GB2261875A - Triazolopyrimidine herbicides - Google Patents

Abstract

Compounds of formula <IMAGE> Y and Z independently being hydrogen or halogen, alkyl, alkoxy, haloalykl or haloalkoxy; and R being a group -OR<1> or SR<1> in which R<1> is hydrogen, alkyl, aryl, or a salt-forming cation, or a group -NHSO2R<2> in which R<2> is alkyl or optionally substituted aryl, or a salt-containing group derived therefrom, are useful as herbicides.

Description

TRIAZOLOPYRIMIDINE HERBICIDES The present invention relates to triazolopyrimidine herbicides, their preparation and their use.

Triazolopyrimidine herbicides are known conventionally to find use in the control of dicotyledonous weeds in monocotyledonous crops. The compounds of EP-A-142,152 are one such group of herbicidal triazolopyrimidines.

U.S. Patent Specification No. 4,981,507 discloses a broad group of triazoloazines, which also exhibit the conventional triazolopyrimidine herbicidal activity:

in which A stands for nitrogen or for a radical C-R3, R1, R2 and R3 independently of one another each stand for hydrogen, hydroxyl, halogen, for optionally substituted alkyl, for alkoxy, alkythio or for optionally substituted aryl or either R1 and R3 together or R3 and R2 together stand for a fused, optionally substituted carbocyclic or heterocyclic ring, X stands for oxygen, sulphur, a sulphinyl group or a sulphonyl group and Ar stands for in each case optionally substituted aryl or heteroaryl.

Thirty two compounds, all bar one having X as sulphur or sulphonyl, are described in the Preparation Examples, and, in the description, Table 1 provides a listing of 126 compounds as hypothetical illustrations of compounds of the group which may be mentioned individually. One of the latter compounds has the structure

(9th Compound of Table 1, Column 6 of US-A-4,981,507) The 8th compound of Column 12 and 9th compound of Column 14, other hypothetical compounds of Table 1, are variants of the above compound. There is no indication that any of the above compounds of Columns 6, 12 and 14 have been prepared and tested.

The U.S. document teaches that such compounds can be employed with particularly good success for combating dicotyledon weeds in monocotyledon crops such as barley or wheat, and two of the exemplified compounds

(Example 24) and

are noted as having superior herbicidal activity against dicotyledon weeds for a similar selectivity to crop plants, as compared with a triazolopyrimidine of EP-A-142,152:

Accordingly, it is to be expected that all of the triazoloazines would show the useful triazolopyrimidine selective action against dicotyledonous weeds coupled with low activity to monocotyledonous crops, for example cereals.

To prepare the compounds of US-A-4,981,507, two process routes are suggested, one a method of nucleophilic substitution to obtain compounds in which the X linking group is oxygen or sulphur and the other by oxidising such compounds in which X is sulphur to derive the sulphinyl or sulphonyl analogues.

It has been found that a small group of triazolopyrimidines which lie within the general disclosure of US-A-4,981,507 have exceptional herbicidal activity, both pre-emergence and post-emergence, which, in contrast to the conventional use expected for triazolopyrimidine herbicides, is broad spectrum in nature, with certain of the group possessing a selectivity advantageous for use in the dicotyledonous crops of sugar beet and, especially soya.

The activity of the compounds of the present invention has been found to be peculiar to certain triazolopyrimidines which, using the symbols of US-A-4,981,507, have the combination of X as oxygen and Ar as a phenyl group ortho-substituted by a carboxy-based grouping. Comparisons with compounds differing only by having X as S, SO or SO2, or differing only by having Ar as phenyl which is unsubstituted or has a different ortho-substituent, show the distinctly different type, and characteristic advantageously high level, of activity for the compounds of the present invention.

One of the compounds of the present invention which is hypothetically listed in US-A-4,981,507 has been found to show an advantageous high level of broad spectrum activity and not the conventional triazolopyrimidine herbicidal activity that would be expected for it from the prior art. Rather than being suitable for use on cereal crops, the compound has been found to be very harsh on a representative cereal species Zea mays (maize). Compounds of the Preparation Examples of US-A-4,981,507 and even analogous compounds of Table 1 have been found to show the activity expected for herbicidal triazolopyrimidines. The listed compound is thus anomalous in activity with compounds of US-A-4,981,507.

