DE3145422A1 - Heterocyclyloxyphenylureas - Google Patents

Abstract

1,3,4-Oxadiazolyloxyphenylureas of the formula I have selectively-herbicidal properties and can be used in a variety of crops such as, for example, cereals, maize, rice, cotton, sugar beet, sugar cane and soya beans. <IMAGE> In formula I, X is hydrogen, halogen or C1-C3-haloalkyl, Y is hydrogen, C1-C3-haloalkyl, C1-C6-alkyl, C2-C4-alkoxyalkyl, C3-C6-cycloalkyl or phenyl, R1 is hydrogen or C1-C4-alkyl, R2 is hydrogen, C1-C6-alkyl, C3-C6-alkenyl, C3-C6-alkynyl or C3-C6-cycloalkyl, and R3 has the same meaning as R2 but can additionally be C1-C6-alkoxy. R2 and R3 can also together with the nitrogen atom to which they are bonded form a 5- to 6-membered heterocycle which can additionally contain an oxygen or sulphur atom or an optionally C1-C3-alkyl-substituted imino group.

Description

Heterocyclyloxy-phenylureas

The present invention relates to new heterocyclyloxyphenylureas, namely 1,3,4-oxadiazol-2-yloxy-phenylureas with herbicidal action, method for their production, agents containing them as active ingredients and their use for selective weed control in various crops such as grain, maize, Rice, cotton, sugar beet, soy and sugar cane.

The new 1,3,4-oxadiazol - yloxyphenylureas correspond to the general formula 1 wherein X is hydrogen, halogen or C1-C3-haloalkyl, Y is hydrogen, C1-C3-haloalkyl, C1-C6-alkyl, C2-C4-alkoxyalkyl, C3-C6-cycloalkyl or phenyl, R1 is hydrogen or C1-C4-alkyl, R2 is hydrogen, C1-C6-alkyl, C3-C6-alkenyl, C3-C6-alkynyl or C3-C6-cycloalkyl and R3 has the same meaning as R2, but can also stand for C1-C6-alkoxy or R2 and R3 together with the nitrogen atom to which they are bound can form a 5- to 6-membered heterocycle which can also contain an oxygen or sulfur atom or an imino group optionally substituted by C1-C3-alkyl.

Among alkyl or alkyl parts of substituents such as alkoxy, haloalkyl or alkoxyalkyl are to be understood, depending on the number of carbon atoms, for example: Methyl, ethyl, n-propyl, i-propyl, the four isomeric butyl radicals and n-pentyl, Neopentyl, tert-pentyl or the isomeric hexyl radicals.

Alkyl substituents which stand for Y are preferably branched such as i-propyl, s-butyl, i-butyl, tert-butyl, 2-pentyl, 3-pentyl, tert-pentyl, Neopentyl or 2- (2-ethyl) butyl.

Halogen as a substituent or part of a substituent represents fluorine, Chlorine, bromine and iodine, but preferably for fluorine and chlorine.

Examples of cycloalkyl radicals are cyclopropyl, cyclobutyl and cyclopentyl and cyclohexyl.

Correspondingly, for example, alkoxy radicals are: methoxy, ethoxy and Propyloxy; Haloalkyl radicals: fluoromethyl, chloromethyl, trifluoromethyl, perfluoroethyl or difluoromethyl, preferably trifluoromethyl; and alkoxyalkyl radicals: methoxymethyl, Ethoxymethyl, methoxyethyl and ethoxyethyl.

Examples of heterocycles created by R2 and R3 together with them bonding nitrogen atoms are formed are pyrrolidine, piperidine, pyrrole, imidazole, Imidazolidine, pyrazole, pyrazolidine, pyrrole, imidazoline, pyrazoline, piperazine, morpholine or thiomorpholine.

Herbicidal phenylureas have long been known and introduced.

Due to their spreading, cultures such as grain on the one hand could largely be rid of weeds, on the other hand there is a proliferation of weeds that were resistant to such herbicides.

On the one hand, the present invention is also intended to date resistant weeds can be controlled, on the other hand crops can be protected such as soy, which opposes the phytotoxicity of most known herbicides were not resistant enough.

