GB2203739A - Herbicidal tetrazoles - Google Patents

Abstract

Herbicidal tetrazoles of the formula:- <IMAGE> wherein R1 represents an optionally substituted phenyl group and R2 represents a substituted pheny] group, which group which must be substituted by at least one haloalkoxy group and is optionally further substituted; together with their preparation, their formulation and use as herbicides; and novel intermediates used in their preparation having formula wherein the OR1 group is replaced by halogen, or having the formulae R2-N=C(Hal)(OR1), R2-N=C(Hal)2 and HCONH-R2.

Description

HEmROCYCLiC HERBICIDES The present invention relates to novel tetrazole compounds, to their preparation, to herbicidal compositions containing such compounds, and to a method of controlling undesired plant growth using such compounds.

The herbicidal effectiveness of certain 1-phenyl-5-phenoxy-lH-tetrazole compounds is disclosed in EP-A-149269.

It has now been found that certain 1-phenyl-5-phenoxy-IH- tetrazoles selected from the generality of compounds claimed in EP-A-149269 have useful and surprising herbicidal properties, in particular in their enhanced activity against certain important broad leaved weeds. Accordingly the present invention provides a compound of the general formula : -

wherein R1 represents an optionally substituted phenyl group and R2 represents a substituted phenyl group which must be substituted by at least one haloalkoxy group and is optionally further substituted.

RI may suitably be optionally substituted by one or morse, suitably 1-3, substituents independently chosen form halogen, especially fluorine or chlorine, atoms, or amino, C1-4 alkyl, alkoxy, haloalkoxy or haloalkyl groups, especially methyl, isopropyl, methoxy, or trifluoromethyl. Although nore than one such substituent may be present, it is preferred that a phenyl ring R1 should be monosubstituted or, most preferably, unsubstituted.

R2 must be substituted by a haloalkoxy group, suitably of 1-6 carbon atoms and preferably of 1-4, and may be further substituted by one or more moieties, preferably 1-3, independently selected from further such haloalkoxy groups, and halogen, especially chlorine or fluorine, atoms, nitro, C1-4 alkyl, haloalkyl and haloalkylsulphonyl groups, especially methyl, trifluoromethyl and trifluoromethylsulphonyl. A haloalkoxy group is suitably substituted by one or more, suitably 1 to 3, fluorine and/or chlorine atoms. F1 3 fluoromethoxy groups are rrost preferred. Preferably, the group RI bears a haloalkoxy substituent at the 3-position.Most preferably, R2 is unsubstituted in the remaining sites.

The invention also provides a process for the preparation of a novel compound of the general formula I, which comprises reacting a 5-halo tetrazole of formula II

with an alcohol of formula R1OH, wherein RI is as defined above, or an alkali metal salt of such an alcohol. The said 5-halo tetrazole may be prepared by (i) reacting an inorganic azide with an isocyano dihalide having the formula R2-N=C(Hal)2 wherein RI is as defined above and Hal represents a halogen, preferably chlorine, atom or (ii) reacting an aluminium azide with @@ isocyanate of formula R2NCO followed by treatment with phosphor@s pentachloride.

The invention also provides an alternative process for the preparation of a novel compound of the general formula I, which comprises reacting a compound of the formula R2-N=C(Hal) (OR1) (III) with an inorganic azide. The compound III may be prepared by reacting a compound of formula R2-N=C(Hal)2 (IV) with an alcohol of formula R1OH.

The inorganic azide used in the tetrazole cyclisation step in either of the processes is suitably hydrazoic acid, ammonium azide, or an alkali or alkaline earth metal azide, in particular an alkali metal azide such as sodium azide. The halogen displacement reaction suitably takes place in the pressence of a base, for example potassium carbonate. Both steps of the processes are conveniently carried out in an inert solvent, which may be organic, such as aceto@@, or inorganic, e.g. water, or a mixture thereof, and at a temperature in the range of 0 to 120 C.

