NO753099L - - Google Patents

Description

"Thiadiazole derivatives with herbicidal action".

The present invention relates to thiadiazole derivatives with herbicidal action and more particularly 1-thiadiazolyl-6-acyloxytetrahydropyrimidinones with the general formula:

where R is alkyl, alkenyl, haloalkyl, alkoxy, alkylthio, alkylsulfonyl, alkylsulfonyl or cycloalkyl, R 2 is alkyl, alkenyl, haloalkyl or 4 5 3 where R and R are each hydrogen or alkyl and R is hydrogen or where R is alkyl, haloalkyl . alkenyl, lower chloroalkyl, lower bromoalkyl, trifluoromethyl, lower alkoxy, lower alkylthio, lower alkylsulfonyl, lower alkylsulfinyl or cycloalkyl having 2 from 3 to 7 carbon atoms, R is lower alkyl, lower alkenyl, lower chloroalkyl, lower bromoalkyl or 4 5 3 where R and R each is hydrogen or lower alkyl, and R is hydrogen or where R<6>is lower alkyl, lower chloroalkyl, lower bromoalkyl, lower alkenyl, lower alkoxyalkyl, cycloalkyl having from 3 to 7 carbon atoms or

where X is lower alkyl, lower alkoxy, halogen or lower haloalkyl, and m and n are each numbers from 0 to 3.

The term "lower" as used herein denotes a linear or branched carbon chain of up to six carbon atoms.

The compounds according to the invention are unexpectedly useful as herbicides.

3 The compounds according to the invention where R is

and R' is as described above, can be prepared by reacting a corresponding compound according to the invention where R 3 is hydrogen having the formula 1 2 where R and R are as described above, with an acid anhydride of the formula where R^ is as described above, in the presence of a catalytic amount of toluenesulfonic acid. This reaction can be carried out by combining the reactants and the catalyst at room temperature in an inert organic reaction medium and then heating the reaction mixture on a steam bath at a temperature of from 50 to 90°C with stirring for a period of from 1/2 to 4 hours. The reaction mixture can then be cooled and the desired product can be obtained by filtration if a precipitate has formed or by evaporation of the organic reaction medium if the product is soluble in it. In some cases, the acid anhydride can be used as solvent for the compound of formula II, which makes the use of an inert solvent as reaction medium redundant. When lower alkanoic anhydrides are used, water can be added to the reaction mixture to precipitate the desired product when the reaction is complete. The product can then be purified by using conventional methods such as e.g. recrystallization and the like. 3 The compound according to the invention where R is can also be prepared by reacting the compound of formula II with an acid halide of the formula

where R is as described above, in the presence of an acid acceptor such as e.g. a tertiary amine. This method can be used when the desired anhydride of formula III is not available. This reaction can be carried out by slowly adding acid

the chloride of formula IV with stirring to a solution of approx. equimolar amount of the compound of formula II in an inert organic solvent in the presence of an acid acceptor at a temperature of approx. 10 to 30°C. After the addition is complete, the reaction mixture can be heated to a temperature varying up to the reflux temperature of the mixture to ensure that the reaction is completed. The desired product can then be obtained by first filtering the reaction mixture to remove the acid acceptor chloride, followed by evaporation of the solvent if the product is soluble in it, or, if present as a precipitate, by filtration and subsequent washing and purification.

The compounds according to the invention where R 3 is hydrogen can be prepared by heating a compound with the formula:

12 7 8

where R and R are as described above and R and R are methyl or ethyl, in a dilute, aqueous, acidic reaction medium for a period of approx. 10 to approx. 60 minutes. Temperatures of from approx. 70°C

until the reflux temperature of the reaction mixture can be used. The reaction medium may comprise a dilute, aqueous, inorganic acid such as, for example hydrochloric acid in a concentration of from approx. 0.5 to approx. 5%. When the reaction is finished, the desired product can be obtained as a precipitate by cooling the reaction mixture. This product can be used as is or can be further purified by using conventional methods such as e.g. recrystallization and the like.

The compounds of formula IV can be prepared

by reacting one mole of an isocyanate dimer with the formula:

