Oxadiazole compounds of the formula ##STR1## wherein X is sulfur or oxygen; Y is sulfur or oxygen; R.sub.1 is methyl, ethyl isopropyl or cyclopropyl; and R.sub.2 is ethyl or isopropyl, provided that when R.sub.1 is methyl or ethyl, R.sub.2 is not ethyl, are effective as corn root worm insecticides.

BACKGROUND OF THE INVENTION 
This invention relates to certain novel 3-alkyl-5-(alkoxy- or 
alkylthio-phosphynyl or phosphinothioylthiomethyl)-1,2,4-oxadiazoles and 
their use as soil insecticides to combat corn root worm. In particular I 
have found that the compounds of this invention show surprisingly good 
activity in killing Diabrotica larvae. 
German Offenlegungschrift No. 2,919,621 discloses insecticidal compounds of 
the general formula: 
##STR2## 
wherein X is oxygen or sulfur; R.sub.1 is hydrogen, C.sub.1 to C.sub.4 
alkyl optionally substituted with halogen, C.sub.1 to C.sub.3 alkoxy, or 
phenyl; R.sub.2 is C.sub.1 to C.sub.4 alkyl; and R.sub.3 is C.sub.1 to 
C.sub.4 alkyl, C.sub.1 to C.sub.6 alkylamino, allylamino or di-(C.sub.1 to 
C.sub.3) alkylamino where the two alkyl groups on the nitrogen may form a 
5- or 6-membered ring which optionally may contain an oxygen atom. 
The compounds of the German Offenlegungschrift were disclosed as effective 
against "sucking" and "biting" insects as well as mites and ticks of the 
order Acarina. The examples showed testing certain of the compounds for 
insecticidal activity on red spider mites, bean aphids, houseflies, German 
cockroach, Mexican bean beetle larvae, corn beetle larvae, flour weevils 
and African boll weevil larvae. 
Commonly-assigned, U.S. Pat. No. 4,237,121 discloses the use of corn root 
worm insecticides of compounds of the formula: 
##STR3## 
wherein X, Y, Z and V are sulfur or oxygen and R.sup.1, R.sup.2, R.sup.3 
are alkyl of 1 to 4 carbon atoms. 
Commonly-assigned U.S. Pat. No. 4,213,973 discloses the use of compounds of 
the formula 
##STR4## 
wherein X, Y, Z and V are oxygen or sulfur; R.sub.1 is hydrogen or alkyl 
of 1 to 6 carbon atoms and R.sup.2 and R.sup.3 are alkyl of 1 to 6 carbon 
atoms, as corn root worm insecticides. 
U.S. Pat. No. 3,432,519 discloses insecticidal and acaricidal compounds of 
the general formula 
##STR5## 
wherein R represents a hydrogen atom, an alkyl group containing 1 to 6 
carbon atoms optionally carrying an alkoxy substituent containing 1 to 4 
carbon atoms or an aryl group (preferably phenyl) which may carry one or 
more substituents selected from hydrogen atoms, the nitro group and alkyl, 
alkoxy and alkylthio groups containing 1 to 4 carbon atoms, R.sub.1 
represents a hydrogen atom or an alkyl group containing 1 to 4 carbon 
atms, R.sub.2 represents an alkyl group containing 1 to 4 carbon atoms and 
X represents an oxygen or sulfur atom. 
British Pat. No. 1,213,707 discloses insecticidal compounds of the general 
formula 
##STR6## 
wherein X.sub.1 and X.sub.2 which may be the same or different, each 
represents an oxygen or sulfur atom; A represents an alkylene group; 
R.sub.1 represents an alkyl group, R.sub.2 represents an alkyl or alkoxy 
group; and R.sub.3 represents a hydrogen atom or an optionally substituted 
carbamoyl or amino group. 
The examples of the British patent show testing of certain of the compounds 
for insecticidal activity on adult houseflies; mosquito larvae, diamond 
back moth larvae, aphids and adult mustard beetles; red spider mites; and 
white butterfly larvae. None of these tests involved application and use 
of the insecticide in the soil habitat of the insects. 
