WO1992010484A1

WO1992010484A1 - Herbicides

Info

Publication number: WO1992010484A1
Application number: PCT/GB1991/002167
Authority: WO
Inventors: Christoph Harde; Gabriele KRÜGER; Gerhard Tarara; Nikolaus Heinrich; Klaus-Peter Gerbling; Richard Rees; Gerhard Johann; Graham Peter Jones
Original assignee: Schering Agrochemicals Ltd
Current assignee: Bayer CropScience Ltd Great Britain
Priority date: 1990-12-13
Filing date: 1991-12-06
Publication date: 1992-06-25
Anticipated expiration: 1993-06-13
Also published as: AU9069391A; DE4040118A1

Abstract

Herbicidal acetic acid derivatives of formula (I) where: R is a group -CO2?R?1, -CH2?OH, -CONHSO2?R?a or -CONHSO2?NR?aR?b, where R?1 is hydrogen or a salt- or ester-forming group, R?a is alkyl or aryl, and R?b is hydrogen, alkyl or aryl; R?2 and R?3, which may be the same or different, are each halogen, alkyl, alkoxy, alkylthio, alkylamino or dialkylamino; A is a substituted or unsubstituted aryl, heterocyclyl or benzoheterocyclyl group, or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group; X is oxygen or sulfur; Y is -CH= or -N=; and Z is oxygen or sulfur; and salts thereof, herbicidal compositions containing them, processes for their preparation, and methods of using them.

Description

Title; Herbicides

Field of the invention

This invention concerns new pyrimidinyloxy, pyrimidinylthio, triazinyloxy and triazinylthio acetic acid derivatives having herbicidal activity, processes for their preparation and compositions containing them.

Prior Art

Various pyrimidine and triazine derivatives are known to possess herbicidal activity, being described for example in European Patents nos 223406, 249707, 249708, 287072 and 287079. However, the herbicidal action of such compounds is not entirely satisfactory, particularly as regards their selectivity in important agricultural crops.

Description In one aspect, the invention provides the acetic acid derivatives of the formula:

H - C - Z - A I X

(i)

where:

R is a group -COjR¹, -CH₂0H, -C0NHS0₂R* or - C0NHS0₂NR"R^b, where R¹ is hydrogen or a salt- or ester- forming group, R* is alkyl or aryl, and R^b is hydrogen. alkyl or aryl;

R² and R³, which may be the same or different, are each halogen, alkyl, alkoxy, alkylthio, alkylamino or dialkylamino; A is a substituted or unsubstituted aryl, heterocyclyl or benzoheterocyclyl group, or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group;

X is oxygen or sulfur; Y is -CH= or -N=; and Z is oxygen or sulfur; and salts thereof.

When R¹ is an ester-forming group, it may for example be a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group. It is preferably an unsubstituted group, especially an unsubstituted alkyl group.

R* and R^b are each preferably methyl, ethyl, n- propyl, isopropyl or phenyl. When R² or R³ is halogen, it is preferably chlorine. However, R² and R³ are each preferably alkyl or alkoxy, and both are preferably the same.

The group A is preferably a substituted or unsubstituted phenyl, pyridyl, naphthyl, furyl, thienyl, pyrrolyl, benzofuranyl , benzothiophenyl, indolyl, oxazolyl, thiazolyl or imidazolyl group, or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group.

When A is a substituted phenyl, heterocyclyl or benzoheterocyclyl group, the substituent groups thereon are each preferably alkyl, alkoxy, amino, dialkylamino, nitro, halogen, trifluoromethyl or phenyl.

Any alkyl group in the compounds of the invention is preferably of 1 to 10, especially 1 to 4, carbon atoms, for example methyl, ethyl, n-propyl, isopropyl or t- butyl.

Any alkenyl or alkynyl group in the compounds of the invention is preferably of 2 to 10, especially 2 to 4 carbon atoms, for example vinyl, allyl or propargyl. Any cycloalkyl group in the compounds of the invention is preferably of 3 to 8 carbon atoms, for example cyclopentyl or cyclohexyl.

