GB2205101A - Oxadiazole derivatives useful as herbicides - Google Patents

Abstract

1,2,4-Oxadiazole derivatives of formula: <IMAGE> wherein Ar represents the 3,5-bistrifluoromethylphenyl group, R<1> and R<2>, each represents hydrogen or alkyl, R<3> represents halogen, carboxy, nitro or cyano, amino (which may be substituted by one or two alkyl groups), alkoxycarbonyl, or a group R, RO, RS, RSO or RSO2 in which R represents alkyl optionally substituted by halogen, X represents =CH - or nitrogen, m is zero or 1 to 3 when X represents =CH - or zero, 1 or 2 when X represents nitrogen and n is an integer from 1 to 6, and agriculturally acceptable salts thereof are useful as herbicides: their preparation, compositions containing them and their use are described.

Description

"HERBICIUES" This invention relates to 1,2,4-oxadiazole derivatives, compositions containing them and their use as herbicides.

The present invention provides new 1,2,4-oxadiazole derivatives of the general formula I herein depicted wherein Ar represents the 3,5-bistrifluoromethylphenyl group, R1 and R2, which may be the same or different, each represents the hydrogen atom or a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms, R3 represents a halogen atom, a carboxy, nitro or cyano group, the amino group which may be substituted by one or two straight- or branched-chain alkyl groups containing from 1 to 6 carbon atoms), a straight- or branched- chain alkoxycarbonyl group containing from 2 to 7 carbon atoms or a group R, RO, RS, RSO or RSO2 in which R represents a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms which is optionally substituted by one or more halogen atoms, X represents the group =CH- or the nitrogen atom, m is zero or an integer from 1 to 3 when X represents the group =CH- or zero or the integer 1 or 2 when X represents the nitrogen atom and n is an integer from 1 to 6, and agriculturally acceptable salts thereof, which possess valuable herbicidal properties.

It is to be understood that when m is the integer 2 or 3, the substituents R3 may be the same or different.

It is to be understood that when n is an integer from 2 to 6, the substituents R1 and R2 may be the same or different.

The person skilled in the art will perceive that certain of the compounds of general formula I, for example those containing amino groups, will tend to have basic properties whilst certain of the compounds, for example those containing carboxy groups, will tend to have acidic properties. Agriculturally acceptable salts formed by such compounds with acids or bases, respectively, are included in the scope of general formula I and it is to be understood that reference to compounds of general formula I is meant to include reference to the aforementioned salts whenever the context so permits.

By the term "agriculturally acceptable salts" as used in this specification is meant salts of acids or of bases which are known and accepted in the art for the formulation of salts of biologically active compounds for agricultural or horticultural use.

Suitable salts of acids include salts of inorganic acids such as hydrochlorides, sulpbates, phosphates and nitrates and salts of organic acids, for example acetates. Suitable salts of bases include alkali metal, e.g. sodium or potassium, salts, alkaline earth metal, e.g. calcium or magnesium, salts and salts of ammonia or of organic bases, e.g amines (e.g diethanolamine or triethanolamine).

Furthermore, it will be understood by those skilled in the art that the compounds of general R1 formula I wherein represents an alkyl group and R2 represents the hydrogen atom or a different alkyl group exhibit chirality. Furthermore, in certain cases the substituents R1, R2 and R3 contribute to optical and/or stereoisomerism. All such forms are embraced by the present invention.

Of particular interest as herbicides are the following compounds of general formula I: 1. 5-(3,5-bistrifluoromethylphenyl)-3-[1-(4,6- dimethylpyrimid-2-ylthio)ethyl]-1,2,4-oxadiazole 2. 5-(3,5-bistrifluoromethylphenyl)-3-[1-(4,6- dimethylpyrimid-2-ylthio)propyl]-1,2,4-oxadiazole 3. 5-(3,5-bistrifluoromethylphenyl)-3-[2-(4,6- dimethylpyrimid-2-ylthio)ethyl]-1,2,4-oxadiazole 4. 3-(4-aminopyrimid-2-ylthiomethyl)-5-(3,5-bistri- fluoromethylphenyl)-1,2,4-oxadiazole 5. 5-(3,5-bistrifluoromethylphenyl)-3-(4-methyl- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 6. 5- (3, 5-bistrifluoromethylphenyl)-3-(5-methyl- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 7. 5-(3,5-bistrifluoromethylphenyl)-3-(5-chloro- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 8. 5-(3,5-bistrifluoromethylphenyl)-3-(4,5-dimethyl- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 9. 5-(3 ,5-bistrifluoromethylphenyl)-3-(4, 6-dimethyl- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 10. 5- (3 ,5-bistrifluoromethylphenyl)-3-(6-methyl- 4-trifluoromethylpyrimid-2-ylthiomethyl) - 1,2,4-oxadiazole 11. 5-(3 ,5-bistrifluoromethylphenyl)-3- (4-ethyl- 6-methylpyrimid-2-ylthiomethyl)-1,2,4-oxadiazole 12. 5-(3 ,5-bistrifluoromethylphenyl)-3-(6-methyl- 4-propylpyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole 13. 5-(3,5-bistrifluoromethylphenyl)-3-(4-butyl 6-methylpyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole 14. 5-(3,5-bistrifluoromethylphenyl)-3-[6-methyl- 4-(2-methylpropyl)pyrimid-2-ylthiomethyl]-1,2,4- oxadiazole 15. 5-(3,5-bistrifluoromethylphenyl)-3-(4,5,6-tri- tnethylpyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole 16. 5- (3, 5-bistrifluoromethylphenyl) -3-pyrimid- 2-ylthiomethyl-1,2,4-oxadiazole 17. 5-(3,5-bistrifluoromethylphenyl)-3-(4-methoxy- 6-methyl-1,3,5-triazin-2-ylthiomethyl)-1,2,4- oxadiazole 18. 5-(3,5-bistrifluoromethylphenyl)-3-(4,6-dimethOxy- 1,3,5-triazin-2-ylthiomethyl)-1,2,4-oxadiazole.

The numbers 1 to 18 are assigned to the above compounds for identification and reference hereinafter.

The compounds of general formula I can be prepared by the application or adaptation of known methods (i.e. methods heretofore used or described in the chemical literature), for example as hereinafter identified.

According to a feature of the present invention, the compounds of general formula I may be prepared by the cyclisation of a compound of general formula II optionally in the presence of a dehydrating agent. for example a molecular sieve, at a temperature of from 100 C to the reflux temperature of the reaction mixture in an inert organic solvent, e.g toluene.

