Note: Descriptions are shown in the official language in which they were submitted.
~OS7197
CONTROL OF ANIMAL PARASITES
WITH BENZIMIDAZOLES
The control of animal parasites is one of the oldest
and ~ost important problems of the animal husbandry industry.
Many types of parasites afflict virtually all species of
anl~al~. Most animals are afflicted by free-flying parasites
such as flies, crawling ectoparasites such as lice and mites,
burrowing parasites such as bots and grubs, and by microscopic
endopar~sites such as coccidia, as well as by larger endo-
parasites such as worms. Thus, the control of parasites evenin a single host species is a complex and many-sided problem.
The insect and acarina parasites which consume
living tissues of a host animal are particularly harmful. The
group includes parasites of all the economic animals, including
ruminant and monogastric mammals and poultry, and of companion
animalQ such as dogs as well.
Many methods of control of such parasites have been
tried. The screwworm has been practically eradicated in Florida
by the release of great numbers of sterile male blowflies. The
method obviously is applicable only to an easily lsolated area.
The free-flying insects are usually controlled by routine
methods such as air-dispersed and contact insecticides and fly
traps. The skin-inhabiting, crawling parasites are usually
controlled by dipping, drenching, or spraying the animal~
with appropriate parasiticides.
Some progress has been made in the systemic control of
some parasites, particularly those which burrow in or migrate
through the host animal. Systemic control of animal parasites
is accomplished by absorbing a parasiticide in the bloodstream
or other tissues of the h~st animal. Parasites which eat or
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come into contact with the parasiticide-containing tissue are
killed, either by ingestion or contact. A few phosphate, phos-
phoramidate, and phosphorothioate insecticides and acaricides
have been found to be sufficiently nontoxic to be used
systemically in animals.
Recently, the field of benzimidazole chemistry has
beon extremely active. A great many patents and publications
have appeared disclosing a variety of substituted benzimida-
zoles, some of which have insecticidal and acaricidal activity.
For example, Belgian Patent 766,870 teaches a group
of acaricidal benzimidazoles characterized by l-carboxylate
and 2-chlorofluoroalkyl substituents and a variety of sub-
stituents, including halo, nitro, and trifluoromethyl, on the
benzene ring.
Newbold et al., U. S. Patent 3,542,923, discloses
an insecticidal method making use of benzimidazoles having
no l-substituent or a l-carboxylate substituent, a 2-perfluoro-
alkyl substituent, and as many as four benzene ring substituents
chosen from among a large group of substituents including nitro,
halo, alkyl, carboxy, and so forth.
British Patent 1,122,988 teaches insecticidal and
acaricidal benzimidazoles of structures notable for the ex-
tremely w~e ~J~r;ety of the henzene r; ng substituents, of which
the compounds can have as many as four. The 2-substituents of
the compounds are perfluoroalkyl, and the l-substituent, if
present, is alkyl or aryl.
British Patents, 1,087,561 and 1,144,620 provide
further disclosure of insecticidal 2-perfluoroalkyl ben-
zimidazoles.
French Patent 1,430,139 adds another group of in-
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secticidal, acaricidal, and nematocidal benzimidazoles bearing
as many as four benzene ring substituents chosen from the group
including nitro, chloro, and cyano, among others, and a 2-halo-
alkyl substituent.
British patent 1,113,999 discloses a group of l-thio-
carbamoylbenzimidazoles which are insecticides active against
pests such as mustard beetles, aphids, and mosquitoes.
South African Patent 69.02813 teaches the biological
activity of a family of benzimidazoles including compounds with
l-caxboxylate and l-sulfonyl substituents. The compounds are
insecticides and acaricides.
Holan et al., U. S. Patent 3,448,115 discloses a
family of substituted benzimidazoles characterized by a 2-
dichlorofluoromethyl or chlorodifluoromethyl substituent. The
compounds of the patent are stated to be anthelmintics and her-
bicides.
Hannah et al., U. S. Patent 3,749,734, disclose a
group of l-cyanobenzimidazoles having chlorine atoms on the
phenyl ring which are said to be anthelminticq and ectopara-
siticides.
This invention provides a new means of killing byingestion insect and acarine parasites which consume living
tissues of a host animal. It comprises an orally or per-
cutaneously administerable composition comprising an adjuvant
suitable for oral or percutaneous administration to an animal
and as an active ingredient a parasiticidally-effective
amount of a compound of the formula
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lOS7197
OzN \ R1
R / ~ R~ (I)
wherein R is chloro, trifluoromethyl, difluoromethyl, chloro-
difluoromethyl;
Ol Ol O
Rl is hydrogen, -C-o-R3, -C-R4, -~-R5,
~ o 'i1
-C-NtCl-C3 alkyl)2, -O-(Cl-C3 alkyl), or -O-C-R ;
R2 is chlorodifluoromethyl, trifluoromethyl, 1,1,2,2-
tetrafluoroethyl, pentafluoroethyl, heptafluoro-
propyl, or heptafluoroisopropyl;
R3 is Cl-C6 alkyl, C2-C3 alkenyl, phenyl, or benzyl;
R4 is Cl-C5 alkyl, phenyl, chlorophenyl, anisyl, or
tolyl;
R5 is Cl-C3 alkyl, or phenyl;
or the ammonium, alkali metal, or alkaline earth metal salts
of the compounds of formula (I) wherein Rl is hydrogen.
A preferred group of compounds which are particularly
useful in the invention have the formula
02N IR7
~ / ~ CF2R~ (II)
wherein R6 is chloro, fluoro, difluoromethyl, or trifluoro-
methyl; R7 is hydrogen, phenylsulfonyl, phenoxycarbonyl,
Cl-C4 alkoxycarbonyl, Cl-C3 alkoxy, or
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- C - N(Cl-C3 alkyl)2;
R is chloro or trifluoromethyl; or the ammonium, alkali metal,
or alkaline earth metal salts of the compounds of formula (II)
wherein R7 is hydrogen.
The general chemical terms in the above generic
formulae are used in the sense in which they are usually under-
stood in organic chemistry. The following specific examples of
sub tituents referred to by the general chemical terms are
presented to assure clarity.
Alkali metal refers to atoms such as sodium,
potassium, and lithium.
Alkaline earth metal refers to atoms such as calcium,
magnesium, and strontium.