Any cycloalkenyl group in the compounds of the invention is preferably of 4 to 8 carbon atoms, for example cyclopentenyl or cyclohexenyl.

When any alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group present is substituted, it may, for example, be substituted by one or more alkoxy, alkylthio, amino, alkylamino, dialkylamino, nitro, halogen or phenyl groups. Any cycloalkyl or cycloalkenyl group present may additionally be substituted by one or more alkyl groups.

R¹ is preferably hydrogen, methyl or ethyl.

R² and R³ are preferably each methoxy or each methyl.

A is preferably alkyl of 1 to 4 carbon atoms, cyclopentyl, cyclohexyl, or phenyl substituted by a methyl group or by one or two chlorine atoms.

X is preferably sulfur.

Y is preferably -CH=.

Z is preferably sulfur. Specific preferred compounds of formula I are those of the Examples provided hereinafter. Particular mention may be made, however, of methyl 2-(4,6-dimethoxy- pyrimidin-2-ylthio)-2-(phenylthio)acetate.

The compounds of formula I where R is other than CH₂OH may be prepared by a process in which a substituted pyrimidine or triazine of the formula: Q

where Y, R² and R³ are as defined hereinbefore is reacted in the presence of a base with an acetic acid derivative of the formula:

R i H - C - Z - A (III)

I

Q' where A, Z and R are as defined hereinbefore but R is other than CH₂0H, one of the groups Q and Q' being a group

XH, where X is as defined hereinbefore, and the other being a leaving group, to give the desired compound. The leaving group may be any convenient such group, for example a halogen atom, an alkylsulfinyl group, a phenylsulfinyl group, and alkylsulfonyl group or a phenylsulfonyl group.

The reaction is conveniently effected in a suitable solvent medium, eg an aromatic hydrocarbon, eg benzene, toluene, xylene, halogenated hydrocarbon solvents such as methylene chloride or chloroform, alcohols such as methanol, ethanol or isopropanol, ethers such as diethyl ether, di-isopropyl ether, tetrahydrofuran or 1,4- dioxane, ketones such as acetone or methyl ethyl ketone, esters such as methyl acetate or ethyl acetate, polar aprotic solvents such as dimethylformamide, dimethyl acetamide or dimethylsulfoxide, or nitriles, eg acetonitrile, or in water. The base employed may be any convenient base, for example an alkali-metal or alkaline earth metal hydride. hydroxide or carbonate, eg sodium hydride, potassium hydride, calcium hydride, sodium hydroxide, potassium hydroxide, sodium carbonate or potassium carbonate.

The reaction temperature employed may be from 0°C to the boiling point of the reaction mixture, eg from 0 to 100°C.

The compounds of formula I in which R represents a group CH₂OH may be prepared by reduction of the corresponding compounds of formula I in which R represents -COOR¹.

The reduction may be achieved for example by means of borane-dimethyl sulfide complex under conventional conditions for the use thereof.

The compounds of formula I may also be prepared by a method in which a compound of the formula:

H C - Hal

I

X

(IV)

where R, R², R³, X and Y are as defined hereinbefore, and Hal represents halogen, is reacted in the presence of a base with a compound of formula A-Z-H, where A and Z are as defined hereinbefore, to give the desired compound.

The reaction is conveniently effected in a suitable solvent medium, eg an aprotic solvent such as benzene, toluene, xylene, tetrahydrofuran, diethyl ether, hexane, dimethylformamide or dimethyl sufoxide, and at a temperature of from -78°C to the boiling point of the reaction mixture, eg 0°C to 100°C. The base employed may be any convenient base, for example sodium hydride, potassium t-butylate or lithium di-isopropylamide.

In turn, the compounds of formula IV may themselves be prepared by a process in which a compound of the formula:

R l H - C - H I

(V)

where R, R², R³, X and Y are as defined hereinbefore, is reacted in a suitable solvent with a halogenating agent to give the desired compound.