where R 1 is as described above, with approx. two moles of an acetal with the formula: 2 7 8 '' "* ' where R , R and R are as described above. This reaction can be carried out by heating a mixture of the isocyanate dimer and the acetal in an inert organic reaction medium such as e.g. benzene at the reflux temperature of the reaction mixture. Heating under reflux may be continued for a period of from about 2 to about 30 minutes to ensure completion of the reaction. Thereafter, the desired product may be obtained by evaporation of the reaction medium and may be used as is or may is further purified by using standard techniques in the field. The isocyanate dimer of formula VI can be prepared by reacting a thiadiazole of the formula: where R is as described above, with phosgene. This reaction can be carried out by adding a slurry or solution of the thiadiazole in a suitable organic solvent such as ethyl acetate, to a saturated solution of phosgene in an organic solvent such as ethyl acetate The resulting mixture can be stirred v ed ambient temperature for a period of from approx. 4 to approx. 24 hours. The reaction mixture can then be purged with nitrogen gas to remove unreacted phosgene. The desired product can then be obtained by filtration if it is present in the form of a precipitate or by evaporation of the organic solvent used if the product is soluble in it. This product can be used as is or can be further purified if desired. Examples of thiadiazoles with formula VIII which can be used for the preparation of the compounds according to the invention are: 5-methyl-2-amino-1,3,4-thiadiazole, 5-ethyl-2-amino-1,3,4-thiadiazole, 5-propyl-2-amino-1,3,4-thiadiazole, 5-allyl-2-amino-1,3,4-thiadiazole, 5-pent-3-enyl-2-amino-1,3,4- thiadiazole, 5-chloro-methyl-2-amino-1,3,4-thiadiazole, 5-(3-chloroethyl-2-amino-1, 3, 4-thiadiazole, 5-^-chloropropyl-2-amino-1 ,3,4-thiadiazole, 5-trichloromethyl-2-amino-1,3,4-thiadiazole, ;i 5-methoxy-2-amino-1,3,4-thiadiazole, 5-ethoxy-2-amino-1 ,3,4-thiadiazole, 5-propoxy-2-amino-1,3,4-thiadiazole, 5-butyloxy-2-amino-1,3,4-thiadiazole, 5-hexyloxy-2-amino-1,3 ,4-thiadiazole, 5-methylthio-2-amino-1,3,4-thiadiazole, 5-ethylthio-2-amino-1,3,4-thiadiazole, 5-propylthio-2-amino-1,3,4 -thiadiazole, 5-butylthio-2-amino-1,3,4-;thiadiazole, 5-methylsulfonyl-2-amino-1,3,4-thiadiazole, 5-ethylsulfonyl-2^amino-1,3,4- thiadiazole, 5-butylsulfonyl-2-amino-1,3,4-thiadiazole, 5-methylsulfinyl-2-amino-1,3,4-thiadiazole, 5-ethylsulfinyl-2-amino-1,3,4-thiadiazole, 5-propylsulfinyl-2-am ino-1,3,4-thiadiazole, 5-t-butyl-2-amino-1,3,4-thiadiazole, 5-trifluoromethyl-2-amino-1,3,4-thiadiazole, 5-cyclopropyl-2- amino-1,3,4-thiadiazole, 5-cyclobutyl-2-amino-1,3,4-thiadiazole, 5-cyclopentyl-2-amino-1, 3, 4-thiadiazole, 5-cyclohexyl-2-amino- 1,3,4-thiadiazole, 5-cycloheptyl-2-amino-1,3,4-thiadiazole and the like. ;The acetal of formula VII can, when it is not readily available, be prepared by reacting an amine of formula ; ; where R 2 is as defined above, with the dimethyl or diethyl acetal of p-bromopropionaldehyde. This reaction can be carried out by combining from approx. 1 to approx. 2 mol of the amine of formula IX with a molar amount of the acetal of p-bromopropionaldehyde in an approximately equimolar ratio in an inert organic reaction medium such as e.g. methanol. The reaction mixture can then be heated under reflux for a period of from approx. 4 to approx. 8 hours. The reaction mixture can then be cooled to room temperature and an alkali metal hydroxide or carbonate can be added in an amount sufficient to neutralize the reaction mixture. Stirring can be continued at room temperature for up to approx. 24 hours to ensure the break is complete. The reaction mixture can then be filtered and the filtrate distilled under reduced pressure so that the desired product is obtained. ;Examples of compounds of formula IX are: methylamine, ethylamine, propylamine, isopropylamine, n-butylamine, t-butylamine, pentylamine, hexylamine, allylamine, propargylamine, 2-butenylamine, 3-butenylamine, 3-pentenylamine, 4-pentenylamine, 5 -hexenylamine, l-methyl-2-propynylamine, 1,l-dimethyl-2-propynylamine, l-ethyl-2-propynylamine, 1,l-diethyl-2-propynylamine, 1-propyl-2-propynylamine, 1 „1-dipropyl-2-propylylamine, 1-chloroallylamine, 1-bromoallylamine, 4-chloro-2-butenylamine, 6-chloro-4-hexenylamine and the like. Examples of suitable acid anhydrides of formula II are: acetic anhydride, propionic anhydride, butanoic anhydride, pentanoic anhydride; hexanoic anhydride, acrylic anhydride, butenoic anhydride, pentenoic anhydride, chloroacetic anhydride, bromoacetic anhydride, p-chlorobutanoic anhydride, cyclohexylcarboxylic anhydride, benzoic anhydride, toluene anhydride, 4-chlorobenzoic anhydride, 3- bromobenzoic acid anhydride, 4-fluorobenzoic anhydride, 4-methoxybenzoic anhydride, 4-ethoxybenzoic anhydride, 4-chloromethylbenzoic anhydride, 4-trifluoromethylbenzoic anhydride, 3,4,5-trichlorobenzoic anhydride, phenylacetic anhydride acid anhydride, 4-methylphenylacetic anhydride, p-phenylpropionic anhydride, t-phenylbutanoic anhydride, propionic anhydride, butyric anhydride, methoxyacetic anhydride, p-methoxypropionic anhydride, ^-ethoxybutanoic anhydride and the like. Examples of suitable acid chlorides of formula IV which can be used for the preparation of the compounds according to the invention are the acid halides of the same acids given above in the examples of acid anhydrides. The method for producing the compounds according to the invention is more particularly illustrated in the following examples. ;Example 1. ;Preparation of 5-methyl-1,3,4-thiadiazol-2-yl-isocyanate dimer. ;A saturated solution of phosgene in ethyl acetate (100 ml) is added to a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-methyl-2-amino-1,3,4-thiadiazole (40 grams) in ethyl acetate (300 ml) is added to the reaction vessel and the resulting mixture is stirred for approx. 16 hours, resulting in the formation of a precipitate. The reaction mixture is then blown through with nitrogen gas to remove unreacted phosgene. ;The purified mixture is then filtered to preserve the precipitate. The precipitate is then recrystallized and the desired product, 5-methyl-1,3,4-thiadiazol-2-yl-isocyanate dimer, is obtained. ;Example 2. ;Preparation of 3-methylaminopropionaldehyde-dimethyl acetal. ;Methylamine (1.0 mol), 3-bromopropionaldehyde-dimethyl acetal (0.5 mol) and methanol (100 ml) are added to a glass reaction vessel equipped with a mechanical stirrer, a thermoneter and a reflux condenser. The reaction mixture is heated at reflux with stirring for approx. 4 hours. The reaction mixture is then cooled to room temperature and sodium hydroxide (20 grams) is added. The reaction mixture is then stirred for a further approx. 8 hours. The reaction mixture is then filtered and the filtrate is distilled under reduced pressure so that the desired product, ε-methyl-aminopropionaldehyde-dimethyl acetal, is obtained. ;Example. 