Herbicidal esters of 2-bromo-4-methylimidazole-5-carboxylic acid

BACKGROUND OF THE INVENTION 
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. 
DESCRIPTION OF THE INVENTION 
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. 
EXAMPLE I 
Isopropyl ester of 2-Bromo-4-methyl-5-imidazolecarboxylic acid 
##STR8## 
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. 
EXAMPLE II 
Isopropyl ester of N-(4-Pyridylmethyl)-2-bromo-4-methyl-5-imidazole 
carboxylic acid 
##STR9## 
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. 
TABLE I 
______________________________________ 
##STR10## 
Compound physical 
Number R Y constant 
______________________________________ 
1 ethyl 4-pyridyl golden oil 
2 isopropyl 4-pyridyl golden oil 
3 isopropyl 3-pyridyl dark oil 
4 ethyl 3-pyridyl dark oil 
5 isopropyl 2-pyridyl golden oil 
6 ethyl 2-pyridyl golden oil 
7 isopropyl 2-benzimidazoyl 
golden oil 
______________________________________ 
Herbicidal Screening Tests 
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. 
TABLE II 
______________________________________ 
Pre-Emergence Herbicidal Activity Application Rate - 4.48 kg/hr 
Cmpd. 
No. AMG VL MD CD 
______________________________________ 
1 0 0 0 0 
2 -- 0 65 40 
3 55 50 100 60 
4 0 0 0 0 
5 0 0 0 0 
6 0 0 100 90 
7 0 0 100 70 
______________________________________ 
-- = Not tested. 
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. 
TABLE III 
______________________________________ 
Post-Emergence Herbicidal Activity Application Rate - 4.48 kg/ha 
Cmpd. 
No. AMG VL MD CD 
______________________________________ 
1 20 20 40 0 
2 100 100 100 0 
3 100 80 100 100 
4 55 30 60 0 
5 45 25 100 0 
6 100 65 100 80 
7 100 100 100 100 
______________________________________ 
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.