Cl-C3 alkyl, Cl-C6 alkyl, Cl-C4 alkyl, C2-C3 alkenyl,
Cl-C3 alkoxy, and Cl-C5 alkyl refer to substituents such as
methyl, ethyl, isopropyl, isobutyl, hexyl, 2-pentyl, vinyl,
allyl, t-butyl, methoxy, propoxy, and 3-hexyl.
The following specific compounds are presented to
assure that those skilled in the organic chemlcal and para-
sitological arts understand the scope of the invention.
2-chlorodifluoromethyl-4-nitro-6-trifluoromethyl-
benzimidazole
6-nitro-2,4-bis(trifluoromethyl)benzimidazole
l-benzoyloxy-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole
5-nitro-2,6-bis(trifluoromethyl)benzimidazole
4-nitro-2-pentafluoroethyl-6-trifluoromethylbenzimi-
dazole
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l-ethoxy-4-nitro-2,6-bis(trifluoromethyl)benzimida-
zole
4-nitro-2,6-bis(trifluoromethyl)benzimidazole
6-difluoromethyl-4-nitro-2-trifluoromethylbenzimi-
dazole
allyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
4-nitro-N,N-dipropyl-2,6-bis(trifluoromethyl)thio-1-
benzimidazolecarboxamide
7-nitro-N,N-dipropyl~2,5-bis(trifluoromethyl)thio-1-
benzimidazolecarboxamide
ethyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
phenyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
N,N-diethyl-4-nitro-2,6-bis(trifluoromethyl)thio-1-
benzimidazolecarboxamide
l-acetyl-7-nitxo-2,5-bis(trifluoromethyl)benzimi-
dazole
2,6-bis(trifluoromethyl)-4-nitro-1-phenylsulfonyl-
benzimidazole
~ anisoyl)-4-nitro-2,6-bis(trifluoromethyl)ben-
zimidazole
l-methoxy-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole
2,6-bis(trifluoromethyl)-4-nitrobenzimidazole, sodium
salt
n-hexyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
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isopropyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
l-benzoyl-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole
1-(4-chlorobenzoyl)-4-nitro-2,6-bis(trifluoromethyl)
benzimidazole
N,N-dimethyl-4-nitro-2,6-bis(trifluoromethyl)thio-1-
benzimidazolecarboxamide
N,N-dimethyl-7-nitro-2,5-bis(trifluoromethyl)thio-1-
benzimidazolecarboxamide
benzyl 2,6-bis(trifluoromethyl)-4-nitro-1-benzimi-
dazolecarboxylate
benzyl 2,5-bis(trifluoromethyl)-7-nitro-1-benzimi-
dazolecarboxylate
methyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
methyl 7-nitro-2,5-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
isopropyl 2-chlorodifluoromethyl-4-nitro-6-trifluoro-
methyl-l-benzimidazolecarboxylate
l-acetyl-4-nitro-2,6-bis(trifluoromethyl)benzimidazole
l-hexanoyl-7-nitro-2,5-bis(trifluoromethyl)benzimi-
dazole
l-hexanoyl-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole
7-nitro-2-(1,1,2,2-tetrafluoroethyl)-5-trifluoro-
methylbenzimidazole
l-ethoxy-4-nitro-2-pentafluoroethyl-6-trifluoromethyl-
benzimidazole
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phenyl 2-chlorodifluoromethyl-4-nitro-6-trifluoro-
methyl-l-benzimidazolecarboxylate
5-chloro-6-nitro-2-trifluoromethylbenzimidazole
6-chloro-2-trifluoromethyl-4-nitrobenzimidazole
4-chloro-5-nitro-2-trifluoromethylbenzimidazole
4-chloro-7-nitro-2-trifluoromethylbenzimidazole
4-chloro-6-nitro-2-trifluoromethylbenzimidazole
5-chloro-4-nitro-2-trifluoromethylbenzimidazole
5-chloro-2-heptafluoropropyl-7-nitrobenzimidazole
1~ 4-chlorodifluoromethyl-6-nitro-2-trifluoromethyl-
benzimidazole
5-nitro-2,6-bis(trifluoromethyl)benzimidazole,
potassium salt
7-nitro-2,5-bis(trifluoromethyl)benzimidazole,
calcium salt
6-difluoromethyl-4-nitro-1-propoxy-2-trifluoro-
methylbenzimidazole
4-chloro-6-nitro-2-trifluoromethyl-1-(~-xyloyl)ben-
zimidazole
1-acetoxy-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole
6-chloro-2-heptafluoroisopropyl-1-butyryloxybenzimi-
dazole
l-methylsulfonyl-4-nitro-2,6-bis(trifluoromethyl)ben-
zimidazole
l~propylsulfonyl-7-nitro-2,5-bis(trifluoromethyl)ben-
zimidazole
l-butyryl-7-nitro-2,5-bis(trifluoromethyl)benzimi-
dazole
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The preferred compounds of this invention are the
following.
phenyl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimi-
dazolecarboxylate
isopropyl 4-nitro-2,6-bis(trifluoromethyl)-1-ben-
zimidazolecarboxylate
2-chlorodifluoromethyl-4-nitro-6-trifluoromethyl-
benzimidazole
l-ethoxy-4-nitro-2-pentafluoroethyl-6-trlfluoro-
methylbenzimidazole
phenyl 2-chlorodifluoromethyl-4-nitro-6-trifluoro-
methyl-l-benzimidazolecarboxylate
ethyl 2-chlorodifluoromethyl-4-nitro-6-trifluoro-
methyl-l-benzimidazolecarboxylate
isopropyl 4-nitro-2-(1,1,2,2-tetrafluoroethyl)-6-
trifluoromethyl-l-benzimidazolecarboxylate
Organic chemists are now aware of the synthetic
methods which are used to make the benzimidazoles of this method.
Some explanation of the synthetic methods and a few specific
examples will be given, however, to assure that all may obtain
the compounds.
The method of synthesis depends on the l-substituent
of the benzimidazole to be made. The synthesis of all the
benzimidazoles except the l-alkoxy and l-acyloxy-substituted
compounds begins with the reaction of an appropriately sub-
stituted o-phenylenediamine with a fluoroalkanoic acid. The
reaction can be done in 5N acid, such as HCl, at reflux temp-
erature. The 2-substituent of the benzimidazole to be
synthesized comes from the substituents of the alkanoic acid.