Furthermore, it is believed not to be possible to prepare the carboxy-based compounds listed in US-A-4,981,507, and the related compounds of the present invention, by a nucleophilic substitution method such as described in US-A-4,981,507. Attempts made to use such a method were unsuccessful. Without intending to be limited to any theory on the matter, it is thought that the position and nature of the ortho-carboxy-based substituent of the phenyl ring gives rise to steric hindrance or, possibly, electron-withdrawal which interferes with the substitution reaction.

Accordingly, the present invention provides a compound of the general formula

in which Y and Z independently represent a hydrogen or halogen atom, or an alkyl, alkoxy, haloalkyl or haloalkoxy group; and R represents a group of the general formula - OR1 or -SR1 in which R1 represents a hydrogen atom, a salt-forming cation, an alkyl group, or an aryl group, or a group of the general formula -NHSO2R2 in which R2 represents an alkyl group or an optionally substituted aryl group, or a salt-containing group derived therefrom.

The present invention also provides a process for the preparation of the compounds of the invention, which process comprises converting a compound of the general formula

in which Y and Z are as defined above, into a compound of general formula I under oxidising conditions, and if desired or required converting the resulting product into another compound of general formula I.

An alkyl group as a substituent or as the alkyl portion of another substituent group may be a straight chain or branched chain group, and suitably has, for example, up to 12 carbon atoms. Preferably such an alkyl group has up to 6 carbon atoms, especially up to 4 carbon atoms. As a substituent of another group, e.g. an alkoxy or a haloalkyl group, an alkyl group suitably has 1 or 2 carbon atoms.

Halogen is fluorine, chlorine, bromine or iodine.

Haloalkyl and haloalkoxy is preferably mono-, di- or tri-fluoro-alkyl or -alkoxy, especially trifluoromethyl or trifluoromethoxy.

An aryl group is preferably a phenyl group.

Where substituents are present in the R2 aryl group, the substituent groups may be any of those customarily employed in the modification and/or development of pesticidal compounds and are especially substituents that maintain or enhance the herbicidal activity associated with the compounds of the present invention, or influence persistence of action, soil or plant penetration, or any other desirable property for herbicidal compounds. There may be one or more of the same or different substituents present.

Suitable examples of optional substituents for aryl group R include halogen atoms, especially fluorine, chlorine or bromine atoms; nitro groups; cyano groups; modified hydroxy groups; modified carboxy groups, including alkylamide or dialkylamide groups; alkyl groups unsubstituted or substituted by one or more halogen atoms, especially fluorine atoms; and aryl groups, suitably phenyl groups, unsubstituted or substituted by one or more halogen atoms, especially chlorine atoms, or nitro, cyano or haloalkyl groups.

Modified hydroxy and carboxy groups are to be understood to be groups derived from hydroxy or carboxy groups by, for example, etherification, esterification, acylation, amidation or salt formation, as appropriate for the group in question.

A salt-forming cation is suitably an agrochemically acceptable cation, preferably an alkali metal, alkaline earth metal cation, or a quaternary ammonium cation, for example a sodium, potassium, calcium, magnesium or tetrabutylammonium cation.

Y and Z may be different, for example one of Y and Z may be an alkoxy group, eg. methoxy, and the other a halogen atom, e.g. chlorine, or one may be a halogen atom, e.g. chlorine, and the other an alkyl group, e.g.

methyl. Preferably, however, Y and Z are the same and each represents a C14 alkyl group, especially a methyl group.

Preferably R represents a group OR1 in which R1 represents a hydrogen atom, a salt-forming cation or an alkyl group; it is further preferred that R1 represents a hydrogen atom, an alkali metal cation or an alkyl group having up to 4 carbon atoms. It is especially preferred that R1 represents a hydrogen atom, a sodium ion or a methyl group.

As a sulphonamide group R it is preferred that the substituent R2 represents a C14 alkyl group, especially methyl, or a phenyl group optionally substituted by one or more halogen atoms, e.g. chloro-substituted, especially an unsubstituted phenyl group.

Salt formation can occur at the -NH- of the sulphonamide group of R. Suitable salts are agrochemically acceptable salts and include alkali metal, e.g. sodium, salts and ammonium, e.g.

tetrabutylammonium, salts. Sodium salts are especially preferred.

Particularly advantageous herbicidal activity is given by compounds of formula I in which Y and Z are both methyl and R represents a sulphonamide group -NHSO2R2in which R2 is methyl or phenyl, and sodium salts thereof. R2 as phenyl is especially preferred in such compounds.

The preparation of the compounds of the invention is by an oxidising reaction in which the ortho methyl group of a compound of formula II is converted into a carboxy-based group.