According to a further feature of the present invention, the compounds of general formula I may be prepared by the reaction of a compound of general formula III wherein Y represents a halogen, preferably chlorine, atom and Ar, R1, R2 and n are as hereinbefore defined with a thio compound of general formula IV wherein R3, X and m are as hereinbefore defined in the presence of an inorganic base, e.g.

sodium hydride or potassium hydroxide, or an organic base, e.g. triethylamine, in an inert organic solvent, e.g. tetrahydrofuran, methanol or ethanol, at from ambient temperature to the reflux temperature of the reaction mixture.

According to a further feature of the present invention, the compounds of general formula I may also be prepared by the reaction of a compound of general formula IIIa wherein Ar, R1, R2 and n are as.

hereinbefore defined with a compound of general formula IVa wherein Y represents a halogen, preferably chlorine, atom and R3, X and m are as hereinbefore defined.

Alternatively, a l-haloalkyl/ 2-haloalkyl compound of general formula III may be replaced by the alk-l-enyl compound of general formula V wherein Ar, R1 and R2 are as hereinbefore defined in the reaction with a compound of general formula IV in the presence of an organic base, e.g. triethylamine, in an inert organic solvent; followed by the separation of a mixture of products.

Compounds of general formula II may be prepared by the application or adaptation of known methods, for example in a similar manner to that outlined in stage (iii) of Reaction Scheme A shown in Figure I, replacing chloroacetamidoxime by a compound of general formula VI wherein the various symbols are as hereinbefore defined, and for example methods similar to those described hereinafter in the following Examples and Reference Examples.

Compounds of general formulae III, IIIa and V may be prepared by the application or adaptation of known methods, for example (a) by reacting 3,5-bistrifluoromethylbenzoic acid anhydride with a compound of general formula VII wherein R4 represents a Cl(CRlR2)n- group, a HS(CR1R2)n group or a group of formula R2R1C=C(R1)-, (b) by dehydrating a compound of general formula VIII, or (c) by brominating a compound of general formula IX.

By way of example, the compounds of general formula III wherein n represents the integer 1 and and R2 both represent hydrogen atoms may be prepared according to Reaction Schemes A and B shown in Figures I and II.

Compounds of general formula IX may be prepared by the suitable hydroxy-group-protection of the corresponding cyanoalkanol followed by reaction with hydroxylamine and 3,5-bistrifluoromethylbenzoyl chloride or 3,5-bistrifluoromethylbenzoic acid anhydride and by subsequent deprotection as illustrated in Reaction Scheme B shown in Figure II.

Compounds of general formulae VI and VIII and intermediates for their preparation maybe prepared by the application or adaptation of known methods, for example methods similar to those described hereinafter in the following Examples and Reference Examples.

Compounds of general formulae II, III, lira, V, VI, VIII and IX which are new and processes for the preparation thereof form further features of the present invention.

Reaction Scheme A

(i) In MeOH and add catalytic quantity of NeO - Na+ at room temperature.

(ii) Add a solution of H2NOH in MeOH to first solution, stir at room temperature, rotary evaporate to an oil (keep temp. < 40DC), take up in CH2C12 and rotary evaporate to white solid.

(iii) Treat the above solid with 1 equivalent of tCOC1 and Et3N in dioxan or THF, add H2 0, filter, and recryst MeOH. 3 (iv) Reflux in acetic acid for 2 - 15 hours.

(v) Treat with (ArCO) 20 in CH2Cl2.

FIGURE I Reaction Scheme P

(i) In H 20.

(ii) Add dioxan and (CH3)3COC1.

(iii) H2NOH.HCl in pyridine and triethylamine.

(iv) Add triethylamine and ArCOCl in dioxan or THF.

(v) Acetic acid and reflux from 2 to 15 hours.

(vi) Add (ArCO)2O in CH2Cl2 (vii) NaOH in aqueous MeOH.

(viii) PBr3 in toluene.

FIGURE II The following Examples and Reference Examples illustrate the preparation of compounds according to the present invention.

EXAMPLE 1 ComPounds 1 to 3 A solution of 0-(3,5-bistrifluoromethylbenzoyl) 2-( 4 ,6-dimethylpyrimid-2-ylthio)propionamidoxime (13.5 g) in dry toluene containing molecular sieve (4A, 10 g) was heated at reflux for 5 hours. The mixture was filtered and the filtrate was evaporated under reduced pressure to give a brown oil which was dissolved in a mixture of dichloromethane and ethyl acetate (10:1) and the solution was filtered through a column of silica. The filtrate was evaporated under reduced pressure and the solid residue was recrystallised from hexane to give 5-(3,5-Distrifluoromethylphenyl)-3-[1-(4,6-dimethyl- pyrimid-2-ylthio)ethyl)-1,2,4-oxadiazole (7.6 g) as a white crystalline solid, m.p. 100.6-1020C.

By proceeding in a similar manner but replacing 0-(3,5-bistrifluoromethylbenzoyl)-2-(4,6-dimethylpyrimid2-ylthio)propionamidoxime with the following starting materials the indicated products were prepared: 0-(3,5-bistrifluoromethylbenzoyl)-2- (4, 6-dimethylpyrimid-2-ylthio ) butanamidoxime; 5-(3,5-bistrifluoromethylphenyl)-3-[1-(4,6- dimethylpyrimid-2-ylthio)propyl]-1,2,4-oxadiazole which was recrystallised from a mixture of ethanol and water to give a white solid, m.p. 57.5-58.80C.

0-(3,5-bistrifluoromethylbenzoyl)-3-(4,6-dimethyl- pyrimid-2-ylthio)propionamidoxime; 5- (3, 5-bistrifluoromethylphenyl) -3- [2- (4,6- dimethylpyrimid-2-ylthio)ethyl]-1,2,4-oxadiazole which was purified by chromatography on silica, eluted with a mixture of dichloromethane and ethyl acetate (20:1) to give a pale yellow solid, m.p. 95-960C.