U.S. Pat. No. 4,028,377 discloses insecticidal compounds of the general 
formula: 
##STR7## 
wherein R.sub.1 represents hydrogen, unsubstituted alkyl, benzyl or 
phenyl, R.sub.2 represents methyl or ethyl, and R.sub.3 represents 
unsubstituted C.sub.1 -C.sub.7 alkyl optionally interrupted by oxygen or 
represents C.sub.3 -C.sub.4 alkenyl. 
The examples of the U.S. Pat. No. 4,028,377 show testing of certain of the 
compounds for insecticidal activity on ticks in cotton wool; larvae of 
ticks; mites; and on root-gall-nematodes in soil. In the latter test, the 
soil infested with the root-gall-nematodes was treated with the compounds 
to be tested and then tomato seedlings were planted either immediately 
after the soil preparation or after 8 days waiting. 
British Pat. No. 1,261,158 discloses compounds of the general formula: 
##STR8## 
wherein R.sub.1 represents an alkyl group, R.sub.2 represents an alkyl or 
alkoxy group, X represents an oxygen or sulfur atom; A represents a 
saturated divalent aliphatic hydrocarbyl group; Y represents a halogen 
atom or an alkyl or alkoxy carbonyl group; and n is 0, 1 or 2. The 
compounds of the examples of British Pat. No. 1,261,158 were tested for 
insecticidal effectiveness on flies, mosquito larvae, moth larvae, mustard 
beetles, aphids, spider mites and butterfly larvae. 
As described in the Ortho Seed Treater Manual, copyright 1976, Chevron 
Chemical Company, page 27, corn root worms have been controlled with 
chlorinated hydrocarbon insecticides, but in areas where resistance to 
such treatment has developed, good control has been obtained with organic 
phosphorus or carbamate soil insecticides such as Diazinon and Carbofuran 
insecticides. The chemical names and formulas for these latter 
insecticides are given below: 
##STR9## 
SUMMARY OF THE INVENTION 
The 3-alkyl-5-(alkoxy- or alkylthio-phosphynyl or 
phosphinothioyl-thiomethyl)-1,2,4-oxadiazole compounds of this invention 
are represented by the formula: 
##STR10## 
wherein X is sulfur or oxygen, Y is sulfur or oxygen, R.sub.1 is methyl, 
ethyl, isopropyl, or cyclopropyl and R.sub.2 is ethyl or isopropyl, 
provided that when R.sub.1 is methyl or ethyl, R.sub.2 is not ethyl. 
Among other factors, the present invention is based on my finding that the 
substituted oxadiazole compounds of my invention are surprisingly 
effective as insecticides for killing corn root worms. The compounds are 
very effective in killing corn root worms when applied to their soil 
habitat. This is especially surprising, since certain closely related 
compounds have shown poor activity as insecticides against corn root worm. 
Preferred compounds include those where X is sulfur, R.sub.1 is methyl or 
ethyl and R.sub.2 is isopropyl. 
As used herein, the following terms have the following meanings, unless 
expressly stated to the contrary. 
The term "root worm" is used herein to include the Northern, Southern and 
Western species of the corn root worm. All of these are of the Diabrotica 
genus. The scientific name of the Northern species is Diabrotica 
longicornis, the scientific name of the Southern species is Diabrotica 
undecimpunctata howardi, and the scientific name of the Western species is 
Diabrotica virgifera. 
DETAILED DESCRIPTION OF THE INVENTION 
The compounds used in the present invention may be prepared by subjecting 
the appropriate 3-alkyl-5-chlo-1,2,4-oxadiazoles (II) to a phosphorylation 
reaction. 
##STR11## 
The phosphinate salts have the general formula (III) wherein X, Y and 
R.sub.2 are as previously defined and M is a group IA metal cation or 
NH.sub.4.sup.+. The phosphorylation reaction may be carried out in an 
inert organic solvent such as methyl ethyl ketone, acetone, acetonitrile, 
ether, methanol or benzene. Preferably, equimolar amounts of reactants are 
employed, although a small excess of either may be used. Either reactant 
may be added to the other reactant in the solvent; however, it is 
preferred to add the solid phosphinate salt to a solution of the 
3-alkyl-5-chloromethyl)-1,2,4-oxadiazole (II). The addition is carried out 
at temperatures in the range of 15.degree. to 30.degree. C. Upon 
completion of addition of the salt, the temperature of the salt is raised, 
preferably to about 50.degree. C.; the reaction mixture is then stirred 
until the reaction is complete, about 1 to about 24 hours. 
