Delivery System for Agricultural Chemicals

I. Field of the Invention

The invention relates to a delivery system for agriculturally active chemicals. More particularly, the invention relates to an emulsifiable concentrate of difficult to dissolve agricultural chemicals.

II. Description of the Prior Art

Agricultural chemicals are most preferably applied in the form of aqueous emulsions, solutions, or suspensions. Occasionally, they may also be applied in the form of a dust wherein the active ingredient is adsorbed onto or mixed with a finely divided inert carrier material, such as, china clay, or the like. With such powdered or dust compositions, drift due to wind is a problem and consequently, liquid formulations are preferred.

One of the problems with such liquid formulations is the fact that chemicals having agricultural activity often exhibit extreme insolubility in water. This results in their having to be dissolved either in organic solvents or utilized in the form of emulsions or suspensions. With respect to the use of organic solvents, these are generally disadvantageous from an environmental and cost viewpoint. Particularly, such organic chemicals may exhibit toxicity or side-effects which may be adverse to the effect of the agricultural chemical itself or to the subsequent fruit or vegetable produced in the particular agricultural use. This toxicity may also be disadvantageous with respect to handling.

When attempts are made to provide emulsified or suspension formulations, difficulties are encountered with respect to providing a desirably high concentration of the agriculturally active ingredient. Thus, when such agriculturally active chemicals are formulated into an emulsion, it is difficult to maintain the emulsified state. This makes it difficult to maintain a uniform formulation, particularly, when the formulation is diluted with water for application to the plants.

Typically, for example, the agriculturally active ingredient is mixed with one or more of a variety of conventional solvents and an emulsifying agent to form a concentrate. This concentrate may be an emulsion, suspension, or solution. The concentrate is then stored until it is transported to the site of use or may simply be transported and stored at the site of use. In any event, the concentrate normally will undergo some period of storage until it is ready for use. Understandably, it is most desirable to be able to transport the agriculturally active ingredient at the highest concentration possible so as to minimize the volume of material which need be transported. By the same token, however, at the use site, it is normally not feasible to admix ingredients together or to process them other than to dilute the concentrate with water. Accordingly, it is important that the concentrate emulsify easily, i.e., exhibit good "bloom", upon the addition of water. In addition, at the use site, it is often necessary to store the diluted concentrate for extended time periods until the actual application to the plants. Consequently, it is important that the diluted form of the concentrate exhibit good stability with respect to the uniformity of the emulsion and to avoid precipitation of the active ingredients. If non-uniformity or precipitation occurs in the diluted form, then non-uniformity will result in the application of the diluted formulation to the plants.

An attempt to provide concentrates of agriculturally useful chemicals is disclosed in South African patent application No. 695,393, filed Jul. 25, 1969. This application is directed to the formulation of a concentrate substantially water-insoluble pesticides for agricultural use. The pesticides, either in oil or solid form, are mixed with pyrrolidones having a hydrogen or a lower alkyl group containing from 1 to 4 carbon atoms attached to the nitrogen atom of the pyrrolidone ring. The application discloses that concentrated solutions of difficult to dissolve pesticides could be formulated and that such concentrates exhibited good stability. The concentrates utilized are those containing the pesticidal active ingredient, the particular lower alkyl pyrrolidone, a co-solvent which is usually a common organic solvent, such as, an aromatic including xylene, methylated and polyalkylated naphthalenes and aliphatic solvents, and a dispersing or emulsifying agent, such as, a surfactant, including polyoxyethylene alkylphenols, polyoxyethylene fatty esters, polyoxyethylene sorbitan fatty esters which may be blended with oil-soluble sulfonates, calcium and aminosulfonate salts, and the like.

This prior art does not offer a solution to the problem arising from the difficulty in maintaining the stability of the emulsion after the concentrate is diluted with water. Consequently, unless the diluted form of the concentrate is used immediately after emulsification, it is difficult to provide a stable diluted formulation for application to the plants.

