CA1083461A

CA1083461A - Process for the preparation of concentrated suspensions of pesticides

Info

Publication number: CA1083461A
Application number: CA266,069A
Authority: CA
Inventors: Hildegard Schnoring; Dietmar Bonisch
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1975-11-19
Filing date: 1976-11-18
Publication date: 1980-08-12
Also published as: IL50917A0; ES453428A1; DK519776A; PT65848B; JPS5264431A; CH620570A5; NL7612725A; BE848481A; IL50917A; AU1968176A; FR2332053A1; ZA766913B; PT65848A; GB1518568A; BR7607707A; EG12569A; AT349830B; ATA861376A; SE7612887L; AR220098A1

Abstract

ABSTRACT OF THE DISCLOSURE
Concentrated aqueous suspensions which contain pesticidal active compounds which are only sparingly soluble in water and have a small average particle size and a particle size distribution which is suitable for stable suspensions can be prepared when a melt of a pest-icidal active compound, which is only sparingly soluble in water, and an acid, which is the basis of an anionic emulsifier, and, optionally, formulation auxiliaries is introduced, whilst stirring vigorously and preventing the access of air, into an aqueous phase which contains 0.5 to 1.5 equivalents - based on the acid component of the anionic emul-sifier - of a base and, optionally, one or more water-soluble pesticidal active compounds and, optionally, formulation auxiliaries and has a temperature below the solidification point of the melt.

Description

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The present invention relates to a process for the preparation o~ concentrated aqueous suspensions o~ pesticidal active compounds.
It has already been disclosed that it is possible, with the aid of agitated spherical grinding media made o~ glass, quartz, ceramics, metal or plastics, and optionally in the presence o~ di~persing agents, finely to divide organic solids in solvents in which they are only sparingly soluble (see German Patent Speci~ications 619,662 and 915,408, ~ritish Patent Speci~cation 909,609, U.S. Patent Speci~ications

2,212,641, 2,361,059 and 2,581,414, "Feinzerkleinern in der chemischen Industrie" ("Fine comminution in the Chemical Industry") by N.Rink and G.Giersiepen in "Aufbereitungs-technik" ~2, (9), 562-572 (1971) and "Na~feinstmahlung in Ruhrwerkskugelmuhlen" ("E~tremely ~ine Wet Grinding in Stirred ~all Mills") by W.~itz in Chem. Techn. 26 (7), 412-416 (1971)). ~hus, it is possible, for example, to prepare suspensions o~ pesticides by ~inely grinding a cry~talline or pasty active compound in the pre~ence o~ a liquid carrier pha8e ("~ine ~et grinding") and optionally subsequently diluting to bhe desired concentration by adding a diluent in ~hich the active compound either i~ virtually insoluble or is only sparingly soluble. However, this process is ~ub;ect to several disadvantages. For e~ample, it is very expen~ive in respect o~ work and energy since, at the stage o~ fine wet comminution, several grinding 0teps are ~requently required in order to obtain the ~inenes~ of particle size which is nece~sary i~ the æqueous suspension is to have adequate stability. ~urthermore, wet grinding mills, such as corundum disc mills or bead mills, are subject to relatively high ~ ., '' ~e A 16 581 - 2 -, . ~ .. . . .. ,., . . . . ~ .

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material wear. In addition, when carrying out fine wet comminution, it is necessary to ensure, by means of suitable devices, that the moist product to be ground does not take up any air bubbles, so that the formation of a stable foam is prevented. A further disadvantage, in addition to those al-ready mentioned, is that the through-crystallisation of active compounds which are obtained as molten material from the chemical process of preparation is frequently poor and, therefore, such compounds can be comminuted mechanically only with great diificulty because the crystal hardness necessary ior this is lacking. An expedient used in such cases is to carry out dry comminution with the addition of grinding aids.
However, thls frequently results in the ground substrate having properties which are disadvantageous for the pre-paration of concentrated aqueous suspensions. For example, it is then not possible to obtain a particularly desired high concentration of suspended solids in the suspension to be prepared.
~urthermore, it is known to prepare suspensions of pesticidal active compounds by dispersing a solid active com-pound, which has been iinely divided by means o~ a jet of air, in a liquid phase, with the addition oi dispersing agents and emulsiiiers, or by dispersing a premi~ oi the active compound and formulation auxiliaries, which has been subjected to a jet of air, in a liquid phase. Ii the fact that this process also requires a comminution of the active compound, which comminution is e~pensive in respect oi work and energy,is disregarded, the essential disadvantage is that it is not possible to divide the acti~e component as iinely and uniformly as in the case oi iine wet grinding. The result o~ this is ~e A 16 581 - 3 -,~ , , .

