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

Herbicidal compounds having the structural formula ##STR1## wherein R is C.sub.1 -C.sub.10 alkyl; C.sub.3 -C.sub.8 cycloalkylalkyl wherein the alkyl has 1 to 6 carbon atoms; and Y is benzyl or mono-substituted benzyl wherein the substituent is halogen, amino, nitro or C.sub.1 -C.sub.4 haloalkyl.

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 
##STR4## 
wherein R is C.sub.1 -C.sub.10 alkyl, preferably C.sub.2 -C.sub.5 alkyl, 
most preferably ethyl, isopropyl and isobutyl, or C.sub.3 -C.sub.8 
cycloalkylalkyl wherein the alkyl has 1 to 6 carbon atoms, preferably 
cyclopropylmethyl; Y is benzyl or mono-substituted benzyl wherein the 
substituent is halogen, preferably chlorine, nitro or amino or C.sub.1 
-C.sub.4 haloalkyl, preferably trifluoromethyl, preferably the substituent 
is on the meta- or para-position. 
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, 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. 
##STR5## 
wherein R is as defined. and TEC is a transesterification catalyst such as 
Ti(O-alkyl).sub.4, preferably Ti(isopropoxy).sub.4. 
##STR6## 
wherein R is as defined, Y-X is a benzyl halide wherein Y is as defined 
and X is chlorine, bromine or iodine. 
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 benzene or toluene, at a 
temperature of from about 25.degree. to 100.degree. C., preferably reflux 
temperature, using equal mole amounts of the two reactants and the 
tertiary amine base. Preferably, the tertiary amine base is 
diazabicycloundecane. 
The reaction product is a mixture of (1) and (3) isomers and is worked up 
by conventional techniques. 
The (1) and (3) isomers can be separated by chromatography or silica gel. 
The (3) isomer which is the subject of this invention is the desired 
product and it is more herbicidally active than the (1) isomer which has 
very little or no herbicidal activity. 
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 
##STR7## 
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 precipitate crystalline solid was filtered and air 
dried to give 3.4 g of the desired product. 
EXAMPLE II 
Isopropyl Ester of 2-bromo-3-(4-nitrobenzyl)-4-methyl-5-imidazolecarboxylic 
acid 
##STR8## 
To a solution of 2 g (8.1.times.10.sup.-3 moles) of i-propyl ester of 
2-bromo-4-methyl-5-imidazolecarboxylic acid in 20 ml of benzene was added 
1.2 ml (8.1.times.10.sup.-3 moles) of diazabicycloundecane, followed by 
1.7 g (8.1.times.10.sup.-3 moles) of p-nitrobenzylbromide. The resulting 
mixture was heated to reflux overnight, cooled to room temperature and 
filtered. Concentration in vacuo gave a golden oil. This residue was 
purified by medium pressure liquid chromatography on silica gel to yield 
2.1 g (70%) i-propyl 
1-(4-nitrobenzyl)-2-bromo-4-methyl-5-imidazolecarboxylate as a yellow oil 
and 600 mg (20%) of the desired product, i-propyl 
2-bromo-3-(4-nitrobenzyl)-4-methyl-5-imidazolecarboxylate also a yellow 
oil. 
The following is a table of certain selected compounds that are preparable 
according to the procedure described herein. Compund numbers are assigned 
to each compound and are used throughout the remainder of the application. 
TABLE I 
______________________________________ 
##STR9## 
Compound n.sub.D.sup.25 
Number R Y or m.p. .degree.C. 
______________________________________ 
1 ethyl 4-Clbenzyl clear oil 
2 i-propyl benzyl clear oil 
3 i-propyl 4-Fbenzyl yellow oil 
4 ethyl 4-NO.sub.2benzyl 
63-64 
5 ethyl 3-CF.sub.3benzyl 
174-176 
6 sec-butyl 4-NO.sub.2benzyl 
85-86 
7 ethyl 3-NO.sub.2benzyl 
yellow oil 
8 i-propyl 3-NO.sub.2benzyl 
waxy solid 
9 i-propyl 4-CF.sub.3benzyl 
109-111 
10 ethyl 4-CF.sub.3benzyl 
yellow oil 
11 i-butyl 3-CF.sub.3benzyl 
yellow oil 
12 i-propyl 4-NH.sub.2benzyl 
tan solid 
.sup. 13.sup.(a) 
i-propyl 4-NO.sub.2benzyl 
107-109 
______________________________________ 
.sup.(a) Prepared in Example II. 
