BG61838B1 - 2-(2'-methyl-3',4'-trisubstituted benzoyl)-1,3-cyclohexanedions, method for unwanted vegetation control and herbicidic composition using these compounds - Google Patents

Abstract

The invention relates to herbicidic compositions having theformulawhere R1 is hydrogen or C1-C4 alkyl, R2 is hydrogen or C1-C4alkyl, R3 is hydrogen or C1-C4 alkyl, R4 is hydroxy, hydrogen orC1-C4 alkyl or R3 and R4 together represent carbonyl (=0) providedthat R1, R2, R5 & R6 are C1-C4 alkyl, R5 is hydrogen or C1-C4alkyl, R6 is hydrogen, C1-C4 alkyl, C1-C4 alkylthio or C1-C4alkylsulphonyl provided that when R6 is C1-C4 alkylthio or C1-C4alkylsulphonyl, then R3 & R4 do not form together carbonyl, R7 ismethyl or ehtyl and R8 is halogen, nitro or RbSOn, n being aninteger 0 or 2, and Rb is C1-C4 alkyl. The invention also relatesto their salts.12 claims

Description

Technical field

The invention relates to 2- (2-methyl3,4'-trisubstituted benzoyl) -1,3-cyclohexanediones, to a method of combating unwanted vegetation and to a herbicidal composition using those compounds which are useful in the conservation of useful crops in agriculture .

BACKGROUND OF THE INVENTION

EP Application 0 186 120, published July 2, 1986, relates to 2- (2'-methyl-3,4-substituted benzoyl) -1,3-cyclohexane-1,3-dione known in the art and their use as herbicides. The compounds may have the following formula

3 ', 4'-trisubstituted benzoyl) -1,3-cyclohexanedione, to a method for combating unwanted vegetation and to a herbicidal composition containing these compounds.

New compounds of formula are included within the scope of the invention

wherein R ¹ to R ⁸ are substantially the same as those defined below except R ⁷ , which may be alkoxy or trifluoromethoxy.

The compounds of the invention exhibit unexpectedly greater herbicidal activity than the compounds cited in the prior art, or unexpectedly impair some cereals.

SUMMARY OF THE INVENTION

The invention relates to 2- (2'-methyl, wherein R ¹ is hydrogen or C 1 -C 4 -alkyl, preferably methyl, R ² hydrogen or C 1 -C ₄ alkyl, preferably methyl, R ³ -hydrogen or C] -C 4 -alkyl, preferably methyl, R ⁴ hydroxy, hydrogen or C 1 -C 4 -alkyl, preferably methyl, or R ³ and R ⁴ together are carbonyl (= O) provided that R ¹ , R ² , R ⁵ and R ⁶ are C 1 -C 4 -alkyl, preferably all are methyl, R ⁵ is hydrogen or C 1 -C ₄ -alkyl, preferably methyl, R ⁶ is hydrogen, C 1 -C 4 -alkyl, preferably methyl, C1-C4 alkylthio, preferably methylthio or C1-C4-alkylsulfonyl, preferably meth ifsulfonyl, provided that when R ⁶ is (C 1 -C 4 -alkylthio or (C 1 -C 4 -alkylsulfonyl), then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or ethyl and R ⁸ is (1) halogen , preferably chlorine or bromine (2) nitro, or (3) R ^b SOn- in which η is an integer 0 or 2, preferably 2, and R ^b is (a) C 1 -C ₄ -alkyl, preferably methyl or ethyl.

The term "C ₁ -C ₄ -alkyl" includes methyl, ethyl, η-propyl, isopropyl, n-butyl, vorbutyl, isobutyl and tert-butyl. The term "halogen" includes chlorine, bromine, iodine and fluorine.

The salts of the compounds described (as defined below) are also contemplated by the invention.

The compounds of the invention may be of the following four formulas due to the presence of tautomerism:

wherein R ¹ , R ² , R ³ , R ⁴ R ⁵ , R ⁶ , R ⁷ and R ⁸ are as defined above.

The enclosed proton in each of the four tautomers is moderately labile. These protons are acidic and can be taken off any base to give a single anion salt according to the following four resonance forms

characterized in that R ¹ , R ² , R ³ , R ⁴ , R ⁵ , R ⁶ , R 'and R ⁸ are as defined above.

Examples of cations on these bases are inorganic ions such as alkali metals, i. E. lithium, sodium and potassium or organic cations such as substituted ammonium, sulfonium or phosphonium. in which the substituent is an aliphatic or aromatic group.

The compounds of the invention and their salts are active herbicides of the general type. This means that they are herbicidal against a wide variety of plant species. The method of combating unwanted vegetation comprises administering, according to the invention, a herbicidal action amount of the described compounds to the area in which control is desired.

The compounds of the invention can be prepared by the following two-step general method.

The process goes through the preparation of an intermediate enol ester as shown in reaction (1). The final product is obtained by rearrangement of the enol ester as shown in reaction (2). The two reactions can be carried out as separate steps by isolating and separating the enol ester using conventional technique to the controlled step (2), or by adding a cyanide source to the reaction medium after the enol ester is formed, or in one step by incorporating of the cyanide source at the beginning of reaction / 1 /.

wherein R ¹ to R ⁸ are as defined and Y is halogen, preferably chlorine. C 1 -C ₄ alkyl-C (O) -O-, C 1 -C ₄ alkoxy-C (O) -O- or

in which R ⁷ and R ⁸ in this portion of the molecule are identical to those of the reagent shown above and the moderate base is as defined, preferably tri-C 1 -C ₆ alkylamine, pyridine, alkali metal carbonate or alkali metal. metallic phosphate.

Generally, in step (1) molar amounts of the dione and the substituted benzoyl reagent are used in conjunction with a molar amount or excess of base. The two reagents are mixed in an organic solvent such as metal chloride, toluene, ethyl acetate or dimethylformamide. The base or benzoyl reagent is added to the reaction mixture, preferably under cooling. The mixture was stirred at 0-50 ° C until the reaction was substantially complete.

The reaction product is treated in the conventional manner.

*

Moderate base

* = Cyanide source Moderate base = as determined in which R ¹ to R ⁸ are as defined.

Usually in step / 2/1 mol of the intermediate enol ester compound reacts with 1 to 4 mol of the base, preferably 2 mol of moderate base and 0.01 mol to about 0.5 mol or more, preferably about 0.1 mol of cyanide source / i.e. potassium cyanide or acetone cyanohydrin. The mixture is stirred in the reaction vessel until the rearrangement is substantially complete at below 80 ° C, preferably about 20 ° C to about 40 ° C, and the desired product is separated in the conventional manner.