3. Preparation of 3-[1-methyl-3-(5-methyl-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde dimethyl acetal. ;A mixture of 5-methyl-1,3,4-thiadiazol-2-yl-isocyanate dimer (0.05 mol), 3-methylaminopropionaldehyde dimethyl acetal (0.1 mol) and benzene (60 ml) is added to a glass reaction vessel with a mechanical stirrer and reflux cooler. The reaction mixture is heated under reflux. for about. 15 minutes. The benzene is then evaporated from the mixture under reduced pressure and a solid product is obtained as a residue. The residue is then recrystallized so that the title compound is obtained. Example 4. Preparation of tetrahydro-1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-methyl-3-(5-methyl-1,3,4-thiadiazol-2-yl) ureido]propionaldehyde dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are added to a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The reaction mixture is then filtered while hot and the giltrate is cooled so that a precipitate forms. The precipitate is taken care of by filtration, dried and recrystallized so that the title compound is obtained. ;Example 5. ;Preparation of tetrahydro-1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-methyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), acetic anhydride (0.11 mol ), toluenesulfonic acid (0.05 gram) and benzene (100 ml) are added to a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated on a steam bath with stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue behind. The residue is recrystallized so that the title compound is obtained. ;Example 6. ;Preparation of 5-methoxy-1,3,4-thiadiazol-2-yl-isocyanate dimer. ;A saturated solution of phosgene in ethyl acetate (100 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-methoxy-2-amino-1,3,4-thiadiazole (40 grams) in ethyl acetate (300 ml) is added to the reaction vessel and the resulting mixture is stirred for approx. 16 hours, resulting in the formation of a precipitate. The reaction mixture is then blown through with nitrogen gas to remove unreacted phosgene. The purified mixture is then filtered to preserve the precipitate. The precipitate is recrystallized so that the desired product, 5-methoxy-1,3,4-thiadiazol-2-yl-isocyanate dimer, is obtained. ;Example 7. ;Preparation of 3-ethylaminopropionaldehyde-dimethyl acetal. ;Ethylamine (2.0 mol), 3-bromopropionaldehyde-dimethyl acetal (1.0 mol) and methanol (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux with stirring for approx. 5 hours. The reaction mixture is then cooled to room temperature and sodium hydroxide (20 grams) is added. The reaction mixture is then stirred for a further approx. 12 hours. The reaction mixture is then filtered and the filtrate is distilled under reduced pressure so that the desired product, 3-ethylaminopropionaldehyde-dimethyl acetal, is obtained. ;Example 8. ;Preparation of 3-[1-(ethyl-3-(5-methoxy-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde-dimethyl acetal. ;A mixture of 5-methoxy-1 ,3,4-thiadiazol-2-yl isocyanate dimer (0.05 mol), 3-ethylaminopropionaldehyde dimethyl acetal (0.1 mol) and benzene (60 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and reflux condenser. The reaction mixture is heated under reflux for about 15 minutes. The benzene is then evaporated from the mixture under reduced pressure so that a solid product is obtained as a residue. The residue is then recrystallized so that the title compound is obtained. ;Example'9. ;Preparation of tetrahydro-1-( 5-Methoxy-1,3,4-thiadiazol-2-yl)-3-ethyl-6-hydroxy-2(1H)-pyrimidinone.;3-[1-ethyl-3-(5-methoxy-1,3 ,4-thiadiazol-2-yl) ureido]propionaldehyde dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for about 15 minutes the extract is then filtered while it is hot and the filtrate is cooled so that a precipitate is formed. This precipitate is taken care of by filtration, dried and recrystallized so that the title compound is obtained. ;Example 10. ;Preparation of. tetrahydro-1-(5-methoxy-1,3,4-thiadiazol-2-yl)-3-ethyl-6-propionyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-methoxy-1,3,4-thiadiazol-2-yl)-3-ethyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), propionic anhydride (0.11 mol ), toluenesulfonic acid (0.05 gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated on a steam bath while stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue. The residue is recrystallized so that the title compound is obtained. ;Example 11. ;Preparation of 5-methylthio-1,3,4-thiadiazol-2-yl-isocyanate dimer. ;A saturated solution of phosgene in ethyl acetate (100 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-methylthio-2-amino-1,3,4-thiadiazole (45 grams) in ethyl acetate (300 ml) is added to the reaction vessel and the resulting mixture is stirred for approx. 16 hours, whereby a precipitate occurs. The reaction mixture is then blown through with nitrogen gas to remove unreacted phosgene. The purified mixture is then filtered to preserve the precipitate. The precipitate is recrystallized so that the desired product, 5-methylthio-1,3,4-thiadiazol-2-yl-isocyanate dimer, is obtained. Example 12. Preparation of 3-propylaminopropionaldehyde. dimethyl acetal. Propylamine (2.0 mol), 3-bromopropionaldehyde-dimethylacetal (1.0 mol) and methanol (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux with stirring for approx. 3 hours. The reaction mixture is then cooled to room temperature and sodium hydroxide (20 grams) is added. The reaction mixture is then stirred for a further approx. 6 hours. The reaction mixture is then filtered and the filtrate is distilled under reduced pressure so that the desired product, 3-propyl-amino-propionaldehyde-dimethyl acetal, is obtained. ;Example 13. ;Preparation of 3-[1-propyl-3-(5-methylthio-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde dimethyl acetal. ;A mixture of 5-methylthio-1,3,4-thiadiazol-2-yl-isocyanate dimer (0.05 mol), 3-propylaminopropionaldehyde dimethyl acetal (0.1 mol) and benzene (60 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer and reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The benzene is then evaporated from the mixture under reduced pressure so that a solid product is obtained as a residue. The residue is then recrystallized so that the desired product, 3-[1-propyl-3-(5-methylthio-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde dimethyl acetal, is obtained. Example 14. Preparation of tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-propyl-3-(5-methylthio-1,3,4-thiadiazol-2-yl)ureido]propionaldehyde dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The reaction mixture<n>is then filtered while hot and the filtrate is cooled to form a precipitate. The precipitate is collected by filtration, dried and recrystallized so that the desired product, tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-hydroxy-2(1H)- pyrimidinone. Example 15. Preparation of tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-butanoyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), butanoic anhydride (0.11 mol ), toluenesulfonic acid (0.05) gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated on a steam bath with stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue. The residue is recrystallized so that the desired product, tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-butanoyloxy-2(1H)-pyrimidinone, is obtained. ;Example 16. ;Preparation of 5-methylsulfonyl-1,3,4-thiadiazol-2-yl isocyanate dimer. ;A saturated solution of phosgene in ethyl acetate (100 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-methylsulfonyl-2-amino-1,3,4-thiadiazole (50 grams) in ethyl acetate (300 ml) is added to the reaction vessel and the resulting mixture is stirred for approx. 