that the suspensions prepared in this way are generally less stable than those which are prepared by the process of fine wet comminu- -tion; this is because sedimentation takes place more rapidly the larger the size of the solid particles contained in a suspension and, moreover, large differences in the particle size favour so-called Ostwald ripening, which is to be understood as growth of the large crystals at the expense of the small crystals. It is `
also a considerable disadvantage that it is necessary with all types of dry grinding - but especially when grinding with a jet of air -to eliminate the dust formed during the grinding process, so that -the pollution of the environment, and the danger to operating per-sonnel, due to dust, and especially due to toxic substances, is reduced to a minimum.
According to the present invention, there is provided a process for the preparation of a concentrated aqueous suspension ;~
which contains a pesticidally active compound, which is only sparingly soluble in water and which has an average particle size between 1 `;
and 100 ~ and the particle size distribution of which is such that 80 percent of the suspended particles are smaller than 50 ~, in which process a melt of the pesticidally active compound which has a melt-ing point between 40C and 300C and has a solubility in water of at most 1.5 percent by weight at 25C, and an acid which is the basis of an anionic emulsifier, is introduced, whilst stirring vigorously and preventing the access of air, into an aqueous phase which contains 0.5 to 1.5 equivalents - based on the acid component of the anionic emulsifier - of a base and which has a temperature between 20 and 90C said temperature being at least 20C below the solidification -point of the melt. ~;

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It is to be regarded as extremely surprising that it is possible, by the process according to the invention, to prepare stable aqueous concentrated suspensions which contain pesticidal active compounds which are only sparingly soluble in water and have a small particle size and a particle size distribution which is suitable for stable aqueous suspensions since, on the basis of the known state of the art, it was to be expected that, as a result of Ostwald ripening also, the crystals present in the suspension would gradually grow at room temperature and that relatively large agglomerates or even a melt cake would form, which ultimately would result in separation of the solid phase from the liquid phase.
The process according to the invention has a number of advantages. Thus, even on a relatively large scale, it can be carried out simply with a relatively low expenditure on apparatus and energy. Furthermore, in contrast to the conventional methods, the process according to the invention does not include any grinding processes and there is therefore no pollution of the environment due to the formation of dust and no danger to the operating personnel due to dust or spray. Moreover, the washing water used to clean the apparatus required can be collected and, if the product is not changed, can be processed as a constituent of the aqueous phase in subsequent batches. Thus with the process according to the invention no con-taminated or toxic effluents are _ 5 -; ~; , , ;

101~13461 ~: ~
obtained. Furthermore, the process according to the invention makes it possible to prepare concentrated aqueous suspensions which, despite their high solids content, are capable of flow and display good low-temperature stability. Additional advant-ages of the process according to the invention are that the preparation of the suspensions can be carried out free from foam and that the size of the particles in the suspension can to a certain degree be controlled by the nature and amount of the emulsifier, i.e. by the nature and amount of the acid component ;
of the anionic emulsifier and of the base and also by the stoichiometric ratio of the acid component of the anionic ~ -emulsifier to the base. Finally, when suitable surface-active substances (formulation auxiliaries) are also used, the process according to the invention can be so guided that, in the cases in which the pesticidal active compound to be suspended can be present in several crystal modifications, the particularly desired crystal modification is formed in a controlled manner in the suspension to be prepared.
In the present case pesticidal active compounds are to be understood as active compounds which can customarily be ~ -used for plant protection. These include, for example, insecticides, nomatocides, acaricides, rodenticides, fungicides, herbicides and plant-growth regulators.
With the aid of the process according to the invention ;~
it is possible to prepare concentrated aqueous suspensions -of those pesticidal active compounds which have a melting point between 40~C and 300~C, preferably between 60 C and 280C, and a solubility in water of at most 1.5% by weight at 25C.
Examples of such active compounds which may be mentioned ~;