EXAMPLE 2 Compounds 4 to 15 To a rapidly stirred suspension of sodium hydride (0.26 g) in dry tetrahydrofuran was added 4-amino2-mercaptopyrimidine (1.27 g) followed by 5-(3,5-bis- trifluoromethylphenyl)-3-chloromethyl-1,2,4-oxadiazole (3.31 g). The mixture was stirred for 18 hours and the solvent was removed under reduced pressure to give a solid residue which was dissolved in a mixture of dichloromethane and ethyl acetate (4:1). The solution was filtered through a column of silica. The filtrate was evaporated under reduced pressure and the solid residue was recrystallised from toluene to give 3- ( 4-aminopyrimid-2-ylthiomethyl) -5- (3, 5-bistrifluoro- methylphenyl)-1,2,4-oxadiazole (3.0 g) as a white crystalline solid, m.p. l50.5l520C.

By proceeding in a similar manner but replacing 4-amino-2-mercaptopyrimidine by the following starting materials the indicated products were prepared: 2 -mercapto- 4-methylpyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(4-methyl- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole which was purified by chromatography on silica, eluted with a mixture of dichloromethane and ethyl acetate (40:1), to give a white solid, m.p. 52.9-53.60C.

2-mercapto- 5-methylpyrimidine; 5- (3, 5-bistrifluoromethylphenyl)-3- (5-methyl- pyrimid-2-ylthiomethyl)-1, 2, 4-oxadiazole which was recrystallised from a mixture of ethanol and water to give a white crystalline solid, m.p. 102.9-103.7 C.

5-chloro-2-mercaptopyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(5-chloro- pyrimid-2-ylthiomethyl)-1,2,4-oxadiazole which was recrystallised from ethanol to give an off-white solid, m.p. 68.1-70.70C.

4,5-dimethyl-2-mercaptopyrimidine; 5- (3, 5-bistrifluoromethylphenyl) -3- (4, 5-dimethyl- pyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole which was recrystallised from a mixture of ethyl acetate and hexane to give a white solid, m.p. 95.1-95.50C.

4,6-dimethyl-2-mercaptopyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(4,6-dimethyl- pyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole which was recrystallised from a mixture of toluene and hexane to give an off-white solid, m.p. 92.9-94.70C.

2-mercapto- 6-methyl- 4-trifluoromethylpyrimidine; 5- (3, 5-bistrifluoromethylphenyl) -3- (6-methyl- 4-trifluoromethylpyrimid-2-ylthiomethyl)-1,2,4-oxadiazole which was recrystallised from hexane to give a white solid, m.p. 73.5-75.5 C.

4-ethyl-2-mercapto-6-methylpyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(4-ethyl- 6-methylpyrimid-2-ylthiomethyl)-1, 2, 4-oxadiazole which was recrystallised from hexane to give a white crystalline solid, m.p. 65.8-67.9 C.

2-mercapto-6-methyl-A-propylpyrimidine; 5-(3,5-bistrifluoromethylpanenyl)-3-(6-methyl- 4-propylpyrimid-2-ylthiomethyl) -1,2, 4-oxadiazole which was purified by chromatography on silica, eluted with a mixture of hexane and ether to give a yellow, viscous oil.

4-butyl-2-mercapto-6-methylpyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(4-butyl- 6-methylpyrimid-2-ylthiomethyl)-1,2,4-oxadiazole which was purified by chromatography on silica, eluted with a mixture of hexane and ether to give a pale yellow oil.

2-mercapto-6-methyl-4-(2-methylpropylOpyrimidine; 5- (3, 5-bistrifluoromethylphenyl) -3- [6-methyl- 4-( 2-methylpropyl)pyrimid-2-ylthiomethyl)-l, 2,4- oxadiazole which was purified by chromatography on silica, eluted with a mixture of hexane, dichloromethane and ethyl acetate to give a pale yellow, viscous oil.

2-mercapto-4,5,6-trimethylpyrimidine; 5-(3,5-bistrifluoromethylphenyl)-3-(4,5,6-trimethyl pyrimid-2-ylthiomethyl)-l,2,4-oxadiazole which was recrystallised from a mixture of ethyl acetate and hexane to give a white crystalline solid, m.p. 120-1210C.

EXAMPLE 3 Compound 16 5- (3 , 5-bistrifluoromethylphenyl) -3-pyrimid- 2-ylthiomethyl-1,2,4-oxadiazole was prepared by reacting one equivalent of the sodium salt of 2-mercaptopyrimidine (prepared from one equivalent of sodium, dissolved in methanol and one equivalent of the thiol) with one equivalent of the chloromethyl oxadiazole in methanol at reflux.

After cooling water was added until the precipitated sodium chloride dissolved and further water was added until the product was completely precipitated.

The precipitate was washed with aqueous methanol and recrystallised from methanol, m.p. 83-840C.

EXAMPLE 4 Compounds 17 and 18 A stirred solution of 2-mercapto-4-methoxy-6methyl-1,3,5-triazine (1.58g) and 5-(3,5-bistrifluoro methylphenyl)-3-chloromethyl-1, 2, 4-oxadiazole (3.32g) in dry tetrahydrofuran (40ml) at ambient temperature was treated with triethylamine (1.7ml). The mixture was stirred for 2 hours, and then it was diluted with ethyl acetate (200ml). It was then washed with dilute hydrochloric acid, dilute sodium hydroxide solution and water. The organic solution was removed and dried over magnesium sulphate and evaporated under reduced pressure and the solid residue was recrystallised from hexane (20ml), to give 5-(3,5-bistrifluoromethylphenyl)3-(4-methoxy-6-methyl-1,3,5-triazine-2-ylthiomethyl)1,2,4-oxadiazole (2.17g) in the form of a white crystalline solid, m.p. 98.5-99 C.

By proceeding in a similar manner but replacing the 2-mercapto-4-methoxy-6-methyl-1,3,5-triazine, used as starting material, with the appropriate quantity of 2-mercapto-4,6-dimethoxy-1,3,5-triazine, there was prepared: 5-(3,5-bistrifluoromethylphenyl)-3-(4,6 dimethoxy-1,3,5-triazin-2-ylthiomethyl)-1,2,4- oxadiazole, recrystallised from hexane, in the form of a white crystalline solid, m.p. 104-104.50C.

REFERENCE EXAMPLE 1 3,5-Bistrifluoromethylbenzoyl chloride (8.3 g) was added at -5 to 0 C to a stirred solution of 2-(4,6-dimethylpyrimid-2-ylthio)propionamidoxime (6.8 g) and triethylamine (7.8 ml) in dichloromethane (100 ml).

The mixture was stirred at 0 C for 30 minutes and at ambient temperature for 18 hours. The mixture was washed with water, dried over magnesium sulphate and evaporated under reduced pressure to give 0-(3,5-bistri fluoromethylbenzoyl) -2- (4, 6-dimethylpyrimid-2-ylthio) - propionamidoxime (13.5 g) as a white solid, m.p. 125.4 126.50C.