For example, if a 2-trifluoromethylbenzimidazole is to be made,
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the phenylenediam~ne is reacted with trifluoroacetic acid. If
the benzimidazole is to have a 2-heptafluoropropyl substituent,
the reactant is heptafluorobutyric acid.
Higher yields of the benzimidazoles are obtained by
reacting the o-phenylenediamine with the fluoroalkanoic acid in
the presence of a halide such as phosphorus oxychloride or
phosphorus pentachloride in a solvent such as pyridine. It is
also possible to perform the synthesis in the presence of an
acid chloride formed in situ in the reaction mixture. The
. _
reaction goes quickly at reflux temperature.
The benzene ring substituents of the benzimidazole
are the ring substituents of the o-phenylenediamine. For
example, if the benzimidazole is to have a 4-chloro-6-nitro
substitution, the reactant is 3-chloro-5-nitro-o-phenylenedia-
mine. If the benzimidazole is to be a 7-nitro-5-chlorodifluoro-
methyl compound, the reactant is 6-nitro-4-chlorodifluoro-
methyl-_-phenylenediamine.
The l-substituents of the benzimidazoles, other than
l-alkoxy and l-acyloxy, are conveniently made by the direct
attachment of the desired l-substituent to the benzimidazole.
The sulfonyl, carboxylate, thiocarbamoyl, and acyl substituents
are attached to the l-position of the benzimidazole ring system
by direct reaction of the benzimidazole with a halide derivative
of the desired substituent. For example, an ethylsulfonyl i9
provided by reaction with ethylsulfonyl chloride; a propyl-
carboxylate, by reaction with propyl chloroformate; an anisoyl
substituent, by reaction with anisoyl chloride; and an N,N-
diethylthiocarbamoyl substituent, by reaction with N,N-diethyl-
thiocarbamoyl bromide. The reaction goes easily at room temp-
erature in solvents such as acetonitrile, tetrahydrofuran, and
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benzene. Either the benzimidazole itself or an alkali metal
salt of it may be used as the starting compound for the
reaction. Examples 2-4 below illustrate the synthesis.
The benzimidazoles with l-alkoxy and l-acyloxy sub-
stituents are prepared through a l-hydroxybenzimidazole inter-
mediate, which is prepared by reductive ring closure of an
appropriate substituted acetanilide, which is prepared in turn
from an o-nitroaniline.
A l-alkoxy-substituted benzimidazole is easily made
by reacting the l-hydroxybenzimidazole intermediate with an
alkyl halide in the presence of an alkali metal alkoxide,
hydroxide, or carbonate at ambient or elevated temperature.
A l-acyloxybenzimidazole is synthesized at room temperature by
reaction of a l-hydroxybenzimidazole with an acyl chloride.
For example, a l-benzoyloxybenzimidazole is made with benzoyl
chloride as the reactant, carrying out the reaction at room
temperature in pyridine.
Alkali metal, alkaline earth metal, and ammonium salts
of the l-unsubstituted benzimidazoles are easily made by the
common methods. For example, alkali metal and alkaline earth
metal salts are made by reaction of a benzimidazole with a
methoxide of the metal in methanol at room temperature. Such
salts are also conveniently prepared from hydroxides of the
alkali and alkaline earth metals by dissolving the hydroxide
in an appropriate solvent such as water, aqueous alcohol, or
aqueous acetone, and adding the benzimidazole compound to the
solution at room temperature. Ammonium salts are prepared by
contacting a benzimidazole with ammonium hydroxide or by bub-
bling ammonia gas through a solution of the benzimidazole.
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The examples immediately below show the synthesis of
typical ex~mplary compounds. Organic chemists, guided by the
above general teaching as well as the common skill of the
chemical art, can use the methods of the examples below to
prepare all the benzimidazoles useful in this method.
The first example illustrates the synthesis of an
intermediate o-phenylenediamine, as well as the synthesis of a
typical benzimidazole.
Example 1
4-nitro-2-pentafluoroethyl-6-trifluoromethylbenzimidazole
A solution of 40.5 g. of 2,6-dinitro-4-trifluoro-
methyl-l-chlorobenzene in 300 ml. of benzene was mixed with
250 ml. of 14N ammonium hydroxide. The mixture was stirred at
room temperature for about 1-1/2 hours, when another 100 ml. of
14N ammonium hydroxide was added. The mixture was stirred for
2 hours more. The mixture was allowed to separate in layers,
and the organic layer was separated, washed with water, and
dried. Evaporation of the solvents under vacuum gave 2,6-
dinitro-4-trifluoromethylaniline, m.p. 142-144C. after re-
crystallization from hexane-benzene.
A 24 g. portion of the above product was dissolved in
300 ml. of ethanol. The solution was heated to about 35C. and
110 ml. of 20 percent aqueous ammonium polysulfide, containing
5 percent free sulfur, was added. The temperature of the mix-
ture rose spontaneously to about 60C., at which temperature
it was maintained for about 10 minutes. The reaction mixture
was then cooled to about 40C. and poured into water. The re-
sulting mixture was filtered. Acetone was added to the pre-
cipitate to remove residual product from the sulfur, and the
resulting suspension was filtered also. Excess benzene was
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added to the combined filtrates, and the liquid mixture was then
evaporated to dryness. Recrystallization of the dry solid
produced 3-nitro-5-trifluoromethyl-o-phenylenediamine, m.p.
121-123C.
A 44 g. portion of the above intermediate product was
mixed with 100 ml. of pyridine and 35 g. of pentafluoropropionic
acid. The mixture was stirred while 65 g. of phosphorus oxy-
chloride was added dropwise. The mixture was then heated at
reflux temperature for 5 minutes and cooled. When the temp-
erature of the mixture had decreased to about 70C., 300 ml. of
water was added, and the mixture was vigorously stirred while
it was cooled to room temperature. A light brown solid pre-
cipitated which was separated by filtration and air-dried. The
product was 59 g. of 4-nitro-2-pentafluoroethyl-6-trifluoro-
methylbenzimidazole, m.p. 124-125C.
The following synthetic examples illustrate the
synthesis of l-substituted benzimidazoles.
Example 2
4-nitro-1-PhenYlsu onyl-2,6-bis(trifluoromethyl)benzimidazole
A solution of 3.5 g. of phenylsulfonyl chloride in
20 ml. of anhydrous acetonitrile was added to a solution of
6.4 g. of 4-nitro-2,6-bis(trifluoromethyl)benzimidazole, sodium
salt in 50 ml. of anhydrous acetonitrile. The mixture was
stirred at room temperature for 2 hours, and the reaction mix-
ture was filtered. The filtrate was evaporated to dryness under
vacuum, and the residue was recrystallized from benzene-pentane
to yield 4-nitro-1-phenylsulfonyl-2,6-bis(trifluoromethyl)ben-
zimidazole, m.p. 183-185C.