Suitable halogenating agents include in particular the N-halosuccinimides, especially N-bromosuccinimide. Naturally, the compounds of formula I may be interconverted into further compounds of formula I by ^• methods known per se. For example, alkali-metal, alkaline earth metal, ammonium and substituted ammonium salts of the compounds may be prepared by reaction of the compounds, particularly those where R represents -COOH, with a suitable alkali-metal, alkaline earth metal, or ammonium-containing base in a suitable polar solvent medium, and such salts may if desired be hydrolysed by the action of an appropriate acid to give the corresponding compounds in which R represents -COOH.

Other derivatives of the acid function may of course be prepared from the acids by esterification or amide formation techniques known per se.

The compounds of formula I are herbicidally-active against a wide range of broad-leaved and grassy weeds. but are comparatively safe to certain crop species. They may thus be of use as herbicides, and especially as selective herbicides, particularly in the control of a range of weeds in cereals or other crops, eg wheat, rice, barley, maize, soya beans, oilseed rape, cotton or sugar beet. One very important weed combated particularly well by the compounds of the present invention is cleavers ■Galium aparine..

In another aspect, therefore, this invention provides a herbicidal composition which comprises one or more compounds of formula I in association with a suitable carrier and/or surface active agent.

The compositions of the invention usually contain from 0.01 to 99% by weight of the present compounds, and are normally produced initially as concentrates containing from 0.5 to 99%, preferably from 0.5 to 85%, and especially from 10 to 50% by weight thereof. Such concentrates are diluted if necessary before application to the locus to be treated such that the active ingredient comprises from 0.01 to 5% by weight of the formulation applied.

The carrier may be water, in which case an organic solvent may also be present, though this is not usually employed. A flowable suspension concentrate may be formed by grinding the compound with water, a wetting agent and a suspending agent,eg xanthan gum.

The carrier may alternatively be a water immiscible organic solvent, eg a hydrocarbon which boils within the range 130-270C, eg xylene, in which the compound is dissolved or suspended. An emulsifiable concentrate containing a water immiscible solvent may be formed with a surface active agent so that the concentrate acts as a self-emulsifiable oil on admixture with water.

The carrier may alternatively be a water-miscible organic solvent eg 2-methoxy ethanol, methanol, propylene glycol, diethylene glycol, diethylene glycol monoethyl ether, methylformamide or dimethylformamide.

The carrier may alternatively be a solid, which may be finely divided or granular. Examples of suitable solids are limestone, clays, sand, mica, chalk, attapulgite, diatomite, perlite, sepiolite, silicas, silicates, lignosulfonates and solid fertilizers. The carrier can be of natural or synthetic origin or can be modified natural material. Wettable powders soluble or dispersible in water may be formed by admixing the compound in particulate form with a particulate carrier or spraying molten compound on to the particulate carrier, admixing a wetting agent and a dispersing agent and finely grinding the mixture. An aerosol composition may be formed by admixing the compound with a propellant, eg a polyhalogenated alkane such as dichlorofluoromethane, and suitably also with a solvent.

The term 'surface active agent' is used in the broad sense to include materials variously called emulsifying agents, dispersing agents and wetting agents. Such agents are well known in the art.

The surface active agents used may comprise anionic surface active agents, for example mono- or di-esters of phosphoric acid with a fatty alcohol ethoxylate, or salts of such esters, fatty alcohol sulfates such as sodium dodecyl sulfate, ethoxylated fatty alcohol sulfates, ethoxylated alkylphenol sulfates, lignin sulfates, petroleum sulfonates, alkylaryl sulfonates such as alkyl-benzene sulfonates or lower alkylnaphthalene sulfonates, salts of sulfonated naphthaleneformaldehyde condensates, salts of sulfonated phenolformaldehyde condensates, or more complex sulfonates such as the amide sulfonates, eg the sulfonated condensation product of oleic acid and N-methyl taurine or the dialkyl sulfosuccinates eg the sodium sulfonate of dioctyl succinate.

