Herbicidal Esters of 2-Bromo-4-Methylimidazole-5-Carboxylic Acid

Compounds having the structural formula ##STR2## wherein R is hydrogen, alkyl or substituted alkyl and Y is hydrogen, alkyl, substituted alkyl, halogen, cyano or nitro are described in U.S. Pat. No. 3,501,286 as being herbicides.

A compound of the formula ##STR3## is taught by Pyman and Timmis, J. Chem. Soc., pp. 494-498 (1923). However, no utility for this compound is taught other than its use as an intermediate in the preparation of pharmaceuticals.

This invention relates to esters of 2-bromo-4-methylimidazole-5-carboxylic acid as herbicides. The novel compounds of this invention have the following structural formula (A) ##STR4## wherein R is (1) C.sub.1 -C.sub.10 alkyl, preferably C.sub.2 -C.sub.6 alkyl, more preferably C.sub.2 -C.sub.5 alkyl, most preferably isopropyl, isobutyl, isopentyl or sec-pentyl, or less preferably the following: (2) C.sub.3 -C.sub.8 cycloalkyl, preferably C.sub.4 -C.sub.6 cycloalkyl, more preferably cyclopentyl or cyclohexyl; (3) C.sub.3 -C.sub.8 cycloalkylalkyl wherein the alkyl has 1 to 6 carbon atoms, preferably cyclopropylmethyl or cyclopentylmethyl; (4) C.sub.3 -C.sub.10 alkenyl, preferably allyl or 2-methyl-3-butenyl-1; (5) C.sub.5 -C.sub.8 cycloalkenyl; (6) benzyl or (7) di-substituted benzyl wherein the substituents are C.sub.1 -C.sub.4 alkyl, halogen, nitro or C.sub.1 -C.sub.4 haloalkyl and Y is substituted or unsubstituted 2-, 3- or 4-pyridyl or 2-benzimidazoyl, wherein the substituent is halogen, more preferably trihalomethyl, C.sub.1 -C.sub.4 alkyl, preferably methyl or --C(O)OR.sup.2 wherein R.sup.2 is C.sub.1 -C.sub.4 alkyl; C.sub.1 -C.sub.4 alkoxy, preferably methoxy or CN.

The structural formula (A) when R and Y are as defined is intended to define compounds of either of the following two structural isomers ##STR5## or mixtures of the two isomers in any proportion.

Both isomers are herbicidally active.

In the above description of the compounds of this invention alkyl includes both straight and branched configurations; for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl, the amyls, the hexyls, the heptyls, the nonyls and the decyls.

The compounds of this invention are active herbicides of a general type. That is, they are herbicidally effective against a wide range of plant species. The method of controlling undesirable vegetation of the present invention comprises applying an herbicidally effective amount of the above-described compounds to the area where control is desired.

The compounds of the present invention can be prepared by the following general method. ##STR6## wherein R is as defined. and TEC is a transesterification catalyst such as Ti(O-alkyl).sub.4, preferably Ti(isopropoxy).sub.4. ##STR7## wherein R is as defined, Y--CH.sub.2 --X is a halomethylpyridine or a halomethylbenzimidazole wherein Y is as defined and X is chlorine.

Generally, for step (1) at least one mole of the alcohol is used for the reaction with the ethyl ester to prepare the imidazoles. Preferably, a slight mole excess of the alcohol is used. The reaction mixture is refluxed until completion of the reaction. The reaction product is recovered by removing the volatile materials. Atmospheric, subatmospheric or superatmospheric pressures can be used, depending on the boiling point of the solvent used. Ethanol is conveniently stripped at elevated temperatures and reduced pressure.

Reaction step (2) is run in a solvent such as tetrahydrofuran, at a temperature of about 25.degree., preferably room temperature, using equal mole amounts of the two reactants and a hydride base. Preferably, the hydride base is sodium hydride.

The reaction product is a mixture of (1) and (3) isomers and is worked up by conventional techniques.

The following example teaches the synthesis of a representative compound of this invention.

To a suspension of 6.4 grams (g) (2.7.times.10.sup.-2 moles) of ethyl-2-bromo-4-methyl-5-imidazole carboxylate in 70 milliliters (ml) isopropanol was added 0.6 ml (2.4.times.10.sup.-3 moles) tetraisopropyl titanate. The resulting mixture was heated to reflux for 3 days, then concentrated in vacuo to one-half the original volume. The solution was cooled on ice and the precipitated crystalline solid was filtered and air dried to give 3.4 g of the desired product.

To a suspension of 195 milligrams (mg) (8.13 mM) of sodium hydride in 20 ml of anhydrous tetrahydrofuran was added, in portions, 2 g (8.13 mM) of isopropyl 2-bromo-4-methyl-5-imidazolecarboxylate. The resulting suspension was cooled to 0.degree. C. and 1.03 g (8.13 mM) of 4-chloromethylpyridine was added. The reaction mixture was stirred overnight at 50.degree. C. The precipitated sodium chloride was removed by filtration and concentration in vacuo of the filtrate gave 2.5 g (92%) of isopropyl N-(4-pyridylmethyl)-2-bromo-4-methyl-5-imidazole carboxylate as a tan solid.

