Herbicidal compositions and pyrazole derivatives

#This invention relates to the use of pyrazole derivatives as a herbicide and also to a certain group of new pyrazole derivatives.

#More particularly, it is concerned with a herbicidal composition which comprises as an active ingredient a compound having the formula ##STR3## (wherein R.sub.1 represents hydrogen atom or a lower alkyl group, R.sub.2 represents a lower alkyl group or a lower alkenyl group, X represents a halogen atom, nitro group, a lower alkyl group, a halogenated lower alkyl group, a lower alkoxy group, a lower alkanesulfonyl group, cyano group, a lower alkylthio group or an aliphatic acyl group and n is an integer of 1 to 4 and when n is 2, 3 or 4, X's may be the same or different), a salt thereof or an organic acid ester thereof, and an agriculturally acceptable carrier, with a method for the destruction of undesirable weeds which comprises applying to said weeds a herbicidal amount of the compound having the above formula (I), as well as with some new pyrazole derivatives having the formula ##STR4## (wherein R.sub.1 represents hydrogen atom or a lower alkyl group, R.sub.2 represents a lower alkyl group or a lower alkenyl group, Z represents a halogen atom, nitro group, a lower alkyl group, a halogenated lower alkyl group, a lower alkoxy group, a lower alkanesulfonyl group, cyano group, a lower alkylthio group, an aliphatic acyl group or benzoyl group, n is an integer of 1 to 4, when n is 2, 3 or 4, Z's may be the same or different and Y represents oxygen atom or sulfur atom; provided that those wherein R.sub.1 and R.sub.2 are methyl groups, Z is chlorine atom at 2-position, n is 1 and Y is oxygen atom and wherein R.sub.1 and R.sub.2 are methyl groups, Z is nitro group at 4-position, n is 1 and Y is oxygen atom are employed.

#The compounds of the above-mentioned formula (I) may be present in the form of the tantomerism as shown under. ##STR5## (wherein R.sub.1, R.sub.2, X, and n have the same meanings as above). It is, of course, to be noted that the same tantomerism as shown above may be observed with respect to the compounds (II).

#In 22 ml. of dry dioxane is dissolved 2.24 g. of 1,3-dimethyl-5-pyrazolone and then 2.96 g. of calcium hydroxide is added thereto. 3.71 g. of p-nitrobenzoyl chloride is added dropwise thereto while stirring at room temperature. After completion of the dropwise addition, the mixture is heated under reflux for 1 hour. After completion of the reaction, the reaction mixture is allowed to cool and then 40 ml. of a 2 N hydrochloric acid solution is added thereto. Crystalline substances thus separated are recovered by filtration and washed with water to give 4.38 g. of crude crystals. This product is recrystallized from methanol to give 3.62 g. of the desired product as pale yellow columns having a melting point of 234.degree.-235.degree. C. Yield 69.3%

#Analysis for C.sub.12 H.sub.11 N.sub.3 C.sub.4 (%): Calculated: C, 55.17; H, 4.24; N, 16.09. Found: C, 55.17; H, 4.14; N, 16.06.

#In 65 ml. of isopropanol are suspended 4.48 g. of 1,3-dimethyl-5-pyrazolone and 3 g. of calcium hydroxide and the resulting suspension is heated under reflux for 30 minutes with stirring. After cooling, 8.4 g. of 2,4-dichlorobenzoyl chloride is added dropwise thereto. After completion of the dropwise addition, the mixture is heated under reflux for 2 hours. The solvent is distilled off from the reaction mixture and 15 ml. of water is added to the residue. The mixture is made acidic with 23 ml. of a 2 N hydrochloric acid solution and extracted with 60 ml. of chloroform. The chloroform layer is washed with water and the organic phase is separated and dried. The chloroform is distilled off. The residue is recrystallized from ethanol to give 7.6 g. of the desired product as colorless prisms of mp. 165.degree.-166.degree. C. Yield 66.7%