The surface active agents may also comprise non-ionic agents, for example condensation products or fatty acid esters, fatty alcohols, fatty acid amides or alkyl-substituted phenols with ethylene oxide, fatty esters of polyhydric alcohol ethers eg sorbitan fatty acid esters, condensation products of such esters with ethylene oxide eg polyoxyethylene sorbitan fatty acid esters, block copolymers of ethylene oxide and propylene oxide, acetylenic glycols such as 2,4,7,9-tetramethyl-5- decγn-4,7-diol, or ethoxylated acetylenic glycols. The surface active agents may also comprise cationic agents, for example alkyl- and/or aryl-substituted quaternary ammonium compounds such as cetyl trimethylammonium bromide, or ethoxylated tertiary fatty amines.

Preferred surface active agents include ethoxylated fatty alcohol sulfates, lignin sulfonates, alkyl-aryl sulfonates,salts of sulfonated naphthaleneformaldehyde condensates, salts of sulfonated phenolformaldehyde condensates, sodium oleoyl N-methyltauride, dialkyl sulfosuccinates, alkyl phenol ethoxylates, and fatty alkyl ethoxylates. The present active compounds may be admixed with another pesticide, eg a herbicide, fungicide or insecticide, or a plant growth regulator, particularly another herbicide. Suitable further herbicides include trietazine, linuron, CPA, dichlorprop, isoxaben, diflufenican, metolachlor, fluometuron, oxyfluorfen, fomesafen, bentazone, prometryne, norflurazon, chlomazone, EPTC, imazaquin, and especially isoproturon, methabenzthiazuron, trifluralin, ioxynil, bromoxynil, benazolin, mecoprop, fluroxypyr, alachlor, acifluorfen, lactofen, metribuzin, pendimethalin, ethofumesate, benfuresate, phenmedipham, benzophenap, butachlor, chlomethox fen, dimepiperate, mefenacet, molinate, naproanilide, oxadiazon, piperophos, pro etryne, pyrazoxyfen, pyrazosulfuron-ethyl, bensulfuron, simetryne, pyrazolate, pretilachlor, thiobencarb and pyributicarb.

In a further aspect, the invention provides a method of combating weeds at a locus infested or liable to be infested therewith which comprises applying to said locus an effective amount of one or more compounds of formula I.

The present compound may be applied to plants, the soil, land or aquatic areas, and particularly to a locus at which a crop is growing. The compounds are active pre-emergence but particularly post-emergence, and especially at rates of application of from 0.005 to 1 kg/ha, more particularly from 0.01 to 0.5 kg/ha, especially 0.03 to 0.2 kg/ha.

Examples

The invention is illustrated by the following Examples, in which Me = methyl, Et = ethyl, Pr = propyl, Bu = butyl, and Ph — phenyl. Example 1 Methyl 2- ( .6-dimethoxypyrimidin-2-ylthio) -2- fphenylthio)acetate

Methyl (phenylthio)acetate (5g) , N-bromosuccinimide (5.8g) and benzoyl peroxide (O.lg) were suspended in carbon tetrachloride (150ml) , and the mixture was refluxed for 45 minutes. It was then cooled to 5°C and filtered, and the yellow solution was concentrated in a rotary evaporator. The oil obtained (7.1g) was dissolved in dimethylformamide (50ml) and was dripped into a suspension of 2-mercapto- ,6-dimethoxypyrimidine (4.68g) and potassium carbonate (1.87g) in dimethylformamide (50ml) . This mixture was stirred for 16 hours at room temperature, and was then poured into ice/water (150ml) and extracted three times with ethyl acetate (100ml) . The combined ethyl acetate phases were washed with water, and dried over magnesium sulfate to yield an oil which was purified by chromatography through silica gel eluting with hexane/ethyl acetate to give 3.64g of the desired product, mp 69-70°C. Example 2 2- (4.6-Dimethoxypyrimidin-2-ylthio. -2-(phenylthiolacetic acid

The product of Example 1 (1.5g) was suspended in water (25ml) and methanol (10ml) , and potassium hydroxide (0.24g) was added. The mixture was heated for 3 hours at 80^βC, then acidifed with 10% hydrochloric acid to Ph=2, after which the organic phase was washed with water, dried over sodium sulfate, and dried in a rotary evaporator to give 0.41g of the desired product, mp 114- 115°C. Example 3

