PYRETHROID FORMULATIONS OF REDUCED PARESTHESIA

Abstract: Pyrethroids which otherwise tend to induce paresthesia during handling are formulated for agricultural usage in a manner which lessens or avoids this tendency. This is achieved by using the pyrethroid in the form of a solution in an aromatic solvent having a flash point above 50 DEG C, the most preferred solvents being those with flash points within the range of about 90-125 DEG C. The formulations for which the invention is of particular interest are granular formulations.

Description: PYRETHROID FORMULATIONS OF REDUCED PARESTHESIA This invention relates to pyrethroids, and in particular to formulations of pyrethroids for agricultural use. BACKGROUND OF THE INVENTION Pyrethroids, which are synthetic derivatives of naturally occurring pyrethrins, are well known as insecticidal agents offering the powerful and selective insecticidal action of the pyrethrins without the rapid decomposition which the pyrethrins undergo upon exposure to the environment. The handling of pyrethroid formulations is known in some cases to provoke an adverse skin reaction. This reaction has been described as a burning, tingling, numbing or prickling sensation, which is most pronounced on regions of the handler's face, unaccompanied by redness or irritation. This paresthesia (or paraesthesia) is generally associated with trace amounts of the pyrethroid being transferred to the handler's face through inadvertent touching by a contaminated hand. The problem is particularly acute in solid formulations (including formulations containing solid phases) such as dusts and granules. Attempts to lessen or avoid paresthesia have included the taking of precautions to ensure that containers are tightly sealed against the escape of dust, and the use of facial barrier creams. These measures are not of uniform effectiveness, and require extra care to ensure that they are followed. SUMMARY OF THE INVENTION It has now been discovered that the tendency of a pyrethroid formulation to produce paresthesia is markedly reduced by the inclusion of certain types of aromatic solvents in the formulation, particularly those aromatic solvents having relatively high flash points. Evidence of the reduced paresthesia is observable directly as well as by a decrease in the tendency of the pyrethroid to form microscopic crystals in the formulation. The pyrethroid is thus dissolved in the aromatic solvent to form an organic solution which is combined with other ingredients commonly used in agricultural formulations, particularly those formulations in which the pyrethroids are commonly used. The solvent may be used in place of the conventional solvents which are normally used in preparing the formulation in accordance with standard procedures. DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS The aromatic solvents utilized in the practice of the present invention form organic solutions of the pyrethroids, the organic solutions then incorporated into the formulations, preferably with substantially full retention of the aromatic solvent. The formulations themselves may be of any conventional type which includes an organic solution of the pyrethroid. As stated above, the aromatic solvent will be one which has a relatively high flash point, generally above about 50*C. Preferred solvents are those with flash points of about 50"C to about 200'C, more preferably about 75 β C to about 150 β C, and most preferably about 90'C to about 125*C. The solvent may be a single species or a mixture of species. Mixtures may include those combining different aromatics as well as those combining aromatics with other species such as paraffins and cycloparaffins. Mixtures of C 8 aromatics and higher, particularly C 10 -C l5 , are particularly useful. Among the many examples of such solvents are the various pesticide solvents available commercially, such as AROMATIC 200 and SOLVESSO 200, both products of Exxon Corporation, Houston, Texas. The relative amounts of pyrethroid and solvent in the solution may vary widely for field application purposes, and the actual proportion is not critical. In certain situations, the proportions may be limited by considerations of economy and efficiency, and the particular type of formulation ultimately prepared. Solubility limits may also exist in some cases. In most applications, weight ratios ranging from about 0.1:1 to about 10:1 (pyrethroid to solvent) , will provide the best results. Preferred weight ratios are 0.3:1 to 3:1, with 1:1 to 2:1 particularly preferred for granular formulations. Among the various types of formulations which the solutions may ultimately assume are granules, microcapsules, emulsifiable concentrates, and the solutions themselves. Granules are of particular interest in the present invention, due to the manner in which they are handled and the manner in which they expose a large surface area of the solution to the environment. The solution resides in the open pores of the granules and generally coats the granule surface. A wide range of granular materials may be used, notably attapulgite, bentonite, kaolinite, ontmorillonite and pyrophyllite clays, and fuller's earth, diatomaceous earth, vermiculite, perlite, calcium carbonate, calcium sulfate and silica. Granules thus bearing these solutions are prepared according to conventional techniques. Preformed granules, for example, may be impregnated with the solution using conventional equipment such as rolling pans or mills. Alternatively, the solution can be incorporated during formation of the granule itself. This method is of particular applicability to granules formed by the use of an agglomerator. As an example of this method, the pyrethroid is first prepared as an oil-in-water emulsion, the oil phase being the solution of the pyrethroid in the aromatic solvent, optionally containing