The isocyanodihalide reactant may be prepared by standard synthetic procedures, for example from the corresponding aniline of formula R2NH2 by reaction with formic acid suitably at a temperature of 20 to 60 C followed by a mixture of a sulphuryl halide and a thionyl halide, both preferably chlorides, suitably at temperature of 40 C to reflux.

The preparation of the compounds of formula I is summarised in the reaction scheme below :

Compounds of the formula II, III, IV and V are believed to be novel and therefore constitute a further aspect of the invention.

The aniline starting compounds are known (e.g. the 3-haloalkoxy anilines with Registry numbers 717-84-0 and 60985-04-8) or may be prepared from known starting materials by standard techniques.

The compounds of the general formula I have useful herbicidal properties, and accordingly the invention provides a herbicidal composition containing a compound of formula I, and a method of making a herbicidal composition, which comprises mixing a compound of formula I with one or more carriers. The invention also provides the use as a herbicide of a compound of formula I or a composition containing such a compound. Further in accordance with the invention there is provided a method of combating undesired plant growth at a locus by treating the locus with a compound or composition according to the invention. Application to the locus may be pre-emergence or post-emergence. The dosage of active ingredient used may, for example, be from 0.01 to 10kg/ha, preferably from 0.05 to 4kg/ha.A carrier in a composition according to the invention is any material with which the active ingredient is formulated to facilitate application to the locus to be treated, which may for example be a plant, seed or soil, or to facilitate storage, transport or handling. A carrier may be a solid or a liquid, including a material which is normally gaseous but which has been compressed to form a liquid, and any of the carriers normally used in formulating herbicidal compositions may be used. Preferably compositions according to the invention contain 0.5 to 95% by weight of active ingredient.

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

Suitable liquid carriers include water; alcohols, for example isopropanol and glycols; ketones, for exarrpjle acetone, methyl ethyl ketone, methyl isobutyl ketone and cyclohexanone; ethers; aramatic 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 or 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 surfaceactive agent.

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

The compositions of the invention may for example be formulated as wettable powders, dusts, granules, solutions, emulsifiable concentrates, emulsions, suspension concentrates and aerosols. Wettable powders usually contain 25, 50 or 75% w of active ingredient and usually contain in addition to solid inert carrier, 3-10% w of a dispersing agent and, where necessary, 0-10% w of stabiliser(s) and/or other additives such as penetrants or stickers. Dusts are usually formulated as a dust concentrate having a similar composition to that of a wettable powder but without a dispersant, and are diluted in the field with further solid carrier to give a composition usually containing b-10% w of active ingredient.Granules are usually prepared to have a size between 10 and 100 BS mesh (1.676 - 0.152 mm), and may be manufactured by agglomeration or impregnation techniques. Generally, granules will contain -75% w active ingredient and 0-10% w of additives such as stabilisers, surfactants, slow release modifiers and binding agents. The so-called "dry flowable powders" consist of relatively small granules having a relatively high concentration of active ingredient. flnulsifiable concentrates usually contain, in addition to a solvent and, when necessary, co-solvent, 10-50% w/v active ingredient, 2-20% w/v emulsifiers and 0-20% w/v of other additives such as stabilisers, penetrants and corrosion inhibitors.Suspension conentrates are usually compounded so as to obtain a stable, nonsedimenting flowable product and usually contain 10-75% w active ingredient, 0.5-15% w of dispersing agents, 0.1-10% w of suspending agents such as protective colloids and thixotropic agents, 0-10% w of other additives such as defoamers, corrosion inhibitors, stabilisers, penetrants and stickers, and water or an organic liquid in which the active ingredient is substantially insoluble; certain organic solids or inorganic salts may be present dissolved in the formulation to assist in preventing sedimentation or as anti-freeze agents for water.

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

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

The following Examples illustrate the invention.

Example 1 1-(3'-Difluoromethoxy)-5-phenoxy-1H-tetrazole A) Preparation of 1-formamido-3-difluoromethoxybenzene 3-Difluorcçethoxylaniline (lOg) and formic acid (lOmI) in benzene were stirred and heated under reflux, whilst water was removed using a Dean Stark apparatus. When thin layer chrornotography indicated complete reaction benzene was removed by evaporation and the residue dissolved in diethyl ether. The ethereal solution was washed with sodium bicarbonate solution, dried and evaporated to yield the product as a white solid (11.3g) m.pt. 54-57 C.