16 hours, resulting in the formation of a precipitate. The reaction mixture is then blown through with nitrogen gas to remove unreacted phosgene. The purified mixture is then filtered so that the precipitate is taken care of. The precipitate is recrystallized so that the desired product, 5-methylsulfonyl-1,3,4-thiadiazol-2-yl-isocyanate dimer, is obtained. ;Example 17. ;Preparation of 3-allylaminopropionaldehyde-dimethyl acetal. Allylamine (1.0 mol), 3-bromopropionaldehyde-dimethylacetal (0.5 mol) and methanol (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermoneter and a reflux condenser. The reaction mixture is heated under reflux with stirring for approx. 8 hours. The reaction mixture is then cooled to room temperature and sodium hydroxide (20 grams) is added. The reaction mixture is then stirred for a further approx. 14 hours. The reaction mixture is filtered and the filtrate is distilled under reduced pressure so that the desired product, 3-allylaminopropionaldehyde-dimethyl acetal, is obtained. ;Example 18. ;Preparation of 3-[1-allyl-3-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-ureido]propionaldehyde dimethyl acetal. ;A mixture of 5-methylsulfonyl-1,3,4-thiadiazol-2-yl-isocyanate dimer (0.05 mol), 3-allylaminopropionaldehyde dimethyl acetal (0.1 mol) and benzene (60 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The benzene is then evaporated from the mixture under reduced pressure so that a solid product is obtained as a residue. The residue is then recrystallized so that the title compound is obtained. ;Example 19. ;Preparation of tetrahydro-1-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-methyl-3-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde-dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are introduced in a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The reaction mixture is then filtered while it is warm and the filtrate is cooled so that a precipitate is formed. The precipitate is collected by filtration, dried and recrystallized so that the desired product, tetrahydro[1-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-hydroxy-2(1H)-pyrimidinone , is achieved. ;Example 20. ;Preparation of tetrahydro-1-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-cyclohexylcarbonyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), cyclohexanecarboxylic acid anhydride ( 0.11 mol), toluenesulfonic acid (0.05 gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated, on a steam bath while stirring for approx. 2 hours. The mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue. The residue is recrystallized so that the desired product, tetrahydro-1-(5-methylsulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-cyclohexyl-carbonyl-oxy-2(1H)-pyrimidinone, is obtained . ;Example 21 . ;Preparation of 5-cyclopropyl-1,3,4-thiadiazol-2-yl-isocyanate dimer. A saturated solution of phosgene in ethyl acetate (100 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-cyclopropyl-2-amino-1,3,4-thiadiazole (50 grams) in ethyl acetate (300 ml) is added to the reaction vessel and the resulting mixture is stirred for approx. 16 hours, whereby a precipitate is obtained. The reaction mixture is then blown through with nitrogen gas to remove unreacted phosgene. The purified mixture is then filtered to preserve the precipitate. The precipitate is then recrystallized so that the desired product, 5-cyclopropyl-1,3,4-thiadiazol-2-yl-isocyanate dimer, is obtained. ;Example 22. ;Preparation of 3-propargylaminopropionaldehyde dimethyl acetal. ;Propargylamine (2.0 mol), 3-bromopropionaldehyde dimethylacetal (1.0 mol) and methanol (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux with stirring for approx. 6 hours. The reaction mixture is then cooled to room temperature and sodium hydroxide (20 grams) is added. The reaction mixture is then stirred for a further approx. 18 hours. The reaction mixture is then filtered and the filtrate is distilled under reduced pressure so that the desired product, 3-propargylaminopropionaldehyde^dimethyl acetal, is obtained. ;Example 23. ;Process of 3-[1-propargyl-3-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-ureido]propionaldehyde dimethyl acetal. ;A mixture of 5-cyclopropyl-1,3,4-thiadiazol-2-yl-isocyanate dimer (0.05 mol), 3-propargylaminopropionaldehyde dimethyl acetal (0.1 mol) and benzene (60 ml) is introduced into a glass reaks ion vessel equipped with a mechanical stirrer and a reflux cooler. The reaction mixture is heated under reflux for approx. 15 minutes. The benzene is then evaporated from the mixture under reduced pressure so that a solid product is obtained as a residue. Recrystallize the residue so that the desired product, 3-[1-propargyl-3-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)ureido]propionaldehyde dimethyl acetal, is obtained. ;Example 24.1;Preparation of tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-propargyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-propargyl-3-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)ureido]propionaldehyde dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are introduced in a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The reaction mixture is then filtered while hot and the filtrate is cooled so that a precipitate forms. The precipitate is collected by filtration, dried and recrystallized so that the desired product, tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-3-propargyl-6-hydroxy-2(1H)-pyrimidinone , is achieved. ;Example 25. ;Preparation of tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-3-propargyl-6-benzoyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-3-propargyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), benzoic anhydride (0.11 mol ), toluenesulfonic acid (0.05 gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated on a steam bath with stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure. A residue is obtained which is recrystallized and gives the desired product, tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-3-propargyl-6-benzoyloxy-2(1H)-pyrimidinone, ; Example 26. Preparation of 5-trifluoromethyl-1,3,4-thiadiazol-2-yl-isocyanate dimer. ;A saturated solution of phosgene in ethyl acetate (100 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-trifluoromethyl-2-amino-1,3,4-thiadiazole (45 grams) in ethyl acetate (300 ml) was added to the reaction vessel and the resulting mixture was stirred for approx. 