At completion of the reaction, the solvent is stripped under reduced 
pressure. The product, a liquid, is then isolated by conventional 
procedures such as extraction, chromatography, filtration. 
The salts used in the phosphorylation reaction may be prepared according to 
the reaction scheme: 
##STR12## 
wherein X, Y and R.sub.2 are as defined in conjunction with Formula I and 
M is a group IA (alkali) metal cation or NH.sub.4.sup.+. 
Reaction (2) is carried out by adding an approximately equimolar amount of 
V to a stirred solution of IV in benzene. An approximately equimolar 
amount of VI was slowly added in a dropwise amount over a period of from 
about 0.5 to 1 hour. After the addition was complete, the reaction mixture 
was stirred for an extended period of time, about 16 hours, filtered and 
the solvent stripped. Other inert organic solvents such as toluene may be 
used in place of benzene. 
The MSH used in reaction (3) is prepared in situ by dissolving MOH in 
isopropyl alcohol by stirring, followed by a period of additional stirring 
from about 2 to 4 hours. Hydrogen sulfide (gas) was added by bubbling it 
through the MOH-alcohol mixture. The resulting mixture was then stirred 
for about 2 to 4 hours to give the (VIII). 
Reaction (3) was carried out by adding product VII (of Reaction (2)) to 
mixture VIII in a ratio of about two equivalents of VIII per equivalent of 
VII in several portions. The reaction mixture was stirred for an extended 
period of time, about 5 to about 12 hours, and then refluxed for about 1 
to about 3 hours. The solvent was stripped, and toluene was used to chase 
the solvent. The product, (III), was washed with hexane and ethyl ether. 
The 3-alkyl-5-chloromethyl-1,2,4-oxadiazoles, II, used in the preparation 
of the compounds of this invention may be prepared by the condensation of 
the appropriate alkylamidoximes with alpha-chloroacetyl chloride according 
to the following reaction scheme: 
##STR13## 
wherein R.sub.1 is as previously defined in connection with Formula I. 
Further details of this preparation are disclosed in commonly-assigned 
U.S. Pat. No. 4,237,121 to King and Wheeler, which is incorporated by 
reference. 
An alternate method of preparing the oxadiazole intermediates of formula II 
which is suitable for the large scale production of such compounds and 
which produces those intermediates in increased yields is disclosed in the 
commonly-assigned, copending U.S. patent application of R. N. Reynolds 
titled "Process for Preparing 5-Halomethyl-1,2,4-Oxadiazoles and 
Intermediates Therefor." 
In the use of the compounds of my invention as corn root worm insecticides, 
optimum formulation concentrations and the manner and frequency of 
application may vary somewhat with the particular species of corn root 
worm, the degree of infestation, the environment, including type of soil, 
soil conditions and weather conditions (e.g. rain fall), and can be 
obtained by routine experimentation. 
A further understanding of my invention can be had from the following 
non-limiting examples.

EXAMPLE 1 
Preparation of Ethyl-O-isopropyldithiophosphinate Potassium Salt 
##STR14## 
To a stirred mixture of 74.2 g (0.455 moles) 
##STR15## 
Ethylthiophosphoric acid dichloride in 400 ml benzene, 30.1 g (0.5 moles) 
isopropyl alcohol was added. To that mixture 50.6 g (0.5 moles) 
triethylamine was added at a dropwise rate overnight. The mixture was then 
warmed for about 1 hour. The mixture was filtered by gravity. Most of the 
solvent (benzene) was stripped off under reduced pressure and heat to give 
##STR16## 
The KSH was prepared in situ by the following procedure: 56.5 g (1 mole) 
KOH was dissolved in about 350 ml isopropyl alcohol with stirring; the 
mixture was allowed to stir for about 2 hours. H.sub.2 S was added to the 
mixture by bubbling the gas through it (about 35 g). The resulting KSH 
mixture was then allowed to stir for 1 hour. 
To the KSH mixture, the product of the first step, 
##STR17## 
was added in several portions, cooling the reaction mixture with water if 
needed. The reaction mixture was stirred overnight and then refluxed for 
two hours. The solvent was removed under reduced pressure and toluene was 
used to chase the solvent. The product was then washed with hexane:ethyl 
ether (3:2). 