B) Preparation of 3-Difluoromethoxyphenyl isocyanodichloride The product of step A) above (5.61g) was added portionwise to thionyl chloride (15ml) and the solution stirred for 2 hours at 400C. Sulphuryl chloride (4.05g) was then added dropwise, over 30 minutes, whilst the mixture was stirred. When the addition was complete the mixture was heated slowly to reflux and refluxed for 30 minutes. The excess thionyl chloride was evaporated off. Thin layer chromatography showed two major spots which were separated on a silica column using 5% (v/v) dichloromethane/hexane as eluant. The second fraction comprised 3 components which were separated by high pressure liquid chromatography, giving the title compound in 0.8g yield.

C) Preparation of 5-chloro-1-(3'-Difluor -Difluoromethoxyphenyl) -1H- tetrazole A solution of the isocyanodichloride prepared in B) (0.8g), in acetone (30ml) was added to a stirred solution of sodium azide (0.22g) in water (10ml). The reaction mixture was stirred and heated under reflux for 1 hour. The reaction was colled to room temperature, poured into water and extracted with diethyl ether. The combined extracts were dried and evaporated and the residue purified by chromatography on silica using dichloromethane as eluant, to give the product as a pale yellow oil (0.7g).

D) Preparation of 1-(3'-difluoromethoxyphenyl)-5-phenoxy-1H- tetrazole Anhydrous potassium carbonate (0.78g) was added to a stirred solution of the product obtained in C) (0.7g) and phenol (0.27g) in acetone (30ml). The reaction mixture was stirred, and heated at reflux overnight, then poured into water, and extracted with diethyl ether. The dried extracts were evaporated and the residue purified by chromatography on silica, using dichloromethane as eluant. The product (0.6g) was a colourless oil.

Analysis Calc. C 55.3 H 3.3 N 18.4% Found C 54.7 H 3.3 N 18.4% Example 2 Herbicidal Activity S.) To evaluate its herbicidal activity, the compound of Example 1 was tested using as a representative range of plants: maize, Zea mays (Mz); rice, oryza sativa (R); barnyard grass, Echinochloa crusgalli (BG); oat, Avena sativa (0); linseed, Linum usitatissisum (L); mustard, Sinapsis alba (M); sugar beet, Beta vulgaris (SB) and soya bean, Glycine max (S).

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

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

The 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 5kg or lkg of active material per hectare in volume equivalent to 900 litres per hectare in the soil spray and foliar spray tests, and at a dosage 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 are recorded in Table 1 below on a 0-100 scale. A rating 0 indicates growth as untreated control, a rating 100 indicates death. An increase in 10 units on the linear scale approximates to a 10% increase in the level of effect.

TABLE 1 Test Species Mz R BG O L M SB S Soil drench (lOkg/ha) 56 33 56 33 67 67 56 33 Foliar spray (5 kg/ha) 33 33 67 56 100 100 78 45 Foliar Spray (lkg/ha) 22 22 45 33 78 67 67 33 Pre-emergence (5kg/ha) 33 22 89 67 78 100 89 22 Pre-emergence (lkg/ha) 11 0 89 33 45 67 56 0 B) A further biological evaluation was carried out with the compound of Example 1, which compared its properties with those of 1- (3 '-trifluoromethylphenyl) -5-phenoxy-lH-tetrazole, (hereinafter designated as "A") specifically described as Example 1 of EP-A-149269.

The tests conducted were foliar spray tests, in which seedling plants were sprayed with the test compounds. The test plant species were wheat (vie), veronica persica (SW) and galium aparine (GG). The plants were at the stage of 1-3 true leaves.