Because of their effectiveness, the following subgroups are preferred: compounds, in which a) R1 is hydrogen, b) the radicals R2 and R3 both open-chain or also as part of a heterocycle together a maximum of 6 carbon atoms contain, c) the oxadiazolyloxy radical in the phenyl nucleus occupies the 3- or 4-position and d) the substituent X is hydrogen or halogen.

Combining the features results in the following in particular preferred groups: compounds in which R1 is hydrogen and in which R2 and R3 both open-chain or as components of a heterocycle together contain a maximum of 6 carbon atoms.

Compounds in which R1 is hydrogen, R2 is methyl and R3 is methyl or Methoxy and the oxadiazolyloxy radical in the phenyl nucleus are in the 3- or 4-position occupied.

Compounds in which the oxadiazolyloxy radical is in the 3- or 4-position of the phenyl nucleus and in which X and R1 are hydrogen, R2 is methyl and R3 is methoxy or methyl.

A preferred individual compound is N- [4- (5-tert-butyl-1,3,4-oxadiazol-2-yloxy) -phenyl] -N ', N'-dimethylurea.

The 1,3,4-Oxadiazolyloxyphenylureas are new, but can after methods known per se are produced.

According to a first process according to the invention, the 1,3,4-oxadiazolyloxyphenylureas of the formula 1 are prepared by adding a hydroxyphenylurea of the formula IIt to partners in the presence of an acid-binding agent wherein X, R1, R2 and R3 have the meaning given under formula I, with a 1,3,4-oxadiazolyl derivative of the formula III, in which Y has the meaning given under formula I and Z is a leaving group 1, for example halogen or alkylulfOtlYl).

According to a further process according to the invention, the 1,3,4-oxadiazolyloxy-phenylureas of the formula I are prepared by adding a 1,3,4-oxadiazolyloxy-aniline of the formula IV, wherein Y and R1 have the meaning given under formula, in the presence of an acid-binding agent, with a carbamoyl acid halide of the formula V, in which -Hal is chlorine or bromine and R2 and R3 have the meaning given under formula I.

The 1,3,4-oxadiazolyloxyphenylureas of the formula I, in which R1 is hydrogen, can also be prepared according to the invention by adding a 1,3,4-oxadiazolyloxyaniline of the formula IV, in which R1 is hydrogen, by means of phosgene to the 1 , Converts 3,4-oxadiazolyloxyphenyl isocyanate of the formula VI, wherein X and Y have the meaning given under formula I, and this reacts with an amine of formula VII, wherein R2 and R3 have the meaning given under formula I.

According to a variant of this process, the 1,3,4-oxadiazolyloxy-phenylureas of the formula I, in which R1 is Cl-C4-alkyl, are prepared according to the invention by adding a 1,3,4-oxadiazolyloxy-aniline of the formula IV, in which R1 is C1-C4-alkyl, in the presence of an acid-binding agent, reacts with phosgene to form the phenylcarbamoyl chloride of the formula VIa, in which X and Y have the meaning given under formula I and R1 is C 1 -C 4 -alkyl, and this reacts with an amine of the formula VII in the presence of an acid-binding agent, in which R2 and R3 have the meaning given under formula I.

These reactions are advantageous in relation to the reactants inert organic solvents carried out. Examples of such solvents are alcohols such as methanol, ethanol, propanol and i-propanol; Esters such as ethyl acetate; Ethers such as diethyl ether, tetrahydrofuran and dioxane; Hydrocarbons such as petroleum ether, Cyclohexane, benzene and toluene; Halogenated hydrocarbons such as methylene chloride, chloroform and carbon tetrachloride; or polar solvents such as dimethylformamide, acetonitrile or dimethyl sulfoxide. It is advantageous if the solvents are miscible with water are, since the reaction products of the formula I can easily be precipitated by adding water are.

Acid-binding agents that can be used include sodium or potassium hydroxide, Sodium or potassium carbonate, magnesium or calcium oxide, but also sodium or Potassium methylate or ethylate can be used.

The reaction temperature is 0-150 "C, mostly alternating worked between room temperature and the boiling point of the reaction mixture. These Reactions are usually carried out under ordinary pressure. At manufacture However, for larger quantities, pressure vessels and higher pressures are recommended.

The starting compounds of the formulas II, V and VII are known and can partly be purchased in stores.