The term "cyanide source" refers to a substance or substances which, under conditions of regrouping, contain or form a hydrogen cyanide and / or cyanide anion.

The process is carried out in the presence of a catalytic amount from a source of cyanide anion and / or hydrogen cyanide together with a molar excess of a moderate base with respect to the enol ester.

Preferred cyanide sources are alkali metal cyanides such as sodium or potassium cyanide, cyanohydrins of methyl having from 1-4 carbon atoms in the alkyl groups, such as acetone or methylisobutylketone cyanohydrins, cyanohydrins of benzaldehyde or of C ₂ -C ₅ aliphatic aldehydes such as acetaldehyde , propionaldehyde, etc. cyanohydrins, zinc cyanide, tri / lower alkyl / silyl cyanides, preferably trimethylsilyl cyanide, and hydrogen cyanide itself. Hydrogen cyanide has the greatest advantage because it causes a relatively rapid reaction and is not expensive. Among the cyanohydrins, the preferred cyanide source is acetone cyanohydrin.

The cyanide source is used in an amount up to about 50% molar, based on the enol ester. It can be applied at least about 1% molar to cause a detectable reaction rate on a small scale at about 40 ° C. Larger scale reactions produce more reproducible results at a slightly higher catalyst level of about 2% molar. Typically, about 1-10% of the cyanide source moles are preferred.

The process is run at a molar excess on a moderate basis with respect to the enol ester. The term "moderate base" means a substance that acts as a base but whose strength or activity as a base is between that of strong bases such as hydroxides (which may cause hydrolysis of the enol ester) and that of weak bases such as bicarbonates / which do not to act effectively. Moderate bases suitable for this purpose include both organic acids such as tertiary amines and inorganic bases such as alkali metal carbonates and phosphates. Suitable tertiary amines include trialkylamines such as triethylamine, trialkanolamines such as triethanolamine and pyridine. Suitable inorganic bases include potassium carbonate and trisodium phosphate.

The base is used in an amount of from about 1 to about 4 moles per molar enol ester, preferably about 2 moles per mol.

When the cyanide source is an alkali metal cyanide, in particular potassium cyanite, a phase transfer catalyst may be included in the reaction. Particularly suitable phase transfer catalysts are Crown Ethers.

Different solvents may be used in the reaction depending on the nature of the acid chloride or the acylated product. A preferred solvent for this reaction is 1,2-dichloroethane. Other solvents that may be used depending on the reagents or products include toluene, acetonitrile, methylene chloride, ethyl acetate, dimethylformamide and methyl isobutyl ketone (MlBK).

Usually, depending on the nature of the reagents and the cyanide source, the rearrangement can be carried out at temperatures up to about 50 ° C.

The substituted benzoyl chlorides described above can be prepared from the corresponding substituted benzoic acids according to Reagents for Organic Synthesis, Vol 1 L.G. Fieser and M. Fieser, pp - 767-769 (1967)

& which R ⁷ and R ⁸ are as described.

The described 5-hydroxy-4,4,6,6-tetra-substituted 1,3-cyclohexanediones can be prepared according to the following reaction.

in which R \ R ^2, R ⁵ and R ⁶ are as have been described and R ³ is a C _t -C ₄ alkyl.

In this reaction, the lithium compound is added to the solution of the Sinc Carboxylic acid reagent under controlled conditions and reacted at room temperature. The reaction solution was then acidified and the product separated in a conventional manner.

Substituted 1,3-cyclohexanedions according to the formula wherein R 1, R ² , R ⁵ and R ⁶ are as defined and R ⁶ is hydrogen.

In this reaction, NaBH ₄ is added to a basic methanolic solution of syncarboxylic acid under controlled conditions and it is carried out at room temperature. The reaction solution was acidified and the product was separated in a conventional manner.

When R ³ is C 1 -C ₄ alkyl, the dione can be obtained by reacting a nucleophile such as methyl-β tilithium with 4,4,6,6-tetra-substituted 1,3,5-cyclohexanthrion, as shown in the following reaction.

R ³ Li / THF

wherein R ¹ to R ⁵ are as described and R ⁶ is C 1 -C ₄ alkylthio or C 1 -C ₄ alkylsulfonyl can be prepared by a variety of general methods according to Modem Synthetic Reactions, 2-nd Edition, Chapter 9, HOHouse , WW A.Benjamin, Inc., Menlo Parc, CA (1972).

The intermediates of the trisubstituted benzoic acid chloride can be prepared by the following general method, as shown in the following scheme, in which R is C 1 -C ₄ alkyl, R ¹ is -CH 2 CH 2 OCH 3 or -CH 2 CH ² OC ² H 5, R ² is C] - C4 alkyl and X is halogen, preferably chlorine or bromine.

UNC

UNC

he

OH NO ₂

® kJco ₃

COOR

CH ₅ OR NO 2

(Fl ^R ' ^{Y w} KgCO3

R * Y K ₂ CO 3

COOR

COOR

COOR

COOR

NqOCI

UNC

0H ^{e he} e

X

UNC in

With regard to the scheme, in particular for the reaction steps from / A / to / J / the following should be considered:

Typically, in step (A) of the reaction, a molar amount of aniline hydrochloride reacts slowly with a slight molar excess of sodium nitrate and a molar excess of sulfuric acid.

The reaction temperature was maintained at about 0 ° C to 15 ° C until a solution was obtained. The solution was slowly added to the heated aqueous sulfuric acid solution and heated to reflux. The solid product as a result of the reaction is separated and purified by conventional methods.

In step (B) of the reaction, 2-methyl-3-hydroxybenzoic acid is reacted with C ₍ -C ₄ alcohol with concentrated sulfuric acid at reflux temperatures.) The reaction product is separated and purified in conventional manner.

In step (C) of the reaction, a molar amount of C 2 -C ₄ alkyl ester of 2-methyl-3-hydroxybenzoic acid is reacted with a molar amount of tertiary butylamine and 1 mol of bromine or chlorine in a solvent such as methylene chloride at -50 ° C to room temperature. .