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ExamPle 3
phe_yl 4-nitro-2,6-bis(trifluoromethyl)-1-benzimidazole-
carboxYlate
The procedure of Example 2 was repeated, using
phenylchloroformate in place of phenylsulfonyl chloride. The
product was isolated by the procedure of Example 2 and re-
crystallized from pentane to yield phenyl 4-nitro-2,6-bis-
(trifluoromethyl)-l-benzimidazolecarboxylate, m.p. 100-103C.
The method of Example 2 is also used, substituting
an N,N-dialkylthiocarbamoyl chloride for the sulfonyl chloride,
in the synthesis of the l-thiocarbamoyl-substituted compounds.
The l-acylbenzimidazoles are easily synthesized by
a method exemplified by the following.
Exam~le 4
-
l-acetyl-2,6(2,5)-bis(trifluoromethyl)-4(7)-nitrobenzimidazole
A 9 g. portion of 4-nitro-2,6-bis(trifluoromethyl)-
benzimidazole was dissolved in about 600 ml. of dry benzene,
and 3.3 g. of triethylamine was added. To the solution was
added dropwise 2.5 g. of acetyl chloride dissolved in 75 ml. of
benzene. The addition was over a period of about 2.5 hours.
The mixture was then stlrred overnight at room temperature. In
the morning, the reaction mixture was filtered, and the filtrate
was evaporated under vacuum to give a yellow-orange solid
residue, m.p. 100-114C. Recrystallization of the residue from
benzene gave a product in the form of gummy platelets, m.p.
115-125C. Nuclear magnetic resonance analysis of the product
indicated a 50-50 mixture of the two acetyl isomers, 1-acetyl-2,
5-bis(trifluoromethyl)-7-nitrobenzimidazole and 1-acetyl-2,6-
bis(trifluoromethyl)-4-nitrobenzimidazole, which were separated
by column chromatography.
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Benzimidazoles which have l-alkoxy and l-acyloxy sub-
stituents are prepared through a l-hydroxybenzimidazole inter-
mediate. The example below illustrates the synthesis of 1-
hydroxybenzimidazoles.
ExamPle 5
l-hydroxy-4-nitro-2,6-bis(trifluoromethyl)benzimidazole
A solution of 25.1 g. of 2,6-dinitro-4-trifluoro-
methylaniline in 100 ml. of pyridine was treated with trifluoro-
acetyl chloride, which had been prepared from 10 ml. of tri-
fluoroacetic acid. Ethanol was added to the resulting mixtureuntil it was homogeneous, and the reaction mixture was then
evaporated under vacuum. The residue after evaporation was
washed with water, dried, dissolved in acetone, and filtered.
Chloroform was added to the filtrate until the product pre-
cipitated. The precipitate was separated by filtration and
dried to obtain the purified intermediate, 2',6'-dinitro-4'-
trifluoromethyl-2,2,2-trifluoroacetanilide.
A 1.75 g. portion of the above intermediate was dis-
solved in 100 ml. of ethyl acetate. One hundred mg. of 5 percent
palladium on carbon was added, and the mixture was hydrogenated
at an initial pressure of 13 psig. and room temperature until
0.01 mole of hydrogen had been taken up. The reaction mixture
was then filtered and evaporated to dryness. The solid residue
was taken up in about 300 ml. of ether, extracted into 5 percent
Na2CO3, and acidified. The desired l-hydroxy-4-nitro-2,6-bis-
(trifluoromethyl)benzimidazole precipitated and was separated by
filtration. The product was then taken up in ether and dried
over MgSO4, and the ether was evaporated. The product was
crystallized from chloroform to produce 900 mg. of 1-hydroxy-4-
nitro-2,6-bis(trifluoromethyl)benzimidazole, m.p. 222-224C.
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The l-alkoxy compounds are made from a l-hydroxy
intermediate as shown in the following example.
Example 6
l-ethox~-4-nitro-2,6-bis(trifluoromethyl)benzimidazole
A 6 g. portion of 1-hydroxy-4-nitro-2,6-bis(tri-
fluoromethyl)benzimidazole was mixed with 50 ml. of methanol,
10 ml. of ethyl iodide, and 2.5 g. of sodium ethoxide. The mix-
ture was heated at reflux temperature overnight with stirring,
and~was then cooled and evaporated to dryness. The residue was
taken up in ether, and the ether solution was washed with water.
The ether layer was then evaporated to dryness, and the residue
was recrystallized from petroleum ether to produce the desired
l-ethoxy-4-nitro-2,6-bis(trifluoromethyl)benzimidazole, m.p.
94-96C.
Similarly, the l-acyloxy compounds are readily syn-
thesized by reacting the appropriate l-hydroxybenzimidazole with
an acyl chloride. For example, l-benzoyloxy-4-nitro-2,6-bis-
(trifluoromethyl)benzimidazole is made by reacting l-hydroxy-
4-nitro-2,6-bis(trifluoromethyl)benzimidazole with benzoyl
chloride at room temperature in pyridine.
The example below illustrates the synthesis of
benzlmldazole salts.
Exam~ 7
4-nitro-2,6-bis(trifluoromethyl)benzimidazole, sodium salt
A mixture of 6 g. of 4-nitro-2,6-bis(trifluoromethyl)-
benzimidazole and 1.1 g. of sodium methoxide in 100 ml. of
methanol was prepared. The reaction mixture was shaken for a
few minutes at room temperature and filtered. Evaporation of
the filtrate to dryness under vacuum produced the sodium salt
X-3999A -17-
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of 4-nitro-2,6-bis(trifluoromethyl)benzimidazole, m.p. about
200C.
The instant method of parasite control is of the
systemic type. The benzimidazole compounds described above
have the ability to permeate the living tissues of a host
animal to which one of the compounds is administered. Insect
and acarina parasites which consume blood or other living
tissues of the host animal ingest the compounds with which the
tissue is permeated, and are thereby killed. It is probable
that the blood is the agency through which the compound is dis-
persed through the host animal, but parasites such as screw-
worms, which do not suck blood, are killed by this method, in-
dicating that the compounds permeate other tissues as well as
blood.