The starting compounds of formula III are new and can after customary processes. For example, the connections of the Formula III, in which Z is an alkylsulfonyl group, prepared according to scheme A 10 will.

Scheme A: In scheme A, Y has the meaning given under formula I. Alkyl stands for alkyl radicals with a maximum of 5 carbon atoms. Sodium and potassium hydroxide are particularly suitable as bases. Suitable oxidizing agents are potassium permanganate, chromium trioxide, sodium and potassium dichromate, hydrogen peroxide, but also organic peracids such as peracetic acid, perbenzoic acid, monoperphthalic acid and 3-chloroperbenzoic acid.

The aniline of the formula IV is, for example, by condensation of a nitrophenol of the formula X. wherein X has the meaning given under formula I, with the 1,3,4-oxadiazolyl derivative of the formula III and subsequent reduction of the nitro group to the amine. The aniline obtained in this way can, if desired, also be (mono) -alkylated with a C1-C4-alkyl halide.

The compounds of formula I are extremely selective herbicidal Properties in general and prove to be particularly advantageous for Control of weeds in crops of useful plants, especially in crops of soy, cotton, grain, corn, rice, sugar beet and sugar cane.

The active ingredients of the formula I are suitable both for use in the pre-emergence process, as well as contact herbicides in post-emergence use. With the two application methods a different selectivity spectrum is achieved in each case.

With a sufficiently large application rate, however, it is also total herbicidal Effect present. It can be used both pre-emergence and post-emergence be made. The application rates can vary within wide limits, e.g. between 0.01 and 10 kg of active ingredient per hectare, but preferably 0.05 up to 5 kg of active ingredient used per hectare.

The compounds of the formula I are stable. Your handling needs no precautionary measures. They are in the usual organic solvents relatively good and poorly soluble in water. Their formulation as a liquid herbicidal Agents are therefore only successful with the aid of customary solubilizers and / or dispersants.

The compounds of the formula I disintegrate in the soil after a relatively short period of time Time into nitrogen-rich decomposition products, which are beneficial for plant nutrition are.

For use in herbicidal compositions, the compounds of the formula I as a dusting agent, emulsion concentrate, as granules, dispersion or as Solution or slurry can be processed in the usual formulation.

In addition to the active ingredient of the formula, the agents according to the invention contain I a suitable carrier and / or other additives.

Suitable carriers and additives can be solid or liquid and correspond to the substances commonly used in formulation technology such as

natural or regenerated mineral substances, solvents, thinners, Dispersants, emulsifiers, wetting agents, adhesives, thickeners, binders and / or fertilizers.

The agents according to the invention are prepared in a manner known per se Way by intimately mixing and grinding active ingredients of the general formula I with suitable carriers and / or distribution agents, optionally under Addition of antifoam, wetting, dispersion and / or inert to the active ingredients Solvents. The active ingredients can be in the following working-up forms and are used: Solid reconditioning forms: dusts, grit, granulates, Coating granules, impregnating granules and homogeneous granules; Dispersible in water Active ingredient concentrates: wettable powder, pastes, suspension concentrates (flowables), emulsions and emulsion concentrates.

Liquid processing forms: solutions.

The active ingredient concentrations are in the agents according to the invention usually 1 to 80 percent by weight and can be used if necessary also be present in low concentrations such as about 0.05 to 1%.

Other biocidal active ingredients can be added to the agents according to the invention or add agents. So can the new means in addition to the compounds mentioned of the general formula I e.g. insecticides, fungicides, bactericides, fungistatic agents, Bacteriostatics, nematicides or other herbicides to broaden the spectrum of activity contain.

In the examples below, the temperatures are in degrees Celsius indicated, parts and percentages relate to weight.

Example 1: a) Representation of an intermediate product: 5-tert-butyl-2-mercapto-1,3,4-oxadiazole Zür solution of 17.4 g of pivalic acid hydrazide and 9.4 g of potassium hydroxide in 300 ml of ethanol is allowed to drop 10 ml of carbon disulfide.