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individually are: N-(2-benzthiazolyl)-N,N'-dimethylurea, 3-methylthio-4-amino-6-tert.-butyl-1,2,4-triazin-5-one, 3-methyl-thio-4-isobutylideneamino-6-tert.-butyl-1,2,4-triazin-5-one, 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine, N'-(3,4-dichlorophenyl)-N,N-dimethylurea, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl methyl-carbamate, 3,5-dimethyl-4-methylthiophenyl N-methylcarbamate, 0,0-diethyl-0-(3-chloro-4-methyl-7-coumarinyl) -thiophosphate, ~-hexachlorocyclohexane, 6,7,8,9,10,10-hexachloro-1,5,5A,6,9,9A-hexahydro-6,9-methane-2,4,3-benzo-dioxathiepine 3-oxide, 1,4,5,6,7,8,8-heptachloro-4,7-endomethylene-3A,4,7,7A-tetrahydroindene, N-trichloromethylmercapto-4-cyclohexene-1,2-dicarboximide, N-trichloromethylthiophthalimide, 2-(2-furyl)-benzimidazole, 5-amino-1-bis-(dimethylamido)-phosphoryl-3-phenyl-1,2,4-triazole, 6-methyl-2,3-quinoxaline dithiolcyclo-carbonate and 4-hydroxy-3-(1,2,3,4-tetrahydro-1-naphthyl)-coumarin.

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, ., . : , ~3~61 Substances which can be used as the acid components of anionic emulsifiers, which can be added to the melt of the active compound in the process according to the invention, are ; . .
all those acids which form the basis of anionic emulsifiers and are stable in the melt. These include, preferably, fatty acids with 10 to 22 carbon atoms and especially with 16 to 20 carbon `- :
atoms, and also certain aromatic carboxylic acids and sulphonic acids as well as particular alicyclic carboxylic acids. Examples of such acid components which may be mentioned individually are:
lauric acid, stearic acid, oleic acid, benzoic acid, abietic acid, coconut fatty acid, resin acids and 4-(n-dodecyl)-benzene- ~ -sulphonic acid.
Substances which can be used as bases, which can be . , added to the aqueous phase in the process according to the in-vention, are all the customary acid-binding agents, with the proviso that they have an adequately strong basic reaction and do not have , ;
an adverse effect on the activity of the resulting emulsifier. ;~ -~
These include, preferably, alkali metal hydroxides, such as, for -example, sodium hydroxide or potassium hydroxide, and also aluminium ~.
hydroxide, as well as amines, such as, for example, triethanolamine, or, for example, also basic stearyl taurate.

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The amounts of acid components of anionic emulsifiers, and of bases, to be employed can be varied within a relatively wide range. In general, the acid component and the base are used in amounts such that the concentration of the acid and of the base is between 0.2 and 12 per cent by weight, preferably between 2 and 6% by weight, based on the resulting suspension.
The stoichiometric ratio of the acid component of an anionic emulsifier to the base can also be varied within a relatively wide range. In general, 0.5 to 1.5 equivalents of the base are employed per 1 equivalent of the acid component of an anionic emulsifier; the equivalent ratio of the acid component to the base is preferably between 1:0.8 and 1:1.2.
If ionic emulsifiers are used when carrying out the process according to the invention care must be taken that the pH value of the aqueous phase is kept within a range in which these emulsifiers are active.
The process according to the invention is preferably carried out in the additional presence of formulation auxiliaries.
The latter can be added to the melt and/or to the aqueous phase.
Formulation auxiliaries include: solid excipients, surface-active substances which have an emulsifying and/or dispersing action, or-ganic solvents, anti-foaming agents, thickeners and antifree7e agents. Solid excipients which can be used are, for example:
ground natural minerals, such as kaolins, aluminas, talc, chalk, quarts, attapulgite, montmorillonite and diatomaceous earth, and ground synthetic _ 9 -~08341~