The salts used to make the compounds in Table I may be prepared according 
to the above procedure. Optionally, an NaSH mixture is substituted for the 
KSH mixture. 
EXAMPLE 2 
Preparation of 
##STR18## 
To about 75 ml methyl ethyl ketone, 3.3 g (0.025 moles) 
3-methyl-5-chloromethyl-1,2,4-oxadiazole and 6.7 g (0.03 moles) of the 
product of Example 1 were added with stirring. The reaction mixture was 
heated to about 55.degree. C. with stirring for 6 hours. The methyl ethyl 
ketone was stripped under reduced pressure to give the crude product. 
Water (about 50 ml) and methylene chloride (about 75 ml) were added to the 
product and the resulting mixture stirred. The product was extracted into 
the methylene chloride and washed twice with 50 ml water. The product was 
separated with the methylene chloride (organic) phase. Magnesium sulfate 
was added to the methylene chloride phase to dry it. Filtering of the 
methylene chloride phase followed by chromatography on silica gel eluting 
with hexane and methylene chloride, yielded 6.4 g of the product, a light 
yellow liquid. 
Elemental analysis for C.sub.9 H.sub.17 N.sub.2 O.sub.2 PS.sub.2 showed: 
calculated %C 38.6, %H, 6.11, and %N 9.99; found %C 40.8, %H 6.43, and %n 
10.08. 
EXAMPLE 3 
Preparation of 
##STR19## 
To 75 ml methyl ethyl ketone, 3.3 g (0.025 moles) 
3-methyl-5-chloromethyl-1,2,4-oxadiazole and 7.2 g (0.03 moles) 
ethyl-S-isopropyldithiophosphinate potassium salt were added with 
stirring. The reaction mixture was heated to 55.degree. C. with stirring 
for 6 hours. The methyl ethyl ketone was stripped under reduced pressure 
to give the crude product. Water (about 50 ml) and methylene chloride 
(about 75 ml) were added to the product and the mixture was stirred for 
about 10 min. The aqueous and methylene chloride phases were separated, 
the product separating with the methylene chloride phase. The methylene 
chloride phase was dried with magnesium sulfate and filtered to give 5.2 g 
of the product, a yellow liquid which was chromatographed on silica gel 
and eluted with hexane:methylene chloride (1:1). 
Elemental analysis for C.sub.9 H.sub.17 N.sub.2 OPS.sub.3 showed: 
Calculated %C 36.5, %H 5.78, and %N 9.45; found %C 38.6, %H 6.05, and %N 
10.85. 
EXAMPLE 4 
Preparation of 
##STR20## 
To 75 ml acetone, 2.8 g 3-isopropyl-5-chloromethyl-1,2,4-oxadiazole was 
added and the resulting mixture stirred for a few minutes. To that mixture 
2.9 g 
##STR21## 
Ethyl-O-ethylthiophosphinate sodium salt was added and the resulting 
mixture stirred for about 10 minutes and then refluxed for about 4 hours. 
The reaction mixture was then stirred overnight. The acetone was stripped 
under reduced pressure to give the crude product. Methylene chloride 
(about 75 ml) and water (about 50 ml) were added. The water served to wash 
the product, removing NaCl resulting from the reaction. The aqueous and 
methylene chloride phases were separated, the product separating with the 
methylene chloride phase. The methylene chloride phase was dried with 
magnesium sulfate. The product was obtained by column chromatography of 
the methylene chloride phase, eluting first with hexane and then 
hexane:methylene chloride (1:1). 
Elemental analysis for C.sub.10 H.sub.19 N.sub.2 O.sub.3 PS showed: 
calculated %C 43.16, %H 6.88, and %N 10.07; found %C 42.82, %H 6.91, and 
%N 10.62. 
Compounds made in a manner consistent with Examples 1 to 4 are found in 
Table I. 
EXAMPLE 5 
Control of Diabrotica Larvae 
A number of the compounds of the present invention were evaluated for 
control of Diabrotica larvae by the following procedure: 
For each test compound, a dilution series to give 6.4, and 2.5 ppm 
(weight:weight) active ingredient in soil was prepared by diluting an 
acetone-test compound mixture with the appropriate amount of water 
containing a small amount of Ortho X-77 nonionic spreader. 