After the reaction mixture has been refluxed for 3 hours is, the solvent is evaporated, the residue is taken up in water and acidified with hydrochloric acid. By extraction with methylene chloride, drying and evaporation 35 g of the above product, m.p. 84-850C, are obtained in the organic phase.

b) Representation of an intermediate product: 5-tert-Butyl-2-methylthio-1,3,4-oxadiazole: To dissolve 27.2 g of 5-tert-butyl-2-mercapto-1,3,4-oxadiazole in 172 ml of 10% Sodium hydroxide solution is added dropwise at a temperature of 20 to 30 ° C. 25.6 g of dimethyl sulfate. After the reaction mixture has been stirred for one hour, it is extracted with chloroform, the organic phase is dried and evaporated. Distillation gives 27 from the residue 2 g of the above product, bp 750C / O, lmb.

c) Representation of a further intermediate product: 5-tert-butyl-2-methylsulfonyl-1,3,4-oxadiazole is allowed to dissolve 15.5 g of 5-tert-butyl-5-methylthio-1,3,4-oxadiazole in 40 ml of glacial acetic acid Add dropwise a solution of 23.8 g of potassium permanganate in 350 ml of water, the temperature in the reaction vessel not being allowed to rise above 350.degree. After the reaction mixture has been stirred for a further hour, sulfur dioxide is passed in until the solution is discolored. The precipitated product is filtered off and dried, mp 79-810C.

d) Presentation of an end product: N- [4- (5-tert-butyl-1,3,4-oxadiazol-2-yloxy) -phenyl)] - N ', N' -dimethylurea: A solution of 9.0 g of N- (4- Hydroxyphenyl) -N ', N'-dimethylurea and 3.3 g of potassium hydroxide in 150 ml of dimethyl sulfoxide are mixed in portions with 10.2 g of 5-tert-butyl-2-methylsulfonyl-1,3,4-oxadiazole. After the reaction mixture has been stirred for 15 hours, it is taken up with ice water and extracted with methylene chloride. 13.2 g of the above product, melting point 131-133 ° C., are obtained by drying and evaporating the organic phase.

This urea and other compounds produced in an analogous manner are listed in Tables 1 and 2 below.