Any suitable conventional oxidising system may be used, for example those reviewed in the book "Oxidation in Organic Chemistry", Part A [edited by Wiberg, published by Academic Press, New York, 1965], or known from general scientific literature, for example: hydrogen bromide/cobalt II acetate/acetic acid/oxygen, Can. J. Chem., 43, 1306, (1965); oxygen/potassium t-butoxide/diphenylsulphoxide, J. Org. Chem., 29, 2907, (1966); dilute nitric acid/liquid mercury, Chem. Ber., 94, 834, (1961); aqueous ammonium sulphate/ sulphur, J. Am. Chem. Soc., 82, 1911, (1960); ozone/cobalt II acetate/acetic acid, J. Org. Chem., 25, 616, (1960); nickel benzoate/air, Zur. Russ. Fiz-chim, 27, (1957); chromium trioxide/acetic acid/sulphuric acid, J. Am.

Chem. Soc., 78, 1689, (1956); chlorine gas, J. Am.

Chem. Soc., 73, 455, (1951); selenium oxide/water, J. Chem. Soc., 687, (1951); manganese dioxide/conc.

sulphuric acid, Zur. Russ. Fiz-chim., 15, 962, (1965); potassium permanganate/magnesium sulphate, Helv. Chim.

Acta, 27, 888, (1944); air/cobalt II bromide/tetrahexylammonium hydrogen sulphate, EP 300922; potassium hydroxide/ 18-crown-6/glyme, Tet. Lett., 25, 4989, (1984); bromamine B/sodium hydroxide, JP 8057337; and ruthenium III chloride/sodium hypochlorite/ tetrabutylammonium bromide, J. Org. Chem., 51, 2880, (1986). Particularly useful is a sodium dichromate, acetic acid and concentrated sulphuric acid oxidising system.

The reaction conditions for the oxidation will be those most suited to the oxidising system used. For example for a dichromate, acetic acid, sulphuric acid system, no additional solvent is required and the reaction has to be carried out under carefully controlled conditions. Thus, the reaction temperature is suitably maintained below 20"C, preferably below 15"C, and the addition of the acetic acid is staggered.

Conveniently an equivalent to an excess of oxidising agent is utilised in the reaction.

A compound of formula I obtained by the process of the invention may be converted into a different compound of formula I by methods known to those skilled in the art. For example, where COR is a carboxy group, conversion to a salt or to an ester may be carried out by conventional techniques.

Where the sulphonamide group is desired for R this may be prepared by reacting an acid, ester or salt group COR, after conversion to the corresponding acid chloride or acid anhydride if necessary, with a sulphonamide of the general formula R2SO2NH2 (III) in which R2 is as hereinbefore defined, or a salt thereof, in the presence of a carboxyl-activating agent, if appropriate.

Suitable carboxyl-activating agents include 2-chloro-N-methyl pyridinium iodide, dicyclohexylcarbodiimide and carbonyldiimidazole. The acid reactant is suitably activated by the carboxylactivating agent in the presence of an inert organic solvent, for example an ether such as tetrahydrofuran, at ambient or elevated temperature, for example at a temperature in the range of from 20"C to the reflux temperature of the mixture, prior to the addition of reactant III, and preferably in the presence of a tertiary amine, for example triethylamine, pyridine or 1,8-diazabicyclo(5.4.0]- undec-7-ene. If the acid reactant has been converted into an acid chloride or anhydride, then no carboxyl-activating agent is necessary.

Compounds of formula II may suitably be prepared from the corresponding compounds of the general formula

by the action of a suitably substituted 1,3-dicarbonyl compound, for example pentandione, and an organic acid, for example acetic acid, at elevated temperature, for example at the reflux temperature of the reaction medium. The organic acid may conveniently serve as the reaction medium, if present in excess.

Compounds of formula IV may be prepared from compounds of the general formula

under the action of an inorganic base, for example sodium hydroxide, in a suitable organic solvent, for example methanol or ethanol, at elevated temperature, for example under reflux.

Compounds of formula V may be prepared by reacting, with care, a methylphenylcyanate of the formula

with hydrazine hydrate in a suitable organic solvent, for example methanol or ethanol, at a reduced temperature, for example at a temperature in the range of from -20 C to 09C. The reaction generates a significant exotherm and it is necessary to add the hydrazine hydrate dropwise and with care.