U. S. Pat. No. 4,798,837 discloses an emulsifiable concentrate of the pesticidal compound (CGA): ##STR1##

This active concentrate contains 10% of the active ingredient using 30% cyclohexanone as the solvent. However, cyclohexanone is highly toxic. For such agricultural uses, it is desirable to avoid the use of toxic solvents, including those of Lists 1 and 2 of 40 C.F.R. 154.7 dated Apr. 22, 1987, which includes inerts of toxicological concern and solvents having high flash points, as well as to increase the amount of the agriculturally active material in the concentrate.

We have discovered a novel emulsifiable concentrate of an agriculturally active chemical, which concentrate provides, upon dilution, a highly stable emulsion and avoids precipitation of the active ingredient on extended storage. In addition, the inventive emulsifiable concentrates may contain relatively high concentrations of the agriculturally active ingredient, sometimes referred to as a "loading", making it advantageous from both economic and handling viewpoints. Also, the concentrates of the present invention utilize organic materials which do not pose environmental problems either in use or handling.

More particularly, the emulsifiable concentrate of the present invention is composed of an agriculturally active chemical, a surfactant, an organic diluent, and a hydrophobic solvent having the following Hansens' solubility parameters:

Dispersive component from about 56 to 75%;

Polar component from about 8 to 24%; and

H-bonding component of from about 10 to 30%.

This solvent should also have surfactant properties and act as a non-ionic surfactant with an HLB value ranging from about 2 to 8.

For a discussion of the solubility parameters, see C.R.C. Handbook of Solubility Parameters and Other Cohesion Parameters, Allan F.M. Barton, 1983, Table 9, p. 167-170.

As used herein, the term "agriculturally active chemical" includes compounds and mixtures thereof which can be used as agricultural fertilizers, nutrients, plant growth accelerants, herbicides, plant growth controlling chemicals, and chemicals which are effective in killing plants, insects, microorganisms, fungi, bacteria and the like which are commonly referred to as insecticides, bactericides, fungicides, nematocides, fumigants, and the like, as well as any other chemicals having properties which are suitable for agricultural uses in terms of application to plants or domestic uses for controlling insects and pests. Particularly, such chemicals would normally take the form of water-immiscible or oily liquids and/or solids which is substantially insoluble in water. By the term "substantially insoluble", it is meant that for all practical purposes, the solubility of the compound in water is insufficient to make the compound practicably usable in an agricultural end use without some modification either to increase its solubility or dispersability in water, so as to increase the compound's bioavailability or avoid the use of excessively large volumes of solvent.

Suitable agriculturally active chemicals which can be used with the present invention include insecticides, such as, cyclocompounds, carbamates, animal and plant derivatives, synthetic pyrethroids, diphenyl compounds, non-phosphates, organic phosphates, thiophosphates, and dithiophosphates. (See Agricultural Chemicals, Book I, Insecticides, 1989 Revision by W.T. Thomson, Thomson Publications.) Typical of the insecticides are:

Typical herbicides include phenoxy compounds, benzoic, acetic, and phthalic acids, aniline derivatives, nitriles, amides, acetamides, anilides, carbamates, thiocarbamates, and heterocyclic nitrogen derivatives, e.g., triazines, pyridines, pyridazones, picolinic acid, and urea derivates and phosphates. (See Agricultural Chemicals, Book II, Herbicides, 1986-87 Edition, W.T. Thomson, Thomson Publications, Fresno, CA 93791.) Exemplary of the above compounds are:

Typical fungicides include (See Agricultural Chemicals, Book IV, Fungicides, 1989 Revision, W.T. Thomson, Thomson Publications, Fresno, CA 93791):

Typical fumigants, growth regulators, repellants, and rodenticides include (See Agricultural Chemicals, Book III, Fumigants, 1988-1989 Revision, W.T. Thomson, Thomson Publications, Fresno, CA 93791):

Pesticides may be characterized by their physical properties, depending on their physical state at normal or ambient conditions, i.e., between 40.degree. F. and 90.degree. F. and their solubility or miscibility with water or other common organic solvents, e.g., aromatics, such as, toluene, xylene, methylated and polyalkylated naphthalenes, and aliphatic solvents.