In step (E) of the reaction, a mole amount of C 2 -C ₄ alkyl ester of 2-methyl-3-hydroxy -4-bromobenzoic acid is alkylated with a mole amount of the required alkylating agent such as C ₍ -C ₄ alkyl iodide or chloride or di-C 1 -C ₄ alkyl sulfate and a molar amount of a base such as potassium carbonate in a solvent such as a mixture of acetone and dimethylformamidine (DMF) The reaction may be carried out at reflux temperatures and the reaction product may be separated by conventional methods.

In step (E) of the reaction, a molar amount of 2-methyl-3-hydroxybenzoic acid C 1 -C ₄ alkyl ester is reacted with at least 2 mol of nitric acid in glacial acetic acid. The reaction may be carried out at room temperature. The reaction product is separated by conventional methods.

In step / F / reaction molar amount of C, -C ₄ alkyl ester of 2-methyl-S-hydroxy-4-nitrobenzoic acid is reacted with a molar amount of an appropriate alkylating agent such as C _{(-C 4} alkyl chloride or iodide or di- With C 1 -C ₄ alkyl sulfate and a molar amount of base such as potassium carbonate in a solvent such as a mixture of acetone and DMF The reaction is carried out at reflux temperatures and the reaction product is separated in a conventional manner.

In step / G / reaction molar amount of C, -C ₄ alkyl ester of 2-methyl-3- / C _at C ₄ alkoxy, _Ci-4 haloalkoxy 2-methoxyethoxy or 2-ethoxyethoxy / -4-bromobenzoic acid with a mole amount C ₁ -C ₄ alkyl mercaptan in the presence of a molar excess of a base such as potassium carbonate in a solvent such as dimethylformamide. The reaction is carried out for several hours at a temperature between 50 and 100 ° C and stirring under an inert atmosphere such as nitrogen. The desired reaction product is separated in a conventional manner.

| The reaction step (G) can also be carried out by reacting a molar amount of C ₁ -C ₄ alkyl ester of 2-methyl-

3- / C, -C, alkoxy, C, -C, haloalkoxy 2-methoxyethoxy, or 2-ethoxyethoxy / -4-bromobenzoic acid with a molar amount of C-C, alkylthioglycollate according to US patent application 07/590 115 registered at 28 September 1990 and entitled "Detailed Method for the Preparation and Derivatives of 4methylsulfonyl Benzoic Acid", incorporated herein by reference.

In the step (H) of the reaction, a molar amount of C ₍ -C ₄ alkyl ester of 2-methyl-3 / C, -C 1 alkoxy, C-C, haloalkoxy 2-methyl 14,14 toxyethoxy or 2-ethoxyethoxy / -4- nitrobenzoic acid is reacted with a molar amount of C 1 -C ₄ alkylmercaptan in the presence of a molar excess of a base such as potassium carbonate in a solvent such as dimethylformamide The reaction is carried out for several hours at a temperature between 50 and 100 ° C with stirring under an inert atmosphere such as nitrogen.

The desired reaction product is eliminated in the conventional manner.

The (H) reaction step can also be carried out by reacting a molar amount of a C ₁ -C ₄ alkyl ester of 2-methyl-3- (C 1 -C ₄ alkoxy, C 1 -C ₄ haloalkoxy 2-methoxyethoxy or 2 -ethoxyethoxy / -4-nitrobenzoic acid with a mole content of C 1 -C ₄ alkylthioglycollate according to patent application US 07/590 115, registered September 28, 1990 and entitled "Detailed Method for the Preparation of 4-Methylsulfonyl Derivatives and Intermediates benzoic acid ”, incorporated herein by reference.

In step (I) of the reaction, a molar amount of C 1 -C ₄ alkyl ester of 2-methyl-3- (C ₁ -C ₄ alkoxy, C 1 -C, haloalkoxy 2-methoxyethoxy or 2-ectoHeTokcH / -4- / Cj -C ₄ alkylthio / benzoic acid is reacted with at least 3 mol of an oxidant such as acetyl peroxyacid or chloroprobenzoic acid in a suitable solvent such as methylene chloride while stirring the reagent solution at a temperature of 20 to 40 ° C. The desired reaction product is eliminated in the conventional manner. During this reaction step, the C ₍ -C ₄ alkylthio substituent is oxidized to the corresponding C 1 -C ₄ alkylsulfonyl substituent without hydrolysis of the ester group to an acid group.

In the reaction step (I) of the 2-methyl-3- (N-N-alkoxy, N-C ₄ haloalkoxy 2-methoxyethoxy or 2-ethoxyethoxy- (N-C ₄ -alkylsulfonyl) -benzoic acid hydrolysis hydrolyzate to the corresponding trisubstituted benzoic acid by reaction with a molar amount of sodium hydroxide in aqueous medium. The hydrolysis takes place at a temperature between 20 and 100 ° C with stirring. The reaction product was separated in a conventional manner.

In step / K / of the reaction the molar amount of H-C ₄ alkyl ester of 2-methyl-3 / H-C ₄ alkoxy, Z-Z haloalkoxy 2-methoxyethoxy or 2-ethoxyethoxy / -4 / C, -C, alkylthio / benzoic acid is reacted with at least 5 mol of oxidant such as sodium hypochlorite in a suitable solvent such as dioxane while heating the reagent solution to a temperature of 60 to 80 ° C. After an exothermic reaction, the mixture was cooled and acidified with hydrochloric acid. The desired intermediate of trisubstituted benzoic acid is a precipitate and separated by filtration.

In the step (L) of the reaction, a molar amount of C ₂ -C ₄ alkyl ester of 2-methyl-3 (C-C) alkoxy, C 1 -C. halogenoalkoxy 2-methoxyethoxy or 2-ethoxyethoxy (-4- (C 1 -C 4 or 4 kilthio) benzoic acid is hydrolyzed with the base as sodium base to the corresponding 2-methyl-3- (N-C ₄ alkoxy or N-C ₄ haloalkoxy). -4- (C 1 -C ₄ alkylthio) benzoic acid. The hydrolysis takes place in a solvent, such as an 89% methanol-aqueous mixture. The reaction was carried out at 25 to 100 ° C with stirring, and the desired reaction product was separated in a conventional manner.

In step (M) of the reaction, a molar amount of 2-methyl-3-hydroxy benzoic acid is reacted with at least 2 mol of nitric acid in a solvent such as glacial acetic acid. The reaction is carried out at room temperature and the reaction product is separated in a conventional manner.

