This invention concerns novel diphenyl ethers which show activity as herbicides, herbicidal compositions which contain these compounds, and methods of controlling, i.e. combating, weeds with these herbicidal compositions.

Certain substituted diphenyl ethers have been shown to be effective weed control agents such as those described in West German Offenlegungsschrift 2753900. In this OLS, there are disclosed herbicidal substituted diphenyl ethers amongst which are those of the formula:

wherein X' is hydrogen, halogen, trihalomethyl, (C₁-C₄)alkyl or cyano; Y'is hydrogen, halogen or trihalomethyl; R is hydrogen or (Cl-C4)alkyl; and Z is alkenyl, haloalkenyl, alkynyl, or haloalkynyl.

The herbicidal effectiveness of a given diphenyl ether cannot be predicted from an examination of the substituent groups attached to the phenyl rings in the ether, and often quite closely related compounds will have quite different weed control abilities. Various diphenyl ethers may have overlapping or complementary areas of activity or selectivity, and can thus be useful in combination to control a variety of weeds upon application of a.single composition. Furthermore, the diphenyl ethers heretofore disclosed as herbicides are not completely effective. An ideal herbicide should give selective weed control, over the full growing season, with a single administration at low rates of application. It should be able to control all common weeds by killing them as the seed, the germinating seed, the seedling; and the growing plant. At the same time, the herbicide should not be phytotoxic to the crops to which it is applied and should decompose or otherwise be dissipated so as not to poison the soil permanently. The known diphenyl ether herbicides fall short of these ideals, and it would thus be desirable to have new herbicides which show even more selective control of undesirable plants among desirable crop,plants or which complement known herbicides in activity.

In accordance with the present invention, there is provided a class of novel diphenyl ethers having the formula:

wherein X is hydrogen, halogen (preferably fluorine or chlorine), trifluoromethyl, (C_l-C₄)alkyl (preferably methyl) or cyano; Y is hydrogen or halogen (preferably fluorine or chlorine); R¹ is hydrogen, hydroxy, (C₁-C₄)alkoxy, (C_l-C₄) alkyl (optionally substituted with one or more of halogen, hydroxy, (C_l-C₄)alkoxy, cyano, thiol, (C₁-C₇)alkylthio, carboxy, an agronomically-acceptable salt of carboxy and alkoxycarbonyl having 1 - 4 carbon atoms in the alkoxy moiety) or monocyclic (C₅-C₇)cycloalkyl; R² is hydrogen, (C_l-C₄) alkyl (optionally substituted with one or more of halogen, hydroxy, (C₁-C₄)alkoxy, cyano, thiol, (C₁-C₄)alkylthio, carboxy, an agronomically-acceptable salt of carboxy and alkoxycarbonyl having 1 - 4 carbon atoms in the alkoxy moiety) or monocyclic (C₅-C₇)cycloaklyl; or R¹ and R² can be joined to form, together with the attached nitrogen atom, a saturated heterocyclic ring having 4 to 6 carbon atoms and up to one additional hetero nitrogen, oxygen or sulfur atom.

When the X, R¹ or R² substituent is an alkyl group, it can have either a straight- or branched-chain configuration. When _R¹ or _R² is a substituted alkyl group, it will preferably have a single substituent.

These novel compounds have been found to show unexpected activity as weed control agents. In a preferred embodiment of the invention, X is a halogen atom, most preferably a chlorine atom, Y is a hydrogen atom and R¹ and R² are individually a hydrogen atom or a substituted or unsubstituted (C_I-C₄)alkyl group, more preferably a hydrogen atom or an unsubstituted (C₁-C₄)alkyl group. Most preferably either R¹ or R² is a _hy-drogen atom, and the other an unsubstituted (C₁-C₄)alkyl group.

Examples of the compounds of the invention embraced by Formula I include:

• 2-Nitro-5-(2-chloro-4-trifluoromethylphenoXy)-N-methylbenzamide 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N,N-diethylben- zamide
• 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N-t-butylbenzamide 2-Nitro-5-(2-bromo-4-trifluoromethylphenoxy)-N-(2-hydroxyethyl) benzamide
• 2-Nitro-5-(2-fluoro-4-trifluoromethylphenoxy)-N,N-4-oxapenta- methylenebenzamide
• 2-Nitro-5-(2,6-dichloro-4-trifluoromethylphenoxy)-N-methyl-N-(2-hydroxypropyl)benzamide
• 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N-cyclohexylben- zamide
• 2-Nitro-5-(2-cyano-4-trifluoromethylphenoxy)-N-carboxymethyl- benzamide
• 2-Nitro-5-(2,4-bistrifluoromethylphenoxy)-N-ethyl-N-(methylthioethyl)benzamide
• 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N-(2-ethoxyethyl) benzamide
• 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N-ethylbenzamide 2-Nitro-5-(2-fluoro-4-trifluoromethylphenoxy)-N-methyl-N-(1- ethoxycarbonyl)ethylbenzamide
• 2-Nitro-5-(2-chloro-6-fluoro-4-trifluoromethylphenoxy)-N-methyl- benzamide
• 2-Nitro-5-(4-trifluoromethylphenoxy)-N,N-pentamethylenebenzamide 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N-carboxymethyl-N-(2-hydroxyethyl)benzamide
• 2-Nitro-5-(2-cyano-4-trifluoromethylphenoxy)benzamide 2-Nitro-5-(4-trifluoromethylphenoxy)-N-(2-cyanoethyl)benzamide 2-Nitro-5-(2-chloro-4-trifluoromethylphenoxy)-N, N'-bis-(2-hydroxyethyl)benzamide
• 2-Nitro-5-(2-fluoro-4-trifluoromethylphenoxy)-N-hydroxybenzamide 2-Nitro-5-(2,6-dichloro-4-trifluoromethylphenoxy)-N-methoxybenzamide

The novel diphenyl ethers of the invention are useful both as preemergence and postemergence herbicides. Preemergence herbicides are ordinarily used to treat the soil in which the desired crop is to be planted by application either before seeding, during seeding, or, as in most applications, after seeding and before the crop emerges. Postemergence herbicides are those which are applied after the plants have emerged and during their growth period. Compounds of the invention are particularly active against broadleaf weeds.

Among the crops on which the diphenyl ethers of the invention can be advantageously employed are, for example, soybeans, peanuts, cotton, corn, (i.e.. maize), wheat, barley, rice and other cereal crops.

When used in transplanted rice crops, the ethers can be applied either preemergence or postemergence to the weeds - that is, they can be applied to the growth medium of the transplanted plants either before the weed plants have emerged or while they are in their early stages of growth. The ethers can be applied to the growth medium either before or after the rice has been transplanted to that medium.

The diphenyl ethers of the invention can be applied in any amount which will give the desired degree of weed control. A preferred rate of application of the herbicides of the invention is from about 0.112 to 13.45 kg/hectare, and most preferably about 0.28 to 4.48 kg/hectare (0.1 to 12 preferably 0.25 to 4 lb/acre) of the diphenyl ether.

Under some conditions, the diphenyl ethers of the invention may be advantageously incorporated into the soil or other growth medium prior to planting a crop. This incorporation can be carried out by any convenient means, including by simple mixing with the soil, by applying the diphenyl ether to the surface of the soil and then discing or dragging into the soil to the desired depth, or by employing a liquid carrier to accomplish the necessary penetration and impregnation.

A diphenyl ether of the invention can be applied to the growth medium or to plants to be treated either by itself or, as is generally done, as a component in a herbicidal composition or formulation which also comprises an agronomically-acceptable carrier. By agronomically-acceptable carrier is meant any substance which can be used to dissolve, disperse, or diffuse a herbicidal compound in the composition without impairing the effectiveness of the herbicidal compound and which by itself has no detrimental effect on the soil, equipment, crops, or agronomic environment. Mixtures of the diphenyl ethers of the invention may be used in any of these herbicidal formulations. The herbicidal compositions of the invention can be either solid or liquid formulations or solutions. For example, the diphenyl ethers can be formulated as wettable powders, emulsifiable concentrates, dusts, granular formulations, aerosols, or flowable emulsion concentrates. In such formulations, the compounds are extended with a liquid or solid carrier and, when desired, suitable surfactants are incorporated. Guidance as to formulations and the mode of application of the diphenyl ethers may be derived from OLS 2,753,900 cited above. The diphenyl ethers of the invention can be used in conjunction with other herbicides such as those listed in OLS 2,753,900.

The ethers of the invention can be prepared by reacting an acid halide, preferably an acid chloride of a diphenyl ether of the formula:

wherein X and Y are as defined above, with an excess of an amine of the formula

wherein R¹ and R² are as defined above. This reaction is generally carried out in a solvent in which the acid chloride is soluble, such as diethyl ether, a chlorinated hydrocarbon or an aromatic hydrocarbon, at a temperature of 0 to 100°C, preferably at 0 to 40°C. The amination reaction can also be carried out under Schotten-Bauman conditions, where one equivalent of an amine of Formula III is first added to a mixture of an organic solvent, such as diethyl ether, and an aqueous solution of a strong inorganic base, such as sodium hydroxide, followed by the slow addition of an organic solution of the acid chloride, for example in toluene, to the agitated two-phase system. This reaction is generally carried out at a temperature of 0 to 100°C, preferably 10 to 40°C.