Some parasites, such as most ticks, feed on living
tissues of the host animal during most of the parasite's life.
Other parasites, such as screwworms, feed on the host only in
the larval stage. A third group of parasites, such as the
bloodsucking flies, feed on animal hosts only in the adult
stage. Administration of the benzimidazoles of this method to
host animals kills parasites which feed on the llving tissues
of the animals, no matter what the life stage of the feeding
parasite.
All the species of insect and acarina parasites which
feed on the living tissues of animals are killed by this method.
The parasites which suck the host animal's blood, those which
burrow into and feed on the animal's tissue, and those, like the
larvae of the bot flies, which enter a natural orifice of the
host, attach to the mucous membranes, and feed therefrom are all
equally effectively killed. For the sake of clarity, a number
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of specific parasites of various host animals which are con-
trolled by this method will be mentioned. The parasitic life
stage and the means by which it inests the host animal are
given for each parasite.
Parasites of Horses
horsefly, adult, bloodsucking
stable fly, adult, bloodsucking
black fly, adult, bloodsucking
horse sucking louse, immature, adult, bloodsucking
mange mite, nymph, adult, skin burrowing
scab mite, adult, skin-eating
common horse bot fly, larva, migrating in alimentary
canal
chin fly, larva, migrating in alimentary canal
nose bot fly, larva, migrating in alimentary canal
Parasites of Bovines
horn fly, adult, bloodsucking
cattle biting louse, adult, skin-eating
cattle bloodsucking louse, nymph, adult, bloodsucking
cattle follicle mite, adult, skin-burrowing
cattle tick, larva, nymph, adult, bloodsucking
ear tick, nymph, bloodsucking
Gulf Coast tick, adult, bloodsucking
Rocky Mountain spotted-fever tick, adult, bloodsucking
lone-star tick, adult, bloodsucking
heel fly, larva, migrating through the body
bomb fly, larva, migrating through the body
blowfly, larva, infesting wounds
X-3999A -19-
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Parasites of Swine
hog louse, nymph, adult, bloodsucking
chigoe flea, adult, bloodsucking
Parasites of Sheep
bloodsucking body louse, adult, bloodsucking
bloodsucking foot louse, adult, bloodsucking
sheep ked, adult, bloodsucking
sheep scab mite, nymph, adult, skin-eating
nose fly, larva, migrating in the sinuses
greenbottle fly, larva, infesting wounds
black blowfly, larva, infesting wounds
secondary screwworm, larva, infesting wounds
Parasites of Poultry
bed bug, nymph, adult, bloodsucking
Southern chicken flea, adult, bloodsucking
fowl tick, nymph, adult, bloodsucking
chicken mite, nymph, adult, bloodsucking
scaly-leg mite, adult, skin-burrowing
depluming mite, adult, skin-burrowing
0 Parasites of Dogs
horse fly, adult, bloodsucking
stable fly, adult, bloodsucking
mange mite, nymph, adult, skin-burrowing
dog follicle mite, adult, burrowing in hair follicles
flea, adult, bloodsucking
It will be understood that the parasites mentioned
above are not confined to the single host animal with which
each is here identified. Most parasites inhabit various hosts,
although each parasite has a favorite host. For example, the
0 mange mite attacks at least horses, hogs, mules, humans, dogs,
X-3999A -20-
1057~97
cats, foxes, rabbits, sheep, and cattle. Horseflies freely
attack horses, mules, cattle, hogs, dogs, and most other
animals. This method effectively kills parasites of the types
described above growing in the host animals mentioned above,
and in other host animals as well. For example, this inven-
tion is effective in cats, goats, camels, and zoo animals.
The host animals in which this method is preferably
practiced are dogs, bovines, sheep, or horses. The method is
preferably used for the control of ticks, fleas, flies, or
screwworms.
The time, manner, and rates at which the compounds of
this method are effectively administered may be varied over a
wide range. Detailed explanation of the ways in which this
method is practiced will be given.
The compounds are administered to the animals at
rates from about 1 to about 100 mg./kg. which is a parasiti-
cidally-effective amount. The best rate for killing a given
parasite infesting a given animal must be determined in-
dividually, but it will be found that in most cases the optimum
rate is within the preferred range of from about 2.5 to about
50 mg./kg. The optimum rate for a given instance depends on
such factors as the health of the animal to be treated, the
susceptibility of the parasite of primary concern, the expense
which can be borne by the animal, and the degree of control
desired. Lower rates are safer for the host animal, less ex-
pensive, and often easier to administer, but are likely to give
incomplete or minimum control of the parasite so that re-
infestation may occur. On the other hand, higher rates of
administration give more complete control of the parasites, but
are more expensive and may impose a stress on the treated
X-3999A -21-
1057197
animals .
The comp~unds of this method are effective when
administered at any time of year to animals of any age. It is
possible to administer the compounds of this method to the
animals continuously, as by constant feeding of a diet which
contains one of the compounds, and thus assure that all para-
sites which contact the treated animals will be killed. Such
administration is by no means economical, and it will usually
be found best to administer the compounds at such times as to
give the best return of parasite control for the compound ex-
pended. Certain parasites, such as cattle grubs, which are
the larvae of the heel fly and the bomb fly, have a known
active season when they attack animals. If such a parasite is
of primary importance, this method can be practiced only during
that season with assurance of year-round control of the para-
site. Other parasites, such as ticks, infest and bite animals
essentially the year round. Control of such parasites can
still be accomplished with relatively brief periods of admini-
stration by administering the compound to all the animals on a
farm or in an area for a short period o time, such as for a
few weeks. All the parasites of a generation are thus killed,
and the animals can be expected to remain parasite-free for a
considerable length of time, until reinfested by parasites
arriving with imported animals or the like.
The compounds of this method may be administered by
any of the usual oral and percutaneous routes. It should be
noted that many of the compounds of this method are chemically
changed by passage through the rumen of a ruminant animal.
Oral administration to ruminant animals is therefore advisable
only if the compounds are protected from the rumen environment
X-3999A -22-
105719~
by a special formulation. Such formulations will be dis-
cussed below.
The formulation and administration to animals of
biologically-effective comp~unds is a very old and developed
art. Some explanation of the different formulations and
methods of administration will be given to enable all to
practice this method of parasite control.
