Method for stabilizing acephate and a dry pesticidal formulation containing the stabilized acephate

The present invention relates to a method for stabilizing acephate which comprises adding a sodium salt of condensed phosphate and/or a synthetic silicic acid in which the surface silanol groups being alkylsilylated to acephate or acephate-containing dry pesticidal formulation and a stabilized acephate having added a sodium salt of condensed phosphate and/or a synthetic silicic acid in which the surface silanol groups being alkylsilylated.

The present invention relates to a method for stabilizing acephate and a 
dry pesticidal formulation containing the stabilized acephate. 
Acephate (O, S-dimethyl acetylphosphoramidothioate) is a known compound 
having an insecticidal activity as described on page 1 of The Pesticide 
Manual 8th edition (published by The British Crop Protection Council, 
1987) and used as an active ingredient for agricultural insecticide now, 
because of having effective controlling activities to various pests. 
On the contrary to other organic phosphoric compounds having an 
insecticidal activity, acephate has a lower stability in a pesticidal 
formulation. Accordingly, acephate in the formulation is vigorously 
decomposed depending on the storage condition and the activity of acephate 
could not be often exhibited efficiently. Under the circumstances, there 
has been demanded a method for imparting a stability to acephate in the 
formulation and development of such a pesticidal composition which is 
capable of exhibiting the pesticidal activity of acephate efficiently. 
The present inventors have conducted extensive study of such a subject 
matter. As a result, they have discovered that a sodium salt of condensed 
phosphate and/or a synthetic silicic acid in which the surface silanol 
groups being alkylsilylated may improve the stability of acephate in a dry 
formulation and the present invention has been completed. 
Therefore, the present invention relates to a method for stabilizing 
acephate by adding an effective amount of a sodiums salt of condensed 
phosphate and/or an effective amount of a synthetic silicic acid in which 
the surface silanol groups being alkylsilylated, to the acephate, a method 
for stabilizing acephate in a dry formulation by mixing acephate with an 
effective amount of a sodium salt of condensed phosphate and/or an 
effective amount of a synthetic silicic acid in which the surface silanol 
groups being alkylsilylated and a dry pesticidal formulations containing 
acephate and an effective amount of a sodium salt of condensed phosphate 
and/or an effective amount of a synthetic silicic acid in which the 
surface silanol groups being alkylsilylated. 
In the context of the present invention, the sodium salt of condensed 
phosphate refers to a compound in which two or more sodium phosphates are 
condensed via an oxygen atom, for example, sodium polyphosphate, sodium 
tripolyphosphate or sodium pyrophosphate. 
The synthetic silicic acid in which the surface silanol groups being 
alkylsilylated used in the present invention may be usually prepared by 
alkylsilylating the surface silanol groups of a synthetic silicic acid 
produced by the wet process obtained by adding a mineral acid such as 
hydrochloric acid and sulfuric acid to an aqueous sodium silicate solution 
or of a synthetic silicic acid produced by the dry process obtained by 
decomposing silicon tetrachloride with an oxyhydrogen flame etc. with 
dialkyldichlorosilane or alkyltrichlorosilane. Said alkyl group is usually 
a lower alkyl group such as methyl and ethyl and the number of the surface 
silanol group is usually reduced substantially to 3 or less/nm.sup.2. The 
synthetic silicic acid in which the surface silanol groups being 
alkylsilylated thus obtained is commercially available as Carplex.RTM. 
CS-701 mfg. by Shionogi Pharmaceuticals, Carplex.RTM. CS-801 mfg. by 
Shionogi Pharmaceuticals, Reolosil.RTM. MT-10 mfg. by Tokuyama Soda, 
Aerosil.RTM. R 972 mfg. by Degussa, Sipernat.RTM. D 17 mfg. by Degussa or 
Sipernat.RTM. D 10 mfg. by Degussa. 
The amount of the sodium salt of condensed phosphate useful for 
stabilization of acephate is generally 0.01 to 10 parts by weight, 
preferably 0.05 to 1 part by weight to one part by weight of acephate. 
The amount of the synthetic silicic acid in which the surface silanol 
groups being alkylsilylated which is useful for stabilization of acephate 
is generally 0.05 parts by weight or more, preferably 0.05 to 10 parts by 
weight to one part by weight of acephate. 
The content of acephate in the dry pesticidal formulation of the present 
invention is generally 0.5 to 99% by weight, preferably 5 to 95% by 
weight. The content of the sodium salt of condensed phosphate in the dry 
pesticidal formulation is an amount in which acephate may be stabilized, 
usually 0.01 to 50% by weight, preferably 1 to 20% by weight, more 
preferably 1 to 10% by weight. The content of the synthetic silicic acid 
in which the surface silanol groups being alkylsilylated is an amount in 
which acephate may be stabilized, usually 1 to 99% by weight. 
The dry pesticidal formulation using the sodium salt of condensed phosphate 
may usually contain a solid carrier for pesticidal formulation in addition 
to acephate and sodium salt of condensed phosphate. Said solid carriers 
include, for example, a mineral carrier such as kaolin clay, attapulgite 
clay, sericite clay, pyrophyllite clay, montmorillonite clay, zeolite, 
bentonite, acid clay, activated clay, serpentine, talc and diatomaceous 
earth, an inorganic salt such as sulfate, nitrate, chloride and carbonate, 
an inorganic carrier such as a synthetic carrier (e.g., silica), or an 
organic carrier such as sugars, starch, dextrin, flour, soy meal, corn 
meal and wood powder. 
The dry pesticidal formulation of the present invention using the synthetic 
silicic acid in which the surface silanol groups being alkylsilylated may 
be ones consisting of acephate and the synthetic silicic acid in which the 
surface silanol groups being alkylsilylated, but additionally a solid 
carrier for the preparation may be contained therein. Said solid carriers 
include, for example, ones as mentioned above. 
The solid carrier may be usually contained in 1 to 90% by weight, 
preferably 20 to 70% by weight in the dry pesticidal formulation. 
The dry pesticidal formulation of the present invention may contain 
auxiliaries for pesticidal formulation, for example, at least one selected 
from the group consisting of surface active agent, coloring matter, 
perfume and known stabilizer, which are usually contained in 0.1 to 35% by 
weight, preferably 2 to 10% by weight. 
The surface active agents that can be used in the present invention 
includes, for example, anionic surface active agents such as alkyl 
sulfates (e.g., sodium lauryl sulfate), alkylaryl sulfonates (e.g., sodium 
alkylnaphthalene sulfonate), lignin sulfonates (e.g., sodium lignin 
sulfonate), succinic acid ester derivative, polycarbonate, 
polyethyleneglycol alkylaryl ether sulfonate and a formaldehyde condensate 
of aromatic sulfonate, or nonioinic surface active agents such as 
polyoxyethylene alkylether, polyoxyethylene alkylarylether and 
polyoxyethylene arylarylether. 
The dry pesticidal formulation of the present invention may additionally 
contain other pesticidal active ingredients, for example, pyrethroid 
compound such as Fenpropathrin, Fenvalerate and Esfenvalerate. 
The dry pesticidal formulation of the present invention may be in the form 
of, for example, dust, driftless dust, wettable powder, water soluble 
powder, granule, water soluble granule, water dispersible granule, dry 
flowable, tablet or pellet, and these dry pesticidal formulations may be 
used by packaging those in a packaging container such as water soluble 
pack. 
The dry pesticidal formulation of the present invention may be prepared 
according to a conventional method, for example, by admixing acephate and 
sodium salt of condensed phosphate and/or synthetic silicic acid in which 
the surface silanol groups being alkylsilylated, additionally a solid 
carrier and auxiliaries such as a surfactant if necessary in a mixer, 
pulverizing the mixture with a grinder such as air-mill, hammer mill, jet 
pulverizer and centrifugal pulverizer into, for example 20 .mu.m or less 
of average particle size to obtain a powdery pesticidal formulation of the 
present invention, alternatively molding those pulverized mixture into 
granules using a compression press such as a roller compactor, extrusion 
granulator, pan granulator, fluidized bed granulator or rolling granulator 
to obtain a dry pesticidal formulation of the present invention.