By proceeding in a similar manner but replacing 2- (4, 6-dimethylpyrimid-2-ylthio)propionamidoxime by the following starting materials the indicated products were prepared: 2- (4, 6-dimethylpyrimid-2-ylthio ) butanamidoxime; 0-(3,5-bistrifluoromethylbenzoyl)-2-(4,6-dimethyl- pyrimid-2-ylthio)butanamidoxime as an off-white solid, m.p. 136.5-137.70C.

3- (4, 6-dimethylpyrimid-2-ylthio )propionamidoxime; 0- (3, 5-bistrifluoromethylbenzoyl) -3- (4, 6-dimethyl- pyrimid-2-ylthio)propionamidoxime as a brown, viscous oil.

REFERENCE EXAMPLE 2 To sodium (2.64 g) dissolved in methanol (50 ml) was added, with stirring, a solution of hydroxylamine hydrochloride (7.64 g) in methanol (200 ml) followed by a solution of 2-( 4, 6-dimethylpyrimid-2-ylthio)propionitrile (17.40 g) in methanol (50 ml). The mixture was heated at reflux for 4 hours, filtered whilst hot, and the filtrate was evaporated under reduced pressure to dryness. The solid residue was recrystallised from toluene to give 2-(4,6-dimethylpyrimid-2-ylthio)propionamidoxime (11.40 g) as a pale cream crystalline solid, m.p. 138-1400C.

By proceeding in a similar manner but replacing 2-(4,6-dimethylpyrimid-2-ylthio)propionitrile by the following starting materials the indicated products were prepared: 2- (4, 6-dimethylpyrimid-2-ylthio )butyronitrile; 2- (4, 6-dimethylpyrimid-2-ylthio)butanamidoxime which was recrystallised from toluene to give a white crystalline solid, m.p. 125.5-126.50C.

3- (4, 6-dimethylpyrimid-2-ylthio)propionitrile; 3- (4, 6-dimethylpyrimid-2-ylthio)propionamidoxime which was purified by chromatography on silica, eluted with a mixture of dichloromethane and ethyl acetate (10:1) to give a white solid, m.p. 107-1090C.

REFERENCE EXAMPLE 3 2-Chloropropionitrile (8.95 g) was added, over 30 minutes to a stirred solution of 4,6-dimethyl-2-mercaptopyrimidine (12.62 g) and potassium hydroxide (6.27 g) in ethanol (100 ml) at ambient temperature. The mixture was heated at reflux for 2 hours, allowed to cool to ambient temperature and filtered. The filtrate was evaporated under reduced pressure to give 2(4, 6-dimethylpyrimid-2-ylthio)propionitrile as a brown oil.

By proceeding in a similar manner but replacing 2-chloropropionitrile with 2-bromobutyronitrile was prepared: 2- (4, 6-dimethylpyrimid-2-ylthio)butyronitrile as a brown oil.

REFERENCE EXAMPLE 4 Triethylamine (4.04 g) was added to a solution of 4,6-dimethyl-2-mercaptopyrimidine (5.60 g) and acrylonitrile (2.12 g) in dry acetonitrile (125 ml) and the mixture was heated at reflux for 8 hours. The solvent was evaporated under reduced pressure and the residue was treated with a mixture of ether and dichloromethane (20:1, 50 ml). The mixture was filtered and the filtrate was evaporated under reduced pressure to give 3- (4, 6-dimethylpyrimid-2-ylthio)propionitrile (7.16 g) as a pale yellow solid, m.p. 85-870C.

RERERENCE EXAMPLE 5 Concentrated hydrochloric acid (35 ml) was added to a stirred suspension of thiourea (6.85 g) in a mixture of ethanol (175 ml) and heptan-2,4-dione (12.81 g). The resulting solution was stirred at ambient temperature for 3 hours and allowed to stand for 72 hours. Water (250 ml) was added to the reaction mixture and the aqueous solution was washed with ether, basified with 50% sodium hydroxide solution and washed again with ether.

The aqueous solution was acidified to pH 4 with glacial acetic acid and extracted with dichloromethane. The dichloromethane extract was dried over magnesium sulphate and evaporated under reduced pressure to give 2-mercapto 6-methyl-4-propylpyrimidine (11.08 g) as a yellow oil.

By proceeding in a similar manner but replacing heptan-2,4-dione by the following starting materials the indicated products were prepared: hexan-2,4-dione; 4-ethyl-2-mercapto-6-methylpyrimidine as a pale yellow solid, m.p. 2270C (with decomposition).

octan-2,4-dione; 4-butyl-2-mercapto-6-methylpyrimidine as a pale yellow oil.

6-methylheptan-2,4-dione; 2-mercapto-6-methyl-4-( 2-methylpropyl)pyrimidine as a yellow glass.

1,1, 1-trifluoropentan-2 , 4-dione; 2-mercapto-4-methyl-6-trifluoromethylpyrimidine which was recrystallised from ethanol to give a bright yellow crystalline solid, m.p. 17500 (with decomposition).

REFERENCE EXAMPLE 6 t-Butyl hypochlorite (12.0 g) was added in the dark, at -150C, to a stirred solution of 2-chloro-N-(3,5bistrifluoromethylbenzoyl) acetamidine (33.3 g) in ethanol (165 ml) and the mixture was stirred at -15 to -100C for 2 hours. Sodium hydroxide solution (2K, 80 ml) was added to the mixture which was warmed to 560C and allowed to cool to ambient temperature.The mixture was extracted with hexane (3 x 200 ml), and the combined extracts were dried over magnesium sulphate, evaporated under reduced pressure and the solid residue was recrystallised from a mixture of ethanol and water to give 5-( 3, 5-bistrifluoromethylphenyl) -3-chloromethyl- 1,2,4-oxadiazole (26.7 g) as a white crystalline solid, m.p. 63.0-63.6 C.

REFERENCE EXAMPLE 7 A solution of 3,5-bistrifluoromethylbenzoyl chloride (100 g) in dichloromethane (180 ml) was added at -5 C, over 3.5 hours to a rapidly stirred suspension of chloroacetamidine hydrochloride (44.5 g) in a mixture of triethylamine (100.3 ml) and dichloromethane (520 ml).