Table 1: No. XY R1 R2 R3 physical data 1 H t-C4Hg H CH3 CH3 m.p. 130-1310C 2 H C6H5 H CH3 CH3 m.p. 139-1400C 3 H cycl-C6H11 H CH3 OCH3 m.p. 110C 4 H cycl-C6H11 H CH3 CH3 m.p. 102-104 ° C 5 H i-C3H7 H CH3 CH3 6 H i-C3H7 H CH3 OCH3 7 H CH3 H CH3 CH3 8 H CH3 H CH3 OCH3 9 H C2H5 H CH3 CH3 10 H C2H5 H CH3 OCH3 11 H cycl-C3H5 H CH3 CH3 m.p. 102 ° C 12 H cycl-C HH CH3 OCH3 m.p. 75-770C 13 H s-C4Hg H CH3 C113 m.p. 900C Continuation (table 1): No. XY R1 R2 R3 physical data $ OCH3 14 H S-C4H9 H CH3 OCH3 15 H i-C4Hg H CH3 OCH3 16 H i-C4Hg H CH3 CH3 17 H CH (C2H5) 2 H CH3 CH3 18 H CH (C2H5) 2 H CH3 OCH3 19 4-C1 t-C4Hg H CH3 CH3 20 4-C1 t-C4Hg H CH3 OCH3 21 4-C1 C C6H5 H CH3 CH3 22 4-C1 C6H5 H CH3 OCH3 23 4-Cl C6H5 H CH3 CH3 24 4-C1 C6H5 H CH3 CH3 25 4-Cl t-C4H9 H - (CH2) 2-CH (CH3) - (CH2) 2- 26 H t-C4H9 H - (CH2) 2-CH (CH3) - (CH2) 2- semi-solid 27 H t-C4H9 H - (CH2) 4- 28 H t -C4 H9 H CH3 -CH (CH3) -C # CH m.p. 123 ° C 29 H t-C4Hg H CH3 OCH3 m.p. III-1120C 30 H t-C4Hg H CH3 n-C4H9 oil 31 H t-C4Hg HH CH3 m.p. 124-126 ° C Table 2: No. XY R1 R2 R3 physical data 101 H t-C4Hg H CH3 CH3 1 m.p. 131-133 ° C 102 H C6H5 H CH3 CH3 m.p. 166-167 ° C 103 H C6H5 H CH3 OCH3 m.p. 145-146 ° C 104 H cycl-C6H11 H CH3 OCH3 m.p. 137-139 ° C 105 H cycl-C6H11 H CH3 CH3 m.p. 1390C 106 H i-G4Hg H CH3 OCH3 m.p. 96-97 ° C 107 H i-C4Hg H CH3 CH3 m.p. 83- (4 ° C 108 3-Cl t-C4H9 H CH3 CH3 m.p. 193-195 ° C 109 H t-C4Hg H CH3 OCH3 m.p. 990C 110 H t -C4Hg H CH3 -CH (CH3) -C # CH m.p. 920C 111 H t-C4Hg H CH3 n-C4H9 m.p. 102 ° C 112 H t -C4Hg H - (CH2) 2 -CH ~ (CH3) - (CH2) 2 m.p. 1279C 113 3-CF3 t-C4Hg HH CH3 114 3-CF3 t-C4H9 H CH3 CH3 115 3-CF3 t-C4Hg H CH3 OCH3 116 H i-C3H7 HH CH3 117 H i-C3H7 H CH3 CH3 118 H i-C3H7 H CH3 POCH3 119 H i-C3H7 H CH3 n-C4H9 120 H i-C3H7 H CH3 -CH (CH3) -C # CH Continuation (table 2): No. XY R1 R2 R3 physical data 121 3-Cl i-C3H7 H CH3 CH3 122 3-C1 i-C3H7 H CH3 OCH3 123 H CH3 H CH3 CH3 124 H CH3 H CH3 OCH3 125 3-C1 CH3 H CH3 CH3 126 3-C1 CH3 H CH3 OCH3 127 H C2H5 H CH3 CH3 128 H C2H5 H CH3 OCH3 129 3-C1 C2H5 H CH3 CH3 130 3-Cl C2H5 H CH3 OCH3 131 H cycl-C3H5 H CH3 CH3 m.p. 130-131 ° C 132 H cycl-C3H5 H CH3 OCH3 m.p. 98 ° C 133 4-C1 cycl-C3H5 H CH3 CH3 m.p. 140-142 ° C 134 4-Cl cycl-C3H5 H CH3 OCH3 m.p. 104 ° C 135 H i-C4H9 H CH3 CH3 136 Hi-C4H) H CH3 OCH3 137 H CH3-O-CH2-H CH3 CH3 138 H CH3-O-CH2-H CH3 OCH3 139 H n -C4H9 H CH3 CH3 140 H s-C4H9 H CH3 OCH3 141 H s-C4H9 H CH3 CH3 m.p. 95-96 ° C 142 3-Cl s-C4H9 H CH3 CH3 Continuation (Table 2): No. XY R1 R2 R3 physical data 143 H t -C4H9 CH3 H CH3 144 H -CH (C2H5) 2 H CH3 CH3 145 H - (CH (C2H5) 2 H CH3 OCH3 146 3-C1-CH (C2H5) 2 H CH3 CH3 147 3-C1 - (CH (C2H5) 2 CH3 11 CH3 148 3-CF3 -CH (C2H5) 2 H CH3 CHZ3 149 H n -C3H7 H CH3 CH3 10 H n -C3H7 H CH3 OCH3 151 H t-C4H9 HH CH3 m.p. 184-5 ° C Example 2: Wettable powder To produce a) 70% and b) 10% wettable powder, the following ingredients are used: a) 70 parts of active ingredient No. 1, 5 parts of sodium dibutylnaphthylsulphonate, 3 parts of naphthalenesulphonic acid-phenolsulphonic acid-formaldehyde condensate 3: 2: 1, 10 parts of kaolin, 12 parts of chalk; b) 10 parts of active ingredient No. 2, 3 parts of a mixture of the sodium salts of saturated fatty alcohol sulfates, 5 parts of naphthalenesulfonic acid-formaldehyde condensate, 82 parts of kaolin.

The specified active ingredient is based on the appropriate carrier (kaolin and chalk) and then mixed and ground with the rest Components. The spray powder obtained has excellent wettability and suspension properties. Such wettable powders can be diluted with water to produce suspensions of e.g. 0.1% active ingredient content, which is suitable for weed control in plant cultures suitable.

