Background of the invention

Deltamethrin is a non-composite synthetic pyrethroid and a broad spectrum insecticide. It is a fast-acting neurotoxic agent with good contact and stomach action. Its biological activity is very stable in the environment since it has good residual activity on many insectsband most surfaces. Deltamethrin is non-systemic in plants. It is of moderately high toxicity in mammals, and is readily metabolized with rapid loss of toxicity. It has a repellent effect for some insects.

Deltamethrin chemically is (S)- -cyano-3-pehoxybenzyl(lR)-cis-3-(2,2-dibromovinyl)-2,2- dimethyl cyclopropane carboxylate. The compound was formerly known as Decamethrin and has the following structural formula:

Deltamethrin is effective as larvicide, ovicide and adulticide against a number of plant parasitic pests (Lepidoptera, Homoptera, Coleoptera, Diptera and Acarides). It is also effective against a number of biting, disease vector and nuisance insects of man and animals.
Oil-in water emulsion (EW) formulations are proving to be effective alternatives for emulsifiable concentrate (EC) formulations for reducing or eliminating the Volatile Organic Compounds (VOCs). EW formulations are also safer to use & have reduced dermal toxicity.

The customary deltamethrin formulation is emulsifiable concentrates (EC) which are usually based on aromatic hydrocarbons like heavy aromatic naphtha, Solvent C-9, xylene etc.
The main advantages of EW formulation over EC formulations include total elimination of aromatic hydrocarbon solvents, Non-flammable or low flammability, Low dermal toxicity, Non- Phytotoxic, Safety in manufacture and use, Low formulation cost etc.EW formulations are already emulsions unlike EC's before the actual spray mix preparation, and thus can be easily diluted making this more advantageous than EC formulations.

In WO 90/09103, oil-in-water emulsion formulations are disclosed. In such formulations, part of the organic hydrocarbon solvent is substituted by water in order to provide an environmental friendly product.

EP0587368 discloses EC's containing deltamethrin, in which aromatic hydrocarbons have been replaced by a combination of polar co-solvents and vegetable oil, to achieve improved inhalation tolerance.

EP 1210877 discloses EW formulations with organic mono, di or tri-substituted carboxylic acid esters as solvent and polar solvents like cyclohexanone as a co-solvent.

Summary of the invention:

It is an object of the invention to provide an EW formulation of deltamethrin with significantly reduced toxicity based on carboxylic acid esters as organic solvent.

It is another object of the invention to provide an EW formulation of deltamethrin with excellent storage stability.

Detailed description of the invention:

According to the invention, Deltamethrin oil-in-water emulsion formulation comprises of:

a) Deltamethrin active ingredient,
b) Esters of aromatic di-carboxylic acid as organic solvent,
c) An emulsifier system consisting a blend of anionic and non-ionic surfactants,
d) Antifreeze agent,
e) Antifoaming agent,
f) Preservative and
g) Water

The concentration of active substance, deltamethrin is generally 0.1 to 20%, in particular 0.5 to 5%.

Examples of aromatic di-substituted carboxylic acid ester as organic solvents include the phthalates (such as dimethyl phthalate, diethyl phthalate, dibutylphthalte, dioctyl phthalate etc). The formulation generally comprises of 2 to 25% of organic solvent, and in particular 5 to 15%.

Examples of anionic emulsifiers are phosphate esters and sulfate esters of poly ethoxylated fatty alcohols, phosphate esters of polyethoxylated aryl phenols, sodium or potassium or calcium salt of alkyl benzene sulfonates, or sodium or potassium or calcium salt of poly carboxylic acids.

Examples of non-ionic emulsifiers are polyethoxylated alkyl phenols, poly ethoxylated castor oils, polyethoxylated alcohols etc. The formulation preferably comprises 1 to 30 weight percent of a combination of anionic and nonionic emulsifiers and in particular 2 - 20% by weight.
Examples of suitable antifreeze agents are ethylene glycol, propylene glycol, hexylene glycol, glycerols etc. They are added in an amount of preferably 1 to 25% by weight, particularly 5 to 15% by weight.

Examples of suitable preservatives are aqueous dipropylene glycol solution of 1,2- benzisothiazolin-3-one (commercially available as Proxel GXL), potassium sorbate etc. They are added in amount of preferably 0.01 to 5%, particularly 0.1 to 1% by weight.
Preferred antifoams and defoamers are based on silicone, particularly preferred are an aqueous emulsion of dialkylpolysiloxanes. Antifoams are added in an amount of generally 0.01 to 3% by weight, preferably 0.05 to 1% by weight

The formulation generally comprises 20 to 85% by weight, preferably 50 to 75% by weight, of water.

The emulsions formulations of the invention demonstrate excellent storage stability and are capable of re-emulsification even on long standing. The formulations made according to this invention, even after dilution of 5 ml of formulation in 95 ml of water demonstrated good stability. The product is intended to be diluted with water before use.

Time Observation

0 hours Emulsification complete
0.5 hours Cream not observed
2 hours No creaming / sedimentation observed
24 hours Re-emulsification complete. No creaming /sedimentation after 24.5 hours.

product was also subjected to stress and stability testing and the observations are as follows:

Storage temperature 0°C for 7 days,
Physical appearance white homogeneous emulsion on gentle stirring.

Cream No creaming

Particulate matter Slight solid in the bottom, which becomes homogeneous on gentle agitation. pH No change in pH value observed
Assay No decomposition /degradation in active ingredient observed.

The product was also subjected to stability study at 54 ± 2°C for 14 days and found to be highly stable in terms of all testing parameters.

The main advantages of this invention over the prior art formulations is the elimination of hydrocarbons and other polar organic co-solvents. This process uses only aromatic di- substituted carboxylic acid ester as organic solvent with no hydrocarbons or other polar co- solvents.

Examples

Example 1

Ingredients Quantity %w/w
Deltamethrin technical 2.0
Diethyl phthalate 10.0
Propylene glycol 8.0
Blend of anionic and nonionic emulsifier 10.0
Silicone antifoaming agent 0.1
Proxel GXL 0.5
Water 69.3

Example 2

Ingredients Quantity %w/w
Deltamethrin technical 2.0
Diethyl phthalate 10.0
Ethylene glycol 7.0
Blend of anionic and nonionic emulsifier 12.0
Silicone antifoaming agent 0.1
Proxel GXL 0.5
Water 68.3

Manufacturing process

Organic phase was prepared by dissolving the deltamethrin active in an organic co-solvent such as di-substituted carboxylic acid ester and mixing it with emulsifiers and anti-freeze agent. Aqueous phase was prepared by mixing silicone antifoaming agent and preservative in water. Organic phase was slowly charged to the aqueous phase under stirring in a high shear Silverson mixer at around 1300 RPM. After completion of addition of organic phase to aqueous phase, the entire mass was agitated in a high shear Silverson mixer at around 9000 RPM for a period of 30 minutes to get stable deltamethrin oil in water emulsion.

Claims

We claim that the present invention relates to oil in water emulsion formulation of Deltamethrin and a process for its manufacture.