In step / N / reaction 2-methyl -3hidroksi-4-nitrobenzoic acid is reacted with 2 mol Z-C ₄ alkyl iodide or Z-C ₄ alkyl chloride and 2 mol of a base such as potassium carbonate in a solvent like a mixture of acetone and DMF. The reaction is carried out at reflux temperatures and the reaction product is separated in a conventional manner.

The reaction product is 2-methyl-3- (N-C ₄ alkoxy) -4-nitrobenzoic acid C 1 -C ₄ alkyl ester. C 1 -C ₄ alkyl groups are identical. The reaction product is useful as an intermediate or can be used as a reagent in the reaction steps (H / to / L) described below.

The benzoic acids described herein can be easily converted to their corresponding acid chlorides and then to their acid cyanides, if necessary, by the following two reactions. First, mol oxalyl chloride and a catalytic amount of dimethylformamide in a suitable solvent such as methylene chloride at 20 to 40 ° C is heated for 1 to 4 hours with a mole of MegflHHHaTa benzoic acid. The cyanide of the corresponding benzoic acid can be easily obtained from the benzoic acid chloride by reaction with cuprocyanide at a temperature of 50 to 220 ° C for 1 to 2 hours. These acid chlorides are reacted with the 1,3-cyclohexanediones described above to produce the herbicidal 2,3,4-trisubstituted benzoyl-1,3-cyclohexanedions described above according to the following two-step reaction.

The tri-substituted benzoic acid chlorides used as intermediates are useful in the preparation of the herbicidal 2- (2 ', 3', 4'-tri-substituted benzoyl) -1,3-cyclohexanedione described above.

The following series of examples show the preparation of representatives of intermediates according to the invention. The structures of all the compounds of the examples and tables were confirmed by nuclear magnetic resonance (NMR), infrared spectroscopy ((IR) and mass spectroscopy (MS).

Examples of carrying out the invention

Example 1.

3-hydroxy-2-methylbenzoic acid.

To a suspension of aniline hydrochloride (12.5 g, 0.067 mol) in water / ice / concentrated H ₂ SO ₄ (60ml / 37 g / 37 ml) was slowly added a solution of NaNO ₂ (4.76 g, 0.069 mol) over a 5 minute period. in H ₂ O (12 ml). The reaction temperature was maintained at 5 ° C by external cooling with an ice bath. The solid was transferred to a solution and the yellow solution was stirred for a further 15 minutes. The solution was transferred to another funnel and added dropwise over a period of 25 minutes to a heated solution of concentrated H ₂ SO ₄ / H ₂ 0 ( 44 ml / 34ml). The reaction mixture was heated to reflux for a further 5 min, cooled to room temperature and then immersed in an ice bath. The precipitate formed was collected by filtration and dissolved in 5 ethyl acetate (EtOAc). The mother liquor was extracted twice with EtOAc. The combined ethyl acetate phases were dried over magnesium sulfate (MgSO ₄ ), filtered and concentrated to a yellow solid (10.0 g, 0.065 mol, yield 97%). The structure of the compound was demonstrated by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopic analysis (MS).

Example 2.

3-hydroxy-2-methylbenzoate

To a solution of acid (8.0 g, 0.053 mol) in ethanol anhydride (250 ml) was added concentrated sulfuric acid (1.0 ml). Allow the reaction mixture to reflux for 20 h and then cool it to room temperature. Ethanol was removed on a rotary evaporator and the residue was dissolved in EtAc. The organic layer was washed successively with H ₂ O, saturated aqueous NaHCO ₃ (2x), H ₂ O, dried (MgSO ₄ ), filtered and concentrated to a solid (5.6 g, 0.031 mol, 59%), m. t. 58-60 ° C. The structure of the compound was verified by nuclear magnetic resonance (NMR), infrared spectroscopy (1R) and mass spectroscopy (MS).

Example 3.

4-bromo-3-hydroxy-2-methylbenzoate

To a solution of tertiary-butylamine (1.9 g, 0.026 mol) in CH ₂ Cl ₂ (100 ml), at 78 ° C was added a solution of bromine (4.0 g, 0.026 mol) in CH ₂ Cl ₂ (30 ml) dropwise. for 30 min. The mixture was stirred for a further 30 min at -78 ° C. A solution of phenol (4.6 g, 0.026 mol) in CH ₂ Cl ₂ (30 mol) was then added dropwise over 30 minutes. The reaction mixture was warmed to room temperature and stirred for 18 h. Aqueous treatment followed by flash chromatography afforded the product as a yellow oil (2.8 g, 42%). The structure of the compound was carried out by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

4-bromo-3-ethoxy-2-methylbenzoate

Example 4.

Acetone / DMB

A mixture of phenol (2.6 g, 0.01 mol), diethyl sulfate (1.7 g, 0.011 mol), and K ₂ CO _{3 (} 1.52 g, 0.011 mol) in acetone (DMF) (20 ml / 20 ml) was heated at reflux temperature. for 50 min and then cooled to room temperature and stirred overnight. The reaction mixture was filtered and the acetone solvent removed on a rotary evaporator. The residue was poured onto ice / H ₂ O.

Organic matter is recovered in hexane (2x). The combined hexane layers were dried (MgSO ₄ ), filtered and concentrated to an oil of ₁₅ (3.0 g, 0.01 mol, 100%).

The structure of the compound was verified by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

Example 5.

3-ethoxy-2-methyl-4-methylthiobenzoate

MeSH / K ₂ CO ₃

DMF

Methanethiol (1.5 g, 0.03 mol) was condensed in a stirred mixture of the starting bromine material (2.8 g, 0.01 mol), K ₂ CO _{3 (} 2.0.07 g, 0.015 mol) in DMF (30 ml) at 0 ° C. The reaction vessel was washed with acetone (10 ml). The mixture was stirred at room temperature overnight, then adjusted for 6 hours at reflux temperature. Gas chromatographic analysis showed 54% performance. The mixtures were again cooled to 0 ° C, more CH ₃ SH (2.5 g, 0.05 mol) was condensed and more K ₂ CO _{3 (} 4.6 g, 0.033 mol) was added. The mixture was again heated to reflux for 6 h. After cooling to room temperature, the reaction mixture was poured onto ice-cold aqueous 1 N HCl. The organic materials are extracted into Et 2 O / 2x. The combined organic layers were washed with 1 N HCl, 5% K ₂ CO ₃ (2x), dried (MgSO ₄ ), filtered and concentrated to an oil (2.25 g, 0.009 mol, 90%). The structure of the compound was verified by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

Example 6

3-Ethoxy-2-methyl-4-methylthiobenzoic acid

NaOH / KOH /

EtOH / HjO ------->

To a solution of the ester (2.2 g, 0.009 mol) in THF (20 ml) was added H ₂ O (20 ml), followed by solid NaON (1.7 g, 0.043 mol). The mixture was stirred for 2 hours at room temperature and then for another 2 hours at reflux temperature. KOH (2.4 g, 0.043 mol) and ethanol (5 ml) were added and the mixture was heated to reflux for 20 h. The mixture was cooled to room temperature and poured into a separatory funnel (the flask was rinsed with Et ₂ O).

