Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Having -c- – wherein x is chalcogen – bonded directly to...
Reexamination Certificate
1999-03-09
2001-09-25
Dees, Jose′ G. (Department: 1616)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Having -c-, wherein x is chalcogen, bonded directly to...
C424S405000, C424S406000, C424S490000, C424S497000, C424S498000, C424S678000, C514S430000, C514S449000, C514S450000, C514S769000, C514S772100, C514S772300, C514S974000
Reexamination Certificate
active
06294570
ABSTRACT:
BACKGROUND OF THE INVENTION
Numerous patent applications have already described the microencapsulation of pesticidal active ingredients. Formulations of this type can, for example, release the encapsulated active ingredient in a delayed manner and various undesirable properties of the active ingredient, such as toxicity to the user or leachability into ground water, can be beneficially influenced by this means.
DESCRIPTION OF THE RELATED ARTS
For example, EP-A-134 674 discloses the reduction of skin toxicity of difonate in rabbits, EP-A-183 999 discloses the reduction of fish toxicity of permethrin, EP-A-368 576 discloses the reduction of the toxicity of chlorpyrifos in carp, JP-A-6-256116 discloses the reduction of skin toxicity of fenobucarb and WO-A-95/123506 discloses the reduction of fish toxicity and of food toxicity in mice.
Of the different variants of microcapsules, capsule dispersions have proved to be particularly useful. They may be produced by enveloping, for example, water-insoluble active ingredient in an aqueous environment with a polymer skin, stabilizing the resulting dispersion, if appropriate, with dispersants and producing a water-diluteable concentrate directly in this manner. With these formulations, as with all multiphase formulations, care must be taken to ensure that thickening, coagulation or sediment formation does not occur during storage; the user must at least, with reasonable effort, be able to reverse these changes which diminish quality. It is in the nature of things that active ingredients of high density are therefore the most difficult to process to form microcapusle dispersions. Requirements of physical stability must be complied with by suitable composition of the aqueous carrier phase.
The pesticide-containing capsules are subject to two further essential, contradictory requirements. On the one hand, a sufficiently stable coating must ensure that the sought-after goal of the encapsulation is achieved, namely the binding of the active ingredient to the capsule interior. This means, for example in the case of insecticides toxic to homoiotherms, that the active ingredient is not released from its sealing until the user has typically diluted and applied the formulation and the sprayed coating has dried onto the target surface.
On the other hand, said coating must on no account be so strong that the active ingredient exits too slowly after application. The lowest limit of the release rate in this case is predetermined by many factors, e.g. physicochemical conditions, biological mode of action, type of the pest organism to the controlled, tolerance of plant protection residues in the treated crop.
The insecticidal active ingredient endosulfan is included, on account of its toxicity, among those requiring appropriate labelling in accordance with the German Regulation on Hazardous Substances. However, endosulfan has a great number of merits, so that it has nevertheless to a greater extent established itself as the standard insecticide in various crops. Thus, there has long been a requirement for a commercial form of endosulfan in the form of a microcapsule dispersion which satisfies said requirements.
The most usual way of building up said capsule wall around the active ingredient to be enveloped is an interfacial polymerization in oil-in-water emulsions, the organic phase including, in addition to the active ingredient, an oil-soluble prepolymer having free isocyanate groups.
U.S. Pat. No. 3 577 515 describes how, after addition of water-soluble polyamines, the droplet surface in such emulsions cures as a result of addition to the prepolymers containing the isocyanate groups. This forms a polyurea outer wall.
U.S. Pat No. 4 140 516 discloses that, even in the absence of external water-soluble amines, microcapsules having outer wall of the polyurea type can be produced by permitting partial hydrolysis in the emulsion of the prepolymer bearing the isocyanate functions. In the course of this, some of the amino groups are reformed from the isocyanate groups and, as a result of internal polyaddition with subsequent curing, the desired capsule wall is likewise formed. The use of tolylene diisocyanate, hexamethylene diisocyanate, methylenebis(phenyl isocyanate) and of its higher homologs is described. If curing is to be performed using an external polyamine, this usually originates from the group consisting of ethylenediamine, propylenediamine, hexamethylenediamine, diethylenetriamine and tetraethylenepentamine.
Formulations including microencapsulated endosulfan have already been described several times in the patent literature.
DE-A-2 757 017 relates to internally structured microcapsules whose wall material has the nature of a mixed polymer crosslinked by urea and urethane moieties. The active ingredient is situated in the interior of the capsule, dissolved in an organic solvent. Typically, to make up the capsule wall here, 10% of prepolymer, based on the total formulation, is required. There is no information on the reduction in acute oral toxicity by this type of formulation.
The same prepolymer is also used in WO-A-96/09760 to encapsulate endosulfan. Although good insecticidal activity is described, no advantage is described with respect to unwanted toxic action.
WO-A-95/23506 relates to endosulfan-charged polyurea microcapsules in which the active ingredient is present as a cooled melt. As prepolymer, a mixture of methylenebis(phenyl isocyanate) and its higher homologs is described; the amount of prepolymer used is over 6%, based on the total formulation. Curing is performed using a mixture of polyamines. Apart from the data on the greatly reduced toxicity of this type of formulation, no indications are given there of advantages in biological activity or with respect to residues.
There continued to be, therefore, a desire for an insecticidal formulation including microencapsulated endosulfan, which formulation complies with the following requirements:
simple nonhazardous preparation
good storage stability
reduced toxicity to the user and to useful organisms
good initial biological activity
no risk of increased residues of unreleased active ingredient on the treated plant parts.
It has now surprisingly been found that a microcapsule dispersion which is prepared by the interfacial polymerization process known per se and includes up to 30% by weight or more of endosulfan, preferably approximately 300 to 330 g of endosulfan/l, complies with the abovementioned requirements if, for its preparation, relatively small amounts of an isocyanate-containing prepolymer (of the order of magnitude of approximately 1% by weight) are used, in addition to any water-soluble diamine required. The very small amount of prepolymer forming the capsule wall means in fact that the onset of the insecticidal activity is not retarded under practical conditions. Addition of a sufficiently large amount of a water-soluble inorganic salt such as sodium chloride to the aqueous phase, and an associated increase in density, can prevent the microcapsules from sedimenting after a certain time and possibly forming a bottom sediment which is difficult to redisperse.
Microcapsule dispersions of this type, because of their favorable acute toxicity to homoiotherms, permit the toxicological classification “harmful”, and surprisingly exhibit—if they contain calcium chloride as density-increasing agent—a considerably lower fish toxicity than those microcapsule dispersions which do not contain calcium chloride. Commercial emulsifiable concentrates are known to have a by far still higher fish toxicity.
SUMMARY OF THE INVENTION
The invention relates to aqueous endosulfan microcapsule dispersions in which the dispersed microcapsules comprise endosulfan, an organic solvent or solvent mixture and a capsule-forming material based on isocyanate prepolymers and the aqueous phase which represents the dispersion medium comprises surfactants with or without other formulation aids, and which microcapsule dispersion contains, based on the total dispersion, 20-40% by weight of endosulfan, 10-35% by weigh
Bremmer Jan Nicolaas
Krause Hans-Peter
Maier Thomas
Aventis CropScience GmbH
Choi Frank
Dees Jose′ G.
Frommer & Lawrence & Haug LLP
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