16 hours so that a precipitate formed. The reaction mixture was then purged with nitrogen gas to remove unreacted phosgene. The purified mixture was filtered and 48 grams of a white solid was obtained. This solid was recrystallized from dimethylformamide and the desired product 5-trifluoromethyl-1,3,4-thiadiazol-2-yl-isocyanate dimer was obtained. ;Example 27. ;Preparation of 3-[1-methyl-2-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-ureido]propionaldehyde dimethyl acetal. ;A mixture of 5-trifluoromethyl-1,3,4-thiadiazol-2-yl-isocyanate dimer (9.5 grams), 3-methyl-aminopropionaldehyde dimethylacetal (5.8 grams) and benzene (60 ml) is introduced in a glass reaction vessel equipped with a mechanical stirrer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The benzene is then evaporated from the mixture under reduced pressure, whereby a solid product is obtained as a residue. This product is recrystallized so that the desired product, 3-[1-methyl-3-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde dimethyl acetal, is obtained. ;Example 28. ;Preparation of tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-methyl-3-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde-dimethyl acetal (15 grams), water (400 ml) and hydrochloric acid (4 ml) are introduced in a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is heated under reflux for approx. 15 minutes. The reaction mixture is filtered while it is hot and the filtrate is cooled, whereby a precipitate is obtained. The precipitate is collected by filtration, dried and recrystallized so that the desired product, tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone ; is achieved. ;Example 29. ;Preparation of tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), acetic anhydride (0, 11 mol), toluenesulfonic acid (.0.05 gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermoneter. The reaction mixture is heated in a water bath while stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue. The residue is recrystallized so that the desired product, tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone, is obtained. ;Example 30. ;Preparation of 5-t-butyl-1,3,4-thiadiazol-2-yl-isocyanate dimer. A saturated solution of phosgene in ethyl acetate (100 ml) was introduced into a glass reaction vessel equipped with a mechanical stirrer. A slurry of 5-t-butyl-2-amino-1,3,4-thiadiazole (10 grams) in ethyl acetate (300 mL) was added to the reaction vessel and the resulting mixture was stirred for approx. 16 hours so that a precipitate formed. The reaction mixture was purged with nitrogen gas to remove unreacted phosgene. The purified mixture was then filtered so that the desired product, 5-t-butyl-1,3,4-thiadiazol-2-yl-isocyanate dimer, was obtained as a solid with a melting point of 261-263°C. ;Example 31. ;Preparation of 3-[1-methyl-3-(5-t-butyl-1,3,4-thiadiazol-2-yl)ureido]-propionaldehyde dimethyl acetal. ;A mixture of 5-t-butyl-1,3,4-thiadiazol-2-yl-isocyanate dimer (6 grams), 3-methylaminopropionaldehyde-dimethyl acetal (4.0 grams) and benzene (50 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer and a reflux condenser. The reaction mixture is heated under reflux with stirring for approx. 5 minutes. The benzene is then evaporated from the reaction mixture so that a residue is obtained. The residue is recrystallized so that the desired product, 3-[1-methyl-3-(5-t-butyl-1,3,4-thiadiazol-2-yl) ureido]propionaldehyde dimethyl acetal, is obtained. ;Example 32. ;Preparation of tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone. ;3-[1-methyl-3-(5-t-butyl-1,3,4-thiadiazol-2-yl) ureido]-propionaldehyde dimethyl acetal (16 grams), concentrated hydrochloric acid (10 ml) and water ( 500 ml) is introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. The reaction mixture is filtered while hot and the filtrate is cooled, resulting in a precipitate. The precipitate is collected by filtration, dried and recrystallized so that the desired product, tetrahydro-1-(5-t-tbutyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H )-pyrimidinone, is obtained. ;Example 33. ;Preparation of tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone (0.1 mol), acetic anhydride (0, 11 mol), toluenesulfonic acid (0.05 gram) and benzene (100 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer and a thermometer. The reaction mixture is heated in a steam bath with stirring for approx. 2 hours. The reaction mixture is then cooled to room temperature and the solvent is evaporated under reduced pressure, leaving a residue. The residue is recrystallized so that the desired product, tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone, is obtained. ;Example 34. ;Preparation of tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-benzoyloxy-2(1H)-pyrimidinone. ;Tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone (0.05 mol), triethylamine (0.06 mol ) and benzene (50 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. Benzoyl chloride (0.05 mol) is then added dropwise with stirring. After the addition is complete, the reaction mixture is heated under reflux with continued stirring for approx. 30 minutes. The reaction mixture is then filtered and the solvent is evaporated from the filtrate under reduced pressure so that a solid test is obtained. The residue is recrystallized so that the desired product, tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-benzoyloxy-2(1H)-pyrimidinone, is obtained. Example 35. Preparation of tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-benzoyloxy-2(1H)-pyrimidinone. ;i ;Tetrahydrid-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone (0.05 mol), triethylamine ( 0.06 mol) and benzene (50 ml) are introduced into a glass reaction vessel equipped with a mechanical stirrer, a thermometer and a reflux condenser. Benzoyl chloride (0.05 mol) is then added dropwise with worm stirring. After the addition is complete, the reaction mixture is heated under reflux with continued stirring for approx. 