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 
eight different 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 green foxtail (FT) (Setaria viridis), watergrass (WG) (Echinochloa 
crusgalli), wild oat (WO) (Avena fatua), annual morningglory (AMG) 
(Ipomoea lacunosa), velvetleaf (VL) (Abutilon theophrasti), Indian mustard 
(MD) (Brassica juncea), curly dock (CD) (Rumex crispus), and yellow 
nutsedge (YNG) (Cyperus esculentus). 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 substitued 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 contol. 
The results of the tests are shown in the following Table II. 
TABLE II 
______________________________________ 
Pre-Emergence Herbicidal Activity 
Application Rate - 4.48 kg/ha 
Cmpd. 
No. FT WG WO AMG VL MD CD YNG 
______________________________________ 
1 45 15 0 0 0 95 0 0 
2 0 0 0 0 0 0 0 0 
3 40 40 20 20 20 60 0 0 
4 60 60 20 50 60 60 60 0 
5 80 60 30 90 100 100 60 60 
6 0 0 0 0 0 0 0 0 
7 0 0 0 0 0 20 0 0 
8 0 0 0 0 0 0 0 0 
9 0 0 0 0 0 90 30 0 
10 0 0 0 0 0 0 0 0 
11 30 45 20 35 50 100 100 0 
12 60 60 85 100 100 100 95 0 
13 100 60 60 90 60 70 60 0 
______________________________________ 
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. FT WG WO AMG VL MD CD YNG 
______________________________________ 
1 100 45 35 100 -- 100 75 20 
2 60 60 20 60 60 60 60 0 
3 0 0 0 80 100 100 20 0 
4 100 100 100 100 100 100 100 0 
5 100 100 100 100 100 100 100 20 
6 0 0 0 20 50 20 0 0 
7 20 0 20 100 70 100 15 0 
8 90 35 0 100 95 100 100 0 
9 90 30 90 100 100 100 100 0 
10 0 0 0 60 60 80 35 0 
11 70 0 80 100 95 100 95 0 
12 100 85 100 100 100 100 70 0 
13 100 100 100 100 80 100 100 0 
______________________________________ 
-- = Not tested. 
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. 
Wettable powders are in the form of finely divided particles which disperse 
readily in water or other dispersants. The wettable powder is ultimately 
applied to the soil either as a dry dust or as a dispersion in water or 
other liquid. Typical carriers for wettable powders include fuller's 
earth, kaolin clays, silicas and other readily wet organic or inorganic 
diluents. Wettable powders normally are prepared to contain about 5% to 
about 95% of the active ingredient and usually also contain a small amount 
of wetting, dispersing, or emulsifying agent to facilitate wetting and 
dispersion. 
Emulsifiable concentrates are homogeneous liquid compositions which are 
dispersible in water or other dispersant, and may consist entirely of the 
active compound with a liquid or solid emulsifying agent, or may also 
contain a liquid carrier, such as xylene, heavy aromatic naphtha, 
isophorone and other non-volatile organic solvents. For herbicidal 
application, these concentrates are dispersed in water or other liquid 
carrier and normally applied as a spray to the area to be treated. The 
percentage by weight of the essential active ingredient may vary according 
to the manner in which the composition is to be applied, but in general 
comprises about 0.5% to 95% of active ingredient by weight of the 
herbicidal composition. 