minerals, such as highly disperse silica, aluminium oxide and silicates; sur~ace-active substances having an emulsifying and/or dispersing action which can be used are, for example:
polyoxyethylene fatty acid esters, polyoxyethylene fatty alcohol ethers, for example alkylaryl polyglycol ethers, alkylsulphonates, alkylsulphates, arylsulphonates and lignin-sulphonates; organic solvents which can be used are, for example: aromatic compounds, such as xylene, toluene, benzene or alkylnaphthalenes, chlorinated aromatic compounds or chlorinated aliphatic hydrocarbons, such as chlorobenzene~ and chloroethylenes, aliphatic hydrocarbons, ~uch as cyclohexane or paraf~ins, for example mineral oil fractions, alcohols, such a~ butanol, or glycols and their ethers and esters, ketones, such as acetone, methyl ethyl ketone, methyl isobutyl `~
ketone or cyclohexanone, and strongly polar solvents, such as dimethylformamide and dimethylsulphoxide; anti-foaming agents which can be used are, fo~ example, a fatty acid sulphonamide and ~ilicone anti-foaming agents based on silicone oil and highly disperse ~ilica; thickeners which can be used are, for example, carboxymethylcellulose, starch, polyacrylates, alginic acid and highly polymeric polyvinyl alcohols or poly-vlnyl acetates; and antifreeze agents which can be used are:
ethylene glycol, glycerol and urea.
The suspensions which can be prepared according to the invention can contain solid excipient~ in concentrations of up to 20yo by weight (based on the ~inished suspension) and preferably i~ up to 10~o by weight; surface-active substances in concentrations of up to 10~o by weight and preferably of up to 7% by weight; organic solvents in concentrations of up to 15% by weight and pre~erably of up to 10% by weight; anti-~e A 16 581 - 10 -.. . . . .
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46~ i ~: ' foaming agents in concentrations of up to 5% by weight and preferably of up to 2% by weigh~; thickeners in concentrations of up to 5% by weight and preferably of up to 1% by weight; and antifreeze agents in concentrations of up to 30% by weight and preferably of up to 20% by weight.
If necessary, dyestuffs and/or preservatives can also be added to the suspensions which can be prepared according to the invention.
Active compounds which can be used as the water-soluble pesticidally active compounds in the process according to the invention are, preferably, salts of phenoxycarboxylic acids. Examples which may be mentioned are: the potassium salt of a-(2,4-dichlorophenoxy)-pro-pionic acid, the monomethylammonium salt of a-(2,4-dichlorophenoxy)-propionic acid, the sodium salt of 2,4-dichlorophenoxyacetic acid and the sodium salt of 2,4-5-trichlorophenoxyacetic acidO
The concentration of water-soluble pesticidal active com-pounds can be varied within a relatively wide range in the suspensions which can be prepared according to the invention. In the finished sus-pension it can be up to 50% by weight and is preferably up to 40% by weight.
The content of suspended solids can be varied within a i relatively wide range in the suspensions which can be prepared accord-ing to the invention. It can be up to 70% by weight, and is preferably up to 60% by weight, based Oll the finished suspension.
When aqueous suspensions of pesticidally active compounds are prepared by the process according to the invention it is '. , ,' ' , ,: . .
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possible to vary the size of the suspended particles wlthin a re-latively wide range with the aid of the stirring speed. The particle size in the resulting suspension will be smaller the greater the stirring speed, or the stronger the shearing forces which act when the melt is distributed in the aqueous phase. In the process accord- , ing to the invention the stirring speeds are so chosen that the average size of the suspended particles is generally between 1 and 100 ~u and preferably between 1 and 50 ,u.
The average size of the suspended particles cannot only be controlled by the stirring speed but can also be varied to a certain : -extent by the nature and amount of the acid component of the anionic emulsifier, and of the basej and by the stoichiometric ratio of the acid component to the base. The average particle size will be smallest -when 0.5 to 1.0 equivalent of the base is employed per 1 equivalent of the acid component of an anionic emulsifier.
With the process according to the invention it is also possible to vary the particle size distribution within a relatively wide range. In general, the particle size distribution is such that 50% by weight of the suspended particles are smaller than 10 ~ and 80% by weight are smaller than 50 ,u; preferably, the particle size distribution is such that 50% by weight of the suspended particles are smaller than 5 ~ and 80% by weight are smaller than 40 ,u.
When carrying out the process according to the invention it is possible ~ . :
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to vary the temperature o the aqueous phase within a relatively wide range. The temperature of the aqueous phase is generally be-tween 20C and 90C and preferably between 30C and 45C. In every case the temperature of the aqueous phase is at least 20C below the solidification point of the melt to be suspended.
The process according to the invention is generally carried out under normal pressure. However, it is also possible to work under higher pressures. If the process according to the invention is carried out under higher pressures, khe temperature of the aqueous phase can also be raised to above 90C if the substances contained in the suspension to be prepared are stable under the particular reaction conditions. Under a pressure of 9 atmospheres, the water temperature can be, for example, up to 180C.
As already mentioned, it is possible, when suitable surface-active substances ~formulation auxiliaries) are also used, so to guide the process according to the invention that, in those i cases in which the pesticidal active compound to be suspended can be present in several crystal modifications, the particularly de-sired crystal modification is formed in a controlled manner in the suspension to be prepared. However, the particular surface-active substances which are suitable for this purpose must always be de-termined empirically from case to case.
In general, the process according to the invention is `
carried out in such a way that the melt to be suspended is .',.'~ ' ,.
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108~46:1 introduced slowly into the aqueous phase, which is kept at as uniform a temperature as possible, whilst preventing the access of air and whilst stirring ~igorously, and the coarsely dispersed mixture thus ~ormed is ~inely dispersed (homo-genised), a~ter previously having been trans~erred rapidly into another ~essel, with the aid o~ a stirrer which produces strong shearing forces. If necessary, it is possible sub-sequently to homogenise the resulting suspension, optionally after prior addition of formulation auxiliaries, using con-ventional homogeni.sing equipment.
In a particularly advantageous embodiment of the process according to the invention it is also possible ~inely to disperse the melt direct in the aqueous phase without prior coarse dispersion. In this case the procedure is such that the aqueous phase is stirred intensively with the aid of a stirrer which produces strong shearing forces and the melt to be suspended is then so introduced into the aqueous phase, which i3 kept at as uni~orm as possible a temperature, whilst preventing the access of air, that it passes directly into the stirring zoneu In this case also the resulting suspension can be sub~ected, optionally after the prior addition o~
~ormulation augiliarie~, to subsequent homogenisation with the aid oi a conventional homogenising apparatus.
The process according to the invention can be carried out either discontinuously or continuously, as desired.
The suspensions which can be prepared by the process according to the invention are ~table. As a rule they are liquid but, depending on the active compound or the concen-tration o~ the active compound, they can also have a thixo-tropic or pa1ty character. ~he ~ree-~lowing suspension~ can ~e A 16 581 - 14 -.. . . , ~ , , - ,:,: , . . .. .
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1~1339~61 be employed according to customary methods for plant protectlon, either as such or after the prior addition of diluents and, optionally, formulation auxiliaries. The suspensions which are not capable of flow can be used in accordance with the methods customary in plant protection after the addition of diluents and, optionally, formulation auxiliaries. However, it is also possible to convert the suspensions which can be prepared according to the invention, and especially the suspensions which are not capable of flow, into powders or granules by removing the volatile constituents. The powders or granules can then be applied by the methods customary in plant protection.
The process according to the invention is illustrated by the examples which follow. In these examples, reference is made to the accompany-ing figures of drawings, in which Figures 1 and 2 represent in diagrammatic form suitable apparatus for the discontinuous or continuous preparation, respectively, of suspensions according to the invention.
Example 1 The discontinuous preparation was effected of a suspension which contained N-~2-benzthiazolyl)-N,N'-dimethylurea as the pesticidal component.
The flowsheet for the apparatus in which the suspension was prepared in the present case is illustrated in Figure 1.
A mixture of 2,000 g of N-(2-benzthiazolyl)-N,N'-dimethylurea, 100 g of oleic acid and 20 g of a silicone anti-foaming agent (an anti-foaming agent based on silicone oil and highly disperse silica) was melted by warming to 130C in a steam-heated kettle (1) (see Figure 1). This melt ~-was introduced in the course of 10 minutes into a mixture of 2,800 g : .. . .. .
of water, 19.9 g of potassium hydroxide, 26.5 g of APM* emulsifier (an emulsifier based on the monoethanolamine salt of an alkylarylsulphonic ;
acid and on an arylalkyl polyglycol ether), 33.2 g of urea, 40.7 g of paraffin oil, 26.6 g * Trademark '~',''~'.'''' ~ - 15 -. ~ .