The layers were separated and the organic layer was extracted with aqueous 5% K ₂ CO ₃ . The combined base layers were acidified at low temperature with concentrated HCl and the expected acid extracted in EtOAc. The EtOAc layer was dried (MgSO ₄ ), filtered and concentrated to a cream solid (2.2 g, 100%); 193-196 ° C. The structure of the compound was verified by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

Example 7.

3-Ethoxy-2-methyl-4-methylsulfonylbenzoic acid

CH ₃ COOH (32%) ^CH 2 ^Cl 2 -------->

To a suspension of acid (2.2 g, 0.01 mol) in CH ₂ Cl ₂ (50 ml) at 0 ° C was added a solution of 32% peracetic acid (4.6 ml, 0.022 mol) slowly. The solid was transferred to a solution, the mixture was warmed to room temperature and stirred for 3 days. More peracetic acid (1ml) was added and the mixture heated to reflux for 20 h. The mixture was poured into a separatory funnel and the CH ₂ Cl ₂ layer was washed once with H ₂ 0. The aqueous layer was back-extracted with CH ₂ Cl ₂ . The combined organic layers were dried (MgSO ₄ ), filtered and concentrated to a white solid (2.3 g, 90%); 132-136 ° C. The structure of the compound was verified by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

Example 8.

Ethyl 2-methyl-3-hydroxy-4-nitrobenzoate

To the phenolic solution (0.5 g, 0.0028 mol) in glacial acetic acid was added ice (10 g), followed by concentrated acetic acid (specific relative weight 1.42: 0.2 ml, 0.003 mol). The mixture was then stirred at room temperature for 45 min and another portion of nitric acid (0.2 ml / 0.003 mol) was added thereto. Stirring is continued for 50 h and the excess ice is added to the reaction mixture. A yellow solid precipitates, which is collected by suction filtration. The expected nitrated phenol was obtained by air drying (0.3 g, 48%). The structure of the compound was verified by nuclear magnetic resonance (NMP), infrared spectroscopy (IR) and mass spectroscopy (MS).

Example 9.

4-Bromo-2-methyl-3- (2-methoxyethoxy) benzoic acid

A mixture of ethyl 4-bromo-2-methyl-3- (2-methoxyethoxy) benzoate (6.6 g, 0.021 mol), potassium base (5.9 g, 0.105 mol) and sodium base (4.2 g, 0.105 mol) in tetrahydrofuran (5) ml), ethanol (5 ml) and water (100 ml) are heated at reflux for 3 hours. To cool to room temperature, the reaction vessel was cooled in an ice / water bath. The contents were acidified to pH <1 with concentrated hydrochloric acid and extracted with diethyl ether. The organic layer was dried (magnesium sulfate), filtered and concentrated in vacuo to give the expected free acid as a slightly yellowish solid.

The benzoic acid described above is converted to its acid chlorides using oxalic chloride and a catalytic amount of dimethylformamide. The acid chloride is reacted with a suitably substituted dione to obtain the herbicidally-acting 2,3,4-trisubstituted benzoyl 20 1,3-cyclohexanediones described below according to the two-step reaction described.

The following example shows the synthesis of the representative 2- (2 ', 3', 4'-trisubstituted / 1,3-cyclohexanedione of the invention.

Example 10.

2- [4'-Bromo-2'-methyl-3 '- / 2-methoxyethoxy / benzoyl] -5-methyl-1,3-cyclohexanedione

4-Bromo-2-methyl-3- (2-methoxyethoxy) benzoic acid (1.5 g, 0.0052 mol) was diluted in methylene chloride (30 ml), 5 drops of dimethylformamide were added, followed by slow addition of oxalyl chloride (2.0 g, 0.0156 mol / at 0 ° C. After the addition was complete, the reaction mixture was heated at reflux for 2 h, cooled and concentrated in vacuo. The crude acid chloride was dissolved in methylene chloride (10 ml) and the solution was slowly added to a mixture of 5-methyl = 1,3-cyclohexanedione (0.72 g, 0.0057 mol) and triethylamine (1.6 g, 0.0156 mol (acetonitrile) (30 ml). at 0 ° C. The reaction mixture was stirred for 3 hours at room temperature and acetocyanochydrin (10 drops) was added. Stirring is continued throughout the night. The solvents were removed in vacuo and ethyl ether was added to the residue. The organic 4Q layer was washed with aqueous 1 normal hydrochloric acid solution (2-fold). The acidic materials are recovered in aqueous 5% potassium carbonate (3x). The combined base layers were acidified to pH 6 (at 0 ° C) with concentrated hydrochloric acid and the expected product was extracted with methylene chloride (2-fold). Further purification as copper (II) chelate yielded the expected compound (1.1 g, 53% yield) as a light yellow oil. The following 50 table lists some selected compounds which are preferably according to the procedure described.

Table 1

Compound

No R ¹ R ² R ³ R ⁴ R ⁵ R ⁶ R ⁷ R ⁸ mp, ° C 1 a / N. N. dream ₃ N. N. N. dream ₃ Br butter 2 N. N. n N. N. N. dream ₃ Br butter

a / obtained in example 10

Herbicide trial tests

As mentioned, the compounds described herein are prepared as phytotoxic compounds which are useful and valuable in the fight against various plant species. Selected compounds of the invention are tested as herbicides as follows.

Multiple weed herbicide test before emergence. On the day preceding cultivation, seeds of eight different weed species are planted 30 in clay-sandy soil in individual rows, using one species per row despite the width of the area. The weeds used are amaranth (PW (Amaranthus retroflex,) giant fox tail / CFT / 6

Setenia faberi), Green Fox Tail / FT (Setaria viridis), Water Grass (WWG) Echinochloa crusqalli Broadleaf Signal Grass (BSC) (Brachiaria platyphylla), Year-round Gramophone (AMG) (Ipomoea lacunosa), velvet Abophyllio (VL) and beetle (CB) (Xanthum sp) .Sow plenty of seeds to sprout about 20 to 40 seedlings per row after emergence, depending on the size of the plants.