Example 3: Paste The following are used to produce a 45% paste Substances used: 45 parts of active ingredient No. 101, 5 parts of sodium aluminum silicate, 14 Parts of cetyl polyglycol ether with 8 moles of ethylene oxide, 1 part of oleyl polyglycol ether with 5 moles of ethylene oxide, 2 parts of spindle oil, 10 parts of polyethylene glycol (average molecular weight 400 g / mol), 23 parts of water.

The active ingredient is mixed with the additives in suitable devices intimately mixed and ground. A paste is obtained from which, by diluting it make suspensions of any desired concentration with water.

Example 4: Emulsion concentrate For the production of a 25% emulsion concentrate 25 parts of active ingredient No. 103, 10 parts of a mixture of nonylphenol polyoxyethylene or calcium dodecylbenzenesulfonate, 10 parts of cyclohexanone and 55 teaspoons of xylene together mixed. This concentrate can be mixed with water to form emulsions at suitable concentrations be diluted by e.g. 0.1%. Such emulsions are suitable for combating Weeds in crops.

To prove the usefulness as herbicides (pre- and post-emergent) and to prove the superiority over known active substances of similar structure The following test methods are used: Example 5: Pre-emergent herbicidal effect (germ inhibition) In the greenhouse, the test plants are placed in seed trays immediately after sowing the earth's surface with an aqueous dispersion of the active ingredients obtained from a 25% emulsion concentrate, or from a 25% wettable powder for active ingredients, which are not produced as an emulsion concentrate due to insufficient solubility can, treated. Four different concentration series were used, corresponding to 2, 1, 0.5 and 0.25 kg of active substance per hectare. The seed trays are in a greenhouse at 22-25 ° C and 50-70% rel. Humidity and the experiment after 3 weeks evaluated.

The tested compounds of the formula I showed in this experiment excellent action against dicotyledonous and also against most grassy ones Weeds, while crops such as corn, millet, soy and cotton and partly Wheat and rice were also not damaged or only insignificantly damaged.

Example 6: Post-emergent herbicidal effect (contact herbicide) A larger number of weeds and cultivated plants, both 1 mon »cwotylts 1 as well as dicotyle, were after emergence (in the 4 to 6 leaf stage) with an aqueous active ingredient dispersion in doses of 0.25, 0.5, 1, 2 and 4 kg of active ingredient per hectare on the plants sprayed and this kept at 24 ° -26 ° C and 45-60% relative humidity.

The experiment is evaluated at least 15 days after the treatment.

In this experiment, too, the compounds of the formula I showed excellent results Action against dicotyledonous and most of the grassy weeds, being the cultivated plant maize, the cereals barley, millet and rice as well as cotton and soy were not damaged or only damaged with a higher amount of active ingredient.

Example 7: Growth inhibition in grasses In plastic dishes with a mixture of earth, peat and sand (6: 3: 1) were seeds of the grasses Lolium perenne, Poa pratensis, Festuca ovina and Dactylis gromerata sown and watered normally. The accrued grasses were pruned weekly to a height of 4 cm and 40 days after sowing and 1 day after the last cut with an aqueous spray mixture of an active ingredient Formula I splattered. The amount of active ingredient was the equivalent of 5 kg of active ingredient per Hectares. The growth of the grasses was assessed 10 and 21 days after the application.

Example 8: Growth inhibition in cereals Spring wheat was placed in plastic cups (Triticum aestivum), spring barley (Hordeum vulgare) and rye (Secale) in sterilized Sown soil and grown in the greenhouse. The grain sprouts are 5 days after Sowing treated with a spray mixture of the active ingredient.

The foliar application corresponded to 6 kg of active ingredient per hectare. The evaluation takes place after 21 days.

The t? Active ingredients according to the invention cause a noticeable inhibition of growth both in grain and grass.