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B of xylene, 19.9 g of Wanin S (a dispersing agent based on lignin sulphonate) and 161.7 g of Baykanol S~ (a dispersing agent based on a diphenyl ether-sulphonic acid/formaldehyde condensate in the ~orm of an alkali metal salt), which was in a water-cooled mixing kettle (2), whilst pre~enting the access of air and whilst stirring. The temperature of the aqueous pha~e, which initially was 20C, rose to 35C on addition of the melt. ~he pH value of the aqueous phase changed from 13.5 down to 8.5 as the melt was stirred in.
The coarsely dispersed suspension which was formed in mixing kettle (2) was already transferred continuously into the reactor (3) during the addition of the melt and was ~inely dispersed (homogenised) in this reactor with the aid o~ a stirrer which produced strong shearing forces, and was then recycled into the mixing kettle (2). Homogenisation was complete 15 minutes a~ter all of the melt had been added to the aqueous pha~e. A stable, slightly thixotropic suspension which had a solids content of 55% by weight was obtained in this way. ~he particle sizes o~ the suspended particles were between 1 ~ and 100 ~. ~he particle size distribution was such that 50% o~ the su3pended particles were smaller than 5 ~ and 80~ were smaller than 40 ~.
E~campl.e~- ?
In the same manner as described in Example 1, a melt which consisted o~ 1,500 g o~ N-(2-benzthiazolyl~N,N'-dimethylurea and 75 g o~ stearic acid and which had been heated to 130C was introduced into an aqueous phase which consisted o~ 1,300 g o~ water, 14.7 g o~ potassium hydroxide and 20 g of the silicone anti-~oaming agent, as used in Example 1, and ~inely dispersed. A stable su~pension which ~r~leh~ k Le A 16 581 - 16 -. .