Percutaneous administration of the benzimidazole com-
pounds is carried out in the ways usual in the animal veteri-
nary art. If a water-insoluble benzimidazole is desired,
it is practical to dissolve the compound in a physiologically-
acceptable solvent, such as the polyethylene glycols for ex-
ample. It is likewise practical to formulate an injectable
suspension of the benzimidazole as a fine powder, suspended in
a formulation of physiologically-acceptable nonsolvents, sur-
factants, and suspending agents.
The nonsolvent can be, for example, a vegetable oil
such as peanut oil, corn oil or sesame oil, a glycol such as a
polyethylene glycol, depending on the benzimidazole chosen.
The compounds used in this invention are admini-
stered as compositions wherein the adjuvant employed is a sub-
stance other than water or common organic solvents. Suitable
physiologically-acceptable adjuvants are necessary to keep the
benzimidazole suspended. The adjuvants can be chosen from
among the emulsifiers, such as salts of dodecylbenzene sulfate
and toluenesulfonate, ethylene oxide adducts of alkylphenol,
and oleate and laurate esters, and from the dispersing agents
such as salts of naphthalenesulfonate, lignin sulfonate, and
fatty alcohol sulfates. Thickeners such as carboxymethyl cel-
lulose, polyvinylpyrrolidone, gelatin and the alginates are
X-3999A -23-
1057197
also used as adjuvants for injectable suspensions. Many
classes of surfactants, as well as those which have been dis-
cussed above, serve to suspend the benzimidazoles. For example,
lecithin and the polyoxyethylene sorbitan esters are useful
surfactants.
Percutaneous administration is conveniently accom-
plished by subcutaneous, intramuscular, and even intravenous
injection of the injectable formulation. Conventional needle-
type injection devices as well as needle-less air-blast in-
jection devices are useful.
It is possible to delay or sustain the permeation ofthe benzimidazole compound through the animal's living tissues
by proper formulation. For example, a very insoluble benzimi-
dazole may be used. In that event, the slight solubility of
the compound causes sustained action because the body fluids
of the animal can dissolve only a small amount of the compound
at any one time.
Sustained action of the benzimidazole can also be
obtained by formulating the compound in a matrix which will
physically inhibit dissolution. The formulated matrix i9 in-
jected into the body where it remains as a depot from which the
compound slowly dissolves. Matrix formulations, now well known
in the art, are formulated in waxy semisolids such as vegetable
waxes and high molecular weight polyethylene glycols.
Even more effective sustained action is obtained by
introducing into the animal an implant containing one of the
compounds. Such implants are now well known in veterinary
medicine, and are usually made of a silicone-containing rubber.
The benzimidazole compound is dispersed through a solid rubber
implant or is contained inside a hollow implant. Care must be
X-3999A -24-
1057~97
taken to choose a benzimidazole compound which is soluble in the
rubber from which the implant is made, since it is dispersed by
first dissolving in the rubber, and then leaching out of the
rubber into the body fluids of the treated animal.
The rate at which the compound is released from an
implant, and hence the lenqth of time during which the implant
remains effective, is controlled with good accuracy by the
proper adjustment of the concentration of the compound in the
implant, the external area of the implant, and the formulation
of the polymer from which the implant is made.
Administration of benzimidazole compounds by means of
an implant is a particularly preferred method of this invention.
Such administration is highly economical and efficacious,
because a properly designed implant maintains a constant concen-
tration of the compound in the tissues of the host animal. An
implant can be designed to supply compound for several months,
and is easily inserted in the animal. No further handling of
the animal or concern over the benzimidazole dosage is neces-
sary after the insertion of the implant.
Oral administration of a benzimidazole may be per-
formed by mixing the compound in the animal's feed, or by
administering oral pharmaceutical dosage forms such as drenches,
tablets, or capsules.
When a compound of this method is to be administered
orally to a ruminant animal, it is necessary to protect the
compound from the deleterious effect of the rumen processes.
The veterinary pharmaceutical art is now aware of effective
methods for coating and encapsulating drugs to protect them from
the rumen. For example, coating materials and methods are dis-
closed in Grant et al., U. S. Patent 3,697,640. Grant teaches
X-3999A -25-
1057197
a method of protecting substances from action of the rumen
by coating the substances with a film of cellulose propionate
3-morpholinobutyrate. Such a film can be used to protect the
benzimidazoles of this method. Conveniently, tablets, or cap-
sules containing a benzimidazole are coated with the film in a
coating pan or a fluidized bed spray apparatus. Pellets of the
parasiticide may be made, coated with the film, and filled into
capsules. Alternatively, a solid mixture of the benzimidazole
and the film-forming agent may be made and broken or ground into
small particles, each of which comprises the benzimidazole en-
closed in a matrix of the film-forming agent. The particles may
be filled into capsules for oral administration, or made into
an oral suspension.
The formulation of veterinary drugs in animal feed
is an extremely well-known art. It is usual to formulate the
compound first as a premix in which the benzimidazole is dis-
persed in a liquid or particulate solid carrier. The premix
may conveniently contain from about 1 to about 400 g. of drug
per pound, depending on the desired concentration in the feed.
The premix is in turn formulated into feed by dispersing it in
the feed mixture in a conventional mixer. The correct amount
of benzimidazole, and hence of premix, to mix in the feed is
easily computed by taking into account the weight of the ani-
mals, the approximate amount each animal eats per day, and the
concentration of the benzimidazole in the premix.
The compounds can easily be formulated into tablets
and capsules according to the conventional methods, about which
no teaching is required here. Drench formulations comprise the
benzimidazole compound dissolved or dispersed in an aqueous
liquid mixture. Again, it is most convenient to make the drench
X-3999A -26-
1057197
-
by dissolving a water-soluble benzimidazole salt. It is almost
as convenient, however, and equally efficacious to use a dis-
persion of the compound made in the same way that the drinking
water formulations discussed above are made.
The examples immediately below show the great
effectiveness of this method in controlling a number of parasites
which normally affect economic animals when those parasites were
fed on guinea pigs to which the compounds of this method had
been administered. The compounds were tested against screwworms,
which are larvae of the black blowfly, against the stable fly,
and against nymphs of the lone star tick. The blowfly and
stable fly are insects; the lone star tick is representative of
the acarina.