The phenylcyanates of formula VI may be prepared from o-cresol by reaction with cyanogen bromide in the presence of a base, for example a tertiary amine such as triethylamine, in a suitable solvent, for example an ether such as tetrahydrofuran, again at a low temperature, suitably in the range of from -5 to +5 C.

The sulphonamides of formula III are well known or easily preparable by standard techniques; benzenesulphonamide, for example, features in Beilstein 11, 39.

Acid and salt conversion reactions may be carried out using conventional techniques as appropriate.

The prepared compounds of formula I may, if desired, be isolated and purified using conventional techniques.

Compounds of the general formula I have been found to have interesting activity as herbicides having a wide range of pre- and post-emergence activity against representative narrow-leaf and broad-leaf plant species.

The present invention therefore provides a herbicidal composition which comprises a compound of the present invention in association with a carrier.

The present invention additionally encompasses the preparation of such a herbicidal composition by the process of bringing a carrier into association with a compound of the present invention.

Preferably there are at least two carriers in a composition of the present invention, at least one of which is a surface-active agent.

The present invention further provides the use of a compound according to the invention as a herbicide.

The present invention particularly provides the use as a broad-spectrum herbicide, of a compound of general formula I in which R represents the group OR1 or SR The present invention especially provides the use as a selective herbicide for broad-leaf crops, for example sugar beet and soya, of a compound of the general formula I in which R represents the group -NHSO2R2, or a salt thereof.

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 composition or compound according to the invention. The locus may, for example, be the soil or plants in a crop area.

The compounds of the invention in which R represents -NHS02R2, or a salt thereof, are especially suited for )t( the selective control of weeds in broad-leaf crops, for example sugar beet and soya bean crops. Application to the locus may be pre-emergence or post-emergence. The dosage of active ingredient used may, for example, be in the range of from 0.01 to lokg/ha, preferably 0.1 to 2 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 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 products 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 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 herbicidal composition of the invention may also contain other active ingredients, for example compounds possessing insecticidal or fungicidal properties, or other herbicides.

The following Examples illustrate the invention.

The structures of the compounds prepared in the following Examples were confirmed by mass spectrometry and NMR.

Example 1

2-(2-Carboxyphenoxy) -5,7-dimethyl-1,2 ,4-triazolo- F 1,5-al -pyrimidine a) 1,4-diamino-1,4-di(2-methylphenoxy)-2,3- diazabutadiene o-Methylphenylcyanate was prepared from o-cresol (10.8 g, 0.1 moles) and an appropriate amount of cyanogen bromide in tetrahydrofuran under basic conditions provided by triethylamine, by the following method: to o-cresol (1.17g, 0.011 moles) dissolved in 20 ml tetrahydrofuran, was added 1.5 ml triethylamine and the reaction mixture cooled to 0-5iC using an ice-bath; cyanogen bromide (1.15 g, 0.011 moles) in 5 ml tetrahydrofuran was then added gradually and the reaction medium stirred. When the reaction was complete, the cyanate product was obtained from the reaction mixture.

The cyanate (0.1 moles) was dissolved in methanol (80 ml) and the reaction mixture cooled to -10 C using acetone-drikold. Hydrazine hydrate (2.5 ml, 0.05 moles) was then added dropwise with care and the reaction temperature allowed to rise to ooh.. After a few drops were added, a precipitate formed and a violent exotherm was noted. After the addition of all of the hydrazine hydrate, the reaction mixture was stirred for ten minutes to ensure complete reaction had occurred; the precipitate was then filtered off and washed with a small amount of aqueous methanol.

1,4-diamino-1,4-di(2-methyl phenoxy)-2,3-diazabutadiene was obtained in the form of a colourless solid of melting point 184.0 C (10.5 g, 70% yield).

b) 2-(2-methyl-phenoxy)-5-amino-1,2,4-triazole To the product of a) above (0.52g, 1.74 x -3 10 3 moles) in 5 ml of methanol, was added 10 ml of 2M sodium hydroxide and the mixture refluxed for 4 hours until thin layer chromatography showed the reaction to be complete. A clear solution resulted. The methanol was evaporated off and water (10 ml) added. The aqueous phase was extracted with chloroform, then acidified to pH2 and extracted twice more with chloroform. After evaporating to dryness a colourless solid was formed. The solid was purified twice more using 2 x 20 ml of methanol. An off-white waxy solid (0.25 g) of melting point l37.50C was obtained.