Claims (19)

Claims: 1. 1,3,4-oxadiazol-2-yloxy-phenylureas of the general formula I. wherein X is hydrogen, halogen or C1-C3-haloalkyl, Y is hydrogen, Cl-C3-haloalkyl, Cl-C6-alkyl, C2-C4-alkoxyalkyl, C3-C6-cycloalkyl or phenyl, R1 is hydrogen or C1-C4-alkyl, R2 is hydrogen, C1-C6-alkyl, C3-C6-alkenyl, C3-C6-alkynyl or C -C -cycloalkyl and 3.6 R3 has the same meaning as R2, but can also be C1-C6-alkoxy or R2 and R3, together with the nitrogen atom to which they are bonded, can form a 5- to 6-membered heterocycle which can also contain an oxygen or sulfur atom or an imino group optionally substituted by C 1 -C 3 -alkyl. 2. Compounds of the formula I according to claim 1, characterized in that that R1 means hydrogen. 3. Compounds of formula I according to claim 1, characterized in that that the radicals R2 and R3 both open-chain or as a heterocycle together contain a maximum of 6 carbon atoms. 4. Compounds of the formula I according to claim 1, characterized in that that the oxadiazolyloxy radical in the phenyl nucleus occupies the 3- or 4-position. 5. Compounds of Pornel r, according to claim 1, characterized in that that X stands for hydrogen or halogen 6. Compounds of formula I according to claims 2 and 3, characterized in that R1 is hydrogen and R2 and R3 are both open-chain or as components of a heterocycle together at most 6 carbon atoms contain. 7. Compounds of the formula I, according to claims 4 and 6, characterized gekemlzeichnct, that R1 is hydrogen, R2 is methyl and R3 is methoxy or methyl and that the Oxadiazolyloxy radical occupies the 3- or 4-position on the phenyl nucleus. 8. Compounds of formula I according to claims 5 and 7, characterized in that that the oxadiazolyloxy radical occupies the 3- or 4-position on the phenyl nucleus and X and R1 is hydrogen, R2 is methyl, R3 is methoxy or methyl. 9. The compound M- [4- (5-tert-butyl-1,3,4-oxadiazol-2-yloxy) -phenyl} -N ', N'-dimethylurea. 10. A process for the preparation of the compounds of the formula I according to claim 1, characterized in that in the presence of an acid-binding agent, a hydroxyphenylurea of the formula II wherein X, R1, R2 and R3 have the meaning given under formula I, with a 1,3,4-oxadiazolyl derivative of the formula III, wherein Y has the meaning given under formula I and Z denotes halogen, alkylsulfonyl or arylsulfonyl. 11. A process for the preparation of the 1,3,4-oxadiazolyloxyphenylureas of the formula I according to claim 1, characterized in that a 1,3,4-oxadiazolyloxyaniline of the formula IV wherein Y and R1 have the meaning given under formula I, reacts with a carbamoyl acid halide of the formula V in the presence of an acid-binding agent where Hal is chlorine or bromine and R2 and R3 have the meaning given under formula I. 12. A process for the preparation of the compounds of the formula I according to claim 1, in which R1 is hydrogen, characterized in that a 1,3,4-oxadiazolyloxy-aniline of the formula IV, in which R1 is hydrogen, is converted to 1 by means of phosgene Converts 3,4-oxadiazolyloxa-phenyl isocyanate of the formula VI, wherein X and Y have the meaning given under formula I, and this reacts with an amine of formula VII, wherein R2 and R3 have the meaning given under formula I. 13. A process for the preparation of the compounds of the formula I according to claim 1, in which R1 is C 1-C4-alkyl, characterized in that a 1,3,4-oxndiazolyloxy-aniline of the formula IV, in which R1 is C 1- C4-alkyte means, reacts with phosgene in the presence of an acid-binding agent to form the phenylcarbamoyl chloride of the formula VIa, where X and Y have the meaning given under formula I and R1 is G 1-G4-alkyl, and this reacts in the presence of an acid-binding agent with an amine of formula VII, where R2 and R3 have the meaning given under formula I. 14. Herbicidal agent, characterized in that it is in addition to carrier and / or other additives as an active ingredient at least one 1,3,4-oxadiazolyloxyphenylurea of formula I, claim 1 contains. 15. Herbicidal agent according to claim 14, characterized in that that it contains compounds according to any one of claims 2 to 10 as active ingredient. 16. Use of the compounds of the formula I according to claim 1 or agents containing them as selective herbicides. 17. Use of the 1,3,4-oxadiazolyloxyphenylureas according to claim 16 for pre- or post-emergence control of weeds in crops of useful plants. 18. Use of the 1,3,4-oxadiazolylloxaphenylureas of the formula I, according to claim 1, or agents containing them as plant growth regulators in stands of monocotyledonous plants. 19. Use according to claim 17 for combating weeds in Grain and cotton crops.