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

The compounds were tested as technical materials and formulated in a 1:1 acetone water mix containing up to 0.2% of the alkylphenol/ethylene oxide wetting agent, Triton X155 (trade mark) and applied as single dose foliar sprays in a total volume of 600 litres/hectare. Application was at 3 different dosage levels, 3.0, 1.0, and 0.3 kg/ha, designed to produce a range of responses. At least two replicate pots were used for each treatment. Untreated seedling plants were used as controls.

Phytotoxicity compared with the untreated control was assessed visually approximately 2 weeks after treatment as mean percentage effect, 0% indicating no effect and 100% death. The results are presented in Table 2 below.

Table 2

Mean % effect Selectivity factor mean GG/ mean SW/ mean WH mean WH Test Compound Dose WH GG SW A kg/ml 3.0 44 86 92 1.0 50 78 78 0.3 0 56 44 Mean 31 73 71 2.4 2.3 Example 1 3.0 39 89 100 1.0 0 78 94 0.3 0 67 78 Mean 13 78 91 6.0 7.0 It is apparent that the compound of Example 1 can combat the weeds veronica persica and galium aparine in wheat crops with much less damage to the crops than the prior art compound A.

Claims (15)

1. A compound of the general formula

wherein R1 represents an optionally substituted phenyl group and R2 represents a substituted phenyl group, which group must be substituted by at least one haloalkoxy group and is optionally further substituted.

2. A compound as claimed in claim 1 wherein RI represents a phenyl group, optionally substituted by one or more substltuents independently selected from halogen atoms and anLno, alkyl, alkoxy, haloalkyl and haloalkoxy groups.

3. A compound as claimed in either of claims 1 or 2 wherein R2 represents a phenyl group substituted by a haloalkoxy group and optionally substituted by one or more further substituents independently selected from halogen atoms and nitro, alkyl, haloalkyl, haloalkylsulphonyl and further haloalkoxy groups.

4. A compound as in claim 3 wherein R2 represents a phenyl grown substituted at the 3-position by a haloalkoxy group.

5 A process for the preparation of a compound as claimed in any of claims 1 to 4, which comprises reacting a 5-halotetrazole of formula II

with an alcohol of formula RICH, or an alkali metal salt of such an alcohol.

6. Process as claimed in claim 5 wherein the 5-halotetrazole of formula II is prepared by reacting (i) an isocyanate of formula R2NCO with aluminium azide followed by phosphorus pentachloride, or (ii) an isocyano dihalide of formula R2N=C (Ha1)2 with an inorganic azide wherein Hal represents a halogen atom.

7. A process for the preparation of a compound of formula I as claimed in any of claims 1 to 4, wherein a compound of the general formula R2-N=C(Hal)(OR1) (III) wherein Hal represents a halogen atom is reacted with an inorganic azide.

8. A process for the preparation of a compound of formula III, as claimed in claim 7, which comprises reacting a compound of the general formula.

R2-N=C(Hal)2 ('V) wherein Hal represents a halogen atom, with an alcohol of formula R1-OH

9. A process for the preparation of a compound of formula IV, as defined in claim 6 or 8, which comprises reacting an aniline of formula R2NH2 with formic acid to produce a compound of formula HCONH-R2 (V) followed by treatment of the product with sulphuryl and thionyl halides.

10. A compound of formula II,III,IV or V as defined in any one of claims 5 to 9.

11. A compound of formula I, as claimed in any of claims 1 to 4, whenever prepared by a process as claimed in claim 5 or 7; or a compound of formula II,III,IV or V, wherever prepared by a process as claimed in claim 6,8 or 9.

12. method of combating undesired growth at a locus, which comprises treating the locus with a compound of formula I as-claimed in any of claims 1 to 4, or 11.

14. Use as a herbicide of a substituted tetrazole of formula I, as defined in any one of claims 1 to 4, or 11.

14. A herbicidal composition comprising a compound of formula I as claimed in any of claims 1 to 4, or 11, with at least one carrier and/or surface-active agent.

15. A compound of formula I,II,III,IV or V, or a process for the preparation thereof, or the use of a compound of formula I in combating undesired plant growth, or a herbicidal composition containing a compound of formula I; any such aspect being substantially as hereinabove described.