Based on the physical properties, the pesticides may be classified into two groups. The first group includes those which are oily liquids at ambient temperatures and are immiscible with water. Specific pesticides include:

Common esters of 2,4-dichlorophenoxyacetic acid,

Common esters of 2,4,5-trichlorophenoxyacetic acid,

Common esters of 2-(2,4-dichlorophenoxy) propionic acid,

Common esters of 2-(2,4,5-trichlorophenozy) propionic acid,

Common esters of 2,4-dichlorobutyric acid,

Common esters of 2,methoxy-3,6-dichlorobenzoic acid,

Common esters of 2-methyl-4-chlorophenoxyacetic acid,

Piperonyl butoxide 3,4-methylenedioxy-6-propyl benzyl n-butyl diethylene glycol ether,

Bromophos ethyl: 0,0-diethyl-0-2,5-dichloro-4-bromophenyl thionophosphate,

N-(2-mercaptoethyl) benzene-sulfenamide (BETASAN.RTM.),

Isobornyl Thiocyanoacetate (Thanite.RTM.),

Ioxynil ester of octanoic acid,

Molinate S-ethyl hexahydro - 1 H - azepine-1-carbothioate,

PP 511 0,0-dimethyl-(2-diethylamine 4-methyl-6-pyrimidinyl) carbamate,

PP 211 0,0-diethyl O-(2-diethylamine-4-methyl-6-pyrimidinyl) phosphorocarbamate,

Chlordane

5-Ethoxy-3-(trichlorometyl)-1,2,4-thiadiazole (TERRAZALE.RTM.),

Ethyl-s-s-dipropyl-phosphodithioate (MOCAP.RTM.),

S-Ethyl dipropylthiocarbamate (EPTAM.RTM.)

S-Ethyl diisobutylthiocarbamat (SUTAN.RTM.),

S-n. propyl-di-n-propylthiocarbamate (VERNAM.RTM.),

S-propyl butylethylthiocarbamatae (TILLAM.RTM.),

S-ethyl ethylcyclohexylthiocarbamate (RO-NEET.RTM.),

Malathion (S-(1,2-dicarboxyethyl)-0,0-dimethyl phosphorodithioate),

Diazinon (0,0-diethyl, 0-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphorothioate,

O-Ethyl-S-phenyl-ethylphosphonodithioate (DYFONATE.RTM.),

Toxaphene (Octachlorocamphene),

Bromoxynil (3,5-dibromo-4-hydroxy benzonitrile ester of n.octanoic acid,

2-chloro-N-2,6-diethylphenyl-N-methoxymethylacetamide (LASSO.RTM.),

Diallate S-2,3-dichloroallyl N,N-diisopropylthiolcarbamate,

Triallate S-2,33-trichloroallyl N,N-diisopropylthiolcarbamate.

The second group comprises those pesticides which are solids at ambient temperatures and for all practical purposes, insoluble in water.

2,4,5-T (2,4,5-trichlorophenoxy acetic acid)

Monuron (3-(p-chlorophenyl)-1,1-dimethyl urea)

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethyl urea)

Bromacil (5 bromo-3-sec. butyl-6-methyl uracil)

Isocil (5 bromo-3-isopropyl-6-methyl uracil)

Linuron (3-(3,4 dichlorophenyl)-1-methoxy-1 methyl urea

Atrazine (2-chloro-4-ethylamino-6 isopropylamino-s-triazine) Simazine (2-chloro-4,6,-bis (ethylamino)-s-triazine

Dodine (n-dodecylguanidine acetate)

Thiram (tetramethylthiuram disulfide)

N-(mercaptomethyl)phthalimide s-(o,o dimethylphosphorodithioate) (IMIDAN.RTM.)

Lindane (gamma 1,2,3,4,5,6 hexachlorocyclohexane)

Folpet (N-trichloromethylphthalimide)

Manazon (s-(4,6-diamino-1,3,5-triazin-2-yl methyl)dimethyl phosphorothiolthionate)

Barban (4-chloro-2 butynyl m-chlorocarbanilate)

Tricumba 2-methoxy-3,5,6-trichlorobenzoic acid

Trifluralin (2,6-dinitro-N,N-dipropyl-4-trifluoromethylamiline) (2,3 dihydro-5-carboxanilido-6-methyl-1,4-oxathiin) (VITAVAX.RTM.)