Yield: 76% The procedure was repeated using 8.0g (0.027 moles) of the starting material 1,4-diamino-1,4-di(2-methylphenoxy)-2,3- diazabutadiene and 4.5g of 2-(2-methylphenoxy) 5-amino-1,2,4-triazole was obtained; a yield of 89%.

c) 2-(2-methylphenoxy)-5,7-dimethyl-1,2,4-triazolo- [1,5-a) pyrimidine Pentandione (1.58 g, 1.60 ml, 0.0158 moles) was added to a solution of 2-(2-methylphenoxy) 5-amino-1,2,4-triazole (2 g, 0.0105 moles) in acetic acid (45 ml) and the reaction mixture refluxed for 6 hours. Thin layer chromatography showed the reaction components plus two products.

Evaporating off the acetic acid yielded an oily solid residue. Crystallisation from ethyl acetate was attempted. Material insoluble in ethyl acetate was identified as an unwanted by-product (0.53 g). On cooling, the desired product crystallised out from the mother liquor and 0.6 g of 2-(2-methylphenoxy)-5,7-dimethyl 1,2,4-triazolo[l,5-a]pyrimidine was obtained by filtration; a further 0.2 g of the desired product was isolated from the mother liquor by chromatography.

Total product obtained: 0.8 g Melting Point: 149.4 C Yield: 43% d) 2-(2-carboxyphenoxy)-5,7-dimethyl-1,2,4- triazolo (1, 5-a) -pyrimidine A solution of the product of c) (0.6 g, 2.36 x 10 3 moles) in 6 ml of acetic acid was cooled to approximately 12 C. Concentrated sulphuric acid (1.83 moles) was added dropwise with care whilst keeping the temperature of the reaction mixture below 15"C. A yellow solution resulted to which a solution of sodium dichromate -3 (1.05 g, 3.54 x 10 3 moles) in acetic acid was added over 30 minutes, the reaction temperature being maintained at from 10 to 15 C.After stirring for 10 minutes at 10-15"C the solution was allowed to warm to room temperature and stirred for a further hour. Finally the reaction mixture was quenched with ice-water (70 ml) and refrigerated overnight. A small amount of yellow precipitate was obtained and filtered from the solution. The pH of the mother liquor was adjusted from h to approximately 4 using 4 M sodium hydroxide. The colourless solid which then precipitated was filtered off and dried: 0.14 g of the desired product. The filtrate was treated once more with concentrated alkali and a further 0.32 g of colourless product obtained: total product 0.46 g; yield 69%.

The procedure was repeated under identical conditions but using 11.7 g of the starting material 2-(2-methylphenoxy)-5,7-dimethyl-1,2,4- triazolotl,5-a]-pyrimidine to give 9.5 g (a yield of 73%) of 2-(2-carboxyphenoxy)-5,7-dimethyl 1,2,4-triazolo[1,5-a] pyrimidine.

Melting Point: 171.4 C Example 2 to 5 Further examples of compounds of the invention were prepared by conventional procedures from the acid of Example 1: Example 2

2-(2-Methoxycarbonylphenoxy)-5,7-dimethyl-1,2,4triazolo[1,5-a]pyrimidine Concentrated sulphuric acid (8 drops) was added to a stirred suspension of the product of Example 1 (5.0g, 0.0176 mol) in methanol (150 ml). The mixture was refluxed overnight. The methanol was then evaporated in vacuo and the residue was purified by flash chromatography (chloroform/methanol 95:5) to give the title compound (4.3 g, 82%) as an oil. On trituration with diethylether this crystallised to give an off-white solid, m.p. 140.O'C.

Example 3

Sodium salt of 2-(2-carboxoPhenoxy)-57-dimethyl-l24-tria F 1,5-al pyrimidine A solution of sodium hydroxide (0.105g, 2.6 mmol) in water (5ml) was added dropwise to a stirred suspension of the product of Example 1 (0.75g, 2.6 mmol) in water (5 ml). The mixture was stirred at room temperature for 4 hours then evaporated to dryness.

The residue was triturated with methanol and ether to give the title compound (0.60 g, 75%) as an off-white solid which decomposed on melting.

Example 4

2-(2-Methanesulphonamidocarbonylphenoxy)-5,7-dimethyl 1,2, 4-triazolo F 1,5-al pyrimidine A solution of the product of Example 1 (1.42 g, 5.0 mmol) in dry tetrahydrofuran (10 ml) was added dropwise to a stirred solution of carbonyldiimidazole (0.89 g, 5.5 mmol) in dry tetrahydrofuran (10 ml) under nitrogen. The mixture was stirred for 30 minutes at room temperature and then refluxed for 30 minutes.