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had a solids content of 52~o by weight was obtained.
I~xamPle In the same manner as described in Example 1, a melt which consisted of 2,000 g of N-(2-benzthiazolyl)-N,N'-B 5 dimethylurea, 100 g of oleic acid, 20 g of Dresinate 731 (an emulsifier based on alkali metal ealt~ of re~in acid~) and 20 g of a silicone anti-foaming agent, as used in Example 1, and which had been heated to 130C was introduced into an aqueou~ phase which consisted of 1,800 g o~ water, 19.9 g of 10 potassium hydroxide, 161.7 g of Baykanol, 26.5 g of APM
emulsifier, 33.2 g of urea, 40.7 g of paraffin oil, 26.6 g of xylene and 19.9 g of Wanin*S and finely dispersed. A
stable suspension which had a solids content of 55% by weight and a particle size distribution of 1 to 100 ~ was obtained.
15 Example 4 The continuous preparation was ef~ected of a suspension which contained N-(2-benzthiazolyl)-N,N'-dimethylurea as the ~-pesticidal component. The flowsheet for the apparatus in which the suspenæion was prepared in the present case is 20 illustrated in Figure 2. All of the figures given in brackets in the present example relate to Figure 2.
20 litres of a mixture consisting of 42.18 parts by weight o~ water, 0.47 part by weight of potassium hydroxide,