30 minutes. The reaction mixture is then filtered and the solvent is evaporated from the filtrate under reduced pressure so that a solid residue is obtained. The residue is recrystallized so that the desired product, tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-benzoyloxy-2(1H)-pyrimidinone, is obtained. Several compounds which are within the scope of the invention and which can be prepared by the methods in the preceding examples are: tetrahydro-1-(-ethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acryloyloxy -2(1H)-pyrimidinone, tetrahydro-1-(5-propyl-1,3,4-thiadiazol-2-yl)-3-butyl-6-but-3-enoyloxy-2(1H)-pyrimidinone, tetrahydro -1-(5-butyl-1.,3,4-thiadiazol-2-yl)-3-pentyl-6-pent-3-enoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-pentyl- 1,3,4-thiadiazol-2-yl)-3-hex-4-enoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-hexyl-1,3,4-thiadiazol-2-yl)- 3-pent-3-enyl-6-pentanoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-cyclopropyl-1,3,4-thiadiazol-2-yl)-3-hex-4-enyl-6 -hexanoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-cyclobutyl-1,3,4-thiadiazol-2-yl)-3-bromo-methyl-6-butanoyloxy-2(1H)-pyrimidinone, tetrahydro -1-(5-cyclopentyl-1,3,4-thiadiazol-2-yl)-3-trichloromethyl-6-chloroacetyl-oxy-2(1H)-pyrimidinone, tetrahydro-1-(5-cyclohexyl-1,3 ,4-thiadiazol-2-yl)-3-(3-chlorohexyl-6-bromoacetyloxy-2(1H)-pyrimidinone, tetrahydro-1 -(5-cyclohepty 1-1,3,4-thiadiazol-2-yl)-3-(3-bromomethyl-6-S-chlorobutanoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-allyl-1 ,3,4-thiadiazol-2-yl)-3-(1,1-diethylprop-2-ynyl)-6-cyclopropyl-carbonyloxy-2(1H9-pyrimidinone, tetrahydro-1-(5-but-3-enyl -1,3,4-thiadiazol-2-yl)-3-(1,1-dipropylprop-2-ynyl)-6-cyclobutyl-carbonyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-pent- 4-enyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-cyclopentylcarbonyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-hex-4-enyl-1,3,4 -thiadiazol-2-yl)-3-methyl-6-cyclohexylcarbonyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-chloromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6 -cycloheptyl-carbonyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-bromomethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-methylthiobenzoyloxy)-2(1H) -pyrimidinone, tetrahydro-1-(5-trichloromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-ethylthiobenzoyloxy)-2 ( my -pyrimidinone, tetrahydro-1-(5- (3-chloroethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(3-propylthiobenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-p-bromomethyl-1, 3,4-thiadiazole-2 -yl)-3-methyl-6-(3-hexylthiobenzoyloxy)-2(yne)-pyrimidinone, ;tetrahydro-1-(5- -chlorohexyl-1,3,4-thiadiazol-2-yl)-3-methyl -6-(3,4,5-trichlorobenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-ethoxy-1,3,4-thiadiazol-2-yl)-3-methyl-6-(3 -ethylbenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-propoxy-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-propylbenzoyloxy)-2(1H)- pyrimidinone, tetrahydro-1-(5-butoxy-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-butylbenzoyloxy);-2(1H)-pyrimidinone, tetrahydro-1-(5 -hexyloxy-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-hexylbenzoyloxy)-2(1H)-pyrimidinone, tetra-hydro-1-(5-ethylthio-1,3, 4-thiadiazol-2-yl)-3-methyl-6-(4-bromobenzoyl-oxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-propylthio-1,3,4-thiadiazol-2-yl )-3-methyl-6-(4-iodobenzoyloxy)-2(1H)-pyrimidinone, tetra-hydro-1-(5-hexylthio-1,3,4-thiadiazol-2-yl)-3-methyl-6 -(4-fluoro-benzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-ethylsulfonyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(2-ethoxybenzoyloxy)- 2(1H)-pyrimidinone, tetrahydro-1-(5-propylsulfonyl-1,3,4). -thiadiazol-2-yl)-3-methyl-6-(3-propoxybenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-butylsulfonyl-1,3,4-thiadiazol-2-yl)-3 -methyl-6-(4-hexyloxy-benzouloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-hexylsulfonyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(3 -chloromethylbenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-(5-ethylsulfinyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-trifluoromethylbenzoyloxy)-2(1H)- pyrimidinone, tetrahydro-1-(5-propylsulfinyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(4-S-bromomethylbenzoyloxy)-2(1H)-pyrimidinone, tetrahydro-1-( 5-hexylsulfinyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2 -yl)-3-methyl-6-bromoacetyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-trifluoromethyl-1>3,4-thiadiazol-2-yl)-3-methyl-6-f3- chloropropanoyl-oxy-2(1H)-pyrimidinone, tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-(3-bromopentanoyloxy-2(1H)-pyrimidinone , tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl- ;6- -chlorohexanoyloxy-2(1H)-pyri midinone, tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-but-3-enoyloxy-2(1H)-pyrimidinone, tetrahydro-1-( 5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-pent-4-enoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-t- butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hex-4-enoyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-t-butyl-1,3,4 -thiadiazol-2-yl)-3-methyl-6-but-3-ynyloxy-2(1H)-pyrimidinone, tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl) -3-methyl-6-hex-4-ynoyloxy-2(1H)-pyrimidinone and the like. For practical use as herbicides, the compounds according to the invention are usually mixed into herbicidal preparations which comprise an inert carrier and a herbicidally toxic amount of such a compound. Such herbicidal preparations, which can also be called formulations, make it possible to use the active compound in an appropriate manner in the place where the weed is found in a desired amount. These preparations can be solid substances such as e.g. dust, granules or wettable powders, or they can be liquids such as e.g. solutions, aerosols or emulsifiable concentrates. Dust can, for example, be produced by grinding and mixing the active compound with a solid, inert carrier such as e.g. talc, clay, silicon dioxide, pyrophyllite and the like. Granular preparations can be prepared by impregnating the compound, usually dissolved in a suitable solvent, onto and into granular carriers such as e.g. attapulgites or vermiculites, usually with a particle size of from approx. 0.3 to 1.5 mm. Wettable powders, which can be dispersed in water or oil to any desired concentration of the active compound, can be prepared by mixing wetting agents into concentrated dust preparations. In some cases, the active compounds are sufficiently soluble in common organic solvents such as e.g. kerosene or xylene, so that they can be used directly as solutions in these solvents. Solutions of herbicides can often be dispersed under superatmospheric pressure as aerosols. However, preferred liquid herbicidal preparations are emulsifiable concentrates, which comprise an active compound according to the invention and which inertly carry a solvent and an emulsifier. Such emulsifiable concentrates can be diluted with water and/or oil to desired concentrations of active compound for application as a spray in places where the weed is found. The most commonly used emulsifiers in these concentrates are non-ionic or mixtures of non-ionic and anionic surfactants. By using some emulsifiers, an inverted emulsion (water-in-oil) can be produced for direct application to the weeds. A typical herbicide preparation according to the invention is illustrated by the following example, where the amounts are given as parts by weight. Example* 36.

