Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Biocides; animal or insect repellents or attractants
Reexamination Certificate
1999-07-29
2002-08-27
Levy, Neil S. (Department: 1616)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Biocides; animal or insect repellents or attractants
C424S406000, C514S109000, C514S120000, C514S121000, C264S004330
Reexamination Certificate
active
06440443
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to formulations of organophosphate pesticides. In particular, the invention provides microencapsulated formulations of the insecticide
ematicide, cadusafos, that are equally effective, yet reduced in toxicity, as compared with conventional formulations.
BACKGROUND OF THE INVENTION
The organophosphate compound, S,S-di-sec-butyl-O-ethyl phosphorodithioate (cadusafos), is an effective insecticide and nematicide. However, the toxicity of cadusafos impairs its safe use. For instance, a 100 g/l aqueous microemulsion formulation of cadusafos presently in commercial use recommends that the user wear complete body protection for handling and applying the formulation. The labeling also indicates that the formulation is highly toxic to mammals, fish, arthropods and birds.
Accordingly, a need exists to develop formulations of cadusafos that maintain its effectiveness as an insecticide or nematicide, but reduce its toxicity to mammals, birds, fish and other non-target organisms. Such formulations would improve safety to humans and would minimize any negative impact on the environment resulting from use of this compound.
SUMMARY OF THE INVENTION
Provided in accordance with the present invention are pesticidally effective, microencapsulated formulations of cadusafos having low or moderate toxicity to non-target organisms, among other advantages.
According to one aspect of the invention, the formulation comprises an aqueous suspension of microcapsules, which are composed of a polyurea shell surrounding a core of the cadusafos. The polyurea shell is formed from interfacial polymerization of a polyisocyanate and one or more polyfunctional amines, the polyurea. shell being sufficiently impenetrable to the cadusafos so as to effect the aforementioned reduction in mammalian toxicity of the formulation, as compared with known aqueous microemulsion cadusafos formulations of an equivalent or lesser cadusafos concentration.
According to another aspect of the invention, a granular cadusafos formulation is provided, which comprises the aforementioned microcapsules containing cadusafos affixed to a granular carrier.
Also provided in accordance with the present invention are processes for making the aforementioned aqueous capsule suspension (CS) or granular microencapsulated cadusafos formulations.
The microencapsulated cadusafos of the present invention possesses lower skin, oral, and inhalation toxicity to mammals, thereby enabling safer handling and use of the pesticide. According to United States Environmental Protection Agency (“EPA”) guidelines, the formulations of the present invention are rated as Category II (warning) or Category III (caution) compositions at twice the concentration of non-microencapsulated liquid formulations of the same active ingredient, which are rated as Category II. The microencapsulated formulations exhibit no loss of pesticidal activity or physical and chemical stability as compared to non-microencapsulated formulations. In addition, the microencapsulated formulations of the present invention are consistent in color, which is not the case in aqueous microemulsion formulations of the compound if the technical cadusafos is pre-treated with copper salts to remove unpleasant odor for commercial use.
DETAILED DESCRIPTION OF THE INVENTION
The microencapsulated cadusafos of the invention is made according to the following basic steps: (a) providing an aqueous phase (also referred to herein as a “continuous” phase) containing an emulsifier and an antifoam agent; (b) providing a water-immiscible phase (also referred to herein as a “discontinuous” phase) containing the cadusafos along with a first polyfunctional compound; (c) emulsifying the aqueous phase with the water-immiscible phase to form a dispersion of water-immiscible droplets in the aqueous phase; and (d) adding to the dispersion, either neat or in an aqueous solution, a second polyfunctional compound, thus forming a polymeric shell known herein as a microcapsule, around the water-immiscible droplets; i.e., forming microcapsules of cadusafos The first polyfunctional compound is any suitable compound having two or more reactive groups, such as, but not limited to, an isocyanate monomer. The second polyfunctional compound is any suitable compound having two or more reactive groups, such as, but not limited to, a polyfunctional amine; wherein the first and second polyfunctional compounds are different. The suitability of the first and second polyfunctional compounds is that they have the ability to form a heteromeric structure at the interface between the dispersed cadusafos and the aqueous phase. Such compounds will include both hydrophobic and hydrophilic groups between the two compounds, such that such groups can both be in a single such compound or can be exclusive to one or the other such compound. The last step is referred to as interfacial polymerization due to the fact that the polyurea shell is formed by polymerization of the first and second polyfunctional compounds, which are preferably an isocyanate and a polyfunctional amine(s) at the interface of the water-immiscible phase (the droplets) and the aqueous phase, thereby forming, predferably, a polyurea shell.
Once the microcapsules are formed, the suspension is preferably cured, i.e., moderately heated to complete polymerization, after which one or more additives, such as propylene glycol, xanthan gum, urea, bactericides, amphoteric surfactants, inert dyes or ionic dispersing agents (e.g., alkyl naphthalene sulfonate), may be added.
The addition of materials after encapsulation and curing to adjust viscosity, stability and suspension/dispersion characteristics preferably do not affect the reduction of toxicity or the pesticidal efficacy of the formulation. A preferred further step comprises adjusting the pH of the formulation to neutral, i.e., from about pH 6.5 to about pH 7.5, which results in improved stability. The use of the modifier “about” with respect to pH is used herein to indicate a variance of at least one-half a pH unit, and preferably indicates a variance of one-half a pH unit. In other contexts herein where the modifier “about” is used to qualify a non-log unit, the “about” is intended to indicate a variance of ±15%, yet more preferably a variance of ±10%.
The aqueous phase ordinarily contains about 0.3 to about 3.0, preferably about 0.7 to about 2.5, weight percent of one or more emulsifiers. The emulsifier preferred for use in the present invention is polyvinyl alcohol. Other emulsifiers suitable for use in the present invention include, but are not limited to, nonylphenol ethoxylate, sorbitan mono- and trioleate, and ethoxylated oleate.
The aqueous phase also contains about 0.1 to about 1.0, preferably about 0.3 to about 0.9 weight percent of one or more antifoam agents. Antifoam agents suitable for use in the present invention include, but are not limited to, silicon based antifoam agents such as Dow Corning Antifoam DC1500 and DC1520.
The aqueous phase optionally may also include a viscosity modifier/stabilizer, such as xanthan gum from about 0.05 to about 0.50, preferably about 0.06 to about 0.40, weight percent, as well as one or more bactericides from about 0.02 to about 0.10, preferably about 0.03 to about 0.05, weight percent. Bactericides useful for the present invention include, but are not limited to, Legend MK (Rohm & Haas Co.), Proxel GXL (Zeneca, Inc.) and Dowicide A (Dow Chemical).
The water-immiscible phase (also referred to in the examples as the polyisocyanate solution) ordinarily contains from about 50 to about 98, preferably about 53 to about 92 weight percent cadusafos and about 2 to about 35, preferably about 4 to about 25, weight percent of the first polyfunctional compound, preferably an isocyanate monomer. Polymethylene polyphenyl isocyanate (PMPPI) is particularly preferred for use in the present invention; e.g., Mondur MR (Miles, Inc.), Papi 27 or 135 (Dow Chemical) and Desmodur (Bayer). Other suitable first polyfunctional compounds can also be used in
Lee Fui-Tseng H.
Nicholson Paul
Sommer William T.
Szamosi Janos
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