The stable fly is a common free-flying, bloodsucking
parasite; the lone star tick is a typical bloodsucking parasite
which spends the nymphal and part of the adult periods of the
life cycle attached to the host animal, usually cattle. Blow-
fly larvae, or screwworms, hatch from eggs laid near a wound of
the host animal by the free-flying insect. The larvae eat their
way into the healthy flesh exposed by the wound and pass part
of the life cycle therein, feeding one host's flesh and blood.
The stable fly is parasitic on horses, mules,
cattle, hogs, dogs, cats, sheep, goats, rabbits, and humans.
The lone star tick is primarily a cattle parasite, but also
attacks horses, mules, and sheep. Blowfly larvae attack any
wounded animal, but are particularly harmful to cattle, hogs,
horses, mules, sheep, and goats.
The test animals were male guinea pigs weighing 400-
500 g. The test compounds were administered to the animals at
the rate of 10 mg./kg. Each compound was administered orally
X-3999A -27-
~05719~7
to one animal, and injected subcutaneously (SC) to another
animal. The test compounds were administered as dispersions
in sorbitan monolaurate. ~ach group of treated guinea pigs
was tested along with two pigs to which a sorbitan monolaurate
blank was administered.
Each guinea pig was infested with 25 nymphs of the
lone star tick 48 hours before treatment. Twenty-four hours
before treatment, each pig was wounded, and the wounds were
infested with larvae of the black blowfly. At 4 hours, 24
hours, and in some cases at 48 hours, after treatment, stable
flies were fed on the guinea pigs.
The animals and the parasites with which they were
infested were observed. The stable flies were observed 24 hours
after they fed on the pigs and the number of flies killed by
the blood they ingested was counted. The blow fly larvae were
removed from the wounds 24 hours after treatment, and the num-
ber of dead larvae was counted. The ticks were observed during
their engorgement period, and the number of them killed by the
blood they sucked from the guinea pigs was counted also. The
observations are reported below as the percent of each parasite
which was killed.
X-3999A -28-
1057197
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X- 3999A -29-
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X-3999A -30-
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105719'7
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X-3999A -32-
:~ ~057197
It is clear from the tests reported above that this
method of animal parasite control is effective in controlling
the dif~erent types of insect and acarina parasites which
consume the host's living tissues. The tests, carried out in
a standard laboratory animal, show the high potency of the
benzimidazoles of this method in killing parasites which
burrow into and consume the flesh of the host animal, which
periodically suck blood of the animal, and which suck the host's
blood while remaining affixed to the animal's skin. Both oral
and percutaneous administration of the compounds to the animals
controlled the parasites.
The examples below report tests of the parasiticidal
method in dogs. The dogs used in the test were suffering from
natural infestations of dog ticks and fleas. The compounds
were administered intravenously or subcutaneously as aqueous
dispersions.
It will be noted that, in most of the tests, the 48-
and 72-hour data indicate that male ticks are killed more
effectively than are females. It is believed that the dif-
ference is due to the feeding habits of the sexes. Males feedmore or less continuously, while females feed in periodic large
meals. It is to be expected that the kill of female ticks will
increase with time after the injection of the compound, as the
compound moves through the host's body.
Example _
Two dogs were treated with 2.7 mg./kg. of isopropyl
4-nitro-2,6-bis(trifluoromethyl)-1-benzimidazolecarboxylate as
a single intravenous injection. Twenty-four hours after admin-
istration of the compound, one of the dogs had died. The cause
of death was not determined.
X-3999A -33-
-
1057197
Both ticks and fleas on the surviving dog were
visibly affected by the compound 24 hours after administration.
Forty-eight hours after administration, it was found that 10
percent of the female ticks, 20 percent of the male ticks, and
95 percent of the fleas were dead.
Example _
Two other dogs were injected with 10 mg./kg. of ethyl
2-chlorodifluoromethyl-4-nitro-6-trifluoromethyl-1-benzimi-
dazolecarboxylate as a single intravenous administration. When
the animals were first observed, 24 hours after administration
of the compound, there was no visible effect on the tick pop-
ulation, but the fleas were visibly injured.
The parasite population of the dogs was counted 48
hours after administration. At that time, 10 percent of the
fema~e ticks, 40 percent of the male ticks, and 100 percent
of the fleas on both dogs were dead.
Example 24
Four dogs were treated with 25 mg./kg. of isopropyl
4-nitro-2,6-bis(trifluoromethyl)-1-benzimidazolecarboxylate as
a single subcutaneous injection. At the 24-hour observation,
there was in general no effect on the parasites of the dogs,
although the fleas on one dog were visibly affected.
At 48 hours, the flea populations on all the dogs were
visibly reduced, and the ticks on two dogs were visibly injured
by the compound.
X-3999A -34-
1057197
The parasites remaining on the dogs were counted after
72 hours, and the p`ercent killed was found to be as follows.
Female Male
Dog Ticks Ticks Fleas
l 20% 80% 100%
2 40 100 100
3 60 60 lO0
4 0 0 95
Example 25
Another group of four dogs was injected with 50
mg./kg. of ethyl 2-chlorodifluoromethyl-4-nitro-6-trifluoromethyl-
l-benzimidazolecarboxylate as a single subcut.aneous injection.
Neither the ticks nor the fleas were seen to be affected 24
hours after administration. The fleas on all the dogs were
injured 48 hours after administration, as were the ticks on
one dog.
The 72-hour parasite counts showed the following per-
cent of kill.
Female Male
Dog Ticks Ticks Fleas
l 100% 100% 100%
2 lO 50 lO0
3 50 90 100
4 10 60 100
The examples above show the outstanding value of
this method of parasite control. Single percutaneous injections
of the compounds gave essentially complete control of fleas,
30 and worthwhile control of ticks. The data indicate that, as
X-3999A -35-
1057~97
the compounds continue to permeate through the tissues of the
host, the tick kill will continue to improve.
X-3999A -36-
1057197
SUPPLEMENTARY DISCLOSURE
The principal disclosure provides a means of
killing insect and acarina parasites which consume living
tissues of a host animal which comprises an orally or pre-
cutaneously administerable composition comprising an adjuvant
suitable for oral or percutaneous administration to an animal
and as an active ingredient a parasiticidally-effective amount
of a compound of the formula
02N ~ I
~ ¦ ~ Ra (I~
wherein R is chloro, trifluoromethyl, difluoromethyl, or
chlorodifluoromethyl;
o o o
Rl is hydrogen, -C-o-R3~ -C-R4, -S-R5,
S O
-C-N(Cl-C3 alkyl)2, -O-(Cl-C3 alkyl), or -O-C-R ;
R is chlorodifluoromethyl, trifluoromethyl,
1,1,2,2-tetra~luoroethyl, pentafluoroethyl,
heptafluoropropyl, or heptafluoroisopropyl;
R is Cl-C6 alkyl, C2-C3 alkenyl, phenyl, or benzyl;
R is Cl-C5 alkyl, phenyl, chlorophenyl, anisyl,
or tolyl;
R5 is Cl-C3 alkyl, or phenyl;
or the ammonium, alkali metal~ or alkaline earth metal
salts of the compounds of the formula (I) wherein Rl is
hYdrogen.