After allowing the mixture to cool to room temperature again, methanesulphonamide (0.48 g, 5.0 mmol) was added in a single portion. After stirring for a further 10 minutes, a solution of 1,8-diazabicyclol5.4.0jundec-7- ene (0.76 g, 5.0 mmol) in dry tetrahydrofuran (5 ml) was added dropwise. The reaction mixture was stirred overnight and then poured into 1N hydrochloric acid (100 ml). The product was extracted into dichloromethane (3x50 ml). The combined organic phases were dried (magnesium sulphate) and evaporated in vacuo. The residual oil solidified on standing and was recrystallised from isopropanol to give the title compound (0.13 g, 7%) as white crystals, m.p.

166-l71C.

Example 5

Sodium salt of 2-(2-BenzenesulPhonamidocarbonsl- phenoxy)5,7-dimethyl-1,2,4-triazolorl,5 pyrimidine A solution of the product of Example 1 (1.42g, 5.0 mmol) in dry tetrahydrofuran (10 ml) was added dropwise to a stirred solution of carbonyldiimidazole (0.89 g, 5.5 mmol) in dry tetrahydrofuran (10 ml) under nitrogen. The mixture was stirred for 30 minutes at room temperature and then refluxed for 30 minutes.

After allowing the mixture to cool to room temperature again, benzenesulphonamide (0.79 g, 5.0 mmol) was added in a single portion. After stirring for a further 10 minutes, a solution of l,8-diazabicyclo(5.4.0)undec-7-ene (0.76 g, 5.0 mmol) in dry tetrahydrofuran (5 ml) was added dropwise. The reaction mixture was stirred overnight and then poured into 1N hydrochloric acid (100 ml). The product was extracted into dichloromethane (3 x 50 ml) and the combined organic phases were dried (magnesium sulphate) and evaporated in vacuo. The residue was slurried with sodium hydride (0.12 g, 5.0 mmol) in dry tetrahydrofuran (15 ml). The mixture was then evaporated to dryness to yield the title compound (0.61 g, 28%) as a white solid.

Example 6 Herbicidal Activity To evaluate their herbicidal activity, a number of compounds were tested using, as a representative range of monocotyledon plants: maize, Zea mays (Mz); rice, OrYza-sativa (R); barnyard grass, Echinochloa crus-galli (BG); and oat, Avena sativa (0). As a representative range of dicotyledon plants, the following were also used: linseed, Linum usitatissimum (L); mustard, Sinapsis alba (M); sugar beet, Beta vulqaris (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 species 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 test compound, 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 formulations 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 corresponding 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 IIIa and Table IIIb below. An asterisk indicates that no result was obtained.

The compounds designated 'C' compounds in Table IIIa are specifically described Examples or hypothetical compounds disclosed in US-A-4,981,507; details are given in Table II below, with reference to the following general formula from US-A-4,981,507:

Table II

Compound Compound Designation R1 R2 A X Ar Designation in Herein US-A-4,981,507 Table 2 C1 CH3 CH3 CH S Mz EG. No. 11 Table 2 C2 CH3 CH3 CH SO2 < EG. No. 15 column 7 Table 1 C3 CR3 CH3 CR S 10th compound 00CR3 Column 9 Table 1 C4 CH3 CH3 CH SO Mz 1st compound 00CR3 Column 10 Table 1 C5 CH3 CH3 CH S02 2nd compound The compounds of Table IIIb are identified by reference to the preceding Examples of the present invention The results of Table IIIa confirm that exemplified compounds of US-A-4,981,507 (Bayer), that is Compounds C1 and C2, do show activity against the representative broad-leaf plant species, with no activity against the representative narrow-leaf plant species, Mz, R, BG and 0, thus making them suitable to combat dicotyledon weeds in monocotyledon crops. The activity is most pronounced for the post-emergence application techniques of foliar spray for C1 and, for C2, soil drench.

The results for the Compounds C3, C4 and C5, ortho-methoxycarbonylphenyl-thio, -sulphinyl and -sulphonyl triazolopyrimidines listed in Bayer, show good activity especially in foliar spray post-emergence application against the broad-leaf representative plant species with limited or no activity against the narrow-leaf species; thus those compounds are still suitable for use as broad-leaf weed killers in monocotyledon crops.