2,4-dichlorophenoxyacetic acid

4-(4-chloro-2 methylphenoxy) butyric acid

2-(2,4-dichlorophenoxy) propionic acid

Ioxynil: 3,5 diiodo-4-hydroxybenzonitrile

Bromoxynil: 3,5 dibromo-4-hydroxybenzonitrile

Carbaryl: 1-naphthyl-N-methylcarbamate

Methoxychlor: 2,2,-Bis(p-methoxyphenyl)-1,1-trichloroethane

PP 781: 4(2-chloro phenylhydrazono)-3-methyl-5-isoxazolone*

PP 675: 5-butyl-2-dimethylamino-4-hydroxy-6-methyl pyrimidine*

PP 062: 5,6-dimethyl-2-dimethylamino-4 pyrimidinyl dimethylcarbamate*

PP 149: 5-n-butyl-2 ethylamino-4-hydroxy-6 methylpyrimidine*

C 6313 N'-(4-bromo-3-chlorophenyl)-N-methoxy-N-methylurea

C 6989 2,4'dinitro-4-trifluoromethyl-diphenylether

Chloroxuron N'-4-(chlorophenoxy) phenyl-NN-dimethylurea

Dichlobenil 2,6-dichlorobenzonitrile

Diphenamid NN-dimethyl-2,2-diphenylacetamide

Fenac 2,3,6-trichlorophenylacetic acid

Fluometuron N'-(3-trifluoromethylphenyl)-NN-dimethylurea

GS 14260 4-ethylamino-2-methylthio-6-t-butyl-amino-1,3,5-triazine

PCP Pentachlorophenol

Lenacil 3-cyclohexyl-6,7-dihydro-1H-cyclo-pentapyrimidine-2,4-(3H,5H)-dione

Pyrazon 5-amino-4-chloro-2-phenyl-3-pyridazone

Metrobromuron N'-(4-bromophenyl)-N-methoxy-N-methylurea

Metoxymarc N-(4-methoxybenzoyl)-N-(3,4-dichlorophenyl)-N',N'-dimethylurea

Neburon N-butyl-N'-(3,4-dichlorophenyl-N-methylurea

NIA 11092 1,1-dimethyl-3-[3-(n-t-butyl carbamyloxy)phenyl] urea

Mecoprop 2-(4-chloro-2 methylphenoxy)propionic acid

Monolinuron N'-(4-chlorophenyl)-N-methoxy-N-methylurea

Nitrofen 2,4-dichlorphenyl 4-nitrophenylether

Propanil N-(3,4-dichlororphenyl)propionamide

Pyriclor 2,3,5-trichloro-4-pyridinol

Solan 3'-chloro-2-methyl-p-volerotoluidide

Terbacil 5-chloro-3-t-butyl-6-methyluracil

UC 22463 (SIRMATE)-3,4-dichlorobenzyl N-methylcarbamate

WL 9385 2-Azido-4-ethylamino-6-t-butylamino-s-triazine

Propachlor 2-chloro-N-isopropylacetanilide

CP 50144 2-chloro-N-2,6-diethylphenyl-N-methoxymethylacetamide

CP 31675 2-chloro-N-(2 methyl-6-t-butylphenyl)acetamide

Cypromid 3',4'-dichlorocyclopropane carboxanilide

Fenuron NN-dimethyl-N'phenylurea

Chlorbromuron N'-(4-bromo-3-chlorophenyl)-N-methoxy-N-methylurea

Ametryne 2-methylmercapto-4-ethylamino-6-isopropyl-amino-s-triazine

Prometryne 2-methylmercapto-4,6-bisisopropyl amino-s-triazine

DCPA dimethyl 2,3,5,6, tetrachloroterephthalate

Benefin N-butyl-N-ethyl-2,2,2-trifluoro-2,6-dinitro-p-toluidine

Nitralin 2,6-dinitro-4-methylsulfonyl-NN-dipropyl-aniline

PP 493 2,6-difluoro-3,5-dichloro-4-hydroxy pyridine

CNP 2,4,6-trichlorophenyl-4'-nitrophenyl ether

Pentachloro nitrobenzine

1-(butile carbamoyl)-2-benzimidazol carbamic acid, methyl ester (BENLATE.RTM.)