3.8 parts by weight of Baykanol~S~, 0.63 part by weight of A ~ emul9ifier, 0.78 part by weight of urea, 0.96 part by weight of para~fin oil, 0.63 part by weight of xylene, 0.46 part by weight of Wanin S and 0.9 part by weight of a sili-cone anti-foaming agent, as used in ~xample 1, were initially introduced into a water-cooled circulation kettle (4). This mixture was recirculated through a dispersing kettle (6) with the aid of a ~x-pump (5). ~he dispersing kettle (6) was ~e A 16 581 - 17 -~33461 connected to a centrifugal homogenising machine (8) via a feed pipe (7). The mixture which flowed through the centri-fugal homogenising machine (8) was recycled into the dis-persing kettle (6). The amount of mixture issuing into the dispersing kettle (6) was so regulated with the aid of the B pump (5) that the level of liquid was about 1 cm above the feed pipe (7) and this resulted in a slight vortex being formed at the orifice of the feed pipe (7). At start-up the aqueous phase had a temperature of 20C and a pH value of 13.5.
10.5 kg of a melt which consisted of 46.87 parts by weight of ~-(2-benzthiazolyl)-N,N'-dimethylurea and 2.36 parts by weight of oleic acid and was at a temperature of 1~0C
were introduced, per hour, into the vortex which formed at the orifice of the feed pipe (7) as a result o~ the suction by the centrifugal homogenising machine (8). The melt was produced in a melt screw (9), which was charged, by means of a metering screw (10), with, per hour, 10 g of N-(2-benzthiazolyl)-~,N'-dimethylurea in powder form and, at the same time, via a piston metering pump (11) with, per hour, 0.5 kg of oleic acid, which was contained in a storage kettle (12). The melt was added until the mixture contained in the dispersing :
kettle (6) had a pH value of 8.5 and the temperature of the mixture was about 35a. Aqueous phase of the above-mentioned composition was now additionally fed continuously from a storage ve~sel (13) via a piston metering pump (14) into the dispersing kettle (6) and ~n particular was introduced in such an amount that the pH value in the dispersing kettle (6) was virtually constant at 8.5. The feed of the aqueous phase was therefore controlled, with the aid of a regulator (15), by means of the pH value of the mixture in the dispersing kettle (6).

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About 20 kg of a stable suspension which had a solidS
content of 55% by weight left the circulation kettle (4) per hour. ~he particle sizes of the suspended particles were between 1 and 100 ~.
~he installation was shut down after an operating period of 10 hours. ~he suspension collected in a storage vessel (16) was subsequently fed through a homogenising apparatus.
The particle sizes of the suspended particles were then betwee~ l ~ and 50 ~.

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Example 7 In the same manner as described ~ Example 1, a melt 'which consisted of 920 g of'N'-(3,4-dichlorophenyl)-N,N-dimethylurea, 240 g of the emulsifier used in E~ample 6 and 50 g of olèic aci'd and which had oeen heated to 160C was lntroduced in the course of 10 minutes into an aqueous phase which consisted of 2,032 g of water, ~80 g of 3-amino-1,2,4-triazole, 120 g of urea, 80 g Polydiol 100 (see E~ample 6), -~
8 g of Erkantol B~G (see ExamDle 6), 20 g of finely disperse silica, 7 g of the silicone anti-foaming agent used in Example 6 a~d 10 g of potassium hydroxide, whilst preventing the access of air and whilst stirring. During the addition of the melt the '' reactior. mixture was cooled so that the temperature of said ~mixture did not exceed 3~C. A~terwards, the coursely dispe~sed suspension which had form~d was finely dispersed. A stable ` ~ sus~ension containing solld particles of an average par-icle .
- size of 3/um as well as a few particles of a size of up to 15/um ~' '- was obtained.
ExamPle 8 ' -20 ' The discontinuous preparation was effected of a SuspensiGn ~ ' ~' - which contained 3,5-dimethyl-4-methyl-mercaptophenyl-N- ~ ^ ~ '' -methylcarbamate as the pesticidal component flowsh~et for the apparatus in which'the suspension was prepared - -is illustrated in ~igure 1.
In the sar,e manner as described in Example 1, a melt which consisted of 1,000 g of 3,5-dimethyl-4-methyl-mercaptcphcn~
methylcarbaMate and 125 g of n-dcdecylbenzenesulphonic acid and which haa been hea~ed to 120C was introduced in the cou~se o ~ 2 Le A 16 581 - 1-~ c . -~, :

( ~
-~33~61 .

7 minutes into an aqueous phase which consisted of 1,500 g of water, 680 g of an aqueous phosphate bu~fer solution of a pH-value of 6, 500 g of Polydiol 400 (see Example 6), 2,5 g of Biopolymer XB 23 (anionic heteropolysacharid of Xantanrubber, ;~;
the average molecular weight being several millions), 20,3 g `
of potassiujm hydroxide and 150 g of emulsifier (an emulsifier based on alkylarylpolyglycol ether), whilst preventing the access of air and whilst stirring. During the addition of the melt the reaction mixture was cooled so that the temperature ~ .. . .
of said mixture did not exceed 35C. Aftenlards the coursely dlspersed suspension which had fGrmed was finely dispersed. A
stable suspension wherein the solid particles had particle sizes between 3 and 150/um was obtained.