Compounds of the invention can also be prepared by reacting an ester of a diphenyl ether of Formula II with an amine of Formula III, using an acid catalyst, such as p-toluenesulfonic acid, hydrochloric acid or sulfuric acid, in a suitable inert solvent, such as tetrahydrofuran, glyme, toluene or xylene, at a temperature of 20° to the reflux temperature of the solvent. In another route to the compounds of the invention, an ammonium salt of a diphenyl ether of Formula II, in which the cation has the formula:

wherein R and R2 are as defined above, is heated at a temperature of 100° to 200° in a high-boiling inert solvent, such as toluene, xylene or diglyme, to produce the amide directly.

The diphenyl ether precursors can be prepared by reacting a suitably substituted phenol, or the potassium or sodium salt of the phenol, with a suitably substituted halobenzene, such as a chloro- or fluorobenzene in the presence of an alkaline agent. Such precursors and their preparation are described in U.S. Patent Nos. 3,928,416 and 4,031,131.

Another route to the compounds of the invention involves the nitration of a diphenyl ether of the formula:

wherein X, Y, R¹ and R² are as defined above, using typical nitrating agents such as potassium nitrate in sulfuric acid, acetyl nitrate, mixed sulfuric acid/nitric acid or nitro- sonium tetrafluoroborate. The nitration reaction is generally carried out at 20 to 100°C, preferably 0 to 5⁰C, optionally in the presence of an inert organic solvent, such as methylene chloride or other chlorinated hydrocarbon.

The compounds of the invention can also be prepared by condensing a phenol of the formula:

wherein X and Y are as defined above with a substituted halobenzene of the formula:

wherein X¹ is a halogen atom, preferably a fluorine atom, and R¹ and R² are as defined above. This reaction is generally carried out at a temperature of 0 to 250°C, preferably 75 to 200°C, optionally in the presence of an appropriate solvent, such as sulfolane, dimethylsulfoxide, dimethylformamide, hexamethylphosphorustriamide, or other inert polar organic solvent.

The following Example will illustrate the preparation of compounds according to the invention. In Table I, typical diphenyl ethers of the invention'are listed together with their elemental analyses. In Table I, "--" indicates "not determined".

Example 1

Experimental:

Preparation of 2-nitro-5-(2-chloro-4-trifluciromethylphenoxy)-N-methylbenzamide (Compound No.2, Table I)

A solution of 2-nitro-5-(2-chloro-4-trifluoromethylphenoxy) benzoyl chloride (lOg, 0.026 mole) and an excess of methylamine was stirred at room temperature in toluene for five hours. Amine hydrochloride was filtered off and the filtrate stripped to yield 2-nitro-5-(2-chloro-4-trifluoromethyl- phenoxy)benzoyl chloride (8g) m.p. 118-120°C.

The following Example 2 shows.the herbicidal properties of diphenyl ethers of the invention.

Example 2

Using the procedure described below,diphenyl ethers were evaluated for control of various plant species.

The following test procedure was employed. Seeds of selected crops and weeds were planted in soil in trays. For preemergence tests, the trays were treated with the test compound immediately after the planting. For postemergence tests, the seeds were allowed to germinate, and after two weeks the trays were treated with the test compound immediately after the planting. The compound to be evaluated was dissolved in acetone, diluted with water, and sprayed over the trays using a carrier volume equivalent to 468 1/ha (i.e. 50 U.S. gallons per acre) at the rate of application of 2.24 or 4.48 kg/ha. About two weeks after the application of the test compound, the state of growth of the plants was observed and the phytotoxic effect of the compound evaluated. The results of typical tests are summarised in Table II, which gives the average percent control achieved by the test compounds with 0 representing no control and 100 complete kill of the plant.

The following species were tested:

Example 3

The following example shows the selectivity of the diphenyl ethers of the invention towards several common crops. Using a procedure similar to Example 2, the following crops were planted and treated: corn (CN - otherwise termed maize), cotton (COT), rape (RA), rice (RI), sugarbeet (SB), soybeans (SOY) and wheat (WHT). The result of typical tests are summarised in Table III, which gives the average percent injury caused by the test compound with 0 representing no injury and 100 complete kill of the plant.