The above ingredients are mixed in a mechanical grinding-mixing machine and ground until a homogeneous, free-flowing dust with the desired particle size is obtained.' This dust is suitable for direct application on weed-infested sites.

The compounds according to the invention can be used

as herbicides in all ways recognized in the art. A method for combating weeds comprises bringing the site where the weed is found into contact with a herbicidal preparation comprising an inert carrier and, as a decisive, active ingredient in an amount that is herbicidally toxic to said weed, a compound according to the invention the concentration of the new compounds according to the invention in the herbicidal preparations will vary greatly with the type of preparation and the purpose for which it is intended, but usually the herbicidal preparations comprise from approx. 0.05 to approx. 95% by weight of the active compounds according to the invention. In a preferred embodiment of the invention, the herbicidal preparations comprise from approx. 5 to approx. 75% by weight of the active compound. The preparations may also include such additional substances as other pesticides, such as e.g. insecticides, nematocides, fungicides and the like, besides stabilizers, dispersants, inactivators, adhesives, adhesives, fertilisers, activators, synergistic agents and the like.

The compounds according to the invention are also useful when combined with other herbicides and/or defoliants, desiccants, growth inhibitors and the like in the herbicidal preparations described above. These other materials can include from approx. 5 to approx. 95% of the active ingredients in the herbicidal preparations'. Use of combinations of these other herbicides and/or defoliating agents, desiccants, etc. with the compounds, according to the invention, gives herbicidal preparations that are more effective for fighting weeds and often gives results that cannot be achieved with separate preparations of the individual herbicides.

Weeds are unwanted plants that grow in places

they should not be, they have no economic value and disturb

the production of cultivated crops and ornamental crops or may harm the health of livestock. Many weed types are known and include annual weeds such as sedge, sedge, foxtail, finger millet, field mustard, meadowsweet, common ryegrass, gooseberry, sedge, ryegrass, sedge, purslane, chickpea, "smartweed", knotweed, hook seed, wild buckwheat, kochia, snail columbine, ragwort, ragweed, dill, "coffeweed ", croton, "cuphea", creeping thread, earth smoke, field pig flower vdå, knavel, wart milk, common lindendel, "emex", jungle rice", tjønnaks, top goose flower, "carpetweed", wormwood, ant, duck food, "naiad", rye fax, autumn millet , prickly pear, common vetch, "switchgrass", "watergrass", "teaweed", wild turnips and "sprangletop", biennial weeds such as wild carrot, "matric-aria", wild barley, cock's comb, gooseberry, burdock, primrose, sedge, thistle, dog's tongue, "moth mullein" and violet thistle-bud, or perennial weeds such as white sedge, perennial ryegrass, vetch, Johnsongrass (a species of sorghum), eel thistle, beach-wort, Bermuda grass, sorrel, curly sorrel, cypress, sedum, dandelion, bluebell, fieldwort, Russian knotweed, "mesquit e", cod's mouth, common yarrow, asters, stone seed, sedge, "ironweed", "sesgania", sivax, dunkjevle, wintercress, sweet willow, "nutsedge", "milkweed" and scrinneblom.

Such weeds can be classified as broadleaf or grassy weeds. It is economically desirable to combat the growth of such weeds without harming useful plants or livestock.

The new compounds according to the invention are particularly valuable for weed control because they are toxic to many species and groups of weeds, while they are relatively non-toxic to many useful plants. The exact amount of compound required will depend on many factors, such as the resistance of the particular weed species in question, the weather, the type of soil, the method of application, which useful plants are in the same area and the like. While thus application of up to only approx. 0.7 or 1.4 g/yr may be sufficient for effective control of small populations of weeds growing under difficult conditions, application of 112 g/yr or more of an active compound may be necessary for effective control of large populations of stubborn perennial weeds that grow under favorable conditions.

The herbicidal toxicity of the new compounds according to the invention can be illustrated using many of the established test techniques known in the field, such as e.g. pre- and post-germination testing.

The herbicidal activity of the compds

according to was demonstrated by experiments carried out for pre-emergence control of various weeds. In these experiments, seeds of various weeds were sown in small plastic pots filled with dry soil. Twenty-four hours or less after sowing, the pots were sprayed with water until the soil was wet and the test compound in the form of an aqueous emulsion of an acetone solution containing emulsifiers was sprayed in the indicated concentrations on the soil surface.