~ ,. . . :

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.~ . , : .
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:, ?C~ 2 Le A 16 581 . :~
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' ': ' ' ''~., ,: . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a concentrated aqueous suspension which contains a pesticidally active compound, which is only sparingly sol-uble in water and which has an average particle size between 1 and 100 µ and the particle size distribution of which is such that 80 percent of the sus-pended particles are smaller than 50 µ, in which process a melt of the pest-icidally active compound which has a melting point between 40°C and 300°C and has a solubility in water of at most 1.5 percent by weight at 25°C, and an acid which is the basis of an anionic emulsifier, is introduced, whilst stirring vigorously and preventing the access of air, into an aqueous phase which contains 0.5 to 1.5 equivalents - based on the acid component of the anionic emulsifier - of a base and which has a temperature between 20 and 90°C said temperature being at least 20°C below the solidification point of the melt.

2. A process according to claim 1, in which a fatty acid with 10 to 22 carbon atoms is employed as the acid component of an anionic emulsifier.

3. A process according to claim 2, in which oleic acid or stearic acid is employed as the acid component of an anionic emulsifier.

4. A process according to claim 1, in which the base in the aqueous phase is an alkali metal hydroxide, aluminium hydroxide, an amine or basic stearyl taurate.

5. A process according to claim 4, in which the base is sodium hydroxide, potassium hydroxide or triethanolamine.

6. A process according to claim 2 or 3, in which the total amount of the acid component of the anionic emulsifier and of the base is from 0.2 to 12% by weight of the total suspension.

7. A process according to claim 1, 4 or 5, in which the total amount of the acid component of the anionic emulsifier and of the base is from 2 to 6% by weight of the total suspension.

8. A process according to claim 1, 2 or 5, in which the equivalent ratio of the acid component to the base is between 1:0.8 and 1:1.2.

9. A process according to claim 1 or 5, in which the pesticidally active compound has a melting point between 60°C and 80°C.

10. A process according to claim 1, in which the pesticidally active compound is selected from N-(2-benthiazolyl)-N,N'-dimethylurea, 3-methylthio-4-amino-6-tert.-butyl-1,2,4-triazin-5-one, 3-methylthio-4-isobutyl-idene-amino-6-tert.-butyl-1,2,4-triazin-5-one, 2-chloro-4-ethylamino-6-isopropyl-amino-1,3,5-triazine, N'-(3,4-dichlorophenyl)-N,N-dimethylurea, 2,3-dihydro-2,2-dimethyl-7-benzofuranyl-methyl-carbamate, 3,5-dimethyl-4-methyl-thio-phenyl-N-methyl-carbamate, 0,0-diethyl-0-(3-chloro-4-methyl-7-coumarinyl thiophosphate, .gamma.-hexachlorocyclohexane, 6,7,8,9,10,10-hexachloro-1,5,5A,6, 9,9A-hexahydro-6,9-methane-2,4,3-benzo-dioxathiepine 3-oxide, 1,4,5,6,7,8,8-heptachloro-4,7-endomethylene-3A,4,7,7A-tetrahydroindene, N-trichloromethyl-mercapto-4-cyclohexene-1,2-dicarboximide, N-trichloromethylthiophthalimide, 2-(2-furyl)-benzimidazole, 5-amino-1-bis-(dimethylamido)-phosphoryl-3-phenyl-1,2-4-triazole, 6-methyl-2,3-quinoxaline dithiol-cyclocarbonate and 4-hydroxy-3-(1,2,3,4-tetrahydro-1-naphthyl)-coumarin.

11. A process according to claim 1 or 5, in which the pesticidally active compound is N-(2-benzthiazolyl)-N,N'-dimethylurea.

12. A process according to claim 1 or 10, in which the temperature of the aqueous phase is maintained at 30°C to 45°C.

13. A process according to claim 1, in which one or more formulation auxiliaries are included in the melt and/or in the aqueous phase.

14. A process according to claim 13, in which the formulation auxili-aries in the melt and/or in the aqueous phase are those surface-active sub-stances which, in the case of pesticidally active compound to be suspended which can be present in several crystal modifications, effect the formation of the desired crystal modification in a controlled manner in the suspension.

15. A process according to claim 1, 10 or 14, in which one or more water-soluble pesticidally active compounds are included in the aqueous phase.