Weigh, on a piece of glass paper, an analytical balance of 37.5 mg of the compound to be tested. Place the paper and compound in a clean 60 ml wide-necked bottle and dissolve in 45 ml of acetone or a substituted solvent. Transfer 18 ml of this solution into a 60 ml clear wide-necked bottle and dilute with 22 ml water and acetone in a mixture (19: 1) containing a sufficient amount of polyoxyethylene sorbitan monolaurin emulsifier to obtain a final solution of 0.5% (V / V). The solution is sprayed onto the sown area with a linear spreading plane calibrated to deliver 40 gallons per acre (748 Ι / ha). The application rate is /0.28 kg / ha /.

After treatment, the areas are placed in the greenhouse at 70 to 80 ° F and irrigated by sprinkling. Two weeks after treatment, the degree of damage or destruction is determined by comparison with untreated control plants of the same age. The damage from 0 to 100% for each species is reported as percentage destruction, with 0% reporting the absence of damage and 100% representing complete destruction. The test results are shown in the following Table 2.

Herbicide activity before emergence

Degree of application -0.25 lb / A

Table 2

Compound #

FT GFT WC BSG

AMG ML

PW ST

1 10 20 100 100 40 100 20 100 2 100 100 100 100 15 100 95 100

Post-emergence multi-weed herbicide test. This test is carried out in the same way as the pre-emergence multi-weed herbicide test procedure, except that the seeds of the twelve species translated have emerged 10-12 days before treatment.

Furthermore, irrigation of the cultivated area is limited to the surface of the soil. 15 and not on the green part of the sprouted plants. The results of the post-emergence multi-weed herbicide test are summarized in Table 3.

Table 3.

Post-emergence multi-weed herbicidal activity Application rate -0.28 kg / ha.

Compound

No FT GFT WC BSG AMG VL PW CB 1 10 100 100 100 100 100 100 100 2 100 100 100 100 100 100 100 100

The compounds of the invention are useful as herbicides and can be applied in many ways at different concentrations. In practice, the compounds defined herein are incorporated into herbicidal compositions by mixing in herbicidally effective amounts, with excipients and carriers commonly used to facilitate the dispersion of the active ingredients for agricultural applications, taking into account the fact that the form and method of administration of a toxic substance may affects the activity of the materials in an application. Thus, these active herbicidal substances can be applied as granules with a relatively large particle size, such as moisturizing powders, emulsifying concentrates, powders of powders, solutions or as any of the other known several forms of administration, depending on the desired method. application. Preferred germicidal application forms prior to emergence are wettable powders, emulsifiable concentrates and granules. These forms may contain at least up to about 0.5% and up to about 95% or more by weight of the active ingredient. The herbicidally active amount depends on the nature of the seeds or plants that will need to be destroyed, and the application rate ranges from about 0.05 to about 10 pounds per acre, preferably from about 0.1 to about 4 pounds per acre.

The moisturizing powders are in the form of finely divided particles which are quickly dispersed in water or other dispersant. The humidifying powder is applied exclusively as a dry powder on the soil or as a dispersion in water or other liquid. Common carriers of wettable powders are pottery clay, kaolin clay, silica, and other directly wetted organic or inorganic diluents. Moisturizing powders are generally prepared to contain about 5 to about 95% of the active ingredient and typically also contain a small amount of a moisturizing, dispersing or emulsifying agent to facilitate moistening and dispersion.

Emulsifiable concentrates are homogeneous liquid compositions that are dispersed in water or other dispersant, and may consist entirely of the active compound only with a liquid or solid emulsifying agent, or may also contain a liquid carrier, such as xylene, heavy aromatic naphthalene, isophorone and other non-volatile organic solvents. For herbicidal applications, these concentrates are dispersed in water or other liquid carrier and are generally applied as a spray on the area to be treated. The percentage by weight of the active ingredient may vary depending on how the composition will be administered, but typically comprises about 0.5 to 95% of the active ingredient by weight of the herbicidal composition.

Granular administration forms in which the toxic substance is carried on relatively coarse coarse-grained particles are generally applied without dilution to the area in which vegetation suppression is desired. Typical carriers for granular forms are sand, pottery clay, bentonite, vermiculite, perlite and other organic or inorganic materials that absorb or may be coated with the toxic substance. Granular formulations are generally prepared to contain from about 5 to about 25% of the active ingredients, which may include surfactants such as heavy aromatic hydrocarbons, kerosene or other petroleum fractions, or vegetable oils, and / or binders such as dextrins , adhesive or synthetic resins.

Typical moisturizing dispersing or emulsifying agents used in agricultural formulations, for example, include alkyl and alkylaryl sulfonates and sulfates and their sodium salts, polyhydric alcohols, polyhydric alcohols, and other types of surfactants, many of them commercially available. When a surfactant is used, it usually covers from 0.1 to 15% by weight of the herbicidal compositions.

Powders, which are free-flowing mixtures of the active ingredient with finely divided solids such as talc, adhesives, flours and other organic and inorganic solids, acting as dispersants and carriers for the toxic substance, are useful forms of application for incorporation into soil.

Pastes, which are homogeneous suspensions of a finely divided solid toxic substance in a liquid carrier such as water or oil, are used for specific purposes. These forms of administration typically contain about 5 to about 95% of the active ingredient by weight, and may also contain small amounts of moisturizing, dispersing or emulsifying agents to facilitate dispersion. For application, the paste is usually diluted and applied as a spray on the area to be affected.

Other useful forms of herbicidal application include simple solutions of the active ingredient in a dispersant in which it is completely soluble in the desired concentration, such as acetone, alkylated naphthalene hydrocarbons, xylene and other organic solvents. Pressure sprays, typical aerosols in which the active ingredient is dispersed in a finely divided form as a result of evaporation of a low-boiling dispersion-soluble carrier, such as freons, may also be used.