The present invention will be explained with reference to the following 
formulation examples and test examples in detail, but the invention should 
not be construed as being limited to these examples only. 
FORMULATION EXAMPLE 1 
25 Parts by weight of acephate, 5 parts by weight of sodium 
tripolyphosphate, 4 parts by weight of sodium dodecylbenzenesulfonate, 2 
parts by weight of sodium arylsulfonate formaldehyde condensate, 20 parts 
by weight of Tokusil.RTM. GU-N (synthetic silicic acid mfg. by Tokuyama 
Soda), and 44 parts by weight of kaolin clay were pulverized with a jet 
pulverizer and mixed in a mixer to obtain a wettable powder which is a dry 
pesticidal formulation of the present invention. 
FORMULATION EXAMPLE 2 
A wettable powder of the present dry pesticidal formulation was obtained 
according to Formulation Example 1, except that 10 parts of sodium 
tripolyphosphate were used instead of 5 parts of sodium tripolyphosphate 
and 39 parts of kaolin clay were used instead of 44 parts of kaolin clay. 
FORMULATION EXAMPLE 3 
25 Parts by weight of acephate, 20 parts by weight of Carplex.RTM. CS-701, 
4 parts by weight of sodium dodecylbenzenesulfonate, 2 parts by weight of 
sodium arylsulfonate formaldehyde condensate and 49 parts by weight of 
kaolin clay were pulverized with a jet pulverizer and mixed in a mixer to 
obtain a wettable powder which is the present dry pesticidal formulation. 
COMATIVE FORMULATION EXAMPLE 1 
Comparative Formulation 1 was obtained according to Formulation Example 1, 
except that 5 parts by weight of kaolin clay were used instead of 5 parts 
by weight of sodium tripolyphosphate. 
COMATIVE FORMULATION EXAMPLE 2 
Comparative Formulation 2 was obtained according to Formulation Example 3, 
except that 20 parts by weight of Tokusil.RTM. GU-N (synthetic silicic 
acid mfg. by Tokuyama Soda) were used instead of 20 parts by weight of 
Carplex.RTM. CS-701. 
TEST EXAMPLE 
Each formulation obtained by said Formulation Examples and Comparative 
Formulation Examples was enclosed in an aluminum-laminated bag and stored 
in a temperature controlled container set at a specified temperature. The 
content of acephate before and after storage was determined with a gas 
chromatography, and the decomposition rate was calculated according to the 
following equation: 
##EQU1## 
Tables 1, 2 and 3 show the results. 
TABLE 1 
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Decomposition rate (%) 
40.degree. C. 
Assayed Formulation 
after 1 month 
after 3 months 
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Formulation Example 1 
0 16 
Formulation Example 2 
1 13 
Comparative Formulation 
4 31 
Example 1 
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TABLE 2 
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Decomposition rate (%) 
50.degree. C. 
Assayed Formulation 
after 2 weeks 
after 1 month 
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Formulation Example 1 
3 26 
Formulation Example 2 
2 20 
Comparative Formulation 
15 44 
Example 1 
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TABLE 3 
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Decomposition rate (%) 
50.degree. C. 
Assayed Formulation 
after 2 weeks 
after 1 month 
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Formulation Example 3 
1 8 
Comparative Formulation 
6 33 
Example 2 
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