A 300 g batch of soil was treated with a test compound mixture to give the 
appropriate concentration in soil (i.e. 6.4, 2.5 or 1 ppm). 
About 20 two- to four-day old Diabrotica eggs were placed in the bottom on 
three 8 oz. plastic cups. Half of the treated soil was evenly split 
between the three cups. Ten corn seeds which have been pre-soaked in water 
were evenly distributed on top of the soil in each cup. Ten ml of water 
was gently added to each cup and the remaining soil divided equally 
between the three cups, thus covering the corn seeds. The soil surface of 
the cups was lightly sprayed with water to provide a water seal on each 
cup. The cups were incubated at 70.degree. F. for 10 days, with daily 
watering. 
After 10 days, each test cup was examined under a dissecting scope by 
observing the corn roots and soil through the clear plastic walls of the 
cup. Control of newly-hatched larvae was evaluated by visually evaluating 
the degree of corn root damage by feeding larvae in conjunction with the 
visible presence of live and/or dead larvae. 
The compounds tested, the concentration of test compound in soil (ppm) and 
percent control of Diabrotica larvae are given in Table II. 
I have found from the results of biological testing that certain relatively 
closely related compounds showed no or poor effectiveness in controlling 
corn root worm as measured by the test of Example 5. Some of those 
compounds are shown in Table III, and such compounds are accordingly 
excluded from the scope of the present invention. 
TABLE I 
__________________________________________________________________________ 
Compounds of the Formula 
##STR22## 
Com- ELEMENTAL ANALYSIS 
pound Physical 
% Carbon 
% Hydrogen 
% Nitrogen 
No. X Y R.sub.1 
R.sub.2 
State 
Calc. 
Fd. 
Calc. 
Fd. 
Calc. 
Fd. 
__________________________________________________________________________ 
1 S O CH.sub.3 
CH(CH.sub.3).sub.2 
Yellow 
38.6 
40.8 
6.11 
6.43 
9.99 
10.1 
liquid 
2 S O CH.sub.2 CH.sub.3 
CH(CH.sub.3).sub.2 
Yellow 
40.79 
39.88 
6.51 
6.23 
9.52 
9.74 
liquid 
3 S S CH.sub.3 
CH(CH.sub.3).sub.2 
Yellow 
36.5 
38.6 
5.78 
6.05 
9.45 
10.9 
liquid 
4 S S CH.sub.2 CH.sub.3 
CH(CH.sub.3).sub.2 
Amber 
38.7 
41.3 
6.17 
6.47 
9.03 
10.7 
liquid 
5 O O CH(CH.sub.3).sub.2 
CH.sub.2 CH.sub.3 
Colorless 
43.16 
42.82 
6.88 
6.91 
10.07 
10.62 
liquid 
6 S O CH(CH.sub.3).sub.2 
CH.sub.2 CH.sub.3 
Yellow 
40.8 
41.3 
6.51 
7.05 
9.52 
10.4 
liquid 
__________________________________________________________________________ 
TABLE II 
______________________________________ 
Compound Soil Treatment % Control 
No. ppm Day 0 Day 17 
Day 31 
______________________________________ 
1 6.4 100 95.5 -- 
2.5 97.5 93.5 -- 
6.4 100 96 
2.5 96 94 
2 6.4 62 99.2 
6.4 100 
2.5 100 
2.5 2.5 100 
3 6.4 100 
6.4 100 99.2 
2.5 100 
2.5 9 100 
4 6.4 99.4 -- 52* 
2.5 99.4 -- 23* 
5 6.4 81 -- -- 
2.5 0 -- -- 
6 6.4 99.2 -- -- 
2.5 18 -- -- 
______________________________________ 
*Day 27 
TABLE III 
______________________________________ 
Compounds of the Formula 
##STR23## 
Con- Soil 
Com- cen- Treatment 
pound tration 
% C 
No. X Y R.sub.1 R.sub.2 (ppm) Day 0 
______________________________________ 
11 S O CH.sub.2 CH.sub.3 
CH.sub.2 CH.sub.3 
6.4 0 
2.5 0 
12 0 0 CH.sub.3 
CH.sub.2 CH.sub.3 
6.4 0 
2.5 0 
______________________________________