The mixture was stirred at -5"C for 1.5 hours, allowed to warm to 0 C and petroleum spirit (bp 80-100 C, 1000 ml) was added. The mixture was filtered and the filtrate was concentrated under reduced pressure, at a temperature equal to or less than 20"C, until the volume had been reduced to 250 ml. The precipitate was removed by filtration giving 2-chloro-N-(3,5-bistrifluoromethylbenzoyl)acetamidine (110 g) as an off-white solid, m.p. 79.5-81.0 C.

REFERENCE EXAMPLE 8 A stirred suspension of thiourea (5.36g) in 2-methylpropan-2-ol (lOOml) at 70 C was treated with 2-chloro-4-methoxy-6-methyl-1,3,5-triazine (12.74g), portionwise during 10 minutes. The mixture was heated at reflux for 30 minutes. It was then allowed to cool to ambient temperature and treated with acetone (120ml) to precipitate S-(4-methoxy-6-methyl-l, 3, 5-triazin- 2-yl)isothiouronium chloride, which was filtered off and dried under vacuum. This isothiouronium salt (11.80g) was dissolved in a solution of sodium hydroxide (4.40g) in water (55ml) at ambient temperature and stirred for 30 minutes. The solution was acidified to pH5 by treatment with glacial acetic acid, and extracted with ethyl acetate. The extract was dried over anhydrous magnesium sulphate and evaporated under reduced pressure and the resulting solid residue was recrystallised from water (40ml), to give 2-mercapto-4-methoxy-6-methyl-1,3,5-triazine (3.41g) in the form of a white crystalline solid, m.p. 216"C (with decomposition).

According to a further feature of the present invention, there are provided compositions suitable for herbicidal use comprising one or more of the 1,2,4-oxadiazole derivatives of general formula I in association with, and preferably homogeneously dispersed in, one or more compatible herbicidally-acceptable diluents or carriers and/or surface active agents (i,e.

diluents or carriers and/or surface active agents of the type generally accepted in the art as being suitable for use in herbicidal compositions and which are compatible with compounds of general formula I). The term "homogeneously dispersed" is used to include compositions in which the compounds of general formula I are dissolved in the other components. The term "herbicidal compositions" is used in a broad sense to include not only compositions which are ready for use as herbicides Dut also concentrates which must be diluted before use.

Preferably, the compositions contain from 0.05 to WOV/o by weight of one or more compounds of general formula I.

The herbicidal compositions may contain both a diluent or carrier and surface-active (e.g. wetting, dispersing, or emulsifying) agent. Surface-active agents which may be present in herbicidal compositions of the present invention may be of the ionic or non-ionic types, for example sulphoricinoleates, quaternary ammonium derivatives, products based on condensates of ethylene oxide with alkyl and polyaryl phenols, e.g. nonyl- or octyl-phenols, or carboxylic acid esters of anhydrosorbitols which have been rendered soluble by etherification of the tree hydroxy groups by condensation with ethylene oxide, alkali and alkaline earth metal salts of sulphuric acid esters ana sulphonic acids such as dinonyl- and dioctyl-sodium sulphonosuccinates and alkali and alkaline earth metal salts of high molecular weight sulphonic acid derivatves such as sodium and calcium lignosulphonates and sodium and calcium alkylbenzene sulphonates.

Suitably, the herbicidal compositions according to the present invention may comprise up to 10, e.g. from 0.058h to love, of surface-active agent but, if desired, herbicidal compositions according to the present invention may comprise higher proportions of surface-active agent, for example up to 15 in liquid emulsifiable suspension concentrates and up to 25 in liquid water soluble concentrates.

Examples of suitable solid diluents or carriers are aluminium silicate, talc, calcined magnesia, kieselguhr, tricalcium phosphate, powdered cork, adsorbent carbon black and clays such as kaolin and bentonite. The solid compositions (which may take the form of dusts, granules or wettable powders) are preferably prepared by grinding the compounds of general formula I with solid diluents or by impregnating the solid diluents or carriers with solutions of the compounds of general formula I in volatile solvents, evaporating the solvents and, if necessary, grinding tne products so as to obtain powders.

Granular formulations may be prepared by absorbing the compounds of general formula I (dissolved in suitable solvents, which may, if desired, be volatile) onto the solid diluents or carriers in granular form and, if desired, evaporating the solvents, or by granulating compositions in powder form obtained as described above.

Solid herbicidal compositions, particularly wettable powders and granules, may contain wetting or dispersing agent (for example of the types described above), which may also, when solid, serve as diluents or carriers.

Liquid compositions according to the invention may take the form of aqueous, organic or aqueous-organic solutions, suspension and emulsions which may incorporate a surface-active agent. Suitable liquid diluents for incorporation in the liquid compositions include water, glycols, tetrahydrofurfuryl alcohol, acetophenone, cyclohexanone, isophorone, toluene, xylene, mineral, animal and vegetable oils and light aromatic and naphthenic fractions ot petroleum (and mixtures of these diluents). Surface-active agents, which may be present in the liquid compositions, may be ionic or non-ionic (for example of the types described above) and may, when liquid, also serve as diluents or carriers.

Wettable powders, dispersible granules and liquid compositions in the form of concentrates may be diluted with water or other suitable diluents, for example mineral or vegetable oils, particularly in the case of liquid concentrates in which the diluent or carrier is an oil, to give compositions ready for use. When desired, liquid compositions of the compound of general formula I may be used in the form of self-emulsifying concentrates containing the active substances dissolved in the emulsifying agents or in solvents containing emulsifying agents compatible with the active substances, the simple addition of water to such concentrates producing compositions ready for use.

Liquid concentrates in which the diluent or carrier is an oil may be used without further dilution using the electrostatic spray technique.

Herbicidal compositions according to the present invention may also contain, if desired, conventional adjuvants such as adhesives, protective colloids, thickeners, penetrating agents, stabilisers, sequestering agents, anti-caking agents, colouring agents and corrosion inhibitors. These adjuvants may also serve as carriers or diluents.

