 or 13.
15. The use of a compound as claimed in any one of claims 1 to 8 and 11 as a herbicide.