After spraying, the soil containers were placed

in a greenhouse and supplied with heat as needed and watered daily

or more often. The plants were kept under these conditions for 21 days, at which time the condition of the plants and the degree of damage to the plants were assessed on a scale of 0 to 10,

as follows: 0 = no injury, 1, 2 = slight injury, 3, 4 = moderate injury, 5, 6 - moderately severe injury, 7, 8, 9 = severe injury and 10 = death. The efficacy of this compound is demonstrated by the data in Table I.

The herbicidal activity of the compds

according to the invention was also demonstrated by attempts at post-sprouting control of various weeds. In these experiments, the test compound was applied in the form of an aqueous emulsion and sprayed at the indicated dosage on the leaves of the weed after they had reached a prescribed size. After spraying, the plants were placed in greenhouses and watered daily or more often.

Water was not applied to the leaves of the treated plants. The degree of damage was determined 14 days after the treatment and was assessed

- according to the scale from 0 to 10 described above. The effectiveness of this compound is demonstrated by the data in Table I.

Claims (19)

1. Thiadiazole compound with herbicidal action, characterized in that it has the formula: where R is alkyl, alkenyl, haloalkyl, alkoxy, alkylthio, alkylsulfonyl, alkylsulfinyl or cycloalkyl, R 2 is alkyl, alkenyl, haloalkyl or 4 5 3 where R and R are each hydrogen or alkyl, and R is hydrogen or where R <6> is alkyl, haloalkyl, alkenyl, alkynyl, alkoxyalkyl, cycloalkyl or where X is alkyl, halogen, haloalkyl, nitro, cyano or alkoxy, and m and n are whole numbers from 0 to 3. 2. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-benzoyloxy-2(1H)-pyrimidinone. 3. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-ethyl-6-benzoyloxy-2(1H)-pyrimidinone . 4. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2-yl)-3-propyl-6-butanoyloxy-2(1H)-pyrimidinone. 5. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-methyl-sulfonyl-1,3,4-thiadiazol-2-yl)-3-allyl-6-cyclohexylcarbonyloxy-2(1H) -pyrimidinone. 6. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-methyl-sulfinyl-1,3,4-thiadiazol-2-yl)-3-propargyl-6-benzoyloxy-2(1H)-pyrimidinone . 7. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone. 8. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-t-butyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-acetyloxy-2(1H)-pyrimidinone . 9. Compound according to claim 1, characterized in that it is tetrahydro-1-(5-trifluoromethyl-1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone. 10. Connection according to claim 1, characterized in that it is.tetrahydro-1-(5-t-butyl- 1,3,4-thiadiazol-2-yl)-3-methyl-6-hydroxy-2(1H)-pyrimidinone. 11. Connection according to claim 1, characterized in that it is tetrahydro-1-(5-methylthio-1,3,4-thiadiazol-2J-yl)-3-propyl-6-hydroxy-2 (1H)-pyrimidinone. 12. Herbicidal preparation, characterized in that it comprises an inert carrier and as essential ingredient a compound according to claim 1 in an amount that is toxic to weeds. 13. Method for ug1 .ressb <ek> control, characterized in that it comprises bringing said weed into contact with a herbicidal preparation comprising an inert carrier and as essential active ingredient a compound according to claim 1 in an amount that acts oxic on weeds. 14. Process for producing a thiadiazolyl compound with herbicidal action with the formula: where R is alkyl, alkenyl, haloalkyl, alkoxy, alkylthio, 2 alkylsulfonyl, alkylsulfinyl or cycloalkyl, R is alkyl, alkenyl, haloalkyl or 4 5 where R and R are each hydrogen or alkyl, characterized in that an acetal with the formula: 12 7 8 where R and R are as described above and R and R are methyl or ethyl, is heated in a dilute, aqueous, acidic reaction medium. 15. Method according to claim 14, characterized in that the acetal is heated at a temperature in the range from approx. 70°C to the reflux temperature of the reaction medium. 16. Method according to claim 14, characterized in that the reaction medium comprises an aqueous, inorganic acid in a concentration of from approx. 0.5 to approx. 5% by weight. 17. Process for the preparation of a thiadiazolyl compound with herbicidal activity of the formula: where R"*" is alkyl, alkenyl, haloalkyl, alkoxy, alkylthio, alkylsulfonyl, alkylsulfinyl or cycloalkyl, R 2 is alkyl, alkenyl, haloalkyl or 4 5 6 where R and R are each hydrogen or alkyl and R is alkyl, haloalkyl, alkenyl, alkynyl, alkoxyalkyl, cycloalkyl or where X is alkyl, halogen, haloalkyl, nitro, cyano or alkoxy, and m and n are whole numbers 0 to 3, characterized in that a compound of formula: 12 where R and R are as described above, is reacted with an anhydride of the formula where R is as described above, in the presence of a catalytic amount of toluenesulfonic acid at a temperature of from approx. 50 to approx. 60°C. 18. Process for preparing a compound of formula where R is alkyl, alkenyl, haloalkyl, alkoxy, alkylthio, alkylsulfonyl, alkylsulfinyl or cycloalkyl, R 2 is alkyl, alkenyl, haloalkyl or 4 5 6 where R and R are each hydrogen or alkyl, and R is alkyl, haloalkyl, alkenyl, alkynyl, alkoxyalkyl, cycloalkyl or where X is alkyl, halogen, haloalkyl, nitro, cyano or alkoxy, and m and n are whole numbers from 0 to 3, characterized in that a compound of formula: 12 where R and R are as described above; is reacted with an acid halide of the formula where R <6> is as described above in the presence of an acid acceptor. 19. Method according to claim 18, characterized in that the reaction is carried out in an inert organic reaction medium at a temperature of from approx. 10 to approx. 30°C.