Preferred herbicidal compositions according to the present invention are aqueous suspension concentrates which comprise from 10 to 70% of one or more compounds of general formula I, from 2 to 109L of surface-active agent, from 0.1 to 5% w/v (weight/volume) of thickener and from 15 to 87.9ç/o by volume of water; wettable powders which comprise from 10 to 90% w/w (weight/weight) of one or more compounds of general formula I, from 2 to 10 w/w of surface-active agent and from 8 to 887c w/w of solid diluent or carrier; liquid water soluble concentrates which comprise from 5 to 50%, e.g. 10 to 309/0, w/v of one or more compounds of general formula I, from 5 to 25% w/v of surface-active agent and from 25 to 909Z, e.g. 45 to 85, by volume of water-miscible solvent, e.g.

dimethylformamide, or a mixture of water-miscible solvent and water; liquid emulsifiable suspension concentrates which comprise from 10 to 70% w/v of one or more compounds of general formula I, from 5 to 15% w/v of surface-active agent, from 0.1 to 5% w/v of thickener and from 10 to 84.9 by volume of organic solvent; granules which comprise from 1 to 90E, e.g. 2 to 10%, w/w of one or more compounds of general formula I, from 0.5 to 7%, e.g. 0.5 to 2%, w/w of surface-active agent and from 3 to 58.59/o e.g. 88 to 9795%1 w/w of granular carrier and emulsifiable concentrates which comprise 0.05 to 90Q/0 w/v, and preferably from 1 to 60/o w/v of one or more compounds of general formula I, from 0.01 to 10 w/v, and preferably from 1 to 10 w/v, of surface-active agent and from 9.99 to 99.94%, and preferably from 39 to 98.99%, by volume of organic solvent.

Herbiciaal compositions according to the present invention may also comprise the compounds of general formula I in association with, and preferably homogeneously dispersed in, one or more other pesticidally active compounds and, if desired, one or more compatible pesticidally acceptable diluents or carriers, surface-active agents and conventional adjuvants as hereinbefore described.Examples of other pesticidally active compounds which may be included in, or used in conjunction with, the herbicidal compositions of the present invention include herbicides, for example to increase the range of weed species controlled, tor example alachlor l2-chloro-2',6'-diethyl-N-(methoxymethyl)- acetanilide], asulam lmethyl(4-aminobenzenesulphonyl)- carbamate], alloxydim Na [sodium salt oi 2-(l-allyloxy- aminobutylidene)-5,5-dimethyl-4-methoxycarbonylcyclo- hexane-1,3-dione], atrazine [2-chloro-4-ethylamino-6isopropylamino-1,3,5-triazinej, barban l4-chlorobut-2- ynyl N-(3-chlorophenyl)carbamate], benzoylprop-ethyl (ethyl N-benzoyl-N-(3,4-dichlorophenyl-2-aminopropionate], bromoxynil 13,5-dibromo-4-hydroxybenzonitrile], butachlor LN-(butoxymethyl)-2-chloro-2ls6l-diethylacetanilide]s butylate [S-ethyl N,N-diisobutyl(thiocarbamate)3, carbetamide [D--ethyl-2-(phenylcarbamoyloxy)propion- amide], chlorfenprop-methyl [methyl 2-chloro-3-(4-cnlorophenyl)propionate], chlorpropham lisopropyl N-(3-chloro phenyl)carbamate], chlortoluron [N'-(3-chloro-4-methylphenyl)-N,N-dimethylurea], cyanazine [2-chloro-4-(lcyano-1-methylethylamino)-6-ethylamino-1,3,5-triazine], cycloate [N'-cyclohexyl-N-ethyl-S-ethyl(thiocarbamate), 2,4-D [2,4-dichlorophenoxyacetic acid], dalapon 12,2-dichloropropionic acid], 2,4-DB 14-(2,4-dichloro- phenoxy)butyric acid], desmedipham [3-(ethoxycarbonylamino)phenyl N-phenyl-carbamate], diallate [S-2,3-dichloro- allyl-N,N-di-isopropyl(thiocarbamate)], dicamba 3,6-dichloro-2-methoxybenzoic acid], dichlorprop (+)-2-(2,4-dichlorophenoxy)propionic acid], difenzoquat [1,2-dimethyl-3,5-diphenyl-pyrazolium salts], dimefuron 4-[2.chloro-4-(3,3-dimethylureido)phenyl]-2-t-butyl- l,3,4-oxadiazolin-5-one , dinitramine LN1 ,N1-diethyl- 2,6-dinitro-4-trifluoromethyl-m-phenylenediaminel, diuron [N'-(3,4-dichlorophenyl)-N,N-dimethylurea3, EPTC [S-ethyl N,N-dipropyl(thiocarbamate)l, ethofumesate l2-ethoxy-2,3-dihydro-3,3-dimethylbenzoturan-5-yl methylsulphonate], flampropisopropyl (isopropyl (+)-2-(N benzoyl-3-chloro-4-fluoroanilino)propionate], flampropmethyl [methyl (+)-2-(N-benzoyl-3-chloro-4-fluoroanilino)- propionate], fluometuron IN'-(3-trifluoromethylphenyl)- N,N-dimethylurea], ioxynil 14-hYdroxY-3,5-di-iodobenzo- nitrile], isoproturon LN'-(4-isopropylphenyl)-N,N- dimethylurea], linuron [N-(3,4-dichlorophenyl-N-methoxy N-methylurea], MCPA [4-chloro-2-methylphenoxyacetic acid, MCPB l4-(4-chloro-2-methylphenoxy)butyric acid], mecoprop [()-2-(4-chloro-2-methylphenoxy)propionic acid], metamitron [4-amino-3-methyl-6-phenyl-1,2,4.triazin-5(4H)- one], methabenzthiazuron IN-(benzothiazol-2-yl)-N,N'- dimethylurea], metribuzin [4-amino-6-t-butyl-3-(methylthio)-1,2,4-triazin-5(4H)-one], molinate lS-ethyl N,N-hexamethylene(thiocarbamate)], oxadiazon L3-(2,4-dichloro-5- isopropoxyphenyl)-5-t-butyl-1,3,4-oxadiazolin-2-one], paraquat [l,l'-dimethyl-4,4'-bipyridylium salts], pebulate lS-propyl N-butyl-N-ethyl(thiocarbanate), phenmedipham 13-(methoxycarbonylamino)phenyl N-(3-methyl phenyl)carbamate], prometryne [4,6-bisisopropylamino-2 methylthio-1,3,5-triazine], propachlor [2-chloro-N isopropylacetanilide], propanil [N-(3,4-dichlorophenyl)- propionamide], propham (isopropyl N-phenylcarbamate], pyrazone l5-amino-4-culoro-2-phenylpyridazin-3(2H)-oneZ, simazine 12-chlor-4,6-bisethylamino-1,3,5-triazine], TCA (trichloroacetic acid], thiobencarb [S-(4-chlorobenzyl)-N,N-diethylthiolcarbamate], tri-allate [S-2,3,3-trichloroallyl N,N-di-isopropyl(thiocarbamate)] and trifluralin 12,6-dinitro-N,-dipropyl-4-trifluoro- methylaniline]; insecticides, e.g. carbaryl [naphth-l-yl N-methylcarbamate]; synthetic pyrethroids, e.g.

permethrin and cypermethrin; and fungicides, e.g.