Surprisingly, and in distinct contrast, the ortho-carboxyphenoxytriazolopyrimidines of the present invention have a markedly superior activity against most of the test plant species, at all test dosages and for all test application techniques, both pre- and post-emergence. The sulphonamide variants, the compounds of Examples 4 and 5, have a more selective activity sharing the characteristic, markedly high activity against representative monocotyledon and certain of the representative broad-leaved plant species, yet with a surprisingly low activity against certain useful dicotyledonous plant species, namely sugar beet (SB) and soya (S).

The compound of Example 2 has the same structure as the hypothetical compound which is the 9th compound of Table 1 of US-A-4,981,507, and is shown by the test results to have a markedly different activity than that suggested for the compounds of US-A-4,981,507 and indeed as shown by the compounds C1 to C5.In particular the compound is shown to be very harsh to the representative species Mz, cereal species maize, giving scores of 9 (complete kill) and 8 in the pre-emergence and post-emergence soil drench tests. Table IIIa

Compound Soil drench 10 kg/ha Dosage Foliar spray Pre-emergence 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 Cl 0 0 0 0 0 0 0 0 5 0 0 0 0 3 3 3 0 0 * 0 0 0 0 0 0 1 0 0 0 0 1 2 1 0 0 * 0 0 0 0 0 0 C2 0 0 0 0 2 4 4 0 5 0 0 0 0 0 3 3 0 0 0 0 0 0 2 3 0 1 0 0 0 0 0 2 1 0 0 0 0 0 0 0 1 0 C3 7 6 3 5 0 0 4 0 5 4 4 3 1 0 2 6 2 3 6 6 4 0 0 0 0 1 2 1 1 0 0 0 1 0 1 4 3 2 0 0 0 0 C4 4 3 0 0 0 0 3 0 5 3 0 0 0 0 2 3 2 0 0 0 0 0 0 0 0 1 2 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 C5 0 0 0 0 0 0 0 0 5 3 0 0 2 2 6 5 3 0 0 0 0 0 0 2 0 1 0 0 0 0 0 1 1 0 0 2 0 0 0 0 0 0 Table IIIb

Compound Soil drench 10 kg/ha Dosage Foliar spray Pre-emergence 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 8 6 8 5 5 7 8 8 5 7 7 8 7 7 8 8 8 9 8 8 6 7 7 8 8 1 7 6 6 5 7 7 6 7 8 6 8 5 6 6 8 8 2 8 6 8 7 6 8 8 7 5 7 7 8 7 7 8 9 8 9 8 8 7 7 6 7 8 1 7 6 8 6 7 8 7 7 8 7 8 5 6 6 7 6 3 8 7 8 5 5 7 8 7 5 7 6 8 6 7 8 9 8 9 8 8 6 7 7 8 8 1 7 6 7 3 6 7 7 7 8 7 8 2 6 4 7 8 4 * * * * * * * * 5 5 6 7 7 2 8 0 0 8 8 9 6 0 7 0 0 1 * * * * * * * * * * * * * * * * 5 7 7 7 8 0 8 0 0 5 7 5 6 8 6 7 5 4 9 8 9 8 7 8 7 5 1 2 2 3 7 4 7 0 0 7 5 4 7 0 7 0 2 Example 7 To investigate whether the unexpectedly different herbicidal effect of the compounds of the present invention arises purely from the oxy linkage as opposed to a sulphur, sulphinyl or sulphonyl linking group, the herbicidal activity of other oxy analogues of compounds described in Bayer was assessed.

Following the test procedures of Example 6 and using the same representative range of test plant species, the herbicidal activity of the following compounds was evaluated:

Compound Designation R1 R2 A X Ar Herein C6 CH3 CH3 CH O C7 CH3 CH3 CH O Compound C6 is the oxy analogue of Examples 11 and 15 of US-A-4,981,507 (Comparison Compounds C1 and C2 herein) Compound C7 is the oxy analogue of Examples 5 and 6 of US-A-4,981,507.

The results are given in Table IV below.

Compound C6 can be seen to be virtually inactive, thus demonstrating that it is not the replacement of the linking group that confers the greater activity.

Indeed the contrary is true; the results from compounds C1 and C2 show a greater activity at a Skg/ha dosage for the sulphur and sulphonyl compounds.

Activity is shown by compound C7 but not the high level of activity shown by the compounds of the invention.