Ethyl 2-ethoxγ-2- ( .6-dimethoxypyrimidin-2-γloxy.acetate

Ethyl 2-ethoxy-2-hydroxyacetate (6.4g) was dissolved in dimethylformamide (50ml) and potassium carbonate (2.5g) was added. After stirring for 20 minutes, 4,6- dimethoxy-2-methylsulfonylpyrimidine (8.0g) was added, and the mixture was heated for 12 hours at 90°C. It was then poured into ice/water (100ml) and was extracted three times with ethyl acetate. The ester phases were washed with water, dried over sodium sulfate and evaporated. The residue was purified by chromatography on silica gel, eluting with a hexane/ethyl acetate mixture, and the product was recrystallised from diisopropyl ether to yield 2.3g of the desired product, mp 71-72°C. Example 4

Methyl 2-f4,6-dimethoxypyrimidin-2-ylthio. -2- phenoxyacetate

Methyl phenoxyacetate (log) , N-bromosuccinimide (12.8g) and benzoyl peroxide (O.lg) were suspended in carbon tetrachloride (300ml) and the mixture was refluxed for 45 minutes. It was then cooled to 5°C and filtered, and the yellow solution was concentrated in a rotary evaporator. The oil obtained (14.7g) was dissolved in dimethylformamide (100ml) , and was dripped into a suspension of 2-mercapto-4,6-dimethoxypyrimidine (10.3g) and potassium carbonate (4.1g) in dimethylformamide (150ml) . The resulting mixture was stirred at room temperature for 16 hours, and was then poured into ice/water (200ml) , and extracted three times with ethyl acetate (150ml) . The combined ester phases were washed with water, dried over sodium sulfate, and purified by chromatography on silica gel, eluting with a mixture of hexane and ethyl acetate, to give 2.8g of the desired product, mp 67-68°C. Examples 5-24

The following compounds of formula I where R² and R³ are both methoxy, Y is -CH=, and X and Z are both S were made by methods analogous to those of Examples 1 to 4:

COOEt Oil

COOH 166-167

COOMe Oil

COOMe 57-60

COOEt Oil

COOEt Oil

Further compounds of formula I in which R² and R³ are both methyl, Y is -CH=, and X and Z are both S were made by methods analogous to those of Examples 1 to 4:

23 Me COOEt Oil

24 3-ClPh COOEt Oil Example 25 2- (4.6-Dimethoxypyrimidin-2-ylthio)-2-(methylthio.ethanol Borane-di ethyl sulfide complex (BH₃.S(CH₃)₂) (7.2ml of 2M in tetrahydrofuran) was added dropwise to a stirred solution of the compound of Example 11 (2g) in dry tetrahydrofuran (40ml) , and the mixture was stirred overnight. 2N hydrochloric acid was then added, and the aqueous layer was extracted with ether (3 x 75ml) . The combined extracts were dried and evaporated, and the residue was suspended in hot di-isopropyl ether and filtered. The filtrate was evaporated again and was chromatographed (5% ethyl acetate in hexane) to give 1.84g of the desired product. Example 26

Ethyl 2- ( .6-Dimethoxypyrimidin-2-ylthio)-2- (ethylthio)acetate (a) Ethyl 2-(4.6-Dimethoxypyrimidin-2-ylthio.acetate

Potassium carbonate (27.6g) was added to a stirred suspension of 4,6-dimethoxy-2-mercaptopyrimidine (34.4g) in dimethylformamide (400ml) . After stirring for 30 minutes, ethyl bromoacetate (33.4g) was added dropwise over 5 minutes whilst keeping the temperature below 27°C by water-bath cooling. The reaction mixture was stirred at room temperature for 2% hours, and was then poured into water (2 litres) , and was extracted with ether (3 times) . The combined extracts were washed with saturated sodium chloride solution, dried and stripped to give a colourless oil. Residual dimethylformamide was removed under high vacuum at 60°C to yield 50g of the desired product which solidified on cooling, (b) Ethyl 2-bromo-2-(4,6-Dimethoxypyrimidin-2- ylthio)acetate

N-bromosuccinimide (17.8g) was added to a stirred solution of the product of stage (a) in carbon tetrachloride (250ml) , and the resulting suspension was gently refluxed over a 500W lamp for 3% hours. The solid was filtered off, and the filtrate was stripped to give a yellow liquid which was purified by flash chromatography (5% diethyl ether in hexane) to give 28.5g of the desired product.