emulsifiers conventionally used for this purpose. The emulsion is then combined with the solid material from which the granule is made plus additional water to aid in the emulsification and to serve as a source for hydrating the solid granule material. The additional water may optionally contain an agglomeration accelerator. The combined materials are metered at preselected proportions into an agglomerating device, such as the type supplied by Schugi Process Engineers U.S.A., Skillman, New Jersey, which forms the mixture into granules which are dropped directly into a fluid bed dryer which removes the free water. The dryer discharges the granules to a vibratory screen which sizes the granules to the desired size range, and the fines are recycled. In a typical system, an oil-in-water emulsion is formed by combining the following ingredients in the proportions given: Technical pyrethroid: x parts by weight T EEN 40: 77.8 parts by weight SPAN 40: 8.1 parts by weight AROMATIC 200: 246.7 parts by weight water: to 1000 parts by weight total emulsion where TWEEN 40 and SPAN 40 are emulsifiers (a polyoxyethylene sorbitan monopalmitate and a sorbitan monopal itate, respectively, supplied by ICI Americas Inc. , Wilmington, Delaware) , and the amount of pyrethroid (designated x above) is selected to achieve 350 parts by weight of pyrethroid per 1000 parts by weight of the emulsion. This is combined with free water containing 1.0% by weight K 2 S0 4 (agglomeration accelerator) , and plaster of paris (calcium sulfate) . The feed rate of the free water is approximately 24% of that of the plaster of paris, and the emulsion rate is selected such that the final product after removal of free moisture (i.e., exclusive of water of hydration) will contain approximately 15 parts by weight of pyrethroid per 1000 parts by weight of the total impregnated granule. The particles are sized to -20,+50 mesh, with a bulk density (untamped) of 47-54 lb/ft 3 . This invention is applicable to pyrethroids in general. This covers a wide variety of species, and the invention bears varying degrees of importance depending on the tendency of these species and formulations containing them to induce paresthesia. Examples of pyrethroids to which the invention may be applied are: allethrin alphametrin barthrin biopermethrin bioresmethrin cismethrin cyclethrin cyfluthrin cyhalothrin cypermethrin deltamethrin dimethrin fenothrin fenpropanate fenvalerate flucythrin fluvalinate furethrin indothrin permethrin phthalithrin resmethrin tefluthrin tetramethrin Pyrethroids of particular interest for the purposes of the present invention are those having the formula in which R 1 and R 2 are independently methyl, halo, or trifluoromethyl; R 3 is hydrogen or cyano; R 4 is C^Ca alkyl, C 2 -C 6 alkenyl, phenyl or benzyl; X is oxygen or sulfur; m is zero or one; and n is zero to four. Species of particular interest within the scope of this formula are those in which R 1 and R 2 are independently chloro or trifluoromethyl; R 3 is hydrogen or cyano; R 4 is methyl or phenyl; X is oxygen; m is zero or one; and n is zero to four. Specific species of particular interest within the formula are: 3-(phenoxypheny1) methyl (IRS) -ciε,trans-3-(2,2- dichloroethenyl)-2,2-dimethyl cyclopropane carboxylate (permethrin) : α-cyano-3-phenoxybenzyl (±) cis Λ trans-3-(2-chloro-2- trifluoromethylvinyl)-2,2-dimethyl cyclopropane carboxylate (cyhalothrin) : 2 , 3 , 5 , 6-tetraf luoro-4-methylbenzyl cis-3- (Z-2-chloro- 3 , 3 , 3-trif luoroprop-1-enyl) -2 , 2- dimethylcyclopropanecarboxylate (tefluthrin) : The following examples are offered for purposes of illustration and are intended neither to limit nor to define the invention in any manner. EXAMPLES Granular formulations of the pyrethroid 2,3,5,6- tetrafluoro-4-methylbenzyl cis-3-(Z-2-chloro-3,3,3- trifluoroprop-1-enyl)-2,2-dimethylcyclopropanecarboxylate were prepared by dissolving the technical pyrethroid in a variety of solvents to a concentration of approximately 70 weight percent, combining the solution with S-1100-S granules (supplied by Oil-Dri Corp., Chicago Illinois) to achieve impregnated granules containing approximately 1.67% by weight of the pyrethroid. The solvents were as follows: AROMATIC 200 a solvent mixture containing 98% aromatics and 2% paraffins, with a flas point of 103"C and a distillation range of 225-279"C, with aromatics compositio (by mass spectrograph) as follows: C 10 16% Cn 50% C 12 26% C 13 16% supplied by Exxon Corporation, Houston, Texas TENNECO 500-100 a solvent mixture containing 94% aromatics, with a flash point of 38°C and a distillation range of 143-174°C; supplied by Tenneco Oil, Houston, Texas EXXSOL D-80 a solvent mixture containing 58% paraffins, 41% cycloparaffins, and 0.8% aromatics; with a flash point of 73°C, and a distillatio range of 202-232°C; supplied by Exxon Corporation, Houston, Texa ISOPAR M a solvent mixture containing 99.8% paraffins and 0.2% aromatics; with a flash point of 80°C and a distillation range of 207-264 β C; supplied by Exxon Corporation, Houston, Texas The granules were gypsum, with average particle diameter of from -10 to 60 U.S. sieve mesh and a bulk density of from 45 to 60 pounds per cubic foot. The impregnated granules were placed in closed jars an observed visually over a period of several days. Dust formation was observed on all granules except those prepared with AROMATIC 200. Observation under a microscope indicated that the dust was actually rod-shaped crystals, which were confirmed as the pyre¬ throid in crystalline form. The foregoing is offered primarily for purposes of illustration. It will be readily apparent to those skilled in the art that variations and substitutions in and alternatives to the various materials, conditions and procedures described herei may be made without departing from the spirit and scope of the invention.