2,6-dimethyl-4-tridecyl-morpholine, methyl N-(l-butylcarbamoyl-benzimidazol-2-yl)carbamate, 1,2-bis (3-methoxycarbonyl-2-thioureido)benzene, isopropyl l-carbamoyl-3-(3,5-dichlorophenyl)hydantoin and 1-(4-chloro-phenoxy)-3,3-dimethyl-1-(1,2,4-triazol- l-yl)-butan-2-one. Other biologically active materials which may be included in, or used in conjunction with, the herbicidal compositions of the present invention are plant growth regulators, e.g. succinamic acid, (2-chloroethyl)trimethylammonium chloride and 2-chloroethane-phosphonic acid; or fertilizers, e.g.

containing nitrogen, potassium and phosphorus ana trace elements known to be essential to successful plant lite, e.g. iron, magnesium, zinc, maganese, cobalt and copper.

Pesticidally active compounds and other biological active materials which may be included in, or used in conjunction with, the herbicidal compositions of the present invention, for example those hereinbefore mentioned, ano which are acids, may, if desired, be utilized in the form of conventional derivatives, for example alkali metal and amine salts and esters.

According to a further feature of the present invention tnere is provided an article of manufacture comprising at least one ot the 1,2,4-oxadiazole derivatives of general formula I or, as is preferred, a herbicidal composition as hereinbefore described, and preterably a herbicidal concentrate which must be diluted before use, comprising at least one of the 1,2,4-oxadiazole derivatlec of general formula I within a container for the aforesaid derivative or derivatives of general formula I, or a said herbicidal composition, and instructions physically associated with the aforesaid container setting out the manner in which the aforesaid derivative or derivatives of general formula I or herbicidal composition contained therein is to be used to control the growth of weeds.The containers will normally be of the types conventionally used for the storage of chemical substances which are solid at normal ambient temperatures and herbicidal compositions particularly in the form of concentrates, for example cans and drums of metal, which may be internally-lacquered, and plastics materials, bottles of glass and plastics materials and, when the contents of the container is a solid, for example granular, herbicidal compositions, boxes, for example of cardboard, plastics materials and metal, or sacks. The containers will normally be of sufficient capacity to contain amounts of the 1,2,4-oxadiazole derivative or herbicidal compositions sufficient to treat at least one acre of ground to control the growth of weeds therein but will not exceed a size which is convenient for conventional methods of handling.The instructions will be physically associated with the container, for example by being printed directly thereon or on a label or tag affixed thereto. The directions will normally indicate that the contents of the container, after dilution if necessary, are to be applied to control the growth of weeds at rates of application between 0.1 kg and 20 kg of active material per hectare in the manner and for the purposes hereinbefore described.

The following Examples illustrate herbicidal compositions according to the present invention: EXAMPLE 5 A wettable powder was formed from: 5-- (3, 5-bistrifluoromethylphenyl)- 3-[l-(4,6-dimethylpyrimid-2-ylthio)ethyl]- 1,2,4-oxadiazole 502 w/w Ethylan BCP (a nonylphenol/ethylene oxide condensate containing 9 moles of ethylene oxide per mol of phenol) 5% w/w Aerosil (silicon dioxide of microfine particle size) 5 w/w Celite PF (synthetic magnesium silicate carrier) 40 w/w by absorbing the Ethylan BCP onto the Aerosil, mixing with the other ingredients and grinding the mixture in a hammer-mill to give a wettable powder.

Similar wettable powders may be prepared as described above by replacing 5-(3,5-bistrifluoromethyl- phenyl)-3-[1-(4,6-dimethylpyrimid-2-ylthio)ethyl]- 1,2,4-oxadiazole by other compounds of general formula I.

EXAMPLE 6 An aqueous suspension concentrate was formed from: - 5-(3,5-bistrifluoromethylphenyl) 3-ll-(4,6-dimethylpyrimid-2-ylthio)ethyl]- 1,2,4-oxadiazole 50% w/v Ethylan BCP 1.0% w/v Sopropon T36 (sodium salt of polycarboxylic acid) 0.2% w/v Ethylene glycol 5% w/v Rhodigel 23 (polysaccharide xanthan gum thickener) 0.15% w/v distilled water to 100% by volume by intimately mixing the ingredients and grinding in a ball-mill for 24 hours.

Similar aqueous concentrate may be prepared as described above by replacing 5-(3,5-bistrifluoromethyl phenyl)-3-[1-(4,6-dimethylpyrimid-2-ylthio)ethyl]- 1,2,4-oxadlazole by other compounds of general formula I.

According to a feature of the present invention, there is provided a method for controlling the growth of weeds (i.e. undesired vegetation) at a locus which comprises applying to the locus a herbicidally effective amount of at least one 1,2,4-oxadiazole derivative of general formula I. For this purpose, the 1,2,4-oxadiazole derivatives are normally used in the form of herbicidal compositions (i.e. in association with compatible diluents or carriers and /or surface active agents suitable for use in herbicidal compositions), for example as hereinafter described.

The compounds ot general formula I show herbicidal activity against dicotyledonous (i.e. broad-leafed) and monocotyledonous (e.g. grass) weeds by pre- and/or, post-emergence application.