The phytotoxic compositions of the invention are applied to plants in a conventional manner. For example, dust and liquid formulations can be applied to plants with energy-driven nebulizers, hand sprays, and brooms and nebulizers. The compositions can also be administered by airplane as a powder or spray as they are effective at very low doses. In order to modify or destroy the growth of germinating seeds or sprouting seedlings as a typical example, dusty and liquid compositions are applied to the soil according to conventional methods and distributed in the soil at least 1/2 inch deep below its surface. Phytotoxic compositions do not need to be mixed with soil particles, as these compositions can also be used simply by spreading or spreading the soil surface. The phytotoxic compositions of the invention can also be applied by adding to the irrigation water supplied to the field to be treated. This application method allows the compositions to penetrate the soil as water is absorbed by the soil. Dust compositions, granular compositions, or liquid forms applied to the soil surface may be distributed below the soil surface in the most conventional manner, such as disk harrowing, hauling or displacement operations.

Emulsifiable concentrate forms of administration

General formula with rows A specific formula Herbicidal compound 5-55 Herbicidal compound 54 Surface active A peculiar mixture of substance (s) 5-25 oily soluble sul- Solvent (s) 20-90 phonates and polyoxyetho- 100% flax ethers 10

Polar solvent 27

Petroleum hydrocarbon 9

100%

Formulations of moisturizing powders

Herbicidal compound 3-90 Herbicidal compound 80 Moisturizing agent 0.5-2 Sodium dialkyl naphthalene sulfonate 0.5 Dispersing agent 1-8 Sodium lignosulfonate 7 Diluent (s) 8,5-87 Glue from atapulgit 12.5 100% 100%

Extrusion granular forms of application

Herbicidal compound 1-20 Herbicidal compound 10 Binder 0-10 Ligninsulfonate 5 Diluent (s) 70-99 Calcium carbonate 85 100% 100% Current forms of application Herbicidal compound 20-70 Herbicidal compound 45 Surface active Polyoxyethylene ether 5 substance (s) 1-10 Atagel 0.05 Suspension substance (s) 0.05-1 Propylene glycol 10 Antifreeze 1-10 BIT 0.03 Antimicrobial substance 1-10 Silicone defoamer 0.02 Antifoaming agent 0.1-1 Water 39.9 Solvent 7.95-76.85

100% 100%

When salts are used as the active ingredient in the herbicidal compositions according to the invention, agriculturally acceptable salts are recommended.

The phytotoxic compositions of the invention may also contain other additives, for example fertilizers, other herbicides and other pesticides used as adjuvants or in combination with any of the excipients described. Useful for combining the active ingredient with fertilizers are, for example, ammonium nitrate, urea and superphosphate.

The herbicidal compositions of the invention may be administered in combination with other herbicidal compounds to broaden the spectrum of the fight against unwanted vegetation. Examples of other herbicidal compounds are the following:

1. Anilides

Alachlor-2-chloro-2 ', 6'-diethyl-N- (methoxymethyl) acetanilide

Metolachlor-2-chloro-2'-methyl-6'-ethyl-Methoxy-isopropyl-2-acetanilide

Propanyl-N- (3,4-dichlorophenyl) propionanilide

Acetachlor-2-chloro-2'-methyl-6'-ethyl-methoxymethyl-acetanilide

2. Triazines

Atrazine-2-chloro-4- (ethylamino) -6-isopropylamino) -S-triazine

Cyanazine-2-chloro-4- (1-cyano-1-methylethylamino) -6-ethylamino-8-triazine

Metribuzin-4-amino-6-tert-butyl-3- (methylthio) -1,2,4-triazin-5 / 4H / one

3. Thiocarbamates

Molinate-8-ethyl hexahydro-1H-azepine-1-carbothioate

Butylate-B-ethyl diisobutylthiocarbamate

4. Urea

Monuron-3- (p-chlorophenyl) -1,1-dimethylcarbamide

L inuron-3- (3,4-dichlorophenyl) -1-methoxy-1-methylurea

5. Toluidines

Trifluralin-α α α-trifluoro-2,6-dinitro-N, N-dipropyl-β-toluidine

Pendimethalin-N- (1-ethylpropyl) -3,4 dimethyl-2,6-dinitro-benzoamine

6. Hormones

2,4-D- / 2,4-Dichlorophenoxy / acetic acid

MCPA- (2-methyl-4-chlorophenoxy) acetic acid

7. Diazines

Bentazone-3-isopropyl-1H-2,3,1-benzothiadiazine-4 (3H) -one 2,2-dioxide

Oxadiazon-2-tert-butyl-4- (2,4-dichloro-5-isopropoxy-phenyl) -A ² -1,3,4-oxadiazolin-5-one

8. Diphenyl ethers

Acifluorfen sodium 5- (2-chloro-4- / trifluoromethyl / phenoxy) -2-nitrobenzoate

Fluazifop-butyl- [±] -butyl 2- (4 ((5- (trifluoromethyl / 2-pyridinyl / oxy) phenoxy) propanoate)

Chloromethoxinyl-2,4-dichlorophenyl-3methoxy-4-nitro-phenyl ether

9. Imidazolinones

Imazacquin-2- (4,5-dihydro-4-methyl-4/1-methylethyl) -5-oxo-1H-imidazol-2-yl) -3 quinoline carboxylic acid

10. Sulfonylureas

Bensulforon methyl-methyl 2 - ((((((4- (6-dimethoxypyrimidin-2-yl / amino) carbonyl) amino) sulfonyl) methyl) benzoate

Chlorimuron ethyl-ethyl 2 - ///// 4-chloro-

6-methoxypyrimidin-2-yl / amino / carbonyl / amino / sulfonyl / benzoate

11. 2- (2-substituted benzoyl) -1,3-cyclohexanedione

2- (2'-chloro-4-methylsulfonyl benzoyl) 1,3-cyclohexanedione

12. Miscellaneous compounds

Dimethazone-2- (2-chlorophenyl) methyl-4,4-dimethyl-3-isoxazolidinone

Norflurazone-4-chloro-5- (methylamino) 2-, a, a, a-trifluoro-1H-toluene / -3- (2H) -pyridazinone

Dalapone-2,2-cyclopropionic acid

Glycosate-isopropylamine salt of N / phosphonomethyl / glycine

Phenoxaprop-ethyl- (±) -ethyl-2,4 - [(6-chloro-2-benzoxazolyloxy) phenoxy] propanoate

Claims (12)