The following is a table of certain selected compounds that are preparable according to the procedure described herein. Compound numbers are assigned to each compound and are used throughout the remainder of the application.

As previously mentioned, the herein described compounds produced in the above-described manner are phytotoxic compounds which are useful and valuable in controlling various plant species. Selected compounds of this invention were tested as herbicides in the following manner.

Pre-emergence herbicide test. On the day preceding treatment, seeds of five different broadleaf weed species are planted in loamy sand soil in individual rows using one species per row across the width of a flat. The seeds used are annual morningglory (AMG) (Ipomoea lacunosa), velvetleaf (VL) (Abutilon theophrasti), Indian mustard (MD) (Brassica juncea) and curly dock (CD) (Rumex crispus). Ample seeds are planted to give about 20 to 40 seedlings per row, after emergence, depending upon the size of the plants.

Using an analytical balance, 600 milligrams (mg) of the compound to be tested are weighed out on a piece of glassine weighing paper. The paper and compound are placed in a 60 milliliter (ml) wide-mouth clear bottle and dissolved in 45 ml of acetone or substituted solvent. Eighteen ml of this solution are transferred to a 60 ml wide-mouth clear bottle and diluted with 22 ml of a water and acetone mixture (19:1) containing enough polyoxyethylene sorbitan monolaurate emulsifier to give a final solution of 0.5% (v/v). The solution is then sprayed on a seeded flat on a linear spray table calibrated to deliver 80 gallons per acre (748 L/ha). The application rate is 4 lb/acre (4.48 Kg/ha).

After treatment, the flats are placed in the greenhouse at a temperature of 70.degree. to 80.degree. F. and watered by sprinkling. Two weeks after treatment, the degree of injury or control is determined by comparison with untreated check plants of the same age. The injury rating from 0 to 100% is recorded for each species as percent control with 0% representing no injury and 100% representing complete control.

The results of the tests are shown in the following Table II.

Post-emergence Herbicide Test: This test is conducted in an identical manner to the testing procedure for the pre-emergence herbicide test, except the seeds of the eight different weed species are planted 10-12 days before treatment. Also, watering of the treated flats is confined to the soil surface and not to the foliage of the sprouted plants.

The results of the post-emergence herbicide test are reported in Table III.

The compounds of the present invention are useful as herbicides, and can be applied in a variety of ways at various concentrations. In practice, the compounds herein defined are formulated into herbicidal compositions, by admixture, in herbicidally effective amounts, with the adjuvants and carriers normally employed for facilitating the dispersion of active ingredients for agricultural applications, recognizing the fact that the formulation and mode of application of a toxicant may affect the activity of the materials in a given application. Thus, these active herbicidal compounds may be formulated as granules of relatively large particle size, as wettable powders, as emulsifiable concentrates, as powdery dusts, as solutions or as any of several other known types of formulations, depending upon the desired mode of application. Preferred formulations for pre-emergence herbicidal applications are wettable powders, emulsifiable concentrates and granules. These formulations may contain as little as about 0.5% to as much as about 95% or more by weight of active ingredient. A herbicidally effective amount depends upon the nature of the seeds or plants to be controlled and the rate of application varies from about 0.05 to approximately 25 pounds per acre, preferably from about 0.1 to about 10 pounds per acre.

The phytotoxic compositions of this invention are applied to the plants in the conventional manner. Thus, the dust and liquid compositions can be applied to the plant by the use of power-dusters, boom and hand sprayers and spray dusters. The compositions can also be applied from airplanes as a dust or a spray because they are effective in very low dosages. In order to modify or control growth of germinating seeds or emerging seedlings, as a typical example, the dust and liquid compositions are applied to the soil according to conventional methods and are distributed in the soil to a depth of at least 1/2 inch below the soil surface. It is not necessary that the phytotoxic compositions be admixed with the soil particles since these compositions can also be applied merely by spraying or sprinkling the surface of the soil. The phytotoxic compositions of this invention can also be applied by addition to irrigation water supplied to the field to be treated. This method of application permits the penetration of the compositions into the soil as the water is absorbed therein. Dust compositions, granular compositions or liquid formulations applied to the surface of the soil can be distributed below the surface of the soil by conventional means such as discing, dragging or mixing operations.

The phytotoxic compositions of this invention can also contain other additaments, for example, fertilizers and other herbicides, pesticides and the like, used as adjuvant or in combination with any of the above-described adjuvants. Fertilizers useful in combination with the active ingredients include, for example, ammonium nitrate, urea and superphosphate. Other useful additaments include materials in which plant organisms take root and grow such as compost, manure, humus, sand, and the like.