By the term "pre-emergence application" is meant application to the soil in which the weed seeds or seedlings are present before emergence of the weeds above the surface of the soil. By the term 'post-emergence application' is meant application to the aerial or exposed portions of the weeds which have emerged above the surface of the soil.For example, the compounds of general formula I may be used to control the growth of broad-leafed weeds, for example, Aethusa cynapium, Abutilon theophrasti, Amaranthus retroflexus, Amsinckia intermedia, Anagallis arvensis, Anthems arvensis, Atriplex patula, Bidens pilosa, Brassica nigra, Capsella bursa-pastoris, Chenopodium album, Chrysanthemum segetum, Cirsium arvense, Datura stramonium, Desmodium tortuosum, Emex australia, Euphorbia helioscopia, Fumaria officinalis, Galeopsis tetrahit, Galium aparine, Geranium dissectum, Ipomea purpurea, Lamium purpureum, Lapsana communis, Matricaria inodora, Monochoria vaginalis, Papaver rhoeas, Physalis longifolia, Plantago lanceolata, Polygonum spp., (e.g. Polygonum lapathifolium, Polygonum aviculare, Polygonum convolvulus and Polygonum persicaria), Portulaca oleracea, Raphanus raphanistrum, Rotala indica, Rumex obtusifolius, Saponaria vaccaria, Scandix pecten-veneris, Senecio vulgaris, Sesbania florida, Sida spinosa, Silene alba, Sinapis arvensis, Solanum nigrum, Sonchus arvensis, Spergula arvensis, Stellaria media, Thlaspi arvense, Tribulus terrestria, Urtica urens, Veronica hederifolia, Veronica persica, Viola arvensis and Xanthium strumarium, and grass weeds, tor example, Apera spica-venti, Digitaria sanquinalis, Echinochloa crus-galli, Eleusine indica, Setaria viridis.

The amounts of compounds of general formula I applied vary with the nature of the weeds, the compositions used, the time of application, the climatic and edaphic conditions and (when used to control the growth of weeds in crop-growing areas) the nature of the crops. When applied to a crop-growing area, the rate of application should be sufficient to control the growth of weeds without causing substantial permanent damage to the crop. In general, taking these factors into account, application rates between 0.1 kg and 20 kg of active material per hectare give good results. However, it is to be understood that higher or lower application rates may be used, depending upon the particular problem of weed control encountered.

The compounds of general formula I may be used to control selectively the growth of weeds, for example to control the growth of those species hereinbetore mentioned, by pre- or post-emergence application in a directional or non-directional fashion, e.g. by directional or non-directional spraying, to a locus of weed infestation which is an area used, or to be used, for growing crops, for example cereals, e.g. wheat, barley, oats, maize and rice, soya beans, field and dwarf beans, peas, lucerne, cotton, peanuts, flax, onions, carrots, cabbage, oilseed rape, sunflower, sugar beet, and permanent or sown grassland before or after sowing of the crop or before or after emergence of the crop.For the selective control of weeds at a locus of weed infestation which is an area used, or to be used, for the growing of crops, e.g. the crops hereinbefore mentioned, application rates between 0.1 kg and 8.0 kg, and preferably between 0.1 kg and 4.0 kg, of active material per hectare are particularly suitable.

The compounds of general formula I may also be used to control the growth of weeds, especially those indicated above, by pre- or post-emergence application in established orchards and other tree-growing areas, for example forests, woods and parks, and plantations e.g.

sugar cane, oil palm and rubber plantations. For this purpose they may be applied in a directional or non-directional fashion (e.g. by directional or non-directional spraying) to the weeds or to the soil in which they are expected to appear, before or after planting of the trees or plantations at application rates between 0.5 kg and 10.0 kg, and preferably between 1,0 kg and 8.0 kg, of active material per hectare.

The compounds of general formula I may also be used to control the growth of weeds, especially those indicated above, at loci which are not crop-growing areas but in which the control of weeds is nevertheless desirable.

Examples of such non-crop-growing areas include airtielas, industrial sites, railways, roadside verges, the verges of rivers, irrigation and other waterways, scrublands and fallow or uncultivated land, in particular where it is desired to control the growth of weeds in order to reduce fire risks. When used for such purposes in which a total herbicidal effect is frequently desired, the active compounds are normally applied at dosage rates higher than those used in crop-growing areas as hereinbefore described. The precise dosage will depend upon the nature of the vegetation treated and the effect sought.Pre- or post-emergence application, and preferably pre-emergence application, in a directional or non-directional fashion (e.g. by directional or non-directional spraying) at application rates between 1.0 kg and 20.0 kg, and preferably between 5.0 and 10.0 kg, of active material per hectare are particularly suitable for this purpose.

When used to control the growth of weeds by pre-emergence application, the compounds of general formula I may be incorporated into the soil in which the weeds are expected to emerge. It will be appreciated that when the compounds of general formula I are used to control the growth of weeds by post-emergence application, i.e. by application to the aerial or exposed portions of emerged weeds, the compounds of general formula I will also normally come into contact with the soil and may also then exercise a pre-emergence control on later-germinating weeds in the soil.

Where especially prolonged weed control is required, the application of the compounds of general formula I may be repeated if required.

VII R4C(=NOH)NH2 VII R4C(=NOCOAr)NH2 VIII

Claims (9)

1. CLAIMS 1. A 1,2,4-Oxadiazole derivative of the general formula:

   wherein Ar represents the 3,5-bistrifluoromethylphenyl group, R1 and R2, which may be the same or different, each represents the hydrogen atom or a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms, R3 represents a halogen atom, a carboxy, nitro or cyano group, the amino group (which may be substituted by one or two straight- or branched-chain alkyl groups containing from 1 to 6 carbon atoms), a straight- or branched-chain alkoxycarbonyl group containing from 2 to 7 carbon atoms or a group R, RO, RS, RSO or RS02 in which R represents a straight- or branched-chain alkyl group containing from 1 to 6 carbon atoms which is optionally substituted by one or more halogen atoms, X represents the group OH- or the nitrogen atom, m is zero or an integer from 1 to 3 when X represents the group =CH- or zero or the integer 1 or 2 when X represents the nitrogen atom and n is an integer from 1 to 6, the groupings CR1R2 being the same or different when n is greater than 1 and the substituents R3 being the same or different when m is greater than 1, and agriculturally acceptable salts thereof.
2. 2. A compound according to claim 1 hereinbefore identified as any one of compounds 1 to 18.
3. 3. A process for the preparation of a compound according to claim 1 substantially as hereinbefore described.
4. 4. A process for the preparation of a compound according to claim 1 substantially as hereinbefore described in any one of Examples 1 to 4.
5. 5. A compound according to claim 1 when prepared by a process according to claim 3 or 4.
6. 6. A herbicidal composition which comprises a 1,2,4-oxadiazole derivative according to claim 1, 2 or 5, or an agriculturally acceptable salt thereof, in association with an agriculturally acceptable diluent or carrier and/or surface active agent.
7. 7. A herbicidal composition according to claim 6 substantially as hereinbefore described.
8. 8. A method of controlling the growth of weeds at a locus which comprises applying thereto a 1,2,4-oxadiazole derivative according to claim 1, 2 or 5 or an agriculturally acceptable salt thereof.
9. 9. A method according to claim 8 substantially as hereinbefore described.