Claims: WHAT IS CLAIMED IS: 1. A solid granule formulation of a pyrethroi insecticide, said formulation comprising a solution of s pyrethroid insecticide in an organic solvent comprising aromatic composition having a flash point above about 50 wherein said solid granule is impregnated with said solu 2. A formulation in accordance with claim 1 comprising solid granules impregnated with said solution. 3. A formulation in accordance with claim 1 i which said aromatic composition has a flash point of abou 50*C to about 200'C. 4. A formulation in accordance with claim 1 i which said aromatic composition has a flash point of abou 75*C to about 150'C. 5. A formulation in accordance with claim 1 i which said aromatic composition has a flash point of abou 90'C to about 125*C. 6. A formulation in accordance with claim 1 i which said pyrethroid insecticide is a compound having th formula in which R 1 and R 2 are independently selected from the grou consisting of methyl, halo, and trifluoromethyl; R 3 is hydrogen or cyano; R 4 is selected from the group consisting of Cτ-C 6 alkyl, C 2 -C 6 alkenyl, phenyl and benzyl; X is oxygen or sulfur; m is zero or one; and n is zero to four. 7. A formulation in accordance with claim 6 in which R 1 and R 2 are independently selected from the group consisting of chloro and trifluoromethyl; R 3 is hydrogen or cyano; R 4 is selected from the group consisting of methyl and phenyl; X is oxygen; m is zero or one; and n is zero to four. 8. A formulation in accordance with claim 6 in which said compound is 2,3,5,6-tetrafluoro-4-methylbenzyl cis-3-(Z-2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2- dimethylcyclopropanecarboxylate. 9. A formulation in accordance with claim 1 in which the weight ratio of said pyrethroid insecticide to said organic solvent in said solution is about 0.1:1 to about 10:1. 10. A formulation in accordance with claim 1 in which the weight ratio of said pyrethroid insecticide to said organic solvent in said solution is about 0.3:1 to about 3:1. 11. A formulation in accordance with claim 1 in which the weight ratio of said pyrethroid insecticide to said organic solvent in said solution is about 1:1 to about 2:1. 12. A method for preparing a granular formulation of a pyrethroid insecticide, said method comprising dissolving said pyrethroid insecticide in an organic solvent comprising an aromatic composition having a flash point above about 50 * C to form a solution, and preparing porous granules impregnated with said solution. 13. A method in accordance with claim 12 in which said aromatic composition has a flash point of about 50*C to about 200*C. 14. A method in accordance with claim 12 in which said aromatic composition has a flash point of about 75 * C to about 150 β C. 15. A method in accordance with claim 12 in which said aromatic composition has a flash point of about 90 β C to about 125 β C. 16. A method in accordance with claim 12 in which said pyrethroid insecticide is a compound having the formula n n B —R* in which R 1 and R 2 are independently selected from the group consisting of methyl, halo, and trifluoromethyl; R 3 is hydrogen or cyano; R 4 is selected from the group consisting of C^C έ alkyl, C 2 -C 6 alkenyl, phenyl and benzyl; X is oxygen or sulfur; m is zero or one; and n is zero to four. 17. A formulation in accordance with claim 16 in which R 1 and R 2 are independently selected from the group consisting of chloro and trifluoromethyl; R 3 is hydrogen or cyano; R 4 is selected from the group consisting of methyl and phenyl; X is oxygen; m is zero or one; and n is zero to four. 18. A formulation in accordance with claim 16 in which said compound is 2,3,5,6-tetrafluoro-4-methylbenzyl cis-3-(Z-2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2- dimethylcyclopropanecarboxylate. 19. A method in accordance with claim 12 in which the weight ratio of said pyrethroid insecticide to said organic solvent is about 0.1:1 to about 10:1. 20. A method in accordance with claim 12 in which the weight ratio of said pyrethroid insecticide to said organic solvent is about 0.3:1 to about 3:1. 21. A method in accordance with claim 12 in which the weight ratio of said pyrethroid insecticide to said organic solvent is about 1:1 to about 2:1.

Inventors: FERSCH KENNETH E, FERSCH, KENNETH, E.
Applicants: ICI AMERICA INC, ICI AMERICAS INC.
Application year: 1990
Main classification: A01N25
IPC codes: A01N25, A01N53