1. 2- (2'-methyl-3 ', 4'-trisubstituted benzoyl) -1,3-cyclohexanedione compounds of formula wherein R ¹ is hydrogen or C 1 -C 4 -alkyl, R ² hydrogen or C- lower alkyl, R ³ -hydrogen or C, -C4 alkyl, R ⁴ - hydroxy, hydrogen or (C 4 -alkyl, or R ³ and R ⁴ together are carbonyl (= 0) with the proviso that R ', R ² , R ⁵ and R ⁶ are C 1 -C 6 alkyl, R ⁵ is hydrogen or C 1 -C 4 -alkyl, R ⁶ is hydrogen, (C 1 -C 4 -alkyl, (C 1 -C 4 -alkylthio or C-C ₄ - alkylsulfonyl, provided that when R ⁶ is C ¹ -C ⁴ -alkylthio or C ₁ -C ₄ -alkylsulfonyl, then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or ethyl and R ⁸ is (1) halogen; (2) nitro; or (3) RhSC ^ - where η is an integer 0 or 2, a R ^b is (a) (C-SC-alkyl, and its salts. The compound of claim 1, wherein R ¹ is hydrogen or methyl, R ² is hydrogen or methyl, R ³ is hydrogen or methyl, R ⁴ is hydrogen or methyl, or R ³ and R ⁴ together are carbonyl, provided that that R ', R ² , R ⁵ and R ⁶ are all methyl, R ⁵ is hydrogen or methyl, R ^{6 is} hydrogen, methyl, methylthio or methylsulfonyl provided that when R ⁶ is methylthio or methylsulfonyl then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or ethyl, R ⁸ is chlorine, bromine, nitro or R ^{b is} SO 2 -B which R ^b is C (-C ₂ alkyl). The compound of claim 2, wherein R * is hydrogen, R ^{2 is} hydrogen, R ³ is methyl, R ^{4 is} hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ⁷ is methyl and R ⁸ is bromine. The compound of claim 2, wherein R ¹ is hydrogen, R ² is hydrogen, R ³ is hydrogen, R ⁴ is hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ^{7 is} methyl and R ⁸ is bromine. 5. A method of controlling undesirable vegetation comprising administering to the area where control is desired an effective herbicidal amount of a compound of formula I according to claim 1, wherein R ¹ is hydrogen or C 1 -C 4 alkyl, R ² is hydrogen or C] -C ₄ -alkyl, R ³ - H or (W-C-alkyl, R4 - hydroxy, hydrogen or C1-C4-alkyl, or R ³ and R ⁴ together are carbonyl (= 0) provided that R ', R ^2, R ⁵ and R ⁶ are C 1 -C ₄ -alkyl, R ⁵ is hydrogen or C] -C4 alkyl, R ⁶ - hydrogen, CrC4-alkyl, C ₁ -C ₄ - alkylthio or C ₁ -C ₄ alkylsulfonyl, provided that when R ⁶ is C [-C 4 -alkylthio or (C STsalkilsulfonil, m Gaba R ³ and R ⁴ together do not represent a carbonyl, then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or 5 ethyl and R ⁸ is (1) halogen, (2) nitro, or (3) R ^b SOn - in which η is an integer 0 or 2 and R ^b is (a) (C1-C6-alkyl, and salts thereof. The method of claim 5, wherein R ¹ is hydrogen or methyl, R ² is hydrogen or 10 methyl, R ³ is hydrogen or methyl, R ⁴ is hydrogen or methyl, or R ³ and R ⁴ together are carbonyl, provided that R 1, R ⁵ , R ⁵ and R ⁶ are all methyl, R ⁵ is hydrogen or methyl, R ^{6 is} hydrogen, methyl, methylthio or methylsulfonyl 15 provided that when R ⁶ is methylthio or methylsulfonyl, then R ³ and R ⁴ does not together represent carbonyl, R ⁷ is methyl or ethyl, R ⁸ is chlorine, bromine, nitro or R ^{b is} SO 2 - in which R ^b is C 1 -C 2 alkyl. 20 The method of claim 6, wherein R ¹ is hydrogen, R ₂ is hydrogen, R ³ is methyl, R ^{4 is} hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ⁷ is methyl and R ⁸ is bromine. The method of claim 6, wherein R ¹ is hydrogen, R ² is hydrogen, R ³ is hydrogen, R ⁴ is hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ^{7 is} methyl and R ⁸ is bromine. A herbicidal composition, characterized in that it contains, as an active substance 30 is a herbicidally effective amount of a compound of general formula I wherein R ¹ is hydrogen or C 1 -C 4 alkyl, R ² hydrogen or C 1 -C 4 alkyl, R ³ hydrogen or C 1 -C 4 alkyl, R ⁴ is hydroxy, hydrogen or C 1 -C 6 alkyl; or R ³ and R ⁴ together 35 represent carbonyl (= O) provided that R 1, R ² , R ⁵ and R ⁶ are C 1 -C ₄ -alkyl, R ⁵ is hydrogen or C 1 -C 4 -alkyl; R ⁶ is hydrogen or C 1 -C 4 alkyl, (C ₁ -C ₄ alkylthio or C ₁ -C ₄ alkylsulfonyl, provided that when R ⁶ is (C ₁ -C ₄ alkylthio or 40 C 1 -C 4 alkylsulfonyl, then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or ethyl and R ⁸ is (1) halogen, (2) nitro, or (3) R ^b SOn-.B which η is an integer 0 or 2, and R ^b is (a) C 1 -C ₄ alkyl, and salts thereof. 45 A herbicidal composition according to claim 9, wherein R ¹ is hydrogen or methyl, R ² is hydrogen or methyl, R ^{3 is} hydrogen or methyl, R ⁴ is hydrogen or methyl, or R ³ and R ⁴ together are carbonyl , 50 provided that R ', R ² R ⁵ and R ⁶ are all methyl, R ^J is hydrogen or methyl, R ⁶ is hydrogen, methyl, methylthio or methylsulfonyl provided that when R ⁶ is methylthio or methylsulfonyl, then R ³ and R ⁴ do not together represent carbonyl, R ⁷ is methyl or ethyl, R ⁸ is chlorine, bromine, nitro or R ^b SO, - wherein R ^b is C 1 -C 6 alkyl. 5 A herbicidal composition according to claim 10, characterized in that R 1 is hydrogen, R ² is hydrogen, R ³ is methyl, R ⁴ is hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ⁷ is methyl and R ⁸ is bromine. A herbicidal composition according to claim 10, wherein R ¹ is hydrogen, R ² is hydrogen, R ³ is hydrogen, R ^{4 is} hydrogen, R ⁵ is hydrogen, R ⁶ is hydrogen, R ⁷ is methyl and R ^{8 is} is bromine.