Examples of appropriate hydrophobic solvents include alkylpyrrolidones having an alkyl portion containing from 6 to 14 carbon atoms, e.g., octylpyrrolidone, dodecylpyrrolidone, or N-(2'-ethylhexylpyrrolidone), alkyl gammabutyrolactones, alkyl cyclic carbonates and combinations thereof, wherein the alkyl chains contain from 6 to 14 carbon atoms. The alkyl portion may be distributed at one or more sites on the ring so long as one portion contains at least 6 carbon atoms and the total number of alkyl carbon atoms does not exceed 14. Preferred 6 to 14 carbon alkyl portions are composed of straight chains. Branched or cyclic alkyl portions may also be used.

The hydrophobic solvent is preferably selected from pyrrolidones having the formula ##STR2## wherein R.sub.2 is hydrogen or alkyl having from 6 to 14 carbon atoms and R.sub.3 is alkyl having from 6 to 14 carbon atoms with the proviso that at least one of R.sub.2 or R.sub.3 must contain at least 6 carbon atoms and the sum of the carbon atoms in R.sub.2 and R.sub.3 cannot exceed 14.

The inventive composition further comprises an organic diluent which is a synthetic or naturally occurring oil having a high hydrophobic character or having a fractional dispersive solubility parameter of greater than 70% and preferably greater than 85% and a molar volume of greater than 90 cm.sup.3 /mole. These properties are defined in the C.R.C. Handbook referred to hereinabove. Typical diluents include soybean oil, rapeseed oil, long chain alcohols, long chain ketones, long chain esters, and ethers. As used herein, "long chain" means with 6 or more carbon atoms. Also suitable as the organic diluent are aromatic petroleum oils including those which are commercially available distillates from crude oils having an average boiling point greater than 200.degree. C. Typical of such materials are those sold under the trademarks Exxon 200 or Texaco 400. Of course, such aromatics should be approved for use as a carrier for agriculturally active chemicals.

The composition of the aromatic petroleum oil is generally:

Heavy aromatic solvent naphtha--about 60%;

Middle distillate solvent extractant--about 40%.

Normally, these oils contain predominantly the C.sub.9 -C.sub.15 aromatic hydrocarbons and primarily the C.sub.10 -C.sub.12 hydrocarbons having a flash point of about 203.degree. F.

In the inventive composition, the amount of solvent is in the range from about 20 to 90%, and the amount of diluent is about 80 to 10%, based on the weight of solvent and diluent in the composition.

The inventive composition also contains one or more additional emulsifier(s) or surfactant(s) which is generally selected on a case by case basis in order to optimize the solubility and stability of the emulsion. Typically, such emulsifiers include ethoxylated alkyl phenols, linear aliphatic polyesters, linear aromatic polyesters, polyethoxylated alcohols, linear aliphatic ethoxylates, polyethoxylated castor oil, polyethoxylated carboxylates, and polyethoxylated alkylamines. Anionic surfactants may be used as the emulsifier and include phosphate esters and their salts, alkyl sulfonamides, salts of sulfated nonylphenoxypoly(ethyleneoxy) ethanol, salts of alkylbenzene sulfonates, salts of alkylnaphthalene sulfonate, and sulfonated aliphatic polyesters and their salts. Also suitable are complex phosphate esters of nonionic surfactants of the ethylene oxide type which are mixtures of diesters of phosphoric acid. (See, for example, McCutcheon's, Emulsifiers and Detergents (1989), published by McCutcheon's Division of M.C. Publishing Co., Glen Rock, New Jersey.) Generally, the amount of emulsifier (surfactant) is from about 1 to 25% based on the total weight of the composition.

The agriculturally active chemical (sometimes referred to herein as AAC) concentration should be as high as possible so long as it does not precipitate out upon dilution of the concentrate with water for a reasonable period of time and achieves the desired effect. Precipitation (crystal formation) on standing not only depletes the solution of AAC, it can also lead to fouling of application equipment, i.e., sprayers, etc. With the present invention, it is possible to obtain concentrates with agriculturally active chemical concentrations in excess of 5 weight percent which form a stable emulsion upon being diluted with water. Depending on the particular agriculturally active chemical, the concentration of the AAC is from about 5 to 25% based on the total weight of the composition before dilution.