Granular formulations wherein the toxicant is carried on relatively coarse 
particles, are usually applied without dilution to the area in which 
suppression of vegetation is desired. Typical carriers for granular 
formulations include sand, fuller's earth, bentonite clays, vermiculite, 
perlite and other organic or inorganic materials which absorb or which may 
be coated with the toxicant. Granular formulations normally are prepared 
to contain about 5% to about 25% of active ingredients which may include 
surface-active agents such as wetting agents, dispersing agents or 
emulsifiers; oil such as heavy aromatic naphthas, kerosene or other 
petroleum fractions, or vegetable oils; and/or stickers such as dextrins, 
glue or synthetic resins. 
Typical wetting, dispersing or emulsifying agents used in agricultural 
formulations include, for example, the alkyl and alkylaryl sulfonates and 
sulfates and their sodium salts; polyhydroxy alcohols; and other types of 
surface-active agents, many of which are available in commerce. The 
surface-active agent, when used, normally comprises from 0.1% to 15% by 
weight of the herbicidal composition. 
Dusts, which are free-flowing admixtures of the active ingredient with 
finely divided solids such as talc, clays, flours and other organic and 
inorganic solids which act as dispersants and carriers for the toxicant, 
are useful formulations for soil-incorporating application. 
Pastes, which are homogeneous suspensions of a finely divided solid 
toxicant in a liquid carrier such as water or oil, are employed for 
specific purposes. These formulations normally contain about 5% to about 
95% of active ingredient by weight and may also contain small amounts of a 
wetting, dispersing or emulsifying agent to facilitate dispersion. For 
application, the pastes are normally diluted and applied as a spray to the 
area to be affected. 
Other useful formulations for herbicidal applications include simple 
solutions of the active ingredient in a dispersant in which it is 
completely soluble at the desired concentration, such as acetone, 
alkylated naphthalenes, xylene and other organic solvents. Pressurized 
sprays, typically aerosols, wherein the active ingredient is dispersed in 
finely-divided form as a result of vaporization of a low boiling 
dispersant solvent carrier, such as the Freons, may also be used. 
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 hard 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 formlations 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, perticides and 
the like, used as adjuvant or in combination with any of the 
above-described adjuvants. Other phytotoxic compounds useful in 
combination with the above-described compounds include, for example, 
2,4-dichlorophenoxyacetic acids, 2,4,5-trichlorophenoxyacetic acid, 
2-methyl-4-chlorophenoxyacetic acid and the salts, esters and amides 
thereof, triazine derivatives, such as 
2,4-bis(3-methoxypropylamino)-6-methylthio-s-triazine, 
2-chloro-4-ethylamino-6-isopropylamino-s-triazine, and 
2-ethylamino-4-isopropyl-amino-6-methyl-mercapto-s-triazine; urea 
derivatives, such as 3-(3,5-dichlorophenyl)-1,1-dimethylurea and 
3-(p-chlorophenyl)-1,1-dimethylurea; and acetamides such as 
N,N-diallyl-.alpha.-chloroacetamide, and the like; benzoic acids such as 
3-amino-2,5-dichlorobenzoic acid; thiocarbamates such as S-propyl 
N,N-dipropylthiocarbamate, S-ethyl N,N-dipropylthiocarbamate, S-ethyl 
cyclohexylethylthiocarbamate, S-ethyl hexahydro-1H-azepine-1-carbothioate 
and the like; anilines such as 
4-(methylsulfonyl)-2,6-dinitro-N,N-substituted aniline, 
4-trifluoromethyl-2,6-dinitro-N,N-di-n-propyl aniline, 
4-trifluoromethyl-2,6-dinitro-Nethyl-N-butyl aniline, 
2-[4-(2,4-dichlorophenoxy)phenoxy]propanoic acid, 
2-[1-(ethoxyimino)butyl]-5-[2-ethylthio)propyl]-3-hydroxy-2-cyclohexene-1- 
one, (.+-.)-butyl- 
2-[4-[(5-trifluoromethyl)-2-pyridinyl)oxy]phenoxy]propanate, sodium 
5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoate, 
3-isoporpyl-1H-2,1,3-benzothiadiazine-4-(3H)-one-2,2-dioxide, and 
4-amino-6-tert-butyl-3-(methylthio)-as-triazin-5(4H)-one or 
(4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one). 
Fertiliziers useful in combination with the active indredients 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.