The present disclosure further develops the method
of the principal disclosure in that the compounds of the above
formula are modified in that R can also represent hydroxy.
These compounds are also useful as parasiticides.
- 37 -
J
l. .^ ,
1057197
Thus, this Supplementary Disclosure provides a further
means of killing by ingestion insect and acarina parasites
which consume living ~issues of a host animal which comprises
an orally or percutaneously administerable composition comprising
an adjuvant suitable for oral or percutaneous administration to
an animal and as an active ingredient a parasiticidally-effective
amount of a compound of the formula
OH
OzN
1~ /~ ~ (I)
wherein R is
chloro,
trifluoromethyl,
difluoromethyl, or
chlorodifuloromethyl; and
R2 is
chlorodifluoromethyl,
0
trifluoromethyl,
1,1,2,2-tetrafluoroethyl,
pentafluoroethyl,
heptafluoropropyl, or
heptafluoroisopropyl.
A preferred group of compounds which are particu-
larly useful in this invention have the formula
OH
02N ~ \ ~
~ CFzR~ (II)
R3
herein R6 is chloro, fluoro, difluoromethyl, or
trifluoromethyl; and
- 38 -
~05719'7
R8 is chloro or trifluoromethyl.
The following specific compounds are presented to
assure that those skilled in the organic chemical and para-
sitological arts understand the scope of this invention.
5-chloro-1-hydroxy-7-nitro-2-trifluoromethyl-
benzimidazole
2-chlorodifluoromethyl-1-hydroxy-4-nitro-6-
trifluoromethylbenzimidazole
6-chloro-1-hydroxy-4-nitro-2-(1,1,2,2-tetra-
fluoroethyl)benzimidazole
7-difluoromethyl-1-hydroxy-5-nitro-2-pentafluoro-
ethylbenzimidazole
6-chlorodifluoromethyl-2-heptafluoropropyl-1-
hydroxy-4-nitrobenzimidazole
2-heptafluoroisopropyl-1-hydroxy-6-nitro-5-tri-
fluoromethylbenzimidazole
The preferred compound of this invention is
l-hydroxy-4-nitro-2-(l,i,2,2-tetrafluoroethyl)-6-trifluoro-
methylbenzimidazole.
Organic chemists are now aware of the synthetic
methods which are used to make the benzimidazoles of this
method. Some explanation of the synthetic methods and a few
specific examples will be given, however, to assure that all
may obtain the compounds.
The l-hydroxybenzimidazoles are prepared by
reductive ring closure of an appropriately substituted
acetanilide, which is prepared in turn from an _-nitro-
aniline.
The example immediately below shows the synthesisof typical exemplary compounds. Organic chemists, guided by
the above general teaching as well as the common skill of
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105719'7
the chemical art, can use the methods of the example below
to prepare all the benzimidazoles useful in this method.
Example 26
A solution of 25.1 g. of 2,6-dinitro-4-trifluoro-
methylaniline in 100 ml. of pyridine was treated with tri-
fluoroacetyl chloride, which had been prepared from 10 ml.
of trifluoroacetic acid. Ethanol was added to the resulting
mixture until it was homogeneous, and the reaction mixture
was then evaporated under vacuum. The residue after
evaporation was washed with water, dried, dissolved in
acetone, and filtered. Chloroform was added to the filtrate
until the product precipitated. The precipitate was
separated by filtration and dried to ob~ain the purified
intermediate, 2',6'-dinitro-4'-trifluoromethyl-2,2,2-tri-
fluoroacetanilide.
A 1.75 g. portion of the above intermediate was
dissolved in 100 ml. of ethyl acetate. One hundred mg. of 5
percent palladium on carbon was added, and the mixture was
hydrogenated at an initial pressure of 13 psig. and room
temperature until 0.01 mole of hydrogen had been taken up.
The reaction mixture was then filtered and evaporated to
dryness. The solid residue was taken up in about 300 ml. of
ether, extracted into 5 percent Na2CO3, and acidified. The
desired l-hydroxy-4-nitro-2,6-bis(trifluoromethyl)benzimi-
dazole precipitated and was separated by filtration. The
product was then taken up in ether and dried over MgSO4, and
the ether was evaporated. The product was crystallized from
chloroform to produce 900 mg. of 1-hydroxy-4-nitro-2,6-bis-
(trifluoromethyl)benzimidazole, m.p. 222-224C.
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1057197
All of the specific details set out in the principal
disclosure as to methods of formulation, dosages, methods of
application, etc. apply equally well to the additional compounds
described herein.
The following example reports representative results
of a bio-assay test.
Example 27
Larvae of the black blowfly were used as assay
organisms in a bio-assay test system. The tests were
carried out by administering a compound of formula I as
a single subcutaneous injection to a calf. Samples of
blood were withdrawn from the calf on successive days
after the administration of the compound, and blowfly
larvae were fed on the withdrawn whole blood. The end
point of the test was recorded as the last day on which
90 percent or more of the blowfly larvae were killed.
Aqueous suspensions of l-hydroxy-4-nitro-2-
(1,1,2,2-tetrafluoroethyl)-6-trifluoromethylbenzimidazole
were administered at rates of 5, 10 and 15 mg./kg. The 15
mg./kg. rate killed 90 percent or more of the larvae for
four successive days, and administration at 10 mg./kg.
killed the larvae for three days. The 5 mg./kg. rate was
not effective.
In the tests of this example, the parasites were
exposed to the treated animal's blood indirectly, instead of
directly by feeding the parasites on the animal. The
control obtained, however, is obviously as significant as
if the parasites had sucked blood directly from the animal.
The value of the method in protecting animals from the
very injurious parasite, the blowfly, is clearly demon-
strated by the tests, since several days of parasite con-
trol were obtained from a single administration of a com-
pound of this invention.