The advantageous activity of the compounds of the invention thus appears to derive from a specific combination of substituents, which combination could not have been expected from the disclosures of US-A-4,981,507 to yield a herbicidal effect of the high level found.

Table IV

Compound Soil drench 10 kg/ha Dosage Foliar spray Pre-emergence 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 C6 * * * * * * * * 5 0 0 0 0 0 0 0 0 0 0 0 0 0 2 0 0 1 * * * * * * * * * * * * * * * * C7 7 4 4 2 3 7 7 2 5 7 0 5 0 3 7 6 1 8 3 4 0 0 3 3 0 1 6 0 0 0 0 4 4 1 7 1 0 0 0 0 2 0 Example 8 Herbicidal Selectivity A further series of biological evaluations were carried out to investigate the selectivity of the compound of Example 5.

The test was conducted as a post-emergence foliar spray test in which soil in which seedling plants were sprayed with the test compound. In the test the effect of the test compound on the broad-leaf crop soya bean (SO), and on the weed species, barnyard grass (BG), pigweed (PI), velvet leaf (VL), jimson weed (JW), black nightshade (NB), fat hen (FA) and morning glory (MG).

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

The compound was tested as a technical material and formulated in a 1:1 acetone:water mix containing up to 0.2% of the wetting agent, Triton X155, and applied as a single dose spray in a total volume of 900 litres/hectare. Application was at different dosage levels in the range of from 0.08 to 1.2 kg/ha designed to produce a range of responses. Three replicate pots were used for each treatment, and untreated sown soil pots were used as controls, Phytotoxicity compared with the untreated control was assessed visually using the standard 0-9 scale, 0 indicating no effect and 9 indicating death, 17 days after treatment.

The results were subjected to a standard probit analysis by computer to calculate the dosage of each compound in kg/ha required to kill 50% of the weed species and to produce 10% level of effect on the crop species. These dosages are referred to as the GID50 and GID10 dosage respectively.

These GID50 and GID10 were then used to calculate (to 2 decimal places) the selectivity factors for soya bean by dividing the GID10 of the crop by the GID50 of each weed species. The numbers indicate selectivity between the crop and weed; the greater the value the better the selectivity.

The results are set out in Table V below.

Table V Results of Post-emerqence Tests on the Compound of Example 5

Test GID Selectivity Species value Factor (soya) SO 0.430 BG 0.370 1.16 PI 0.148 2.90 VL 0.252 1.71 JW 0.103 4.17 NB 0.078 5.51 FA 0.407 1.06 MG 0.388 1.11 From the above results, it can be seen that the compound of Example 5 has advantageous selectivity for use in soya crops in respect of the important weeds BG, PI, VL, JW, NB, FA and MG.

Claims (10)

1. A compound of the general formula

in which Y and Z independently represent a hydrogen or halogen atom, or an alkyl, alkoxy, haloalkyl or haloalkoxy group; and R represents a group of the general formula -OR1 or SR1 in which R1 represents a hydrogen atom, a salt-forming cation, an alkyl group, or an aryl group, or a group of the general formula -NHSO2R2 in which R2 represents an alkyl group or an optionally substituted aryl group, or a salt-containing group derived therefrom.

2. A compound as claimed in claim 1, in which Y and Z are the same and each represents a methyl group.

3. A compound as claimed in claim 1 or claim 2, in which R represents a group -OR1 in which R1 represents a hydrogen atom, a sodium ion or a methoxy group, or R represents a -NHSO2R2 or -N@SO2r2.Na@ group in which R2 represents a methyl or phenyl group.

4. A compound as claimed in claim 3, in which R2 represents the group -N@SO2R2.Na@ in which R2 represents a phenyl group.

5. A process for the preparation of a compound as claimed in claim 1, which comprises converting a compound of the general formula

in which Y and Z are as defined in claim 1, into a compound of general formula I under oxidising conditions, and if desired or required converting the resulting product into another compound of general formula I.

6. A herbicidal composition which comprises a compound as claimed in any one of claims 1 to 4, in association with a carrier.

7. 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 4, or with a composition as claimed in claim 6.

8. The use of a compound as claimed in any one of claims 1 to 4, in combating undesired plant growth.

9. The use as a broad spectrum herbicide of a compound of general formula I as claimed in claim 1 in which R represents the group -OR1 or SR1, R1 being as defined in claim 1.

10. The use as a selective herbicide for broad-leaf crops of a compound of general formula I as claimed in claim 1 in which R represents the group -NHSO2R, R being as defined in claim 1, or a salt thereof.