The final use concentration values depend on the AAC. However, it is important that upon dilution, the diluted form remain stable for a time sufficient to allow it to be applied. This, of course, will vary with the schedule for the application in the field. Normally, the diluted concentrate is applied within four hours of dilution. It is possible, however, due to equipment and personnel delays, that a standing period of up to 24 hours may be encountered. With the present invention, prolonged stability of the emulsified concentrate, as is, as well as in the diluted form is obtained. In particular, the emulsified concentrate in accordance with the present invention can be diluted to final use concentrations in the range from about 10 ppm to 2 percent, depending on the specific AAC, without any adverse effects, and specifically, precipitation of the AAC from the solution.

The following examples illustrate the present invention*:

A series of experiments was carried out wherein the type and amount of agriculturally active chemical, hydrophobic solvent, diluent, and other components were varied. The samples were evaluated for ease of emulsion and emulsion stability by measuring the amount of separation before and after mixing. The compositions used and results obtained are set forth in the tables that follow.

Formulations were prepared by weighing the exact proportion of ingredients and mixing them together in a bottle. The solvents were weighed in first. The AAC was dissolved completely in the solvent system followed by addition of the wetting agent or emulsifying agent. Typically, about 10 g of each of the formulations was prepared.

The contents were stirred well in an automatic rocking shaker for about 30 minutes when the AAC dissolved completely. The samples thus prepared were evaluated for freeze-thaw stability on storage and ease of emulsification and emulsion stability on dilution. For dilution, 2 grams of concentrate were diluted to 50 grams using World Health Organization (WHO) standard (6 g of CaCl.sub.2 and 2.78 g of MgCl.sub.2 6H.sub.2 O dissolved in 20 L) hard water having a hardness of 342 ppm expressed as Na equivalent.

The concentrates were stored for a period of 24 hours in the cold (temperature 5.degree. C.) in a refrigerator and taken out and thawed to room temperature and then stored at 55.degree. C. in an oven for a period of 24 hours. The alternate storage in the cold (5.degree. C.) and warm condition at 55.degree. C. was repeated for three cycles. Any separation during the storage was recorded. A concentrate is "stable" if there is no substantial separation after the 24 hour cycles at each temperature. All of the solutions exemplified hereinafter exhibited stability according to this test between the temperatures of 5.degree. C. and 55.degree. C. Some of the solutions were even stable at a lower range of -5.degree. C.

A Nessler tube (1.8 cm diameter; 28 cm long) was filled with an appropriate quantity (47-48 g) of WHO water. Using a serological pipette, 0.5-2.5 g of emulsion concentrate was dropped into the Nessler tube containing 47.5-49.5 g water. The initial bloom was observed at zero time without stirring and the quality of the bloom was graded by visual appearance as shown below. The Nessler tube was stopped and inverted 20 times; the bloom was again recorded and so also stability as judged by volume or height of the sedimentation (cream/ppt/oil) followed at different intervals of time: 0, 1 hour, 2 hours, up to 24 hours.

The composition of the concentrate (EC) diluted with water was considered "stable" if at EC concentrations of from 0.2 to 1%, the composition after mixing (twenty inversions) exhibited two mm or less cream and no oil in one hour. Both top and bottom should be checked.

Each of the emulsifiable concentrates thus prepared were analyzed for ease of emulsification (bloom) upon addition of water and after twenty inversion of the sample as well as emulsion stability upon dilution with water. The composition of the samples are set forth in Table A and the results of the analysis are set forth in Table B.

A number of the samples were evaluated for precipitation of AAC, i.e., crystal growth over varying time periods. This was done by placing the diluted sample in a 100 ml beaker and stirring continuously. The samples were examined at 1, 4, 7, and 24 hour intervals and were examined for the presence of crystals under 200 .times. magnification. Samples were also tested for sediment by pouring through U.S. Standard screens (60, 100 and 250 mesh).

The components set forth in the Tables are referred to by their commercial names for purposes of brevity. The chemical nomenclature of the materials is as follows: