Emulsifying Dispersant and Biocidal Composition Containing Same

The present invention relates to an emulsifying dispersant. More particularly, the present invention relates to an emulsifying dispersant that makes it possible to incorporate a chemically unstable biocidal agent in a stable biocidal preparation.

Biocidal agents are formed into various preparations, such as emulsions, wettable powders, flowable agents, granules and dusts, and they are marketed in the form of such preparations. Among these preparations, emulsions and wettable powders are most popular, and various measures have been taken in the prior art for obtaining stable preparations of these types. The decomposition of a biocidal agent during storage is a fatal defect for a commercial preparation, and entails a risk of phytotoxicity caused by substances produced by such decomposition. As factors which cause the decomposition of a biocidal agent during storage of a preparation containing the agent, heat, light (ultraviolet radiation), water heavy metals, emulsifiers and dispersants are considered most important. The effects of external factors, such as light and heat, can be eliminated by using a specially designed packaging vessel or by similar measures which protect the biocidal composition from the external factor. The problem of hydrolysis caused by water can be solved by employing an organic solvent-based emulsion other than a flowable composition.

When an agricultural biocidal composition is actually used, it is diluted with water and then sprayed onto the plants. Therefore, it is necessary to incorporate into the composition an emulsifier capable of emulsifying a water-insoluble organic solvent and a water-insoluble agricultural biocidal agent. However, from the results of our research, we have found that one type of decomposition of agricultural biocides, which we consider is due to the presence of a primary hydroxyl group in the emulsifier molecules, cannot be avoided when known emulsifiers for agricultural biocides having primary hydroxyl groups are used. Moreover, even in the case of wettable powders containing an inorganic carrier, decomposition due to (a) water contained in the inorganic substance, (b) surface hydroxyl groups, (c) heavy metals and (d) dispersants cannot be avoided. At present, this problem can be solved only with difficulty by modifying the surface of the inorganic carrier or by adding a decomposition-preventing agent, but no commercially satisfactory results have yet been obtained.

We have studied the problem of minimizing or preventing decomposition of agricultural chemicals, particularly pesticides, caused by emulsifiers or dispersants. We found that the decomposition is mainly due to the presence of a hydroxyl group in the molecular skeleton of the surface active agent that is employed as an emulsifier or dispersant. Accordingly, we continued our research with a view to developing a surface active agent free of this defect, and as a result, we have now completed the present invention.

More specifically, in accordance with the present invention, there is provided an emulsifying dispersant (surfactant) for forming a stable preparation of a biocidal agent, which surfactant comprises a nonionic surface active agent substantially free of terminal primary hydroxyl groups. The surfactant of this invention is obtained by esterifying or etherifying a terminal hydroxyl group of an alkylene oxide adduct of a hydroxyl compound or an alkylene oxide adduct of a carboxyl compound. The hydroxyl and carboxyl compounds according to this invention are preferably compounds having carboxylic or hydroxyl-substituted hydrocarbon groups. The emulsifying dispersant of the present invention not only prevents decomposition of the biocidal agent, but also has excellent emulsifying and dispersing effects.

The present invention also provides a biocidal composition which is emulsifiable in water. The biocidal composition according to the present invention contains an effective amount of a water-insoluble biocide, an amount of an organic solvent effective to dissolve the biocide, and an emulsifier which comprises the nonionic surface active agent of the invention described above. The emulsifier is used in an amount effective to emulsify the organic solvent containing the biocide dissolved therein in water.

The nonionic surfactant used in the emulsifying dispersant of the present invention cannot readily be expressed using a generic chemical formula because it includes nonionic surfactants of complex formulas made from polyhydric alcohols, such as polyoxyethylene glycerol trioleate, polyoxyethylene sorbitol hexaoleate, and similar compounds. However, the simpler nonionic surfactants used in the present invention can be expressed by the following general formula:

wherein R.sup.1 and R.sup.2 are each a saturated or ethylenically unsaturated hydrocarbon group, with the proviso that at least one of R.sup.1 and R.sup.2 has at least 8 carbon atoms, Y.sup.1 is --COO-- or --O--, Y.sup.2 is --OC-- or represents a direct valence bond between --(R.sup.3 O).sub.n -- and --R.sup.2, R.sup.3 is C.sub.2 -C.sub.4 alkylene, and n is an integer of from 1 to 100.

More specifically, the nonionic surfactants have one of the following formulas:

The biocidal composition of the present invention preferably contains 10 to 90 wt.% of the water-insoluble biocide, 15 to 50 wt.% of the organic solvent, and 1 to 50 wt.% of the emulsifier. The organic solvent is preferably an aromatic hydrocarbon. particularly xylene. The biocide is any water-insoluble insecticide, herbicide or other pesticide. Mose preferably, the biocidal composition contains 10 to 60 wt.% of the biocide, 20 to 50 wt.% of the organic solvent, and 5 to 25 wt.% of the emulsifier.

As the hydroxyl compound used for preparing the surface active agent of the present invention, there can be used natural and synthetic aliphatic alcohols such as methyl alcohol, ethyl alcohol, propyl alcohol, butyl alcohol, octyl alcohol, 2-ethylhexyl alcohol, lauryl alcohol, tridecyl alcohol, cetyl alcohol, stearyl alcohol and oleyl alcohol, polyhydric alcohols such a glycerol, polyglycerol, sorbitol, sucrose, pentaerythritol and trimethylolpropane, alkylphenols such as octylphenol and nonylphenol, and aromatic-substituted phenols such as phenylphenol, tribenzylphenol and styrenated phenol.

As the carboxyl compound used for preparing the surface active agent of this invention, carboxylic acids having 2 to 22 carbon atoms can be used, such as acetic acid, propionic acid, caprylic acid, capric acid, 2-ethylhexanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid.

The alkylene oxide adduct can be prepared from a hydroxyl or carboxyl compound as described above according to known methods, for example, a method comprising reacting a hydroxyl or carboxyl compound with an alkylene oxide compound in the presence of an alkali or acid catalyst.

As the alkylene oxide compound, there can be used ethylene oxide, propylene oxide and butylene oxide. Ethylene oxide is especially preferred. If an alkylene oxide mixture is used, the content of ethylene oxide is preferably at least 30 mole %. The number of moles of added alkylene oxide is 1 to 100, preferably 5 to 50 moles, per 1 mole of the hydroxyl or carboxyl compound to be reacted therewith.

Esterification or etherification of the alkylene oxide adduct can be performed according to known methods. For example, an esterification method may be used which comprises dehydrating and esterifying the alkylene oxide adduct with a fatty acid in the presence of an acid or alkali catalyst. An etherification method comprising dehydrohalogenating the alkylene oxide adduct with an alkyl halide in the presence of caustic alkali can also be used.

A fatty acid halide or fatty acid anhydride can be used as the esterifying agent instead of the abovementioned fatty acid. An esterifying agent having a saturated or unsaturated hydrocarbon group of 1 to 21 carbona toms, such as capric acid, lauric acid, stearic acid or oleic acid, is preferred.

An alkyl halide having a saturated or unsaturated hydrocarbon group of 1 to 22 carbon atoms is preferred as the etherifying agent. For example, methyl chloride, ethyl chloride, propyl chloride, octyl bromide, lauryl chloride and stearyl chloride can be used.

The compound obtained by esterification or etherification is a nonionic surface active agent substantially free of a terminal hydroxyl group. It is essential that at least one of either (1) the hydrocarbon group of the starting hydroxyl or carboxyl compound or (2) the hydrocarbon group of the esterifying or etherifying agent should have at least 8 carbon atoms.

As specific examples of the nonionic surface active agents of the present invention, there can be mentioned polyoxyethylene(15) lauryl methyl ether, polyoxyethylene(20) stearyl methyl ether, polyoxyethylene(20) methyl ether oleate, polyoxyethylene(15) methyl ether laurate, polyoxyethylene(15) nonylphenyl methyl ether, polyoxyethylene(30) nonylphenyl octanoate, polyoxyethylene(30) styrylphenyl methyl ether, polyoxyethylene(30) sorbitol hexaoleate, polyoxyethylene styrenated phenyl lauryl ether, polyoxyethylene glycerol trioleate, polyoxyethylene tribenzylphenyl ethyl ether, polyoxypropylene polyoxyethylene laurylphenyl methyl ether, polyoxyethylene pentaerythritol tetra-2-ethyl hexyl ether.

Because the nonionic surface active agent of the present invention has no primary hydroxyl group, it does not decompose biocidal agents. Furthermore, because it has an excellent surface activating property, it forms a stable emulsion or dispersion of a biocidal agent.

It is preferred that the emulsifying dispersant of the present invention contain an anionic surface active agent in addition to the above-mentioned specific nonionic surfactant. As such anionic surface active agents, there can be used calcium alkylbenzenesulfonate and triethanolamine alkylbenzenesulfonate. In preferred embodiments of the invention, the emulsifier consists essentially of a mixture of 55 to 80 wt.% of the nonionic surface active agent and 45 to 20 wt.% of the anionic surface active agent.

The present invention will now be described in detail with reference to Synthesis Examples, Examples and Comparative Examples.

An emulsifier composition was first prepared according to an emulsifier formulation example, and then a preparation according to each example or comparative example was formed by emulsifying a solvent and an agricultural biocide with the emulsifier composition. Then, the stability of each resulting preparation was tested.

In this Synthesis Example, polyoxyethylene(20) methyl ether oleate was synthesized.

An autoclave (formed of SUS) having a capacity of 3.0l and provided with an electromagnetic stirrer was charged with 64 g (2.0 moles) of methanol and 2.2 g of caustic potash. The inner atmosphere of the autoclave was purged with nitrogen and the charge was heated to 90 .+-.5.degree. C. Then, 1762 g of ethylene oxide was fed under pressure at 90 to 130.degree. C. over a period of 4 to 5 hours so that the reaction pressure did not exceed 3.5 kg/cm.sup.2 G, whereby the reaction was completed.

The reaction product was neutralized with acetic acid to obtain POE(20) methyl ether having a hydroxyl value of 62 mg KOH/g and a color of APHA 20. Then, a 2-liter capacity 4-neck flask provided with a thermometer, a stirrer, a water removing tube and a nitrogen inlet tube was charged with 932 g (1.03 mole) of the thus-obtained POE(20) methyl ether, 274 g (1.0 mole) of oleic acid and 2.4 g of 85 % H.sub.3 PO.sub.4, the mixture was heated at 215.degree..+-.5.degree. C., and reaction was carried out at this temperature for about 7 to 8 hours to obtain a liquid reaction product having a color of APHA 150 to 200, an acid value of 6 mg KOH/g, a saponification value of 48 mg KOH/g and a hydroxyl value of 9 mg KOH/g.

The following emulsifier formulations were then prepared, using the thus-prepared polyoxyethylene(20) methyl ether oleate and other surfactants, as follows:

The storage stability and emulsion stability of each of the preparations obtained in Examples 1 through 4 and Comparative Examples 1 through 4 were examined according to the methods described below. The obtained results are given in Table 1.

(1) Storage Stability (retention of active ingredient)

Each preparation was stored at 50.degree. C. for 3 months, and the content of the active ingredient was determined by gas chromatography according to the Japanese officially determined method for agricultural chemicals.

(2) Emulsion Stability

Each preparation was diluted by 20 times with standard water of 3 HD or 10 HD, and, after 2 hours, the emulsion stability was evaluated using the following criterion:

A: creaming or sedimentation was not observed at all

AB: less than 1 mm creaming and sedimentation

B: 1 to less than 3 mm creaming and sedimentation

C: 3 to less than 5 mm creaming and sedimentation

As is apparent from the results shown in Table 1, when the emulsifying dispersant of the present invention is used, the storage stability of the biocidal agents and the emulsion stability can be maintained at the same high levels as at the time of formation of each preparation, even after storage for up to 90 days.