(c) Ethyl 2-(4 ,6-Dimethoxypyrimidin-2-ylthio)-2- (ethylthio)acetate

The product of stage (b) (1.7g) in dimethylformamide (5ml) was added to a stirred solution/suspension of ethanethiol (0.31g) and potassium carbonate (0.76g) in dimethylformamide (15ml) , and the resulting suspension was stirred at room temperature for 2 hours. The mixture was poured into water (80ml) , and was extracted with ether (2 x 80ml) . The combined extracts were washed with saturated sodium chloride solution, dried and stripped to give a colourless oil, which was purified by flash chromatography (5% diethyl ether in hexane) to give 0.41g of the desired product, identical to that of Example 12. Example 27

2-(4,6-Dimethoxypyrimidin-2-ylthio)-2-(methylthio. -N- fphenylsulfonyl)acetamide Carbonyl diimidazole (0.72g) was added to a stirred solution of the product of Example 11 (l.i5g) in dry tetrahydrofuran (30ml) at room temperature, and the mixture was stirred for 2\ hours under nitrogen. Sodium benzenesulfonamide (1.79g) was added, and the mixture was stirred overnight.

The solvent was evaporated off, and water (50ml) was added. The water layer was washed with ethyl acetate (2 x 50ml) , was acidified with 2N hydrochloric acid to Ph=l, and was extracted with ethyl acetate (2 x 100ml) . The combined extracts were dried and evaporated to give a yellow oil which was recrystallised from di-isopropyl ether/ethyl acetate (8:2) to give the desired product (1.66g) as a white solid, mp 128-130°C. Examples 28-30 The following compounds were prepared by methods analogous to that of Example 27: Ex A R M Pt f°C.

28 Me C0NHS0₂Me 158-160

29 Me CONHS0₂iPr 134-135 30 Me CONHS0₂NMe₂ 146-148

HERBICIDAL EXAMPLE A .Pre-Emercrence.

Seeds of the test species listed below were each sown in 8.5cm square pots filled to within 2cm of the top with sterile loam, and were covered with a 2-5mm layer of loam. The pots were watered, and then treated with the compounds of the Examples listed below formulated as a solution/suspension in 3:1 by volume of acetone and the wetting agent polyoxyethylene (20 mols) monolaurate solution (10 g per litre) by application to the soil surface in a spray cabinet. The concentration of each test compound and volume of application were calculated to give the desired rate of application of the compound in 200 litres per hectare.

After 3 to 4 weeks growth in a glasshouse (minimum temperature 16°C, 16 hours per day photoperiod) the plants were visually assessed for any herbicidal response. All differences from an untreated control were scored accordingly to an index where 0 = no effect, 1 =

1-24% effect, 2 = 25-69% effect, 3 = 70-89% effect and 4 = 90-100% effect.

In the table below, the following letters are used to denote the plant species: a - Triticu aestivum (wheat) b - Hordeu vulgare (barley) c - Beta vulgaris (sugar beet) d - Brassica napus (rape) e - Alopecurus myosuroides (blackgrass) f - Avena fatua (wild oat) g - Elymus repens (couch) h - Bromus sterilis (barren brome) i - Viola arvensis (field pansy) j - Stellaria media (chickweed) k - Galium aparine (cleavers)

1 - Matricaria inodora (scentless mayweed) m - Polyqonum lapathifolium (Pale persicaria) n - Veronica persica (Buxbau 's speedwell) . The results obtained were as follows:

Ex Kg/ha a b c d e f g h i i jc l i n

1 0.5 2 2 2 2 2 2 2 2 3 4 3 2 3 4 6 0.5 1 2 4 4 2 0 2 1 3 4 2 2 2 4

12 0.5 2 1 2 3 1 0 2 1 2 2 1 1 2 3

HERBICIDAL EXAMPLE B (Post-Emergence.

The plant species listed below were grown in 8.5cm square pots containing sterile loam in a glasshouse (minimum temperature 16°C, 16 hours per day photoperiod) , and were treated in a spray cabinet at the 2-3 leaf stage with the compounds of the Examples listed below formulated as a solution/suspension in 3:1 by volume of acetone and the wetting agent polyoxyethylene (20 mols) monolaurate solution (10 g per litre) . The concentration of each test compound and volume of application were calculated to give the desired rate of application of the compound in 200 litres per hectare.

After 3-4 weeks, the plants were visually assessed for any herbicidal response. All differences from an untreated control were scored according to an index where

0 = no effect, 1 = 1-24% effect, 2 = 25-69% effect, 3 = 70-89% effect and 4 = 90-100% effect.

In the table below, the letters used denote the same plant species as in Herbicidal Example A: The results obtained were as follows: Ex Kg/ha a b c. d e f_ g h .i .j. k .l m n

1 0.5 2 2 4 4 2 0 1 2 3 3 4 1 3 4 5 0.5 2 2 4 4 2 1 2 2 4 3 4 1 2 3 6 0.25 1 2 4 4 0 2 0 1 4 3 4 0 2 4

8 0.5 1 1 3 3 1 1 1 1 2 2 3 2 2 2

11 0.25 0 1 3 4 0 0 1 0 3 4 4 2 3 3

12 0.5 1 2 4 4 0 2 2 1 3 4 4 2 2 4

13 0.25 1 1 4 3 0 0 0 1 0 2 4 0 3 3 15 0.5 0 0 2 3 0 0 0 0 0 2 3 0 0 2

17 0.5 0 0 2 3 0 0 0 0 0 2 4 0 2 2 19 0.25 0 1 4 4 Q 0 0 0 2 3 4 1 2 4

Claims

1. The acetic acid derivatives of the formula:

H - C - Z - A I X

(I)

where:

R is a group -C0₂R^l, -CH₂OH, -CONHS0₂R* or - CONHS0₂NR¹R^b, where R^l is hydrogen or a salt- or ester- forming group, R" is alkyl or aryl, and R^b is hydrogen, alkyl or aryl;

R² and R³, which may be the same or different, are each halogen, alkyl, alkoxy, alkylthio, alkylamino or dialkylamino;

A is a substituted or unsubstituted aryl, heterocyclyl or benzoheterocyclyl group, or a substituted or unsubstituted alkyl, alkenyl, alkynyl, cycloalkyl or cycloalkenyl group; X is oxygen or sulfur;

Y is -CH= or -N=; and

Z is oxygen or sulfur; and salts thereof.

2. The acetic acid derivatives according to claim 1 in which R^x is alkyl of 1 to 4 carbon atoms.

3. The acetic acid derivative according to claim 2 in which R¹ is methyl or ethyl.

4. The acetic acid derivatives according to any of claims 1 to 3 in which R² and R³ are each alkyl or alkoxy of 1 to 4 carbon atoms.

5. The acetic acid derivatives according to claim 4 in which R² and R³ are each methyl or methoxy.

6. The acetic acid derivatives according to any of claims 1 to 5 in which A is alkyl of 1 to 4 carbon atoms, cyclopentyl, cyclohexyl, or phenyl substituted by one or two chlorine atoms.

7. Methyl 2-(4,6-dimethoxypyrimidin-2-ylthio)-2- (phenylthio)acetate.

8. A herbicidal composition which comprises from 0.01 to 99% by weight of one or more compounds according to any of claims 1 to 7, in association with a suitable carrier and/or surface active agent.

9. A method of combating weeds at a locus infested or liable to be infested therewith which comprises applying to said locus an effective amount of one or more compounds according to any of claims 1 to 7.

10. A method according to claim 9 in which the amount applied is from 0.005 to 1 kg/ha.